[openib-general] Same IP address on multiple net devices and routing

[Hal Rosenstock]

On Thu, 2005-09-29 at 11:48, Roland Dreier wrote:
>     Hal> Hi, Does anyone know what the Linux routing code does in
>     Hal> terms of selecting an outgoing interface when multiple net
>     Hal> devices have been configured with the same IP address ?
> 
> It follows the routing table.  If you assign the same local IP address
> to multiple interfaces then you have to be careful to set up routing
> so that your traffic goes to the right place.
> 
> In fact you can think of Linux networking as attaching IP addresses to
> the system as a whole instead of a particular interface, because for
> example by default Linux will respond to ARP queries on any
> interface.  Assigning addresses to a particular interface is just a
> hint for how the kernel sets up routes by default.

So the routing lookup (ip_route_output_key) is just fine then for
selecting the outgoing interface. Just sometimes if the default is all
that is available, some outgoing interfaces may be less used than
others.

-- Hal