Sometimes web page do not open. But when i refresh again then it open.

my configuration is
1. firewall from mikrotik web page
2. Transparent web proxy.
3. DNS caching. (I used 4.2.2.1 as secondary DNS and now it is removed but problem remains)

Are you using NAT ?????

How connect your Internet to the MK, by pppoe or dhpc-client from a modem.

I got an static public ip from my ISP. Then I masqurade it to my local ip.