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What do ports mean?


I have purchased 2 books and read through documentation on the SG500-52 Switch and am so frustrated at the moment that I'm about to use the 2 switchs for target practice.  I have what I would think is a very simple question that so far has spent 3 days and multiple calls to technical support and still don't have an answer to.


Question:  The switch has ports.  they are all labeled 1-48

The books and documentation tell me how to use the CLI interface and give examples like:

interface fa0/4 but NEVER EXPLAIN what the heck port on the physical device that is.  To make matters worse when I do a show on the switch I get ports like fa1/2/1-48 and fa2/2/1-48 and so forth which doesn't match a single document or google search.


Can someone please please explain to me what the port number is for port 1 and explain to me what all these numbers mean and why it has to be so difficult to figure out.




10 Replies 10

Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master
Port numbering varies per switch (or router).

Generally, the numbering represents a hardware hierarchy, from the general to the most specific. The for example, on a 3750G, interface g2/1/2 would be a gig port on stack member number 2, port bank number 1 (the uplink port bank) and 2nd port within that port bank.

Some devices even add another number, separated with a colon, to indicate sub-module ports.

It can be confusing, and not all devices make it clear what ports correspond to their configuration identify. (Some device offer an option to blink the status light of a port so you can identify the port.)

To futher confuse, some devices start numbering with zero, others with one, and that might vary for what the number represents. Also the number of numbers can vary between devices too.

Thanks for the response.  I still don't know what banks and stacks are because the books and manuals don't mention anything like that.  I just lucked up though.  Normally I have been plugged into the switch while I was working on it and today I have only been using the serial connector.  I was logged in and noticed that which I plugged into a port it threw up a message telling me ga1/1/6 was just activated.  So I unplugged and plugged into other ports and they all threw their port number up on the screen for me to see.  It appears my switch is using ga1/1/port # as the id so will go from there.  if you could explain about the stacks and banks though I would appreciate it.

Thanks again,


Oops, sorry. I had thought of mentioning connecting some device to a port, which brings the port on-line, is another way to identify a port, but wasn't sure what a SG would show. I should have mentioned it anyway. Glad you discovered it yourself.

Books often don't mention the physical details, again, because there's so many varieties.

Some device specific manuals do describe port layouts. In Cisco's case, they often have a hardware installation manual that might further describe the hardware layout of the device.

On your SG, all the ports are likely "built-in", but some other switches and routers offer modular slots, where you can insert various port modules. On those, the number, and kind of ports, can vary, so the port numbering scheme structure is the same for the device, but the actual port identifications might vary depending on what the switch (or router) is populated with at the moment.

Some switches support "stacking", which is where you connect multiple devices together, sometimes with special ports and cables, sometimes with ordinary ports and Ethernet, and then they are configured as one device. For example, in the Cisco enterprise series of switches, some of the 2960 series can be "stacked" and the different 3K series can be stacked. When this is done, you need a way to distinguish between ports on the individual stack members. For that, the first number of the port represents the device number, which by default, often starts with one and increments as you add additional units to the stack (a 3K stack can stack up to 9 units). However, you can often assign the unit number from some range with the restriction that two units, within the same stack, cannot use the same number.

Cisco often keeps the same numbering structure, even when it doesn't apply to a specific device. For example, your SG's first interface number might always be the same number, and ditto for the second. I.e. your SG might logically only needs ports numbered from 1..52. Yet, sometimes Cisco has "plans" for extension to a series. The original 2960 could not be stacked, nor could the 3560, but the later 2960S could, as could the 3750. So, the port numbering that makes sense, and is truly needed on the stackable switches is used on the non-stackable switches too.

Georg Pauwen
VIP Master VIP Master
VIP Master


are these new,out of the box, or second hand switches ? If you go to 'Administration --> System Mode and Stack Management' make sure the switches are not part of a stack but standalone (page 96 of the attached user guide). In standalone mode, the interface numbering is:

Unit/Slot/Port (e.g. 1/1/1 on a standalone switch would be the first port on the SF500, 1/2/1 would be the first port on the SG500). So the unit refers to the position of the switch in a stack, the slot to the type of switch (1 for the SF500, 2 for the SG500).

