Unable to open some sites need permanent soultion

hello friends,

i started a ISP with /30 as WAN pool and /29 as LAN pool from MT.

few days everything move absolutely fine. but now a days my customers are complaining like some site are not opening. then i reached to my provider and they suggested src-nat to my /29 LAN pool.

after doing src-nat all issues solved. but i felt this is not permanent solution. Kindly anyone help me here for permanent fix.

Lets keep your connectivity and ISP issues in one thread please.
http://forum.mikrotik.com/t/unable-to-open-a-particular-website/158174/1