[c-nsp] non-BGP ISP redundancy

Bruce Pinsky bep at whack.org
Thu Aug 18 15:55:38 EDT 2005

Hash: SHA1

Grant P. Moerschel wrote:
> Greetings,
> I have an environment with a full T1 connected to a 1700 to ISP1 and a
> frac T1 (256K) connected to a 1700 to ISP2.  I don't have the resources or
> address space to use BGP.  But I would like to have some egress load
> balancing and some ingress redundancy. I host my mail at this site and my
> web servers elsewhere.  I can accomplish smtp redundancy with MX records.
> Any ideas on some good approaches? Thanks

Rodney Dunn posted this in another thread:

"You must have some form of detection to know that one
of the ISP's is not reachable.

The best solution to that is BGP or either
IP SLA with object tracking.

You could have two default routes in the 2801 each
pointing to the different ISP's.
That would give you CEF loadsharing by default.

However, your return traffic would be a problem
because depending on what your source address is going
out that is what your return path would be.

Most people get around this by doing PAT on the ISP
interface address so that makes sure the return traffic
for that flow comes back via that same link."

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