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Cisco Catalyst 6500 Series Switches

Troubleshooting Switch Port and Interface Problems

Cisco - Troubleshooting Switch Port and Interface Problems

Contents

Introduction

This document is intended to help determine why a port or interface experiences problems. This document applies to Catalyst switches that run CatOS Software on the Supervisor or Cisco IOS® System Software on the Supervisor.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Physical Layer Troubleshooting

Using the LEDs to Troubleshoot

If you have physical access to the switch, it can save time to look at the port LEDs which give you the link status or can indicate an error condition (if red or orange). The table describes the LED status indicators for Ethernet modules or fixed-configuration switches:

Platform URL
Catalyst 6000 Series Switches Ethernet Module LEDs
Catalyst 5000 Series Switches Ethernet Module LEDs
Catalyst 4000 Series Switches Ethernet Module LEDs
Catalyst 3750 Series Switches Front Panel LEDs
Catalyst 3550 Series Switches Front Panel LEDs
Catalyst 2950/2955 Series Switches Front Panel LEDs
Catalyst 2900/3500XL Series Switches Front Panel LEDs
Catalyst 1900 and 2820 Series Switches Front Panel LEDs
Catalyst G-L3 Series Switches Front Panel LEDs

Ensure that both sides have a link. A single broken wire or one shutdown port can cause the problem where one side has a link light, but the other side does not.

A link light does not guarantee that the cable is fully functional. The cable can have encountered physical stress that causes it to be functional at a marginal level. Normally you can identify this situation if the port has many packet errors, or the port constantly flaps (loses and regains link).

Check the Cable and Both Sides of the Connection

If the link light for the port does not come on, you can consider these possibilities:

Possible Cause Corrective Action
No cable connected Connect cable from switch to a known good device.
Wrong Port Make sure that both ends of the cable are plugged into the correct ports.
Device has no power Ensure that both devices have power.
Wrong cable type Verify the cable selection. Refer to the Catalyst Switch Cable Guide.
Bad cable Swap suspect cable with known good cable. Look for broken or missing pins on connectors.
Loose connections Check for loose connections. Sometimes a cable appears to be seated in the jack, but is not. Unplug the cable and reinsert it.
Patch Panels Eliminate faulty patch panel connections. Bypass the patch panel if possible to rule it out.
Media Convertors Eliminate faulty media convertors: fiber-to-copper, etc. Bypass the media convertor if possible to rule it out.
Bad or wrong Gigabit Interface Convertor (GBIC) Swap suspect GBIC with known good GBIC. Verify Hw and Sw support for this type of GBIC. See the Gigabit Ethernet Troubleshooting section of this document.
Bad Port or Module Port or Interface or Module not enabled Move the cable to a known good port to troubleshoot a suspect port or module. Use the show port command for CatOS or the show interface command for Cisco IOS to look for errdisable, disable or shutdown status. The show module command can indicate faulty, which can indicate a hardware problem. See the Common Port and Interface Problems section of this document for more information.

Ethernet Copper and Fiber Cables

Make sure you have the correct cable for the type of connection you are making. Category 3 copper cable can be used for 10 Mbps unshielded twisted pair (UTP) connections, but must never be used for 10/100 or 10/100/1000Mbps UTP connections. Always use either Category 5, Category 5e, or Category 6 UTP for 10/100 or 10/100/1000Mbps connections.

warning Warning: Category 5e and Category 6 cables can store high levels of static electricity because of the dielectric properties of the materials used in their construction. Always ground the cables (especially in new cable runs) to a suitable and safe earth ground before you connect them to the module.

For fiber, make sure you have the correct cable for the distances involved and the type of fiber ports that are used. The two options are singlemode fiber (SMF) or multimode fiber (MMF). Make sure the ports on the devices that are connected together are both SMF, or both are MMF ports.

Note: For fiber connections, make sure the transmit lead of one port is connected to the receive lead of the other port. Connections for transmit-to-transmit and receive-to-receive do not work.

Ethernet and Fast Ethernet Maximum Transmission Distances

Transceiver Speed Cable Type Duplex Mode Maximum Distance Between Stations
10 Mbps Category 3 UTP Full and half 328 ft (100 m)
10 Mbps MMF Full and half 1.2 mi (2 km)
100 Mbps Category 5 UTP Category 5e UTP Full and half 328 ft (100 m)
100 Mbps Category 6 UTP Full and half 328 ft (100 m)
100 Mbps MMF Half 1312 ft (400 m)
    Full 1.2 mi (2 km)
100 Mbps SMF Half 1312 ft (400 m)
    Full 6.2 mi (10 km)

For more details on the different types of cables/connectors, cabling requirements, optical requirements (distance, type, patch cables, etc.), how to connect the different cables, and which cables are used by most Cisco switches and modules, refer to Catalyst Switch Cable Guide.

Gigabit Ethernet Troubleshooting

If you have device A connected to device B over a Gigabit link, and the link does not come up, perform this procedure.

Step-by-Step Procedure

  1. Verify device A and B use the same GBIC, short wavelength (SX), long wavelength (LX), long haul (LH), extended wavelength (ZX), or copper UTP (TX). Both devices must use the same type of GBIC to establish link. An SX GBIC needs to connect with an SX GBIC. An SX GBIC does not link with an LX GBIC. Refer to Mode-Conditioning Patch Cord Installation Note for more information.

  2. Verify distance and cable used per GBIC as defined in this table.

    1000BASE-T and 1000BASE-X Port Cabling Specifications

    GBIC Wavelength (nm) Copper/Fiber Type Core Size1 (Microns) Modal Bandwidth (MHz/km) Cable Distance2
    WS-G5483 1000Base - T (copper)   Category 5 UTP Category 5e UTP Category 6 UTP     328 ft (100 m)
    WS-G5484 1000BASE-SX3 850 MMF 62.5 62.5 50.0 50.0 160 200 400 500 722 ft (220 m) 902 ft (275 m) 1640 ft (500 m) 1804 ft (550 m)
    WS-G5486 1000BASE-LX/LH 1310 MMF4 SMF 62.5 50.0 50.0 8.3/9/10 500 400 500 - 1804 ft (550 m) 1804 ft (550 m) 1804 ft (550 m) 6.2 miles (10 km)
    WS-G5487 1000BASE-ZX5 1550 MMF SMF6 8.3/9/10 8.3/9/10   43.5 miles (70 km)7 62.1 miles (100 km)

    1. The numbers given for multimode fiber-optic cable refer to the core diameter. For single-mode fiber-optic cable, 8.3 microns refers to the core diameter. The 9-micron and 10-micron values refer to the mode-field diameter (MFD), which is the diameter of the light-carrying portion of the fiber. This area consists of the fiber core plus a small portion of the surrounding cladding. The MFD is a function of the core diameter, the wavelength of the laser, and the refractive index difference between the core and the cladding.

    2. Distances are based on fiber loss. Multiple splices and substandard fiber-optic cable reduce cabling distances.

    3. Use with MMF only.

    4. When you use an LX/LH GBIC with 62.5-micron diameter MMF, you must install a mode-conditioning patch cord (CAB-GELX-625 or equivalent) between the GBIC and the MMF cable on both the transmit and receive ends of the link. The mode-conditioning patch cord is required for link distances less than 328 feet (100 m) or greater than 984 feet (300 m). The mode-conditioning patch cord prevents overdriving the receiver for short lengths of MMF and reduces differential mode delay for long lengths of MMF. Refer to Mode-Conditioning Patch Cord Installation Note for more information.

    5. Use with SMF only.

    6. Dispersion-shifted single-mode fiber-optic cable.

    7. The minimum link distance for ZX GBICs is 6.2 miles (10 km) with an 8-dB attenuator installed at each end of the link. Without attenuators, the minimum link distance is 24.9 miles (40 km).

  3. If either device has multiple Gigabit ports, connect the ports to each other. This tests each device and verifies that the Gigabit interface functions correctly. For example, you have a switch that has two Gigabit ports. Wire Gigabit port one to Gigabit port two. Does the link come up? If so, the port is good. STP blocks on the port and prevents any loops (port one receive (RX) goes to port two transmit (TX), and port one TX goes to port two RX).

  4. If single connection or Step 3 fails with SC connectors, loop the port back to itself (port one RX goes to port one TX). Does the port come up? If not, contact the TAC, as this can be a faulty port.

  5. If steps 3 and 4 are successful, but a connection between device A and B cannot be established, loop ports with the cable that adjoins the two devices. Verify that there is not a faulty cable.

  6. Verify that each device supports 802.3z specification for Gigabit auto-negotiation. Gigabit Ethernet has an auto-negotiation procedure that is more extensive than the one used for 10/100 Ethernet (Gigabit auto-negotiation spec: IEEE Std 802.3z-1998). When you enable link negotiation, the system auto-negotiates flow control, duplex mode, and remote fault information. You must either enable or disable link negotiation on both ends of the link. Both ends of the link must be set to the same value or the link cannot connect. Problems have been seen when you connect to devices manufactured before the IEEE 802.3z standard was ratified. If either device does not support Gigabit auto-negotiation, disable the Gigabit auto-negotiation, and it forces the link up. It takes 300msec for the card firmware to notify the software that a 10/100/1000BASE-TX link/port is down. The 300msec default debounce timer comes from the firmware polling timer to the linecards, which occurs every 300 msec. If this link is run in 1G (1000BASE-TX) mode, Gigabit sync, which occurs every 10msec, must be able to detect the link down faster. There is a difference in the link failure detection times when you run GigabitEthenet on copper versus GigabitEthernet over Fibre. This difference in detection time is based on the IEEE standards.

    warning Warning: Disabling auto-negotiation hides link drops or physical layer problems. Disabling auto-negotiation is only required if end-devices such as older Gigabit NICs are used which cannot support IEEE 802.3z. Do not disable auto-negotiation between switches unless absolutely required to do so, as physical layer problems can go undetected, which results in STP loops. The alternative is to contact the vendor for software/hardware upgrade for IEEE 802.3z Gigabit auto-negotiation support.

In order to troubleshoot the error message: %SYS-4-PORT_GBICBADEEPROM: / %SYS-4-PORT_GBICNOTSUPP, refer to Common CatOS Error Messages on Catalyst 6000/6500 Series Switches.

For GigabitEthernet system requirements as well as Gigabit Interface Converters (GBICs), Coarse Wavelength Division Multiplexing (CWDM), and Small Form-Factor Pluggable (SFP) system requirements, refer to these:

For general configuration and troubleshooting information, refer to Configuring and Troubleshooting Ethernet 10/100/1000 MB Half/Full Duplex Auto-Negotiation.

Connected vs Notconnected

Most Cisco switches default to having a port in the notconnect state. This means it is currently not connected to anything, but it will connect if it has a good connection to another operational device. If you connect a good cable to two switch ports in the notconnect state, the link light must become green for both ports, and the port status must indicate connected. This means that the port is up as far as Layer 1 (L1) is concerned.

For CatOS, you can use the show port command to verify whether the port has a connected or notconnect status, or whether it is another state that would cause connectivity to fail, like disabled or errdisable.

Switch> (enable) sh port status 3/1
  Port  Name                 Status     Vlan       Duplex Speed Type
  ----- -------------------- ---------- ---------- ------ ----- ------------
   3/1                       disabled   1            auto  auto 10/100BaseTX
!--- The show port status {mod/port} command show the port is disabled.
!--- Use the set port enable {mod/port}command to try and re-enable it.

For Cisco IOS, you can use the show interfaces command to verify whether the interface is "up, line protocol is up (connected)". The first "up" refers to the physical layer status of the interface. The "line protocol up" message shows the data link layer status of the interface and says that the interface can send and receive keepalives.

Router#show interfaces fastEthernet 6/1
FastEthernet6/1 is down, line protocol is down (notconnect)
!--- The interface is down and line protocol is down.
!--- Reasons: In this case,
!--- 1) A cable is not properly connected or not connected at all to this port.
!--- 2) The connected cable is faulty.
!--- 3) Other end of the cable is not connected to an active port or device.

!--- Note: For gigabit connections, GBICs need to be matched on each 
!--- side of the connection. 
!--- There are different types of GBICs, depending on the cable and 
!--- distances involved: short wavelength (SX), 
!--- long-wavelength/long-haul (LX/LH) and extended distance (ZX). 
!--- An SX GBIC needs to connect with an SX GBIC; 
!--- an SX GBIC does not link with an LX GBIC. Also, some gigabit 
!--- connections require conditioning cables, 
!--- depending on the lengths involved.

Router#show interfaces fastEthernet 6/1
FastEthernet6/1 is up, line protocol is down (notconnect)
!--- The interface is up (or not in a shutdown state), but line protocol down.
!--- Reason: In this case, the device on the other side of the wire is a 
!--- CatOS switch with its port disabled.

Router#sh interfaces fas 6/1 status
Port   Name    Status       Vlan    Duplex   Speed  Type
Fa6/1          notconnect    1       auto     auto   10/100BaseTX
!--- The show interfaces card-type [slot/port] status command is the equivalent
!--- of show port status for CatOS.

If show port shows connected or show interfaces shows up/ line protocol up (connected) but you see errors incrementing in the output of either command, refer to the Understanding Specfic Port and Interface Counter Output for CatOS or Cisco IOS or Common Port and Interface Problems sections of this document for troubleshooting advice.

Most Common Port and Interface Troubleshooting Commands for CatOS and Cisco IOS

This table shows the most common commands used for troubleshooting port or interface problems on switches that run CatOS Software on the Supervisor or Cisco IOS System Software on the Supervisor.

Note: Choose a command in the left hand column to go to documentation for that command. The right hand column gives a brief description of what the command does and lists any exceptions to it's use per platform.

These commands are supported by the Output Interpreter tool for CatOS and can be used to assist in troubleshooting switch port or problems: show version, show module, show port, show counters , or show mac .

If you have the output of the supported commands from your Cisco device, you can use to display potential issues and fixes. In order to use Output Interpreter, you must be a registered user, be logged in, and have JavaScript enabled.

