IPSECAH(4P) Protocols IPSECAH(4P)
NAME
ipsecah, AH - IPsec Authentication Header
SYNOPSIS
drv/ipsecahDESCRIPTION
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(8).
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(8) 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(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Interface Stability | Committed |
+--------------------+-----------------+
SEE ALSO
getipsecalgbyname(3NSL),
ip(4P),
ipsec(4P),
ipsecesp(4P),
attributes(7),
ipsecalgs(8),
ipsecconf(8),
ndd(8) Kent, S. and Atkinson, R.
RFC 2402, IP Authentication Header, The
Internet Society, 1998.
September 25, 2009 IPSECAH(4P)
