Hello, i got a large block list with sites i would like to block. There are about 25547 different sites (ads). I own a RB751G-2HnD. Is there any efficient way to block all these sites with mikrotik? Can it even handle so many entries?

Multiple ways to handle this:

Use firewall and block based on site IP.
Use DNS and block by domain names.
Use Web Proxy and block by domain names / site sections etc.

All of these can be done transparently (just do a redirect rule in your firewall)

and what about the large volume? WIll my router be able to process without issues this large list?

and what about the large volume? WIll my router be able to process without issues this large list?

I personally think if you just want to block a huge list of websites, DNS with a transparent redirect is the best way to go. So I decided to have some fun and try this, since this is pretty interesting. I wrote an AutoIt script to generate a ROS script that adds 25k unique random DNS entries into the "/ip dns static" list. I attached the zipped AutoIt code to this post, so if anyone wants to experiment, try it.

This generates a 1mb .rsc script. I then imported this into a test RB 750GL.
/import DNStest.rsc took about 10 minutes

Picture of the DNS static list in winbox also attached to this post.

The 25k DNS entries consume about 8mb in the 750GL's ram. Doing DNS queries to the 750GL works normal, doesnt seem to introduce any load on the routers CPU when just my PC queries for one of these domains. No idea how this is going to perform when a large number of queries hit the router.

So yeah, fun little experiment for saturday evening.

Seriously... i couldn't expect a better answer! thanks a lot! you are champ!