docs/157453: Document 16-fib cap in setfib.2

[Ben Kaduk]

>Number:         157453
>Category:       docs
>Synopsis:       Document 16-fib cap in setfib.2
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-doc
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          doc-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue May 31 05:00:22 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Ben Kaduk
>Release:        9-current
>Organization:
MIT SIPB
>Environment:
n/a
>Description:
ipfw.8 currently references setfib.1 (though see docs/157452 which changes this to setfib.2) for explaining why the maximum fib value is 15.  But the setfib manual page does not describe this at all.  The attached patch provides the requisite documentation, per sys/net/route.h:96.
>How-To-Repeat:

>Fix:


Patch attached with submission follows:

--- setfib.2.orig	2011-05-31 00:48:50.000000000 -0400
+++ setfib.2	2011-05-31 00:54:57.000000000 -0400
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD: src/lib/libc/sys/setfib.2,v 1.6 2009/09/18 14:17:00 brueffer Exp $
 .\"
-.Dd August 8, 2008
+.Dd May 31, 2011
 .Dt SETFIB 2
 .Os
 .Sh NAME
@@ -49,6 +49,10 @@
 may be retrieved by the 
 .Va net.fibs
 sysctl.
+The system maximum is set in the kernel configuration file with
+.Pq Cd "options	ROUTETABLES=N" .
+However, this maximum is capped at 15 due to the implementation storing
+the fib number in a 4-bit field in mbuf flags.
 The default fib of the process will be applied to all protocol families 
 that support multiple fibs, and ignored by those that do not.
 The default fib for a process may be overridden for a socket with the use


>Release-Note:
>Audit-Trail:
>Unformatted: