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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 30 Configuring Layer 3 Interfaces
Configuring VLANs as Layer 3 Interfaces
Configuring IP MTU Sizes
You can set the protocol-specific maximum transmission unit (MTU) size of IPv4 or IPv6 packets that
are sent on an interface.
For information on MTU limitations, refer to “Maximum Transmission Units” on page 23.
Note To set the nonprotocol-specific MTU value for an interface, use the mtu interface configuration
command. Changing the MTU value (with the mtu interface configuration command) can affect the IP
MTU value. If the current IP MTU value matches the MTU value, and you change the MTU value, the
IP MTU value is modified automatically to match the new MTU. However, the reverse is not true;
changing the IP MTU value has no effect on the value for the mtu command.
For information on how to configure MTU size, refer to “Configuring MTU Sizes” on page 25.
To set the protocol-specific maximum transmission unit (MTU) size of IPv4 or IPv6 packets sent on an
interface, perform this task:
This example shows how to configure IPv4 MTU on an interface:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface vlan 1
Switch(config-if)# ip mtu 68
Switch(config-if)# exit
Switch(config)# end
Switch# show ip interface vlan 1
Vlan1 is up, line protocol is up
Internet address is 10.10.10.1/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 68 bytes
Helper address is not set
.........................(continued)
Command Purpose
Step 1
Switch# configure terminal
Enters global configuration mode.
Step 2
Switch(config)# interface interface-id
Enters interface configuration mode.
Step 3
Switch(config-if)# [no] ip mtu mtu_size
or
Switch(config-if)# [no] ipv6 mtu mtu_size
Configures the IPv4 MTU size
Configures the IPv6 MTU size.
The no form of the command reverts to the default MTU
size (1500 bytes).
Step 4
Switch(config-if)# exit
Exits configuration interface mode.
Step 5
Switch(config)# end
Exits configuration mode.
Step 6
Switch# show run interface interface-id
Displays the running configuration.