From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lists.gentoo.org ([140.105.134.102] helo=robin.gentoo.org) by nuthatch.gentoo.org with esmtp (Exim 4.43) id 1EChpp-0006v0-2X for garchives@archives.gentoo.org; Tue, 06 Sep 2005 18:06:17 +0000 Received: from robin.gentoo.org (localhost [127.0.0.1]) by robin.gentoo.org (8.13.4/8.13.4) with SMTP id j86I0p2Y021878; Tue, 6 Sep 2005 18:00:51 GMT Received: from popmail.jettissystems.com (popmail.jettissystems.com [38.118.146.212]) by robin.gentoo.org (8.13.4/8.13.4) with ESMTP id j86HptCO026205 for ; Tue, 6 Sep 2005 17:51:55 GMT Received: from [10.20.16.109] (unknown [10.20.16.109]) by popmail.jettissystems.com (Postfix) with ESMTP id C0A7E56D482 for ; Tue, 6 Sep 2005 10:55:15 -0700 (PDT) Message-ID: <431DD801.2010300@badapple.net> Date: Tue, 06 Sep 2005 12:55:13 -0500 From: kashani User-Agent: Mozilla Thunderbird 1.0.6 (Windows/20050716) X-Accept-Language: en-us, en Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 To: gentoo-user@lists.gentoo.org Subject: Re: [gentoo-user] Re: Gentoo router redundancy via Ucarp? References: <431BC017.8050306@badapple.net> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Archives-Salt: 21fd360e-187a-430d-a4ce-081732955e6a X-Archives-Hash: ed52d79e321dcf1e3af05b4519daca71 James wrote: > So BGP-4 is still the only solution to multi-homed networks.....? > Here's one treatise on the subject: > http://www.ietf.org/internet-drafts/draft-nagami-mip6-nemo-multihome-fixed-network-03.txt BGP is really your only option, but your providers are not going to give you the option. Let say we actually get bgp setup and it looks like this. your router int fe0/0 description comcast ip address 24.24.24.124/24 int fe1/0 description tmobile ip address 64.64.64.164/24 router bgp 65555 network 24.24.24.124/32 network 64.64.64.164/32 neighbor 24.24.24.1 remote-as $comcast-as# neighbot 64.64.64.1 remote-as $tmobile So at this point you're announcing to 24.24.24.124/32 and 64.64.64.164/32 to both providers. They accept these routes and also announce 0.0.0.0/0 back to your. Your route table will look like this CON 24.24.24.124/24 [1/4] is directly connected CON 64.64.64.164/24 [2/4} is directly connected BGP 0.0.0.0/0 [3/4] via 24.24.24.1 BGP 0.0.0.0/0 [4/4] via 64.64.64.1 If int fe0/0 fails that BGP session will drop and that route will be withdrawn from the routing table. That the basic way BGP works for a multi-homed system. So far so good. However your providers will not announce the /32 routes you are announcing to them to their peers. Ever. Because those routes are too small and the memory requiremets to do that aren't feasible. These days with massive filter you can get a full BGP table down to 140-160k routes. If you allowed routes more specific than a /24 to be announced we'd see a million plus routes and the internet would start breaking. You could say pay your providers enough and they might actually announce the /32 routes, but their peers would filter anything smaller than a /24 route and some peers have been known to filter anything smaller than /22. I want to connect to 24.24.24.124 from my DSL account. The routers between us route my packet to you via the comcast route because BGP on those routers says "24.24.0.0/16 --> Comcast". I never see a "24.24.24.124 --> Comcast or Tmobile" so when Comcast goes down I can't get to you through tmobile because there is no route for that in the routing tables. This is why most important server go to a data center. The data center has a nice big chunk of IP space say 209.247.4.0/22 which they can announce to their multiple providers who is turn pass the route on to the their peers. So the route table might look like this: my DSL -> Level 3 -> XO -> datacenter my DSL -> PSI -> MCI -> datacenter and so on. If this is something you're interested in learning more about the most useful book I found back in my Wan Engineer days was Internet Routing Architectures by Sam Halabi and Danny McPherson. It's a bit Cisco centric, but very readable and has a number of good real world examples. kashani -- gentoo-user@gentoo.org mailing list