Date: Thu, 26 Oct 2000 23:50:02 -0600 (MDT) From: Nick Rogness <nick@rapidnet.com> To: Bakul Shah <bakul@torrentnet.com> Cc: "Richard A. Steenbergen" <ras@e-gerbil.net>, "Ron 'The InSaNe One' Rosson" <insane@lunatic.oneinsane.net>, freebsd-net@FreeBSD.ORG Subject: Re: Multihomed Routing Message-ID: <Pine.BSF.4.21.0010262335480.89387-100000@rapidnet.com> In-Reply-To: <200010270447.e9R4lht14585@bacardi.torrentnet.com>
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On Fri, 27 Oct 2000, Bakul Shah wrote: > > Sure that will work. However, consider the following: > > > > > > > > Network1 (2000 IP's) > > | > > | > > |---Router1 > > | > > machine1---| > > | > > |---Router2 (default gateway) > > > > What happens to Router2 when machine1 is trying to access the IP's > > on Router1's network? Router2 gets clogged down sending ICMP > > redirects for Router1 back to machine1. The problem grows > > exponetially[spelling] when you add more machines to the same > > network machine1 is on. > > Unless I am missing something the redirect traffic won't > grow exponentially. Machine1 will get one redirect per > destination D and will switch its route to D to go via > Router1. From then on it won't bother Router2 for D. So the > total number of redirects is [exponentially was a figure of speech] ;-) Until the routing table on the machine gets flushed. > > SUM(H[i]) for i = 1..number of servers, > where H[i] == number of hosts server i talks to. You are assuming that the network that machine1 lies on has only 1 machine on it. What happens when you add 2 more machines to that network? Now, router1 has to handle redirects for all of those machines as well. 1 machine = 200 redirects 2 machines = 400 redirects (200 for machine1 & 200 for machine2) 3 machines = 600 redirects . . . > > So yes, there is some extra traffic but assuming your local > network is far faster than your external connections this > shouldn't be a problem (unless you send only a single packet > to each destination). > This IS a problem. Traffic analysis on that router1 will show a good load on the router just handling those requests. What if machine1 was a web server and the 2000 IP's you have on Network1 are dialing clients trying to reach that web server? What happens when you add more dial equipment to Network1?...more redirects. You fill up the routing table on your machines with host routes when it can be accomplished with a subnet route. In that case it would pay to run a routing protocol. But yes, sometimes it is not significant traffic, but in my example there is a good reason to run routing protocols on your machines. It just scales better. However, you do have a great point. Nick Rogness - Drive defensively. Buy a tank. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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