@binio  how about enable the "IPv4 routing" option, and then check the firmware version is up to date or not, not pretty after reset can make it work or not. By default, the VLAN interface can talk to each other cause there has a routing policy enable after set up the IP interface.

Also turn off the firewall on PC to have a try?

 

  

@binio 

IPv4 routing enable by default

Firmware up to date

firewalls disable

 

@binio 

 

Are your PCs running Windows 10? If so, the Windows Defender Firewall defaults to not allowing responses to ping.

@unmesh 

PCs can pinh one another when the are in the same VLAN (firewall rule disable)

@binio 

Hi there. I got a solution for you. 

I got 

TL-ER6120 v3 and T1700G-28TQ V3.

I followed the article at the link below:

https://www.tp-link.com/tr/support/faq/887/

 

Its merely taking this approach with some caveats. Its an incomplete article at least for T1700G-28TQ V3.

 

@ TL-ER6120 v3

I setup Transmission/Multi-NET NAT to help VLANs retrieve internet from WAN connection. it has no function whatsoever to regulate/establish interVLAN traffic. 

I setup Transmission/Routing which help intern VLAN trafficing. Without this inter-VLAN traffic @ T1700G-28TQ V3 can not be established. I thought it was an L3 switch and I bought merely for it having 4 SFP+ ports as uplink to anothere 10G switch. So thats the bust and focal point of your problem to my newbie understanding.  

Anyways, here you go:

@ T1700G-28TQ V3

VLAN 1 (System-VLAN)

interface ip 10.0.1.2 255.255.255.0

port 1/0/24-28 untagged / rest is tagged 

VLAN 2 (LPT)

interface ip 10.0.10.1 255.255.255.0

port 1/0/1 untagged / rest is tagged (if you want no connection between specific ports on a different vlan just remove the tagged port and you wont provide access to it)

VLAN 3 (NODE)

interface ip 10.0.20.1 255.255.255.0

port 1/0/2 untagged / rest is tagged (if you want no connection between specific ports on a different vlan just remove the tagged port and you wont provide access to it)

VLAN 4 (NAS)

interface ip 10.0.30.1 255.255.255.0

port 1/0/3-4 untagged / rest is tagged (if you want no connection between specific ports on a different vlan just remove the tagged port and you wont provide access to it)

Cordially, I setup DHCP for each VLAN.

I setup static routing 0.0.0.0 /0.0.0.0/10.0.1.1 so that connection between TL-ER6120 v3 and T1700G-28TQ V3 is established.

 

NAS device needs extra step for multi-VLAN access. Briefly, NAS device could be accessed via computers provided that they are on the same subnet. Therefore, Log on the NAS console via internet explorer and add VLAN ID 1, 2 and 3 respectively to the network adapter. DHCP would assign VLAN IDs for the NAS immediately and that way you would be able to access your NAS via file explorer. If you do not assign multi VLAN IDs on the NAS network adapter, you won't have SMB access while NAS management console via internet explorer is accessible.    

 

@ a PC in VLAN 3, I am able to ping VLAN 4 and VLAN 2 succesfully. 

NAS on VLAN 4 can be accessed both at SMB level and internet consol. 

a PC on VLAN3 is able to connect VLAN4 NAS or a PC in VLAN2

 

I hope this is helpful. I have been pulling hair for the last 2 weeks and this is the only solution I can come up with. If anyone can come with a better idea of activating L3 protocol in T1700G-28TQ V3 (if its capable), be my guest. 

Okay. Just an update. I have an access point linked to Router. That access point is able to get the DHCP from the switch yet wouldnt let any device to appear on any device linked to the switch. I realized that the VLANs 2-4 did not have router uplink untagged. As soon as I changed router uplink (port 1/0/24), both PC on access point side and the PC on switch VLAN 3 (i.e.) were able to publish themselves on their network list. If you would need a graphical representation I may jot something up for you.