You can use this access list-based directive to bind outgoing TCP connections to specific local addresses. It might be useful if your system has multiple network interfaces, and you want to make sure all of Squid’s traffic leaves through one and not the other. Another possibility is that you have two or more interfaces with different costs or characteristics. You may want to send privileged user’s traffic through the expensive, uncongested link, while other users go out the cheap, low-quality connection. Don’t use this directive if your system has only one network interface.
If you have an tcp_outgoing_address rule with no ACLs, that address is used for requests that don’t match any of the other rules.
acl SomeUsers src 10.0.0.0/24 acl OtherUsers src 10.0.1.0/24 tcp_outgoing_address 172.16.0.1 SomeUsers tcp_outgoing_address 192.168.0.1 OtherUsers tcp_outgoing_address 172.16.5.1