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HSRP between pairs of routers

turkeyqp
turkeyqp used Ask the Experts™
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Have not setup HSRP before but it doesn't seem challenging until you get to the physical connections which I can't find documented anywhere.

See Diagram for better understanding.

So my scenario is two headend routers running HSRP  handing off one Cat-5e cable each to my 2 cisco routers which will be running HSRP on my end.

Challenge:
Do I need to place a switch between these two pairs of routers?  
Can I plug these single connections for their two routers directly into my two routers?  Will this allow for redundancy against all possible situations?
I know HSRP communicates via multicast but don't undestand exactly what requirements are needed to provide a "path" for this communication.

What is best practice here?

Thx!
HSRP-Scenario.jpg
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Don JohnstonInstructor
Top Expert 2015

Commented:
>Do I need to place a  switch between these two pairs of routers?

No. Although it would provide better redundancy. Assuming you're running a routing protocol between the routers. HSRP is a "next-hop" redundancy protocol for devices that don't support a routing protocol (PC's, servers, etc.).

Personally, I'd go with scenario A and run a routing protocol between the four routers.
Commented:
If I understand you correctly, you do. In Scenrio A, you configure 192.168.2.1 as a default gateway. The way HSRP works, you create an HSRP group and only one server responds to the virtual router ip address. In your scenarios, your set up an HSRP group for you and assign 134.42.39.2 IP to the virtual router. Your routers have 134.42.39.2 as the default gateway.

In scenario A, if either right or left ISP router fails, your routers can still access the virtual router.
In scenario B, if either right or left ISP router fails, only one of the routers can access the virtual router's IP address. Since you most likely would like to balance load on your routers, it is possible that 50% of your traffic will not be able to reach the default gateway in Scenario B

Author

Commented:


Currently the headend routers are setup for HSRP using the 192.168.1.2 HSRP address and default routing down to our router using our outside interface address.  So currently we are only using one router and default route to the HSRP address (192.168.1.2).  Curently, there is only static routing going on as the environment is not that big and doesn't need it.  I'd like to add redundancy at the edge routing and since they are default routing to one ip I was thinking about using HSRP as the continued default GW from their perspective and we would continue to default route up to their HSRP address.

So in essence they would be running HSRP and I would be running HSRP.  All static routing.  In my mind I would think I would need a switch in between these devices just to allow the multicast communications between the HSRP routers.  My only concern is with adding it is the increased footprint and would need to secure and management this edge switch.  Just trying to help justify it's existence.

Thanks for all the help!

Don JohnstonInstructor
Top Expert 2015
Commented:
Without a switch, you won't be able to run HSRP. The routers must have their interfaces on the same broadcast domain.

Commented:
Just to be clear, donjohnston, according to Cisco the destination address of HSRP hello packets is the all routers multicast address (224.0.0.2), not broadcast (see http://www.cisco.com/en/US/tech/tk648/tk362/technologies_q_and_a_item09186a00800a9679.shtml)
Don JohnstonInstructor
Top Expert 2015

Commented:
That doesn't matter. The interfaces of the routers must be on the same broadcast domain/network/VLAN.