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Old 09-07-2007, 04:30 AM   #1
nx5000
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No dhcp offer on cable modem


Hi
Maybe somebody can help here, my problem gets me nuts.
I go to a friend who has cable modem (and an ipv4to6 tunnel). I have never had cable modem so I'm a bit lost. Maybe somebody who has cable link can help me.
He has XP and he gets his adress by DHCP.
I tried to replace it with my laptop running debian.
When starting the dhcp client and a network analyzer, the only thing I see is:

dhcp discover from 0.0.0.0 (me) to 255.255.255.255 id X
lots of arp who has (broadcast) <- that's cable yes
dhcp offer from 1.2.3.4 (cisco) id Y <-- some people get an offer
dhcp ack from 1.2.3.4 (cisco) id Y <-- and they really get an IP

Unfortunatly never an answer with id X so my dhclient never gets anything.

I tried tweaking all the obscure timeouts of dhcp but no way, the damned thing doesn't like me.

Next I started FC7 live and same thing (appart from the fact that fc7 tells me oh yeah you're connected while in fact I'm not.. wrong information)

I also started the XP again and released the lease, thinking the dhcpserver doesn't want to assign another one while one is still attributed (?)
ipconfig/release *
ipconfig/all then shows that everything is released.

Plugged the debian again, nothing.
Plugged the fc7 again, nothing.

Geeettts me nuts. Even more when my friend looks at me and says:
"See, I plug my xp and I have nothing to do, it just works"

Could it be that my dhcp frames contain wrong info?
Maybe I should install a sniffer on his xp and compare my frame?
Or something wrong with the 4to6 tunnel (I am a bit in the dark with ipv6)?
I have no firewall btw.

Any idea or experience very welcome!

Last edited by nx5000; 09-07-2007 at 04:32 AM.
 
Old 09-07-2007, 08:23 AM   #2
choogendyk
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Who's the cable provider?

Did you try turning the cable modem off, waiting a bit, and then turning it back on again? Maybe followed by starting up your laptop (not having it started or connected when the cable modem is turned back on)?

I'm on Comcast (actually Earthlink subcontracted to Comcast), and I sometimes (but not really very often) have to do that.

I just set up wireless with a linksys wrt54g for my daughter through her landlady's Comcast cable connection. The landlady had an XP computer and has a cable modem with telephone over IP and built in battery backup (double). It was a real voodoo trip. I couldn't turn off the cable modem because of the batteries. I didn't want to mess too deeply, because her house phone was plugged into it, but I just couldn't get an IP on our Mac laptop. Finally, I had the linksys clone the ethernet address of the XP computer. It still didn't work. Then I booted up the XP computer, and at some point the linksys got its IP and then our Mac laptop got its.

I was wildly guessing that Comcast had the account locked into the one ethernet address and somehow the XP computer had to speak through the connection to get something coming back that would work. But I admit it felt like voodoo, and I don't really feel comfortable with any logical explanation of what was going on.
 
Old 09-07-2007, 08:54 AM   #3
sunils1973
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I have just installed debian etch in my AMD sempron machine. I am also using cable modem. I didn't faced any problem for the net connection. Just installed debian and i am getting the net well.
 
Old 09-07-2007, 11:08 AM   #4
nx5000
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Quote:
Originally Posted by choogendyk View Post
Who's the cable provider?
I'll have a look. It's in germany. First time I see ip4to6 for home users.
Quote:
Did you try turning the cable modem off, waiting a bit, and then turning it back on again? Maybe followed by starting up your laptop (not having it started or connected when the cable modem is turned back on)?

I'm on Comcast (actually Earthlink subcontracted to Comcast), and I sometimes (but not really very often) have to do that.
I did it a week ago when I went to my friend but I didn't do it yesterday. Thanks for reminding me to do this!
Quote:
I just set up wireless with a linksys wrt54g for my daughter through her landlady's Comcast cable connection. The landlady had an XP computer and has a cable modem with telephone over IP and built in battery backup (double). It was a real voodoo trip. I couldn't turn off the cable modem because of the batteries. I didn't want to mess too deeply, because her house phone was plugged into it, but I just couldn't get an IP on our Mac laptop. Finally, I had the linksys clone the ethernet address of the XP computer. It still didn't work. Then I booted up the XP computer, and at some point the linksys got its IP and then our Mac laptop got its.

I was wildly guessing that Comcast had the account locked into the one ethernet address and somehow the XP computer had to speak through the connection to get something coming back that would work. But I admit it felt like voodoo, and I don't really feel comfortable with any logical explanation of what was going on.

Yeah last time I also tried to hijack some IPs of poor people (only for seeing my email!!) but noway Changed also mac adress to the XP but noway.

Ok I'll make some new voodoo incantations next time I go there.
 
Old 09-07-2007, 11:19 AM   #5
rickh
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May cable modems these days are also routers. The router should be handling DHCP. I assume you have verified that the NAT firewall normally built into routers is not somehow blocking unknown machines ... like yours.

It would not surprise me to find that default firewall settings by the provider would reject any computers other than the one they originally configured.
 
Old 09-07-2007, 11:38 AM   #6
nx5000
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Quote:
Originally Posted by rickh View Post
May cable modems these days are also routers. The router should be handling DHCP. I assume you have verified that the NAT firewall normally built into routers is not somehow blocking unknown machines ... like yours.
No, you assume wrongly
As I said, I played with mac adress but no luck. I also did some
Actually she has something like 3 boxes installed, it's a very strange stuffs, I've never seen this. It was installed by his father who is working in telecom networks. Unfortunatly he's not there anymore.. The modem/router or modem is a very old stuff, that's really funny it still works.

When you arrive in a new network and you have not one information; how do you want to connect on the router! I have not any IP, nothing. And this + the fact that there is a local 4to6 tunnel doesn't help me _that_ much (there are actually 3 connections for one wire!). I know pppoa (router), pppoe (modem-bridge) but never had cable.

Quote:
It would not surprise me to find that default firewall settings by the provider would reject any computers other than the one they originally configured.
I'll make a mess next time I visit my friend :-]

Thanks rickh
 
Old 09-07-2007, 04:26 PM   #7
nx5000
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Quote:
Originally Posted by choogendyk View Post
Did you try turning the cable modem off, waiting a bit, and then turning it back on again?
THAT'S IT!!!
Eventhough I used to do this at home for pppoe to get a clean connection, I didn't think of it this time, I only did off followed by on.
Now I let it off 5 minutes and bingo on restart I got an answer.

Many thanks!!!

Actually it's a modem "scientific atlanta" and no clue whos the provider
 
  


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