>Number: 183265
>Category: kern
>Synopsis: ICMP6_PACKET_TOO_BIG doesn't create an entry in hostcache if
>multifib is active
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Thu Oct 24 09:20:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator: Luc Revardel
>Release: 8.2
>Organization:
NVidia
>Environment:
Linux 2.6.24-24-generic #1 SMP Fri Jul 24 22:46:06 UTC 2009 i686 GNU/Linux
>Description:
This issue occurs when running in multifib (MAXROUTES=11)
Upon reception of an ICMP6 PACKET_TOO_BIG, the hostcache isn't updated with the
MTU provided by the ICMP error message.
Subsequent IPv6 packet are not fragmented according to the new MTU value as
they should be.
>How-To-Repeat:
Ensure the kernel is compiled with MAXROUTES>1.
Ping a remote destination on the internet using large ping packets (>1500). The
route to the destination should contain a segment on which the MTU is smaller
than 1500 (say X) in order to reproduce the problem.
First ping packet (IPv6 fragment)should be emitted with a size of 1500.
The host shold receive an ICMP6 packet with a smaller MTU (X).
Next ping packet will be re-emitted with a size of 1500 instead of X.
>Fix:
It looks like the fibnum isn't managed by icmp6_mtudisc_update.
tcp_macmtu6 doesn't find a route matching the searched address.
Fixing inc.inc_fibnum in icmp6_mtudisc_update() seems to solve the problem:
icmp6_mtudisc_update()
[...]
bzero(&inc, sizeof(inc));
inc.inc_flags |= INC_ISIPV6;
inc.inc6_faddr = *dst;
+ inc.inc_fibnum = M_GETFIB(ip6cp->ip6c_m);
if (in6_setscope(&inc.inc6_faddr, m->m_pkthdr.rcvif, NULL))
return;
if (mtu < tcp_maxmtu6(&inc, NULL)) {
tcp_hc_updatemtu(&inc, mtu);
ICMP6STAT_INC(icp6s_pmtuchg);
}
[...]
>Release-Note:
>Audit-Trail:
>Unformatted:
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