Mikrotik Web Proxy question

RouterOS General
1

hi,

I have a Mikrotik CCR configured for Web Proxy.
it has 2 IP addresses on the same interface. Example.

100.100.100.1
200.200.200.1

the web proxy uses 200.200.200.1 as the src.address however on the PC browsers proxy, I configured 100.100.100.1 and it still worked, i checked via whatismyipaddress.com and it shows 200.200.200.1.

How does mikrotik know to translate 100.100.100.1 to 200.200.200.1 without any nat rules?

thanks!