device(config-intf-ve-5)# ip mtu 9011
MTU can be configured globally or for each individual GRE tunnel interface.
To configure the MTU for a GRE Tunnel, the MTU is first configured in a VE. This VE is then applied to the tunnel. This causes the VE's MTU to be used as the tunnel's MTU .
When configuring the MTU either globally or for use with a tunnel interface, take into account the 24 bytes reserved for the GRE Tunnel Header. Reduce 24 bytes from your target MTU and configure it as the MTU. When applying, the 24 bytes reserved for the GRE Tunnel Header is added to your configured MTU value and applied.
For example, if you want to set the MTU to 1750, reduce the 24 bytes from this value and configure 1726 bytes as the MTU value for the VE. The targeted MTU value of 1750 bytes (1726 bytes + 24 bytes) will be applied to the VE and on the tunnel. This applies to all MTU configurations.
In the case where you want to assign the maximum permissible MTU of 9194 bytes, you must manually reduce the reserved 24 bytes. In this case, you should set the MTU value at 9170 bytes. (9194 bytes - 24 bytes = 9170 bytes).
Note
The 24 bytes consists of a 4 byte GRE Outer Header and a 20 byte Outer IP Header.This example summarizes the commands in this procedure.
device# configure terminal device(config)# interface ve 5 device(config-intf-ve-5)# ip mtu 1500
This example configures the MTU value to the maximum permitted value.
device# configure terminal device (config)# interface ve 5 device (config-intf-ve-5)# ip mtu 9170