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============
INTRODUCTION
============

map646 is a one to one IPv4-IPv6 address mapping program for protocol
translation.

This program is used in a scenario when you have a pure IPv6 network
but want to open some of the server services to IPv4 users.  To do
this, you need the following things.

  - IPv4 connectivity at the boundary of your IPv6 network.
  - Enough number of global IPv4 addresses that you want to map your
    IPv6 servers.


==============
HOW TO COMPILE
==============

Just type 'make'.  The program is developed for the FreeBSD operating
system and the Linux operating system, but if your operating system
supports the tun interface, then you can probably compile the program.


================
HOW TO CONFIGURE
================

In this section, we assume that you have IPv6 address space
2001:db8:0:0::/64 for your pure IPv6 network.  Also, we assume that
you have 192.0.2.0/24 as global IPv4 address space.  Your IPv6 nodes
don't have any global IPv4 addresses, so they cannot communicate with
IPv4 nodes.

First we need to define the mapping information of your IPv6 servers
and your global IPv4 addresses.  As an example, let's define the
following mapping.

  192.0.2.1 <=> 2001:db8:0:0::100
  192.0.2.2 <=> 2001:db8:0:0::500

With the above mapping, you are now exposing two of your IPv6 servers
to the global IPv4 Internet, using 192.0.2.1 and 192.0.2.2.  The
program reads the configuration information from the configuration
file located at /etc/map646.conf.  The file contents should be as
follows.

----
mapping-prefix 64::
map-static 192.0.2.1 2001:db8:0:0::100
map-static 192.0.2.2 2001:db8:0:0::500
----

The first line defines the pseudo IPv6 prefix of the mapping system.
When your IPv6 server communicates with an IPv4 node, the IPv4 node
address is mapped to that prefix range.  For example, if your server
is contacting to 202.214.86.196, the endpoint address seen from your
IPv6 server will be 64::cad6:56c4.  The IPv4 addresses are mapped to
the lower 4 bytes of the pseudo IPv6 address in a hexadecimal form (in
this case, 0xCA (202), 0xD6 (214), 0x56 (86), and 0xC4 (196)).

Similary, any IPv4 nodes can contact to your IPv6 server using the
global address mapped to your server address.  If the IPv4 node (which
IPv4 address is 202.214.86.196) contacts to 192.0.2.2, then your IPv6
server (2001:db8:0:0::500) will receive an incoming packet from
64::cad6:56c5.

To use the program, you need to setup your node as a router by
enabling forwarding function.  The following example is a sample
startup operation procedure for the FreeBSD operating system.

# (run map646 in background.)
# sysctl -w net.inet.ip.forwarding=1
# sysctl -w net.inet6.ip6.forwarding=1

The below is an example in the Linux case.

# (run map646 in background)
# sysctl -w net.ipv4.conf.all.forwarding=1
# sysctl -w net.ipv6.conf.all.forwarding=1

Once you have done all the settings, your mapping server is ready.


=================
DNS CONFIGURATION
=================

You need to configure your IPv4 global addresses used to map your IPv6
servers in your DNS server database.  The example entries are like below.

your-ipv6-sever-1    IN    A    192.0.2.1
your-ipv6-sever-2    IN    A    192.0.2.2

Any IPv4 host can now contact to your IPv6 server 1
(2001:db8:0:0::100) by contacting your-ipv6-server-1.example.com.  At
this point, your IPv6 servers are fully accessible from any IPv4 hosts
in the Internet.

The reverse direction is a bit complicated.  You need a modified DNS
server for your pure IPv6 network, since the DNS server must reply a
pseudo IPv6 address associated to the real IPv4 address that the
server want to contact to.  When your IPv6 server asks AAAA record of
www.yahoo.com (assuming that it doesn't have IPv6 addresses and its
IPv4 address is 72.30.2.43), your internal DNS server must reply
64::481e:22b.

Unfortunately, this map646 package doesn't include the modified DNS
server.  You may be interested in using Trick Or Treat Daemon (totd)
for this function
(http://www.vermicelli.pasta.cs.uit.no/software/totd.html)