i still advertise the aggregate as a backing route. one reason i might like advertising a /24 is (usually) it's a nice way to gently attract return traffic down a certain path so i can do maintenance on the other side. plenty of other ways to do this, i know (prepending, communities, etc). On Thu, Oct 2, 2014 at 9:17 AM, Peter Persson <peter.persson@bredband2.se> wrote:
Just a stupid question. Why do you announce a /24 of a /22? Why not announce the whole /22 directly?
Regards, Peter
2014-10-02 18:03 GMT+02:00 ryanL <ryan.landry@gmail.com>:
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.
example: http://ryry.foursquare.com/image/0e0K1K0t0W2M
it's been a bit of a frustrating experience talking to their noc to demonstrate it, but i'm able to duplicate it on demand. even pushing routes using their communities to offload the circuit takes forever to propagate even on their own looking-glasses.
thx
ryan