kern/158307: ipv6_pktinfo breaks IPV6_USE_MIN_MTU

[Mark Andrews]

>Number:         158307
>Category:       kern
>Synopsis:       ipv6_pktinfo breaks IPV6_USE_MIN_MTU
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Jun 26 09:40:01 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Mark Andrews
>Release:        FreeBSD 8.2-STABLE i386
>Organization:
ISC
>Environment:
System: FreeBSD sex.dv.isc.org 8.2-STABLE FreeBSD 8.2-STABLE #10: Sat Feb 26 18:02:12 EST 2011 marka at sex.dv.isc.org:/usr/obj/usr/src/sys/DEBUG i386


>Description:

	If IPV6_PKTINFO is set as a control with sendmsg() then
	IPV6_USE_MIN_MTU state set by setsockopt() is ignored.
	
>How-To-Repeat:

	Run named and look at any IPv6 UDP response > 1280 bytes.
	These are all supposed to be fragmented at 1280 as named
	sets IPV6_USE_MIN_MTU to 1 on all IPv6 UDP sockets.

	PMTUD really doesn't work well for DNS which is one of the
	reasons why IPV6_USE_MIN_MTU was defined in the first place.

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