HSRP possible Split Brain scenario

[Mike Elliott]

I am not sure if I am using the right terminology but I am attempting to build a HSRP pair of 2911s. 

The inside interfaces with be Gi0/1-2 and will be Port Channeled to a 3750x.  I have setup HSRP on both routers and it's behaving as expected.

The Outside interfaces will be on Gi0/0 and will be setup with HSRP with some static nat translations that are tied to the HSRP group.

I want to know if the HSRP gets triggered from either the inside or the outside, will both the port channel, and outside interfaces switch, or only the one that goes down?  Can I setup the inside interfaces to track the outside interfaces and vice versa?

[Richard Burts]

I am sure that there are parts of your environment that we do not understand. And some of them might change the answers that we would provide. But based on what you have given us so far here are my answers:

- If the inside interface(s) go down and not the outside interfaces then only the inside will switch HSRP. Same if the outside goes down but not the inside then only the outside will switch HSRP. You can set up HSRP to track the state of interfaces on the router. One thing to be careful about with interface tracking is that it tracks the interface line protocol status and will trigger HSRP change if the line protocol change from up to down. But there can be problems that impact connectivity over the interface that do not cause the line protocol to change to down.

HTH

Rick

[Mike Elliott]

good answer, What about IP SLA tracking to the ISP's gateway?  Could I set all interfaces to track to that gateway and if there is no answer from it, decrease it's priority so the HSRP group standby router would take over?

[JohnTylerPearce]

Mike,

You can do something like that. Since you have two HSRP groups, one going to your ISP it sounds like, and one going to your LAN.

For instance, on your LAN you can configure 'standby track

The will cause the priority for this specific group to decrease to whatever value you

put there. This value needs to be enough to cause the standby router, to become active (as long as preempt is configured on the standby router obviously).

[Richard Burts]

The original poster is correct that using IP SLA gets around the limitation of depending on the line protocol to go down. And IP SLA is supported within HSRP. See this link for a discussion and examples of using IP SLA with HSRP.

http://www.cisco.com/c/en/us/td/docs/switches/blades/3040/software/release/12-2_44_se/configuration/guide/swhsrp.html#wp1084266

HTH

Rick