The authentication header (AH) in IPSec includes a message authentication code (MAC), which is calculated over all of the fields of the IPSec packet except IP header fields that either do not change in transit (immutable) or that are predictable in value upon arrival at the endpoint for the AH SA. Fields that may change in transit and whose value on arrival are unpredictable are set to zero for purposes of calculation at both source and destination.

a. For each of the fields in the IPv4 header, indicate whether the field is immutable, mutable but predictable, or mutable.

b. Do the same for the IPv6 header. In each case, justify your decision for each field.