This was found by Vandz years ago. he was the first to get to round 2147 legit (by pausing the game every few hours).
The concept of the stratergy (which was practically a glitch) was that you had to be past round 26 i believe, and had to start off at the end of the bridge (the end closest to the flogger). after about 5-10 seconds after the round started, you walked forwards. by then, 20-25 zombies would've spawned within the fishing hut area. Either switching on the flogger, or me personally, using the DG-2, you could kill all the zombies that spawned. then thats it. round over. This was by far the most efficient way of getting to a higher round (solo only), however i think of it more as a glitch, considering their is only 25 zombies spawning. after round 266, the zombies started to glitch up, and you had a 50% of having a round full of "round 1 zombies", which meant you could kill them instantly, as apposed to using 1000 thompson bullets to kill them.