Configuring Mtu Sizes - Cisco Catalyst 4500 Series Configuration Manual

Chapter 7 Configuring Interfaces
The MTU of a packet is not checked on the ingress side for an SVI; it is checked on the egress side of
an SVI. If the MTU of a packet is larger than the MTU of the egress SVI, the packet is sent to the CPU
for fragmentation processing. If the "do not fragment" bit is not set, the packet is fragmented. Otherwise,
the packet is dropped.

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#
For details on how to configure IP MTU size, refer to
OL-25340-01
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.
"Configuring IP MTU Sizes" section on page
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
Configuring Optional Interface Features
32-9.
7-27