nanog mailing list archives
Re: BGP Multihoming 2 providers full or partial?
From: Blake Hudson <blake () ispn net>
Date: Mon, 01 Jun 2015 16:05:55 -0500
William Herrin wrote on 6/1/2015 3:28 PM:
Thanks. I see what you mean. I was coming from the vantage point of taking full routes and assuming that the prefix information existed and simply hadn't filtered down to the op's equipment yet. It was there, just upstream a hop or two. This could be due to a newly advertised route, path changes, or initial BGP convergence. In this case, a backup route provides the necessary bridge while BGP converges. I see what you mean about one ISP having a route and the other not; Taking full routes resolves any question about the best (only) path.On Mon, Jun 1, 2015 at 2:40 PM, Blake Hudson <blake () ispn net> wrote:A gateway of last resort, also called a backup default route, will take care of partitionsNo, Blake, it won't. A partition means one of your ISPs has no route to the destination. Route the packet to that ISP via a default route and it gets sent to /dev/null. More, during a partition you don't get to pick which of your ISPs lack the route. Regards, Bill Herrin
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.
--Blake
Current thread:
- Re: BGP Multihoming 2 providers full or partial? Pawel Rybczyk (May 31)
- <Possible follow-ups>
- Re: BGP Multihoming 2 providers full or partial? Scott Weeks (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Mike Hammett (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Blake Hudson (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Baldur Norddahl (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Maqbool Hashim (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Blake Hudson (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Jeremy Malli (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? William Herrin (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Blake Hudson (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? William Herrin (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Baldur Norddahl (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? William Herrin (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Patrick W. Gilmore (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Baldur Norddahl (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Mike Hammett (Jun 01)
- Re: BGP Multihoming 2 providers full or partial? Mike Hammett (Jun 02)