assumed to be unavailable and a new master is elected from the existing backups. The timeout interval for a VR
is three times the advertisement interval configured on the VRs in the network or subnet. In the default VRRP
configuration, the advertisement interval is one second and the resulting timeout interval is three seconds.
NOTE:
All VRRP routers belonging to the same VR must be configured with the same advertisement
interval. As required in RFC 3768, if a locally configured advertisement interval does not match the
interval received in an inbound VRRP packet, the VR drops that packet.
Most IPv6 host configurations learn the default gateway IPv6 address using router advertisements. The VR that
becomes the master sends router advertisements for its virtual IP address.
Owner router
An owner router for a VR is the default master router for the VR and operates as the owner for all subnets
included in the VR. The VRRP priority on an owner router is always 255 (the highest.)
NOTE:
On a multinetted VLAN where multiple subnets are configured in the same VR, the router must be
either the owner for all subnets in the VR or a backup for all subnets in the VR.
Backup router
There must be at least one backup router. A given VR instance on a backup router must be configured with the
same VIP as the owner for that VR (and both routers must belong to the same network or subnet.) Router 2 in
Figure 55: Example of using VRRP to provide redundant network access
on page 337 illustrates this point.
VR priority operation
In a backup router's VR configuration, the virtual router priority defaults to 100. (The priority for the configured
owner is automatically set to the highest value: 255.) In a VR where there are two or more backup routers, the
priority settings can be reconfigured to define the order in which backups are reassigned as master in the event of
a failover from the owner.
Preempt mode
Where multiple backup routers exist in a VR, if the current master fails and the highest-priority backup is not
available, VRRP selects the next-highest priority backup to operate as master. If the highest-priority backup later
becomes available, it preempts the lower-priority backup and takes over the master function. If you do not want a
backup router to have this preemptive ability on a particular VR, you can disable this operation with the
no
preempt-mode
command. (Preempt mode applies only to VRRP routers configured as backups.)
Virtual router MAC address
When a VR instance is configured, the protocol automatically assigns a MAC address based on the standard
MAC prefix for VRRP packets, plus the VRID number (as described in RFC 3768.) The first five octets form the
standard MAC prefix for VRRP, and the last octet is the configured VRID. that is:
00-00-5E-00-01-
VRid
For example, the virtual router MAC address for the VR in
Figure 55: Example of using VRRP to provide
on page 337 is 00-00-5E-00-01-01.
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Switch 16.08
