Date: Mon, 9 Oct 2000 08:16:08 -0500 (CDT) From: Curtis Coleman <curtis-lists-freebsd-cluster@pangea.ca> To: freebsd-cluster@freebsd.org Cc: curtis@pangea.ca Subject: Simple fallover using GateD and OSPF Message-ID: <Pine.BSF.4.21L2.0010090703110.529-100000@sds05.pangea.ca>
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I've been using a fallover scheme for a few (well, two) years now that is
so simple, I wish I had thought of it myself.
If you have a couple of hosts behind a router capable of running OSPF, you
can use GateD to allow for fallover. The general premise is to have two
or more hosts announce a stub host route for a loopback interface, with
the same IP address on each machine, with differing costs large enough to
be dominant over the link costs. If the primary host goes down, loses
it's ethernets, or gated is otherwise killed, then the next highest cost
route gets chosen.
For example, a gated config for a loopback 172.16.0.1/32 would look
something like this:
ospf yes {
backbone {
interface fxp0 fxp1 cost 1;
stubhosts {
# for the backup host, change the
# "cost" below to, say, 200
172.16.0.1 cost 100;
};
};
};
export proto ospfase type 1 {
proto direct {
ALL metric 888;
};
proto static {
ALL metric 999;
};
};
Aside from running OSPF, there is no special requirements of the gateway
router(s). By binding a few loopbacks on each machine, it's not hard to
extrapolate on this so that you can distribute load using DNS round-robin
or some fancier source address-based policy routing.
The idea was stolen from a message Danny McPherson of Genuity posted to
the isp-caching list back in August '98. I believe that Vixie's
j.root-servers.net has been doing something similar to this for quite a
while.
Curtis Coleman "Space is big. Really big. You just won't believe how
Pangea.CA, Inc. vastly hugely mindboggingly big it is. I mean you may
curtis@pangea.ca think it's a long way down the road to the chemist, but
CC263 that's just peanuts to space. Listen..." -- HHGTTG
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