[c-nsp] Problems with peers that don't have full routing tables

[Bob Tinkelman]

> Bob Tinkelman wrote:

>> However,
>>
>>    When ISPnet gets traffic for the /24, it routes it
>>    through NTT, and
>>
>>    NTT filters based on source address and, if it gets
>>    traffic from ISPnet with a yahoo source ip address,
>>    it just drops it on the floor.
>>
>>
>> Our quick work-around was to get our customer to bgp-announce
>> the /24 to both their upstreams.  This cleared the problem
>> but isn't giving them the inbound routing policy they
>> wanted.

> Why not just filter 165.254.65.0/24 from the feed you
> receive from NTT? You'd still see the /20, but should prefer
> your direct connection to your customer (fewer AS hops) so
> long as your link to them is up.

Andrew, thanks for your reply.

You're correct.  Your solution would give the customer
exactly what he wants, all traffic for his /24 arriving via
his other upstream.

In that sense it's better than Gert's suggestion to have the
customer use our communities to instruct us not to export
this route, as that results some small amount of traffic for
the /24 being sent from us to our customer.

In this particular case, that would be acceptable to our
customer.  As I'd really like to avoid cluttering our
configurations with prefix-lists that need to be maintained
manually, I'm inclined to use the community approach, here.
I *really* like pushing "special case stuff" off to the
customer routers.  That's why we did all the work to support
customer-set 22691:* communities.


As I wrote in my reply to Gert, my major interest now is to
write a script to notice cases like this one before I have a
customer who calls (after spending a long frustrating time
looking elsewhere for the cause of the problem).

I'd be interested to hear if anyone else is doing that or,
of course, if people think I'm wasting my time.
--
Bob Tinkelman          <bob at tink.com>
ISPnet, Inc.  http://www.ispnetinc.net

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