> Before I saw PPPoE, I would have agreed with you.  But it now seems to
> me that PPP is a layer that can be layered on top of - at least - a tty
> line or an Ethernet interface.

Or an ISDN line. Or a sync interface card. See sys/net/if_sppp*, which is
used for both (where the ISDN drivers are not integrated, but available).

And exactly because of the "not easy to get a filedescriptor for the lower
layer" this is a pure in-kernel implementation of PPP, which only needs a
few parameters set by "spppcontrol". Not a briliant design, and not good
it's a complete separate implementation.

I was very reserved until I found (a) a remote machine which worked with
if_sppp and refused to talk to pppd and (b) the time to establish a
connection (on demand) decreased on our 4 MB RAM ISDN router due to one
process less being swapped in from about 30 seconds down to 1-2 seconds. But
beware - the PPP implementation in if_spp* is buggy, and it's not the newest
version (as used by FreeBSD), because that version has introduced other
bugs.


Martin