[LARTC] Problems getting multipath routes to balance

[Tore Anderson <tore@linpro.no>]

   Hi.  I've trying to balance outgoing traffic by using multipath
  routes, but I can't get it to work.  Only one of the routes are used.

   I'm adding the route like this:

     ip route add table 101 default \
       nexthop via X.X.X.X nexthop via Y.Y.Y.Y

   It shows up the routing table like this:

     default
             nexthop via X.X.X.X  dev vlan110 weight 1
             nexthop via Y.Y.Y.Y  dev vlan120 weight 1

   So it looks quite good.  However, all traffic is routed via Y.Y.Y.Y,
  no matter what I do.  I can increase the weight of X.X.X.X, load and
  unload the various multipath kernel modules (_rr, _random, _wrandom,
  and _drr), flush the cache routing table, delete and re-add the route,
  but still traffic is only sent to X.X.X.X

   If I reverse the order of the nexthops on the command line, that is:

     ip route add table 101 default \
       nexthop via Y.Y.Y.Y nexthop via X.X.X.X

   ...the behaviour is exactly the same, only now the traffic is
  sent only to X.X.X.X.  The ordering of the nexthops on the command line
  is the only thing that appears to make a difference to me.

   I send traffic from a relatively busy network into table 101 (using
  "ip rule add from z.z.z.z/zz table 101 prio 20000"), so there's
  constantly traffic there, and many simultaneous flows.  I tried using
  "equalize" too, though, but it had no effect either.

   How is this actually supposed to work, and what am I missing?  I'm
  grateful for any suggestions.  I'm seeing this behaviour both on 2.6.12
  and 2.6.15.

Thanks
-- 
Tore Anderson
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