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force new IP

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April 21, 2002 3:18:34 AM

I am new to the networking game so I'm playing around with somethings to try to learn more about it... I figured out how to get into my cable modem through http, but I can't seem to make any changes (that I know of). My question is:

How can I force my Surfboard 4100 cable modem to let go of my IP address and obtain a new one? or is that controlled by the lease from the CISP?

My objective is to have my IP changed when/if I want to change it... I'm running WinXP and have changed the IP to another (simply upping the last three digits a coupla numbers) but it doesn't seem to work. As a matter of fact, I even put in the exact same IP, Subnet Mask, Default Gateway, DHCP Server, and primary and secondary DNS numbers but it wouldn't connect unless I let WinXP make the decisions...

Anybody care to school me?


Thanks,
Ret

More about : force

April 21, 2002 3:46:05 AM

The cable company gives you the IP, not the other way around. You have to use that or you don't have access.

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April 21, 2002 1:19:10 PM

I thought that since it was dynamic I could let it go and a different one would come back?


Ret
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April 21, 2002 2:13:57 PM

Yea dynamic enough to assign you the same IP everytime =), my cable actually gives out different IPs to different MAC addresses. So my router gets a different IP than when i hook up straight to the PC.

If you think it is otherwise, just reset the modem and find out if it's different.

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April 21, 2002 2:20:46 PM

Hehehe.. yea, that is my problem.. I've reset it and the same one comes back... I understand it has something to do with having a lease on it. Hmmm.. so, with what you know, I'd have to change the MAC address in order to get another? So that would mean changing the cable modem, eh? What about changing the NIC? or is that a whole other unrelated issue?


Thanks for your knowledge,
Ret
April 21, 2002 2:26:57 PM

No, just changing the NIC in the computer...that's how mine works anyway. I'll test mine out in a sec hehe.

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April 21, 2002 2:50:57 PM

Yup it worked that time too, got 3 different IPs. 2 NICS and a router.

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April 21, 2002 2:57:50 PM

Yea, but I think the cable company only sees the router IP, eh?



Ret
April 21, 2002 2:59:27 PM

Not using the router.

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April 21, 2002 3:00:13 PM

Or I should say not when I am using the NICs.

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April 21, 2002 3:11:56 PM

Hmm... so if I change my NIC it will change my IP?

Ret

<P ID="edit"><FONT SIZE=-1><EM>Edited by Retruglot on 04/21/02 11:12 AM.</EM></FONT></P>
April 21, 2002 3:16:15 PM

Depends on how your ISP handles it, I can only say for sure that it works for mine. Cox HSI.

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April 21, 2002 3:28:42 PM

Cool.. seems like a long way around the horn.. but I'll give it whirl after while and see what happens. Thanks for the schoolage.


Ret
April 21, 2002 3:44:42 PM

if you're just looking to play around, why not get a router? Then you can play to your hearts content.

<i>It's always the one thing you never suspected.</i>
April 22, 2002 4:46:08 AM

why do you want so bad to change your ip address? if you are worried about some one hacking you, changing your ip every couple of days isnt going to help you. get a firewall.

ccna+mcse=debt4life
April 22, 2002 7:15:17 PM

The reason why you get the same ip address when you reconnect with the same NIC is that the DHCP server (at your ISP) is retaining your NIC's built in MAC address. Real DHCP servers (unlike the versions found in cheap routers or within Windows) let their administrators control the lease and disconnection-timeout length's so they can allow you to disconnect and reconnect with the same ip for up to the lease time. Some high-end server NIC's will let you manually change a portion of the MAC address (not the whole address) but this feature isn't available on any single port NIC's that I'm aware of as it's almost never needed.

As far as choosing (guessing) your own new ip, you might get lucky and pick an address that is available and valid for your ISP's network, but you can't use only half of the DHCP client. That means that you might manually pick a good address, but you can't have DHCP assign the DNS addresses for you. You would have to set them manually as well. That's a bad idea unless you're certain of the exact addresses and know that they will never be changed.

"There are no mysteries with computers...just fix it you idiot!" (R. Warren 1909-1990)
April 29, 2002 11:59:16 PM

Thanks for the low down.. I wondered if other addresses had to change when I manually picked the next IP and it didn't work.

Well, as to "why do you wanna do this?" - Basically I am pretty comfortable breaking and fixing PCs, but I don't know anything about Networking... so when my IP was banned from a BBS (ezboard) for challenging the admin's Law I decided it was the perfect opportunity to learn and stroke my ego at the same time... hehehe.. however, I've not desired the ego stroke enough to change the NIC yet..

Which brings me to my next question.. can I put 2-3 NICs in the PC and just plug the cable modem into a different one to get a different IP? (since it will have a different MAC?). Or will multiple NICs freak it out?


Thanks for the lesson's people.. I always know I can find an answer here at the THG Community.


Ret
April 30, 2002 4:00:17 AM

i think the ip is based on the mac address of the cable/dsl modem. some isp only want you to have one computer use the connection so they only allow one internal mac to get outside the modem.

you shot who in the what now?
April 30, 2002 6:04:46 AM

Mine gives me a new number per MAC as I said above =).


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April 30, 2002 6:05:29 AM

No it won't wig out, you'll just have a little icon on your system tray saying it's not plugged in.

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