16An Introduction to IP Routing Protocols

Variable-length subnet masking (VLSM) is the ability to divide an intranet into pieces that match network requirements. Routing is based on the longest subnet mask or network that matches.

IP routing using VLANs

The Nortel Ethernet Routing Switch 5500 Series supports wire-speed IP routing between virtual LANs (VLAN). This type of routing is also referred to as virtual routing. When a virtual router interface is created for a specified VLAN, a specific IP address is associated with the specific VLAN. In this release, the Nortel Ethernet Routing Switch 5500 Series supports static routing, in which the identifiers of the devices being routed between are entered manually.

This virtual router interface does not have an association with any specified port or set of ports (it is called a virtual router interface because it is not associated with any particular port). The VLAN IP address can be reached through any of the ports in the VLAN specified as a virtual router interface, and the assigned IP address is the gateway through which packets are routed out of that VLAN. Routed traffic can be forwarded to another VLAN within the switch or stack of Nortel Ethernet Routing Switch 5500 Series.

Once routing is enabled on two VLANs by assigning IP addresses, routing can be performed between those two VLANs (refer to "IP routing with VLANs" (page 16)).

IP routing with VLANs

IP routing is enabled or disabled globally on the Nortel Ethernet Routing Switch 5500 Series. By default, IP routing is disabled.

Note: All IP routing parameters can be configured on the Nortel Ethernet Routing Switch 5500 Series before routing is actually enabled on the switch.

There is no longer a one-to-one correspondence between the physical port and the router interface, because a given port can belong to multiple VLANs. The VLANs may be configured for routing on the switch.

Nortel Ethernet Routing Switch 5500 Series

Configuration-IP Routing Protocols

NN47200-503 03.01 Standard

5.127 August 2007

Copyright © 2005-2007, Nortel Networks

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Nortel Networks NN47200-503 manual IP routing using VLANs, IP routing with VLANs