[lwip-devel] [patch #7808] IPv6: Add IPV6_V6ONLY functionality

[James Smith]

Follow-up Comment #2, patch #7808 (project lwip):

Ivan says in comment#1
> Could you summarize the RFC requirement, please?

Basically RFC#3493 states that by default AF_INET6 sockets should allow IPv4
connections, but if an application explicitly wants to ignore IPv6 connections
on its IPv6 sockets then it should use the IPV6_V6ONLY option.

Here is a quote of (most) of the relevant section, since it is not too large
(from http://www.faqs.org/rfcs/rfc3493.html):

 5.3 IPV6_V6ONLY option for AF_INET6 Sockets

  This socket option restricts AF_INET6 sockets to IPv6
  communications only. As stated in section
  <3.7 Compatibility with IPv4 Nodes>, AF_INET6 sockets
  may be used for both IPv4 and IPv6 communications.
  Some applications may want to restrict their use of an
  AF_INET6 socket to IPv6 communications only. For these
  applications the IPV6_V6ONLY socket option is defined.
  When this option is turned on, the socket can be used to
  send and receive IPv6 packets only. ...

  ...

  Note - This option has no effect on the use of IPv4 Mapped
  addresses which enter a node as a valid IPv6 addresses for
  IPv6 communications as defined by Stateless IP/ICMP
  Translation Algorithm (SIIT) [5].

Ivan says in comment#1
> ... I will try to implement it ...

Addmittedly the patch I supplied just provides the IPV_V6ONLY sockopt handling
AND a solution for the sequential API (the RAW API users can always call
tcp_listen or tcp_listen_dual as appropriate for their use of lwIP).

However, with the patch applied to the HEAD I can successfully create and
listen on an AF_INET6 socket and have IPv4 or IPv6 clients attach, so what is
in the HEAD "works" with the patch applied. So I think all of the heavy
lifting had already been done and is in the HEAD, since all I had to do (and
what is in the patch) is ensure tcp_listen_dual is called if IPV6_V6ONLY has
NOT been set.

The caveat is that limited testing has been done so far, since I needed to put
this patch in place to allow our stress test setup to operate and to start
making use of lwIP IPv6 support. So far though I have run quite a few test
sessions with IPv4 clients successfully connecting and transferring data
to/from the IPv6 socket.

Admittedly on one architecture I did encounter an assert from within lwIP when
doing a lot of large packet IPv6 transfers; but that issue is more than likely
unrelated to this "allow IPv4 connections by default" change (and is on my
debug pile to investigate :-)

Cheers,
-- Jamie

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