[AFMUG] Weird network issue

[Adam Moffett]

I have a customer who uses us as a backup path to the internet. They 
have BGP sessions with us and another provider, and we just stack a few 
prepends on the routes they send us and re-advertise them.

When their primary connection is out, they report having partial 
connectivity.  We just had a two hour test window where their primary 
connection was shut off on purpose so that we could test. The other 
provider and I spent a ton of time going over BGP and routing stuff and 
finally concluded, "gee, it should be working."

After we gave up looking for a routing problem that isn't there, we did 
some more basic testing and really the only thing I can conclude 
definitely doesn't work when they fail over to us is DNS.  Using 
nslookup they get no response from any DNS servers.

They have a Cisco 2811 running BGP, but that connects to an ASA, and 
everything on their LAN is behind the ASA.

I asked for copies of the configs on the 2811 and the ASA, but I'm not 
even sure what I'm looking for yet.  Any brilliant ideas?