a strange UTP cable story
-
I have a router and two PCs connetced to it via UTP crossed cables. It all works fine. Both of the PCs can see internet. When I switch the cables, one of the PC's is not connected to the network. No green light on the card. When I switch the cables back, both of the PCs are fine again. Both of them on Windows XP. One cable is 3 meters long, the other 25 meters, that is the only difference. Any idea please? Vaclav
-
I have a router and two PCs connetced to it via UTP crossed cables. It all works fine. Both of the PCs can see internet. When I switch the cables, one of the PC's is not connected to the network. No green light on the card. When I switch the cables back, both of the PCs are fine again. Both of them on Windows XP. One cable is 3 meters long, the other 25 meters, that is the only difference. Any idea please? Vaclav
Sounds like the router has a built-in switch, in which case you should not use crossed cables but rather normal straight-through cables. Crossed cables are mostly used to connect e.g. your internet connection and the router (if you have a modem) or to connect two switches. However, the use of crossed cables is slowly becomming obsolete, as many (even low-end) switches and other network nodes has autosensing ports that automatically adjust to the cable being used. I can't think of any reason why it doesn't work when you switch cables, unless you actually leave the cables connected at each PC and just switches the ports used in the router (switch?). Or leaves the cables in the router ports and switches them at the pc end. In that case, I think it could be explained if one of router ports, or one of the PC network cards has autosensing, and possibly you're using the uplink port on the router. Anyway, make sure you aren't using an uplink port, and try with two straight through cables. See if that works. Do you know why it's important to make fast decisions? Because you give yourself more time to correct your mistakes, when you find out that you made the wrong one. Chris Meech on deciding whether to go to his daughters graduation or a Neil Young concert
-
Sounds like the router has a built-in switch, in which case you should not use crossed cables but rather normal straight-through cables. Crossed cables are mostly used to connect e.g. your internet connection and the router (if you have a modem) or to connect two switches. However, the use of crossed cables is slowly becomming obsolete, as many (even low-end) switches and other network nodes has autosensing ports that automatically adjust to the cable being used. I can't think of any reason why it doesn't work when you switch cables, unless you actually leave the cables connected at each PC and just switches the ports used in the router (switch?). Or leaves the cables in the router ports and switches them at the pc end. In that case, I think it could be explained if one of router ports, or one of the PC network cards has autosensing, and possibly you're using the uplink port on the router. Anyway, make sure you aren't using an uplink port, and try with two straight through cables. See if that works. Do you know why it's important to make fast decisions? Because you give yourself more time to correct your mistakes, when you find out that you made the wrong one. Chris Meech on deciding whether to go to his daughters graduation or a Neil Young concert
Thank you for your advice! One of the PCs is a new P4@3GHz, the other is old Celeron 1.2 Ghz. The new one works with both cables, the old one only with the short cable. Is it possible that the new PC is clever enough to work even with a wrong (crossed x straight) cable? Or capable to work with low signal lowered by the 25m cable? Vaclav
-
Thank you for your advice! One of the PCs is a new P4@3GHz, the other is old Celeron 1.2 Ghz. The new one works with both cables, the old one only with the short cable. Is it possible that the new PC is clever enough to work even with a wrong (crossed x straight) cable? Or capable to work with low signal lowered by the 25m cable? Vaclav
One scenario could be that the old pc is connected to the uplink port on the routers buil-in switch via a crossed cable. That would work - even if the NIC in that pc isn't supporting autosense. Then the new PC would be connected through the long cable to a normal port on the switch/router but since its newer NIC supports autosense this works as well with a crossed cable. Let me suggest: Check that both cables ARE crossed - if not, buy a straight-through to replace the one that is crossed. If both cables are crossed, try to switch them in both ends so the old pc uses the same port on the router, but the long cable. If that doesn't work, I don't know... Unless it is homemade cables 25 m shouldn't be a problem. The standard is defined up to around 100m. With homemade cables you may have to replace the connectors on cables if they don't work at all times. I've made cables around 80 m that works perfect (actually, 16 apartments of which one is mine is using that cable, and im online now.. :) ) and I've made a 20 m cable that one specific pc just didn't work with. So you have be a bit careful. Do you know why it's important to make fast decisions? Because you give yourself more time to correct your mistakes, when you find out that you made the wrong one. Chris Meech on deciding whether to go to his daughters graduation or a Neil Young concert
-
One scenario could be that the old pc is connected to the uplink port on the routers buil-in switch via a crossed cable. That would work - even if the NIC in that pc isn't supporting autosense. Then the new PC would be connected through the long cable to a normal port on the switch/router but since its newer NIC supports autosense this works as well with a crossed cable. Let me suggest: Check that both cables ARE crossed - if not, buy a straight-through to replace the one that is crossed. If both cables are crossed, try to switch them in both ends so the old pc uses the same port on the router, but the long cable. If that doesn't work, I don't know... Unless it is homemade cables 25 m shouldn't be a problem. The standard is defined up to around 100m. With homemade cables you may have to replace the connectors on cables if they don't work at all times. I've made cables around 80 m that works perfect (actually, 16 apartments of which one is mine is using that cable, and im online now.. :) ) and I've made a 20 m cable that one specific pc just didn't work with. So you have be a bit careful. Do you know why it's important to make fast decisions? Because you give yourself more time to correct your mistakes, when you find out that you made the wrong one. Chris Meech on deciding whether to go to his daughters graduation or a Neil Young concert