Multi-homed interface and Oracle listener

A slightly different kind of question... Why something does work instead of why something doesn't. :)

As I mentioned in a previous post, the company I work for is going through an IP address change after spinning off from our parent company. Particular server I have a question about is:

HP D350/2-way
HP-UX 10.20
Oracle RDBMS 7.3.2 (I think.. Pretty close on the version number anyway) Current IP address is, say, 19.24.24.24
New IP address is, say, 136.25.25.25

Last week, I installed a couple of patches and got the new IP address configured to the interface with ifalias (ifalias lan0 addmsk 0.0.0.0 136.25.25.25).

Normally, the Oracle listener must be configured to watch port 1521 on each IP address configured on a system (at least when the IP addresses are assigned to different interfaces from previous configurations with multi-NIC systems I set up, as best I can recall). On this system, however, even though the listener configuration wasn't changed, clients are still able to connect to the database using the new IP address.

The only thing I can think of as to why this is working is the OS is doing some transparent translation since the addresses are assigned to the same interface. Would be nice to better understand the dynamic that is allowing this to function. Anyone care to take a stab at it?

-- 
Jeff Traigle
traigle_at_si.umich.edu
http://www-personal.si.umich.edu/~traigle/