On ven, jan 14, 2000 at 11:23:19 -0800, Guy Harris wrote:
> The page at
>
> http://www.isi.edu/in-notes/iana/assignments/ethernet-numbers
>
> describes the Ethernet type you changed Linux-X25 to use as "X.25
> Level 3", which I'd think of as the Packet Layer Protocol, or whatever
> it's called, rather than LAPB.
>
> I'd expect an X.25-layer-3-over-802.x to use LLC, as it's an
> SDLC-derived protocol just as LAPB is, rather than running atop raw
> Ethernet, so I guess I'm not surprised that it's sending LAPB frames
> rather than PLP frames.
>
> If it's doing LAPB-over-Ethernet rather than
> X.25-layer-3-over-Ethernet, that might also explain why it wasn't
> using Ethertype 0805.
>
> Is the Linux-X.25 X.25-over-Ethernet using a standard, or is it a
> Linuxism? If it's a standard, it sounds as if it's doing X.25 Level
> 2, i.e. LAPB, so you'd want to call the LAPB dissector rather than, as
> I did, calling the X.25 dissector.
According to the kernel documentation, Linux can do both. Here is an
extract from the CONFIG_X25 help :
One connects to an X.25 network either with a dedicated network card
using the X.21 protocol (not yet supported by Linux) or one can do
X.25 over a standard telephone line using an ordinary modem (say Y
to "X.25 async driver" below) or over Ethernet using an ordinary
Ethernet card and either the 802.2 LLC protocol (say Y to "802.2
LLC" below) or LAPB over Ethernet (say Y to "LAPB Data Link Driver"
and "LAPB over Ethernet driver" below).
> If there's either a *de jure* or *de facto* standard for
> LAPB-over-Ethernet that adds the length field, such an intermediate
> layer module would be the right thing to do.
>
> It'd be tricky if there isn't a standard Ethertype for it, though, as
> we don't yet have a general mechanism for configuring protcol handoff
> at run time (we have one for plugin protocols, but haven't yet
> generalized it to built-in protocols).
The lapbether.c file in linux-2.3.39 seems to use the ethertype
ETH_P_X25 which is defined as 0x0805 in if_ether.h
Olivier
--
That gets us out of deciding how to spell Reg[eE]xp?|RE . . .
Of course, then we have to decide what ref $re returns... :-)
-- Larry Wall in <199710171838.LAA24968@xxxxxxxx>
