HSRP Interface Tracking
The default decrement in the priority when the tracked interface goes down is 10.
‘show standby’ will show the interface being tracked, the state and the decrement value.
A state change can be caused by either a Layer 1 or Layer 2 failure on the tracked interface.
You can change the default decrement at the end of the standby interface command.
You can track more than 1 interface, be aware of combined decrement values when doing this.
If you see HSRP states regularly transitioning, particularly between Speak and Standby, check your cabling – you’d be surprised how often that happens, especially in labs.
Frankly, most HSRP issues you run into fall into these categories:
- The secondary router didn’t become the Active router when it should have.
- The former Active router didn’t take back over when it came back online.
If either of those happens to you, check these values:
- Is the preempt command properly configured?
- What are the priority values of each HSRP speaker?
- Watch your decrement values with HSRP interface tracking. Don’t get cute with these. If you’re having a problem with interface tracking and you see decrements that don’t end in 0 or 5, I can practically guarantee they’re misconfigured.
Virtual Router Redundancy Protocol
Defined in RFC 2338, VRRP is the open-standard equivalent of the Cisco proprietary HSRP. VRRP works very much like HSRP, and is suited to a multivendor environment.
Very similar operation to HSRP.
There are some differences, a few of which are:
- VRRP’s equivalent to HSRP’s Active router is the Master router. (Some VRRP documentation refers to this router as the IP Address Owner.) This is the router that has the virtual router’s IP address as a real IP address on the interface it will receive packets on.
- The physical routers in a VRRP Group combine to form a Virtual Router. Note that the VRRP Virtual Router uses an IP address already configured on a router in its group, as opposed to how the HSRP router is assigned a separate virtual IP address.
- VRRP Advertisements are multicast to 18.104.22.168.
- VRRP’s equivalent to HSRP’s Standby router state is the Backup state.
- The MAC address of VRRP virtual routers is 00-00-5e-00-01-xx, xx is the group number in hexadecimal.
- “preempt” is a default setting for VRRP routers.
- As of IOS Version 12.3(2)T, VRRP now has an Object Tracking feature. Similar to HSRP’s Interface Tracking feature, a WAN interface can be tracked and a router’s VRRP priority dropped when that interface goes down.