Understanding Interface Types
This section describes the different types of interfaces supported by the switch with references to chapters that contain more detailed information about configuring these interface types.
Port-Based VLANs
A VLAN is a switched network that is logically segmented by function, team, or application, without regard to the physical location of the users. For more information about VLANs, see the Chapter15, “Configuring VLANs” Packets received on a port are forwarded only to ports that belong to the same VLAN as the receiving port. Network devices in different VLANs cannot communicate with one another without a Layer 3 device to route traffic between the VLANs.
VLAN partitions provide hard firewalls for traffic in the VLAN, and each VLAN has its own MAC address table. A VLAN comes into existence when a local port is configured to be associated with the VLAN, when the VLAN Trunking Protocol (VTP) learns of its existence from a neighbor on a trunk, or when a user creates a VLAN.
To configure VLANs, use the
vlan
vlan-id
global configuration command to enter VLAN configuration mode. The VLAN configurations for normal-range VLANs (VLAN IDs 1 to 1005) are saved in the VLAN database. If VTP is version 1 or 2, to configure extended-range VLANs (VLAN IDs 1006 to 4094), you must first set VTP mode to transparent. Extended-range VLANs created in transparent mode are not added to the VLAN database but are saved in the switch running configuration. With VTP version 3, you can create extended-range VLANs in client or server mode. These VLANs are saved in the VLAN database.
Add ports to a VLAN by using the
switchport
interface configuration commands:
-
Identify the interface.
-
For a trunk port, set trunk characteristics, and if desired, define the VLANs to which it can belong.
-
For an access port, set and define the VLAN to which it belongs.
Switch Ports
Switch ports are Layer 2-only interfaces associated with a physical port. You can configure a port as an access port or trunk port or let the Dynamic Trunking Protocol (DTP) operate on a per-port basis to set the switchport mode by negotiating with the port on the other end of the link. Switch ports are used for managing the physical interface and associated Layer 2 protocols.
Configure switch ports by using the
switchport
interface configuration commands. Use the
switchport
command with no keywords to put an interface that is in Layer 3 mode into Layer 2 mode.
Note When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration.
For detailed information about configuring access port and trunk port characteristics, see Chapter15, “Configuring VLANs”
Access Ports
An access port belongs to and carries the traffic of only one VLAN (unless it is configured as a voice VLAN port). Traffic is received and sent in native formats with no VLAN tagging. Traffic arriving on an access port is assumed to belong to the VLAN assigned to the port.
Two types of access ports are supported:
-
Static access ports are manually assigned to a VLAN .
-
VLAN membership of dynamic access ports is learned through incoming packets. By default, a dynamic access port is not a member of any VLAN, and forwarding to and from the port is enabled only when the VLAN membership of the port is discovered. Dynamic access ports on the switch are assigned to a VLAN by a VLAN Membership Policy Server (VMPS). The VMPS can be a Catalyst 6500 series switch; the IE3010 switch cannot be a VMPS server.
You can also configure an access port with an attached Cisco IP Phone to use one VLAN for voice traffic and another VLAN for data traffic from a device attached to the phone. For more information about voice VLAN ports, see Chapter17, “Configuring Voice VLAN”
Trunk Ports
A trunk port carries the traffic of multiple VLANs and by default is a member of all VLANs in the VLAN database.
The switch supports only IEEE 802.1Q trunk ports. An IEEE 802.1Q trunk port supports simultaneous tagged and untagged traffic. An IEEE 802.1Q trunk port is assigned a default port VLAN ID (PVID), and all untagged traffic travels on the port default PVID. All untagged traffic and tagged traffic with a NULL VLAN ID are assumed to belong to the port default PVID. A packet with a VLAN ID equal to the outgoing port default PVID is sent untagged. All other traffic is sent with a VLAN tag.
Although by default, a trunk port is a member of every VLAN known to the VTP, you can limit VLAN membership by configuring an allowed list of VLANs for each trunk port. The list of allowed VLANs does not affect any other port but the associated trunk port. By default, all possible VLANs (VLAN ID 1 to 4094) are in the allowed list. A trunk port can become a member of a VLAN only if VTP knows of the VLAN and if the VLAN is in the enabled state. If VTP learns of a new, enabled VLAN and the VLAN is in the allowed list for a trunk port, the trunk port automatically becomes a member of that VLAN and traffic is forwarded to and from the trunk port for that VLAN. If VTP learns of a new, enabled VLAN that is not in the allowed list for a trunk port, the port does not become a member of the VLAN, and no traffic for the VLAN is forwarded to or from the port.
For more information about trunk ports, see Chapter15, “Configuring VLANs”
EtherChannel Port Groups
EtherChannel port groups treat multiple switch ports as one switch port. These port groups act as a single logical port for high-bandwidth connections between switches or between switches and servers. An EtherChannel balances the traffic load across the links in the channel. If a link within the EtherChannel fails, traffic previously carried over the failed link changes to the remaining links. You can group multiple trunk ports into one logical trunk port, group multiple access ports into one logical access port, group multiple tunnel ports into one logical tunnel port, or group multiple routed ports into one logical routed port.
Most protocols operate over either single ports or aggregated switch ports and do not recognize the physical ports within the port group. Exceptions are the DTP, the Cisco Discovery Protocol (CDP), and the Port Aggregation Protocol (PAgP), which operate only on physical ports.
When you configure an EtherChannel, you create a port-channel logical interface and assign an interface to the EtherChannel. Use the
channel-group
interface configuration command to dynamically create the port-channel logical interface. This command binds the physical and logical ports together.
For Layer 3 interfaces, you manually create the logical interface by using the
interface port-channel
global configuration command. Then you manually assign an interface to the EtherChannel by using the
channel-group
interface configuration command.
For more information, see Chapter38, “Configuring EtherChannels and Link-State Tracking”
Dual-Purpose Uplink Ports
Some switches support dual-purpose uplink ports. Each uplink port is considered as a single interface with dual front ends—an RJ-45 connector and a small form-factor pluggable (SFP) module connector. The dual front ends are not redundant interfaces, and the switch activates only one connector of the pair.
By default, the switch dynamically selects the interface type that first links up. However, you can use the
media-type
interface configuration command to manually select the RJ-45 connector or the SFP module connector. For information about configuring speed and duplex settings for a dual-purpose uplink, see the “Setting the Interface Speed and Duplex Parameters” section.
Each uplink port has two LEDs: one shows the status of the RJ-45 port, and one shows the status of the SFP module port. The port LED is on for whichever connector is active. For more information about the LEDs, see the hardware installation guide.
