On which protocol number does the authentication header operate?
A.
06
B.
47
C.
50
D.
51
Explanation:
Authentication Header (AH) is a member of the IPsec protocol suite. AH guarantees
connectionless integrity and data origin authentication of IP packets. Further, it can optionally
protect against replay attacks by using the sliding window technique and discarding old packets
(see below).
AH operates directly on top of IP, using IP protocol number 51.
Reference: http://en.wikipedia.org/wiki/IPsec