Hi Add in my experience.
I have multiple upstreams, I advertise to all upstreams at the same time, I am not sure why you wouldn't do that. Maybe to control the reverse path. I preference by stuffing AS - seems to work well for us. But I ran into issue with convergence. 1) time it would take for the router to realise the interface was down - like the reference below - WAN links are not direct connected to the router. - Yeah BFD 2) Time it would take to reprocess route table after removing a path So what I have done is try to implement BFD with BGP where I can, not very many ISP have it as an option .. that i found interesting. reduce the keep alive timer for BGP ... So the doco says don't make it too low, because it might start to flap ... What I also did was reduce what routes I accept, so I still take a full table, but only inject around 10K prefixes into my main routing table - this i found help with convergence (out bound). I actually have a script that generates my bgp filter rules based on networks wanted A On 27 February 2018 at 09:37, David Hughes <da...@hughes.com.au> wrote: > > On 26 Feb 2018, at 9:52 pm, Geoff Huston <g...@apnic.net> wrote: > > > a) detecting link down quickly > > You can adjust your BGP session keepalive timers to smaller values and > make the session more sensitive to outages as a result. I also thought that > these days you can get the interface status to directly map to the session > state, but its been a while since I’ve done this in anger and frankly I > have NFC how to do that, even if I used to know! Maybe you are already > doing that anyway. > > > > This is the scenario I was talking about (references below). You can > easily have link on a northbound interface even if the peer isn’t there > (you hit a layer-2 agg switch on the way for example). If the peer fails > but you still have link on the interface you’ll be blindly forwarding > packets to it, even though it’s not there anymore, until the BGP timers > expire. That was the point of the lightning talk I gave way-back -then. > Default timers aren’t helpful in this situation. > > Fast forward to this decade and you have routing protocols that are > “BFD-aware” so you have sub-second link failure detection. That allows the > control plane to pull down the peer session and remove paths to that peer > from the FIB. You can only run BFD if your upstream is as well so you know > they will dump the prefixes from that peer session as quickly as you will. > It makes failing over to a secondary link within the same upstream provider > pretty seamless. > > > Ref : > http://archive.apnic.net/meetings/21/docs/sigs/routing/ > routing-pres-hughes-bgp.pdf > http://lists.ausnog.net/pipermail/ausnog/2015-January/029486.html > > > David > ... > > _______________________________________________ > AusNOG mailing list > AusNOG@lists.ausnog.net > http://lists.ausnog.net/mailman/listinfo/ausnog > >
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