Not always connecting at proper LAN speed (10Mb to 1Gb)

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thewhat

Member
May 9, 2010
186
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PC with motherboard GA-P55A-UD4.
Router WNR3500L.
Cable: 10m Cat 6 (At least I think so, it was cheap from ebay).

As far as I remember it used to work at the rated 1Gbit speed about a year ago.
Nowadays it can work at anything from 10Mb to 1Gb.
Most of the time it's at 100Mb. Then I disconnect the cable at the router and plug it back in and, with some luck, it's working at 1Gb (also indicated by the green light on the router as opposed to the orange one for 100Mb).
But lately it started working at 10Mb and I really don't know what's going on. It also takes a while to establish the connection at Windows startup.

What I tried:
Disconnecting/reconnecting, turning stuff on/off.
Various ethernet drivers on the PC.
Two different BIOS versions on the PC.

I didn't yet try with a different cable, for logistic reasons.
I think I also upgraded the router firmware in the mean time, but I'm not 100% sure.


Any ideas?
 
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Geofram

Member
Jan 20, 2010
120
0
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Have you tried a different NIC? If you have a old PCI gigabit card, you can plug it in, and see if the connection is stable at a gigabit. If it is, you know the problem is your motherboard's onboard NIC.

If you put a different card in and see the same results, you know the problem is not in the computer - could be a bad cable, or something wrong with the ports, etc.
 
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seepy83

Platinum Member
Nov 12, 2003
2,132
3
71
thewhat said:
I didn't yet try with a different cable, for logistic reasons.
Click to expand...

Overcome whatever logistic problems are preventing you from replacing the cable, because there's a very good chance that it is the problem.
 
T

thewhat

Member
May 9, 2010
186
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I haven't tried with a different NIC yet, I don't have one available. But thanks for the suggestion.


Oh and I also tried plugging into different Ethernet ports on the router. Doesn't make a difference, the same problem happens on other router ports with this PC (and cable).
Other PCs (and cables) seem to always work at 1Gbit speeds in all ports, but I didn't try all combinations.

So if (!) I were to rule out the router, it's either this PCs NIC or the cable. But would it even make sense for a faulty cable to work at different speeds so randomly?
 
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thewhat

Member
May 9, 2010
186
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Not saying you guys aren't right when you say it's the cable, but I'm curious (looking for an explanation)..

Wouldn't a damaged cable have a "missing" connection on one or more of the wires and then always perform at the same reduced speed?

The cable wasn't touched at all between the changed speeds. Sure, I guess there's always the micro movement which happens even without touching the cable.

But let's say we exclude even the micro movements, would the speed changes still make sense?
 
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B

Binky

Diamond Member
Oct 9, 1999
4,046
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81
I'm far from a networking expert, but my understanding is that the two connections are negotiating the best connection they can, given the current link quality. Lan speeds of 1-100 only use four of the eight wires, but gigabit lan uses all eight wires. Gigabit needs a cleaner connection, and the NIC's will fall back to lower speeds if they have to. Gigabit is also much more sensitive to the wire used, how you terminated it, how you ran it, interference, and cable length.
 
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thewhat

Member
May 9, 2010
186
6
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So the link quality would have to be changing for the connection speeds to change, right? So there would have to be tiny movements that change the link quality, right?



Follow up:
In the last days it was always connecting at 10Mb. Moving the cable around didn't help. I also noticed a specific pattern when I was plugging the cable in:
1. it takes a while to connect (for the X to disappear from the icon), about 3 retries (with that spinning circle), about 10 seconds for all 3.
2. after that it often shows the "no internet" (! symbol) for about 5 seconds
3. after that it's finally connected normally (but at only 10Mb)

So I brought a second PC to the same room for testing.
I plug the cable in and it connects at 1Gb instantly. So I thought the cable must be ok and it's the first PC (NIC) that's bad. I then plugged the cable back into the first PC and it also connects at 1Gb instantly. Unplug, replug, always 1Gb.
It's as if plugging it into a second PC helped the connection. It's not the first time that I see this, it happened before when I plugged the cable into a laptop for a while (but I thought it was just coincidence).


Bottom line: I have serious doubts that it's the cable. Unless I'm missing something here regarding how this works or the micro movements of the cable are playing some funny tricks on me.
I'm more inclined to think that the connection on this PC gets 'degraded' over time for some reason..



edit: I just now noticed that the BIOS has a "Smart LAN" utility, which is supposed to show if there's a problem with the cable and it tells you the status of the connection. Right now it's not showing any problems with the cable, it's showing 1Gb speed and the cable length as 29m (way too much - could it mean anything?). I never tried this utility during the problematic moments, tho.
 
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Phynaz

Phynaz

Lifer
Mar 13, 2006
10,140
819
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14 days later, you are still trying to figure stuff out, but not taking the first troubleshooting step that everyone has told you.

Why ask if you're not going to listen?

Anyway, do this. Setup both your PC and your switch to not auto negotiate. Fix them both to 1gps, full duplex. Your connection will still be crap, but you'll be connected at 1gps.

The reason for the above is because even in a fully working system (which you don't have) auto negotiate sucks.
 
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thewhat

Member
May 9, 2010
186
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Phynaz said:
14 days later, you are still trying to figure stuff out, but not taking the first troubleshooting step that everyone has told you.

Why ask if you're not going to listen?
Click to expand...
Oh, I do listen.
But, as I kinda hinted at in the OP, replacing this cable is a huge challenge. I didn't emphasize that enough, but trust me that it is. I would want to be not 99%, but 100% sure that it's the cable before I venture into that.

And frankly right now I'm not nearly that sure, in fact I'm very much suspecting it's something else. I'll have to wait for the problem to reoccur to test my suspicions.
 
gsaldivar

gsaldivar

Diamond Member
Apr 30, 2001
8,691
1
81
If possible, run a huge jumper (pick up a spool of cable and run it down the hallway etc.) and route your traffic across the new cable to see if the problem disappears.

Good luck.
 
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seepy83

Platinum Member
Nov 12, 2003
2,132
3
71
thewhat said:
Oh, I do listen.
But, as I kinda hinted at in the OP, replacing this cable is a huge challenge. I didn't emphasize that enough, but trust me that it is. I would want to be not 99%, but 100% sure that it's the cable before I venture into that.

And frankly right now I'm not nearly that sure, in fact I'm very much suspecting it's something else. I'll have to wait for the problem to reoccur to test my suspicions.
Click to expand...

Well good luck to you. It sounds like you might be operating with cabling that is outside of the Category Specifications. A "cheap from ebay" cat 6 patch cable could definitely have bad terminations. Plus, since you have such overwhelming logistical issues with replacing the cable, I imagine that it was pulled through walls where solid-core cable should have been used, or it's being crushed by a piece of heavy furniture that you don't want to move...maybe it's even run next to a heavy piece of manufacturing equipment that's putting out too much EMI.

If you follow category specs, then there are very simple steps to follow to troubleshoot the physical layer. Once you have swapped out patch cables and re-terminated jacks, if the problem persists then you can be pretty confident that either your NIC or switchport are bad or misconfigured.
 
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