The Virtual Router Redundancy Protocol (VRRP), defined in RFC 2338, is a FHRP that is similar to HSRP but capable of supporting multivendor environments. A VRRP router is configured to run the VRRP protocol in conjunction with one or more other routers attached to a LAN. In a VRRP configuration, one router is elected as the virtual router master, with the other routers acting as backups if the virtual router master fails.
VRRP enables a group of routers to form a single virtual router. The LAN clients can then be configured with the virtual router as their default gateway. The virtual router, representing a group of routers, is also known as a VRRP group.
Figure 1 shows a LAN topology with VRRP configured. In this example, two VRRP routers (routers running VRRP) comprise a virtual router. However, unlike HSRP, the IP address of the virtual router is the same as that configured for the LAN interface of the virtual router master, in this example 172.16.128.1.
Router A assumes the role of the virtual router master and is also known as the IP address owner because the IP address of the virtual router belongs to it. As the virtual router master, Router A is responsible for forwarding packets sent to this IP address. Each IP host on the subnet is configured with the default gateway IP address of the virtual route master, in this case 172.16.128.1.
Router B, on the other hand, functions as a virtual router backup. If the virtual router master fails, the router configured with the higher priority becomes the virtual router master and provides uninterrupted service for the LAN hosts. When Router A recovers, it becomes the virtual router master again.
Additionally, like HSRP, VRRP supports object tracking and preemption and SSO awareness.
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SSO awareness for VRRP is enabled by default when the route processor’s redundancy mode of operation is set to SSO (as was shown in the “NSF with SSO” section of this chapter).
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Example 1 shows a VRRP configuration that can be used on the LAN interface of the virtual router master from Figure 1. Each VRRP group on a given subnet requires a unique number; in this example the VRRP group number is set to 10. The virtual IP address is set to the actual LAN interface address, designating this router as the virtual router master. The VRRP priority of this router has been set to 105. Unlike HSRP, preemption for VRRP is enabled by default. Finally, object tracking has been configured so that should the line protocol state of interface Serial0/1 go down (the WAN link for this router, which is designated as object-number 110), the VRRP priority for this interface dynamically decrements (by a value of 10, by default).
Example 1: VRRP Example
Router(config)# track 110 interface Serial0/1 line-protocol Router(config)# interface GigabitEthernet0/0 Router(config-if)# ip address 172.16.128.1 255.255.255.0 Router(config-if)# vrrp 10 ip 172.16.128.1 Router(config-if)# vrrp 10 priority 105 Router(config-if)# vrrp 10 track 110
A drawback to both HSRP and VRRP is that the standby/backup router is not used to forward traffic and wastes both available bandwidth and processing capabilities. This limitation can be worked around by provisioning two complementary HSRP/VRRP groups on each LAN subnet, with one group having the left router as the active/master and the other group having the right router as the active/master router. Then, approximately half of the hosts are configured to use the virtual IP address of one HSRP/VRRP group, and remaining hosts are configured to use the virtual IP address of the second group. Obviously, this requires additional operational and management complexity. To improve the efficiency of these FHRP models without such additional complexity
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