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                        FTSC INFORMATION
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                     The INO4 flag

Publication:    FSP-1038
Revision:       1
Title:          The INO4 flag.
Author(s):      Michiel van der Vlist
Date:           3 November 2013
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Contents:
                1. Introduction.
                2. The problem.
                3. The solution.
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1. Introduction
---------------

  The InterNet is running out of addresses. To solve this problem
  it is slowly migrating from 32 bit addresses (IPv4) to 128 bit
  addresses (IPv6).

  The conversion is largely transparent for the user. When querying
  the DNS system to resolve a host name, an IPv6 capable system
  initiating a connection will look if an AAAA record is present
  and use the IPv6 address if that is the case. If not, it will use
  the IPv4 address. There is no need for a nodelist flag to signal
  IPv6 capability, the lower layers will handle it transparently.


2. The Problem
--------------

  Presently all IPv6 capable nodes in the nodelist also support
  connectivity over IPv4. So there is downward compatibility. At
  present IPv4 only nodes have no problems connecting to IPv6 capable
  nodes, they just connect via IPv4.

  We can however not expect that situation to last forever. While the
  number of IPv6 capable nodes grows, IPv4 connectivity will eventu-
  ally degrade.

  Some day there will be nodes that no longer accept incoming connec-
  tions over IPv4. At best they will be behind a GGNAT or Carrier
  Grade NAT. That is a NAT operated by their ISP, so they will have no
  control over the port forwarding tables. At worst they will have no
  IPv4 at all. Either way, these nodes will not be reachable by nodes
  that do not have IPv6 capability.

  Attempts to connect will fail and most mailers will just repeat
  the attempt at regular intervals until the sysop intervenes. At
  present there is no way to predict such a failure beforehand.

  To avoid this undesirable situation I propose a flag that indicates
  that an otherwise IP capable node does not support incoming connec-
  tions over IPv4.


3. The INO4 flag
----------------

  INO4       Indicates that an otherwise IP capable node is unable to
             accept incoming connections over IPv4.


4. Considerations
-----------------

  Although NOIPV4 would be more clear, it goes against the custom that
  all IP related flags start wit the letter 'I'. It is also needlessly
  long.
  Someone suggested to use IPV6 with the definition of "IPv6 only".
  This is bound to be misunderstood as other capability flags have
  always meant "in addition of". V34 means an additional V34 capabi-
  lity, not "V34 only". X75 does not mean "X75 only". Using IPV6 with
  a definition of "IPv6 only" will raise confusion and hence improper
  use .

  Note that in the very long run as IPv4 gradually fades out, we may
  reach a situation where most of the IP capable nodes in the nodelist
  will carry this flag. If and when this happens, the Fidonet communi-
  ty may consider dropping this flag and marking the minority that
  still accepts incoming connections over IPv4 with an IPV4 flag.


References
----------

  [FTS-5]    "The distribution nodelist", Ben Baker, Rick Moore.
             February 1989. Obsoleted by FTS-5000.

  [FTS-5000] "The distribution nodelist".
             FTSC Members, Administrator and Honoured Guests
             Dec 2012.

  [FTS-5001] "Nodelist flags and userflags".
             FTSC Members, Administrator and Honoured Guests
             March 2013.


Contact Data
------------

  Michiel van der Vlist
  Fidonet:  2:280/5555
  E-mail:   pa0mmv at vrza dot org
  E-mail:   administrator at ftsc dot org

History
-------

   Rev.1, 20131103: Initial Release.
                    Principal author Michiel van der Vlist.





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