On Mon, Aug 24, 2020 at 04:36:10PM +0000, Laura Smith wrote: > Hi, > > Let's say I've got a scenario where I've got transit ISPs and peering > connections. > > My general config rule is that I use med to prioritise peering over transit > (because localpref is too high up in the BGP selection algorithm, so > localpref is a sledgehammer to crack a nut). > > That setup has served me well. But now with increasing peering connections, > I'm seeing the wrong peer being selected for a route, e.g. (IPs and ASNs > obfuscated to protect the innocent) > > *> N 2001:db8:aaaa::/29 2001:db8:aaaa::1111:1 100 100 64512 > 65500 i > * N 2001:db8:aaaa::/29 2001:db8:aaaa::2222:2 100 100 65500 > 65500 i > > In this example, both 64512 and 65500 are peers (med=100) but obviously 65500 > 65500 should be the preferred route. > > What options do I have to resolve this sort of tie-break ? Ideally I'd > like to find something that would resolve all such instances rather than > have to introduce config hacks on a per-peer basis. >
A possible option is to prefer announcements from the neighbor which is the originator. To do this you can use a rule like: match from ebgp source-as neighbor-as set med +100 Now it is a bit strange that an AS is prepending on peering. I wonder why they do that (is their connection to the IX undersized?). -- :wq Claudio
