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 that operate at 10 or 100 Mbps with the system mtu global configuration command. You can increase the MTU size to support jumbo frames on all Gigabit Ethernet interfaces with the system mtu jumbo global configuration command.

You cannot set the MTU size for an individual interface; you set it for all 10/100 or all Gigabit Ethernet interfaces on the switch. When you change the system or jumbo MTU size, you must reset the switch before the new configuration takes effect.

If Gigabit Ethernet interfaces are configured to accept frames greater than the 10/100 interfaces, jumbo frames received on a Gigabit Ethernet interface and sent on a 10/100 interface are dropped.

2970(config)# system mtu 1998
2970(config)# exit
2970# reload

Use the system mtu jumbo command to change the MTU for all Gigabit Ethernet interfaces. This command only affects Gigabit Ethernet Interfaces.

    2970(config)# system mtu jumbo 9000
    2970(config)# exit
    2970# reload

Use the show system mtu command to view the MTU sizes after reload.

    2970# show system mtu
    System MTU size is 1998 bytes
    System Jumbo MTU size is 9000 bytes