Cisco WS-C3560E-48PD-SF Command Reference - Page 686

system mtu Chapter 2 Catalyst 3560 Switch Cisco IOS Commands Note You cannot configure a routing MTU size that exceeds the system MTU size. If you change the system MTU size to a value smaller than the currently configured routing MTU size, the configuration change is accepted, but not applied until the next switch reset. When the configuration change takes effect, the routing MTU size defaults to the new system MTU size. If you enter a value that is outside the range for the specific type of switch, the value is not accepted. Note The switch does not support setting the MTU on a per-interface basis. The size of frames that can be received by the switch CPU is limited to 1998 bytes, regardless of the value entered with the system mtu command. Although forwarded or routed frames are usually not received by the CPU, some packets (for example, control traffic, SNMP, Telnet, and routing protocols) are sent to the CPU. Because the switch does not fragment packets, it drops: • switched packets larger than the packet size supported on the egress interface • routed packets larger than the routing MTU value For example, if the system mtu value is 1998 bytes and the system mtu jumbo value is 5000 bytes, packets up to 5000 bytes can be received on interfaces operating at 1000 Mbps. However, although a packet larger than 1998 bytes can be received on an interface operating at 1000 Mbps, if its destination interface is operating at 10 or 100 Mbps, the packet is dropped. Examples This example shows how to set the maximum jumbo packet size for Gigabit Ethernet ports operating at 1000 Mbps or greater to 1800 bytes: Switch(config)# system mtu jumbo 1800 Switch(config)# exit Switch# reload You can verify your setting by entering the show system mtu privileged EXEC command. Related Commands Command show system mtu Description Displays the packet size set for Fast Ethernet, Gigabit Ethernet, and routed ports. 2-654 Catalyst 3560 Switch Command Reference 78-16405-05