CatOS Commands Cisco IOS Commands Description
show version show version For switches that run CatOS, this command displays software and hardware version info per module and system memory sizes. For switches that run Cisco IOS, this command displays output similar to a Cisco router, like software image name and version information and system memory sizes. Helpful in searching for software/hardware incompatibilities (with the Release Notes or Software Advisor) and bugs (with the Software Bug Toolkit). For more information on the show version command, see the Software Problems section of this document
show module show module For Catalyst 6000, 5000, 4000 and other modular switches that run CatOS or Cisco IOS, this command displays what cards are present in the switch, the version of software they are that run, and what state the modules are in: ok, faulty, etc. Helpful in diagnosing a hardware problem on a module or port. For more information on troubleshooting hardware problems with the show module command, see the Port or Interface Status is disabled or shutdown or the Hardware Problems sections of this document.
show config show that run-config For CatOS, this command displays the non-default configuration settings of the switch (all changes made to the default configuration). All changes to the config in CatOS are saved automatically. For Cisco IOS, this command displays the current configuration file of the switch. Changes are saved to the config in Cisco IOS with the write memory command. Helpful in determining whether a misconfiguration of the mod/port or interface, can cause a problem.
show port show interfaces For CatOS, the show port command displays whether the port is connected, what VLAN it is in, what speed/duplex it is that run at, channel information, errors, etc. For Cisco IOS, the show interfaces command displays the administrative and operational status of a switching port, input and output packets, buffer failures, errors, etc. The output of these two commands is discussed in more detail in the Understanding Port and Interface Counter Output for CatOS and Cisco IOS section of this document.
clear counters clear counters For CatOS and Cisco IOS use the clear counters command to zero the traffic and error counters so that you can see if the problem is only temporary, or if the counters continue to increment.

Note: The Catalyst 6500/6000 series switches do not clear the bit counters of an interface with the clear counters command. The only way to clear the bit counters in these switches is to reload.

show port counters show interfaces counters For CatOS, the show port <mod/port> command displays port error counters like FCS, alignments, collisions, etc. For Cisco IOS on the Catalyst 6000, 4000, 3550, 2950, and and 3750 series, the equivalent command is show interfaces card-type x/y counters errors. The output of these two commands is discussed in more detail in the Understanding Port and Interface Counter Output for CatOS and Cisco IOS section of this document.
show counters show counters interface show controllers ethernet-controller For CatOS, the show counters command displays the 64-bit and 32-bit hardware counters for a given mod/port or interface. Counters vary dependent upon the module type and platform. For Cisco IOS, the show counters interface command was introduced in software version 12.1(13)E for the Catalyst 6000 series only and is the equivalent of the show counters command for CatOS which displays 32-bit and 64-bit error counters. For Cisco IOS on 2900/3500XL, 2950/2955, 3550, 2970 and 3750 series switches, the show controllers Ethernet-controller command is similar to the show counters command on CatOS platforms. Displays discarded frames, deferred frames, alignment errors, collisions, etc.
show mac show interfaces counters For CatOS, the show mac command displays the MAC counters for traffic passing through each port such as, received frames, transmit frames, out-lost, in-lost, etc. (This command does not list the MAC addresses learned on a port by the bridging software. Use the command show cam dynamic for that information.) For Cisco IOS, the show interfaces card-type x/y counters command is similar to show mac for CatOS platforms. The output of these two commands is discussed in more detail in the Understanding Port and Interface Counter Output for CatOS and Cisco IOS section of this document.
show test show diagnostic(s) show post For CatOS, the show test command displays any hardware errors encountered on startup. For Cisco IOS, the equivalent command is show diagnostic which was introduced in 12.1(11b)E for the Catalyst 6000 series and show diagnostics(with an s) which was introduced in for the Catalyst 4000 Series. Both commands display Power-On Self Test (POST) results. For Cisco IOS on the 2900/3500XL, 2950/2955, 3550, 2970 and 3750 series switches, the equivalent command is show post which displays the results of the switch POST. For more information on troubleshooting hardware related errors on Catalyst switches, see the Hardware Problems section of this document.

Understanding Specific Port and Interface Counter Output for CatOS and Cisco IOS

Most switches have some way to track the packets and errors that occur on a port or interface. The common commands used to find this type of information are described in the Most Common Port and Interface Troubleshooting Commands for CatOS and Cisco IOS section of this document.

Note: There can be differences in the implementation of the counters across various platforms and releases. Although the values of the counters are largely accurate, they are not very precise by design. In order to pull the exact statistics of the traffic, it is suggested that you use a sniffer to monitor the necessary ingress and egress interfaces.

Excessive errors for certain counters usually indicate a problem. When you operate at half-duplex setting, some data link errors incrementing in Frame Check Sequence (FCS), alignment, runts, and collision counters are normal. Generally, a one percent ratio of errors to total traffic is acceptable for half-duplex connections. If the ratio of errors to input packets is greater than two or three percent, performance degradation can be noticed.

In half-duplex environments, it is possible for both the switch and the connected device to sense the wire and transmit at exactly the same time and result in a collision. Collisions can cause runts, FCS, and alignment errors due to the frame not being completely copied to the wire, which results in fragmented frames.

When you operate at full-duplex, errors in FCS, Cyclic Redundancy Checks (CRC), alignment, and runt counters must be minimal. If the link operates at full-duplex, the collision counter is not active. If the FCS, CRC, alignment, or runt counters increment, check for a duplex mismatch. Duplex mismatch is a situation where the switch operates at full-duplex and the connected device operates at half-duplex, or vice versa. The results of a duplex mismatch are extremely slow performance, intermittent connectivity, and loss of connection. Other possible causes of data link errors at full-duplex are bad cables, faulty switch ports, or NIC software/hardware issues. See the Common Port and Interface Problems section of this document for more information.

Show Port for CatOS and Show Interfaces for Cisco IOS

The show port {mod/port} command is used when that run CatOS on the Supervisor. An alternative to this command is the show port counters {mod/port} which only displays the port error counters. Refer to Table 1 for explanations of the error counter output.

Switch> (enable) sh port counters 3/1
  
  Port  Align-Err  FCS-Err    Xmit-Err   Rcv-Err    UnderSize
 ----- ---------- ---------- ---------- ---------- ---------
  3/1           0          0          0          0         0
 
  Port  Single-Col Multi-Coll Late-Coll  Excess-Col Carri-Sen Runts     Giants
 ----- ---------- ---------- ---------- ---------- --------- --------- ---------
  3/1           0          0          0          0         0         0         0

The show interfaces card-type {slot/port} command is the equivalent command for Cisco IOS on the Supervisor. An alternative to this command (for Catalyst 6000, 4000, 3550, 2970 2950/2955, and 3750 series switches) is the show interfaces card-type {slot/port} counters errors command which only displays the interface error counters.

Note: For 2900/3500XL Series switches use the show interfaces card-type {slot/port} command with the show controllers Ethernet-controller command.

Router#sh interfaces fastEthernet 6/1
FastEthernet6/1 is up, line protocol is up (connected)
   Hardware is C6k 100Mb 802.3, address is 0009.11f3.8848 (bia 0009.11f3.8848)
   MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
      reliability 255/255, txload 1/255, rxload 1/255
   Encapsulation ARPA, loopback not set
   Full-duplex, 100Mb/s
   input flow-control is off, output flow-control is off
   ARP type: ARPA, ARP Timeout 04:00:00
   Last input 00:00:14, output 00:00:36, output hang never
   Last clearing of "show interface" counters never
   Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
   Queueing strategy: fifo
   Output queue :0/40 (size/max)
   5 minute input rate 0 bits/sec, 0 packets/sec
   5 minute output rate 0 bits/sec, 0 packets/sec

The show interfaces command output up to this point is explained here (in order) :

  • up, line protocol is up (connected) - The first "up" refers to the physical layer status of the interface. The "line protocol up" message shows the data link layer status of the interface and says that the interface can send and receive keepalives.

  • MTU - The Maximum Transmission Unit (MTU) is 1500 bytes for Ethernet by default (for the max data portion of the frame).

  • Full-duplex, 100Mb/s - Full-duplex and 100Mbps is the current speed and duplex setting of the interface. This does not tell you whether autoneg was used to achieve this. Use the show interfaces fas 6/1 status command to display this:

    Router#sh interfaces fas 6/1 status
    	
    	Port    Name               Status       Vlan       Duplex  Speed Type
    	Fa6/1                      connected    1          a-full  a-100 10/100BaseTX
    	!--- Autonegotiation was used to achieve full-duplex and 100Mbps.
    
  • Last input, output - The number of hours, minutes, and seconds since the last packet was successfully received or transmitted by the interface. This is usefulto know when a dead interface failed.

  • Last clearing of "show interface" counters - The last time the clear counters command was issued since the last time the switch was rebooted. The clear counters command is used to reset interface statistics.

    Note: Variables that can affect routing (for example, load and reliability) are not cleared when the counters are cleared.

  • Input queue - The number of packets in the input queue. Size/max/drops = the current number of frames in the queue / the max number of frames the queue can hold before it must start dropping frames / the actual number of frames dropped because the max queue size was exceeded. Flushes is used to count Selective Packet Discard (SPD) drops on the the Catalyst 6000 Series that run Cisco IOS. (The flushes counter can be used but never increments on the Catalyst 4000 Series that run Cisco IOS.) SPD is a mechanism that quickly drops low priority packets when the CPU is overloaded in order to save some processing capacity for high priority packets. The flushes counter in the show interface command output increments as part of selective packet discard (SPD), which implements a selective packet drop policy on the IP process queue of the router. Therefore, it applies to only process switched traffic.

    The purpose of SPD is to ensure that important control packets, such as routing updates and keepalives, are not dropped when the IP input queue is full. When the size of the IP input queue is between the minimum and maximum thresholds, normal IP packets are dropped based on a certain drop probability. These random drops are called SPD flushes.

  • Total output drops - The number of packets dropped because the output queue is full. A common cause of this might be traffic from a high bandwidth link being switched to a lower bandwidth link or traffic from multiple inbound links being switched to a single outbound link. For example, if a large amount of bursty traffic comes in on a gigabit interface and is switched out to a 100Mbps interface, this might cause output drops to increment on the 100Mbps interface. This is because the output queue on that interface is overwhelmed by the excess traffic due to the speed mismatch between the inbound and outbound bandwidths.

  • Output queue - The number of packets in the output queue. Size/max means the current number of frames in the queue/the max number of frames the queue can hold before it is full and must start dropping frames.

  • 5 minute input/output rate - The average input and output rate seen by the interface in the last five minutes. In order to get a more accurate reading by specifying a shorter period of time (to better detect traffic bursts for example), issue the load-interval <seconds> interface command.

The rest of the show interfaces command displays error counter output which is similar or equivalent to CatOS error counter output. See Table 1 for explanations of the error counter output.

!--- ...show interfaces command output continues.
     1117058 packets input, 78283238 bytes, 0 no buffer
      Received 1117035 broadcasts, 0 runts, 0 giants, 0 throttles
      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
      0 watchdog, 0 multicast, 0 pause input
      0 input packets with dribble condition detected
      285811 packets output, 27449284 bytes, 0 underruns
      0 output errors, 0 collisions, 2 interface resets
      0 babbles, 0 late collision, 0 deferred
      0 lost carrier, 0 no carrier
      0 output buffer failures, 0 output buffers swapped out

Note:  There is a difference between the counter of show interface command output for a physical interface and a VLAN interface. The input packet counters increment in the output of show interface for a VLAN interface when that packet is Layer 3 (L3) processed by the CPU. Traffic that is Layer 2 (L2) switched never makes it to the CPU and is not counted in the show interface counters for the VLAN interface. It would be counted on the show interface output for the appropriate physical interface.

The show interfaces card-type {slot/port} counters errors command is the equivalent Cisco IOS command to show port counters for CatOS. See Table 1 for explanations of the error counter output.

Router#sh interfaces fastEthernet 6/1 counters errors
  
 Port        Align-Err    FCS-Err   Xmit-Err    Rcv-Err UnderSize OutDiscards
 Fa6/1               0          0          0          0         0           0
 
 Port      Single-Col Multi-Col  Late-Col Excess-Col Carri-Sen     Runts    Giants
 Fa6/1              0         0         0          0         0         0         0

Table 1:

CatOS error counter output for show port or show port counters for the Catalyst 6000, 5000 and 4000 Series. Cisco IOS error counter output for show interfaces or show interfaces card-type x/y counters errors for the Catalyst 6000 and 4000 Series.