Power over Ethernet Ports
PoE-capable switch ports automatically supply power to these connected devices (if the switch senses that there is no power on the circuit):
-
Cisco pre-standard powered devices (such as Cisco IP Phones and Cisco Aironet access points)
-
802.3af-compliant powered devices
A powered device can receive redundant power when it is connected only to a PoE switch port and to an AC power source.
After the switch detects a powered device, it determines the device power requirements and then grants or denies power to the device. The switch can also sense the real-time power consumption of the device by monitoring and policing the power usage.
This section has this PoE information:
Supported Protocols and Standards
The switch uses these protocols and standards to support PoE:
-
CDP with power consumption—The powered device notifies the switch of the amount of power it is consuming. The switch does not reply to the power-consumption messages. The switch can only supply power to or remove power from the PoE port.
-
Cisco intelligent power management—The powered device and the switch negotiate through power-negotiation CDP messages for an agreed power-consumption level. The negotiation allows a high-power Cisco powered device, which consumes more than 7 W, to operate at its highest power mode. The powered device first boots up in low-power mode, consumes less than 7 W, and negotiates to obtain enough power to operate in high-power mode. The device changes to high-power mode only when it receives confirmation from the switch.
High-power devices can operate in low-power mode on switches that do not support power-negotiation CDP.
Cisco intelligent power management is backward-compatible with CDP with power consumption; the switch responds according to the CDP message that it receives. CDP is not supported on third-party powered devices; therefore, the switch uses the IEEE classification to determine the power usage of the device.
-
IEEE 802.3af—The major features of this standard are powered-device discovery, power administration, disconnect detection, and optional powered-device power classification. For more information, see the standard.
Powered-Device Detection and Initial Power Allocation
The switch detects a Cisco pre-standard or an IEEE-compliant powered device when the PoE-capable port is in the no-shutdown state, PoE is enabled (the default), and the connected device is not being powered by an AC adaptor.
After device detection, the switch determines the device power requirements based on its type:
-
A Cisco pre-standard powered device does not provide its power requirement when the switch detects it, so the switch allocates 15.4 W as the initial allocation for power budgeting.
The initial power allocation is the maximum amount of power that a powered device requires. The switch initially allocates this amount of power when it detects and powers the powered device. As the switch receives CDP messages from the powered device and as the powered device negotiates power levels with the switch through CDP power-negotiation messages, the initial power allocation might be adjusted.
-
The switch classifies the detected IEEE device within a power consumption class. Based on the available power in the power budget, the switch determines if a port can be powered.
Table 13-1
lists these levels.
Table 13-1 IEEE Power Classifications
|
Maximum Power Level Required from the Switch
|
0 (class status unknown)
|
15.4 W
|
1
|
4 W
|
2
|
7 W
|
3
|
15.4 W
|
4 (reserved for future use)
|
treat as class 0
|
The switch monitors and tracks requests for power and grants power only when it is available. The switch tracks its power budget (the amount of power available on the switch for PoE). The switch performs power-accounting calculations when a port is granted or denied power to keep the power budget up to date.
After power is applied to the port, the switch uses CDP to determine the
actual
power consumption requirement of the connected Cisco powered devices, and the switch adjusts the power budget accordingly. This does not apply to third-party PoE devices. The switch processes a request and either grants or denies power. If the request is granted, the switch updates the power budget. If the request is denied, the switch ensures that power to the port is turned off, generates a syslog message, and updates the LEDs. Powered devices can also negotiate with the switch for more power.
If the switch detects a fault caused by an undervoltage, overvoltage, overtemperature, oscillator-fault, or short-circuit condition, it turns off power to the port, generates a syslog message, and updates the power budget and LEDs.
Power Management Modes
The switch supports these PoE modes:
-
auto
—The switch automatically detects if the connected device requires power. If the switch discovers a powered device connected to the port and if the switch has enough power, it grants power, updates the power budget, turns on power to the port on a first-come, first-served basis, and updates the LEDs. For LED information, see the hardware installation guide.
If the switch has enough power for all the powered devices, they all come up. If enough power is available for all powered devices connected to the switch, power is turned on to all devices. If there is not enough available PoE, or if a device is disconnected and reconnected while other devices are waiting for power, it cannot be determined which devices are granted or are denied power.
If granting power would exceed the system power budget, the switch denies power, ensures that power to the port is turned off, generates a syslog message, and updates the LEDs. After power has been denied, the switch periodically rechecks the power budget and continues to attempt to grant the request for power.
If a device being powered by the switch is then connected to wall power, the switch might continue to power the device. The switch might continue to report that it is still powering the device whether the device is being powered by the switch or receiving power from an AC power source.
If a powered device is removed, the switch automatically detects the disconnect and removes power from the port. You can connect a nonpowered device without damaging it.
You can specify the maximum wattage that is allowed on the port. If the IEEE class maximum wattage of the powered device is greater than the configured maximum value, the switch does not provide power to the port. If the switch powers a powered device, but the powered device later requests through CDP messages more than the configured maximum value, the switch removes power to the port. The power that was allocated to the powered device is reclaimed into the global power budget. If you do not specify a wattage, the switch delivers the maximum value. Use the
auto
setting on any PoE port. The auto mode is the default setting.
-
static
—The switch pre-allocates power to the port (even when no powered device is connected) and guarantees that power will be available for the port. The switch allocates the port configured maximum wattage, and the amount is never adjusted through the IEEE class or by CDP messages from the powered device. Because power is pre-allocated, any powered device that uses less than or equal to the maximum wattage is guaranteed to be powered when it is connected to the static port. The port no longer participates in the first-come, first-served model.
However, if the powered-device IEEE class is greater than the maximum wattage, the switch does not supply power to it. If the switch learns through CDP messages that the powered device needs more than the maximum wattage, the powered device is shutdown.
If you do not specify a wattage, the switch pre-allocates the maximum value. The switch powers the port only if it discovers a powered device. Use the
static
setting on a high-priority interface.
-
never
—The switch disables powered-device detection and never powers the PoE port even if an unpowered device is connected. Use this mode only when you want to make sure power is never applied to a PoE-capable port, making the port a data-only port.
For information on configuring a PoE port, see the “Configuring a Power Management Mode on a PoE Port” section.
Power Monitoring and Power Policing
When policing of the real-time power consumption is enabled, the switch takes action when a powered device consumes more power than the maximum amount allocated, also referred to as the
cutoff-power value
.
