This module matches the parameters in Authentication header of IPsec packets.
.TP
[\fB!\fP] \fB--ahspi\fP \fIspi\fP[\fB:\fP\fIspi\fP]
Matches SPI.
.TP
[\fB!\fP] \fB--ahlen\fP \fIlength\fP
Total length of this header in octets.
.TP
.BI "--ahres"
Matches if the reserved field is filled with zero.