Virtual Router Redundancy Protocol (VRRP)Related topics

An older article on the configuration of Cisco’s Hot Standby Routing Protocol was published in The Network Monitor, Volume 1, Number 3. This article, titled Hot Networks: Hot Standby Router Protocol Prevents Network Problems Before They Happen, describes other methods of accomplishing redundancy as well as HSRP.

Why is this important?

How do you know that the routing redundancy that you’ve designed into your network is continuing to operate correctly? Daily verification of routing redundancy avoids ugly surprises. Many of today’s networks require a high level of availability, particularly for business-critical applications and for VoIP.

Routing redundancy, provided by Cisco’s Hot Standby Routing Protocol (HSRP) or vendor-independent Virtual Router Redundancy Protocol (VRRP), eliminates a single point of failure in the routing infrastructure.

We’ve frequently seen outages in redundant network designs because the first failure was not detected and corrected prior to a second failure.

Relying on Syslog or SNMP Traps is insufficient because both of these protocols use UDP, which may be dropped during routing convergence or network congestion.
Manual determination

Manual verification of routing redundancy depends on the vendor and protocol.

Cisco’s HSRP can be checked using the command show standby, looking for the line that shows the backup router: Standby router is 10.20.0.22 expires in 0:00:07. Also check the number of state changes and the time since the last state change to validate the group’s stability.

VRRP on Juniper and Cisco routers can be checked with the command show vrrp.

Unfortunately, standby routers are not known to the primary router because of how VRRP works, so more effort is involved. Each router in the group must be checked to find the backup routers.

HSRP Summary

Automatic determination

Automatic tools that verify the active and backup routers for each redundancy group are imperative for high availability networks. VRRP requires that all routers in a VRRP group be polled to know that there is a backup, just as with the manual process.

Two types of automatic output are useful. The first is a list of all router redundancy groups and their type, the active router details including HSRP Active Router Details and the routers within a group and their active or standby state. Check here for the best wireless routers.
Further reference:

For both HSRP and VRRP on Cisco routers, go to the Cisco web site search box and enter:
“Cisco IOS IP Application Services Configuration Guide, Release 12.4”.

Juniper’s VRRP information is available at the following URL: www.juniper.net/techpubs/software/junos/junos80/swcmdref80-interfaces/html/vrrp-monitor3.html