Counters (in alphabetical order) Description and Common Causes of Incrementing Error Counters
Align-Err Description: CatOS sh port and Cisco IOS sh interfaces counters errors. Alignment errors are a count of the number of frames received that don't end with an even number of octets and have a bad Cyclic Redundancy Check (CRC). Common Causes: These are usually the result of a duplex mismatch or a physical problem (such as cabling, a bad port, or a bad NIC). When the cable is first connected to the port, some of these errors can occur. Also, if there is a hub connected to the port, collisions between other devices on the hub can cause these errors. Platform Exceptions: Alignment errors are not counted on the Catalyst 4000 Series Supervisor I (WS-X4012) or Supervisor II (WS-X4013).
babbles Description: Cisco IOS sh interfaces counter. CatOS counter indicating that the transmit jabber timer expired. A jabber is a frame longer than 1518 octets (which exclude framing bits, but include FCS octets), which does not end with an even number of octets (alignment error) or has a bad FCS error.
Carri-Sen Description: CatOS sh port and Cisco IOS sh interfaces counters errors. The Carri-Sen (carrier sense) counter increments every time an Ethernet controller wants to send data on a half duplex connection. The controller senses the wire and checks if it is not busy before transmitting. Common Causes: This is normal on an half duplex Ethernet segment.
collisions Descriptions: Cisco IOS sh interfaces counter. The number of times a collision occurred before the interface transmitted a frame to the media successfully. Common Causes: Collisions are normal for interfaces configured as half duplex but must not be seen on full duplex interfaces. If collisions increase dramatically, this points to a highly utilized link or possibly a duplex mismatch with the attached device.
CRC Description: Cisco IOS sh interfaces counter. This increments when the CRC generated by the originating LAN station or far-end device does not match the checksum calculated from the data received. Common Causes: This usually indicates noise or transmission problems on the LAN interface or the LAN itself. A high number of CRCs is usually the result of collisions but can also indicate a physical issue (such as cabling, bad interface or NIC) or a duplex mismatch.
deferred Description: Cisco IOS sh interfaces counter. The number of frames that have been transmitted successfully after they wait because the media was busy. Common Causes: This is usually seen in half duplex environments where the carrier is already in use when it tries to transmit a frame.
pause input Description: Cisco IOS show interfaces counter. An increment in pause input counter means that the connected device requests for a traffic pause when its receive buffer is almost full. Common Causes: This counter is incremented for informational purposes, since the switch accepts the frame. The pause packets stop when the connected device is able to receive the traffic.
input packetswith dribble condition Description: Cisco IOS sh interfaces counter. A dribble bit error indicates that a frame is slightly too long. Common Causes: This frame error counter is incremented for informational purposes, since the switch accepts the frame.
Excess-Col Description: CatOS sh port and Cisco IOS sh interfaces counters errors. A count of frames for which transmission on a particular interface fails due to excessive collisions. An excessive collision happens when a packet has a collision 16 times in a row. The packet is then dropped. Common Causes: Excessive collisions are typically an indication that the load on the segment needs to be split across multiple segments but can also point to a duplex mismatch with the attached device. Collisions must not be seen on interfaces configured as full duplex.
FCS-Err Description: CatOS sh port and Cisco IOS sh interfaces counters errors. The number of valid size frames with Frame Check Sequence (FCS) errors but no framing errors. Common Causes: This is typically a physical issue (such as cabling, a bad port, or a bad Network Interface Card (NIC)) but can also indicate a duplex mismatch.
frame Description: Cisco IOS sh interfaces counter. The number of packets received incorrectly that has a CRC error and a non-integer number of octets (alignment error). Common Causes: This is usually the result of collisions or a physical problem (such as cabling, bad port or NIC) but can also indicate a duplex mismatch.
Giants Description: CatOS sh port and Cisco IOS sh interfaces and sh interfaces counters errors. Frames received that exceed the maximum IEEE 802.3 frame size (1518 bytes for non-jumbo Ethernet) and have a bad Frame Check Sequence (FCS). Common Causes: In many cases, this is the result of a bad NIC. Try to find the offending device and remove it from the network. Platform Exceptions: Catalyst Cat4000 Series that run Cisco IOS Previous to software Version 12.1(19)EW, the giants counter incremented for a frame > 1518bytes. After 12.1(19)EW, a giant in show interfaces increments only when a frame is received >1518bytes with a bad FCS.
ignored Description: Cisco IOS sh interfaces counter. The number of received packets ignored by the interface because the interface hardware ran low on internal buffers. Common Causes: Broadcast storms and bursts of noise can cause the ignored count to be increased.
Input errors Description: Cisco IOS sh interfaces counter. Common Causes: This includes runts, giants, no buffer, CRC, frame, overrun, and ignored counts. Other input-related errors can also cause the input errors count to be increased, and some datagrams can have more than one error. Therefore, this sum cannot balance with the sum of enumerated input error counts. Also refer to the section Input Errors on a Layer 3 Interface Connected to a Layer 2 Switchport.
Late-Col Description: CatOS sh port and Cisco IOS sh interfaces and sh interfaces counters errors. The number of times a collision is detected on a particular interface late in the transmission process. For a 10 Mbit/s port this is later than 512 bit-times into the transmission of a packet. Five hundred and twelve bit-times corresponds to 51.2 microseconds on a 10 Mbit/s system. Common Causes: This error can indicate a duplex mismatch among other things. For the duplex mismatch scenario, the late collision is seen on the half duplex side. As the half duplex side is transmitting, the full duplex side does not wait its turn and transmits simultaneously which causes a late collision. Late collisions can also indicate an Ethernet cable or segment that is too long. Collisions must not be seen on interfaces configured as full duplex.
lost carrier Description: Cisco IOS sh interfaces counter. The number of times the carrier was lost in transmission. Common Causes: Check for a bad cable. Check the physical connection on both sides.
Multi-Col Description: CatOS sh port and Cisco IOS sh interfaces counters errors. The number of times multiple collisions occurred before the interface transmitted a frame to the media successfully. Common Causes: Collisions are normal for interfaces configured as half duplex but must not be seen on full duplex interfaces. If collisions increase dramatically, this points to a highly utilized link or possibly a duplex mismatch with the attached device.
no buffer Description: Cisco IOS sh interfaces counter. The number of received packets discarded because there is no buffer space. Common Causes: Compare with ignored count. Broadcast storms can often be responsible for these events.
no carrier Description: Cisco IOS sh interfaces counter. The number of times the carrier was not present in the transmission. Common Causes: Check for a bad cable. Check the physical connection on both sides.
Out-Discard Description: The number of outbound packets chosen to be discarded even though no errors have been detected. Common Causes: One possible reason to discard such a packet can be to free up buffer space.
output buffer failuresoutput buffers swapped out Description: Cisco IOS sh interfaces counter. The number of failed buffers and the number of buffers swapped out. Common Causes: A port buffers the packets to the Tx buffer when the rate of traffic switched to the port is high and it cannot handle the amount of traffic. The port starts to drop the packets when the Tx buffer is full and thus increases the underruns and the output buffer failure counters. The increase in the output buffer failure counters can be a sign that the ports are run at an inferior speed and/or duplex, or there is too much traffic that goes through the port. As an example, consider a scenario where a 1gig multicast stream is forwarded to 24 100 Mbps ports. If an egress interface is over-subscribed, it is normal to see output buffer failures that increment along with Out-Discards. For troubleshooting information, see the Deferred Frames (Out-Lost or Out-Discard) section of this document.
output errors Description: Cisco IOS sh interfaces counter. The sum of all errors that prevented the final transmission of datagrams out of the interface. Common Cause: This issue is due to the low Output Queue size.
overrun Description: The number of times the receiver hardware was unable to hand received data to a hardware buffer. Common Cause: The input rate of traffic exceeded the ability of the receiver to handle the data.
packets input/output Description: Cisco IOS sh interfaces counter. The total error free packets received and transmitted on the interface. Monitoring these counters for increments is useful to determine whether traffic flows properly through the interface. The bytes counter includes both the data and MAC encapsulation in the error free packets received and transmitted by the system.
Rcv-Err Description: CatOS show port or show port counters and Cisco IOS (for the Catalyst 6000 Series only) sh interfaces counters error. Common Causes: See Platform Exceptions. Platform Exceptions: Catalyst 5000 Series rcv-err = receive buffer failures. For example, a runt, giant, or an FCS-Err does not increment the rcv-err counter. The rcv-err counter on a 5K only increments as a result of excessive traffic. On Catalyst 4000 Series rcv-err = the sum of all receive errors, which means, in contrast to the Catalyst 5000, that the rcv-err counter increments when the interface receives an error like a runt, giant or FCS-Err.
Runts Description: CatOS sh port and Cisco IOS sh interfaces and sh interfaces counters errors. The frames received that are smaller than the minimum IEEE 802.3 frame size (64 bytes for Ethernet), and with a bad CRC. Common Causes: This can be caused by a duplex mismatch and physical problems, such as a bad cable, port, or NIC on the attached device. Platform Exceptions: Catalyst 4000 Series that run Cisco IOS Previous to software Version 12.1(19)EW, a runt = undersize. Undersize = frame < 64bytes. The runt counter only incremented when a frame less than 64 bytes was received. After 12.1(19EW, a runt = a fragment. A fragment is a frame < 64 bytes but with a bad CRC. The result is the runt counter now increments in show interfaces, along with the fragments counter in show interfaces counters errors when a frame <64 bytes with a bad CRC is received. Cisco Catalyst 3750 Series Switches In releases prior to Cisco IOS 12.1(19)EA1, when dot1q is used on the trunk interface on the Catalyst 3750, runts can be seen on show interfaces output because valid dot1q encapsulated packets, which are 61 to 64 bytes and include the q-tag, are counted by the Catalyst 3750 as undersized frames, even though these packets are forwarded correctly. In addition, these packets are not reported in the appropriate category (unicast, multicast, or broadcast) in receive statistics. This issue is resolved in Cisco IOS release 12.1(19)EA1 or 12.2(18)SE or later.
Single-Col Description: CatOS sh port and Cisco IOS sh interfaces counters errors. The number of times one collision occurred before the interface transmitted a frame to the media successfully. Common Causes: Collisions are normal for interfaces configured as half duplex but must not be seen on full duplex interfaces. If collisions increase dramatically, this points to a highly utilized link or possibly a duplex mismatch with the attached device.
throttles Description: Cisco IOS show interfaces. The number of times the receiver on the port is disabled, possibly because of buffer or processor overload. If an asterisk (*) appears after the throttles counter value, it means that the interface is throttled at the time the command is run. Common Causes: Packets which can increase the processor overload include IP packets with options, expired TTL, non-ARPA encapsulation, fragmentation, tunelling, ICMP packets, packets with MTU checksum failure, RPF failure, IP checksum and length errors.
underruns Description: The number of times that the transmitter has been that run faster than the switch can handle. Common Causes: This can occur in a high throughput situation where an interface is hit with a high volume of bursty traffic from many other interfaces all at once. Interface resets can occur along with the underruns.
Undersize Description: CatOS sh port and Cisco IOS sh interfaces counters errors . The frames received that are smaller than the minimum IEEE 802.3 frame size of 64 bytes (which excludes framing bits, but includes FCS octets) that are otherwise well formed. Common Causes: Check the device that sends out these frames.
Xmit-Err Description: CatOS sh port and Cisco IOS sh interfaces counters errors. This is an indication that the internal send (Tx) buffer is full. Common Causes: A common cause of Xmit-Err can be traffic from a high bandwidth link that is switched to a lower bandwidth link, or traffic from multiple inbound links that are switched to a single outbound link. For example, if a large amount of bursty traffic comes in on a gigabit interface and is switched out to a 100Mbps interface, this can cause Xmit-Err to increment on the 100Mbps interface. This is because the output buffer of the interface is overwhelmed by the excess traffic due to the speed mismatch between the inbound and outbound bandwidths.

Show Mac for CatOS and Show Interfaces Counters for Cisco IOS

The show mac {mod/port}command is useful when that run CatOS on the supervisor to monitor inbound and outbound traffic on the port as displayed by the receive (Rcv) and transmit (Xmit) counters for unicast, multicast, and broadcast traffic. This output is from a Catalyst 6000 that run CatOS:

Console> (enable) sh mac 3/1
  
  Port     Rcv-Unicast          Rcv-Multicast        Rcv-Broadcast
  -------- -------------------- -------------------- --------------------
   3/1                      177               256272                 3694
  
  Port     Xmit-Unicast         Xmit-Multicast       Xmit-Broadcast
  -------- -------------------- -------------------- --------------------
   3/1                       30               680377                  153
  
  Port     Rcv-Octet            Xmit-Octet
  -------- -------------------- --------------------
   3/1                 22303565             48381168
  
  MAC      Dely-Exced MTU-Exced  In-Discard Out-Discard
  -------- ---------- ---------- ---------- -----------
   3/1              0          0     233043          17
  
  Port  Last-Time-Cleared
  ----- --------------------------
   3/1  Sun Jun 1 2003, 12:22:47

This command also has these error counters: Dely-Exced, MTU-Exced, In-Discard and Out-Discard.

  • Dely-Exced - The number of frames discarded by this port due to an excessive transmit delay through the switch. This counter must never go up unless the port is under very high utilization.

  • MTU Exceed - This is an indication that one of the devices on that port or segment transmits more than the allowed frame size (1518 bytes for non-jumbo Ethernet).

  • In-Discard - The result of inbound valid frames that were discarded because the frame did not need to be switched. This can be normal if a hub is connected to a port and two devices on that hub exchange data. The switch port still sees the data but does not have to switch it (since the CAM table shows the MAC address of both devices associated with the same port), and so it is discarded. This counter can also increment on a port configured as a trunk if that trunk blocks for some VLANs, or on a port that is the only member of a VLAN.

  • Out-Discard - The number of outbound packets chosen to be discarded even though no packet errors have been detected. One possible reason to discard such a packet can be to free up buffer space.

Catalyst 4000 and 5000 series switches that run CatOS have two additional error counters in the show mac command. These are the In-Lost and Out-Lost counters:

MAC      Dely-Exced MTU-Exced  In-Discard Lrn-Discrd In-Lost    Out-Lost
-------- ---------- ---------- ---------- ---------- ---------- ---------- 
5/1              0          0          0          0          0          0
  • In-Lost - On the Catalyst 4000, this counter is the sum of all error packets received on the port. The In-Lost counter on the Catalyst 5000, on the other hand, tracks the sum of all receive buffer failures.

  • Out-Lost - On the Catalyst 4000 and 5000, these are outbound frames that were lost before they were forwarded (due to insufficient buffer space). This is commonly caused by oversubscribing the port.

The show interfaces card-type {slot/port} counters command is used when you run Cisco IOS on the Supervisor.

Note: There are no equivalent counters to the CatOS show mac error counters: Dely-Exced, MTU-Exced and In-Discard in this command There is, however, an Out-Discard counter in the Cisco IOS show interfaces counters errors command which is explained in Table 1.

Router#sh interfaces fas 6/1 counters
  
  Port            InOctets   InUcastPkts   InMcastPkts   InBcastPkts
  Fa6/1           47856076            23        673028           149
  
  Port           OutOctets  OutUcastPkts  OutMcastPkts  OutBcastPkts
  Fa6/1           22103793            17        255877          3280
  Router#
  !--- Cisco IOS counters used to monitor inbound and outbound unicast, multicast
  !--- and broadcast packets on the interface.

Show Counters for CatOS and Show Counters Interface for Cisco IOS

The show counters [mod/port] command offers even more detailed statistics for ports and interfaces. This command is available for CatOS and the equivalent show counters interface card-type {slot/port} command was introduced in Cisco IOS software version 12.1(13)E for the Catalyst 6000 series only. These commands display the 32-bit and 64-bit error counters per port or interface. Refer to the CatOS command documentation for show counters for more information.

