Multihoming without BGP using 2 ISP connections with PAT

My goal is to have 2 ISP connections, loadbalancing and redundant internet links in one single router.

- Both ISP connections will have static ip addresses, one ip per isp.

- If one fails, users will use the other connections for web access

- if both are ok, loadbalancing will ocur

- users will use PAT in one of the ISPs IP address

- Web server and mail server will be configured with port redirect.

- The ISP connections might be dsl and cable connections, so the maximum I can have is a PAT in both of the connections.

- Load balancing will be controlled with equal metrics in the static routes

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Why the redundancy in ISP connections but no 2nd router? I would purchase another router and then use glbp to load balance your connections.

Anyway, the more difficult challenge is to automatically determine that ISP1 for instance has stopped forwarding traffic for some reason. Happens all the time that I still have a link from my cable modem, but I do not have a functioning internet connection. To try to and solve for this, check out this document:

Specifically the ip-route reachibility section.

-k

Hi Kevin,

Thank you for your answer. This concepts are new to me. Would glbp and enhanced object tracking work in a single router?

Thanks, Pedro

You wouldn't use glbp with just one router. I'm not sure if you can use the object tracking to increment a static route's administrative distance based on a test, but if you could that would be the route to go. You might just have to read up on it or maybe someone else can answer that for you. I don't see any examples of it being used that way, but it would sure be a good feature.

Best way to accomplish what you are trying to do is with two routers. That is true redundancy anyway. Your two ISP connections won't help much when your 1 router goes down.

In conclusion, I believe this is the command I would need for 2 isps and one single router:

As Kevin said, this is obviously not a good redundancy solution as I do not have 2 routers, but my customer does not want to pay for them!

Thanks for your help, Pedro

Actually, if you compare the failure rate of typical ISP links with the failure rate of typical Cisco routers, you'll find that it is not that bad a redundancy solution. But you may get burnt by a few other factors, such as failure of your NAT tables to be invalidated when an ISP goes down but the link stays up (if the NAT is being done in the router). Assuming you get the NAT right, the users will also see all their connections fail when you do a fail over (because their outside IP address has changed), but that usually is not a major issue for web surfing unless they are watching videos or otherwise keeping a single link active for a significant period of time.

This issue has been addressed many times over the past few years and would be in the FAQ if Hansang ever got around to updating it (or released control to a new maintainer). Try a search on "ping based routing" which is the classic technique used. Be aware that while there are multiple traps if you use Cisco IOS routers to do the job rather than a cheap SOHO router designed for the purpose, and that many of the cheap routers which claim to have that feature have a tendency to lock up and need rebooting far more frequently than the ISP links have problems, negating their contribution to availability.

Good luck and have fun!