Troubleshooting Ports
This chapter contains the following sections:
About
Troubleshooting Ports
Before a device can
relay frames from one data link to another, the characteristics of the
interfaces through which the frames are received and sent must be defined. The
configured interfaces can be Ethernet interfaces, VLAN interfaces (SVIs), or
the management interface (mgmt0).
Each interface has an
associated administrative configuration and operational status as follows:
-
The administrative
configuration does not change unless you modify it. This configuration has
various attributes that you can configure in administrative mode.
-
The operational
status represents the current status of a specified attribute such as the
interface speed. This status cannot be changed and is read-only. Some values
may not be valid when the interface is down (such as the operation speed).
For a complete
description of port modes, administrative states, and operational states, see
the
Cisco Nexus 9000
Series NX-OS Interfaces Configuration Guide.
Guidelines and
Limitations for Troubleshooting Ports
Follow these
guidelines when you configure a port interface:
-
Before you begin
configuring a device, make sure that the modules in the chassis are functioning
as designed. Use the
show
module command to verify that a
module is OK or active before continuing the configuration.
-
When configuring
dedicated ports in a port group, follow these port mode guidelines:
-
There are no
licensing requirements for port configuration in
Cisco NX-OS.
Initial Port
Troubleshooting Checklist
Begin
troubleshooting the port configuration by checking the following issues:
| Checklist
|
Done
|
|---|
| Check the physical media to
ensure that there are no damaged parts.
|
|
| Verify that the SFP (small
form-factor pluggable) devices in use are those authorized by Cisco and that
they are not faulty.
|
|
| Verify that you have enabled
the port by using the
no
shutdown command.
|
|
| Use the
show
interface command to verify
the state of the interface. See the
Cisco
Nexus 9000 Series NX-OS Interfaces Configuration Guide for reasons why a
port might be in a down operational state.
|
|
| Verify that you have
configured a port as dedicated and make sure that you have not connected to the
other three ports in the port group.
|
|
Viewing Port
Information
You can use the
show interface
counters command to
view port counters. Typically, you only observe counters while actively
troubleshooting, in which case you should first clear the counters to create a
baseline. The values, even if they are high for certain counters, can be
meaningless for a port that has been active for an extended period. Clearing
the counters provides a better idea of the link behavior as you begin to
troubleshoot.
Use one of the
following commands to clear all port counters or the counters for specified
interfaces:
The counters can
identify synchronization problems by displaying a significant disparity between
received and transmitted frames.
Use the following
commands to gather more information about ports:
Troubleshooting Port
Statistics from the CLI
To display complete
information for an interface, use the
show
interface command. In
addition to the state of the port, this command displays the following:
-
Speed
-
Trunk VLAN
status
-
Number of frames
sent and received
-
Transmission
errors, including discards, errors, and invalid frames
switch# show interface ethernet 2/45
Ethernet2/45 is down (Administratively down)
Hardware is 10/100/1000 Ethernet, address is 0019.076c.4dd8 (bia 0019.076c.4dd8)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA
auto-duplex, auto-speed
Beacon is turned off
Auto-Negotiation is turned on
Input flow-control is off, output flow-control is off
Auto-mdix is turned on
Last clearing of "show interface" counters never
1 minute input rate 0 bytes/sec, 0 packets/sec
1 minute output rate 0 bytes/sec, 0 packets/sec
L3 Switched:
input: 0 pkts, 0 bytes - output: 0 pkts, 0 bytes
Rx
0 input packets 0 unicast packets 0 multicast packets
0 broadcast packets 0 jumbo packets 0 storm suppression packets
0 bytes
Tx
0 output packets 0 multicast packets
0 broadcast packets 0 jumbo packets
0 bytes
0 input error 0 short frame 0 watchdog
0 no buffer 0 runt 0 CRC 0 ecc
0 overrun 0 underrun 0 ignored 0 bad etype drop
0 bad proto drop 0 if down drop 0 input with dribble
0 output error 0 collision 0 deferred
0 late collision 0 lost carrier 0 no carrier
0 babble
0 Rx pause 0 Tx pause 0 reset
Receive data field Size is 2112
Troubleshooting Port-Interface Issues
The Interface
Configuration Has Disappeared
You may have a
problem where your interface configuration disappears.
| Symptoms
|
Possible Cause
|
Solution
|
|---|
| The interface configuration
has disappeared.
|
The interface mode has
changed to or from the switchport mode.
|
Cisco NX-OS
removes the interface configuration when you switch between Layer 2 and Layer 3
port mode. You must reconfigure the interface.
|
You Cannot Enable an
Interface
You might have a
problem when enabling an interface.
| Problem
|
Possible Cause
|
Solution
|
|---|
| You cannot enable an
interface.
|
The interface is part of a
dedicated port group.
|
You cannot enable the other
three ports in a port group if one port is dedicated. Use the
show running-config
interface CLI
command to verify the rate mode setting.
|
| The interface configuration
is incompatible with a remote port.
|
Use the
show interface
capabilities
command on both ports to determine if both ports have the same capabilities.
