Connection showing 100mbps instead of 1Gbps, help

Hey all, so a couple years back I wired my home using Monoprice CAT6 cabling. Everything was peachy, or so I thought. So yesterday I got ATT Fiber installed and realized that the connection speed from my Router (or now the ATT Router/Modem) to my Switch at the other end of the cable was showing 100mbps instead of 1Gig.

To see what the issue was I disconnected the Switch (its a Trendnet S80g by the way) and moved it close to the ATT Modem/Router with a new cable and it lit up as 1Gbps. I did the same but plugged the switch into my Netgear R7000 and both the router and switch lit up to indicate 1Gbps. I even tried another switch I have (Trendnet S50g) back on the original attic routed wire and showing 100Mbps.

So at this point the best I can think its one of 3 issues. The wall terminal where the wire goes to my router, the wall terminal where it goes to the switch, or the cable itself. What I'm having trouble understanding is the cable is the same spool I have been using for years. In fact I asked ATT to use it instead of the CAT5 they wanted to run when doing the fiber install. It shows up as 1Gbps for all the other runs but this one. Could it have gotten knicked to cause it to slow down somehow?

I suppose getting new terminals and rewiring the ends is pretty easy so worth investigating first but just odd that this isnt giving me the speeds I would expect. Lastly, incase I didnt mention since they are keystone jacks (terminals), I did verify the additional cables used were also lighting up as 1Gbps to rule them out.

Not sure if I'm missing anything but figured Id run by the experts before I went thru the pain of rerunning the CAT6 thru the attic. Thanks all

I'd check the connectors (keystone jacks at the wall and such) first. That's the most likely culprit. There could be some other interference causing it to negotiate down to a lower speed too, like if you have a long run next to a noisy power line, or just too long of a run to start with.

It could be a nicked or pinched cable somewhere as well, but that's going to be hard to troubleshoot unless you have some good test gear. You can test continuity pretty easy, but anything else is a challenge.

Thanks for the response. What would be considered a 'long run'? Id have to guess this is something like 100 ft between the two vertical walls and then in the attic to the other room.

RoachForLife said:

Thanks for the response. What would be considered a 'long run'? Id have to guess this is something like 100 ft between the two vertical walls and then in the attic to the other room.

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Well, the official spec for gigabit is 100m. So as long as you're under that it should be OK. That being said, it depends largely on the quality of cables and connectors. If everything is PERFECT, 100m should be no problem. If you've got a noisy run next to power lines, or low quality punchdowns/jacks, or just poorly-finished connectors, then you could see this problem too.

Technically 100mbps uses only SOME of the wires in the CAT5/6 cable, and 1Gb uses all 4 pairs. So a bad connector is very likely, since if just one pin is loose, 100Mbps would work fine, but 1Gbps would not. Again, it could also be physical cable damage, but the connectors are where I'd go first.

Ok great, this gives me hope. Maybe I did a shoddy job on the keystone jacks when I installed (and of course never cared to even verify until now lol).

Rerunning the line in the attic isnt the end of the world but a much bigger pain in the ass for sure
Thanks!

I have multiple runs of Cat5e 100m doing Gigabit at customers laying next to 128Amp lines without any problems, unless you live inside the Chernobyl plant i would think you got an bad keystone connection.

Check to make sure the cables are terminated correctly. You need all 4 pairs for gigabit and if one pair is off it will negotiate at 100mb. I'd especially double check it if ATT is the one who installed it.

Hey all, so it was in fact one of the two keystone jacks that was the issue. Redid them both but noticed after the 2nd one the lights on the devices went to 1Gbps so good deal. Thank you all for the comments and help!

RoachForLife said:

Hey all, so it was in fact one of the two keystone jacks that was the issue. Redid them both but noticed after the 2nd one the lights on the devices went to 1Gbps so good deal. Thank you all for the comments and help!

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yup, you only need 4 wires for 100mbps.... need all 8 for 1000mbps.... which means it was pretty high chances it was your jack terminations... you had a 50% chance of it not working at all

RoachForLife said:

Hey all, so it was in fact one of the two keystone jacks that was the issue. Redid them both but noticed after the 2nd one the lights on the devices went to 1Gbps so good deal. Thank you all for the comments and help!

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Cool.

Been crimping network jacks on wires for 25+ years, and still run into the occasional bad crimp, even with a $200+ ratcheting crimp tool. Glad you kicked its ass.