Note: Counter stats for Catalyst 6000 series switches that run Cisco IOS are in Hex.

Console> (enable) sh counters 3/1
  64 bit counters
  0  rxHCTotalPkts                      =               260555
  1  txHCTotalPkts                      =               687411
  2  rxHCUnicastPkts                    =                  177
  3  txHCUnicastPkts                    =                   30
  4  rxHCMulticastPkts                  =               256684
  5  txHCMulticastPkts                  =               687228
  6  rxHCBroadcastPkts                  =                 3694
  7  txHCBroadcastPkts                  =                  153
  8  rxHCOctets                         =             22386167
  9  txHCOctets                         =             48850817
  10 rxTxHCPkts64Octets                 =               228929
  11 rxTxHCPkts65to127Octets            =               701493
  12 rxTxHCPkts128to255Octets           =                  285
  13 rxTxHCPkts256to511Octets           =                17090
  14 rxTxHCpkts512to1023Octets          =                  168
  15 rxTxHCpkts1024to1518Octets         =                    1
  16 txHCTrunkFrames                    =               395217
  17 rxHCTrunkFrames                    =               236459
  18 rxHCDropEvents                     =                    0
  32 bit counters
  0  rxCRCAlignErrors                   =          0
  1  rxUndersizedPkts                   =          0
  2  rxOversizedPkts                    =          0
  3  rxFragmentPkts                     =          0
  4  rxJabbers                          =          0
  5  txCollisions                       =          0
  6  ifInErrors                         =          0
  7  ifOutErrors                        =          0
  8  ifInDiscards                       =     233043
  9  ifInUnknownProtos                  =          2
  10 ifOutDiscards                      =         17
  !--- Output suppressed.

Show Controller Ethernet-Controller for Cisco IOS

For Catalyst 3750, 3550, 2970, 2950/2955, 2940, and 2900/3500XL switches use the command show controller ethernet-controller to display traffic counter and error counter output that is similar to the show port, show interface, show mac and show counters output for Catalyst 6000, 5000 and 4000 series switches.

3550-1#sh controller ethernet-controller fastEthernet 0/1
  !--- Output from a Catalyst 3550.
  
    Transmit FastEthernet0/1           Receive
          0 Bytes                        0 Bytes
          0 Unicast frames               0 Unicast frames
          0 Multicast frames             0 Multicast frames
          0 Broadcast frames             0 Broadcast frames
          0 Discarded frames             0 No dest, unicast
          0 Too old frames               0 No dest, multicast
          0 Deferred frames              0 No dest, broadcast
          0  1 collision frames
          0  2 collision frames          0 FCS errors
          0  3 collision frames          0 Oversize frames
          0  4 collision frames          0 Undersize frames
          0  5 collision frames          0 Collision fragments
          0  6 collision frames
          0  7 collision frames          0 Minimum size frames
          0  8 collision frames          0 65 to 127 byte frames
          0  9 collision frames          0 128 to 255 byte frames
          0 10 collision frames          0 256 to 511 byte frames
          0 11 collision frames          0 512 to 1023 byte frames
          0 12 collision frames          0 1024 to 1518 byte frames
          0 13 collision frames
          0 14 collision frames          0 Flooded frames
          0 15 collision frames          0 Overrun frames
          0 Excessive collisions         0 VLAN filtered frames
          0 Late collisions              0 Source routed frames
          0 Good (1 coll) frames         0 Valid oversize frames
          0 Good(>1 coll) frames         0 Pause frames
          0 Pause frames                 0 Symbol error frames
          0 VLAN discard frames          0 Invalid frames, too large
          0 Excess defer frames          0 Valid frames, too large
          0 Too large frames             0 Invalid frames, too small
          0 64 byte frames               0 Valid frames, too small
          0 127 byte frames
          0 255 byte frames
          0 511 byte frames
          0 1023 byte frames
          0 1518 byte frames
 
 3550-1#
 !--- See table for additional counter output for 2900/3500XL Series switches.

Counter Description Possible Causes
Transmitted Frames
Discarded frames The total number of frames whose transmission attempt is abandoned due to insufficient resources. This total includes frames of all destination types. The traffic load on the interface is excessive and causes the frames to be discarded. Reduce the traffic load on the interface if you see an increasing number of packets in this field.
Too old frames Number of frames that took longer than two seconds to travel through the switch. For this reason, they were discarded by the switch. This only happens under extreme, high stress conditions. The traffic load for this switch is excessive and causes the frames to be discarded. Reduce the switch load if you see an increasing number of packets in this field. You can need to modify your network topology to reduce the traffic load for this switch.
Deferred frames The total number of frames whose first transmission attempt was delayed, due to traffic on the network media. This total includes only those frames that are subsequently transmitted without error and without experiencing a collision. The traffic load destined for this switch is excessive and causes the frames to be discarded. Reduce the switch load if you see an increasing number of packets in this field. You can need to modify your network topology to reduce the traffic load for this switch.
Collision frames The collision frames counters are the number of times a packet was attempted to be transmitted but was not successful, but was successful on its next attempt. This means that if the 2 collision frames counter incremented, the switch attempted to send the packet twice and failed but was successful on its third attempt. The traffic load on the interface is excessive and causes the frames to be discarded. Reduce the traffic load on the interface if you see an increasing number of packets in these fields.
Excessive collisions The excessive collisions counter increases after 16 consecutive late collisions have occurred in a row. After 16 attempts have been made to send the packet the packet is dropped, and the counter increments. If this counter increments, it is an indication of a wiring problem, an excessively loaded network, or a duplex mismatch. An excessively loaded network can be caused by too many devices on a shared Ethernet.
Late collisions A late collision occurs when two devices transmit at the same time, and neither side of the connection detects a collision. The reason for this occurrence is because the time to propagate the signal from one end of the network to another is longer than the time to put the entire packet on the network. The two devices that cause the late collision never see that the other is sending until after it puts the entire packet on the network. Late collisions are not detected by the transmitter until after the first 64 byte slot time. This is because they are only detected in transmissions of packets longer than 64 bytes. Late collisions are a result of incorrect cabling or a non-compliant number of hubs in the network. Bad NICs can also cause late collisions.
Good (1 coll) frames The total number of frames which experience exactly one collision and are then successfully transmitted. Collisions in a half-duplex environment are normal expected behavior.
Good (>1 coll) frames The total number of frames which experience between 2 and 15 collisions, inclusive, and are then successfully transmitted. Collisions in a half-duplex environment are normal expected behavior. Frames that increment at the upper end of this counter run the risk of exceeding 15 collisions and being counted as Excessive collisions.
VLAN discardframes The number of frames dropped on an interface because the CFI bit is set. The Canonical Format Indicator (CFI) bit in the TCI of an 802.1q frame is is set to 0 for the ethernet canonical frame format. If the CFI bit is set to 1, this indicates the presence of a RIF (Routing Information Field) or Token Ring noncanonical frame which is discarded.
Received Frames
No bandwidth frames 2900/3500XL only. The number of times that a port received a packet from the network, but the switch did not have the resources to receive it. This only happens under stress conditions but can happen with bursts of traffic on several ports. So, a small number of No bandwidth frames is not a cause for concern. (It still must be far less than one percent of the frames received.) The traffic load on the interface is excessive and causes the frames to be discarded. Reduce the traffic load on the interface if you see an increasing number of packets in this field.
No buffers frames 2900/3500XL only. The number of times that a port received a packet from the network, but the switch did not have the resources to receive it. This only happens under stress conditions but can happen with bursts of traffic on several ports. So, a small number of No buffers frames is not a cause for concern. (It still must be far less than one percent of the frames received.) The traffic load on the interface is excessive and causes the frames to be discarded. Reduce the traffic load on the interface if you see an increasing number of packets in this field.
No dest, unicast No destination unicast are the number of unicast packets that the port did not forward to any other ports. These are brief descriptions of when the No dest, (unicast, multicast, and broadcast) counters can increment:
  • If a port is an access port, and the port is connected to an Inter-Switch Link Protocol (ISL) trunk port, the No dest counter is very large since all inbound ISL packets are not forwarded. This is an invalid configuration.
  • If a port is blocked by Spanning Tree Protocol (STP), most packets are not orwarded, which results in No dest packets. If a port just acquired a link, there is a very brief (less than one second) period where inbound packets are not forwarded.
  • If the port is in a VLAN by itself, and no other ports on the switch belong to that VLAN, all inbound packets are dropped and the counter increments.
  • The counter also increments when the destination address of the packet is learned on the port that the packet was received on. If a packet was received on port 0/1, with destination MAC address X, and the switch has already learned that MAC address X resides on port 0/1, it increments the counter and discards the packet. This can happen in these situations:
    • If a hub is connected to port 0/1, and a workstation connected to the hub transmits a packets to another workstation connected to the hub, port 0/1 does not forward this packet anywhere because the destination MAC resides on the same port.
    • This can also occur if a switch is connected to port 0/1, and starts to flood packets to all of its ports to learn MAC addresses.
  • If a static address has been set up on another port in the same VLAN, and no static address was set up for the receiving port, the packet is dropped. For example, if a static map for MAC address X was configured on port 0/2 to forward traffic to port 0/3, the packet must be received on port 0/2 otherwise the packet is dropped. If a packet is sent from any other port, in the same VLAN as port 0/2, the packet is dropped.
  • If the port is a secure port, packets with disallowed source MAC addresses are not forwarded and increment the counter.
No dest, multicast No destination multicast are the number of multicast packets that the port did not forward to any other ports.
No dest,broadcast No destination broadcast are the number of broadcast packets that the port did not forward to any other ports.
Alignment errors Alignment errors are the number of frames received that do not end with an even number of octets and have a bad CRC. Alignment errors are due to the frame not being completely copied to the wire, which results in fragmented frames. Alignment errors are the result of collisions at half-duplex, a duplex mismatch, bad hardware (NIC, cable, or port), or connected device generating frames that do not end with an octet and have a bad FCS.
FCS errors FCS error count is the number of frames that were received with a bad checksum (CRC value) in the Ethernet frame. These frames are dropped and not propagated onto other ports. FCS errors are the result of collisions at half-duplex, a duplex mismatch, bad hardware (NIC, cable, or port), or a connected device generating frames with bad FCS.
Undersize frames These are the total number of packets received that were less than 64 octets long (which exclude framing bits, but include FCS) and have a good FCS value. This is an indication of a bad frame generated by the connected device. Verify that the connected device operates correctly.
Oversize frames Number of packets received by the port from the network, where the packets were more than 1514 bytes. This can be an indication of faulty hardware, dot1q or ISL trunking configuration issues.
Collision fragments The total number of frames whose length is less than 64 octets (which exclude framing bits, but which include FCS) and have a bad FCS value. If this counter increments, this is an indication that the ports are configured at half-duplex. Change the duplex setting to full-duplex.
Overrun frames The number of times the receiver hardware was unable to hand received data to a hardware buffer. The input rate of traffic exceeded the ability of the receiver to handle the data.
VLAN filtered frames The total number of frames which are filtered because of the type of VLAN information contained in the frame. The port can be configured to filter 802.1Q tagged frames. When a frame is received which contains an 802.1Q tag the frame is filtered and this statistic is incremented.
Source routed frames The total number of receive frames that are discarded due to the source route bit being set in the source address of the native frame. This kind of source routing is only defined for Token Ring and FDDI. The IEEE ethernet specification forbids this bit to be set in any Ethernet frame. Therefore, the switch discards such frames.
Valid oversize frames The total number of frames received whose length exceeds the System MTU yet which have good FCS values. This statistic counts frames that exceed the configured System MTU but which can have been increased from 1518 bytes to allow for Q-in-Q or MPLS encapsulations.
Symbol error frames Gigabit Ethernet (1000 Base-X) uses 8B/10B Encoding to translate 8bit data from the MAC sublayer(layer 2) to a 10bit Symbol to send over the wire. When a port receives a Symbol, it extracts the 8 bit data from the Symbol (10 bits). A Symbol error means the interface detects an undefined (invalid) Symbol received. Small amounts of symbol errors can be ignored. Large amounts of symbol errors can indicate a bad device, cable, or hardware.
Invalid frames, too large Giant frames or frames received that exceed the maximum IEEE 802.3 frame size (1518 bytes for non-jumbo Ethernet) and have a bad Frame Check Sequence (FCS). In many cases, this is the result of a bad NIC. Try to find the offending device and remove it from the network.
Invalid frames, too small Runt frames or frames received that are less than 64 bytes (which includes the FCS bits and excludes the frame header) and have either an FCS error or an alignment error. This can be caused by a duplex mismatch and physical problems, such as a bad cable, port, or NIC on the attached device.

Show Top for CatOS

The command show top allows you to collect and analyze data for each physical port on a switch. The command displays this data for each physical port:

  • Port utilization (Uti %)

  • Number of in and out bytes (Bytes)

  • Number of in and out packets (Pkts)

  • Number of in and out broadcast packets (Bcst)

  • Number of in and out multicast packets (Mcst)

  • Number of in errors (Error)

  • Number of buffer-overflow errors (Overflow)

 Console> (enable) sh top
Start Time:     Mar 28 2007 06:58:41
End Time:       Mar 28 2007 06:59:11
PortType:       all
Metric:         util
Port  Band- Uti Bytes                Pkts       Bcst       Mcst       Error Over
      width  %  (Tx + Rx)            (Tx + Rx)  (Tx + Rx)  (Tx + Rx)  (Rx)  flow
----- ----- --- -------------------- ---------- ---------- ---------- ----- ----
 3/11  a-10   0               334187       1561         22       1536     0    0
 3/12 a-100   0               333608       1557         22       1532     0    0
 3/25 a-100   0               333622       1555         22       1533     0    0
 6/2   1000   0                    0          0          0          0     0    0
 6/1   1000   0                    0          0          0          0     0    0
 4/8   1000   0                    0          0          0          0     0    0
 4/7   1000   0                    0          0          0          0     0    0
 4/6   1000   0                    0          0          0          0     0    0
 4/5   1000   0                    0          0          0          0     0    0
 4/4   1000   0                    0          0          0          0     0    0
 4/3   1000   0                    0          0          0          0     0    0
 4/2   1000   0                    0          0          0          0     0    0
 4/1   1000   0                    0          0          0          0     0    0
 3/48  auto   0                    0          0          0          0     0    0
 3/47  auto   0                    0          0          0          0     0    0
 3/46  auto   0                    0          0          0          0     0    0

Note: When you calculate port utilization, the command bundles the Tx and Rx lines into the same counter and also looks at the full-duplex bandwidth when it calculates the percentage of utilization. For example, a Gigabit Ethernet port is 2000 Mbps full duplex.

