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• Several virtual master routers configured for mutual backup and load sharing.
Load sharing can be accomplished by assigning a subset of addresses to different
host address pools using the DHCP server. (See “Configuring Address Pools” on
page 17-4.)
Router 1 Router 2
VRID 23 (Master) VRID 23 (Backup)
IP(R1) = 192.168.1.3 IP(R1) = 192.168.1.5
IP(VR23) = 192.168.1.3 IP(VR23) = 192.168.1.3
VR Priority = 255 VR Priority = 100
VRID 25 (Backup) VRID 25 (Master)
IP(R1) = 192.168.1.3 IP(R1) = 192.168.1.5
IP(VR25) = 192.168.1.5 IP(VR25) = 192.168.1.5
VR Priority = 100 VR Priority = 255
LAN Segment A
LAN Segment B
Hosts (192.168.1.10-99)
Hosts (192.168.1.100-250)
Virtual Router Redundancy Protocol
Virtual Router Redundancy Protocol (VRRP) allows you to configure a group of
routers as a single virtual router. The virtual router group is configured with a single
virtual IP address that can be used as the default gateway for host devices on the
attached network.
Configuring VRRP Groups
To configure VRRP, select an interface on each router in the group that will
participate in the protocol as the master router or a backup router. To select a
specific device as the master router, set the address of this interface as the virtual
router address for the group. Now set the same virtual address and a priority on the
backup routers, and configure an authentication string. You can also enable the
preempt feature which allows a router to take over as the master router when it
comes on line if it has a higher priority than the currently active master router.
Command Usage
Address Assignment –
• To designate a specific router as the VRRP master, the IP address assigned to the
virtual router must already be configured on the router that will become the Owner
of the group address. In other words, the IP address for the virtual router exists on
one, and only one, router in the virtual router group, and the network mask for the
virtual router address is derived from the Owner. The Owner will also assume the
role of the Master virtual router in the group.
• If a virtual address is assigned to the group which does not exist on any of the
group members, then the master router is selected based on priority. In cases
18-2
Configuring Router Redundancy
18