multinetted VLAN, multiple VRs can be configured. The owner operates as the VR's master unless it becomes
unavailable, in which case the highest-priority backup becomes the VR's master.
A VR includes the following:
• VR identification (
VRID
) configured on all VRRP routers in the same network or, in the case of a multinetted
VLAN, on all routers in the same subnet .
• Same VIP configured on each instance of the same VR.
• Satus of either owner or backup configured on each instance of the same VR (on a given VR, there can be
one owner and one or more backups.)
• Priority level configured on each instance of the VR (on the owner router the highest priority setting, 255, is
automatically fixed; on backups, the default priority setting is 100 and is configurable.)
• VR MAC address (not configurable.)
Where a VLAN is configured with only one network (IP address), one VR is allowed in that VLAN. In a multinetted
VLAN, there can be one VR per subnet, with a maximum of 32 VRs (16 for the 2930F switch) in any combination
of masters and backups.
NOTE:
All routers in a given VR must belong to the same network (or subnet, in the case of a
multinetted VLAN.)
Virtual IP address (VIP)
The VIP associated with a VR must be a real IP address already configured in the associated VLAN interface on
the owner router in the VR. If the VIP is an IPv6 address, a link-local address must be configured before adding a
global IPv6 address. Also, the owner and all other (backup) routers belonging to the VR have this IP address
configured in their VRID contexts as the VIP. In
Figure 55: Example of using VRRP to provide redundant
on page 337, 10.10.100.1 is a real IP address configured on VLAN 100 in Router 1 and is the
VIP associated with VR 1.
If the configured owner in a VR becomes unavailable, it is no longer the master for the VR and a backup router in
the VR is elected to assume the role of master, as described under
A subnetted VLAN allows multiple VIPs. However, if there are 32 or fewer IP addresses in a VLAN interface, and
you want VRRP support on multiple subnets, the recommended approach is to configure a separate VR instance
for each IP address in the VLAN. In cases where VRRP support is needed for more than 32 IP addresses in the
same VLAN.
Master router
The current master router in a VR operates as the "real" or physical gateway router for the network or subnet for
which a VIP is configured.
Control of master selection
Selection of the master is controlled by the VRRP priority value configured in the VRID context of each router in
the VR. The router configured as the owner in the VR is automatically assigned the highest VRRP priority (255)
and, as long as it remains available, operates as the master router for the VR. The other routers belonging to the
VR as backups are assigned the default priority value (100) and can be reconfigured to any priority value between
1 and 254, inclusive. If the current master becomes unavailable, the protocol uses the priority values configured
on the other, available routers in the VR to select another router in the VR to take over the master function.
Function of the VRRP advertisement
The current master router sends periodic advertisements to inform the other routers in the VR of its operational
status. If the backup VRs fail to receive a master advertisement within the timeout interval, the current master is
Chapter 16 Virtual Router Redundancy Protocol (VRRP)
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