two interfaces one subnet

Kevin Oberman oberman at
Mon May 11 18:47:50 CDT 2009

> Date: Mon, 11 May 2009 18:29:08 -0500
> From: Chris Adams <cmadams at>
> Once upon a time, Kevin Oberman <oberman at> said:
> > > From: Chris Meidinger <cmeidinger at>
> > > For example, eth0 is and eth1 is, nothing like  
> > > bonding going on. The customers usually have the idea of running one  
> > > interface for administration and another for production (which is a  
> > > _good_ idea) but they want to do it in the same subnet (not such a  
> > > good idea...)
> > 
> > This will not work right. One interface can be, but any
> > added interfaces would need to be /32 (
> I don't know which OS(es) you are using, but that's not true in Linux.
> I see this all the time at home; if I plug my notebook into the wired
> LAN and still have the wireless enabled, both will get an IP (in the
> same subnet) from DHCP.  The wired link is the preferred default route
> by default, but you can easily set up routes for some networks via the
> wireless link.
> You can also set up multipath routing to send packets out both links.  I
> think you can also use IP policy routing to control the choice of
> outbound interface by rule (e.g. based on source address).

This is true if you are using the WPA supplicant. It does a bit of
magic. (You can do the magic by hand without the supplicant, but it is a
pain or was the last time I tried.) 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751

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