When PoE is enabled, the switch senses the real-time power consumption of the powered device. The switch monitors the real-time power consumption of the connected powered device; this is called
power monitoring
or
power sensing
. The switch also polices the power usage with the
power policing
feature.
Power monitoring is backward-compatible with Cisco intelligent power management and CDP-based power consumption. It works with these features to ensure that the PoE port can supply power to the powered device. For more information about these PoE features, see the “Supported Protocols and Standards” section.
The switch senses the real-time power consumption of the connected device as follows:
1. The switch monitors the real-time power consumption on individual ports.
2. The switch records the power consumption, including peak power usage. The switch reports the information through the CISCO-POWER-ETHERNET-EXT-MIB.
3. If power policing is enabled, the switch polices power usage by comparing the real-time power consumption to the maximum power allocated to the device. For more information about the maximum power consumption, also referred to as the
cutoff power
, on a PoE port, see the
“Maximum Power Allocation (Cutoff Power) on a PoE Port” section.
If the device uses more than the maximum power allocation on the port, the switch can either turn off power to the port, or the switch can generate a syslog message and update the LEDs (the port LED is now blinking amber) while still providing power to the device based on the switch configuration. By default, power-usage policing is disabled on all PoE ports.
If error recovery from the PoE error-disabled state is enabled, the switch automatically takes the PoE port out of the error-disabled state after the specified amount of time.
If error recovery is disabled, you can manually re-enable the PoE port by using the
shutdown
and
no shutdown
interface configuration commands.
4. If policing is disabled, no action occurs when the powered device consumes more than the maximum power allocation on the PoE port, which could adversely affect the switch.
Maximum Power Allocation (Cutoff Power) on a PoE Port
When power policing is enabled, the switch determines one of the these values as the cutoff power on the PoE port in this order:
1. Manually when you set the user-defined power level that the switch budgets for the port by using the
power inline consumption default
wattage
global or interface configuration command
2. Manually when you set the user-defined power level that limits the power allowed on the port by using the
power inline auto max
max-wattage
or the
power inline static max
max-wattage
interface configuration command
3. Automatically when the switch sets the power usage of the device by using CDP power negotiation or by the IEEE classification
4. Automatically when the switch sets the power usage to be the default value of 15400 mW
Use the first or second method in the previous list to manually configure the cutoff-power value by entering the
power inline consumption default
wattage
or the
power inline
[
auto
|
static max
]
max-wattage
command. If you are not manually configuring the cutoff-power value, the switch automatically determines the value by using CDP power negotiation or the device IEEE classification, which is the third method in the previous list. If the switch cannot determine the value by using one of these methods, it uses the default value of 15400 mW (the fourth method in the previous list).
Power Consumption Values
You can configure the initial power allocation and the maximum power allocation on a port. However, these values are only the configured values that determine when the switch should turn on or turn off power on the PoE port. The maximum power allocation is not the same as the actual power consumption of the powered device. The actual cutoff power value that the switch uses for power policing is not equal to the configured power value.
When power policing is enabled, the switch polices the power usage
at the switch port
, which is greater than the power consumption of the device. When you are manually set the maximum power allocation, you must consider the power loss over the cable from the switch port to the powered device. The cutoff power is the sum of the rated power consumption of the powered device and the worst-case power loss over the cable.
The actual amount of power consumed by a powered device on a PoE port is the cutoff-power value plus a calibration factor of 500 mW (0.5 W). The actual cutoff value is approximate and varies from the configured value by a percentage of the configured value. For example, if the configured cutoff power is 12 W, the actual cutoff-value is 11.4 W, which is 5% less than the configured value.
We recommend that you enable power policing when PoE is enabled on your switch. For example, if policing is disabled and you set the cutoff-power value by using the
power inline auto max 6300
interface configuration command, the configured maximum power allocation on the PoE port is 6.3 W (6300 mW). The switch provides power to the connected devices on the port if the device needs up to 6.3 W. If the CDP-power negotiated value or the IEEE classification value exceeds the configured cutoff value, the switch does not provide power to the connected device. After the switch turns on power on the PoE port, the switch does not police the real-time power consumption of the device, and the device can consume more power than the maximum allocate d amount, which could adversely affect the switch and the devices connected to the other PoE ports.
The switch supports dual power supplies. If a power supply is removed or fails and the switch does not have enough power for the powered devices, the switch first denies power to low-priority ports in descending order of port numbers, and then to high priority ports in descending numbers. The total available PoE power is 65 watts per power supply.
-
If a power supply is removed and replaced by a new power supply with less power and the switch does not have enough power for the powered devices, the switch denies power to the PoE ports in auto mode in descending order of the port numbers. If the switch still does not have enough power, the switch then denies power to the PoE ports in static mode in descending order of the port numbers.
-
If the new power supply supports more power than the previous one and the switch now has more power available, the switch grants power to the PoE ports in static mode in ascending order of the port numbers. If it still has power available, the switch then grants power to the PoE ports in auto mode in ascending order of the port numbers.
Connecting Interfaces
Devices within a single VLAN can communicate directly through any switch. Ports in different VLANs cannot exchange data without going through a routing device.
With a standard Layer 2 switch, ports in different VLANs have to exchange information through a router. By using the switch with routing enabled, when you configure both VLAN 20 and VLAN 30 with an SVI to which an IP address is assigned, packets can be sent from Host A to Host B directly through the switch with no need for an external router (Figure 13-1).
Figure 13-1 Connecting VLANs with a Layer 3 Switch
Using Interface Configuration Mode
The switch supports these interface types:
-
Physical ports—switch ports and routed ports
-
VLANs—switch virtual interfaces
-
Port channels—EtherChannel interfaces
You can also configure a range of interfaces (see the “Configuring a Range of Interfaces” section).
To configure a physical interface (port), specify the interface type, module number, and switch port number, and enter interface configuration mode.
-
Type
—Port types depend on those supported on the switch. Possible types are:
Fast Ethernet (fastethernet or fa) for 10/100 Mb/s Ethernet, Gigabit Ethernet (gigabitethernet or gi) for 10/100/1000 Mb/s Ethernet ports, 10-Gigabit Ethernet (tengigabitethernet or te) for 10,000 Mb/s, or small form-factor pluggable (SFP) module Gigabit Ethernet interfaces.
-
Module number
—
The module or slot number on the switch (always 0).
-
Port number—The interface number on the switch. The port numbers always begin at 1, starting with the far left port when facing the front of the switch, for example, fastethernet0/1 or gigabitethernet0/1. If there is more than one interface type (for example, 10/100 ports and SFP module ports, the port numbers restart with the second interface type: gigabitethernet0/1.
