System Mtu - Cisco Catalyst 3030 Command Reference Manual

system mtu

system mtu
Use the system mtu global configuration command to set the maximum packet size or maximum
transmission unit (MTU) size for Gigabit Ethernet ports. Use the no form of this command to restore the
global MTU value to its default value.
Syntax Description bytes
jumbo bytes
Defaults The default MTU size for all ports is 1500 bytes.
Command Modes
Global configuration
Command History Release
12.2(25)SEE
Usage Guidelines
When you use this command to change the system MTU or jumbo MTU size, you must reset the switch
before the new configuration takes effect.
Gigabit Ethernet ports operating at 1000 Mbps are not affected by the system mtu command, and
10/100-Mbps ports are not affected by the system mtu jumbo command.
If you enter a value that is outside the range for the specific type of switch, the value is not accepted.
The switch does not support setting the MTU on a per-interface basis.
Note
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.
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.
Cisco Catalyst Blade Switch 3030 Command Reference
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system mtu {bytes | jumbo bytes}
no system mtu
The range is 1500 to 1998 bytes. This is the maximum MTU received at
10/100-Mbps Ethernet switch ports.
Set the system jumbo MTU for Gigabit Ethernet ports operating at 1000
Mbps or greater. The range is 1500 to 9000 bytes. This is the maximum MTU
received at the physical port for Gigabit Ethernet ports.
Modification
This command was introduced.
Chapter 2 Cisco Catalyst Blade Switch 3030 Cisco IOS Commands
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