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Configuring Interfaces
Configuring the System MTU
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
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface GigabitEthernet1/18
Switch(config-if)# no switchport
Switch(config-if)# ip address 192.20.135.21 255.255.255.0
Configuring the System MTU
The default maximum transmission unit (MTU) size for frames received and sent 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. You can change the MTU size for routed ports by using the
system mtu routing global configuration command.
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 automatically defaults to
the new system MTU size.
Gigabit Ethernet ports are not affected by the system mtu command. Fast Ethernet ports are not affected by the system
mtu jumbo command because jumbo frames are not supported on 10/100 interfaces, including 100BASE-FX and
100BASE-BX SFP modules. 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 on the
switch. When you change the system MTU size, you must reset the switch before the new configuration takes effect. The
system mtu routing command does not require a switch reset to take effect.
Note: The system MTU setting is saved in the switch environmental variable in NVRAM and becomes effective when the
switch reloads. The MTU settings you enter with the system mtu and system mtu jumbo commands are not saved in
the switch IOS configuration file, even if you enter the copy running-config startup-config privileged EXEC command.
Therefore, if you use TFTP to configure a new switch by using a backup configuration file and want the system MTU to
be other than the default, you must explicitly configure the system mtu and system mtu jumbo settings on the new
switch and then reload the switch.
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 or routed are typically not
received by the CPU, in some cases packets are sent to the CPU, such as traffic sent to control traffic, SNMP, Telnet, or
routing protocols.
Because the switch does not fragment packets, it drops:
switched packets larger than the packet size supported on the egress interface
7. end Return to privileged EXEC mode.
8. show interfaces [interface-id]
show ip interface [interface-id]
show running-config interface [interface-id]
Verify the configuration.
9. copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
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