In Errors is the sum of all error packets received on that port.

Buffer Overflow means that the port receivesg more traffic than it can store in its buffer. This can be caused a bursty traffic, as well an overrun of buffers. The suggested action is to decrease the transmission of the source device.

Also refer to 'In-Lost' and 'Out-Lost' counters from the show mac command.

Common System Error Messages

Cisco IOS sometimes has a different format for system messages. You can examine CatOS system messages and Cisco IOS system messages for a comparison. You can refer to the Messages and Recovery Procedures Guide for the release of software you run. For example, you can look at Messages and Recovery Procedures for CatOS software Version 7.6 and compare them to the Messages and Recovery Procedures for Cisco IOS 12.1 E Releases.

Error Messages on WS-X6348 Modules

Look at these error messages:

  • Coil Pinnacle Header Checksum

  • Coil Mdtif State Machine Error

  • Coil Mdtif Packet CRC Error

  • Coil Pb Rx Underflow Error

  • Coil Pb Rx Parity Error

You can see syslog messages with one of those errors listed:

%SYS-5-SYS_LCPERR5:Module 9: Coil Pinnacle Header Checksum Error - Port #37

If you see this type of message or you notice that groups of 10/100 ports that fail on WS-X6348 modules, refer to these documents for further troubleshooting advice based on the operating system you use:

%PAGP-5-PORTTO / FROMSTP and %ETHC-5-PORTTO / FROMSTP

For CatOS, use the show logging buffer command to view stored log messages. For Cisco IOS, use the show logging command.

Console> (enable) sh logging buffer
  2003 Jun 02 20:12:43 %PAGP-5-PORTTOSTP:Port 3/2 joined bridge port 3/2
  2003 Jun 02 20:59:56 %PAGP-5-PORTFROMSTP:Port 3/1 left bridge port 3/1
  !--- This is the command to view the logging buffer on switches that run CatOS.

This message can cause concern for customers but for the most part it is informational in nature.

%PAGP-5-PORTTO / FROMSTP and %ETHC-5-PORTTO / FROMSTP 

The Port Aggregation Protocol (PAgP) negotiates Etherchannel links between switches. Whenever a device joins or leaves a bridge port, an informational message is displayed on the console. In most cases this message is completely normal, but if you see these messages on ports that should not flap for any reason, you must investigate further.

In CatOS software version 7.x and later, "PAGP-5" was changed to "ETHC-5" to make the message more understandable.

This message is specific to the Catalyst 4000, 5000, and 6000 series switches that run CatOS. There are no error messages for switches that run Cisco IOS that are equivalent to this message. For more information, about error messages on switches that run CatOS, refer to these documents for your platform:

%SPANTREE-3-PORTDEL_FAILNOTFOUND

This message does not indicate a problem with the switch. It normally occurs along with %PAGP-5-PORTFROMSTP messages.

The Port Aggregation Protocol (PAgP) negotiates Etherchannel links between switches. Whenever a device joins or leaves a bridge port, an informational message is displayed on the console. In most cases this message is completely normal, but if you see these messages on ports that should not flap for any reason, you must investigate further.

This message is specific to the Catalyst 4000, 5000, and 6000 series switches that run CatOS. There are no error messages for switches that run Cisco IOS that are equivalent to this message. For more information about error messages on switches that run CatOS, refer to these documents for your platform:

%SYS-4-PORT_GBICBADEEPROM: / %SYS-4-PORT_GBICNOTSUPP

The most common cause of this message is when a non-certified, non-Cisco GBIC is inserted into a gigabit ethernet module. The GBIC does not have a Cisco SEEPROM which results in a generated error message.

GBIC modules WS-G5484, WS-G5486, and WS-G5487 used with a WS-X6408-GBIC can also cause these error messages to appear, but there is not an actual problem with the card or GBICs and there is a software upgrade fix.

Refer to this Common CatOS Error Messages on Catalyst 6000/6500 Series Switches for more information.

%AMDP2_FE-3-UNDERFLO

This error message is caused when a frame is transmitted, and the local buffer of the controller chip local buffer receives insufficient data. The data cannot be transferred to the chip fast enough to keep pace with output rate. Normally, such a condition is temporary, dependent upon transient peak loads within the system. The issue occurs when an excessive amount of traffic is processed by the Fast Ethernet interface. The error message is received when the traffic level reaches about 2.5 Mb. This traffic level constrain is due to hardware limitation. Because of this, a chance exists for the device connected to the catalyst switch to drop packets.

The resolution is that ordinarily the system recovers automatically. No action is required. If the switch overwhelms the Ethernet interface, check the speed and duplex settings. Also use a sniffer program to analyze packets that come in and out of the router fast Ethernet interface. In order to avoid packet drops on the device connected to the catalyst switch, issue the ip cef command on the fast Ethernet interface of the device connected to the switch.

%INTR_MGR-DFC1-3-INTR: Queueing Engine (Blackwater) [1]: FIC Fabric-A Received Unexpected Control Code

The reason for this error message is the receipt of a packet from the switch fabric, where the CRC value in the fabric header on that packet did not match the CRC value calculated by the Fabric Interface Controller (FIC) subblock of the Blackwater ASIC. This indicates that a corruption of the packet occurred within transfer, and Blackwater received the corrupted packet.

Command Rejected: [Interface] not a Switching Port

In switches that support both L3 interfaces and L2 switchport, the message Command rejected: [interface] not a switching port displays when you try to enter a command related to layer 2 on a port that is configured as a layer 3 interface.

In order to convert the interface from layer 3 mode to layer 2 mode, issue the interface configuration command switchport. After you issue this command, configure the port for any layer 2 properties.

Common Port and Interface Problems

Port or Interface Status is Disable or Shutdown

An obvious but sometimes overlooked cause of port connectivity failure is an incorrect configuration on the switch. If a port has a solid orange light, this means the software inside the switch shut down the port, either by way of the user interface or by internal processes.

Note: Some port LEDs of the platform work differently in regard to STP. For example, the Catalyst 1900/2820 turns ports orange when they are in STP blocking mode. In this case, an orange light can indicate the normal functions of the STP. The Catalyst 6000/5000/4000 does not turn the port light orange when it blocks for STP.

Make sure the port or module has not been disabled or powered down for some reason. If a port or module is manually shut down on one side of the link or the other, the link does not come up until you re-enable the port. Check the port status on both sides.

For CatOS, check show port and, if the port is disabled, re-enable it:

Port  Name                 Status     Vlan       Duplex Speed Type
----- -------------------- ---------- ---------- ------ ----- ------------
 3/1                       disabled   1            auto  auto 10/100BaseTX
  !--- Use the set port enable mod/port command to re-enable this port.

Use the show module command to determine if the module is disabled. If it is, re-enable it:

Mod Slot Ports Module-Type               Model               Sub Status
--- ---- ----- ------------------------- ------------------- --- --------
2   2    2     1000BaseX Supervisor      WS-X6K-SUP1A-2GE    yes ok
16  2    1     Multilayer Switch Feature WS-F6K-MSFC         no  ok
3   3    48    10/100BaseTX Ethernet     WS-X6348-RJ-45      no  disable
!--- Use the set module enable mod/port command to re-enable this port.

For Cisco IOS, use the show run interface command and check to see if the interface is in a shutdown state:

Switch#sh run interface fastEthernet 4/2
!
interface FastEthernet4/2
 switchport trunk encapsulation dot1q
 switchport mode trunk
 shutdown
 duplex full
 speed 100
end
!--- Use the no shut command in config-if mode to re-enable this interface.  

If the port goes into shutdown mode immediately after a reboot of the switch, the probable cause is the port security setting. If unicast flooding is enabled on that port, it can cause the port to shut down after a reboot. Cisco recommends that you disable the unicast flooding because it also ensure that no flooding occurs on the port once the MAC address limit is reached.

Port or Interface Status is errDisable

By default, software processes inside the switch can shut down a port or interface if certain errors are detected.

When you look at show port command for CatOS the status can read errdisable:

switch>(enable) sh port 4/3
  Port  Name                 Status     Vlan       Duplex Speed Type
  ----- -------------------- ---------- ---------- ------ ----- ------------
  4/3                        errdisable 150          auto  auto 10/100BaseTX
  !--- The show port command displays a status of errdisable.

Or use the show interface card-type {slot/port} status command for Cisco IOS:

Router#show int fasteth 2/4 status
  
  Port    Name               Status       Vlan       Duplex  Speed Type
  Gi2/4                      err-disabled 1            full   1000 1000BaseSX
  !--- The show interfaces card-type {slot/port} status command for Cisco IOS
  !--- displays a status of errdisabled.
  !--- The show interfaces status errdisabled command shows all the interfaces
  !--- in this status.

The show logging buffer command for CatOS and the show logging command for Cisco IOS also display error messages (exact message format varies) that relate to the errdisable state.

Ports or interlaces being shut down as a result of errdisable are referred to as reasons in CatOS and causes in Cisco IOS. The reasons or causes for this happening range from EtherChannel misconfiguration that causes a PAgP flap, duplex mismatch, BPDU port-guard and portfast configured at the same time, UDLD that detects a one-way link, etc.

You have to manually re-enable the port or interface to take it out the errdisable state unless you configure an errdisable recovery option. In CatOS software 5.4(1) and later you have the ability to automatically re-enable a port after a configurable amount of time spent in the errdisable state. Cisco IOS on most switches also has this functionality. The bottom line is that even if you configure the interface to recover from errdisable the problem reoccurs until the root cause is determined.

For more information on the causes of and recovery from the errdisable status for switches that run CatOS, refer to Recovering From errDisable Port State on the CatOS Platforms.

Note: Use this link as a reference for errdisable status on switches that run Cisco IOS, as well since the root causes are the same no matter which operating system you run.

This table shows a comparison of the commands used to configure verify and troubleshoot the errdisable status on switches that run CatOS and Cisco IOS. Choose a command to go to the command documentation.

CatOS errdisable Commands Action Cisco IOS errdisable Commands
set errdisable-timeout {enable | disable} {reason} set or configure errdisable detect cause errdisable recovery cause
set errdisable-timeout interval {interval set or configure errdisable recovery {interval
show errdisable-timeout verify & troubleshoot show errdisable detect show interfaces status err-disabled

Port or Interface Status is Inactive

One common cause of inactive ports on switches that run CatOS is when the VLAN they belong to disappears. The same problem can occur on switches that run Cisco IOS when interfaces are configured as layer 2 switchports that use the switchport command.

Every port in a Layer 2 switch belongs to a VLAN. Every port on a Layer 3 switch configured to be a L2 switchport must also belong to a VLAN. If that VLAN is deleted, then the port or interface becomes inactive.

Note: Some switches show a steady orange (amber) light on each port when this happens.

For CatOS, use the show port or show port status command along with the show vlan command to verify:

Switch> (enable) sh port status 2/2
Port Name Status Vlan Duplex Speed Type
----- -------------------- ---------- ---------- ------ ----- ------------
2/2 inactive 2 full 1000 1000BaseSX
!--- Port 2/2 is inactive for VLAN 2.
     
Switch> (enable) sh vlan
VLAN Name Status IfIndex Mod/Ports, Vlans
---- -------------------------------- --------- ------- ------------------------
1 default active 5 2/1
!--- VLANs are displayed in order and VLAN 2 is missing.

For Cisco IOS, use the show interfaces card-type {slot/port} switchport command along with show vlan to verify.

Router#sh interfaces fastEthernet 4/47 switchport
  Name: Fa4/47Switchport: Enabled
  Administrative Mode: static access
  Operational Mode: static access
  Administrative Trunking Encapsulation: negotiate
  Operational Trunking Encapsulation: native
  Negotiation of Trunking: Off
  Access Mode VLAN: 11 ((Inactive))
  !--- FastEth 4/47 is inactive.
 
 Router#sh vlan
 
 VLAN Name                             Status    Ports
 ---- -------------------------------- --------- -------------------------------
 1    default                          active    Gi1/1, Gi2/1, Fa6/6
 10   UplinkToGSR's                    active    Gi1/2, Gi2/2
 !--- VLANs are displayed in order and VLAN 11 is missing.
 30   SDTsw-1ToSDTsw-2Link             active	Fa6/45

If the switch that deleted the VLAN is a VTP server for the VTP domain, every server and client switch in the domain has the VLAN removed from their VLAN table as well. When you add the VLAN back into the VLAN table from a VTP server switch, the ports of the switches in the domain that belong to that restored VLAN become active again. A port remembers what VLAN it is assigned to, even if the VLAN itself is deleted.

Refer to Understanding and Configuring VLAN Trunk Protocol (VTP) for more information on VTP.

Note: If the output of the show interface <interface number> switchport command displays the port as a trunk port even after you configure the port as an access port with the switchport access vlan <vlan no:> command, issue the switchport mode access command in order to make the port an access port.

Uplink Port or Interface Status is Inactive

On a Catalyst 4510R series switch, in order to enable both the 10-Gigabit Ethernet and the Gigabit Ethernet SFP uplink ports, there is an optional configuration. In order to enable the simultaneous use of 10-Gigabit Ethernet and the Gigabit Ethernet SFP interfaces, issue the hw-module uplink select all command. After you issue the command, re-boot the switch or else the output of the show interface status module module number command shows the uplink port as inactive.

Cisco IOS Software Release 12.2(25)SG supports the simultaneous use of 10-Gigabit Ethernet and the Gigabit Ethernet SFP interfaces on Catalyst 4500 switches.

