On Mon, Jun 1, 2015 at 5:05 PM, Blake Hudson <bl...@ispn.net> wrote: > After studying failure modes and attempting to optimize BGP using partial > routing tables, I am of the opinion that BGP with a full routing table to > directly connected devices is by far the best way to gain the availability > benefits of BGP. Many attempts to cost save through multi-hop BGP or traffic > engineering end up breaking down when a fault occurs. Some faults, like link > state, are easy to detect and work around. Other faults, like where a peer > is up, but has no outside connectivity, are harder to detect if you're > taking anything less than full routes.
Hi Blake, Yes, it's better to take full routes. But taking a default from two ISPs still has a reliability advantage over using a single ISP. And of course if you have two connections to the same ISP there's limited in taking full routes. Between default routes and full routes there is a range of options with increasing reliability. For example, years ago I had routers with a 256k TCAM as the BGP table approached 256k. The organization I worked for was US-centric. We needed world connectivity, but high reliability to Asia or Europe was not essential. And a large cash expenditure that year would have been bad. By slaving the APNIC /8's to a single accepted BGP route, backed by static routes for those /8's should the master BGP route fail, I maintained full connectivity while suppressing the route count to what the hardware could handle. And of course maintained maximum reliability to the destination region I most cared about. Moral of the story: if you can afford it, always take full routes. If you can't afford it, try to. If you really can't afford it, there's some trickery that can last you a year or two until you can afford it, but make sure new hardware makes it into your budget. Regards, Bill Herrin -- William Herrin ................ her...@dirtside.com b...@herrin.us Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>
