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Understanding VRRP on ACX Series Routers

For Ethernet, Fast Ethernet, Gigabit Ethernet, 10-Gigabit Ethernet, and logical interfaces, you can configure Virtual Router Redundancy Protocol (VRRP). VRRP enables hosts on a LAN to make use of redundant routers on that LAN without requiring more than the static configuration of a single default route on the hosts. The routers running VRRP share the IP address corresponding to the default route configured on the hosts. At any time, one of the routers running VRRP is the master (active) and the others are backups. If the master fails, one of the backup routers becomes the new master router, providing a virtual default router and enabling traffic on the LAN to be routed without relying on a single router. Using VRRP, a backup router can take over a failed default router within a few seconds. This is done with minimum VRRP traffic and without any interaction with the hosts.

Note: You can configure VRRP on Integrated Routing and Bridging (IRB) interfaces.

Routers running VRRP dynamically elect master and backup routers. You can also force assignment of master and backup routers using priorities from 1 through 255, with 255 being the highest priority. In VRRP operation, the default master router sends advertisements to backup routers at regular intervals. The default interval is 1 second. If a backup router does not receive an advertisement for a set period, the backup router with the next highest priority takes over as master and begins forwarding packets.

Note: To minimize network traffic, VRRP is designed in such a way that only the router that is acting as the master sends out VRRP advertisements at any given point in time. The backup routers do not send any advertisement until they take over mastership.

Figure 1 illustrates a basic VRRP topology for IPv4 family. In this example, Routers A, B, and C are running VRRP and together they make up a virtual router. The IP address of this virtual router is 10.10.0.1 (the same address as the physical interface of Router A).

Figure 1: Basic VRRP for IPv4 Family

Because the virtual router uses the IP address of the physical interface of Router A, Router A is the master VRRP router, while Routers B and C function as backup VRRP routers. Clients 1 through 3 are configured with the default gateway IP address of 10.10.0.1. As the master router, Router A forwards packets sent to its IP address. If the master virtual router fails, the backup router configured with the higher priority becomes the master virtual router and provides uninterrupted service for the LAN hosts. When Router A recovers, it becomes the master virtual router again.

Note: ACX Series routers support VRRP version 3 for IPv6 addresses.

ACX routers can support up to 64 VRRP group entries. These can be a combination of IPv4 or IPv6 families. If either of the family (IPv4 or IPv6) is solely configured for VRRP, then 64 unique VRRP group identifiers are supported. If both IPv4 and IPv6 families share the same VRRP group, then only 32 unique VRRP identifiers are supported.