netdev - Re: [PATCH net-next] IPv6: enable TCP to use an anycast address

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Date:	Wed, 22 Jan 2014 06:32:36 -0800 (PST)
From:	François-Xavier Le Bail <fx.lebail@...oo.com>
To:	Alexey Kuznetsov <kuznet@....inr.ac.ru>
Cc:	netdev@...r.kernel.org, David Stevens <dlstevens@...ibm.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	David Miller <davem@...emloft.net>,
	Hideaki Yoshifuji <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH net-next] IPv6: enable TCP to use an anycast address

Hello,

> Actually, I was alerted by reset processing in your patch, it cannot be right.

Perhaps, I missed something.

My tests were:
1) enable anycast in tcp_v6_conn_request().
So, a client-serveur exchange with anycast destination address is possible.

2) try to connect with a port not listen by the server.
With unicast destination address, the client got a reset.
With anycast destination address, no reset, the client try several syn and give up.

3) enable anycast in tcp_v6_send_reset().
With anycast destination address, the client got a reset.
So unicast and anycast behave the same.

Do you see any problem with this behaviour ?

> Do not you think this must not be enabled for common use? At least
> some separate sysctl disabled by default.

We could indeed use a sysctl, disabled by default.

But my goal was to enable anycast address usage transparently, if possible.

It's only a possibility for some use cases and if it's dont break unicast TCP usage,
like I think it, I propose to enable this change without sysctl.

So, my proposals for the TCP case, in descending order of preference are:

1) No sysctl.
2) A sysctl disabled par default, used in tcp_v6_conn_request() and tcp_v6_send_reset().
3) A sysctl disabled par default, used in tcp_v6_send_reset(), if problem only here.

Greetings,
Francois-Xavier

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