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

From: Bill Fink <[email-masked]>
Date: Tue, 7 Jan 2014 17:55:07 -0500

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 <[email-masked]>
> ---
> 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.

					-Bill