[SUMMARY]

This is a shell script to turn on/off an IPv6 tunnel using the tun6to4
interface, which exchanges IPv6 packets by encapsulating them in IPv4
packets and using protocol 41 to the IPv4 anycast address 192.88.99.1

Instructions for doing this typically discuss laborious manual
configuration, tedious calculations, manipulation of various
networking configuration files, and modifications when the host moves
to a different IP address.  Meaning basically no one does it.  This
script instead sets up the tunnel completely automatically, without
monkeying with any networking configuration files.  It attempts to be
robust, for example, if the local host does not have a first-class
IPv4 address the script simply exits with a cogent warning.

However, there are some options for unusual installations.  In
particular, if you are behind a NAT but have configured the NAT to
route protocol 41 packets appropriately, you need to supply the
externally apparent IP address using the -i option.

The invocation conventions are chosen to allow the script to be
installed as /etc/init.d/auto6to4 using the standard mechanisms.

See the top of the script for additional instructions, dependencies,
and configuration information, or invoke with the --help option for
usage summary.

[ALTERNATIVES]

On Debian, a stanza in /etc/network/interfaces of the form

    auto 6to4
    iface 6to4 inet6 6to4
	    local YOUR-IPv4-ADDRESS-HERE

may be an easier way to bring up a 6to4 interface, assuming you have a
static IPv4 address.

[CAUTION]

Unless disabled with the -r option, if radvd is installed an IPv6
subnet will be created, routed through the newly-created tunnel, and
advertised on the local network.  This should enable IPv6
automatically on other machines on the local network.  (If the host is
on more than one local network, one such network will be created,
routed, and advertised for each local network.)

If IPv6 is not working as well as IPv4, and the other machines on the
local network are configured to prefer IPv6 to IPv4 when both are
available for a particular connection (as is the unfortunate default
on most Linux and *BSD distributions), this can cause performance
problems and enormous start-up latency when local machines try to use
IPv6 to communicate with remote hosts for which both IPv4 and IPv6
addresses are available.

[FILES]

When radvd is used to advertise a subnet, the following temporary files
are generated:
 /var/run/radvd/radvd-auto.conf
 /var/run/radvd/radvd-auto.pid

[EXAMPLE]

 auto6to4 -r start
 auto6to4 stop

[AUTHOR]

Barak A. Pearlmutter <barak@pearlmutter.net>

[REPORTING BUGS]

For the latest version, and to report bugs or suggest improvements,
see https://github.com/barak/auto6to4

[COPYRIGHT]

Released under the GNU GPLv2+.