I have the ff. set up:
Fiber optic DSL
Location: Southeast Asia
FW 2.00 (initial)
Settings: default, QOS is activated, static IP addresses for wired devices
I used ShieldsUp! (SU) at grc.com, and it reported that port 50 is open.
I checked for new FW versions using the firmware section of the router configurations and it reported a new version, 2.05, which I installed.
I rechecked with SU and it reported all ports in stealth. However, after several hours, any device connected to the router could no longer access Facebook and Google.
I pinged both sites and results showed no delays or errors. The problem disappeared only if I did one of the ff.:
- Power-cycled the router (and in some cases, the modem as well).
- Released and renewed the DHCP.
- Factory reset the router (and checking to update the router system date and time).
I tried various configurations:
- Disabled unicasting
- Disabled DNS relay
- Disabled QOS
- Removed static IP addresses
- Used another MTU
but they did not work.
I used another router and the problem did not take place.
Finally, I downgraded to FW 2.01 HW B1, and the problem disappeared.