Note: On the Catalyst 4503, 4506, and 4507R series switches, this capability is automatically enabled.

Deferred Counter on the Catalyst Switch Interface Starts Incrementing

The issue is because the traffic load destined for the switch is excessive and causes the frames to be discarded. Normally the deferred frames are the number of frames that have been transmitted successfully after waiting for the media, because the media was busy. This is usually seen in half duplex environments where the carrier is already in use when it tries to transmit a frame. But in full duplex environments the issue occurs when the excessive load is destined for the switch.

This is the workaround:

  • Hardcode both ends of the link to full duplex so that the negotiation mismatch can be avoided.

  • Change the cable and patch panel cord to ensure that the cable and patch cords are not defective.

Note: If the Deferred Counter error increments on a GigabitEthernet of a Supervisor 720, turn on speed negotiation on the interface as a workaround.

Intermittent Failure to set timer [value] from vlan [vlan no]

The issue occurs when Encoded Address Recognition Logic (EARL) is unable to set the CAM aging time for the VLAN to the required number of seconds. Here, the VLAN aging time is already set to fast aging.

When the VLAN is already in fast aging, EARL cannot set the VLAN to fast aging, and aging timer set process is blocked. The default CAM aging time is five minutes, which means that the switch flushes the table of learned MAC addresses every five minutes. This ensures that the MAC address table (the CAM table) contains the most recent entries.

Fast aging temporarily sets the CAM aging time to the number of seconds that the user specifies, and is used in conjunction with the Topology Change Notification (TCN) process. The idea is that when a topology change occurs, this value is necessary to flush the CAM table faster, to compensate for the topology change.

Issue the show cam aging command to check the CAM aging time on the switch. TCNs and fast aging are fairly rare. As a result, the message has a severity level of 3. If the VLANs are frequently in fast aging, check the reason for fast aging.

The most common reason for TCNs is client PCs connected directly to a switch. When you power up or down the PC, the switch port changes state, and the switch starts the TCN process. This is because the switch does not know that the connected device is a PC; the switch only knows that the port has changed the state.

In order to resolve this issue, Cisco has developed the PortFast feature for host ports. An advantage of PortFast is that this feature suppresses TCNs for a host port.

Note: PortFast also bypasses spanning-tree calculations on the port, and is therefore only suitable for use on a host port.

In order to enable PortFast on the port, configure one of these commands:

set spantree portfast mod/port enable | disable

or

set port host mod/port Cisco recommends this command if the switch runs CatOS5.4 or higher versions.

Trunking Mode Mismatch

Check the trunking mode on each side of the link. Make sure both sides are in the same mode (both trunking with the same method: ISL or 802.1q, or both not trunking). If you turn the trunking mode to on (as opposed to auto or desirable) for one port and the other port has the trunking mode set to off, they are not able to communicate. Trunking changes the formatting of the packet. The ports need to be in agreement as to what format they use on the link or they do not understand each other.

For CatOS, use the show trunk {mod/port}command to verify the trunk status and Native VLAN (for dot1q) matches on both sides.

Switch> (enable) sh trunk 3/1
  * - indicates vtp domain mismatch
  Port      Mode         Encapsulation  Status        Native vlan
  --------  -----------  -------------  ------------  -----------
   3/1      desirable    dot1q          trunking      1
  
  Port      Vlans allowed on trunk
  --------  ---------------------------------------------------------------------
   3/1      1-1005,1025-4094
!--- Output truncated.

For Cisco IOS, use the show interfaces card-type {mod/port} trunk command to verify the trunking configuration and Native VLAN.

Router#sh interfaces fastEthernet 6/1 trunk
  
  Port      Mode         Encapsulation  Status        Native vlan
  Fa6/1     desirable    802.1q         trunking      1
  
  Port      Vlans allowed on trunk
  Fa6/1     1-4094
!--- Output truncated.

Refer to these documents for more information on the different trunking modes, guidelines, and restrictions:

Jumbos, Giants, and Baby Giants

The Maximum Transmission Unit (MTU) of the data portion of an ethernet frame is 1500 bytes by default. If the transmitted traffic MTU exceeds the supported MTU the switch does not forward the packet. Also, dependent upon the hardware and software, some switch platforms increment port and interface error counters as a result.

  • Jumbo frames are not defined as part of the IEEE Ethernet standard and are vendor-dependent. They can be defined as any frame bigger than the standard ethernet frame of 1518 bytes (which includes the L2 header and Cyclic Redundancy Check (CRC)). Jumbos have larger frame sizes, typically > 9000 bytes.

  • Giant frames are defined as any frame over the maximum size of an ethernet frame (larger than 1518 bytes) that has a bad FCS.

  • Baby Giant frames are just slightly larger than the maximum size of an ethernet frame. Typically this means frames up to 1600 bytes in size.

Support for jumbo and baby giants on Catalyst switches varies by switch platform, sometimes even by modules within the switch. The software version is also a factor.

Refer to Configuring Jumbo/Giant Frame Support on Catalyst Switches for more information on system requirements, configuring and troubleshooting for jumbo and baby giant issues.

Cannot Ping End Device

Check the end device by pinging from the directly connected switch first, then work your way back port by port, interface by interface, trunk by trunk until you find the source of the connectivity issue. Make sure each switch can see the end device's MAC address in its Content-Addressable Memory (CAM) table.

For CatOS, use the show cam dynamic {mod/port} command.

Switch> (enable) sh cam dynamic 3/1
* = Static Entry. + = Permanent Entry. # = System Entry. R = Router Entry.
X = Port Security Entry $ = Dot1x Security Entry
  
VLAN  Dest MAC/Route Des    [CoS]  Destination Ports or VCs / [Protocol Type]
----  ------------------    -----  -------------------------------------------
2     00-40-ca-14-0a-b1             3/1 [ALL]
!--- A workstation on VLAN 2 with MAC address 00-40-ca-14-0a-b1 is seen in the CAM table
!--- on the trunk port of a switch running CatOS.
Total Matching CAM Entries Displayed  =1
Console> (enable)

For Cisco IOS, use the show mac address-table dynamic command, or substitute the interface keyword.

Router# sh mac-address-table int fas 6/3
Codes: * - primary entry
  
  vlan   mac address     type    learn qos            ports
------+----------------+--------+-----+---+--------------------------
*    2  0040.ca14.0ab1   dynamic  No    --  Fa6/3
!--- A workstation on VLAN 2 with MAC address 0040.ca14.0ab1 is directly connected
!--- to interface fastEthernet 6/3 on a switch running Cisco IOS.

Once you know the switch actually has the MAC address of the device in it's CAM table, determine whether this device is on the same or different VLAN from where you are trying to ping.

If the end device is on a different VLAN from where you are trying to ping, a L3 switch or router must be configured to allow the devices to communicate. Make sure your L3 addressing on the end device and on the router/ L3 switch is correctly configured. Check the IP address, subnet mask, default gateway, dynamic routing protocol configuration, static routes, etc.

Using Set Port Host or Switchport Host to Fix Startup Delays

If stations are not able to talk to their primary servers when connecting through a switch, the problem can involve delays on the switch port becoming active after the physical layer link comes up. In some cases, these delays can be up to 50 seconds.

Some workstations simply cannot wait this long before finding their server without giving up. These delays are caused by STP, trunking negotiations (DTP), and EtherChannel negotiations (PAgP). All of these protocols can be disabled for access ports where they are not needed, so the switch port or interface starts forwarding packets a few seconds after it establishes a link with its neighbor device.

The set port host command was introduced in CatOS Version 5.4. This command sets the trunking and channel modes to off and puts the port in a STP forwarding state.

Switch> (enable) set port host 3/5-10
Port(s) 3/5-10 channel mode set to off.
!--- The set port host command also automatically turns off etherchannel on the ports.
Warning: Spantree port fast start should only be enabled on ports connected
to a single host.  Connecting hubs, concentrators, switches, bridges, etc. to
a fast start port can cause temporary spanning tree loops.  Use with caution.
!--- Notice the switch warns you to only enable port host on access ports.
Spantree ports 3/5-10 fast start enabled.Dot1q tunnel feature disabled on port(s) 3/5-10.
Port(s) 3/5-10 trunk mode set to off.
!--- The set port host command also automatically turns off trunking on the ports.

Note: For CatOS versions earlier than version 5.4, the set spantree portfast {mod/port} enable command was used. In current versions of CatOS, you still have the option to use only this command, but this requires that you turn off trunking and etherchannel separately to help fix workstation startup delays. The additional commands to do this are: set port channel {mod/port} off and set trunk {mod/port} off .

For Cisco IOS, you can use the switchport host command to disable channeling and to enable spanning-tree portfast and the switchport nonegotiate command to turn off DTP negotiation packets. Use the interface-range command to do this on multiple interfaces at once.

Router6k-1(config)#int range fastEthernet 6/13 - 18
Router6k-1(config-if-range)#switchport
Router6k-1(config-if-range)#switchport host
switchport mode will be set to access
spanning-tree portfast will be enabled
channel group will be disabled
!--- Etherchannel is disabled and portfast is enabled on interfaces 6/13 - 6/18.
Router6k-1(config-if-range)#switchport nonegotiate
!--- Trunking negotiation is disabled on interfaces 6/13 - 6/18.
Router6k-1(config-if-range)#end
Router6k-1#

Cisco IOS has the option to use the global spanning-tree portfast default command to automatically apply portfast to any interface configured as a layer 2 access switchport. Check the Command Reference for your release of software to verify the availability of this command. You can also use the spanning-tree portfast command per interface, but this requires that you turn off trunking and etherchannel separately to help fix workstation startup delays.

Refer to Using Portfast and Other Commands to Fix Workstation Startup Connectivity Delays for more information how to fix startup delays.

Speed/Duplex, Autonegotiation, or NIC Issues

If you have a large amount of alignment errors, FCS errors, or late collisions, this can indicate one of these:

  • Duplex Mismatch

  • Bad or Damaged Cable

  • NIC Card Issues

Duplex Mismatch

A common issue with speed/duplex is when the duplex settings are mismatched between two switches, between a switch and a router or between the switch and a workstation or server. This can occur when manually hardcoding the speed and duplex or from autonegotiation issues between the two devices.

If the mismatch occurs between two Cisco devices with the Cisco Discovery Protocol (CDP) enabled, you see the CDP error messages on the console or in the logging buffer of both devices. CDP is useful to detect errors, as well as port and system statistics on nearby Cisco devices. CDP is Cisco proprietary and works by sending packets to a well-known mac address 01-00-0C-CC-CC-CC.

The example shows the log messages that result from a duplex mismatch between two Catalyst 6000 series switches: one that runs CatOS, and the other that runs Cisco IOS. These messages generally tell you what the mismatch is and where it occurs.

2003 Jun 02 11:16:02 %CDP-4-DUPLEXMISMATCH:Full/half duplex mismatch detected on port 3/2
!--- CatOS switch sees duplex mismatch.
Jun  2 11:16:45 %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet6/2
(not half duplex), with TBA04251336 3/2 (half duplex).
!--- Cisco IOS switch sees duplex mismatch.

For CatOS, use the show cdp neighbor [mod/port] detail command to display CDP information for Cisco neighbor devices.

Switch> (enable) sh cdp neighbor 3/1 detail
Port (Our Port): 3/1
Device-ID: Router
Device Addresses:
  IP Address: 10.1.1.2
Holdtime: 133 sec
Capabilities: ROUTER SWITCH IGMP
Version:
  Cisco Internetwork Operating System Software
  IOS (tm) c6sup2_rp Software (c6sup2_rp-PK2S-M), Version 12.1(13)E6, EARLY DEPL
OYMENT RELEASE SOFTWARE (fc1)
  TAC Support: http://www.cisco.com/tac
  Copyright (c) 1986-2003 by cisco Systems, Inc.
  Compiled Fri 18-Apr-03 15:35 by hqluong
Platform: cisco Catalyst 6000
Port-ID (Port on Neighbors's Device): FastEthernet6/1
!--- Neighbor device to port 3/1 is a Cisco Catalyst 6000 Switch on
!--- FastEth 6/1 running Cisco IOS.
VTP Management Domain: test1Native VLAN: 1
Duplex: full
!--- Duplex is full.
System Name: unknown
System Object ID: unknown
Management Addresses: unknown
Physical Location: unknown
Switch> (enable)

For Cisco IOS, use the show cdp neighbors card-type {slot/port} detail command to display CDP information for Cisco neighbor devices.

Router#sh cdp neighbors fastEthernet 6/1 detail
-------------------------
Device ID: TBA04251336
Entry address(es):
  IP address: 10.1.1.1
Platform: WS-C6006,  Capabilities: Trans-Bridge Switch IGMP
Interface: FastEthernet6/1,  Port ID (outgoing port): 3/1
Holdtime : 152 sec 
Version :
WS-C6006 Software, Version McpSW: 6.3(3) NmpSW: 6.3(3)
Copyright (c) 1995-2001 by Cisco Systems
!--- Neighbor device to FastEth 6/1 is a Cisco Catalyst 6000 Switch
!--- on port 3/1 running CatOS.
advertisement version: 2
VTP Management Domain: 'test1'
Native VLAN: 1
Duplex: full
!--- Duplex is full.
Router#

Setting auto speed/duplex on one side and 100/Full-duplex on the other side is also a misconfiguration, and can result in a duplex mismatch. If the switch port receives a lot of late collisions, this usually indicates a duplex mismatch problem and can result in the port being placed in an errdisable status. The half duplex side only expects packets at certain times, not at any time, and therefore counts packets received at the wrong time as collisions. There are other causes for late collisions besides duplex mismatch but this is one of the most common reasons. Always set both sides of the connection to auto-negotiate speed/duplex, or set the speed/duplex manually on both sides.

For CatOS, use the show port status [mod/port] command to display the speed and duplex status as well as other information. Use the set port speed and set port duplex commands to hardcode both sides to 10 or 100 and half or full as necessary.

