AH with the MD5 (Message Digest 5) (an HMAC variant) authentication algorithm.
ESP with the MD5 (HMAC variant) authentication algorithm .
Both the AH and ESP protocols implement security services for IPSec.
AH provides data authentication and antireplay services.
ESP provides packet encryption and optional data authentication and antireplay services.
ESP encapsulates the protected data?either a full IP datagram (or only the payload)?with an ESP header and an ESP trailer. AH is embedded in the protected data; it inserts an AH header immediately after the outer IP header and before the inner IP datagram or payload. Traffic that originates and terminates at the IPSec peers can be sent in either tunnel or transport mode; all other traffic is sent in tunnel mode. Tunnel mode encapsulates and protects a full IP datagram, while transport mode encapsulates/protects the payload of an IP datagram. For more information about modes, refer to the mode (IPSec) command description
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a0080110bb6.html
