Topic: switch uplink question

Hi All,

I have a small (old) 8 port switch with an uplink port, and there is a line drawn between that port and the one next to it like so:


port 1          uplink
|                    |
----------------------

What exactly does this function do ?

Re: switch uplink question

Chaining switches.

Re: switch uplink question

so is port 1 not usable in a regular device?   

if so, does it get turned into an uplink port?

Re: switch uplink question

Many new networking card have an automatic crossover detection. This allows for two PCs to be directly connected without having to resort to a special crossover cable, and it also allows them to connect to the uplink port on switches. The same goes for many new switches, they have uplink port detection.

So the answer is, traditionally, you'd use the uplink port to on a switch to connect to another switch. If you have modern hardware though, you can probably treat it as just another port.

Re: switch uplink question

Maxlor is correct.  In most instances (as I cannot think of any exceptions...), connecting two like devices together -- PC-to-PC, router-to-router, switch-to-switch hub-to-hut, requires the connecting cable to be a cross-over (receive & transmit lines are crossed...).  "Uplinks" build the cross-over requirement into the wiring of the interface such that cross-over cables are no longer required when connecting like devices.  Straight-through cables can be used in all situations.

Re: switch uplink question

Most modern (~3-4 years or newer) network devices don't care if you're using a straight or crossover cable, they will automagically detect what you're using and adjust accordingly.

Trust me, I know what I'm doing.

Re: switch uplink question

really?

i'm not on top of technology, i guess.

Re: switch uplink question

"Most", meaning "definitely not all".  smile  We have a lot of onboard Intel and RealTek network chipsets that don't do auto-mdix on Windows, Linux, or FreeBSD.  We also have a pile of 3Com 3C905 (a,b,c) NICs that don't do auto-mdix.  Actually, I have yet to find, at work, a network chipset that handles auto-mdix properly.

Switch-to-switch detects cross-over and straight-through cables correctly, and the switches configure the port correctly to allow traffic.

But I've yet to get this to work correctly on a NIC-to-NIC, or a NIC-to-switch.  With the one exception of a couple of our high-end gigabit switches.

Re: switch uplink question

I've used straight cabled where cross-over cables `should' be used, and vice versa several times, mostly in a NIC-to-switch configuration, but also NIC-to-NIC, never had any problems ... I don't recall specific card brands/models though ...

Guess I've been lucky then ...

Last edited by Carpetsmoker (2009-03-30 03:56:51)

Trust me, I know what I'm doing.

Re: switch uplink question

whose idea was it to switch the pairs in the first place?

i can't figure out why anyone would think it's useful.