iptables + dhcp_client

[Tom Allison <tallison@tacocat.net>]

I can't seem to find anywhere that this is specifically mentioned, but...

If I have a script of iptables rules... (/etc/network/if-up.d/)
And I'm running as a dhcp_client...

How do I know when my dhcp assigned IP address has changed and re-run 
the iptable rules script?

And to add another level of complexity to the matter, I have one machine 
that runs a pcmcia network card as well.

I wasn't sure if this was somehow built into the Debian infrastructure 
so I thought I should ask.
--
This is the theory that Jack built.
This is the flaw that lay in the theory that Jack built.
This is the palpable verbal haze that hid the flaw that lay in...