Nortel Networks NN47200-503 manual Virtual Router Redundancy Protocol Vrrp configuration

190IP Routing Configuration and Management

A mismatch in maximum transmission unit (MTU) sizes between the routers usually causes this type of problem. For example, one router could be set for a high MTU size and the other router a smaller value. Depending on the size of the link state database, the router with the smaller value may not be able to process the larger packets and thus be stuck in this state. To avoid this problem, ensure that the MTU size value for both routers match. This problem is usually encountered during interoperations in networks with other vendor devices.

Note: The Nortel Ethernet Routing Switch 5500 Series automatically checks for OSPF MTU mismatches.

In the Nortel Ethernet Routing Switch 5500 Series, the supported MTU size for OSPF is 1500 bytes by default. Incoming OSPF database description (DBD) packets are dropped if their MTU size is greater than this value.

Virtual Router Redundancy Protocol (VRRP) configuration

This section describes how to create a basic VRRP configuration on a Nortel Ethernet Routing Switch 5500 Series.

VRRP uses an election process to select a master router that hosts use as the default gateway. If the master router (the default gateway) fails, the VRRP backup router automatically replaces the master router and becomes the new default gateway. In either case, the default gateway IP address and MAC address does not change, thereby providing transparent operation.

The Nortel Ethernet Routing Switch 5500 Series can be configured in a master-master configuration for load-balancing applications that use Split MultiLink Trunking (SMLT). This configuration allows both switches to respond to ARPs and forward traffic.

VRRP Priority settings can be configured to select the VRRP master router for a specified VLAN. The VRRP Priority setting is an integer value, in the range 1 and 255, where the highest value is used to elect the VRRP master router. If two or more switches have the same priority value, the switch with the highest numerical IP address value is selected and becomes the VRRP master. The host is unaware of the entire process.

When a host sends traffic to a different subnet, it sends an ARP request for the MAC address of the default gateway. In this case, the Nortel Ethernet Routing Switch 5500 Series VRRP master router replies with its virtual MAC address. The benefit of using a virtual MAC address is that, if the master router fails, the VRRP backup router uses the same virtual MAC address. The virtual MAC address on the Nortel Ethernet Routing Switch 5500 Series does not need to be configured. The virtual MAC address is automatically set as:

Nortel Ethernet Routing Switch 5500 Series

Configuration-IP Routing Protocols

NN47200-503 03.01 Standard

5.127 August 2007

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