Abstract: Now many university campus networks have two or more exports such as Cernet and ChinaNet. It results in the situation of multi-export route accessing the Internet. This connection greatly increases the access speed of different network resources, but as part of dissymmetries of access path, it results in some problems, such as the E-mail is rejected to accept in case of sending or receiving E-mail. By analyzing and researching the method to control the access path, using the methods of source address-based policy routing and creating the extended NAT address mapping, configuring the router reasonably, the goal of solving these problems can be attained.

Key words: policy routing, source address, control technique, NAT mapping