The AH protocol (IP protocol 51) forms the other part of IPsec. The AH does not encrypt data in the usual sense, by hiding the data, but it adds a tamper evident seal to the data. It also protects the non mutable fields in the IP header carrying the data, which includes the address fields of the IP header. The AH protocol should not be used alone when there is a requirement for data confidentiality. Figure 5 illustrates how AH encapsulates an IP packet.