Udev persistent net rules - how do they work?

[Alan Chandler <alan@chandlerfamily.org.uk>]

For a while now, I have been running a server with two ethernet cards 
in.

In /etc/networks/interfaces I defined the basic interface as eth0 and 
eth1, but in order to create some additional psuedo ip addresses on my 
lan I created eth1:0, eth1:1 ... with static ip addresses.

A couple of days ago I wanted to test something so 
changed /etc/networks/interfaces and turned all eth1 into eth0 
addresses and vica versa.

However, now - when I reboot, I still end up with an additional eth1:0 
interface - and this seems to stop my dhcp server starting.

The reference to eth1:0 is no longer in /etc/networks/interfaces (its 
been changed to eth0:0) and I have grep'ed all of /etc/ and /var/lib 
looking for references but can't find any.

When interfaces apparently appear out of nowhere, I suspect 
hotplug/udev, and in /etc/udev there is a script called 

persistent-net-generator.rules

which in its comments says it is storing the created interfaces so that 
they stay the same across reboots.  But I can't figure out how its 
supposed to work.  Can someone explain what it is doing, and if so how 
I can tell if this is the cause of my problem.

Thanks.
-- 
Alan Chandler
http://www.chandlerfamily.org.uk