2851 Router Configuration help

[dan_track]

Hi

I'm about to buy two 2851 routers for our external ISP connections.

What I would like to do is have one ISP connection into one router, while a second ISP link goes in teh second router. I would like to have the two pairs in active/active mode so showing one IP to the internal hosts. And I would use bgp to force traffic to go through ISP1 and only use ISP2 (on the second router) as backup.

What I'm also thinking about is say router1 is up but the link (ISP1) dies, would traffic heading to router1 be diverted to router2?

IS the above possible using HSRP? If not what would I use?

Thanks in advance

[ethiel]

You didn't mention what the ISP connection is, but assuming it is not using an ethernet port, one option would be as follows:

Connect each Router to the ISP via WAN port.

Connect the two routers to each other via 1 of the gig ports

Connect each router to the inside switch with the other ethernet port.

Set up BGP to each ISP from the connected router.

Set up BGP between the two routers.

Set up HSRP on the inside ethernet of each router, with the primary being active, and set it to track the WAN interface.

Doing this will protect in the following ways:

Primary ISP link failure: HSRP will move to the backup router.

Primary ISP BGP failure: Primary router stays active for HSRP, but routes traffic to secondary since that is the only valid BGP route.

Primary router failure: Secondary router takes over HSRP

Primary router LAN link failure: Secondary takes over HSRP. You could tweak BGP to have the secondary router route across to primary router via other ethernet connection if you want to always use the primary link when it is available, or you can let the secondary router route out its ISP connection.

This setup can handle a lot of combined failures as well, but I won't get into all of the possible combinations.

If you are getting ethernet handoff from your ISP, you could use trunks and sub-interfaces to acheive the above design, but you lose a bit of redundancy and the design might need to be tweaked a bit.

The following link is an HSRP design guide, with info on interface tracking.

http://www.cisco.com/en/US/tech/tk1330/technologies_design_guide_chapter09186a008066670b.html#wp3475

-Eric

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