kern/70399: ipfilter breaks IPv6 path mtu discovery

Mark Andrews marka at
Fri Aug 13 02:40:24 PDT 2004

>Number:         70399
>Category:       kern
>Synopsis:       ipfilter breaks IPv6 path mtu discovery
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Aug 13 09:40:23 GMT 2004
>Originator:     Mark Andrews
>Release:        4.10 stable
FreeBSD 4.10-STABLE FreeBSD 4.10-STABLE #11: Fri Aug 13 15:27:12 EST 2004     marka at  i386

icmp6_error() prepends a mbuf to send ICMP6_PACKET_TOO_BIG.  When
ipfilter is active there is a attempt to pullup the full packet
which fails because there is not a associated cluster.

ICMP6_TIME_EXCEEDED can also demonstate the problem if traceroute6
uses a size of 105 or greater.
      have a inbound interface w/ a mtu of 1500 and a output interface
with a mtu of 1280 (e.g. gif).  Have ipf active.  Attempt to send
a packet > 1280 octets through the router.  The ICMP6_PACKET_TOO_BIG
packet is dropped before it is emitted.

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