You can identify physical interfaces by looking at the switch. You can also use the
show
privileged EXEC commands to display information about a specific interface or all the interfaces. The remainder of this chapter primarily provides physical interface configuration procedures.
Procedures for Configuring Interfaces
These general instructions apply to all interface configuration processes.
Step 1 Enter the
configure terminal
command at the privileged EXEC prompt:
Switch# configure terminal Enter configuration commands, one per line. End with CNTL/Z.
Step 2 Enter the
interface
global configuration command.
Identify the interface type and the interface number, Gigabit Ethernet port 1 in this example:
Switch(config)# interface gigabitethernet0/1
Note Entering a space between the interface type and interface number is optional
Step 3 Follow each
interface
command with the configuration commands that the interface requires. The commands that you enter define the protocols and applications that will run on the interface. The commands are collected and applied to the interface when you enter another interface command or enter
end
to return to privileged EXEC mode.
You can also configure a range of interfaces by using the
interface range
or
interface range macro
global configuration commands. Interfaces configured in a range must be the same type and must be configured with the same feature options.
Step 4 After you configure an interface, verify its status by using the
show
privileged EXEC commands listed in the “Monitoring and Maintaining the Interfaces” section.
Enter the
show interfaces
privileged EXEC command to see a list of all interfaces on or configured for the switch. A report is provided for each interface that the device supports or for the specified interface.
Configuring a Range of Interfaces
You can use the
interface range
global configuration command to configure multiple interfaces with the same configuration parameters. When you enter the interface-range configuration mode, all command parameters that you enter are attributed to all interfaces within that range until you exit this mode.
Beginning in privileged EXEC mode, follow these steps to configure a range of interfaces with the same parameters:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface range
{
port-range
|
macro
macro_name
}
|
Specify the range of interfaces (VLANs or physical ports) to be configured, and enter interface-range configuration mode.
-
You can use the
interface range
command to configure up to five port ranges or a previously defined macro.
-
The
macro
variable is explained in the “Configuring and Using Interface Range Macros” section.
-
In a comma-separated
port-range
, you must enter the interface type for each entry and enter spaces before and after the comma.
-
In a hyphen-separated
port-range
, you do not need to re-enter the interface type, but you must enter a space before the hyphen.
|
Step 3
|
|
Use the normal configuration commands to apply the configuration parameters to all interfaces in the range. Each command is executed as it is entered.
|
Step 4
|
end
|
Return to privileged EXEC mode.
|
Step 5
|
show interfaces
[
interface-id
]
|
Verify the configuration of the interfaces in the range.
|
Step 6
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
When using the
interface range
global configuration command, note these guidelines:
-
Valid entries for
port-range,
depending on port types on the switch:
–
vlan
vlan-ID
-
vlan-ID
, where the VLAN ID is 1 to 4094
– , where the module is always 0
–
fastethernet
module/{first
port
} - {
last port
}, where the module is always 0
–
gigabitethernet
module/{
first port
} - {
last port
}, where the module is always 0
–
port-channel
port-channel-number
-
port-channel-number
, where the
port-channel-number
is 1 to 24
Note When you use the interface range command with port channels, the first and last port-channel number must be active port channels.
-
You must add a space between the first interface number and the hyphen when using the interface range command.
For example, interface range
gigabitethernet
0/1 - 4 is a valid range; interface range
gigabit
ethernet0/1-4 is not.
-
The
interface range
command only works with VLAN interfaces that have been configured with the
interface vlan
command. The
show running-config
privileged EXEC command displays the configured VLAN interfaces. VLAN interfaces not displayed by the
show running-config
command cannot be used with the
interface range
command.
-
All interfaces defined in a range must be the same type (all Fast Ethernet ports, all Gigabit Ethernet ports, all EtherChannel ports, or all VLANs), but you can enter multiple ranges in a command.
This example shows how to use the
interface range
global configuration command to set the speed on ports 1 to 2 to 100 Mb/s:
Switch# configure terminal Switch(config)# interface range gigabitethernet0/1 - 2 Switch(config-if-range)# speed 100
This example shows how to use a comma to add different interface type strings to the range to enable Fast Ethernet ports 1 to 3 and Gigabit Ethernet ports 1 and 2 to receive flow-control pause frames:
Switch# configure terminal Switch(config)# interface range fastethernet0/1 - 3, gigabitethernet0/1 - 2 Switch(config-if-range)# flowcontrol receive on
If you enter multiple configuration commands while you are in interface-range mode, each command is executed as it is entered. The commands are not batched and executed after you exit interface-range mode. If you exit interface-range configuration mode while the commands are being executed, some commands might not be executed on all interfaces in the range. Wait until the command prompt reappears before exiting interface-range configuration mode.
Configuring and Using Interface Range Macros
You can create an interface range macro to automatically select a range of interfaces for configuration. Before you can use the macro keyword in the interface range macro global configuration command string, you must use the
define interface-range
global configuration command to define the macro.
Beginning in privileged EXEC mode, follow these steps to define an interface range macro:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
define interface-range
macro_name
interface-range
|
Define the interface-range macro, and save it in NVRAM.
-
The
macro_name
is a 32-character maximum character string.
-
A macro can contain up to five comma-separated interface ranges.
-
Each
interface-range
must consist of the same port type.
|
Step 3
|
interface range macro
macro_name
|
Select the interface range to be configured using the values saved in the interface-range macro called
macro_name.
You can now use the normal configuration commands to apply the configuration to all interfaces in the defined macro.
|
Step 4
|
end
|
Return to privileged EXEC mode.
|
Step 5
|
show running-config | include define
|
Show the defined interface range macro configuration.
|
Step 6
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
Use the
no define interface-range
macro_name
global configuration command to delete a macro.
When using the
define
interface-range
global configuration command, note these guidelines:
-
Valid entries for
interface-range,
depending on port types on the switch:
–
vlan
vlan-ID
-
vlan-ID
, where the VLAN ID is 1 to 4094
–
fastethernet
module/{first
port
} - {
last port
}, where the module is always 0
–
gigabitethernet
module/{
first port
} - {
last port
}, where the module is always 0
–
port-channel
port-channel-number
-
port-channel-number
, where the
port-channel-number
is 1 to 24
Note When you use the interface range command with port channels, the first and last port-channel number must be active port channels.
-
You must add a space between the first interface number and the hyphen when entering an
interface-rang
.
