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IP routing 37

To conﬁgure routing policies, create the appropriate preﬁx lists and then

assign those preﬁx lists to route maps. Once all route maps have been

created, assign them to the appropriate type of policy.

In a stacked environment, the following rules are applied to routing policies:

•

The policy database is stored in all stack units.

•

Policy conﬁguration is supported from only the base unit. The base

unit sends updates to non-base units to update the policy database in

each stack unit.

•

During database updates, only the database in the base unit is

synchronized with the non-base unit. The database in the non-base

units are deleted during the exchange.

•

Only the policies stored in the base unit are used by RIP and OSPF

for policy application.

Virtual Router Redundancy Protocol (VRRP)

The Virtual Router Redundancy Protocol (VRRP) is designed to eliminate

the single point of failure that can occur when the single static default

gateway router for an end station is lost. VRRP introduces the concept of

a virtual IP address (transparent to users) shared between two or more

routers connecting a common subnet to the enterprise network. With the

virtual IP address as the default gateway on end hosts, VRRP provides

dynamic default gateway redundancy in the event of failure.

VRRP uses the following terms:

• VRRP router - a router running the VRRP protocol.

•

Virtual router - the abstract object managed by VRRP that is assigned

the virtual IP address and that acts as the default router for a set of IP

addresses across a common network. Each virtual router is assigned a

virtual router ID.

•

Virtual router master - the VRRP router that assumes responsibility

for forwarding packets sent to the IP address associated with the virtual

router. The master router also responds to packets sent to the virtual

router IP address and answers ARP requests for this IP address.

•

Virtual router backup - the router or routers that can ser ve as the

failover router if the master router becomes unavailable. If the master

router fails, an election process provides a dynamic transition of

forwarding responsibility to a new master router.

• Priority - an 8-bit value assigned to all VRRP routers. A higher value

represents a higher priority for election to the master router. The priority

can be a value from 1 to 255. When a master router fails, an election

process takes place among the backup routers to dynamically reassign

the role of the master router.

Nortel Ethernet Routing Switch 5500 Series

Conﬁguration-IP Routing Protocols

NN47200-503 03.01 Standard

5.1 27 August 2007