Darren Reed writes:
> >L2TP (and L2F) uses GRE-like headers over UDP/IP (by default), so the
> >stack looks something like:
> >
> > IP / PPP / L2TP-GRE / UDP / IP ...
> >
> >PPTP uses GRE-like headers over raw IP, so the stack is:
> >
> > IP / PPP / PPTP-GRE / IP ...
> >
> >
>
> Why have you inserted PPP in there?
If you're running IP over L2TP, then you generally have PPP as well.
L2TP is designed to tunnel layer two things (such as PPP), not layer
three things (such as IP).
The other possibility, I suppose, is the brand-new pseudo-wire
extensions for L2TP, but I'm not sure that's the right thing to
expect.
The actual bits on the wire would look like:
dd:dd:dd:dd:dd:dd \
ss:ss:ss:ss:ss:ss |- Ethernet
0800 /
45 00 ... - IP
06 A5 06 A5 ... - UDP
00 02 ... - L2TP
00 21 - PPP (protocol ID for IP)
45 00 ... - IP (inner packet)
(OK, well, L2TP is less GRE-ish than GRE-inspired, I suppose. L2F,
one of the L2TP precursors, was more like GRE.)
--
James Carlson, KISS Network <[EMAIL PROTECTED]>
Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677
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