For example,
gigabitethernet
0/1 - 2 is a valid range;
gigabit
ethernet0/1-4 is not.
-
The VLAN interfaces must have been configured with the
interface vlan
command. The
show running-config
privileged EXEC command displays the configured VLAN interfaces. VLAN interfaces not displayed by the
show running-config
command cannot be used as
interface-ranges
.
-
All interfaces defined as in a range must be the same type (all Fast Ethernet ports, all Gigabit Ethernet ports, all EtherChannel ports, or all VLANs), but you can combine multiple interface types in a macro.
This example shows how to define an interface-range named
enet_list
to include ports 1 and 2 and to verify the macro configuration:
Switch# configure terminal Switch(config)# define interface-range enet_list gigabitethernet0/1 - 2 Switch# show running-config | include define Switch# define interface-range enet_list gigabitethernet0/1 - 2
This example shows how to create a multiple-interface macro named
macro1
:
Switch# configure terminal Switch(config)# define interface-range macro1 fastethernet0/1 - 2, gigabitethernet0/1 - 2
This example shows how to enter interface-range configuration mode for the interface-range macro
enet_list
:
Switch# configure terminal Switch(config)# interface range macro enet_list
This example shows how to delete the interface-range macro
enet_list
and to verify that it was deleted.
Switch# configure terminal Switch(config)# no define interface-range enet_list Switch# show run | include define
Configuring Ethernet Interfaces
These sections contain this configuration information:
Default Ethernet Interface Configuration
Table 13-2
shows the Ethernet interface default configuration. For more details on the VLAN parameters listed in the table, see Chapter15, “Configuring VLANs” For details on controlling traffic to the port, see Chapter27, “Configuring Port-Based Traffic Control”
Note To configure Layer 2 parameters, if the interface is in Layer 3 mode, you must enter the switchport interface configuration command without any parameters to put the interface into Layer 2 mode. This shuts down the interface and then re-enables it, which might generate messages on the device to which the interface is connected. When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration.
Table 13-2 Default Layer 2 Ethernet Interface Configuration
|
|
Operating mode
|
Layer 2 or
switching mode
(
switchport
command).
|
Allowed VLAN range
|
VLANs 1 to 4094.
|
Default VLAN (for access ports)
|
VLAN 1 (Layer 2 interfaces only).
|
Native VLAN (for IEEE 802.1Q trunks)
|
VLAN 1 (Layer 2 interfaces only).
|
VLAN trunking
|
Switchport mode dynamic auto (supports DTP) (Layer 2 interfaces only).
|
Port enable state
|
All ports are enabled.
|
Port description
|
None defined.
|
Speed
|
Autonegotiate.
|
Duplex mode
|
Autonegotiate.
|
Flow control
|
Flow control is set to
receive
:
off
. It is always off for sent packets.
|
EtherChannel (PAgP)
|
Disabled on all Ethernet ports. Chapter38, “Configuring EtherChannels and Link-State Tracking”
|
Port blocking (unknown multicast and unknown unicast traffic)
|
Disabled (not blocked) (Layer 2 interfaces only). See the “Configuring Port Blocking” section.
|
Broadcast, multicast, and unicast storm control
|
Disabled. See the “Default Storm Control Configuration” section.
|
Protected port
|
Disabled (Layer 2 interfaces only). See the “Configuring Protected Ports” section.
|
Port security
|
Disabled (Layer 2 interfaces only). See the “Default Port Security Configuration” section.
|
Port Fast
|
Disabled. See the “Default Optional Spanning-Tree Configuration” section.
|
Auto-MDIX
|
Enabled.
Note The switch might not support a pre-standard powered device—such as Cisco IP phones and access points that do not fully support IEEE 802.3af—if that powered device is connected to the switch through a crossover cable. This is regardless of whether auto-MIDX is enabled on the switch port.
|
Power over Ethernet (PoE)
|
Enabled (auto).
|
Keepalive messages
|
Disabled on SFP module ports; enabled on all other ports.
|
Setting the Type of a Dual-Purpose Uplink Port
Some switches support dual-purpose uplink ports. By default, the switch dynamically selects the interface type that first links up. However, you can use the
media-type
interface configuration command to manually select the RJ-45 connector or the SFP module connector. For more information, see the “Dual-Purpose Uplink Ports” section.
Beginning in privileged EXEC mode, follow these steps to select which dual-purpose uplink to activate so that you can set the speed and duplex. This procedure is optional.
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface
interface-id
|
Specify the dual-purpose uplink port to be configured, and enter interface configuration mode.
|
Step 3
|
media-type
{
auto-select
|
rj45
|
sfp
}
|
Select the interface and type of a dual-purpose uplink port. The keywords have these meanings:
-
auto-select
—
The switch dynamically selects the type. When link up is achieved, the switch disables the other type until the active link goes down. When the active link goes down, the switch enables both types until one of them links up. In auto-select mode, the switch configures both types with autonegotiation of speed and duplex (the default). Depending on the type of installed SFP module, the switch might not be able to dynamically select it. For more information, see the information that follows this procedure.
-
rj45
—
The switch disables the SFP module interface. If you connect an SFP module to this port, it cannot attain a link even if the RJ-45 side is down or is not connected. In this mode, the dual-purpose port behaves like a 10/100/1000BASE-TX interface. You can configure the speed and duplex settings consistent with this interface type.
-
sfp
—
The switch disables the RJ-45 interface. If you connect a cable to the RJ-45 port, it cannot attain a link even if the SFP module side is down or if the SFP module is not present. Based on the type of installed SFP module, you can configure the speed and duplex settings consistent with this interface type.
For information about setting the speed and duplex, see the “Speed and Duplex Configuration Guidelines” section.
|
Step 4
|
end
|
Return to privileged EXEC mode.
|
Step 5
|
show interfaces
interface-id
transceiver properties
|
Verify your setting.
|
Step 6
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
To return to the default setting, use the
media-type auto interface
or the
no media-type
interface configuration commands.
e switch configures both types to autonegotiate speed and duplex (the default). If you configure
auto-select
, you cannot configure the
speed
and
duplex
interface configuration commands.
When the switch powers on or when you enable a dual-purpose uplink port through the
shutdown
and the
no shutdown
interface configuration commands, the switch gives preference to the SFP module interface. In all other situations, the switch selects the active link based on which type first links up.
