dual-net problem

T. Horsnell tsh at mrc-lmb.cam.ac.uk
Thu May 26 16:09:10 UTC 2005


>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.





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