On Mon, Dec 18, 2000 at 10:02:08AM +0100, Olaf Kirch wrote:
> > In some mail to tcpdump-workers, Andi Kleen said, when I asked whether
> > there was any way to determine what the ISDN encapsulation was:
> >
> > I don't know of any (except for maybe relying on the unstable
> > /dev/isdnctrl ioctls)
>
> Well, this patch worked reliably on 2.2.x kernels for me. I'll have
> to get ISDN working on 2.4 yet, so I can't tell you about that. I'll
> get back to you on this issue once I've tested it.
>
> > variety of Linux kernels and versions of the ISDN4Linux code?
>
> I'm basically interested in i4l on stable Linux kernels. If tcpdumping
> i4l on a development kernel doesn't work I couldn't care less :)
Currently, we run the "isdn", "isdY", and "ippp" devices in "cooked
mode", which means we use PF_PACKET/SOCK_DGRAM, throwing away the
link-layer header, and construct a link-layer header from the stuff in
the "sockaddr_ll" structure filled in by "recvfrom()".
This should handle ISDN for now; I'm inclined to defer using SOCK_RAW,
which would give us the real link-layer header, for the next release
(especially given that the "ippp" devices have different link-layer
headers on incoming and outgoing packets...).
Note also that, if we do use SOCK_RAW:
DLT_I4L_RAWIP isn't necessary - that's just DLT_RAW;
DLT_I4L_CISCOH can, I think, just be DLT_PPP_SERIAL - that came
from NetBSD, and checks both for a normal PPP header and a Cisco
point-to-point HDLC header (as described in section 4.3.1 of RFC
1547) - that may also apply to DLT_I4L_CISCOHK.
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