Date: Tue, 6 Jan 1998 10:45:20 +0000 From: Chrisy Luke <chrisy@flix.net> To: freebsd-hackers@FreeBSD.ORG Subject: Multipath Routing. Message-ID: <19980106104520.25045@flix.net>
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This is a scouting survey to see if anyone else is interested in what
I've been playing with...
I'm just finishing off a pretty neat kernel hack I started last week to
implement multipath routing in the BSD kernel, using FreeBSD as my
development base. Not much has changed across the BSD's or time to the
code I've changed so it should be portable to other BSD's quite easily.
What it changes is the rule that an entry in the routing table can
only have one next-hop gateway. Unlike Sun's implementation of the
same. this load balances across the installed gateways for a route.
Sun's method merely allowed two nodes in the patricia tree to have the same
network and netmask. On route lookup, it finds the first one and disregards
any others.
You end up with a routing table that looks something like:
chrisy@om[~]> netstat -rn
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif Expire
default UGSc 3 138832
193.131.248.183 46278 fxp0
*193.131.248.254 46277 fxp0
193.131.248.186 46277 fxp0
127.0.0.1 *127.0.0.1 UH 0 2 lo0
193.131.248 *link#1 UC 0 0
193.131.248.2 *0:0:f8:30:2:4b UHLW 0 13785 fxp0 1198
193.131.248.24 *0:0:c0:53:22:e4 UHLW 0 1 fxp0 697
193.131.248.97 *8:0:3:22:47:ae UHLW 0 0 fxp0 572
193.131.248.173 *0:0:c0:3a:22:e4 UHLW 0 772 fxp0 782
193.131.248.179 *0:0:c0:b0:3b:e7 UHLW 0 0 fxp0 1081
193.131.248.180 *8:0:3:23:15:e5 UHLW 0 0 fxp0 571
193.131.248.183 *0:0:c0:78:22:e4 UHLW 4 0 fxp0 682
193.131.248.185 *0:0:c0:6e:22:e4 UHLW 0 0 fxp0 1194
193.131.248.186 *0:0:c0:9c:b1:e3 UHLW 2 0 fxp0 1170
193.131.248.187 *0:0:c0:5c:10:dc UHLW 0 0 fxp0 1198
193.131.248.254 *0:0:f8:30:98:a8 UHLW 4 6076 fxp0 1184
195.40.1 UGSc 0 0
*193.131.248.183 0 fxp0
193.131.248.186 0 fxp0
Note the subtle changes. The '*' that preceeds some of the Gateway fields
shows the target of the next packet to hit ip_output() and is destined for
that network. Note also that each gateway has it's own Use and netif field.
Unfortunately it required quite a bastardisation of the PF_ROUTE protocol,
so all routing tools needed to be modified.
I'm presently convincing gated that it wants to talk multipath too, where the
largest benefits lie.
My prime intention for this feature is in a core-of-the-network scenario
where an IP network has a number of unix nodes and a unix-based set
of BGP speakers, with multiple core routers. These core routers are the
default routes for your regular unix nodes. Using Router discovery, you
can identify all of thse core routers, but it only ever uses the one with
the lowest IP address. That router sees all of the load and the others remain
idle. This will remove that imbalance.
If anyone is interested, I'll put my patches up (they are in beta form
at present - there don't appear to be any leaks but I won't know for sure
until gated loads a full routing table onto it... :-)
Cheers,
Chris.
--
== chris@easynet.net, chrisy@flix.net, chrisy@flirble.org.
== Head of Systems for Easynet Group PLC.
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