![]() If it doesn't work, you've either built it wrong or the CSU/DSU isn't working properly. If it does, you've successfully built the plug. Place the loopback plug into the T1 port and you should see the unit "synch" to itself by indicating either "Link" or having whatever is used for the WAN interface to show the unit now has sync. Test it on a "known good" router with a CSU/DSU (T1 interface). Put the Cat 5 end into the crimper and verify all of the wires are pushed all the way into the pin slots and then crimp it down.ĩ. ![]() You should now have 2 wires "looped" in the cat 5 blank end with pin 1 connecting pin 4 and pin 2 connecting pin 5Ĩ. Put one end of the second wire into pin 2 and bend it in half and put the other end into pin 5.ħ. Put one end of the first wire (either one will do) into pin 1 and bend it in half and put the other end of it into pin 4.Ħ. If you are looking at it this way, the bottom slot is pin 1 and the top is pin 8.ĥ. Identify the pin order on the Cat 5 end: hold it with the movable/press-side of the clip away from you and the metal contacts facing left. usually same colors (brown and brown/white, etc.)Ĥ. An Ethernet loopback plug is a tool that can help troubleshoot problems with network connection or to test the Ethernet cables and networking hardware. ![]() Cut off about 2 to 4 inches of a Cat 5 cableģ. For a diagnostic tool like this to be useful, it has to work 100% of the time, but this experience has shown that it's very flaky.1. Consult the equipment manual of the equipment being tested to determine if gigabit loopback is supportedįrom all my testing and research on this subject my conclusion is that unless you're dealing with exclusively ancient 100Mbps equipment, the loopback adapter concept is now obsolete due to advanced signalling in modern switches. The Gigabit Loopback Jack & Plug is intedned solely for testing systems where the Near End Crosstalk (NEXT) function can be disabled and the equipment under test can support being looped back to itself. Not all gigabit Ethernet systems support loopback operation. Gigabit switches may behave differently (but I’m not sure what the spec says or the real-world variation is)Īlso, even commercial loopback adapters come with a lengthy caveat regarding gigabit compatibility Meaning it’s often only useful on NICs which let you disable crosstalk detection. Gigabit NICs have crosstalk detection (detects how much signal interferes onto other wires), and will likely decide that the loopback is an extreme amount of crosstalk - any may not show link. Turns out "Gigabit loopback is a limited concept" so maybe 100Mbps works ONLY on 100Mbps switch? I could live with that if that's how that works, but what about 1Gbps loopback with 4 pairs? Why is that not lighting up?)Ĭan anyone shed some light on this? I just don't get why it's behaving the way it is. But maybe that's to be expected because that's also what happens when I plug in my other 2 pair 100Mbps RJ45 loopback. The other weird thing is that 1Gbps switch that's 100Mbps capable doesn't detect this at least as 100Mbps (I could live with it not showing up as 1Gig). I also tried several switches, and it's always the same: 100Mbps lights up, 1Gbps doesn't. I'm not new to crimping cables either, so I'm 99% sure I succeeded in crimping it well. I triple checked my pinout and I just can't get it to work. The obvious problem could be that I crimped the cable wrong, but now I'm on the 3rd one and I get exactly same frustrating results. 100 Mbps port on 100 Mbps switch lights up no problem.When I plug it into a 1Gbps port on 100/1G switch the port does not light up.
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