You could also try controlling the advertisement of your /22 in AT&T's network by using BGP communities.
http://onesc.net/communities/as7018/ AT&T connect's a to a large number of autonomous systems. Maybe you could announce the /22 with community 7018:25 so that the route isn't visible to AT&T's transits & peers, only customers. -- Blake Covarrubias On Aug 25, 2014, at 9:43 PM, Alexander Neilson <[email protected]> wrote: > For BGP Longest Match Prefix always wins, no amount of prepending will beat > that (they can of course filter it out etc) > > There are a few ways you could do this: > > 1. Advertise the 48.0/20 out of both providers and then advertise a /22 (or > other longer prefixes) out of selected providers. Then anyone who receives > both will get the /22 as preference over the /20 (no prepending required) > > 2. advertise just the /20 out of each upstream and prepend so that popular > networks get the same path length for both (look at the later on tie > breakers) as some upstreams have more internal AS’s that you may pass through > than others so it can be good to balance up the AS Path lengths to some > popular spots (help to balance out the load a little) - you would need to > prepend different amounts and then test them. > > I have done some similar parts of this on my network. > > Regards > Alexander > > Alexander Neilson > Neilson Productions Limited > > [email protected] > 021 329 681 > 022 456 2326 > > On 26/08/2014, at 3:42 pm, Terri Kelley <[email protected]> wrote: > >> Don't think that would work quite right. Still want the others to come in on >> TW if they want to. >> >> Terri Kelley >> Network Engineer >> 254-697-6710 >> Farm to Market Broadband >> >> >> >> On Aug 25, 2014, at 10:32 PM, Alexandre J. Correa (Onda) wrote: >> >>> Just announce 52.0/22 to TW .. and this 'win' :) >>> >>> >>> On 26/08/2014 00:07, Terri Kelley wrote: >>>> I think I asked this before but can't find it so here it is. I coming up >>>> on the need to load balance between my upstreams from my bgp edge. >>>> Question is, do I have to list each subnet prepending the ones I want or >>>> can I list the whole subnet then follow that with the prepend on the part >>>> that I want. Example is (changing the real IP blocks for the example) with >>>> TW being one of my upstreams and ATT the other all to the same edge router… >>>> >>>> /routing filter >>>> add action=accept chain=TW-out prefix=192.168.48.0/20 >>>> add action=discard chain=TW-out >>>> add action=accept chain=ATT-out prefix=192.168.48.0/20 >>>> add action=accept chain=ATT-out prefix=192.168.52.0/22 set-bgp-prepend=3 >>>> add action=discard chain=ATT-out >>>> >>>> I'm hoping that will move the 192.168.52.0/22 over to the TW side unless >>>> it goes down and leave the rest of the 48.0/20 block on the ATT. Otherwise >>>> I need to list each one subnet out on the ATT entries I think. >>>> >>>> Terri Kelley >>>> Network Engineer >>>> 254-697-6710 >>>> Farm to Market Broadband >>>> >>>> >>>> >>>> -------------- next part -------------- >>>> An HTML attachment was scrubbed... >>>> URL: >>>> <http://mail.butchevans.com/pipermail/mikrotik/attachments/20140825/7723f8d3/attachment.html> >>>> _______________________________________________ >>>> Mikrotik mailing list >>>> [email protected] >>>> http://mail.butchevans.com/mailman/listinfo/mikrotik >>>> >>>> Visit http://blog.butchevans.com/ for tutorials related to Mikrotik >>>> RouterOS >>>> >>> >>> _______________________________________________ >>> Mikrotik mailing list >>> [email protected] >>> http://mail.butchevans.com/mailman/listinfo/mikrotik >>> >>> Visit http://blog.butchevans.com/ for tutorials related to Mikrotik RouterOS >> >> -------------- next part -------------- >> An HTML attachment was scrubbed... >> URL: >> <http://mail.butchevans.com/pipermail/mikrotik/attachments/20140825/715b0c7b/attachment.html> >> _______________________________________________ >> Mikrotik mailing list >> [email protected] >> http://mail.butchevans.com/mailman/listinfo/mikrotik >> >> Visit http://blog.butchevans.com/ for tutorials related to Mikrotik RouterOS > > _______________________________________________ > Mikrotik mailing list > [email protected] > http://mail.butchevans.com/mailman/listinfo/mikrotik > > Visit http://blog.butchevans.com/ for tutorials related to Mikrotik RouterOS _______________________________________________ Mikrotik mailing list [email protected] http://mail.butchevans.com/mailman/listinfo/mikrotik Visit http://blog.butchevans.com/ for tutorials related to Mikrotik RouterOS
