How likely is it for cables to degrade, and destroy a wired connection?

[VirtualLarry]

I was called today this afternoon earlier to help one of my friends, his internet connection was down. He is in a house, with multiple people living there. His connection is fed over from another room, using some sort of switch or hub, and then the connection from there is wired through a heating duct to upstairs, into the "computer room", where the connections all pool into a 16-port linksys switch (about 7 ports used), and then uplinked to a Trendnet 652 router, and then connected to a cable modem.

I am the one that installed the 16-port 10/100 switch and the trendnet 652 router, previously they had a netgear 8-port wired router, that worked, but was dying and was bottlenecking their connection, since it only had about 8Mbit WAN-LAN bandwidth, but comcast increased their connection from 6Mbit to 12Mbit.

Well, the first thing I suspected, was that the TrendNet router was refusing to send out an IP address, as it had been known to do when I first installed it. (For some reason, it would abitrarily refuse to give out IP addresses to certain MAC addresses.) To fix this, I had to go into the static DHCP list and add the MAC address. This of course was no gaurantee that the associated MAC address would actually get the assigned IP address. Oh no, thanks to the wonderful TrendNet firmware, sometimes nodes would show up, having TWO different IP addresses. Let's just say DHCP is buggy on this router. But at least adding to the Static DHCP list, seemed to guarantee that the node would get at least one IP address, and thus be able to access the internet.

Well, I went and checked his machine, and the router, and it seems that he did have an IP address. But nothing was connecting. Ping www.google.com returned a timeout.

So I shut his machine down, went into the router and added his MAC to the static DHCP pool, and then restarted his machine.

IPCONFIG /all returned that he had an IP address. Ping www.google.com returned an IP address, and then the first ping returned, but the last three didn't.
Going to the web browser, I was able to pull up www.google.com using the IP address returned by the ping, and I was able to pull up the router config from 192.168.0.1, but that was all.

Subsequent pings failed.

In the end, we ended up plugging in a USB wifi dongle and using that, he gets 1-5.5 Mbit/sec connections, from the wireless router upstairs.

My diagnosis was that whatever device he had his connection plugged into in the other room was failing. It didn't seem to be a software problem, and the fact that the connection was there, and then it wasn't there, seemed to indicate some sort of physical-layer problem. Does this sound correct?

 

[Emulex]

mismatched duplex or speed will definitely give crappy results. how the pc or router handle that scenario could be random.

 

[Fardringle]

How is the cable "fed" from the room with the switch to the room with the PC? If it is in a traffic area where it could be regularly bumped, kicked, stepped on, bent, etc., then it could be damaged and that would definitely cause connectivity issues.

 

[spidey07]

It happens all the time. Especially with what Fardringle described.

 

[VirtualLarry]

Well, I fixed it. Or rather, my friend fixed it with some parts that I supplied. I was correct in diagnosing that whatever device the friend had plugged into that connected to the wire that runs upstairs had failed. Replaced an 8-year old hub with a brand-new 10/100 switch, and things are good to go again.

I just double-checked, and the good news is, replacing that hub, which was probably 10Mbit, with a 10/100 switch, has allowed the connection from downstairs to upstairs to be upgraded to 100Mbit. Since the cable internet is 12Mbit (plus powerboost), that 10Mbit connection was a bit limiting. I originally thought that the reason the downstairs link was 10Mbit, was because the end of the cable was spliced, instead of just crimping a new end onto it (don't ask me, I would have just replaced the end), and perhaps the wiring on the crimp was fubar, so it was only able to carry a 10Mbit signal. But apparently not true, with replacement of the downstairs hub with a 10/100 switch, now they have a 100Mbit connection downstairs.

 

[Lemon law]

And even as VirtualLarry solves the problem and discovers its not cable termites, its still possible for cables to have problems due to bad initial splicing and crimping. In such cases, the usual diagnostic is to wiggle the cable and see if that kills the connection.

If the wiggle test fails at either end, you are probably barking up the wrong tree, as our OP discovered.