CCR IP as DNS server not working

RouterOS General
1

I have re config my office CCR, with very simple config.

basically on DHCP setup i enter DNS = ISP DNS IP.

now all pc receive 3 address
CCR IP
ISP DNS1
ISP DNS2

on ip>dns i have enable allow remote request.

now i have issue accessing some website from user PC, not working, can ping just fine looks very likely dns issue. i manually enter CCR IP Only as DNS in PC, no website can be reached.
funny thing is on server, if i use those 3 DNS, this bank website not working, but when manually enter only one DNS which is CCR IP, i can open this website, no problem.

but on all windows PC, if i try only using CCR IP as DNS, none is working.

i’m out of ideas, no complicated setup here, only defcon NAT/Mangle, enable LT2P, and firewall rule block ssh.

2

MTU size problem?

3

i have look into MTU, set 1500 MSS 1460, issue persist.

the weird thing is why can;t i use CCR IP as single DNS address, allow remote request is done.

4

btw i’ve set the following as other post suggest

/ip firewall mangle
add action=change-mss chain=forward comment=“Internet MSS Shaping” disabled=
no new-mss=1452 out-interface=Internet protocol=tcp tcp-flags=syn
tcp-mss=1453-65535
add action=change-mss chain=forward disabled=no in-interface=
Internet new-mss=1452 protocol=tcp tcp-flags=syn tcp-mss=
1453-65535


should i also add this firewall on the CRS?

my setup is

ISP MODEM
1x CCR
4x CRS on CCR LAN Bridge