I was looking around on newegg and found a linksys switch with 5 ports, one of them being an uplink port, I googled it and found one site that said it removed the need for a crossover cable between switchs/hubs. Is that really what it is? I remember having a few switchs hooked up at a lan once but im not sure if crossover was used or not.
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What is an Uplink port?
- Thread starter Darakian
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Like you said, an uplink port eliminates the need for a crossover cable when connecting hubs or switches together. An uplink port is an MDI-X(I think) port, so you can just use a standard cable to connect that to a regular MDI port on another switch/hub. A lot of switches nowadays have automatic MDI/MDI-X switching, so one can use a straight-through cable to connect switches together without having to worry about uplink ports or crossover cables. Shit I'm tired.
deadoralive
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yup, that's basically all it does, crosses the cable for u.
r00k
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Try to visualize this: it takes 2 wires to complete a circuit. There are 8 in ethernet cable, so 4 are not used.
4 wires = 2 circuits. 1 circuit to transmit, 1 to receive. Full duplex allows both to work simultaneously.
If you had 2 network cards, they would both be using the same 2 wires to send their data, and the same other 2 wires to receive. Obviously, this cannot happen. So they crossover the send (TX) and receive (RX) wires at some point so each one is sending to the other's receive side. Typically, this cross over is made in the hub or switch.
Likewise, 2 hubs or switches communicate with each other the same way. "Like" devices must connect with crossed wires so they don't talk and listen on the same circuit. That is what the uplink port does - it crosses over the send and receive. So this makes it an "unlike" device to another switch / hub, and allows it to plug into the normal ethernet jack of another switch / hub.
4 wires = 2 circuits. 1 circuit to transmit, 1 to receive. Full duplex allows both to work simultaneously.
If you had 2 network cards, they would both be using the same 2 wires to send their data, and the same other 2 wires to receive. Obviously, this cannot happen. So they crossover the send (TX) and receive (RX) wires at some point so each one is sending to the other's receive side. Typically, this cross over is made in the hub or switch.
Likewise, 2 hubs or switches communicate with each other the same way. "Like" devices must connect with crossed wires so they don't talk and listen on the same circuit. That is what the uplink port does - it crosses over the send and receive. So this makes it an "unlike" device to another switch / hub, and allows it to plug into the normal ethernet jack of another switch / hub.
Cat5 cable wasn't designed for ethernet usage. It was a standard 4 pair cable before ethernet used it. Ethernet only needs two pairs, so that's all it uses. Gigabit ethernet can take advantage of the other pairs, though. Also, some power over ethernet uses the other pairs. The orange and green pairs are normally used according to the standard, and the blue and brown pairs are normally unused. This can vary depending on whether the cable maker followed standards or not.
r00k
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off the top of my head i don't remember which 4 exactly, but if memory serves at all, the green/white, blue, blue/white, and green are the ones used. the other 2 pairs are there for future use. In some cases, companies have incorporated their use for powering small hubs, so they could be set where power could not be gotten to. This, if used at all, is a very rare practice as far as i know, however.
I do remember, when working as a network administrator for my old school district, coming accross the most hilarious / shameful / semi-intuitive use for the other 4 i had ever seen. Basically, whichever slacker who laid the cable in the principle's office, cut the cable open, and split the unused 2 pair off from the used set, and used them for a second connection. This definitely goes against cabling standard, and degrades the signal quite a bit to each pc. I think i even was so amazed they would be so lazy to not run a second line as code requires, that i have a picture of it somewhere.
I do remember, when working as a network administrator for my old school district, coming accross the most hilarious / shameful / semi-intuitive use for the other 4 i had ever seen. Basically, whichever slacker who laid the cable in the principle's office, cut the cable open, and split the unused 2 pair off from the used set, and used them for a second connection. This definitely goes against cabling standard, and degrades the signal quite a bit to each pc. I think i even was so amazed they would be so lazy to not run a second line as code requires, that i have a picture of it somewhere.
r00k
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mikeblas said:
Thanks for the correction. Much appreciated.
zhchua said:
Yes, you'd also have
PC->HUB [STRAIGHT]
HUB->HUB [CROSS]
But these days, it's starting to not matter because many cards, swithces, and hubs have automatic MDI/MDI-X detection, or at least one switchable port. Gigbit-compatible stuff inherently does not require crossover cables because the gigabit spec (IEEE 802.3ab) accounts for it.
.B ekiM
deadoralive
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zhchua said:
crossover, unless it has autodetect.
-(Xyphox)-
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Simple Way... IF you are going from one different device to another different divice you use Crossver... I.E Switch -> Hub, Router -> Switch, Switch -> Hub, And so on...zhchua said:
Straight-Through you use to connect Switch -> Switch, Hub-> Hub,
For Router -> Router, you use the Serial Connections S0,S1
Yeah, I read that earlier and it just didn't make sense but I couldn't put my finger on it. It really doesn't make a damn bit of difference whether you are connecting hubs or switches, you must use a crossover, whether the crossover is done in the hardware or the cable. The general rule is to use a crossover cable to connect similar devices. A hub and a switch are similar since they are both essentially concentrators. A switch and a switch are similar since they are the same thing. A switch and a computer are not similar, so use a straight-through cable. A computer and a computer are similar, so use a crossover. According to xyphox, going from a pc to a switch(different devices) would require a crossover cable, which simply is not correct.zhchua said:
IceWind said:
Many new PoE switches that run the standard 802.3af have built in circits that detect if the device is PoE capable before allowing the power to flow through. I'm sure you can still bypass the check some how but if your wiring is correct you shouldn't fry anything unless you are using pre-standard or lower end PoE equipment.
zhchua said:
Its actually really simple...
Switch -> PC = straight cable
Switch -> Switch = crossover cable
PC -> PC = crossover cable
You can replace Switch with Hub in any of the above examples.
You can replace PC with Router in any of the above examples.
weasel2htm
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r00k said:
The high school In the school district I work for Is wired like that... The whole school!
I call it "jerry-wired"
We've had to re-wire a few things for the newer features of ethernet to work, like out Gigabit uplinks to some of the closer IDFs.
r00k
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