The A2100 starts on the A21 at John's Cross, and finishes at the A21 / A28 junction to the north of Hastings. Along the way it passes through the historic town of Battle, where the A271 terminates on it. This is all a reminder that the A2100 is the former route of the A21 itself, which was diverted to the east onto a less urban route. The A21 entered Hastings along what is now the B2159 and so the easternmost section of the A2100 used to be part of the B2193.
With nearly half of the A2100's route, therefore, passing through the narrow streets of Battle and its southern neighbour of Telham, it is difficult to get any real speed up on the road, especially in summer when the volume of tourists visiting this important little corner of England is substantial. It is hardly surprising that the A21 now follows a different route.
When the A21 was transfered in the 1950,s, on to the B2091 the section between Johns Cross and Battle was numbered the B244 however quoting the reference on the B244 within the sabre wiki it states, This number did not last long, however, and the road soon returned to Class I status as the A2100. It remains this number.