IBM RackSwitch G8000 Application Manual page 348

VRID Virtual Router Identifier. In VRRP, a numeric ID is used by each virtual router to create
its MAC address and identify its peer for which it is sharing this VRRP address. The
VRRP MAC address as defined in the RFC is 00-00-5E-00-01-<VRID>.
If you have a VRRP address that two switches are sharing, then the VRID number
needs to be identical on both switches so each virtual router on each switch knows with
whom to share.
Virtual Router Redundancy Protocol. A protocol that acts very similarly to Cisco's
VRRP
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
broadcasts. If the master stops 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
advertisements. 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.
346
RackSwitch G8000: Application Guide