When a TCP link is created by the remote system targeting one of the alias
IP addresses, your host would respond with the alias IP address as the
source, but if you create a TCP link from your host to a remote host, it
will always use the same source IP address determined by the routing table
for the target subnet. 

If your applications are servers, you can run into issues if you are using
bind() to a specific address instead of INADDR_ANY as connections to the
alias interfaces would be rejected.  
Instead of using INADDR_ANY, you could use bind() to bind a different socket
to each alias interface if you just want the application to receive traffic
for that IP alias. 
  

Dave

> -----Original Message-----
> From: Robert Craig
> Sent: Thursday, February 14, 2008 2:52 PM
> To: technology-networking
> Subject: RE: how to respond to 16 IP addresses on one NIC ?
> 
> Are all of the interfaces on the same subnet or are they all on different
> subnets?  If they're on the same subnet, you may not end up with the
> behaviour you expect....  (You'll end up with packets being received on
> multiple interfaces but only being transmitted by one...)
> 
> 	R.
> 
> -----Original Message-----
> From: Sean Boudreau [mailto:seanb@qnx.com]
> Sent: Thursday, February 14, 2008 2:27 PM
> To: technology-networking
> Subject: Re: how to respond to 16 IP addresses on one NIC ?
> 
> On Thu, Feb 14, 2008 at 02:21:12PM -0500, Dave Bott wrote:
> > I have a requirement to combine 16 individual h/w cards into one PC.
> Each
> card currently has its own IP address, so to remain backward-compatible
> (one
> component in a large system) the new system needs to be able to receive
> packets for all 16 IP addresses, so it knows which logical card is being
> addressed
> >
> > One way might be to run in promiscuous mode, but that could be a problem
> on a noisy network.
> >
> > Is there a 'nice' way to configure a NIC to do this ? Does it make a
> difference if the IP addresses are contiguous or not ?
> >
> > I hope that makes sense !
> >
> > Dave
> 
> You can assign more than one ip address to an interface which
> sounds like it might do what he wants.
> 
> # ifconfig <iface>  alias <ip_addr>         <- add an addr
> # ifconfig <iface> -alias <ip_addr>         <- del an addr
> 
> _______________________________________________
> Technology
> http://community.qnx.com/sf/go/post5040
> 
> _______________________________________________
> Technology
> http://community.qnx.com/sf/go/post5041