Re: Linktype needed

["Guy Harris" <guy () alum mit edu>]

Martin Angler said:
> my name is Martin Angler and I am developing a BACnet MS/TP - enabled
netdevice-driver
> under GNU/Debian Linux. Now I've seen, that there is no linktype that
specifies BACnet
> MS/TP. So I wanted to ask whether you could define/implement a
corresponding linktype.

I infer from some stuff I've seen that BACnet MS/TP is a link-layer
protocol atop which the higher-level BACnet protocols can run (just as
they can run atop UDP and 802.2).

Will your driver supply "raw" packets with a header specified by the
BACnet specification (the ISO standard appears to cost over 350 CHF, so I
haven't bought it), or will it supply some form of "cooked" software that
might not be what other BACnet MS/TP capture mechanisms might supply?  If
the former, the linktype should probably be called DLT_BACNET_MS_TP or
something such as that; if the latter, the name should probably have
something in it to indicate what type of header it is (see, for example,
DLT_ARCNET, which should perhaps have been DLT_ARCNET_BSD, and
DLT_ARCNET_LINUX, or DLT_APPLE_IP_OVER_IEEE1394, which is not raw Firewire
but has a synthetic header).

> Other people that worked on an MS/TP dissector (www.abmlinux.de) already
tried to
> contact you, but without success.

I don't think I've seen that on tcpdump-workers.  Do they have their own
driver and, if so, does it supply the same link-layer header (if not, it'd
need a separate DLT_ value)?



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