Configuring Interface Speed and Duplex Mode
Depending on the supported port types, Ethernet interfaces on the switch operate at 10, 100, or 1000 Mb/s, or 10,000 Mb/s and in either full- or half-duplex mode. In full-duplex mode, two stations can send and receive traffic at the same time. Normally, 10-Mb/s ports operate in half-duplex mode, which means that stations can either receive or send traffic.
Switch models can include combinations of Fast Ethernet (10/100-Mb/s) ports, Gigabit Ethernet (10/100/1000-Mb/s) ports, 10-Gigabit module ports, and small form-factor pluggable (SFP) module slots supporting SFP modules.
These sections describe how to configure the interface speed and duplex mode:
Speed and Duplex Configuration Guidelines
When configuring an interface speed and duplex mode, note these guidelines:
-
Fast Ethernet (10/100-Mb/s) ports support all speed and duplex options.
-
Gigabit Ethernet (10/100/1000-Mb/s) ports support all speed options and all duplex options (auto, half, and full). However, Gigabit Ethernet ports operating at 1000 Mb/s do not support half-duplex mode.
-
For SFP module ports, the speed and duplex CLI options change depending on the SFP module type:
– The 1000BASE-
x
(where -
x
is -BX, -CWDM, -LX, -SX, and -ZX) SFP module ports support the
nonegotiate
keyword in the
speed
interface configuration command. Duplex options are not supported.
– The 1000BASE-T SFP module ports support the same speed and duplex options as the 10/100/1000-Mb/s ports.
– The 100BASE-
x
(where -
x
is -BX, -CWDM, -LX, -SX, and -ZX) SFP module ports support only 100 Mb/s. These modules support full- and half- duplex options but do not support autonegotiation.
For information about which SFP modules are supported on your switch, see the product release notes.
-
If both ends of the line support autonegotiation, we highly recommend the default setting of auto negotiation.
-
If one interface supports autonegotiation and the other end does not, configure duplex and speed on both interfaces; do not use the
auto
setting on the supported side.
-
When STP is enabled and a port is reconfigured, the switch can take up to 30 seconds to check for loops. The port LED is amber while STP reconfigures.
Caution Changing the interface speed and duplex mode configuration might shut down and re-enable the interface during the reconfiguration.
Setting the Interface Speed and Duplex Parameters
Beginning in privileged EXEC mode, follow these steps to set the speed and duplex mode for a physical interface:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface
interface-id
|
Specify the physical interface to be configured, and enter interface configuration mode.
|
Step 3
|
speed
{
10 | 100 | 1000 | auto
[
10
|
100
|
1000
]
| nonegotiate
}
|
Enter the appropriate speed parameter for the interface:
-
Enter
10
,
100
, or
1000
to set a specific speed for the interface. The
1000
keyword is available only for 10/100/1000 Mb/s ports.
-
Enter
auto
to enable the interface to autonegotiate speed with the connected device. If you use the
10
,
100
, or the
1000
keywords with the
auto
keyword, the port autonegotiates only at the specified speeds.
-
The
nonegotiate
keyword is available only for SFP module ports. SFP module ports operate only at 1000 Mb/s but can be configured to not negotiate if connected to a device that does not support autonegotiation.
For more information about speed settings, see the “Speed and Duplex Configuration Guidelines” section.
|
Step 4
|
duplex
{
auto | full | half
}
|
Enter the duplex parameter for the interface.
Enable half-duplex mode (for interfaces operating only at 10 or 100 Mb/s). You cannot configure half-duplex mode for interfaces operating at 1000 Mb/s.
For more information about duplex settings, see the “Speed and Duplex Configuration Guidelines” section.
|
Step 5
|
end
|
Return to privileged EXEC mode.
|
Step 6
|
show interfaces
interface-id
|
Display the interface speed and duplex mode configuration.
|
Step 7
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
Use the
no speed
and
no duplex
interface configuration commands to return the interface to the default speed and duplex settings (autonegotiate). To return all interface settings to the defaults, use the
default interface
interface-id
interface configuration command.
This example shows how to set the interface speed to 10 Mb/s and the duplex mode to half on a 10/100 Mb/s port:
Switch# configure terminal Switch(config)# interface fasttethernet0/3 Switch(config-if)# speed 10 Switch(config-if)# duplex half
This example shows how to set the interface speed to 100 Mb/s on a 10/100/1000 Mb/s port:
Switch# configure terminal Switch(config)# interface gigabitethernet0/2 Switch(config-if)# speed 100
Configuring IEEE 802.3x Flow Control
Flow control enables connected Ethernet ports to control traffic rates during congestion by allowing congested nodes to pause link operation at the other end. If one port experiences congestion and cannot receive any more traffic, it notifies the other port by sending a pause frame to stop sending until the condition clears. Upon receipt of a pause frame, the sending device stops sending any data packets, which prevents any loss of data packets during the congestion period.
Note Ports on the switch can receive, but not send, pause frames.
You use the
flowcontrol
interface configuration command to set the interface’s ability to
receive
pause frames to
on
,
off
, or
desired
. The default state is
off
.
When set to
desired
, an interface can operate with an attached device that is required to send flow-control packets or with an attached device that is not required to but can send flow-control packets.
These rules apply to flow control settings on the device:
-
receive on
(or
desired
): The port cannot send pause frames but can operate with an attached device that is required to or can send pause frames; the port can receive pause frames.
-
receive off
: Flow control does not operate in either direction. In case of congestion, no indication is given to the link partner, and no pause frames are sent or received by either device.
Note For details on the command settings and the resulting flow control resolution on local and remote ports, see the flowcontrol interface configuration command in the command reference for this release.
Beginning in privileged EXEC mode, follow these steps to configure flow control on an interface:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface
interface-id
|
Specify the physical interface to be configured, and enter interface configuration mode.
|
Step 3
|
flowcontrol
{
receive
} {
on
|
off
|
desired
}
|
Configure the flow control mode for the port.
|
Step 4
|
end
|
Return to privileged EXEC mode.
|
Step 5
|
show interfaces
interface-id
|
Verify the interface flow control settings.
|
Step 6
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
To disable flow control, use the
flowcontrol
receive off
interface configuration command.
This example shows how to turn on flow control on a port:
Switch# configure terminal Switch(config)# interface gigabitethernet0/1 Switch(config-if)# flowcontrol receive on
Configuring Auto-MDIX on an Interface
When automatic medium-dependent interface crossover (auto-MDIX) is enabled on an interface, the interface automatically detects the required cable connection type (straight through or crossover) and configures the connection appropriately. When connecting switches without the auto-MDIX feature, you must use straight-through cables to connect to devices such as servers, workstations, or routers and crossover cables to connect to other switches or repeaters. With auto-MDIX enabled, you can use either type of cable to connect to other devices, and the interface automatically corrects for any incorrect cabling. For more information about cabling requirements, see the hardware installation guide.
