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Strange networking problem.

Old 02-01-07, 10:55 AM
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Strange networking problem.

I work for a telco and install high speed internet. I have a customer that has two computers that are wired to a router and that is connected to a DSL modem. Everything has worked fine until a week ago. Now neither computer will obtain an IP when both computers are hooked up to the router. But when you only have one computer hooked up they obtain an IP and the internet works. I have changed the NIC's in both PC's. I have changed the router and the DSL modem. I have cleared out the IP settings in both PC's. The problem still persists. It even does it when I hook my laptop up. What else can I do? Could it be a problem in the DSLAM? I haven't tried changing ports on it yet but I have not ran into this problem before. Thanks for any help.
Old 02-01-07, 12:11 PM
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Just stepping back through what you said

- problem only occurs when both machines are connected to the router

- you changed NICS in both machines and connected your laptop (which assumed is know working)

- You changed the router - *** this is the most important here to me

Then you ask
Could it be a problem in the DSLAM?
To answer this question, disconnect the Ethernet cable going to the DSL modem, the router should still issue IPs out to each client connected whether the DSL connection is there or not. Assuming it is the router doing the DHCP (and it should be)

I know you said you changed NIC cards, I was going to say make sure there is not a duplicate MAC address anywhere (it use to be that this was not possible, but these days it is) but I think you covered that, may want to double check (ipconfig /all will give you MAC info) This is about the only thing that comes to mind for this problem.


You might even want to check the DHCP config, see if it will allow you to reserve an IP per MAC address (most do, some don't), get the MAC of each machine and do a DHCP reserve with a separate IP for each.

You would really need a packet sniffer online to figure out the finer points.

Last edited by 4KRG; 02-01-07 at 12:14 PM.
Old 02-01-07, 07:41 PM
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Originally Posted by 4KRG
J

To answer this question, disconnect the Ethernet cable going to the DSL modem, the router should still issue IPs out to each client connected whether the DSL connection is there or not. Assuming it is the router doing the DHCP (and it should be)

I know you said you changed NIC cards, I was going to say make sure there is not a duplicate MAC address anywhere (it use to be that this was not possible, but these days it is) but I think you covered that, may want to double check (ipconfig /all will give you MAC info) This is about the only thing that comes to mind for this problem.


You might even want to check the DHCP config, see if it will allow you to reserve an IP per MAC address (most do, some don't), get the MAC of each machine and do a DHCP reserve with a separate IP for each.

You would really need a packet sniffer online to figure out the finer points.

Ok I'll try all of the above. Thanks!

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