Nortel Networks WEB OS 212777 - Manual (Page 473)

Web OS 10.0 Application Guide
Glossary n 473
212777-A, February 2002
VRRP (Virtual Router
Redundancy
Protocol) A protocol that acts very similarly to Cisco’s proprietary HSRP address sharing protocol.
The reason for both of these protocols is so devices have a next hop or default gateway that
is always available. Two or more devices sharing an IP interface are either advertising or
listening for advertisements. These advertisements are sent via a broadcast message to an
address such as 224.0.0.18.
With VRRP, one switch is considered the master and the other the backup. The master is
always advertising via the broadcasts. The backup switch is always listening for the broad-
casts. Should the master stop advertising, the backup will take over ownership of the
VRRP IP and MAC addresses as defined by the specification. The switch announces this
change in ownership to the devices around it by way of a Gratuitous ARP, and advertise-
ments. If the backup switch didn’t do the Gratuitous ARP the Layer 2 devices attached to
the switch would not know that the MAC address had moved in the network. For a more
detailed description, refer to RFC 2338.
VSR (Virtual Server
Router) A VRRP address that is a shared Virtual Server IP address. VSR is Web OS proprietary
extension to the VRRP specification. The switches must be able to share Virtual Server IP
addresses, as well as IP interfaces. If they didn’t, the two switches would fight for owner-
ship of the Virtual Server IP address, and the ARP tables in the devices around them would
have two ARP entries with the same IP address but different MAC addresses.