How do I set up RouterOS to use web proxy on another machine?

Solution 1:

No need of setting proxy in RouterOS. You can route all outgoing HTTP traffic to the server directly thru NAT:

ip firewall nat add in-interface=eth1 src-address=!<IP of Squid machine> dst-port=80 protocol=tcp action=dst-nat to-addresses=<IP of Squid machine> to-ports=8080 

The last parameter "src-address=!..." is needed in case which squid machine communicates thru same interface as the other machines. Otherwise it would go like this:

1. Computer sends HTTP request
2. RouterOS destinates this packet to squid
3. Squid sends HTTP request to webserver
4. RouterOS destinates squid request again to squid -> loop

Solution 2:

It can be done with the parent-proxy setting:

/ip proxy
set parent-proxy=<IP of Squid machine> parent-proxy-port=3128

Solution 3:

/ip proxy
set parent-proxy=<IP of Squid machine> parent-proxy-port=3128

/ip firewall nat
chain=dstnat src-address=!<IP of Squid machine> protocol=tcp dst-port=80  src-address-list=<IP of Local machine> action=redirect to-ports=8080