SLIP slipping away

[Robert Watson]

On Fri, 14 Mar 2008, Kai Lockwood wrote:

> I am having difficulty setting up a SLIP connection between a Debian 4.0 box 
> and FreeBSD 7.0-STABLE. I have enabled the sl driver in the kernel. I have 
> tried using slattach on /dev/cuad0 (usually "slattach -s 115200 /dev/cuad0) 
> only to watch slattach immediately die with no output as to why. If I give 
> the -l option it creates the sl0 interface but will not accept traffic. 
> Reading through the years old FAQs states that a 'netstat -i' with the sl 
> driver installed should show sl interfaces but netstat does not list any sl 
> interfaces. I have tried to load the kernel module if_sl but I have had no 
> success.
>
> Has anyone on this list had any success with using SLIP?

A few years ago, I tried to find someone to test SLIP locking patches without 
much luck.  I know of no specific reason why it shouldn't work other than age 
and lack of testing.  If we want to continue to support SLIP, my suggestion 
would be that we move the implementation to userspace with if_tun, avoiding 
the complexities and inter-dependencies of hooking SLIP into the tty line 
discipline code in the kernel.  If something has broken, it might well relate 
to that complexity.  Do you know of anyone using SLIP in production who would 
be willing to do the legwork on testing, etc, or is this a casual "I wonder if 
SLIP still works" sort of thing?  I don't actually know of any sites still 
using it, and I've not seen a report of successful or failed use in years...

Robert N M Watson
Computer Laboratory
University of Cambridge