If you are using Linux 2.4 and iptables, you should probably use the enable-linux-netfilter option when you run (or re-run) ./configure. It enables some Linux-specific code so that Squid can find the IP address of the origin server from where the request was originally sent. Squid normally gets the origin server name (and/or address) from the Host header. The enable-linux-netfilter feature is necessary only for requests that don't have a Host header. Statistics show that almost all requests have the Host header, so you may actually be able to get by without the enable-linux-netfilter option.
If you are using the IPFilter package (with NetBSD, Solaris, and others), you should use the enable-ipf-transparent option for the same reason. On OpenBSD, you should use the enable-pf-transparent option. Each time you run ./configure you must recompile Squid, as described in Section 3.8.
After you get the ./configure options figured out, and Squid recompiled, you can edit squid.conf. As a starting point, make sure the following directives are defined with the given values:
httpd_accel_host virtual httpd_accel_port 80 httpd_accel_uses_host_header on httpd_accel_with_proxy on httpd_accel_single_host off
The httpd_accel_host directive is the key. It instructs Squid to accept HTTP requests with partial URIs. The httpd_accel_uses_host_header directive is enabled so that Squid uses the Host header to reconstruct full URIs. The virtual keyword instructs Squid to put the origin server's IP address in the URL when the Host header is absent.
The httpd_accel_with_proxy directive controls whether or not Squid accepts both HTTP server (partial URI) requests, and proxy (full URI) requests. It should probably be enabled for interception caching. Squid may still work if httpd_accel_with_proxy is disabled as long as none of your clients are explicitly configured for Squid as a proxy.
The httpd_accel_single_host directive is normally disabled, but it was enabled by default in some earlier versions of Squid. I've listed it here to make sure that it is disabled for interception caching.
If you are intercepting more than just port 80, you may want to set httpd_accel_port to 0. See Appendix A for more information.
If you're not using WCCP, you should be ready to start sending intercepted traffic to Squid. Give it a try by surfing the Web with your browser or by making some test requests with squidclient. If you are using WCCP, there is just one more step that you must complete.
The router doesn't send any traffic to Squid until Squid announces itself to the router. To make Squid do that, add these lines to your squid.conf:
wccp_router 172.16.102.65 wccp_version 4
Your router has many interfaces. Be sure to use the IP address of the interface closest to Squid. This is necessary because the WCCP messages coming from the router have the source IP address set to the address of the outgoing interface. Squid rejects WCCP messages if the source address doesn't match the wccp_router value.
The WCCPv1 document specifies 4 as the protocol version number. However, some users report that Cisco IOS 11.2 supports only Version 3. If you are using this version of IOS, change the version in squid.conf: