On 7/05/2014, at 12:22 pm, Alexander Neilson wrote:

Hi All

At $Dayjob I have been working around an aggregation bug in our routers and manually specifying prefix’s at the three levels we operate (/22, /23, /24) and using prefix filters to advertise /24’s to APE / WIX, /23’s to our domestic transit, and only the /22’s to international transit as a method of Traffic Management / Traffic Engineering to utilise cheapest links available.

I have been exploring the looking glass services of a number of entities to see what propagates to them (that they enter into the forwarding database) and I am seeing some entities (who announce peering at APE for example) having the /22 and /23 routes in the LG outputs and following the /23 path in trace route.

I am asking for two fold information. Can someone / everyone point me at their best guide to BGP “Best Practice” regarding advertising prefixes? and also can I get people’s specific advice about what they accept / do to announcements before entering them into their routers as accepted routes and what they would expect to see advertised to ensure my goals are reached.

I made these changes to help reduce my contribution to the ballooning of the global routing table but I also don’t want to go to extremes on polluting the APE routing table by advertising the 12 /24’s plus the 6 /23’s and the 3 /22’s.

Also can I get consensus information (or peoples opinions) about am I abusing / dis respecting APE with my announcements and how I should structure my announcements to be a respectable citizen here while providing the best hints to my preferred handling of traffic? (and feel free to let me know if I should just announce the /22’s and accept that some people choose to prioritise other paths)

Thank you in advance for any input, feel free to reply off list.

Advertise the same prefixes everywhere. NZ people typically localpref routes in order of descending preference: - Settlement free peering (APE/WIX/whatever else) - Domestic transit - All other transit You almost certainly don’t need to help them to do that - I’ve never come across a case where it’s be necessary to deaggregate (or whatever) so an NZ provider sends traffic the “right” way. Not saying it doesn’t happen, but I don’t think it happens nearly enough to warrant complicating your network. So, advertise your /22s everywhere, and be done with it. If you really do decide you need to deaggregate, leave your /22s in place, but my preference is to take it up with the network who’s sending you the traffic and see if you can get them to “fix” their policy. As an aside, you talk about an aggregation bug - in general it’s best to not bother with aggregating, and instead put some null routes for your /22s (or whatever your advertisements are) in to wherever you were aggregating. You don’t want internal network changes/faults to cause external BGP withdrawals, unless those prefixes are also being advertised by another network. -- Nathan Ward -- Nathan Ward