IP Aliasing

[Olivier Nicole]

> 1) is there an upper limit to configuring a number of alias addresses?

I have a machine with 200+ IP without any problem.

> 2) if an interface is configured with an alias address, then what
> address is shown on the traffic leaving this interface? So, for
> example, if I were to ping this machine on its primary address, I
> expect to get a response from the primary address of the interface.
> What happens if I ping an alias address, would I get a response from

By default exiting traffic is using the primary address (the one
defined with no keyword alias in the ifconfig). I think there is a way
to choose the exiting IP.

When a paket is responding, it use the same IP that was used in the
query (else any firewall would be confused in the way).

> 3) In the above scenario, all traffic leaving the interface
> (regardless of the source IP on it) will have the same MAC address
> (the one of the interface) - is that right?

Right except maybe some NIC that allow several MAC addresses? That
could be used in hi availability?

> 4) Does anyone know if there are there any other network
> characteristics or behaviour by which we can distinguish a machine
> having more than one IP address (primary plus alias) configued on one
> of its interface?

Once you cross a router, you don't see the MAC of the machine anymore,
MAC is local to your LAN anyway.

Olivier