How to redirect traffic to a proxy server?

RouterOS Beginner Basics
1

Hello!

it is necessary to redirect traffic to the proxy server port 3128 (squid). Squid does not work in transparent mode.

This example does not work

ip firewall nat add chain=dstnat action=accept \ 
    protocol=tcp src-address-list=192.168.1.123 dst-port=80 
 ip firewall nat add chain=dstnat action=dst-nat \ 
    protocol=tcp src-address-list=clients dst-port=80 \ 
    to-addresses=192.168.1.100 to-ports=3128
2

Is the proxy server installed on your routerboard or is this another proxy server?
See example here on this link.
In dutch but folow the printscreens a made
http://www.wirelessinfo.be/index.php/mikrotik/pages/transparant-proxy

3

another proxy server - pfsense

4

is this another proxy server?

yes - pfsense

5

I think that the problem is that your proxy replies with it’s own address (192.168.1.100) to clients. Make sure that it replies with original destination ip to client (reply to client must be from the same address that client used as destination). Of course you need to forward correctly this on routerboard.

Also I can’t understand the first firewall rule. Why are you filterning in nat / dstnat chain, not in filter forward? And it’s strange name for address-list - 192.168.1.123 . Maybe you want to use just single src-address, not address list?