netdev - Re: [PATCH net-next v5] IPv6: add the option to use anycast addresses as source addresses in echo reply

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Message-ID: <20140107230134.GK30393@order.stressinduktion.org>
Date:	Wed, 8 Jan 2014 00:01:34 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Bill Fink <billfink@...dspring.com>
Cc:	Francois-Xavier Le Bail <fx.lebail@...oo.com>,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki Yoshifuji <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net-next v5] IPv6: add the option to use anycast addresses as source addresses in echo reply

On Tue, Jan 07, 2014 at 05:55:07PM -0500, Bill Fink wrote:
> On Tue,  7 Jan 2014, Francois-Xavier Le Bail wrote:
> 
> > This change allows to follow a recommandation of RFC4942.
> > 
> > - Add "anycast_src_echo_reply" sysctl to control the use of anycast addresses
> >   as source addresses for ICMPv6 echo reply. This sysctl is false by default
> >   to preserve existing behavior.
> > - Add inline check ipv6_anycast_destination().
> > - Use them in icmpv6_echo_reply().
> > 
> > Reference:
> > RFC4942 - IPv6 Transition/Coexistence Security Considerations
> >    (http://tools.ietf.org/html/rfc4942#section-2.1.6)
> > 
> > 2.1.6. Anycast Traffic Identification and Security
> > 
> >    [...]
> >    To avoid exposing knowledge about the internal structure of the
> >    network, it is recommended that anycast servers now take advantage of
> >    the ability to return responses with the anycast address as the
> >    source address if possible.
> > 
> > Signed-off-by: Francois-Xavier Le Bail <fx.lebail@...oo.com>
> > ---
> > v4: update Subject and Documentation, this work also with anycast addresses
> >     created via API, not just with Subnet-Router anycast addresses.
> > 
> > v5: alternative way, replace ipv6_chk_acast_addr() test by
> >     ipv6_anycast_destination() test.
> 
> Why is ICMPV6 Echo Reply special?  Can't the internal structure
> of the network be divined from other ICMPv6 responses such as
> Destination Unreachable, Time Exceeded (Hop Limit), and Parameter
> Problem.

No, here destination must match the source address so that the other side
handles accordingly when the icmp error is pushed up to the socket layer.

Greetings,

  Hannes

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