IPSECAH(7P) Protocols IPSECAH(7P)


NAME


ipsecah, AH - IPsec Authentication Header

SYNOPSIS


drv/ipsecah


DESCRIPTION


The ipsecah module (AH) provides strong integrity, authentication, and
partial sequence integrity (replay protection) to IP datagrams. AH
protects the parts of the IP datagram that can be predicted by the sender
as it will be received by the receiver. For example, the IP TTL field is
not a predictable field, and is not protected by AH.


AH is inserted between the IP header and the transport header. The
transport header can be TCP, UDP, ICMP, or another IP header, if
tunnels are being used.

AH Device


AH is implemented as a module that is auto-pushed on top of IP. The entry
/dev/ipsecah is used for tuning AH with ndd(1M).

Authentication Algorithms


Current authentication algorithms supported include HMAC-MD5 and HMAC-
SHA-1. Each authentication algorithm has its own key size and key format
properties. You can obtain a list of authentication algorithms and their
properties by using the ipsecalgs(1M) command. You can also use the
functions described in the getipsecalgbyname(3NSL) man page to retrieve
the properties of algorithms.

Security Considerations


Without replay protection enabled, AH is vulnerable to replay attacks.
AH does not protect against eavesdropping. Data protected with AH can
still be seen by an adversary.

ATTRIBUTES


See attributes(5) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Interface Stability | Committed |
+--------------------+-----------------+

SEE ALSO


ipsecalgs(1M), ipsecconf(1M), ndd(1M), attributes(5),
getipsecalgbyname(3NSL), ip(7P), ipsec(7P), ipsecesp(7P)


Kent, S. and Atkinson, R. RFC 2402, IP Authentication Header, The
Internet Society, 1998.


September 25, 2009 IPSECAH(7P)