LARTC - Mar 2007 - Problem

Hello.

I am trying to get multi paths running, i.e I want to specify 2 paths
from a particular node to another.

To test this, I am setting up the following scenario:

I create 2 tap devices
    tap0 = 10.1.1.1/32 netmask 255.255.255.0
    tap1 = 10.2.2.2/32 netmask 255.255.255.0

I then issue the route command:

ip route add 10.3.3.3/32 nexthop via 10.1.1.2 nexthop via 10.2.2.3

The route table then looks like:

10.3.3.3
        nexthop via 10.1.1.2  dev tap0 weight 1
        nexthop via 10.2.2.3  dev tap1 weight 1

Pinging 10.3.3.3 causes arp requests on tap1 for 10.2.2.3 and never for
10.1.1.2.
(there is nothing connected to tap0 or tap1 so I don''t expect anything
really, but I do expect the ARP requests, which would show that
splitting would work.

If the two routes were being used equally, I would have expected to see
arp requests for 10.1.1.2 also (wouldn''t I?)

...Michael Flower

-- 


Michael Flower
ES Labs
Elantis Systems Inc.
+61 3 9550 0866

On Monday 12 March 2007 22:26, Michael Flower wrote:
> Hello.
>
> I am trying to get multi paths running, i.e I want to specify 2 paths
> from a particular node to another.
>
> To test this, I am setting up the following scenario:
>
> I create 2 tap devices
>     tap0 = 10.1.1.1/32 netmask 255.255.255.0
>     tap1 = 10.2.2.2/32 netmask 255.255.255.0
>
> I then issue the route command:
>
> ip route add 10.3.3.3/32 nexthop via 10.1.1.2 nexthop via 10.2.2.3
>
> The route table then looks like:
>
> 10.3.3.3
>         nexthop via 10.1.1.2  dev tap0 weight 1
>         nexthop via 10.2.2.3  dev tap1 weight 1
>
> Pinging 10.3.3.3 causes arp requests on tap1 for 10.2.2.3 and never for
> 10.1.1.2.
> (there is nothing connected to tap0 or tap1 so I don''t expect
anything
> really, but I do expect the ARP requests, which would show that
> splitting would work.
>
> If the two routes were being used equally, I would have expected to see
> arp requests for 10.1.1.2 also (wouldn''t I?)
no, route uses src_ip+dst_ip+TOS to build it''s cache, so it will use
the same
cached routing desicion unless you change one of these 3 parameters. After 
cache expires, probably the other hop takes it''s turn.

-- 
Luciano