Switch> (enable) sh port status 3/1
Port  Name                 Status     Vlan       Duplex Speed Type
----- -------------------- ---------- ---------- ------ ----- ------------
 3/1                       connected  1          a-full a-100 10/100BaseTX
Switch> (enable)

For Cisco IOS, use the show interfaces card-type {slot/port} status command to display speed and duplex settings as well as other information. Use the speed and duplex commands from interface configuration mode to hardcode both sides to 10 or 100 and half or full as necessary.

Router#sh interfaces fas 6/1 status
Port    Name               Status       Vlan       Duplex  Speed Type
Fa6/1                      connected    1          a-full  a-100 10/100BaseTX

If you use the show interfaces command without the status option, you see a setting for speed and duplex, but you do not know whether this speed and duplex was achieved through autonegotiation or not.

Router#sh int fas 6/1
FastEthernet6/1 is up, line protocol is up (connected)
  Hardware is C6k 100Mb 802.3, address is 0009.11f3.8848 (bia 0009.11f3.8848)
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Full-duplex, 100Mb/s
!--- Full-duplex and 100Mbps does not tell you whether autoneg was used to achieve this.
!--- Use the sh interfaces fas 6/1 status command to display this.

Bad or damaged cable

Always check the cable for marginal damage or failure. A cable can be just good enough to connect at the physical layer, but it corrupts packets as a result of subtle damage to the wiring or connectors. Check or swap the copper or fiber cable. Swap the GBIC (if removable) for fiber connections. Rule out any bad patch panel connections or media convertors between source and destination. Try the cable in another port or interface if one is available and see if the problem continues.

Auto negotiation and NIC Card Issues

Problems sometimes occur between Cisco switches and certain third-party NIC cards. By default, Catalyst switch ports and interfaces are set to autonegotiate. It is common for devices like laptops or other devices to be set to autonegotiate as well, yet sometimes autonegotation issues occur.

In order to troubleshoot autonegotiation problems it is often recommended to try hardcoding both sides. If neither autonegotiation or hardcoding seem to work, there can be a problem with the firmware or software on your NIC card. Upgrade the NIC card driver to the latest version available on the web site of the manufacture to resolve this.

Refer to Configuring and Troubleshooting Ethernet 10/100/1000 MB Half/Full Duplex Auto-Negotiation for details on how to resolve speed/duplex and autonegotiation issues.

Refer to Troubleshooting Cisco Catalyst Switches to NIC Compatibility Issues for details on how to resolve third-party NIC issues.

Spanning Tree Loops

Spanning Tree Protocol (STP) loops can cause serious performance issues that masquerade as port or interface problems. In this situation, your bandwidth is used by the same frames over and over again, which leaves little room for legitimate traffic.

The STP loop guard feature provides additional protection against Layer 2 forwarding loops (STP loops). An STP loop is created when an STP blocking port in a redundant topology erroneously transitions to the forwarding state. This usually happens because one of the ports of a physically redundant topology (not necessarily the STP blocking port) no longer receives STP BPDUs. In its operation, STP relies on continuous reception or transmission of BPDUs based on the port role. The designated port transmits BPDUs, and the non-designated port receives BPDUs.

When one of the ports in a physically redundant topology no longer receives BPDUs, the STP conceives that the topology is loop free. Eventually, the blocking port from the alternate or backup port becomes designated and moves to a forwarding state. This situation creates a loop.

The loop guard feature makes additional checks. If BPDUs are not received on a non-designated port, and loop guard is enabled, that port is moved into the STP loop-inconsistent blocking state, instead of the listening / learning / forwarding state. Without the loop guard feature, the port assumes the designated port role. The port moves to the STP forwarding state and creates a loop. Refer to Spanning-Tree Protocol Enhancements using Loop Guard and BPDU Skew Detection Features for more information on the loop guard feature.

This document covers reasons that STP can fail, what information to look for to identify the source of the problem, and what kind of design minimizes STP risks.

Loops can also be caused by a uni-directional link. For more information, refer to the UDLD: One-Way link problems section of this document.

UDLD: One-Way Link

A unidirectional link is a link where traffic goes out one way, but no traffic is received coming back. The switch does not know that the link coming back is bad (the port thinks the link is up and working).

A broken fiber cable or other cabling/port issues can cause this one-way only communication. These partially functional links can cause problems such as STP loops when the switches involved do not know that the link is partially broken. UDLD can put a port in errdisable state when it detects a unidirectional link. The command udld aggressive-mode can be configured on switches that run CatOS and Cisco IOS (check release notes for command availability) for point-to-point connections between switches where malfunctioning links cannot be tolerated. The use of this feature can help you identify difficult to find unidirectional link problems

Refer to Understanding and Configuring the Unidirectional Link Detection Protocol (UDLD) Feature for configuration information on UDLD.

Deferred Frames (Out-Lost or Out-Discard)

If you have a large number of deferred frames, or Out-Discard (also referred to as Out-Lost on some platforms), it means that the switch's output buffers have filled up and the switch had to drop these packets. This can be a sign that this segment is run at an inferior speed and/or duplex, or there is too much traffic that goes through this port.

For CatOS, use the show mac command for the module and port or the entire module to look at out-discards:

MAC      Dely-Exced MTU-Exced  In-Discard Out-Discard
-------- ---------- ---------- ---------- -----------
2/1              0          -          0    10175888
2/2              0          -          0     9471889
2/3              0          -          0     9095371
2/4              0          -          0     8918785
!--- The show mac command run on mod 2 at different intervals shows
!--- the out-discard counter incrementing.

For Cisco IOS, use the show interfaces counters error command.

Router#sho interfaces counters error
Port        Align-Err    FCS-Err   Xmit-Err    Rcv-Err UnderSize OutDiscards
Fa7/47              0          0          0          0         0           0
Fa7/48              0          0          0          0         0     2871800
Fa8/1               0          0          0          0         0     2874203
Fa8/2             103          0          0        103         0     2878032
Fa8/3             147          0          0        185         0           0
Fa8/4             100          0          0        141         0     2876405
Fa8/5               0          0          0          0         0     2873671
Fa8/6               0          0          0          0         0           2
Fa8/7               0          0          0          0         0           0
!--- The show interfaces counters errors command shows certain interfaces
!--- incrementing large amounts of OutDiscards while others run clean.

Investigate these common causes of output buffer failures:

Inferior Speed/Duplex for the Amount of Traffic

Your network can send too many packets through this port for the port to handle at its current speed/duplex setting. This can happen where you have multiple high-speed ports flowing to a single (usually slower) port. You can move the device that hangs off this port to faster media. For example, if the port is 10 Mbps, move this device to a 100 Mbps or Gigabit port. You can change the topology to route frames differently.

Congestion Issues: Segment Too Busy

If the segment is shared, other devices on this segment can transmit so much that the switch has no opportunity to transmit. Avoid daisy-chained hubs whenever possible. Congestion can lead to packet loss. Packet loss causes retransmissions at the transport layer which in turn causes users to experience latency at the application level. You can upgrade10Mbps links to 100Mbps or Gigabit Ethernet links when possible. You can remove some devices from crowded segments to other less populated segments. Make congestion avoidance a priority on your network.

Applications

At times the traffic transmission characteristics of the applications used can lead to output buffer problems. NFS file transfers that come from a Gigabit attached server that uses user datagram protocol (UDP) with a 32K window size is one example of an application setting that can bring out this type of problem. If you have checked or tried the other suggestions in this document (checked speed/duplex, no physical errors on the link, all the traffic is normal valid traffic, and so on), then reducing the unit size that is sent by the application can help alleviate this problem.

Software Problems

If you see behavior that can only be considered "strange," you can isolate the behavior to a specific box, and you have looked at everything suggested so far, this can indicate software or hardware problems. It is usually easier to upgrade the software than it is to upgrade hardware. Change the software first.

For CatOS, use the show version command to verify the current software version and free flash memory for the upgrade.

Switch> (enable) sh ver
WS-C6006 Software, Version NmpSW: 6.3(3)
Copyright (c) 1995-2001 by Cisco Systems
NMP S/W compiled on Oct 29 2001, 16:50:33
System Bootstrap Version: 5.3(1)
Hardware Version: 2.0  Model: WS-C6006  Serial #: TBA04251336
PS1  Module: WS-CAC-1300W    Serial #: SON04201377
PS2  Module: WS-CAC-1300W    Serial #: SON04201383
Mod Port Model               Serial #    Versions
--- ---- ------------------- ----------- --------------------------------------
1   2    WS-X6K-SUP1A-2GE    SAD041901PP Hw : 3.6
                                         Fw : 5.3(1)
                                         Fw1: 5.4(2)
                                         Sw : 6.3(3)
                                         Sw1: 6.3(3)
         WS-F6K-PFC          SAD041803S3 Hw : 2.0
!--- Output truncated.
       DRAM                    FLASH                   NVRAM
Module Total   Used    Free    Total   Used    Free    Total Used  Free
------ ------- ------- ------- ------- ------- ------- ----- ----- -----
1       65408K  47274K  18134K  16384K  14009K   2375K  512K  308K  204K
!--- Typical CatOS show version output.
!--- Verify free memory before upgrading.
Uptime is 32 days, 4 hours, 44 minutes
Console> (enable)

For Cisco IOS, use the show version command to verify the current software version along with the dir flash: or dir bootflash: (dependent upon the platform) command to verify the available flash memory for the upgrade:

Router#sh ver
Cisco Internetwork Operating System Software
IOS (tm) Catalyst 4000 L3 Switch Software (cat4000-IS-M), Version 12.1(13)EW, EA
RLY DEPLOYMENT RELEASE SOFTWARE (fc1)
TAC Support: http://www.cisco.com/tac
Copyright (c) 1986-2002 by cisco Systems, Inc.
Compiled Fri 20-Dec-02 13:52 by eaarmas
Image text-base: 0x00000000, data-base: 0x00E638AC
ROM: 12.1(12r)EW
Dagobah Revision 71, Swamp Revision 24
trunk-4500 uptime is 2 weeks, 2 days, 6 hours, 27 minutes
System returned to ROM by redundancy reset
System image file is "bootflash:cat4000-is-mz.121-13.EW.bin"
!--- Typical Cisco IOS show version output.

Router#dir bootflash:
Directory of bootflash:/
1  -rw-     8620144   Mar 22 2002 08:26:21  cat4000-is-mz.121-13.EW.bin
61341696 bytes total (52721424 bytes free)
!--- Verify available flash memory on switch running Cisco IOS.
Router

How to Upgrade Software

For information on upgrading software for Catalyst switches, choose your platform under LAN & ATM Switches and look at the Software Configuration > Software Upgrade and Working With Configuration Files section.

Hardware Software Incompatibility

There can be a situation where the software is not compatible with the hardware. This happens when new hardware comes out and requires special support from the software. For more information on software compatibility, use the Software Advisor tool.

Software Bugs

The operating system can have a bug. If you load a newer software version, it can often fix this. You can search known software bugs with the Software Bug Toolkit.

Corrupt Images

An image can have become corrupted or is missing. For information in regard to the recovery from corrupted images, choose your platform under LAN & ATM Switches and look at the Troubleshooting > Recovery from Corrupted or Missing Software section.

Hardware Problems

Check the results of show module for Catalyst 6000 and 4000 series switches that run CatOS or Cisco IOS.

Switch> (enable) sh mod
Mod Slot Ports Module-Type               Model               Sub
Status
--- ---- ----- ------------------------- ------------------- -----------
1   1    2     1000BaseX Supervisor      WS-X6K-S2U-MSFC2    yes ok
15  1    1     Multilayer Switch Feature WS-F6K-MSFC2        no  ok
3   3    8     1000BaseX Ethernet        WS-X6408A-GBIC      no  faulty
5   5    48    10/100BaseTX Ethernet     WS-X6348-RJ-45      no  faulty
!--- Status of "faulty" indicates a possible hardware problem.
!--- This could be a line card problem, but since two mods are effected,
!--- perhaps there's a problem with the supervisor.
!--- Use the reset command (CatOS) or hw-module{mod}reset command (Cisco IOS),
!--- or try physically reseating the modules and the supervisor.
!--- Also, try moving the supervisor to slot 2.

Check the results of the POST results from the switch to see if there were any failures indicated for any part of the switch. Failures of any test of a module or port show an 'F' in the test results.

For CatOS, use the show test command to see all test results. In order to see test results per module, use the show test {mod} command:

Switch> (enable) sh test 3
Diagnostic mode: complete   (mode at next reset: minimal)
!--- The diaglevel is set to complete which is a longer but more thorough test.
!--- The command to do this for CatOS is set test diaglevel complete.
Module 3 : 16-port 1000BaseX EthernetLine Card Status for Module 3 : PASS
Port Status :
 Ports 1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16
 -----------------------------------------------------
       .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
GBIC Status :
 Ports 1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16
 -----------------------------------------------------
       .  .  .  .  .  N  .  .  .  .  .  .  .  .  N  N
Line Card Diag Status for Module 3  (. = Pass, F = Fail, N = N/A)
Loopback Status [Reported by Module 1] :
 Ports 1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16
 -----------------------------------------------------
       F  F  F  F  F  F  F  F  F  F  F  F  F  F  F  F
!--- The failed loopback tests mean the ports are currently unusable.
!--- Use the reset {mod} command or, if necessary, physically reseat the
!--- module to try and fix this problem.
!--- If these steps fail, open a case with Cisco Technical Support.

For Cisco IOS, on modular switches like the Cat6000 and 4000, use the command show diagnostics. In order to see POST results per module, use the show diagnostics module {mod} command.

ecsj-6506-d2#sh diagnostic module 3
  Current Online Diagnostic Level = Minimal
  !--- The diagnostic level is set to minimal which is a shorter,
  !--- but also less thorough test result.
  !--- You may wish to configure diagnostic level complete to get more test results.
  Online Diagnostic Result for Module 3 : MINOR ERROR
  Online Diagnostic Level when Line Card came up = Minimal
  Test Results: (. = Pass, F = Fail, U = Unknown)
  1 . TestLoopback :
  Port  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
  ----------------------------------------------------------------------------
        .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  F  F  F  F F  F
  !--- Notice the MINOR ERROR test result and failed loopback test which means
  !--- these ports are currently unusable.
  !--- Use the hw-module{mod}reset command or, if necessary, physically reseat the
  !--- module to try and fix this problem.
 
