HSRP with diverse physical links

[g.raymakers]

Hi pls look at attached diagram for reference. Router A is active, Router B is standby. Question is what happens when fibre link 1 (between switch A & B)fails but fibre link 2 (between switch C&D) remains active - which of the two router will be active (both?) and which will be standy (none)?

Many Thanks,

Guy

[thisisshanky]

The answer really depends on your configuration of the FE interfaces of both routers. If you have enabled FE on both interfaces, 0/0 and 0/1 and say under normal conditions, A is active on both interfaces, when the fiber link between s/w A and B fails, on fa0/0, router A and router B will go to HSRP active state as there is no communication between the two routers over that link.

Still on fa0/1 interface, A will be active and B will be standby.

HTH

[thisisshanky]

In my previous post ". If you have enabled FE on both interfaces, 0/0 and 0/1 and say under normal conditions" should have been

". If you have enabled HSRP on both FE interfaces, 0/0 and 0/1 and say under normal conditions"

[Richard Burts]

Guy

Your diagram shows two routers, each with two FastEthernet interfaces (and two independent subnets) and running HSRP. The connection between the routers is through two switches. Your question is what would happen if the link between the two switches failed.

My understanding is that if the link between switches failed each router would lose the HSRP packets from its neighbor on that interface. Each router would promote itself to be active router for HSRP. Neither router would be in standby. (The fact that the routers still have connectivity via the other switches does not change how this works.)

The good news is that each router will provide gateway services to the end stations connected to its switch. (And assuming that there is a dynamic routing protocol running over the second/surviving subnet each router still have full reachability to all destinations.

The bad news is if some remote device were to attempt to communicate with an end station on switch A whose gateway was router A but the packet was sent to router B, the packet would be dropped by router B and not forwarded over the surviving interface/subnet.

HTH

Rick