[Nanog] Cogent Router dropping packets

Joe Greco jgreco at ns.sol.net
Tue Apr 22 08:33:55 CDT 2008


> Well it had sounded like I was in the minority and should keep my mouth 
> shut. But here goes. On several occasions the peer that would advertise 
> our routes would drop and with that the peer with the full bgp tables 
> would drop as well. This happened for months on end. They tried blaming 
> our 6500, our fiber provider, our IOS version, no conclusive findings 
> where ever found that it was our problem. After some testing at the 
> local Cogent office by both Cogent and myself, Cogent decided that they 
> could "make a product" that would allow us too one have only one peer 
> and two to connect directly to the GSR and not through a small catalyst. 
> Low and behold things worked well for some time after that.
> 
>   This all happened while we had 3 other providers on the same router 
> with no issues at all. We moved gbics, ports etc around to make sure it 
> was not some odd ASIC or throughput issue with the 6500.

Perhaps you haven't considered this, but did it ever occur to you that
Cogent probably had the same situation?  They had a router with a bunch
of other customers on it, no reported problems, and you were the oddball
reporting significant issues?

Quite frankly, your own description does not support this as being a
problem inherent to the peerA/peerB setup.

You indicate that the peer advertising your routes would drop.  The peer
with the full BGP tables would then drop as well.  Well, quite frankly,
that makes complete sense.  The peer advertising your routes also
advertises to you the route to get to the multihop peer, which you need
in order to be able to talk to that.  Therefore, if the directly connected
BGP goes away for any reason, the multihop is likely to go away too.

However, given the exact same hardware minus the multihop, your direct
BGP was still dropping.  So had they been able to send you a full table
from the aggregation router, the same thing probably would have happened.

This sounds more like flaky hardware, dirty optics, or a bad cable (or
several of the above).

Given that, it actually seems quite reasonable to me to guess that it
could have been your 6500, your fiber provider, or your IOS version that
was introducing some problem.  Anyone who has done any reasonable amount
of work in this business will have seen all three, and many of the people
here will say that the 6500 is a bit flaky and touchy when pushed into
service as a real router (while simultaneously using them in their 
networks as such, heh, since nothing else really touches the price per
port), so Cogent's suggestion that it was a problem on your side may have
been based on bad experiences with other customer 6500's.

However, it is also likely that it was some other mundane problem, or a 
problem with the same items on Cogent's side.  I would consider it a 
shame that Cogent didn't work more closely with you to track down the 
specific issue, because most of the time, these things can be isolated 
and eliminated, rather than being potentially left around to mess up 
someone in the future (think: bad port).

... JG
-- 
Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.




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