Auto-MDIX is enabled by default. When you enable auto-MDIX, you must also set the interface speed and duplex to
auto
so that the feature operates correctly.
Auto-MDIX is supported on all 10/100 and 10/100/1000-Mb/s interfaces. It is also supported on 10/100/1000BASE-TX small form-factor pluggable (SFP)-module interfaces. It is not supported on 1000BASE-SX or -LX SFP module interfaces.
Table 13-3
shows the link states that result from auto-MDIX settings and correct and incorrect cabling.
Table 13-3 Link Conditions and Auto-MDIX Settings
|
|
|
|
On
|
On
|
Link up
|
Link up
|
On
|
Off
|
Link up
|
Link up
|
Off
|
On
|
Link up
|
Link up
|
Off
|
Off
|
Link up
|
Link down
|
Beginning in privileged EXEC mode, follow these steps to configure auto-MDIX on an interface:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface
interface-id
|
Specify the physical interface to be configured, and enter interface configuration mode.
|
Step 3
|
speed auto
|
Configure the interface to autonegotiate speed with the connected device.
|
Step 4
|
duplex auto
|
Configure the interface to autonegotiate duplex mode with the connected device.
|
Step 5
|
mdix auto
|
Enable auto-MDIX on the interface.
|
Step 6
|
end
|
Return to privileged EXEC mode.
|
Step 7
|
show controllers ethernet-controller
interface-id
phy
|
Verify the operational state of the auto-MDIX feature on the interface.
|
Step 8
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
To disable auto-MDIX, use the
no mdix auto
interface configuration command.
This example shows how to enable auto-MDIX on a port:
Switch# configure terminal Switch(config)# interface gigabitethernet0/1 Switch(config-if)# speed auto Switch(config-if)# duplex auto Switch(config-if)# mdix auto
Configuring a Power Management Mode on a PoE Port
For most situations, the default configuration (auto mode) works well, providing plug-and-play operation. No further configuration is required. However, use the following procedure to give a PoE port higher priority, to make it data only, or to specify a maximum wattage to disallow high-power powered devices on a port.
Note When you make PoE configuration changes, the port being configured drops power. Depending on the new configuration, the state of the other PoE ports, and the state of the power budget, the port might not be powered up again. For example, port 1 is in the auto and on state, and you configure it for static mode. The switch removes power from port 1, detects the powered device, and repowers the port. If port 1 is in the auto and on state and you configure it with a maximum wattage of 10 W, the switch removes power from the port and then redetects the powered device. The switch repowers the port only if the powered device is a Class 1, Class 2, or a Cisco-only powered device.
Beginning in privileged EXEC mode, follow these steps to configure a power management mode on a PoE-capable port:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface
interface-id
|
Specify the physical port to be configured, and enter interface configuration mode.
|
Step 3
|
power inline
{
auto
[
max
max-wattage
] |
never |
static
[
max
max-wattage
]}
|
Configure the PoE mode on the port. The keywords have these meanings:
-
auto
—Enable powered-device detection. If enough power is available, automatically allocate power to the PoE port after device detection. This is the default setting.
-
(Optional)
max
max-wattage—
L
imit the power allowed on the port. The range is 4000 to 15400 milliwatts. If no value is specified, the maximum is allowed (15400 milliwatts).
-
never
—Disable device detection, and disable power to the port.
Note If a port has a Cisco powered device connected to it, do not use the power inline never command to configure the port. A false link-up can occur, placing the port into an error-disabled state.
-
static
—Enable powered-device detection. Pre-allocate (reserve) power for a port before the switch discovers the powered device. The switch reserves power for this port even when no device is connected and guarantees that power will be provided upon device detection.
The switch allocates power to a port configured in static mode before it allocates power to a port configured in auto mode.
|
Step 4
|
end
|
Return to privileged EXEC mode.
|
Step 5
|
show power inline
[i
nterface-id
]
|
Display PoE status for a switch or for the specified interface.
|
Step 6
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
For information about the output of the
show power inline
user EXEC command, see the command reference for this release. For more information about PoE-related commands, see the “Troubleshooting Power over Ethernet Switch Ports” section. For information about configuring voice VLAN, see Chapter17, “Configuring Voice VLAN”
Budgeting Power for Devices Connected to a PoE Port
When Cisco powered devices are connected to PoE ports, the switch uses Cisco Discovery Protocol (CDP) to determine the
actual
power consumption of the devices, and the switch adjusts the power budget accordingly. The CDP protocol works with Cisco powered devices and does not apply to IEEE third-party powered devices. For these devices, when the switch grants a power request, the switch adjusts the power budget according to the powered-device IEEE classification. If the powered device is a Class 0 (class status unknown) or a Class 3, the switch budgets 15,400 milliwatts for the device, regardless of the actual amount of power needed. If the powered device reports a higher class than its actual consumption or does not support power classification (defaults to Class 0), the switch can power fewer devices because it uses the IEEE class information to track the global power budget.
By using the
power inline consumption
wattage
configuration command, you can override the default power requirement specified by the IEEE classification. The difference between what is mandated by the IEEE classification and what is actually needed by the device is reclaimed into the global power budget for use by additional devices. You can then extend the switch power budget and use it more effectively.
For example, if the switch budgets 15,400 milliwatts on each PoE port, you can connect only 24 Class 0 powered devices. If your Class 0 device power requirement is actually 5000 milliwatts, you can set the consumption wattage to 5000 milliwatts and connect up to 48 devices. The total PoE output power available on a 24-port or 48-port switch is 370,000 milliwatts.
Caution You should carefully plan your switch power budget and make certain not to oversubscribe the power supply.
Note When you manually configure the power budget, you must also consider the power loss over the cable between the switch and the powered device.
When you enter the
power inline consumption default
wattage
or the
no
power inline consumption default
global configuration command, or the
power inline consumption
wattage
or the
no
power inline consumption
interface configuration command this caution message appears:
%CAUTION: Interface interface-id: Misconfiguring the 'power inline consumption/allocation' command may cause damage to the switch and void your warranty. Take precaution not to oversubscribe the power supply.
If the power supply is over-subscribed to by up to 20 percent, the switch continues to operate but its reliability is reduced. If the power supply is subscribed to by more than 20 percent, the short-circuit protection circuitry triggers and shuts the switch down.
