Hi @rhimbo, I actually had to see for myself that this model is being sold as new because it looks like it's End Of Life.  You may want to consider returning it.  That said, are you able to ping the 192.168.0.1 address?  Have you tried both http://192.168.0.1 and https://192.168.0.1.  Older firmware may not have the SSL option, new versions may only have SSL enabled.

@D-C Thanks for the reply.  

Actually I purchased the switch back in 2018.  OK, don't laugh... 

I'm revisiting this problem of not being able to access the configuration menus since I first purchased the switch.  Frankly, at that time I opened a help ticket with TP-Link but never heard back... pretty disillusioning.  I'm wondering if this unit really was 'brand new' or if it was a defective unit sold as new even back in 2018.  Pretty disillusioning.  

I didn't follow up after my second attempt (again, no response whatsoever from TP-Link).  To be honest, I know it's my failure to follow up again and again until I got traction, but I was busy being a full-time caregiver for my mother at the time.... not an excuse, just an explanation.

Anyway, now I'm trying to 'recover' this situation because I recently experienced a new problem.  I have two Synology MR2200ac mesh devices connected to my main router, a Synology RT2600ac.  Up until a few weeks ago, everyting has worked fine for years.  Suddenly, I cannot access my 'guest' Wi-Fi network.  The main Wi-Fi network is working fine.

Synology support examined the log files from my device.  It appears that the switch is blocking access to the VLAN (1733) required for guest network communication.  

But I have never been able to access the switch's configuration menu, thus I have never changed anything.  I tried resetting the switch to factory defaults to no avail.  Thus, I presume that the switch is failing in some way.  But I'd like to confirm instead of guessing.  If I can salvage this unit for a while longer, I'd like to delay getting a new switch.  

I can work around the problem now by simply plugging in the Cat6 cables from the two mesh devices directly into my router.  And the hard-wired Cat6 cables (I ran cables to every room in my home) are working fine.  It's only the 'guest' Wi-Fi network that is not working.  But I'd like to understand what the problem is.

Sorry @rhimbo, I did laugh when you said you got the switch in 2018; safe to assume that returning it is not an option.  I don't think a managed switch would have ever worked out of the box, so I can't explain what you're seeing.  I have a T1600G-28TS v3.0 and never had any issues.

Not sure if this is exactly what you've tried over the past 7+ years, but to rule out any external factors and not make any assumptions on my part try these steps...

1. Disconnect all network cables from the switch
2. Factory reset the switch
3. Set your laptop/desktop wired interface to use the static IP address: 192.168.0.2 and subnet mask: 255.255.255.0
4. If you have any firewall, antivirus, VPN or similar software running, disable it
5. Connect your laptop/desktop directly to the switch with a verified working cable
6. Confirm Link/Activity lights on the connected ports
7. Open command window/prompt and type ping 192.168.0.1 (you should get a reply)
8. Open browser's incognito/private window and browse to http://192.168.0.1 and/or https://192.168.0.1

  @D-C Well, it's OK that you laughed...  

I'll follow the procedure you outlined... thanks....

But it is perplexing that everything worked just fine up until a few weeks ago.  I never had a problem with either of the Wi-Fi networks (main and guest).  

That being said, it is possible that the problem started when I installed the MR2200ac mesh devices and I just didn't notice because we never use the guest Wi-Fi network (reserved for actual guests and visitors to our home which doesn't happen often).

Before I purchased the mesh devices, I just had a second Synology RT2600ac router configured in access point mode.  And for sure the Wi-Fi guest network did work as expected.  So I don't have enough detailed information or understanding of the protocols to know what is different between mesh protocols and the protocols used between two routers:  router 1 as main router, and router 2 in access point mode.

Anyway, I did not intend to try to return my TP-Link switch.  I just want to figure out what's wrong so I feel that I can resolve issues.  

I'm currently working around it by plugging the mesh devices directly into the main router (I've wired my home with Cat6 cables from every room to the location of my rack so I only had to unplug the cable from the patch panel and plug it directly into the router).

I'll proceed as you outlined and report back here in case it would be interesting for other folks.

  @rhimbo 

One other idea

Do the factory reset procedure on the switch

Set a static IP address 192.168.0.111 on your laptop/computer ethernet port.

Disconnect Laptop/PC from WiFI

Cable stright from Laptop/PC to switch

Run an IP scan on the laptop (plenty of free software to do this out there)

See what it turns up.  Its possible it isnt defaulting to 192.168.0.1 and might be on another IP

  @GRL OK, thank you.  I'll try all suggestions (a learning experience for me).

Question about running an IP scan.  Will the "arp" command do the trick?  I'm on Fedora Linux.  

When I run it, I see 5 lines of output, 4 showing an IP address, and one showing "_gateway" under the IP Address column, which I can confirm is the MAC address of my router.