router ALWAYS gets the same IP address from cable modem

Hi,

I noticed that my router (Netgear FM114P) always gets the same IP
address from the cable modem.

Now, it used to be that once in a while the IP address changed, when I
powercycled the modem and the router. But now I'm seeing the same IP
address for many months.

So I connected the computer directly to the cable modem, did
ipconfig/release and /renew, and bingo, I got a new IP address. But
when I put the router back between the cable modem and the computer, I
got the same old ip address back again!!

Isn't that weird??? I reloaded the frimware (the same version I already
had installed; there's no newer one), manually reset and reconfigured
the router, but the IP address I got is still the same! How is it
possible?

Thanks!
Tom

Hi Tom. Actually, there's nothing wrong going on here. When your router
device was connected to your cable modem it requested an IP address from
your ISPs DHCP server. The DHCP server assigned an IP address to your
router's MAC address and gave it a lease time. This lease can be anywhere
from an hour to several days. As long as your router is actively connected
when the DHCP server renews the lease you will keep that IP address. The
reason why your computer got a different IP address is because it's NIC has
a different MAC address and is therefore a different connection.

If you want your router to get a new IP address (and even then there's no
guarantee) you would have to take it offline until after the lease expires.

Richard


<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> Hi,
>
> I noticed that my router (Netgear FM114P) always gets the same IP
> address from the cable modem.
>
> Now, it used to be that once in a while the IP address changed, when I
> powercycled the modem and the router. But now I'm seeing the same IP
> address for many months.
>
> So I connected the computer directly to the cable modem, did
> ipconfig/release and /renew, and bingo, I got a new IP address. But
> when I put the router back between the cable modem and the computer, I
> got the same old ip address back again!!
>
> Isn't that weird??? I reloaded the frimware (the same version I already
> had installed; there's no newer one), manually reset and reconfigured
> the router, but the IP address I got is still the same! How is it
> possible?
>
> Thanks!
> Tom
>
>

Hi Richard,

Thanks for your quick reply; it all makes perfect sense now!

The reason I'm looking into this is I'm having connectivity problems
lately, so I thought this IP persistence was a sign of a faulty router.
Thanks again!
Tom

(E-Mail Removed) wrote:
> Hi Richard,
>
> Thanks for your quick reply; it all makes perfect sense now!
>
> The reason I'm looking into this is I'm having connectivity problems
> lately, so I thought this IP persistence was a sign of a faulty
> router. Thanks again!

If your router supports 100 MBit/s Full Duplex, set the NIC to that
explicitely instead of Auto. This seems to have fixed my "connectivity
problem". It was just with one particular machine/NIC that I had these
occaissional drop outs, the machine just disappearing from the LAN for no
obvious reason. Some EtherNet chips and/or drivers seem to have bugs still,
not detecting the link speed correctly and it doesn't help to troubleshoot
in the network layer.

Could be something entirly different in your case of course but it may be
worth a try.

Martin.

Thanks, Martin, I'll take a look; I do think it is set to Auto.

But I doubt this is the primary source of my recent problems: before
that, everything worked fine for years.

This is probably just a coincidence, but the problems started after I
ran Windows XP upgrade advisor on my NT4 box, and it found, among other
things, an incompatibility issue with the "3Com NIC diagnostic module",
or something like that. Now when I try to browse the Internet, I get
"DNS not found" errors all the time. I keep hitting Refresh button like
10 times, and then on the 11th try I finally get to the web page.
Tracert expires with "Unable to resolve target" message most of the
time, but when it does get through, it's painfully slow (although it
does return decent times, mostly well below 100ms).
Oh well, I'll keep trying...

Thank you!
Tom