Alcatel-Lucent 7750 SR OS - Manual (Page 172)

VRRP Components
Page 172 7750 SR OS Router Configuration Guide
Primary and Secondary IP Addresses
A primary address is an IP address selected from the set of real interface address. VRRP
advertisements are always sent using the primary IP address as the source of the IP packet.
A 7750 SR IP interface must always have a primary IP address assigned for VRRP to be active on
the interface. 7750 SR OS supports both primary and secondary IP addresses (multi-netting) on the
IP interface. The virtual router’s VRID primary IP address is always the primary address on the IP
interface. VRRP uses the primary IP address as the IP address placed in the source IP address field
of the IP header for all VRRP messages sent on that interface.
Virtual Router Master
The VRRP router which controls the IP address(es) associated with a virtual router is called the
master. The master is responsible for forwarding packets sent to the VRRP IP addresses. An
election process provides dynamic failover of the forwarding responsibility if the master becomes
unavailable. This allows any of the virtual router IP addresses on the LAN to be used as the default
first hop router by end hosts. This enables a higher availability default path without requiring
configuration of dynamic routing or router discovery protocols on every end host.
If the master is unavailable, each backup virtual router for the VRID compare the configured
priority values to determine the master role. In case of a tie, the virtual router with the highest
primary IP address becomes master.
The preempt parameter can be set to false to prevent a backup virtual router with a better
priority value from becoming master when an existing non-owner virtual router is the current
master. This is determined on a first-come, first-served basis.
While master, a virtual router routes and originates all IP packets into the LAN using the physical
MAC address for the IP interface as the Layer 2 source MAC address, not the VRID MAC address.
ARP packets also use the parent IP interface MAC address as the Layer 2 source MAC address
while inserting the virtual router MAC address in the appropriate hardware address field. VRRP
messages are the only packets transmitted using the virtual router MAC address as the Layer 2
source MAC.