>How would you interface a dial-on-demand daemon to the kernel?
>I'll need such a daemon to manage ISDN connections, but I think a global
>approach which covers PPP and CSLIP connections as well would be 
>the way to go.
>[...]

I one time I saw this implemented (it was under SunOS, I believe), they did
the following:

They ran a user-level process that marked the interface as being "UP" (so it
was valid to send packets over it), but marked it in some other way as being
a demand dial interface.  When a packet was queued for the interface, it
then communicated with the user-level daemon in some way, which then did the
actual dialing.  If the dialing was successful, it then told the interface it
was up for real.  I don't know the details of the way the kernel communicated
with the user-level daemon.

Even though your doing ISDN, aren't you going to need some sort of TCP/IP
encapsulation over the link?  The one time I set up ISDN, we ran PPP over it.

Seems to me that PPP would be a good canidate for this.  pppd already does the
dialing part.

--Ken