[luau] RoadRunner or EarthLink?

[Jeff Wong]

On Wed, 24 Dec 2003, Warren Togami wrote:

> a hassle to change it for the things that I do... and changing the IP 
> address seems to be as simple as changing the MAC address and power 
> cycling the cable modem.
> 
> Strangely changing the MAC address back then power cycling the cable 
> modem always brought it back to the original IP address.
> 

There really is nothing strange about it, that's the way DHCP is supposed
to work.  When a computer requests an IP address, the way in which the
server should reply is specified in the RFCs.  If the computer requests a
specific IP and that IP is both available and within the scope of the
server, the server must reply with that IP.  If computer does not request
a specific IP or the IP requested is not available/within server scope,
the server should return the last IP that the server had assigned to that
MAC address if available/within scope.  If the computer's previous IP is
unavailable, or the server has no record of the MAC address being used,
then I can assign any available IP within it's scope.  Most of the better
dhcp servers will not issue an IP that it has marked as having been used
to a new computer until all possible 'never used' IP's have been
exhausted, in which case it will reissue IP's based on which has been
unused for the longest amount of time.  The only time a computer will get
a IP other than what it previously had is if there are more devices than
there are available IP's, or the scope of available IP's on the dhcp
server changes.

The only way to really force a change of IP is to change the MAC address 
of the device requesting the IP.  This will make the dhcp server think 
it's a new computer and issue a new IP.  When you change the MAC address 
back to to the previous MAC, the server should recognize it as a previous 
client and try to reissue the old IP.

Jeff