Modify the configuration as needed to make the ports compatible.
|
| The Layer 2 port is not
associated with an access VLAN, or the VLAN is suspended.
|
Use the
show interface
brief
command to see if
the interface is configured in a VLAN. Use the
show vlan
brief command to determine
the status of the VLAN. Use the
state
active command in VLAN
configuration mode to configure the VLAN as active.
|
| An incorrect SFP is connected
to the port.
|
Use the
show interface
brief
command to see if
you are using an incorrect transceiver. Replace with a Cisco-supported SFP.
|
You Cannot Configure
a Dedicated Port
You may have a
problem when trying to configure a port as dedicated.
| Problem
|
Possible Cause
|
Solution
|
|---|
| You cannot configure a
dedicated port.
|
The other three ports in the
port group are not shut down.
|
Use the
shutdown command in
interface configuration mode to disable the other three ports in the port
group.
|
| The port is not the first
port in the port group.
|
You can set only the first
port in a port group to the dedicated mode.
|
A Port Remains in a
Link Failure or Not Connected State
You may have a
problem with ports or links becoming operational.
| Problem
|
Possible Cause
|
Solution
|
|---|
| A port remains in a
link-failure state.
|
The port connection is bad.
|
Verify the
type of media in use. Is it
optical, single-mode (SM), or multimode (MM)?
Use the
shutdown command
followed by the
no
shutdown command to disable and enable the port.
If this problem persists, try moving the connection to a different port on the
same or another module.
|
| There is no signal because of
a transit fault in the small form-factor pluggable (SFP), or the SFP may be
faulty.
|
When this problem occurs, the
port stays in a transit port state and you see no signal. There is no
synchronization at the MAC level. The problem might be related to the port
speed setting or autonegotiation. Verify that the SFP on the interface is
seated properly. If reseating the SFP does not resolve the issue, replace the
SFP or try another port on the switch.
|
| The link is stuck in the
initialization state, or the link is in a point-to-point state.
|
Use the
show
logging command to check for a "Link Failure,
Not Connected system" message.
Use the
shutdown command
followed by the
no
shutdown command to disable and enable the port.
If this problem persists, try moving the connection to a different port on the
same or another module.
|
An Unexpected Link
Flapping Occurs
When a port is
flapping, it cycles through the following states, in this order, and then
starts over again:
-
Initializing—The
link is initializing.
-
Offline—The port
is offline.
-
Link failure or
not connected—The physical layer is not operational, and there is no active
device connection.
When you are
troubleshooting an unexpected link flapping, you should know the following
information:
| Problem
|
Possible Cause
|
Solution
|
|---|
| An unexpected link flapping
occurs.
|
The bit rate exceeds the
threshold and puts the port into the errDisabled state.
|
Use the
shutdown command
followed by the
no
shutdown command to return the
port to the normal state.
|
A problem in the system
triggers the link flap action by the end device. Some of the causes are as
follows:
-
A
packet drop in the device occurs because of either a hardware failure or an
intermittent hardware error such as an X-bar sync loss.
-
A
packet drop results from a software error.
-
A
control frame is erroneously sent to the device.
|
Determine the link flap
reason as indicated by the MAC driver. Use the debug facilities on the end
device to troubleshoot the problem. An external device might choose to
reinitialize the link when it encounters the error. In such cases, the method
of reinitializing the link varies by device.
|
A Port Is in the
ErrDisabled State
The ErrDisabled
state indicates that the switch detected a problem with the port and disabled
the port. This state could be caused by a flapping port or a high amount of bad
frames (CRC errors), which could indicate a problem with the media.
| Problem
|
Possible Cause
|
Solution
|
|---|
| A port is in the ErrDisabled
state.
|
The port is flapping.
|
See
Verifying the ErrDisable State Using the CLI
to verify the SFP, cable, and connections.
|
| The device detected a high
amount of bad frames (CRC errors), which might indicate a problem with the
media.
|
Verifying the
ErrDisable State Using the CLI
SUMMARY STEPS1.
switch#
show
interface
interface
slot/port
2.
switch#
show logging
logfile
DETAILED STEPS| | Command or Action | Purpose |
|---|
| Step 1 | switch#
show
interface
interface
slot/port
Example:
switch# show interface ethernet 1/14
e1/7 is down (errDisabled)
|
Verifies that
the device detected a problem and disabled the port.
| Note
|
After
verifying the port is disabled, check cables, SFPs, and optics.
|
|
| Step 2 | switch#
show logging
logfile
Example:
switch# show logging logfile
|
Displays the
switch log file and view a list of port state changes.
|
This example shows
how to display the switch log file and view a list of port state changes. An
error was recorded when someone attempted to add port e1/7 to port channel 7.
The port was not configured identically to port channel 7, so the attempt
failed:
switch# show logging logfile
. . .
Jan 4 06:54:04 switch %PORT_CHANNEL-5-CREATED: port-channel 7 created
Jan 4 06:54:24 switch %PORT-5-IF_DOWN_PORT_CHANNEL_MEMBERS_DOWN: Interface
port-channel 7 is down (No operational members)
Jan 4 06:54:40 switch %PORT_CHANNEL-5-PORT_ADDED: e1/8 added to port-channel 7
Jan 4 06:54:56 switch %PORT-5-IF_DOWN_ADMIN_DOWN: Interface e1/7 is down
(Admnistratively down)
Jan 4 06:54:59 switch %PORT_CHANNEL-3-COMPAT_CHECK_FAILURE:
speed is not compatible
Jan 4 06:55:56 switch%PORT_CHANNEL-5-PORT_ADDED: e1/7 added to port-channel 7
Feedback