The ISA's network cards IP are:172.20.2.1(Internal) and 210.*.*.*,we have 2 segments addresses,A is 172.20.2.*/24;B is 172.20.3.*/24,A to B is linked directly by each router,NOW A and B PING each other are OK,my question is how is the client of 172.20.3.* able to access to Internet by ISA(the client of 172.20.2.* can access Internet via ISA and the routers' setting are all right)?