The following reply was made to PR kern/33672; it has been noted by GNATS.

From: Hauke Fath <hauke@Espresso.Rhein-Neckar.DE>
To: gnats-bugs@NetBSD.org
Cc: Hauke Fath <hauke@Espresso.Rhein-Neckar.DE>
Subject: Re: kern/33672: sl(4) manpage does not document link[0-2]
Date: Sat, 10 Jun 2006 01:11:11 +0200

 Now that the OpenBSD folks have picked up this PR, and updated their
 sl(4) manpage, I might as well com up with a patch myself. I cut it
 from Hellmuth Michaelis' irip(4) manpage, fixed the spelling
 of "Van Jacobson" and adapted it.
  
 Please apply; and, while you're there, think about mentioning that
 sl(4) is a cloning device, now. 
 
 Ah, and please request a pull-up to netbsd-{2,3}.
 
 Index: sl.4
 ===================================================================
 RCS file: /cvsroot/src/share/man/man4/sl.4,v
 retrieving revision 1.10
 diff -u -u -r1.10 sl.4
 --- sl.4	5 Dec 2004 13:27:26 -0000	1.10
 +++ sl.4	9 Jun 2006 22:59:03 -0000
 @@ -45,13 +45,6 @@
  network interfaces using the
  .Tn SLIP
  protocol.
 -The
 -.Nm
 -interface can use Van Jacobson
 -.Tn TCP
 -header compression and
 -.Tn ICMP
 -filtering.
  .Pp
  However,
  .Tn SLIP
 @@ -69,6 +62,26 @@
  has been superceded by the Point-to-Point Protocol
  .Pq Tn PPP ,
  which does all of those things, and much more.
 +.Pp
 +The 
 +.Nm
 +driver provides Van Jacobson header compression,
 +and ICMP filtering, under control of the following options to
 +.Xr ifconfig 8 :
 +.Pp
 +.Bl -tag -width 15n -offset indent -compact
 +.It link0
 +Apply VJ compression to outgoing packets on this interface, 
 +and assume that incoming packets require decompression 
 +(default: disabled).
 +.It link1
 +Filter ICMP to save bandwidth on low-speed lines (default: disabled).
 +.It link2
 +Check incoming packets for VJ compression; 
 +if they appear to be compressed, automatically set 
 +link0 (default: enabled).
 +.El
 +.Pp
  .Sh DIAGNOSTICS
  .Bl -diag
  .It sl%d: af%d not supported .
 @@ -80,6 +93,7 @@
  .Xr inet 4 ,
  .Xr intro 4 ,
  .Xr ppp 4 ,
 +.Xr ifconfig 8 ,
  .Xr slattach 8 ,
  .Xr sliplogin 8 ,
  .Xr slstats 8