Thanks you all to your timely response. i got the problem solved. the problem was not from my LAN, every devices in the LAN got appropritate IP from DHCP and can ping my WAN interface IP, only that NAT was not function properly even though i was corr...
i was able to config LAN dhcp successfuly and my default route wored fine, but i my LAN PCs cant ping public DNS IP nor could they browse internet. only my 800 series router could. pls help.