RFC 2402 (rfc2402) - Page 2 of 22
IP Authentication Header
Alternative Format: Original Text Document
RFC 2402 IP Authentication Header November 1998
3.3.3.2.2 Implicit Packet Padding......................12
3.3.4 Fragmentation..........................................12
3.4 Inbound Packet Processing...................................13
3.4.1 Reassembly.............................................13
3.4.2 Security Association Lookup............................13
3.4.3 Sequence Number Verification...........................13
3.4.4 Integrity Check Value Verification.....................15
4. Auditing.........................................................15
5. Conformance Requirements.........................................16
6. Security Considerations..........................................16
7. Differences from RFC 1826........................................16
Acknowledgements....................................................17
Appendix A -- Mutability of IP Options/Extension Headers............18
A1. IPv4 Options.................................................18
A2. IPv6 Extension Headers.......................................19
References..........................................................20
Disclaimer..........................................................21
Author Information..................................................22
Full Copyright Statement............................................22
1. Introduction
The IP Authentication Header (AH) is used to provide connectionless
integrity and data origin authentication for IP datagrams (hereafter
referred to as just "authentication"), and to provide protection
against replays. This latter, optional service may be selected, by
the receiver, when a Security Association is established. (Although
the default calls for the sender to increment the Sequence Number
used for anti-replay, the service is effective only if the receiver
checks the Sequence Number.) AH provides authentication for as much
of the IP header as possible, as well as for upper level protocol
data. However, some IP header fields may change in transit and the
value of these fields, when the packet arrives at the receiver, may
not be predictable by the sender. The values of such fields cannot
be protected by AH. Thus the protection provided to the IP header by
AH is somewhat piecemeal.
AH may be applied alone, in combination with the IP Encapsulating
Security Payload (ESP) [KA97b], or in a nested fashion through the
use of tunnel mode (see "Security Architecture for the Internet
Protocol" [KA97a], hereafter referred to as the Security Architecture
document). Security services can be provided between a pair of
communicating hosts, between a pair of communicating security
gateways, or between a security gateway and a host. ESP may be used
to provide the same security services, and it also provides a
confidentiality (encryption) service. The primary difference between
the authentication provided by ESP and AH is the extent of the
coverage. Specifically, ESP does not protect any IP header fields
Kent & Atkinson Standards Track