What purpose is the Uplink port in layman's terms and do I need it?

Question

I have an old Linksys switch (EZXS55W) and it has worked fine for many years now, but I tried to hook something up today to the last open port and noticed the device didn't work when I did this. When I looked about my switch, it says that it disables that port when using the Uplink port.

I'm still a bit fuzzy on what the Uplink port does for me, I had always assumed that this Uplink port was for me to plug into from my router which is elsewhere in the house and hooked up to the modem so it could allow the switch to work for my other devices. I guess I need more than 5 ports now, but I see newer switches do not have this Uplink port generally anymore. Can I safely buy a new 8 port switch that does not have an Uplink port and maintain the exact same functionality?

If I understand what I'm reading correctly, newer switches did away with the need for a dedicated Uplink port so now the switches intelligently do whatever the Uplink did? I don't want to get further off from the accurate answer to this, so I just want to understand the technicality behind this so I'm not uninformed.

The one thing I guess I'm seeing from this though, if a switch is say an 8 port switch that means 1 port will be used to feed from the actual internet connection (whichever cable is providing it to the switch) and then the other 7 can be devices that need access to that shared network connection and by that virtue, the internet. It does not however, work like 5 port means it has 6 physical ports with one being the "internet" connection, and the other 5 being devices that need to be hooked up, correct? The latter is how I always thought it worked, but thinking this is incorrect now.

Answer 1

An uplink port is a port on which Transmit and Receive are reversed.

They are used to connect together 2 switches with a standard straight-trough cable. (otherwise it would require a cross cable where the transmit and receive are crossed in the cable rather than on the switch port)

Some switches came with 2 physical ports that were actually the same logical port , the first one being wired normally and the second wired "crossed". So you were able to use only one of the physical port a a time, depending if you connect a PC (or a router) or a switch.

Nowadays this generally doesn't matter anymore since most interfaces are "auto-mdix", meaning that the interface detect the type of device connected and cross transmit and receive internally if needed.

(and if the switch itself is not auto-mdix but the device you connect on it is , it also works).

Note: this apply mostly to 10Base-T / 100Base-TX ports, since Auto MDI-X is nearly ubiquitous on gigabit Ethernet, and doesn't apply to 10GB Ethernet and above where there's no more dedicated transmit / receive wires.

Answer 2

This has to do with how (UTP) Ethernet cabling works. In the old days, end point devices (like your PC) would use wires 1 and 2 to transmit data, and wires 3 and 6 to listen (https://en.wikipedia.org/wiki/File:Ethernet_MDI_crossover.svg) (*). The switch on the other side of the cable would listen on wires 1 and 2, and transmit on 3 and 6. Now if you would connect two siwtches, this would not work with a regular cable, because both switches would use the same wires in the cable to transmit. On solution for this is to use a special crossover cable, within which the cabling is crossed. Another solution is to have a specific "Uplink" port on the switch, which is wired as an end-point and uses the same wires to listen/transmit as a regular PC for instance.

With modern devices this is all a moot point, since practically every device uses "Auto-MDI-X" (https://en.wikipedia.org/wiki/Medium-dependent_interface#Auto_MDI-X) to sense which wire to listen and to transmit on. This standard was introduced in 1998, so it's very rare to find use for your old crossover cables today.

As for your Linksys switch: you can use the Uplink port to connect an end-point if you would use a crossover cable. However, in the internal wiring in the switch the Uplink port is the same port as port number 5 (http://www.linksys.com/id/support-article?articleNum=132646), so you can only use one of them (either the Uplink port, or port 5, not both simultaneously).

(*) This is true for 10BASE-T (10 Mbit/s) and 100BASE-TX (100 Mbit/s) Ethernet. Gigabit Ethernet uses all 8 wires in the cable.