ip mtu

Description

Sets the MTU (maximum transmission unit) for an IP interface. The default value is 1500 bytes.

The no form of this command sets the MTU to the default value of 1500 bytes.

Command context

config-gre-if

config-ip-if

Parameters

<VALUE>

Specifies the MTU in bytes. Range: 1,280 bytes to 9,192 bytes.

Authority

Administrators or local user group members with execution rights for this command.

Usage

The IP MTU is the largest IP packet that can be sent or received by the interface. For a tunnel, the IP MTU is the maximum size of the IP payload. To enable jumbo packet forwarding through the tunnel, set the IP MTU of the tunnel to a value greater than 1500. Also set the MTU and the IP MTU values for the underlying physical interface that the tunnel is using to a value greater than 1,500 bytes. The IP MTU of the tunnel must also be greater than or equal to the MTU of the ingress interface on the switch. The IP MTU value of the tunnel must also be less than or equal to the IP MT of the underlying interface that the tunnel is using.

When defining a GRE tunnel, the MTU has to account for 28 bytes of IP layer overhead, plus a GRE header. It must be larger than the MTU of the interface that the tunnel is using. Packets larger than the MTU are dropped.

Examples

switch(config)# interface tunnel 33 mode gre ipv4
switch(config-gre-if)# mtu 1300

switch(config)# interface tunnel 33 mode gre ipv4
switch(config-gre-if)# ip mtu

Sets the MTU on IPv6 in IPv4 tunnel 27 to 1000 bytes.

switch(config)# interface tunnel 27 mode ip 6in4
switch(config-ip-if)# mtu 1000

Sets the MTU onIPv6 in IPv4 tunnel 27 to the default value.

switch(config)# interface tunnel 27 mode ip 6in4
switch(config-ip-if)# ip mtu

Sets the MTU on IPv6 in IPv6 tunnel 8 to 900 bytes.

switch(config)# interface tunnel 8 mode ip 6in6
switch(config-ip-if)# ip mtu 9000

Sets the MTU on IPv6 in IPv6 tunnel 8 to the default value.

switch(config)# interface tunnel 8 mode ip 6in6
switch(config-ip-if)# ip mtu