I have a router with public address 200.17.198.xxx and it's everything working fine with the internet. But the LAN PCs behind this router can't reach a site hosted on another address that belong to the same AS, link 200.17.199.yyy.

Do I need some specific src-nat, or static routing rule? When I tried to perform a tracert to the site DNS, the LAN Pc is capable of translate to the correct address, but still can't reach the website, or even ping it. I tried to access another sites that I know they are hosted on another IP addressess on the same AS, and I noticed that I cannot access them too.

Thanks for your help, and if you need some specific information for clarification I can provide it .

You need a HairPin NAT.
https://help.mikrotik.com/docs/display/ROS/NAT (about a quarter of the way down the page)

Edit: I misread the question (that's what I get for doing it FAST), so this answer is not likely what you need... sorry.

What subnet mask does the router have on the WAN? If, for example, /22 and the ISP blocks client-to-client traffic on L2, it might not reach the destination address at all.

Or aren't these public IPs assignet using via NAT 1:1?

What does traceroute look like from a PC?

If you are inside the same AS you need isis/ospf for inter-AS routing

You need a HairPin NAT.
https://help.mikrotik.com/docs/display/ROS/NAT (about a quarter of the way down the page)

Edit: I misread the question (that's what I get for doing it FAST), so this answer is not likely what you need... sorry.

Thanks for your help! Yeah, i was imagining if the answer could involve something like HAIRPIN, but if you notice in the example in this link, the LAN PC are trying to access a web page on the same router from where he access the internet. In My case, I'm trying to reach a web page behind another router, with another IP address. This is driving me nuts actually haha