netdev - Strange IPSec / ICMPv6 redirect behavior

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Date:	Fri, 19 Apr 2013 00:03:22 +0200
From:	Florent Fourcot <florent.fourcot@...t-bretagne.fr>
To:	netdev@...r.kernel.org
Subject: Strange IPSec / ICMPv6 redirect behavior

Hi,

I have this kind of configuration on my network:

----------                     -----------------
|        |=======  IPv6  ======|               |
| Client |                     |               |
|  A::1  |                     |               |
----------                     |               |
                                | IPSec Gateway |
-----------------              |               |
|  IPv4 Gateway |=IPv6 in IPv4=|               |
|  to Internet  |              |               |
-----------------              -----------------
     ||
     ||IPv6 in IPv4
     ||
-----------
| Client  |
|  B::2   |
-----------

The IPSec gateway has only one network card, i.e. unencrypted packet 
from the client come in eth0 and go out encrypted from eth0.

This work, but I get ICMP redirect like without IPSec encryption. A 
simplified tcpdump output give this:

IP6 A::1 > B::2: ICMP6, echo request
IP6 fe80::3 > A::1: ICMP6, redirect, B::2 to B::2
IP A.B.C.D > E.F.G.H: ESP(spi=0x3be56104,seq=0xa494)
IP E.F.G.H > A.B.C.D: ESP(spi=0xce300198,seq=0x1958b)
IP6 B::2 > A::1: ICMP6, echo reply

Of course, the redirect is invalid, since the remote address is not 
directly reachable. The kernel of the client complains with 
"rt6_redirect: source isn't a valid nexthop for redirect target".

I can disable acceptance of ICMP redirect on the client, but it does not 
look like a good solution (ICMP redirect still flood the network). Any 
idea to solve this?

Regards,

-- 
Florent Fourcot.
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