netdev - Re: [PATCH net-next v2] IPv6: add option to use Subnet-Router anycast addresses as source addresses

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Date:	Thu, 2 Jan 2014 10:56:17 -0800 (PST)
From:	François-Xavier Le Bail <fx.lebail@...oo.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	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 v2] IPv6: add option to use Subnet-Router anycast addresses as source addresses

On Thu, 1/2/14, Hannes Frederic Sowa <hannes@...essinduktion.org> wrote:

>> This change allows to follow a recommandation of RFC4942.
>> 
>> - Add "enable_anycast_src" sysctl to control the use of Subnet-Router anycast
>>   addresses as source addresses. This sysctl is false by default to preserve
>>   existing behavior.
>> - Use it in ip6_datagram_send_ctl() and icmpv6_echo_reply().
 
 > It is very cool that you are working on this. I had this on my TODO list for a
 long time.

Thanks,I think also it is useful.

>> 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
>> 
>>    [...]
 
> Actually, the restriction was lifted by RFC 4291 ("IP Version 6
> Addressing Architecture").
 
Exact.
 
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index d71afa8..2a062a7 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1094,6 +1094,12 @@ bindv6only - BOOLEAN
>  
>      Default: FALSE (as specified in RFC3493)
>  
> +enable_anycast_src - BOOLEAN
> +    Controls the use of Subnet-Router anycast addresses as source addresses
> +    TRUE:  enabled
> +    FALSE: disabled
> +    Default: FALSE
> +
 
> I wouldn't actually add this knob, we can just enable that by default.

I think we need to keep by default the existing behaviour (ICMPv6 echo reply with unicast)
in case some setups use it, and use "enable_anycast_src" to change the behaviour 
according to RFC4942.

> Also it should be no problem to bind() to those addresses.
 
> I am still unsure what to do with a bind to any or if the address must be
> bound specifically (maybe that is worth a knob).

> In the long term I would like to see that we can add additional anycast
> addresses via iproute:
 
> ip -6 a a 1234::1/64 dev eth0 anycast
 
> or something like that. That should be rather easy, as in just incrementing
> the anycast counter for an interface in inet6_rtm_newaddr
> and adding a flag to ifa_flags which gets passed down by iproute2.
 
> I'll do some research on if this should also get integrated with source address selection.

It can be the objects of future evolutions.
I have to think about these.
 
> Hannes
 
Thanks,
Francois-Xavier
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