Why doesn't DNS resolve (the server is pinged)?

Question

Domain Name System

The problem is unstable, but regular.
DHCP send Google Public DNS
Ping 8.8.8.8 passes.
Nslookup -debug xxx.xxx. 8.8.8.8 issues a timeout.
Similarly for other DNS servers
In the diagnostics of the router, DNS also does not resolve.
The firmware update had no effect.
When connecting the modem directly, the problems disappear
System: Win 7 pro
Router:
Model No. TL-MR3020
Firmware: 3.17.1 Build 130929 Rel.36745n
3g modems - different.
Operator - MTC Belarus
Question: in fact, what is happening and how can I fix it?

Answer 1

Most likely closed DST port: 53 UDP
Turn off the firewall, turn off the antivirus. Check. If it works, then boldly open this port and you will be happy.
If it does not work, then this port is blocked on your router.