The Netgear GS108T and browsers 

Netgear GS108Tv1

Netgear GS108T administration and Browsers


Some time ago I bought a secondhand Netgear GS108T managed switch to use on my small local network. I selected it because of its 'mirroring' capability. This was so that I could run a network monitoring tool such as Wireshark and capture the network traffic going to/from something else my network. (What is that Chinese IP camera connecting to?)

Usually network switches do just that - act as switch and just route traffic between the two (or more) ports that 'need to know'. With mirroring you can tell the switch: "Whatever passes through this port please also copy it to this port". "This port" being the one which the computer running Wireshark is plugged into.

My particular GS108T is a GS108Tv1 running the latest(!) firmware V3.0.4.10 which was released in June 2012.

The GS108T is administered using a web-based interface - you just point a browser at it and away you go. To find out what IP address it is using you can use some Netgear supplied software, or you can just check the 'connected devices' list on your local router.

The Problem

The GS108T is fairly old and the administrative pages use HTML iFrames and JavaScript. I find that modern browsers plainly have issues with these web pages as can be seen in the different rendering of the 'Mirroring' pages illustrated below. Whether this is because the pages are poorly written or the world has moved on I have no idea.

However the real problem is, that having navigated to the 'Mirroring' setup screen and made the changes you want to do, the Apply button does nothing.

Above I say 'modern browsers', but a quick Google shows me that others were complaining about the Apply button not working on Netgear forums back in at least 2016. In my (admittedly not exhaustive) Googling on this topic I have never seen any acknowledgement from the Netgear Support people that there is an actual problem. Their response has always been a steady stream of: "Reset the switch", "Reload the firmware", "Try a different browser", "maybe your hardware is faulty"....

Having said "modern browsers don't work" I have found that the latest version of Internet Explorer (version 11) supplied with Windows 10 does work. I find this a little ironic as (a) Microsoft are trying to get us to dump IE in favour of Edge, and (b) IE versions usually have small quirks in the way they interpret or extend the standards.

Just FYI here are a few screen shots of the Mirroring page on various browsers:

Netgear GS108T mirroring setup page - Windows

The above is what you get with Chrome, Edge and Firefox running on Windows 10.

Netgear GS108T mirroring setup page - Linux

The above is what you get with Opera (v9) and the Chromium browser running on Linux.

Netgear GS108T mirroring setup page - Internet Explorer

The above is what you get with Internet Explorer 11 on Windows 10.

The Solution

Basically there are three options to set up mirroring on the GS108Tv1:

  1. Use Internet Explorer 11
  2. Type in the wanted settings in the URL (see below)
  3. Find an old browser (such as Firefox 3.6.0?)

What should happen when you hit Apply is that the Javascript creates an HTTP URL that passes the new configuration to a cgi script that saves it. The URL that does this is of the form:

Taking the elements of the URL in turn: address of your switch - adjust to suit.
mirror.cgiRun the mirror.cgi script to save the results
?Start of the parameter list
mode=3Sets the mode of operation
0 = Disable
1 = Tx Only
2 = Rx Only
3 = Tx and Rx
&Separator between name/value pairs
mtp=8The number of the monitoring port
&Separator between name/value pairs
config=00100002 A string of 8 digits representing ports 1-8, where
  0 indicates the port is not mirrored.
  1 indicates the port is mirrored.
  2 indicates the port to which everything is mirrored.
In this example port 3 is being mirrored to port 8.

In summary: If you have a Windows 10 box to hand fire up Internet Explorer otherwise spend a few seconds handcrafting the configuration URL in the address bar of what ever browser you happen to be using.

Note: I believe the problem does exist in other Netgear switches of this era which probably share the same code.


Any comments? email me. Added May 2020