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Old 09-02-2013, 10:34 AM   #1
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Default Network Issue

I have 2 rooms I look after at the place I work. I have recently found a problem in which 2 of the computers in the room in random areas cannot connect to the network. They will also not accept static IP's. If I however move them to the other room down the corridor, they work fine and connect automatically.

Any help appreciated.

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Old 09-02-2013, 12:38 PM   #2
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Default Re: Network Issue

Depending on how many machines you have, and how many hierarchies of network switching, you could have overflowed an arp table somewhere (but that is quite unlikely). That would really affect the routing between machines though, rather than the ability to assign an IP to any given machine. If it literally fails to accept the address (e.g. 'ifconfig eth0' as root on linux), then I would consider that a fault with that machine.

I assume by 'random areas' of the room, you mean this occurs on distinct, otherwise unrelated machines. This is what led me to believe it isn't a host-configuration problem, but a subnet address space availability problem.

I hope that helps a little, or provokes some useful though. Good luck.

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Old 09-02-2013, 01:09 PM   #3
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Default Re: Network Issue

Thanks for the reply.

The switch itself has been working fine for a few years, no problems with running this amount of machines.
By area I mean whichever Ethernet port I connect to, I still get the same error with the 2 machines. Any other machine works in in any other position.
The strangest part is like I say when I take it to another room, connect it to the Ethernet cable with automatic IP config, it connects to the network/domain instantly.

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Old 09-05-2013, 09:54 AM   #4
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Default Re: Network Issue

So you machine machines 1 and 2 (the problem machines) and machine 3 can represent any other machine as they all work

then you have switch 1, in room 1 and switch two in room 2.

if you connect machines 1 or 3 to any port in switch 1 then, they don't work (unable to connect to the network)

however machine 3 can connect to any port.

(e.g connect machine 1 to switch port 1 = fail, connect machine 3 to switch port 1 = success) -so the tests are done using the exact same port?

but down the hall you can connect machines 1, 2 or 3 to the switch and it works fine?

here are the questions...

1, Is that assessment correct?

2, What structured cabling are you using? (e.g you have a floor or desk network port, that has a cable going round the room back to the patch panel, then a cable from that going to the switch?)

3, Have you tried connecting the machines directly to the switch with just a long patch cable? (did you see similar results for machines 1, 2 and 3?)

4, Are the machines the same? (same make and model)

5, Are the network cards the same, (are the card in machines 3 and up (the ones that work different) -it could be that you have a cable problem such as an accidental crossover, newer cards have auto MDX (so you don't even need a crossover cable to connect machines directly to each other) whilst older cards don't.

6, What is the variety of switches that you are using? (and are they the same in both rooms) (e.g. cisco 3750)

7, Are they managed switches?

8, If they are managed switches, what is the config applied to each, (e.g. do you have an access rules or VLANs setup or 802.1x that might be rejecting the network connection from these individual machines)

9, When you plug either machine 1 or 2 (the ones that don't work) in room 1, what happens with the activity lights, (are they green/orange etc?)

10, What happens with the activity lights on the network cable connection when plugging in the machine in room 2.

11, Is it the same domain (e.g. company.com) that the machines are connecting to?)

12, Is it the same network address that the machines that work get (e.g 192.168.1.x in each room) or do the machines get 192.168.1.x in room 1 and 192.168.2.x in room 2? (the machines that work of course)

13, What are the addresses that they get (e.g 192.168.x.x 172.16.x.x 10.x.x.x)? what about the subnet mask? (e.g

14, What happens when you plug machine 3 in at room 2 (does it work?)

try taking the questions 1 at a time, you might find that in getting the answers to those questions you actually figure out what the problem is.

(I'm guessing either a broken cable in the structured cabling, or a managed switch setup that has some port authentication set up that these machines are not a part of)
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