docs/150917: icmp.4, wrong description of icmplim and icmplim_output sysctls

[Nikos Vassiliadis]

>Number:         150917
>Category:       docs
>Synopsis:       icmp.4, wrong description of icmplim and icmplim_output sysctls
>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:   Fri Sep 24 13:50:01 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Nikos Vassiliadis
>Release:        9.0-CURRENT
>Organization:
>Environment:
FreeBSD lab.local 9.0-CURRENT FreeBSD 9.0-CURRENT #1 r213086M: Fri Sep 24 15:52:57 EEST 2010     root at lab.local:/usr/obj/usr/src/sys/LAB  i386

>Description:
The icmp manual page describes icmplim and icmplim_output wrongly.

     icmplim	     (integer) Bandwidth limit for ICMP replies in pack-
		     ets/second.  Used when icmplim_output is non-zero.
		     Defaults to 200.

     icmplim_output  (boolean) Enable/disable bandwidth limiting of ICMP
		     replies.  Defaults to true.

The correct description [1] is this:
If you do not want to see messages about this in your log files, but you still want the kernel to do response limiting, you can use the net.inet.icmp.icmplim_output sysctl variable to disable the output like this:
# sysctl -w net.inet.icmp.icmplim_output=0

Finally, if you want to disable response limiting, you can set the net.inet.icmp.icmplim sysctl variable (see above for an example) to 0. Disabling response limiting is discouraged for the reasons listed above.

[1] http://www.freebsd.org/doc/en/books/faq/networking.html#ICMP-RESPONSE-BW-LIMIT
>How-To-Repeat:
n/a
>Fix:
Use the attached patch

Patch attached with submission follows:

Index: src/share/man/man4/icmp.4
===================================================================
--- src/share/man/man4/icmp.4   (revision 213086)
+++ src/share/man/man4/icmp.4   (working copy)
@@ -179,15 +179,16 @@
 the system replies to an ICMP Address Mask Request packet.
 Defaults to 0.
 .It Va icmplim
-.Pq Vt integer
-Bandwidth limit for ICMP replies in packets/second.
-Used when
-.Va icmplim_output
-is non-zero.
+.Pq Vt "unsigned integer"
+Limit for ICMP or TCP RST responses in packets per second.
+Response limiting is disabled by setting
+.Va icmplim
+to 0.
 Defaults to 200.
 .It Va icmplim_output
 .Pq Vt boolean
-Enable/disable bandwidth limiting of ICMP replies.
+Enable/disable logging of
+.Va icmplim .
 Defaults to true.
 .It Va drop_redirect
 .Pq Vt boolean

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