cogent update suppression, and routing loops

Thu Oct 2 22:19:41 UTC 2014

On Thu, 2 Oct 2014, ryanL wrote:

> hi. relatively new cogent customer. is what i've stated in my subject line
> kinda standard fare with them?
>
> i've discovered that when i advertise a /24 from inside a larger /22 to XO,
> (who peers with cogent), and then pull the /24 some time later, that cogent
> holds onto the /24 and then bounces packets around in their network a bunch
> of times for upwards of 8-10 minutes until they finally yank it. this
> effectively blackholes traffic to my /24 for anyone that is using a path
> thru cogent.

Perhaps related, I made an as-path prepend change on a route advertised to 
Cogent yesterday and noticed it took about 10 minutes for that change to 
propagate throughout Cogent's network and be visible on route-views.  A 
moment later, I did the same thing with another carrier, and got the 
expected nearly instant gratification.  Perhaps they've got a bunch of 
routers configured with minimum-advertisement-interval to batch the BGP 
updates and if you're unlucky with the timing, it can take a while for 
routes/changes to percolate through their network?  Imagine driving down a 
long road, where every traffic light turns red just before you get to the 
intersection.  Wait a minute here, wait a minute there...

----------------------------------------------------------------------
  Jon Lewis, MCP :)           |  I route
                              |  therefore you are
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