For more information about the IEEE power classifications, see the “Connecting Interfaces” section.
Beginning in privileged EXEC mode, follow these steps to configure the amount of power budgeted to a powered device connected to each PoE port on a switch:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
no cdp run
|
(Optional) Disable CDP.
|
Step 3
|
power inline consumption default
wattage
|
Configure the power consumption of powered devices connected to each the PoE port on the switch. The range for each device is
4000 to 15400 milliwatts. The default is 15400 milliwatts.
|
Step 4
|
end
|
Return to privileged EXEC mode.
|
Step 5
|
show power inline consumption
|
Display the power consumption status.
|
Step 6
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
To return to the default setting, use the
no power inline consumption default
global configuration command.
Beginning in privileged EXEC mode, follow these steps to configure amount of power budgeted to a powered device connected to a specific PoE port:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
no cdp run
|
(Optional) Disable CDP.
|
Step 3
|
interface
interface-id
|
Specify the physical port to be configured, and enter interface configuration mode.
|
Step 4
|
power inline consumption
wattage
|
Configure the power consumption of a powered device connected to a PoE port on the switch. The range for each device is
4000 to 15400 milliwatts. The default is 15400 milliwatts.
|
Step 5
|
end
|
Return to privileged EXEC mode.
|
Step 6
|
show power inline consumption
|
Display the power consumption status.
|
Step 7
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
To return to the default setting, use the
no power inline consumption
interface configuration command.
For information about the output of the
show power inline consumption
privileged EXEC command, see the command reference for this release.
Adding a Description for an Interface
You can add a description about an interface to help you remember its function. The description appears in the output of these privileged EXEC commands:
show configuration
,
show running-config
, and
show interfaces
.
Beginning in privileged EXEC mode, follow these steps to add a description for an interface:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
interface
interface-id
|
Specify the interface for which you are adding a description, and enter interface configuration mode.
|
Step 3
|
description
string
|
Add a description (up to 240 characters) for an interface.
|
Step 4
|
end
|
Return to privileged EXEC mode.
|
Step 5
|
show interfaces
interface-id
description
or
show running-config
|
Verify your entry.
|
Step 6
|
copy running-config startup-config
|
(Optional) Save your entries in the configuration file.
|
Use the
no description
interface configuration command to delete the description.
This example shows how to add a description on a port and how to verify the description:
Enter configuration commands, one per line. End with CNTL/Z. Switch(config)# interface gigabitethernet0/2 Switch(config-if)# description Connects to Marketing Switch# show interfaces gigabitethernet0/2 description Interface Status Protocol Description Gi0/2 admin down down Connects to Marketing
Configuring the System MTU
The default maximum transmission unit (MTU) size for frames received and transmitted on all interfaces is 1500 bytes. You can increase the MTU size for all interfaces operating at 10 or 100 Mb/s by using the
system mtu
global configuration command. You can increase the MTU size to support jumbo frames on all Gigabit Ethernet interfaces by using the
system mtu jumbo
global configuration command.
You can change the MTU size for routed ports by using the
system mtu routing
global configuration command.
Note You cannot configure a routing MTU size that exceeds the system MTU size. If you change the system MTU size to a value smaller than the currently configured routing MTU size, the configuration change is accepted, but not applied until the next switch reset. When the configuration change takes effect, the routing MTU size automatically defaults to the new system MTU size.
Gigabit Ethernet ports are not affected by the system mtu command; 10/100 ports are not affected by the system mtu jumbo command. If you d o not configure the
system mtu jumbo
command, the setting of the
system mtu
command applies to all Gigabit Ethernet interfaces.
You cannot set the MTU size for an individual interface; you set it for all 10/100 or all Gigabit Ethernet interfaces. When you change the system or jumbo MTU size, you must reset the switch before the new configuration takes effect.The
system mtu routing
command does not require a switch reset to take effect.
Frames sizes that can be received by the switch CPU are limited to 1998 bytes, no matter what value was entered with the system mtu or system mtu jumbo commands. Although frames that are forwarded or routed are typically not received by the CPU, in some cases packets are sent to the CPU, such as traffic sent to control traffic, SNMP, Telnet, or routing protocols.
Routed packets are subjected to MTU checks on the output ports. The MTU value used for routed ports is derived from the applied
system mtu
value (not the
system mtu jumbo
value). That is, the routed MTU is never greater than the system MTU for any VLAN. The routing protocols use the system MTU value when negotiating adjacencies and the MTU of the link. For example, the Open Shortest Path First (OSPF) protocol uses this MTU value before setting up an adjacency with a peer router. To view the MTU value for routed packets for a specific VLAN, use the
show platform port-asic mvid
privileged EXEC command.
Note If Layer 2 Gigabit Ethernet interfaces are configured to accept frames greater than the 10/100 interfaces, jumbo frames received on a Layer 2 Gigabit Ethernet interface and sent on a Layer 2 10/100 interface are dropped.
Beginning in privileged EXEC mode, follow these steps to change MTU size for all 10/100 or Gigabit Ethernet interfaces:
|
|
|
Step 1
|
configure terminal
|
Enter global configuration mode.
|
Step 2
|
system mtu
bytes
|
(Optional) Change the MTU size for all interfaces on the switch that are operating at 10 or 100 Mb/s.
The range is 1500 to 1998 bytes; the default is 1500 bytes.
|
Step 3
|
system mtu
jumbo
bytes
|
(Optional) Change the MTU size for all Gigabit Ethernet interfaces on the switch.
The range is 1500 to 9000 bytes; the default is 1500 bytes.
|
Step 4
|
system mtu routing
bytes
|
(Optional) Change the system MTU for routed ports. The range is 1500 to the system MTU value, the maximum MTU that can be routed for all ports.
Although larger packets can be accepted, they cannot be routed.
|
Step 5
|
end
|
Return to privileged EXEC mode.
|
Step 6
|
copy running-config startup-config
|
Save your entries in the configuration file.
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Step 7
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reload
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Reload the operating system.
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If you enter a value that is outside the allowed range for the specific type of interface, the value is not accepted.
Once the switch reloads, you can verify your settings by entering the show system mtu privileged EXEC command.
This example shows how to set the maximum packet size for a Gigabit Ethernet port to 1800 bytes:
Switch(config)# system mtu jumbo 1800
This example shows the response when you try to set Gigabit Ethernet interfaces to an out-of-range number:
Switch(config)# system mtu jumbo 25000 % Invalid input detected at '^' marker.