Please see kern/18799.

Slip doesn't work for me (even though I used many times successfully
before 1.6).

Last I checked, 1.5.3 worked fine in Oct. 2002.

Also, in Oct. 2002, I knew the serial (non-slip) connection worked fine,
because I could run a getty on it and then login with cu just fine.

And in April 2003, I tried to use slip from NetBSD 1.6.x to FreeBSD box
and that didn't work.

   Jeremy C. Reed
   http://www.reedmedia.net/