Cisco Catalyst 2960 Software Configuration Manual page 377

Chapter 12 Configuring Interface Characteristics
Gigabit Ethernet ports are not affected by the system mtu command; 10/100 ports are not affected by
the system mtu jumbo command. If you do not configure the system mtu jumbo command, the setting
of the system mtu command applies to all Gigabit Ethernet interfaces.
You cannot set the MTU size for an individual interface; you set it for all 10/100 or all Gigabit Ethernet
interfaces. When you change the system or jumbo 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.
If Layer 2 Gigabit Ethernet interfaces are configured to accept frames greater than the 10/100 interfaces,
Note
jumbo frames received on a Layer 2 Gigabit Ethernet interface and sent on a Layer 2 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:
Command
Step 1 configure terminal
Step 2 system mtu bytes
Step 3 system mtu jumbo bytes
Step 4 end
Step 5 copy running-config startup-config
Step 6 reload
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 mtu jumbo 1800
Switch(config)# exit
Switch# reload
This example shows the response when you try to set Gigabit Ethernet interfaces to an out-of-range
number:
Switch(config)# system mtu jumbo 25000
OL-26520-01
Purpose
Enter global configuration mode.
(Optional) Change the MTU size for all interfaces on
the switch stack that are operating at 10 or 100 Mb/s.
The range is 1500 to 1998 bytes; the default is 1500
bytes.
(Optional) Change the MTU size for all Gigabit
Ethernet interfaces on the switch.
(Optional) Change the MTU size for all Gigabit
Ethernet interfaces on the switch stack.
The range is 1500 to 9000 bytes; the default is 1500
bytes.
Return to privileged EXEC mode.
Save your entries in the configuration file.
Reload the operating system.
Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE
Configuring the System MTU
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