On 2 Jul 2003, at 22:56, Dennis Dittmar wrote:
 > I have 2 computers one iwth XP home and one with 98SE. I
 > originally used TimeWarner RoadRunner cable service and
 > it worked fine before changing to AOL Broadband. I
 > contacted both companies and the IP address changes when
 > the router is plugged in. Any ideas?

I assume you have the computers plugged into two ports on
a broadband router and the router plugged directly into a
cable modem. (If you're using DSL instead of Cable, my
message will probably not be relevant to your situation.)
So I assume that when you say "the router is plugged in"
means "when the router is between the computers and the
cable modem".

If you're talking about your WAN IP address changing (the IP
address that the Internet sees), AOL is probably assigning
you an IP address based on the MAC address of the device
directly connected to the cable modem.

Your two computers and the router all have different MAC
addresses (unless you've changed the MAC address of the
router manually). If the cable modem sees the router's
MAC address, AOL will assign you one IP address. If the
cable modem sees the MAC address of one of the computers
(actually the MAC address of the NIC in that computer),
AOL would give you a different IP address.

I understand that some Cable Internet Providers key the IP
address by the MAC address and some don't. Some providers
will force you to call and register the new MAC address of
your computer if it changes. (It would change if you
installing a router, or switch to a different computer, or
just install a different NIC in your computer.) Sometimes
you just have to reboot the cable modem after the MAC address
changes. Sometimes you don't have to even do that.

I use Time Warner Roadrunner of New York and my IP address
only changes if the MAC address of my computer changes.
(My WAN IP address changes when I change routers or when
I change the MAC address of my router using its built in
Setup.) The best situation is to change the router's MAC
address to coincide with the MAC address of one's main
computer.

Maybe once a year Road Runner will change my IP address
for some other reason.

Note that a broadband router has two MAC addresses, one
that it presents to the Internet (the cable modem see this
one) and one that is seen by the computers in your local
(home) network.

Regards,
Bill

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