  !--- If these steps fail, open a case with Cisco Technical Support.

Note: For Catalyst 3750, 3550, 2970 , 2950/2955, and 2900/3500XL Series switches use the show post command, which indicates a simple pass or fail for the hw status. Use the LEDs on these switches to help you understand the POST results. Refer to Understanding Post Results.

For further information on troubleshooting hardware problems on Catalyst switches that run CatOS and Cisco IOS, go to the LAN and ATM Switches support pages, choose your platform and look at the Troubleshooting > Hardware section.

For possible issues related to Field Notices, refer to Field Notices for LAN and ATM Switches.

Input Errors on a Layer 3 Interface Connected to a Layer 2 Switchport

By default, all layer 2 ports are in dynamic desirable mode, so the layer 2 port tries to form a trunk link and sends out DTP packets to the remote device. When a layer 3 interface is connected to a layer 2 switchport, it is not able to interpret these frames, which results in Input errors, WrongEncap errors, and Input queue drops.

In order to resolve this, change the mode of the switch port to static access or trunk as per your requirement.

Switch2(config)#int fa1/0/12
Switch2(config-if)#switchport mode access

or

Switch2(config)#int fa1/0/12
Switch2(config-if)#switchport trunk encapsulation dot1q

Switch2(config-if)#switchport mode trunk

Rapidly Incrementing Rx-No-Pkt-Buff Counter and Input Errors

The Rx-No-Pkt-Buff counter can increase on ports when it has blades, such as WS-X4448-GB-RJ45, WS-X4548-GB-RJ45, and WS-X4548-GB-RJ45V. Also some packet drop incrementation is normal and is the result of bursting traffic.

These types of errors increase rapidly, especially when the traffic that passes through that link is high or when it has devices such as servers connected to that interface. This high load of traffic oversubscribes the ports, which exhausts the input buffers and causes the Rx-No-Pkt-Buff counter and input errors to increase rapidly.

If a packet cannot be completely received because the switch is out of packet buffers, this counter is incremented once for every dropped packet. This counter indicates the internal state of the Switching ASICs on the Supervisor and does not necessarily indicate an error condition.

Pause Frames

When the receive part (Rx) of the port has its Rx FIFO queue filled and reaches the high water mark, the transmit part (Tx) of the port starts to generate pause frames with an interval value mentioned in it. The remote device is expected to stop / reduce the transmission of packets for the interval time mentioned in the pause frame.

If the Rx is able to clear the Rx queue or reach low water mark within this interval, Tx sends out a special pause frame that mentions the interval as zero (0x0). This enables the remote device to start to transmit packets.

If the Rx still works on the queue, once the interval time expires, the Tx sends a new pause frame again with a new interval value.

If Rx-No-Pkt-Buff is zero or does not increment and the TxPauseFrames counter increments, it indicates that our switch generates pause frames and the remote end obeys, hence Rx FIFO queue depletes.

If Rx-No-Pkt-Buff increments and TxPauseFrames also increments, it means that the remote end disregards the pause frames (does not support flow control) and continues to send traffic despite the pause frames. In order to overcome this situation, manually configure the speed and duplex, as well as disable the flow control, if required.

These types of errors on the interface are related to a traffic problem with the ports oversubscribed. The WS-X4448-GB-RJ45, WS-X4548-GB-RJ45, and WS-X4548-GB-RJ45V switching modules have 48 oversubscribed ports in six groups of eight ports each:

  • Ports 1, 2, 3, 4, 5, 6, 7, 8

  • Ports 9, 10, 11, 12, 13, 14, 15, 16

  • Ports 17, 18, 19, 20, 21, 22, 23, 24

  • Ports 25, 26, 27, 28, 29, 30, 31, 32

  • Ports 33, 34, 35, 36, 37, 38, 39, 40

  • Ports 41, 42, 43, 44, 45, 46, 47, 48

The eight ports within each group use common circuitry that effectively multiplexes the group into a single, nonblocking, full-duplex Gigabit Ethernet connection to the internal switch fabric. For each group of eight ports, the frames that are received are buffered and sent to the common Gigabit Ethernet link to the internal switch fabric. If the amount of data received for a port begins to exceed buffer capacity, flow control sends pause frames to the remote port to temporarily stop traffic and prevent frame loss.

If the frames received on any group exceeds the bandwidth of 1 Gbps, the device starts to drop the frames. These drops are not obvious as they are dropped at the internal ASIC rather than the actual interfaces. This can lead to slow throughput of packets across the device.

The Rx-No-Pkt-Buff does not depend on the total traffic rate. It depends on the amount of the packets that are stored in the Rx FIFO buffer of the module ASIC. The size of this buffer is only 16 KB. It is counted with short bursty traffic flows when some packets fill this buffer. Thus, Rx-No-Pkt-Buff on each port can be counted when the total traffic rate of this ASIC port group exceeds 1 Gbps, since WS-X4548-GB-RJ45 is 8:1 oversubscribed module.

When you have devices that need to carry a large amount of traffic through that interface, consider the use of one port of each group so that the common circuitry that shares a single group is not affected by this amount of traffic. When the Gigabit Ethernet switching module is not fully utilized, you can connect balancing port connections across port groupings to maximize available bandwidth. For example, with the WS-X4448-GB-RJ45 10/100/1000 switching module, you can connect ports from different groups, such as ports 4, 12, 20, or 30 (in any order), before you connect ports from the same group, such as ports 1, 2, 3, 4, 5, 6, 7, and 8.

If this does not solve the issue, you need to consider a module without any oversubscription of ports.

Understand Unknown Protocol Drops

Unknown protocol drops is a counter on the interface. It is caused by protocols that are not understood by the router/switch.

This example of the show running-config interface command shows the unknown protocol drops on the Gigabit Ethernet 0/1 interface.

Switch#sh run int Gig 0/1
GigabitEthernet0/1 is up, line protocol is up
  Hardware is BCM1125 Internal MAC, address is 0000.0000.0000 (via 0000.0000)
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation 802.1Q Virtual LAN, Vlan ID  1., loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, media type is RJ45
  output flow-control is XON, input flow-control is XON
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:05, output 00:00:03, output hang never
  Last clearing of "show interface" counters 16:47:42
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     3031 packets input, 488320 bytes, 0 no buffer
     Received 3023 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 63107 multicast, 0 pause input
     0 input packets with dribble condition detected
     7062 packets output, 756368 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     2015 unknown protocol drops
     4762 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

Unknown protocol drops are normally dropped because the interface where these packets are received is not configured for this type of protocol, or it can be any protocol that the router does not recognize.

For example, if you have two routers connected and you disable CDP on one router interface, this results in unknown protocol drops on that interface. The CDP packets are no longer recognized, and they are dropped.

Trunking between a Switch and a Router

Trunk links between a switch and a router can make the switchport go down. Trunk can come up after you disable and enable the switchport, but eventually the switchport can go down again.

In order to resolve this issue, complete these steps:

  1. Make sure Cisco Discovery Protocol (CDP) runs between the switch and router and both can see each other.

  2. Disable the Keepalives on the interface of the router.

  3. Reconfigure the trunk encapsulation on both devices.

When the keepalives are disabled, the CDP enables link to operate normally.

Connectivity Issues due to Oversubscription

When you use either the WS-X6548-GE-TX or WS-X6148-GE-TX modules, there is a possibility that individual port utilization can lead to connectivity problems or packet loss on the surrounding interfaces. Refer to Interface/Module Connectivity Problems for more information on oversubscription.

Subinterfaces in SPA Modules

In SPA modules, after you create a subinterface with 802.1Q, the same VLAN is not usable on the switch. Once you have encapsulation dot1q on a subinterface, you can no longer use that VLAN in the system because the 6500 or 7600 internally allocates the VLAN and makes that subinterface its only member.

In order to resolve this issue, create trunk ports instead of subinterfaces. That way, the VLAN can be seen in all interfaces.

Troubleshooting rxTotalDrops

If all other counters are zero, and the only error counter that reports errors is rxTotalDrops, the most likely cause is that the Spanning Tree blocks one or more VLANs on the uplink port, so the Color Blocking Logic (CBL) drops.

6509> (enable) show counters 1/2
64 bit counters
0  rxHCTotalPkts                      =          32513986812
1  txHCTotalPkts                      =          29657802587
2  rxHCUnicastPkts                    =          18033363526
3  txHCUnicastPkts                    =          29498347453
4  rxHCMulticastPkts                  =          13469995420
5  txHCMulticastPkts                  =             21719352
6  rxHCBroadcastPkts                  =            757199011
7  txHCBroadcastPkts                  =            137735782
8  rxHCOctets                         =       25149393527621
9  txHCOctets                         =       23336028193116
10 rxTxHCPkts64Octets                 =               387871
11 rxTxHCPkts65to127Octets            =          13704213656
12 rxTxHCPkts128to255Octets           =          16915931224
13 rxTxHCPkts256to511Octets           =           1068961475
14 rxTxHCpkts512to1023Octets          =           1945427146
15 rxTxHCpkts1024to1518Octets         =          11340361825
16 txHCTrunkFrames                    =          29657506751
17 rxHCTrunkFrames                    =          32513986812
18 rxHCDropEvents                     =                    0

32 bit counters
0  rxCRCAlignErrors                   =          0
1  rxUndersizedPkts                   =          0
2  rxOversizedPkts                    =          0
3  rxFragmentPkts                     =          0
4  rxJabbers                          =          0
5  txCollisions                       =          0
6  ifInErrors                         =          0
7  ifOutErrors                        =          0
8  ifInDiscards                       =          0
9  ifInUnknownProtos                  =          0
10 ifOutDiscards                      =         98
11 txDelayExceededDiscards            =          0
12 txCRC                              =          0
13 linkChange                         =          1
14 wrongEncapFrames                   =          0
0  dot3StatsAlignmentErrors           =          0
1  dot3StatsFCSErrors                 =          0
2  dot3StatsSingleColFrames           =          0
3  dot3StatsMultiColFrames            =          0
4  dot3StatsSQETestErrors             =          0
5  dot3StatsDeferredTransmisions      =          0
6  dot3StatsLateCollisions            =          0
7  dot3StatsExcessiveCollisions       =          0
8  dot3StatsInternalMacTransmitErrors =          0
9  dot3StatsCarrierSenseErrors        =          0
10 dot3StatsFrameTooLongs             =          0
11 dot3StatsInternalMacReceiveErrors  =          0
12 dot3StatsSymbolErrors              =          0
0  txPause                            =          0
1  rxPause                            =          0
0  rxTotalDrops                       =  253428855
1  rxFIFOFull                         =          0
2  rxBadCode                          =          0
Last-Time-Cleared
--------------------------
Sat Oct 27 2007, 08:24:35
6509> (enable)

When the port blocks VLANs on one side, but the remote side forwards on those VLANs, the interface increments the rxTotalDrops counters.

Compare the VLANs allowed in the trunk on both sides of the link. Also verify the spanning tree state for these allowed VLANs on both sides. BPDUs are still sent on actively configured VLAN, so switch A sends BPDUs on all configured and forwarding ports, but switch B drops them since it does not have those VLANs configured. In other words, switch B gets packets for VLANs for which it is not configured, so it simply drops them. These are not really errors but simple misconfiguration.

ifOutDiscards usually occur when the transmit (Tx) buffer gets full (maybe due to oversubscription) and then starts dropping the packets.

Troubleshoot Output Drops

Typically, the output drops will occur if QoS is configured and it is not providing enough bandwidth to certain class of packets. It also occurs when we are hitting oversubscription.

For example, here you see a high amount of output drops on the interface GigabitEthernet 8/9 on a Catalyst 6500 Series Switch:

Switch#show interface GigabitEthernet8/9
GigabitEthernet8/9 is up, line protocol is up (connected)
  Hardware is C6k 1000Mb 802.3, address is 0013.8051.5950 (bia 0013.8051.5950)
  Description: Connection To Bedok_Core_R1 Ge0/1
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec, 
     reliability 255/255, txload 18/255, rxload 23/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, media type is SX
  input flow-control is off, output flow-control is off
  Clock mode is auto
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:28, output 00:00:10, output hang never
  Last clearing of "show interface" counters never
Input queue: 0/2000/3/0 (size/max/drops/flushes); Total output drops: 95523364
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 94024000 bits/sec, 25386 packets/sec
  5 minute output rate 71532000 bits/sec, 24672 packets/sec
     781388046974 packets input, 406568909591669 bytes, 0 no buffer
     Received 274483017 broadcasts (257355557 multicasts)
     0 runts, 0 giants, 0 throttles 
     3 input errors, 2 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     749074165531 packets output, 324748855514195 bytes, 0 underruns
     0 output errors, 0 collisions, 3 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

In order to analyze the problem, collect the output of these commands:

Last Input Never from the Output of Show interface Command

This example of the show interface command shows the Last input never on the TenGigabitEthernet1/15 interface.

Switch#show interface TenGigabitEthernet1/15
TenGigabitEthernet1/15 is up, line protocol is up (connected)
  Hardware is C6k 10000Mb 802.3, address is 0025.84f0.ab16 (bia 0025.84f0.ab16)
  Description: lsnbuprod1 solaris
  MTU 1500 bytes, BW 10000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 10Gb/s
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:17, output hang never
  Last clearing of "show interface" counters 2d22h
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 46000 bits/sec, 32 packets/sec
     52499121 packets input, 3402971275 bytes, 0 no buffer
     Received 919 broadcasts (0 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     118762062 packets output, 172364893339 bytes, 0 underruns
     0 output errors, 0 collisions, 3 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

This shows the number of hours, minutes, and seconds since the last packet was successfully received by an interface and processed locally on the router. This is useful to know when a dead interface has failed. This counter is updated only when packets are process switched, not when packets are fast switched.

Last input never means there was no successful interface packet transfer to other end point or terminal. Usually this means there was no packet transfer relative to that entity.

Related Information

Updated: Apr 03, 2009
Document ID: 12027