What all is classified as "Interesting traffic?"

Question

So, recently I had read somewhere that when we write ACLs to permit local IP addresses to access those in an IP NAT pool, it's said that, "..when interesting traffic has been matched with the access list, it's pulled into the NAT process to be translated."

Now, my question is: how exactly does this pulling process work? When the ACL is detected, is it first checked with any other process that might use it (NAT for example), and then if it fails that check, only does it apply it to it's default traffic filtering function, or how does it work?

Also, what else comes under the category of "interesting traffic?"

Answer 1

Interesting traffic is literally the traffic you are interested in for a particular reason. In the case you describe, traffic that is permitted by the ACL is the interesting traffic.

When traffic is coming from an inside interface, destined for an outside interface, it is compared against the ACL to see if it should be translated before it is sent through the outside interface. Traffic that matches the ACL is what is interesting to the NAT process.