Cogent input

Stephen Kratzer kratzers at pa.net
Thu Jun 11 09:33:25 CDT 2009


We've only recently started using Cogent transit, but it's been stable since 
its introduction 6 months ago. Turn-up was a bit rocky since we never 
received engineering details, and engineering was atypical in that two eBGP 
sessions were established, one just to advertise loopbacks, and another for 
the actual feed. The biggest issue we have with them is that they don't allow 
deaggregation. If you've been allocated a prefix of length yy, they'll accept 
only x.x.x.x/yy, not x.x.x.x/yy le 24. Yes, sometimes deaggregation is 
necessary or desirable even if only temporarily.

And, they have no plans to support IPv6.

"Cogent's official stance on IPv6 is that we will deploy IPv6 when it
becomes a commercial necessity. We have tested IPv6 and we have our plan
for rolling it out, but there are no commercial drivers to spend money
to upgrade a network to IPv6 for no real return on investment."

Stephen Kratzer
Network Engineer
CTI Networks, Inc.

On Thursday 11 June 2009 09:46:45 Justin Shore wrote:
> I'm in search of some information about Cogent, it's past, present and
> future.  I've heard bits and pieces about Cogent's past over the years
> but by no means have I actively been keeping up.
>
> I'm aware of some (regular?) depeering issues.  The NANOG archives have
> given me some additional insight into that (recurring?) problem.  The
> reasoning behind the depeering events is a bit fuzzy though.  I would be
> interested in people's opinion on whether or not they should be consider
> for upstream service based on this particular issue.  Are there any
> reasonable mitigation measures available to Cogent downstreams if
> (when?) Cogent were to be depeered again?  My understanding is that at
> least on previous depeering occasion, the depeering partner simply
> null-routed all prefixes being received via Cogent, creating a blackhole
> essentially.  I also recall reading that this meant that prefixes being
> advertised and received by the depeering partner from other peers would
> still end up in the blackhole.  The only solution I would see to this
> problem would be to shut down the BGP session with Cogent and rely on a
> 2nd upstream.  Are there any other possible steps for mitigation in a
> depeering event?
>
> I also know that their bandwidth is extremely cheap.  This of course
> creates an issue for technical folks when trying to justify other
> upstream options that cost significantly more but also don't have a
> damaging history of getting depeered.
>
> Does Cogent still have an issue with depeering?  Are there any
> reasonable mitigation measures or should a downstream customer do any
> thing in particular to ready themselves for a depeering event?  Does
> their low cost outweigh the risks?  What are the specific risks?
>
> Thanks
>   Justin






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