v1.4 10th Jan 2002, Pekka Savola <pekkas@netcore.fi>

HOW TO SET UP AN IPV6 TUNNEL
----------------------------

ASSUMPTIONS
-----------

1. You're running Red Hat Linux 7.1 or later.
   
   This is required for correct IPv6 by default settings, and IPv6 being
   enabled as a kernel module by default.  You also need recent enough
   initscripts, provided in RHL71.

2. You have a static, globally unique IPv4 address.

3. Protocol 41 (IPv6-in-IPv4) is not being filtered in any IPv4 firewall.

4. 'iproute' package is installed.  This is used by default for a lot 
   more powerful tunneling capabilities.

INFORMATION NEEDED
------------------

You need to know:

1. The IPv4 address of your tunnel end point
2. The IPv6 address used in your tunnel

The other end needs to know the same things about your setup.

NOTE: It is also possible to set up unnumbered tunnels (no global IPv6
addresses).

You must get these from a party (tunnel broker) who's assigning IPv6 tunnels.  See:
http://www.bieringer.de/linux/IPv6/IPv6-HOWTO/IPv6-HOWTO-1.html#joinIPv6backbone

Example from http://old.freenet6.net:
---
This script will create a tunnel between this computer
and the Freenet6 server (tunnels server)
Your IPv6 address (your tunnel end point) is
3ffe:b00:c18:1fff:0:0:0:7f5 
We establish a tunnel to the Freenet6 server at
3ffe:b00:c18:1fff:0:0:0:7f4 
Your IPv4 address is : 193.xxx.yyy.zzz 
The IPv4 address of the Freenet6 server is : 206.123.31.102 
---

With this information, a tunnel can be set up:

SETTING UP THE TUNNEL CONFIGURATION
-----------------------------------

Now, set up the configuration as follows:

1. Enable IPv6 and set tunnel as default gateway in /etc/sysconfig/network:

   echo "IPV6_DEFAULTDEV=sit1">> /etc/sysconfig/network

2. Create /etc/sysconfig/network-scripts/ifcfg-sit1, with the following:

---
DEVICE=sit1
BOOTPROTO=none
ONBOOT=yes
IPV6INIT=yes
IPV6TUNNELIPV4=206.123.31.102
IPV6ADDR=3ffe:b00:c18:1fff:0:0:0:7f5/128
---

NOTE: You must use _sit1_ (or sit2,...).  sit0 cannot be used, this is a
special device.

NOTE: Some tunnel endpoints might require a different kind of prefix length;
for example, Cisco's usually favour /126.  Using /0 creates a default route 
through that interface.

NOTE: If you're not directly connected to the Internet, you may want to use
ONBOOT=no instead.

TUNNELING
---------

Tunnel can be brought up and down with:

   ifup sit1
   ifdown sit1

NOTE: In initscripts < 6.02 (ie. IPV6_TUNNELMODE=NBMA), even though sit1 is used, 
'ip' sees the tunnel as sit0.  This is due to an "interesting" implementation 
of tunneling -- else multiple tunnels couldn't be used extensibly.

NOTE: iproute tools give more reliable data, try e.g. '/sbin/ip addr ls'.

MORE INFORMATION
----------------

http://www.bieringer.de/linux/IPv6/IPv6-HOWTO/IPv6-HOWTO.html is a good
source of IPv6 related Linux-information.