Authentication Header

Authentication Header
Authentication Header (AH) is IP protocol number 51. It authenticates the
packet, including the IP header, but does not encrypt the packet payload. AH
works by creating an MD5 or SHA-1 hash from the IP header (except any
changeable fields such as Time to Live) and the packet payload. It sends this
hash in an AH header after the Layer 3 IP header. The receiving host also
creates a hash value from the IP header and original payload and compares