manually forcing a IP renewal

Wade Smart wade at
Mon Nov 26 22:34:48 UTC 2007

11262007 1632 GMT-6

I use a sgb900 cablemodem by motorola and I have 22 computers on it. But 
  some cable companies limit the number of cpe's you can have. In my 
case - they do not.

We have done the ip release on windows though I cant see that that would 
matter. When the computer starts up with ubuntu it will still have the 
mac of the ethernet card.


Brian McKee wrote:
> Hash: SHA1
> On 26-Nov-07, at 4:06 PM, Derek Broughton wrote:
>> Brian McKee wrote:
>>>> When he removes this ubuntu computer and connect his Windows  
>>>> computer,
>>>> the windows computers gets a ip right away.
>>> I believe Windows does not release IP addresses  by default.
>>> Try ipconfig /release on the Windows box before you shut it down,
>>> then start up the Linux box and see if it gets issued something.
>> It's worth a try, but I don't believe it can make a difference.  As  
>> far as
>> the DHCP server is concerned, your computer has no OS.  All it sees  
>> is a
>> MAC address.  Since that is the same when you're running in Ubuntu or
>> Windows, you should (and I always do) get the same IP address from the
>> server
> Well, it's been a bit since I was poking at this, so I may be  
> remembering this incorrectly, but - the dhcp server in the cable  
> modem only has a limited number of addresses it will assign (two for  
> my local cable company) and if Windows doesn't release it's lease,  
> then there aren't any more available until one times out, or the  
> modem is power cycled long enough for it to erase it's existing leases.
> When he says the Windows computer gets an ip right away, in fact it's  
> just using the one it had when it shut down.
> You are right that the modem doesn't care what's plugged into it - if  
> he tried a new Windows computer it wouldn't work either.
> Some cable companies preprogram an allowed MAC address into their  
> modems and ask you for that address when you set up your account with  
> them.  That's why a lot of home routers have a option to assign MAC  
> numbers to their WAN port.   If it was something like that he could  
> flop ethernet cards between the Windows box and the linux box just to  
> prove it,  but that doesn't quite fit the symptoms he reports.
> Hope that makes sense,
> Brian
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