[LARTC] load balance/redundancy

[Arthur van Leeuwen arthurvl@sci.kun.nl]

<PRE>On Sun, 10 Dec 2000 <A HREF="mailto:hesselsp@ashaman.dhs.org">hesselsp@ashaman.dhs.org</A> wrote:

&gt;<i> Well, I think I have the redundancy down... In a kludgy way.  Right now I
</I>&gt;<i> have two default routes.
</I>
&gt;<i> route add default gw 24.141.xxx.1
</I>&gt;<i> route add default gw 64.229.xxx.1
</I>
Actually, if I understand the code correctly what you do here is in fact
create a multipath route. A cleaner way to do so is using ip route 2 as
follows:

ip route add default nexthop via 24.141.xxx.1 nexthop via 64.229.xxx.1

This explicitly states that you will be using a multipath route and balances
outgoing routes over the two interfaces.

&gt;<i> I can write a script that if one of connections goes down for x number of
</I>&gt;<i> pings, then remove the route.
</I>
And here's the crux. It would be nice for the kernel to use its idea of
gateway reachability (in the neighbor cache) to automatically ignore an
upstream hop in case it is dead. However, for multipath routes, no
death detection is done on the gateways in the different hops. This is
quite somewhat different from the single default route behaviour 

&gt;<i> Now for the load balancing.
</I>
The kernel balances outgoing routes over the upstream interfaces. Unless all
your packets go to the same address, that should balance your traffic
already. Other than that there's some code based on EQL that will flush the
route cache after every packet, thereby smashing the route-balancing down to
packet-level load balancing. I can't seem to find the URL for that code,
though, unfortunately.

&gt;<i> Can you point me to documentation on iproute?  Other then the Advanced
</I>&gt;<i> Routing HOWTO, unless I am missing something in it.
</I>
<A HREF="http://snafu.freedom.org/linux2.2/iproute-notes.html#doc">http://snafu.freedom.org/linux2.2/iproute-notes.html#doc</A>

There's some more interesting stuff on <A HREF="http://snafu.freedom.org/linux2.2/">http://snafu.freedom.org/linux2.2/</A>
as well. 

Doei, Arthur.

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