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ManOfSteel



Joined: 02 Feb 2005
Posts: 1154
ManOfSteel
Hello,

I have a problem with a cable modem. A PC is plugged to its USB connection and a laptop is plugged to its ethernet connection from time to time.

They both worked perfectly until I tried connecting another laptop through ethernet. The connection worked fine with the second laptop at first, but once I tried the first one again, the ethernet connection stopped working for BOTH laptops even though I hadn't changed any configuration on any of them.
Now I'm getting the "low or no connectivity" message and the "repair connection" doesn't fix anything. I tried uninstaling the ethernet NIC drivers on the laptops to reset any network configuration and then reconfigured everything, but it still doesn't work.

What do you think could be the problem. If you need any additional information, just ask.

Thanks in advance.
Post 24 Jul 2008, 17:37
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
Have you powered-off the modem between changes?
Post 24 Jul 2008, 17:42
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ManOfSteel



Joined: 02 Feb 2005
Posts: 1154
ManOfSteel
No. And it has no on/off button. The only way to shut it down completely is to turn off a UPS. I only did that after I got sick of the whole damn thing.
Post 24 Jul 2008, 17:54
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
So I suppose you gave the modem time to learn the new client MAC address.

If you use Wireshark do you receive some Ethernet frames at least? (an ARP storm is very common where I live for example even when the connection does not work).
Post 24 Jul 2008, 18:55
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ManOfSteel



Joined: 02 Feb 2005
Posts: 1154
ManOfSteel
It works again. After being down for at least 8 hours! What's happening?

Quote:
So I suppose you gave the modem time to learn the new client MAC address.

Does it normally take more than a few seconds?

Quote:
If you use Wireshark do you receive some Ethernet frames at least? (an ARP storm is very common where I live for example even when the connection does not work).

Shouldn't the connection status (tray icon) detect such traffic? Everytime I tried it, the "sent" bytes were just a few hundreds (that's very low) and the "received" bytes were 0.
Post 24 Jul 2008, 19:52
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
No, ARPs are not shown in the tray icon connection status.

About how much it takes to learn the MAC of the PC's network adapter I don't know but it shouldn't take much, but I do know that some modems needs to be powered-off when you plug it to another network adapter because it rejects frames with source MAC address that don't match that of the first seen frame and only allows to pass frames coming from outside that are either broadcast (like ARP requests) or unicast provided the unicast address is the address of the network adapter that the modem thinks it is yours.
Post 24 Jul 2008, 20:16
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ManOfSteel



Joined: 02 Feb 2005
Posts: 1154
ManOfSteel
Ok, thanks for the information.

Quote:
some modems needs to be powered-off when you plug it to another network adapter

The manual isn't very clear about this but I guess it may be one cause of trouble.


I found a page that may explain why the problem was solved just by waiting: http://homepage.ntlworld.com/robin.d.h.walker/cmtips/swap.html
Quote:
With some ISPs, it appears that, although resetting (or power cycling) the cable modem is enough to clear the table of learnt MAC addresses in the cable modem, it is not enough to force the ISP's DHCP server to lease an IP address to the newly connected PC. It is suggested that, before the first PC is disconnected from the cable modem, it should explicitly release its DHCP lease.

If even that is not enough, it might be necessary to wait (with the cable modem powered off) for the expiry time of the original DHCP lease (this is no longer necessary on the NTL network).
Post 25 Jul 2008, 05:43
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