Configuring Mtu Sizes - Cisco Catalyst 4500 Series Software Configuration Manual

Configuring MTU Sizes

To configure the MTU size, perform this task:
Command
Step 1
Switch(config)# interface {{vlan vlan_ID} |
1
{{type slot/port} | {port-channel
port_channel_number} slot/port}}
Step 2
Switch(config-if)# mtu mtu_size
Switch(config-if)# no mtu
Step 3
Switch(config-if)# end
Step 4
Switch(config)# end
Step 5
Switch# show running-config interface
[{fastethernet | gigabitethernet} slot/port]
1. type = fastethernet, gigabitethernet, or tengigabitethernet
Note When you remove a line card, and then reinsert the card, some or all of the MTU values configured on
the ports of that line card may be unconfigured. This occurs if the system wide limit of 32 different
MTUs is reached while the card is removed. Upon reinserting the line card, the system attempts to
reapply the MTU configuration on the ports. If this attempt fails, the MTU values are set to the default.
When configuring the MTU size for VLAN interfaces and Layer 3 and Layer 2 Ethernet ports, note that
Note
the supported MTU values are from 1500 to 9198 bytes.
This example shows how to configure the MTU size on Gigabit Ethernet port 1/1:
switch# conf terminal
switch(config)# interface gi1/1
switch(config-if)# mtu 9198
switch(config-if)# end
switch(config)# end
switch# show interface gigabitethernet 1/2
GigabitEthernet1/2 is administratively down, line protocol is down
Hardware is C6k 1000Mb 802.3, address is 0030.9629.9f88 (bia 0030.9629.9f88)
MTU 9216 bytes, BW 1000000 Kbit, DLY 10 usec,
<...Output Truncated...>
switch#
Interacting with Baby Giants
The baby giants feature, introduced in Cisco IOS Release 12.1(12c)EW, uses the global command system mtu size to set the
global baby giant MTU. This feature also allows certain interfaces to support Ethernet payload size of up to 1552 bytes.
Both the system mtu command and the per-interface mtu command can operate on interfaces that can support jumbo frames,
but the per-interface mtu command takes precedence.
Chapter 9 Configuring Interfaces
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS
Configuring Optional Interface Features
Purpose
Selects the interface to configure.
Configures the MTU size.
Reverts to the default MTU size (1500 bytes).
Exits configuration interface mode.
Exits configuration mode.
Verifies the running configuration.