Date: Fri, 23 Jun 2006 15:51:21 +0200 From: Claudio Jeker <cjeker@diehard.n-r-g.com> To: freebsd-net@freebsd.org Subject: Re: Multiple routes to the same destination Message-ID: <20060623135144.GD12611@diehard.n-r-g.com> In-Reply-To: <50v528$fvu0nd@iinet-mail.icp-qv1-irony1.iinet.net.au> References: <20060623120208.GH36671@gremlin.foo.is> <50v528$fvu0nd@iinet-mail.icp-qv1-irony1.iinet.net.au>
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On Fri, Jun 23, 2006 at 10:19:06PM +1000, Christopher Martin wrote: > > > > -----Original Message----- > > From: Baldur Gislason [mailto:baldur@foo.is] > > Sent: Friday, 23 June 2006 10:02 PM > > To: Christopher Martin > > Cc: FreeBSD Net Mailing list > > Subject: Re: Multiple routes to the same destination > > > > Well, round robin is really not what you want with IP packets. > > And how are you going to detect that a route is good without a routing > > protocol? > > > > Actually, round robin is exactly what I want. And I am not saying I don't > use a routing protocol, in fact I do, but I want packets to be able to use > two or more diverse paths of equivalent cost. I doubt that. Doing a per packet round robin over different pathes will kill your tcp performance because of out of order packets. > > It would seem that you are assuming that I want to load balance two internet > connections which are NATed, in which case round robin might have issues > with lost TCP sessions and weird reactions from servers as the apparent > source address changes from packet to packet, but in a routed internal > network the source address will not be changed by the router, thus negating > that issue. > > It did seem at some stage someone was going to include it in OpenBSD: > http://undeadly.org/cgi?action=article&sid=20040425183024&mode=expanded > That's just part of the it. The rest was added in the last couple of days because multipath routing and accepting more than one route per destination is a scary thing. Additionally dead nexthop detection is not available. > To quote: > "...OSPF also supports multipath equal cost routing". > Yes it does but often you try to avoid that. > It's more of a case where we would like to use BSD as a router/packet > filtering firewall for sites with multiple WAN links between each site, of > equal size, and not have one site idle until the other fails over. Round > robin is better than what we have: nothing. OpenBSD is on the way to support this but it is still a long journey till all issues are resolved. Btw. OpenBSD uses a hash-threshold mechanism to select paths based on source/destination IP address pairs (round robin will never be supported). -- :wq Claudio
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