kern/158307: ipv6_pktinfo breaks IPV6_USE_MIN_MTU

Mark Andrews marka at
Sun Jun 26 09:40:11 UTC 2011

>Number:         158307
>Category:       kern
>Synopsis:       ipv6_pktinfo breaks IPV6_USE_MIN_MTU
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Jun 26 09:40:01 UTC 2011
>Originator:     Mark Andrews
>Release:        FreeBSD 8.2-STABLE i386
System: FreeBSD 8.2-STABLE FreeBSD 8.2-STABLE #10: Sat Feb 26 18:02:12 EST 2011 marka at i386


	If IPV6_PKTINFO is set as a control with sendmsg() then
	IPV6_USE_MIN_MTU state set by setsockopt() is ignored.

	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.


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