dual-net problem

[Jeff Vian]

On Thu, 2005-05-26 at 17:09 +0100, T. Horsnell wrote:
> >On Wed, 2005-05-25 at 19:02 +0100, T. Horsnell wrote:
> >> Hi all,                    
> >> I have a system with dual gigabit ethernet ports.    
> >> I've assigned them each an ip address, and am using  
> >> tcpdump and ping to check that they work as expected.
> >> They dont.
> >>                            
> >> If I ping, from another box, the address associated with eth1,
> >> the traffic appears on eth0. This only happens when I ping from 
> >> another  Linux box - if I ping from one of my Alpha boxes, everything
> >> works as expected, i.e. pings addressed to the ipaddress    
> >> allocated to eth0 appear on eth0, and pings to the ipaddress
> >> allocated to eth1 appear on eth1.
> >> 
> >> I'm running FC3 with kernel 2.6.10 on the dual-eth box, and I've
> >> tried pinging from RH7.3, RH9 and FC3 boxes, all with the same
> >> result. 
> >>      
> >> It appears from the tcpdump output below, that ls1 is returing the
> >> mac address of the eth1 interface *and* the address of the eth0
> >> interface. Is this proper? What am I doing wrong?
> >> 
> >> Cheers,
> >> Terry.
> >> 
> >You are using 2 interfaces on the same subnet on this machine.  This has
> >historically never worked reliably.
> >
> >If you put one of the interfaces on one subnet and the other on a
> >different subnet I expect it will work better (and as expected).
> 
> I see. I think that will require a lot of re-jigging but I'll keep it
> in mind. For the moment, I've added a pile of static routes to the ls1
> host to force the use of eth1 when talking to the subset of machines for
> which I want to use eth1.
> 
> Thanks for your help,
> Terry.

Should not be too hard.
It seems all are likely on the same physical network.

You could give a different subnet to the second nic in this machine,
then assign alias IPs to the cards in the other machines that were on
the new subnet here and set up the naming so that any communication
between this machine and those specified hosts used the new subnet, but
they still had the existing paths as well.

May be easier than doing the static routing.

Jeff