The following instructions apply if you have a Linux platform and want
libpcap to support the 'ACN' WAN/LAN router product from SITA
(http://www.sita.aero)

This might also work on non-Linux Unix-compatible platforms, but that
has not been tested.

See also the libpcap INSTALL.txt file for further libpcap configuration
options.

These additions/extensions have been made to PCAP to allow it to
capture packets from a SITA ACN device (and potentially others).

To enable its support you need to ensure that the distribution has
a correct configure.ac file; that can be created if neccessay by
using the normal autoconf procedure of:

aclocal
autoconf
autoheader
automake

Then run configure with the 'sita' option:

./configure --with-sita

Applications built with libpcap configured in this way will only detect SITA
ACN interfaces and will not capture from the native OS packet stream.

The SITA extension provides a remote datascope operation for capturing
both WAN and LAN protocols.  It effectively splits the operation of
PCAP into two halves.  The top layer performs the majority of the
work, but interfaces via a TCP session to remote agents that
provide the lower layer functionality of actual sniffing and
filtering. More detailed information regarding the functions and
inter-device protocol and naming conventions are described in detail
in 'pcap-sita.html'.

pcap_findalldevs() reads the local system's /etc/hosts file looking
for host names that match the format of IOP type devices.  ie.  aaa_I_x_y
and then queries each associated IP address for a list of its WAN and
LAN devices.  The local system the aggregates the lists obtained from
each IOP, sorts it, and provides it (to Wireshark et.al) as the
list of monitorable interfaces.

Once a valid interface has been selected, pcap_open() is called
which opens a TCP session (to a well known port) on the target IOP
and tells it to start monitoring.

All captured packets are then forwarded across that TCP session
back to the local 'top layer' for forwarding to the actual
sniffing program (wireshark...)

Note that the DLT_SITA link-layer type includes a proprietary header
that is documented as part of the SITA dissector of Wireshark and is
also described in 'pcap-sita.html' for posterity sake.

That header provides:
- Packet direction (in/out) (1 octet)
- Link layer hardware signal status (1 octet)
- Transmit/Receive error status (2 octets)
- Encapsulated WAN protocol ID (1 octet)