Does that make sense ?

Check the below documents for reference:

User Guide:

More than anything so far but still confused. I have 2 books and documentation from Cisco website for instructions on setting up VLAN and assigning ports.  The issue is none of the commands are actually working that they give.  I am figuring out variations on the commands that do work but nothing I'm doing ends up assigning ports to my VLAN.


1) They are new out of the box. 

2) If I connect my computer to port  while connected I get: LINK-I-Up:  gi1/1/35

3) It sounds like you're saying I should be seeing gi1/2/35?

4) if I attempt to enter: interface gi1/1/1-18 I get a bad command but if I enter 1 port at a time it lets me.

5) I then type switchport access vlan 100 and get Port gi1/1/1: Port mode is not ACCESS

6) I then exit and type show vlan tag 100 and it shows vlan name but no ports assigned to it.

7) If I do a show vlan 1 it lists: fa1/2/1-48,                    

It also appears the two documents you provided are for web interface and not CLI.  Do I not need to be using CLI? I am learning this stuff and read in a couple different books that the CLI was the best thing to learn as it was more functional than web interface.  I also need to access the switches on local network at data center as I don't want to have it open to web.  I will also be using ssh to do so.






I have not been working with this model but I have read this model support stack, so if you bought this switch new it should not show differents port identifiers like g1/1/1 and g2/1/1 (this is just an example), it should show something like:






Now on other switches when the switches have been unplugged of the stack they could display like if they are still with the other switches, if you execute: show switch you will see them as provisioned, in order to fix it you must execute: no switch x provisioned  (where x is the number of the switch)



The following link could be useful as reference:


A time ago I was configuring a SG300 and it have some command line limitations, it cannot run some command lines like IOS does. The commands can vary. 


If you want to configure a port as access try:


switchport mode access


In order to make the same configuration for several ports, try using: interface range G1/1/1-18 or with space G1/1/1 - 18


Hope it is useful



>> Marcar como útil o contestado, si la respuesta resolvió la duda, esto ayuda a futuras consultas de otros miembros de la comunidad. <<

show switch comes back as bad command.


I don't know why you keep asking about it being purchased new or not but it arrived in original unopened box and appeared brand new.


I have 2 switches and had them plugged together with the fiber connectors.  I have unplugged the power from one of the swtiches and reboot the first so that it doesn't detect any connectsions to see what changes.  It still shows the same ports listed above and when I unplugged my network connection it shows gi1/1/35 as the port I am disconnecting and connecting from.  I still don't have the show switch command.


I was also using the switchport command albeit slightly different than what is listed in manual, but it doesn't seem to save.  It gives the messages I put above but then when I exit and do a show vlan tag 100 it doesn't show any ports being part of that vlan.


It is amazing me how complicated this process is when I can buy a $300 switch and figure this out in no time.  I thought getting a Cisco switch would get us the best possible solution but this is starting to look bad for me ever figuring it out.


Thanks again for you help,



"It is amazing me how complicated this process is when I can buy a $300 switch and figure this out in no time."

Well then you wouldn't need highly paid network engineers or professional certifications. ;)

The $300 switch tends to not support many, many features the more advanced switches do. Unfortunately, supporting many advanced features often leads to complexity for even configuring simple things.

That said, I have seen sub $100 routers support NAT features (automatically) that could not be configured on multi-thousand dollars switches. (In fact, recently, we had a remote site that had a small DSL link using PPPoE. It needed to be upgraded, and an "Enterprise" level device to to accept the hand-off was rather expensive in comparison to the $50 consumer router we eventually used.)

Not arguing with anything you've said.  However, when I download the manual for a $1200 device and it tells me to type this command to do X and the command comes back not found, this is taking the feature set a bit far. :-)



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