firewall issues with pppoe & nat enable

[jingchen]

I have firewall cource code which works well in the work mode(WAN port) of fixed IP and dhcp on the Vxworks based home gateway board. But when I added some functions for PPPOE work mode, I can not access some web sits like "

http://www.3com.com","www.aol.com"

with nat enable through my firewall(I can access "

http://www.yahoo.com",

"

http://www.cisco.com"

ect..). Also,I can only transfer small size file through the firewall with pppoe/nat enable(PPPOE).
How to fix these issues in my firewall source code to meet the PPPOE/NAT ?