IP Address Problems

Michael J. Lynch mlynch at gcom.com
Mon Jan 9 21:44:04 UTC 2006

dan wrote:
> On 09/01/06, Michael J. Lynch <mlynch at gcom.com> wrote:
>>dan wrote:
>>Ok..first of all are you using static or dynamic IP addresses?
>>If dynamic, your ISP's DHCP server is what assigns the IP address
>>and that's the address you should use regardless of what it is.
> Thats what I thought, but I got a phone call this morning saying that
> every time I connect my computer is assigned a new IP address (looking
> through syslog shows the lease to be ~8 days).  I connect a half dozen
> times a day and supposedly the bloke in charge gets an email every
> time a new address is used and I am using up the avaliable
> addresses...
> But I have been connected to the same network since October 2005, and
> supposedly this has only been happening in the last few weeks or so,
> so I think someone has done something they shouldn't have.
If no changes have been made to your machine and this has just *started
happening*, then I suspect your ISP changed something and that is the
source of the problem.  If your end has alway been functioning the way
it currently functions, it may be that your ISP has updated something
and is now able to detect the problem.

What does your /etc/network/interfaces file look like.  Post it if
there isn't anything you consider a security risk.

I your system is trully configured to use DHCP assigned IP addresses,
then your ISP's DHCP server is what assigns the addresses.  If it is
not obeying it's own lease durations and assigning you a new IP address
each time you log on, the problem is on their end.  That being said,
the DHCP server *will* give you a differenct IP address if your MAC
address is different.  Since you said something about spoofing MAC
addresses, this may be the source of the problem.  Especially if you
are using a different MAC address each time.

>>If static, the file /etc/network/interfaces is what assigns your
>>IP address.  Just change this file if you want to change your IP
>>address.  Use "ifdown" to take your interface(s) down and "ifup"
>>to bring interface(s) up.  BTW - Your ISP is what assigns the IP
>>address you should be using here too.
>>Spoofing a MAC address is also done via the /etc/network/interfaces
>>file.  Try:
>>        man interfaces
>>        man ifup
>>        man ifdown
>>These will show you how to do all of what you want *properly*.
> Thanks for the info; that's the last time I trust wikipedia ;-)
>>There is no need to deconfigure eth0 before shutdown.
> If I dont and leave the cable plugged in, it connects and gets the
> "wrong" IP address, and the tech support emails inbox gets filled up,
> I get a phone call etc.
> Dan
> --
> http://www.danicity.co.uk

Michael J. Lynch

What if the hokey pokey IS what it's all about -- author unknown

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