[plug] Another network question (IP Aliasing)

[Ryan]

On Tue, 2003-06-10 at 11:54, Craig Ringer wrote:
> > ifconfig lo:1 10.0.1.1
> > 
> > Some form of aliasing according to the context I got it from, but I'm not sure 
> > what aliasing means in network terminology.
> 
> It's a linux thing as much as a general networking thing. Basically, 
> what your're doing is creating a second "virtual" network interface 
> attached to the real interface, that can have a different IP address 
> etc. It is a way of having multiple virtual network interfaces on a 
> single physical interface (and medium).

Just curious, and under-educated:

Furthering this a little, I use the odd alias around the place on boxes
at work behind a Cisco with static NATs to certain internal IPs.  If one
of those particular IP is the main IP on an interface and I alias other
internal IPs to that interface that have no corresponding static NATs,
return traffic to the router that entered via the alias IP exits and
hits the static NAT rules as it appears to come from the main physical
interface (which has the static NAT IP).

ie:
           external IP -> static NAT
 	    203.1.1.1      10.1.1.1
            --------        -----
internet --| router |------| box |
            --------        -----
                            alias
                           10.1.1.2    

If the router were to talk to 10.1.1.2 (for example for RADIUS), it
appears from the router's perspective as if it were 10.1.1.1.  Now
assuming the router wasn't configured 100% perfectly (long story) and
data sent to 10.1.1.2 had to appear to return from 10.1.1.2 (the whole
need for the non-static NAT IP alias) - is there any trickery or extra
alias options that can achieve this without a separate physical
interface and 1 extra routing rule (which does fix it).

Supposedly iproute2 can route via aliased IPs, is that the sort of thing
that would fix this issue (after a lot of reading)?

Ryan