Cisco Catalyst 4500 Series Software Configuration Manual page 938

Configuring VLANs as Layer 3 Interfaces
To set the nonprotocol-specific MTU value for an interface, use the mtu interface configuration
Note
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 37.
To set the protocol-specific maximum transmission unit (MTU) size of IPv4 or IPv6 packets sent on an
interface, perform this task:
Command
Step 1
Switch# configure terminal
Step 2
Switch(config)# interface interface-id
Step 3
Switch(config-if)# [no] ip mtu mtu_size
or
Switch(config-if)# [no] ipv6 mtu mtu_size
Step 4
Switch(config-if)# exit
Step 5
Switch(config)# end
Step 6
Switch# show run interface interface-id
This example shows how to configure IPv4 MTU on an interface:
Switch# configure terminal
Enter configuration commands, one per line.
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)
The following example shows how to configure IPv6 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)# ipv6 mtu 1280
Switch(config)# end
This example shows how to verify the configuration
Switch# show ipv6 interface vlan 1
Vlan1 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::214:6AFF:FEBC:DEEA
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
35-10
Chapter 35
Purpose
Enters global configuration mode.
Enters interface configuration mode.
Configures the IPv4 MTU size
Configures the IPv6 MTU size.
The no form of the command reverts to the default MTU
size (1500 bytes).
Exits configuration interface mode.
Exits configuration mode.
Displays the running configuration.
End with CNTL/Z.
Configuring Layer 3 Interfaces