10-17
Catalyst 2960 Switch SoftwareConfiguration Guide
78-16881-01
Chapter10 Configuring Interface Char acteristics
Configuring the System MTU
You cannot set the MTU size for an individual interface; you set it for all 10/100 or all Gigabi t Ethernet
interfaces on the switch. When you change the MTU size, you must reset the switch before the new
configuration takes effect.
Frames sizes that can be received by the switch CPU are limited to 1998 bytes, no matter what value was
entered with the system mtu or system mtu jumbo commands. Although frames that are forwarded are
typically not received by the CPU, in some cases packets are sent to the CPU, such as traffic sent to
control traffic, SNMP, or Telnet.
Note 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.
Beginning in privileged EXEC mode, follow these steps to change MTU size for all 10/100 or Gigabit
Ethernet interfaces:
If you enter a value that is outside the allowed range for the specific type of interface, the value is not
accepted.
Once the switch reloads, you can verify your settings by entering the show system mtu privileged EXEC
command.
This example shows how to set the maximum packet size for a Gigabit Ethernet port to 1800 bytes:
Switch(config)# system jumbo mtu 1800
Switch(config)# exit
Switch# reload
This example shows the response when you try to set Gigabit Etherne t interfaces to an out-of-range
number:
Switch(config)# system mtu jumbo 25000
^
% Invalid input detected at '^' marker.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 system mtu bytes (Optional) Change the MTU size for all interfaces on
the switch that are operating at 10 or 100 Mbps. The
range is 1500 to 1998 bytes; the default is 1500 bytes.
Step3 system mtu jumbo bytes (Optional) Change the MTU size for all Gigabit
Ethernet interfaces on the switch. The range is 1500 to
9000 bytes; the default is 1500 bytes.
Step4 end Return to privileged EXEC mode.
Step5 copy running-config startup-config Save your entries in the configuration file.
Step6 reload Reload the operating system.