Getting new IP from DHCP?!?

Saifon · 24-10-2007, 20:12

Hi Folks

Was wondering if someone can help me with this one...

I'm periodically looking to get new IP's assigned to my cable modem. I had it working fine when I was on XP, I actually had a little program which simply released the IP and and renewed it.. and this would give me a different IP.

But alas my old PC finally died on me, and recently bought a new machine with Vista... but my little program does'nt work on Vista.. probably due to the introduction of IPv6..

What I am looking to do is to release the IP and get a new one.. but from command prompt.. or using a windows based utility.. I cant seem to get it working.. it releases it fine.. and my internet connection drops of course, but when I renew.. it simply assigns the same IP again..

I do manage to do it.. if I release the IP and phyiscally unplug my cable modem and plug it back in again.. and this automatically reassigns another IP... but I dont want to have to keep phyiscally unplugged my cable modem each time....

so does anyone know how do I force a new IP from DHCP by using command prompt or software only?... is there like a software command out there that will give my modem a physical reset without unplugged it?...

any ideas?....

Saifon

on in an hour! · 24-10-2007, 20:18

forgive my ignorance,but why do you constantly need to renew your i.p. address

Jon T · 24-10-2007, 20:20

The problem with your approach is how IP's are assigned by DHCP. Your IP is "leased" to you for a set period of time, and is also associated to you cable modem by MAC address.

Put simply, if you release your IP address, it goes back into the DHCP pool, when try to aqquire an IP adress again, if your old IP hasn't been taken then you will get the old one back as the DHCP server "remembers" your MAC address and creates an association between the two(IP and MAC).

Why do you want to perodically change you IP address anyway?

Saifon · 24-10-2007, 20:32

I understand that.. but when I renew and release when running XP.. it's not a problem.. I can get a new IP.. almost everytime... and it does sometime reassign the same IP... but that's only maybe 1 in every 10.. but I simply release and renew again (in XP that is).. and it will reassign another IP...

And in Vista.. I can get a new IP.. by releasing the IP.. and physically unplugging and plugging in again... and will always get a new IP... again in about 1 out of 10.. it may reassign the same... the only thing I'm trying to get is.. a software solution to do the same thing in Vista

I download files from sites like rapidshare.com or megaupload.com... but these files usually come in split form.... so sometimes it may require a few downloads to get one file... but after each download it requires you to wait 2 hours before you can download part 2... but a cheeky way around it is to change your IP.. that way you get the next part of the file without waiting....

Jon T · 24-10-2007, 20:38

You must live in a very busy(in the broadband sense) area, where any IP's that are released are snapped up straight away.

OS shouldn't make a difference(but for some reason it seem to in your case).

The best way of changing an IP address on cable broadband is by changing the MAC address of the network card that your using, this would then have the side effect of making you switch your cable modem of and on again to make it accept the new mac address.

Saifon · 24-10-2007, 20:46

ahh thanks.. might be on to something with the MAC address... I'll play with that.. and see how I get on.... but I always thought when assigning IP addresses, the DCHP... would just give out the first free available IP... regardless of your IP history... but I'm not really sure... but again.. might be also depending on ISP... hmm.. well.. anyways.. thanks for the info..

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