You can have the proxy access another proxy for some resources instead of accessing the remote server. This means you can chain proxies together. Chaining is a good way to organize several proxies behind a firewall. Chaining also lets you build hierarchical caching.
Access the Server Manager and click the Routing tab.
Click the Set Routing Preferences link. The Set Routing Preferences page displays.
Select the resource from the drop-down list or click the Regular Expression button, enter a regular expression and click OK.
Select the Route Through option in the Routing Through Another Proxy section of the page.
Select the Another Proxy checkbox.
In the Another Proxy field, enter the name or IP address of the proxy sever that you want to route through.
Click OK.
Click Restart Required. The Apply Changes page displays.
Click the Restart Proxy Server button to apply the changes.