All, am I interpresting this card right.

Basicaly if its last piece of ICE on a server, when runner encounters it, unless they break the subroutine, they get sent back to the start at the first piece of ICE on th3e server and have to overcome everything all over again.

Any guidance appreciated.

That's pretty much it. Two points additionally:

one, Cell Portal also de-rezzes itself when the subroutine resolves.

two, the runner can choose to jack out after being returned to the start of the server (unless another effect prevents this).

The derezz was pretty much the only part I was certain on lol. Don't mind if runner jacks out at that point. They have still wasted the same amount of credits.

Many thanks for confirming this.

So if cell portal is the only Ice in front of a server does the Runner continue to hit it over and over again?

Cell Portal with a sufficiently over-advanced Braintrust in the score area was one of the first hypothetical situations to trigger the necessity of an Infinite Loop rule, as detailed in the official FAQ. (You should go read and familiarize yourself with it.)

• If the runner ran through a Whirlpool and cannot choose to jack out, then at some point the Corp must elect not to rez Cell Portal and allow the runner past.
• If the runner can choose to jack out, then the corp can continue to rez Cell Portal until the Runner elects to jack out.

5 hours ago, Kutpurse said:

So if cell portal is the only Ice in front of a server does the Runner continue to hit it over and over again?

Cell Portal derezzes each time the subroutine resolves. The Corp must be able to rez it each time.