Modifying An Ip Router Port; Defining Maximum Transmission Unit (Mtu) Size - Alcatel OmniSwitch 6624 Network Configuration Manual

Configuring VLAN Router Ports

Modifying an IP Router Port

The vlan router ip command is also used to modify one or more existing IP router port parameter values.
For example, the following command changes the existing router port IP address for VLAN 455 to
40.0.0.2:
-> vlan 455 router ip 40.0.0.2
It is not necessary to first remove the IP router port from the VLAN. The changes specified will overwrite
existing parameter values. For example, the following command changes the subnet mask from 255.0.0.0
(the default mask for 40.0.0.2) to a Class C mask of 255.255.255.0, the forwarding status to no forwarding
and the encapsulation to SNAP by overwriting existing router port parameter values defined for VLAN
455. The IP address is not changed in this example, but is required as part of the command syntax to iden-
tify a router port change:
-> vlan 455 router ip 40.0.0.2 255.255.255.0 no forward snap
Note that when changing router port parameters, the subnet mask will revert back to the default mask
value if it was previously set to a non-default value and it is not specified when changing other router port
parameters. In the above example, the mask was set to a Class C value of 255.255.255.0, which is not the
default mask value for the Class A IP address of 40.0.0.1. If a change is made to any of the other parame-
ters and the Class C mask is not specified again in the command syntax, the mask will revert back to the
default Class A value of 255.0.0.0. For example, the following command changes the router port forward-
ing status and will cause the mask to revert back to its default value:
-> vlan 455 router ip 40.0.0.1 forward
To avoid the problem in the above example, simply enter the non-default mask value as shown below:
-> vlan 455 router ip 40.0.0.1 255.255.255.0 forward
Use the show vlan or
information about these commands, see the OmniSwitch CLI Reference Guide.

Defining Maximum Transmission Unit (MTU) Size

The MTU size is configurable on all VLANs, but only restricts the transmission packet size for VLANs
with an IP router port defined. The default MTU size for each VLAN is 1500 bytes (the standard Ethernet
MTU default size) and is sufficient in most cases. In addition, 1500 bytes is also the maximum MTU size
allowed. Frames received with a data portion larger than 1500 are automatically dropped.
To change the MTU size for a specific VLAN, enter vlan followed by an existing VLAN ID then mtu-ip
followed by an MTU size value between 512 and 1500 bytes. For example, the following command sets
the MTU size for VLAN 1504 to 576 bytes.
-> vlan 1504 mtu-ip 576
To view the current MTU size for IP router VLANs, use the
information about this command, see the OmniSwitch CLI Reference Guide.
page 4-12
show vlan router ip commands to verify VLAN IP router port changes. For more
OmniSwitch 6624/6648 Network Configuration Guide
show vlan router ip command. For more
Configuring VLANs
April 2004