I have routerboard 450g and problem with opening facebook and youtube.
Its seems like a firewall blocks it. I checked options in ip- firewall sections, but I dont see any blocked url.
I am beginner
maybe the problem is at your isp
have you tried pinging www.facebook.com and www.youtube.com?
ISP is not problem because I have older router, and it works fine. But with newer rb450g I have problems with facebook and youtube. Sometimes open, but in the most period of day doesnt work.
I tried ping these sites, and pinging is ok, about 100ms
is this router new?
have you tried resetting it?
(maybe it was configured by the former owner to block facebook and youtube)
Just a suggestion, might me MTU related?
You can try to reset configuration
/system reset-configuration
and reapply necessary configuration. Also you can generate and send supout.rif file (http://wiki.mikrotik.com/wiki/Manual:Support_Output_File) to support@mikrotik.com to examine your configuration.
I fixed problem, IP - DNS - flush cache
cache was a problem
thanks to all