Configuring The System Mtu - Cisco Catalyst 3750 Software Configuration Manual

Chapter 9 Configuring Interface Characteristics
Beginning in privileged EXEC mode, follow these steps to configure a Layer 3 interface:
Command
Step 1
configure terminal
Step 2
interface {{fastethernet | gigabitethernet} interface-id}
| {vlan vlan-id} | {port-channel port-channel-number}
Step 3
no switchport
Step 4 ip address ip_address subnet_mask
Step 5
no shutdown
Step 6
end
Step 7
show interfaces [interface-id]
show ip interface [interface-id]
show running-config interface [interface-id]
Step 8 copy running-config startup-config
To remove an IP address from an interface, use the no ip address interface configuration command.
This example shows how to configure a port as a routed port and to assign it an IP address:
Switch# configure terminal
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# no switchport
Switch(config-if)# ip address 192.20.135.21 255.255.255.0
Switch(config-if)# no shutdown

Configuring the System MTU

The default maximum transmission unit (MTU) size for frames received and transmitted on all interfaces
on the switch is 1500 bytes. You can increase the MTU size for all interfaces operating at 10 or 100 Mbps
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. Gigabit Ethernet ports are not affected by the system mtu command; 10/100 ports are not
affected by the system jumbo mtu command.
The switch supports a maxiumum MTU size for 10/100 interfaces of 1546 bytes. The maxiumum MTU
size for Gigabit interfaces is 9000 bytes.
You cannot set the MTU size for an individual interface; you set it for all Fast Ethernet or all Gigabit
Ethernet interfaces on the switch. When you change the MTU size, you must reset the switch before the
new configuration takes effect.
The size of frames that can be received by the switch CPU is limited to 1500 bytes, no matter what value
was entered with the system mtu or system mtu jumbo commands. Although frames that are forwarded
or routed typically are not received by the CPU, in some cases packets are sent to the CPU, such as traffic
sent to control traffic, SNMP, or Telnet, or routing protocols.
Note If Gigabit Ethernet interfaces are configured to accept frames greater than the 10/100 interfaces, jumbo
frames ingressing on a Gigabit Ethernet interface and egressing on a 10/100 interface are dropped.
78-15870-01
Purpose
Enter global configuration mode.
Enter interface configuration mode, and enter the
interface to be configured as a Layer 3 interface.
For physical ports only, enter Layer 3 mode.
Configure the IP address and IP subnet.
Enable the interface.
Return to privileged EXEC mode.
Verify the configuration.
(Optional) Save your entries in the configuration file.
Catalyst 3750 Metro Switch Software Configuration Guide
Configuring the System MTU
9-19