I don't know who set that up but given the setup is very non-standard you need to have a talk with them to fix it.
For example the D-Link Switch would not be used given the story so far. That's only one thing but it's setup is not common and whoever supports it needs to be called in.
My network elements are as follow:
ADSL Modem -> CIsco ASA Firewall+VPN -> D-Link Switch -> TP-Link WiFi router (DHCP)
I just arrived to this office, my new job, and someone else have made this installation of equipment.
WiFi connections drops, for some of the devices connected, and you can't reconnect for some time, but users on LAN which are connected to WiFi router also do not experience any issue at the same time. If I power off and back on WiFi device everyone can connect back normally.
I was under impression that there is something wrong with the WiFi device so I've connected another one - but same thing is happening all over again, but not so often as with the original one. This make me believe that it is not up to the WiFi device itself.
I've checked wifi's log:
DHCP: Client receive ACK from 192.168.1.1, IP=192.168.1.113, Lease time=86400.
DHCP: Client send REQUEST, Request IP 192.168.1.113 from 192.168.1.1.
DHCP: Client receive OFFER from 192.168.1.1.
DHCP: Client send DISCOVER.
DHCPC DHCP Service unavailable, recv no OFFER
does anyone have any advice maybe or suggestion on how to investigate issue?

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