[afripv6-discuss] Introduction to 6to4

JORDI PALET MARTINEZ jordi.palet at consulintel.es
Wed Jun 6 12:40:47 SAST 2007

Hi all,

This is the first email, as indicated a few days ago and in the last AfriNIC
meeting, in order to show 6to4 and Teredo, a couple of very interesting
transition mechanisms, that automatically setup IPv6 connectivity for hosts
and consequently allow IPv6 traffic even if the ISPs don't support it.

Remember that users with Operating Systems supporting IPv6 (most of them
today, some enabled by default), will start using automatic transition
mechanisms (such as 6to4 and Teredo) and there will be more and more IPv6
"transition" traffic in your networks even if you don't deploy IPv6. See the
presentation "The cost of NOT deploying IPv6", which become more relevant in
developing regions where the upstream bandwidth is much more expensive and
some times slower because using satellites. The latest set of slides on this
topic are available at:

The purpose of the complete set of emails is to show how to take advantage,
with almost no cost, of deploying 6to4 and Teredo relays in your networks,
in order to a) be able to save some bandwidth (traffic will stay in your
network or peers instead of traversing long paths looking for third party
relays), b) deliver a much better non-managed IPv6 "quality of service" to
your users (lower RTT).

Please, feel free to make any questions that you have by replying to each

As there will be several emails for each protocol, I will suggest that you
restrict the questions to the contents of each email and keep the same
subject, so people that later on join the topic, can follow easily the email
archive and we avoid answering the same question several times.

For general information about IPv6, please take a look to the training
material at:


Introduction to 6to4

6to4 is a transition mechanism that allows IPv6 to be encapsulated in IPv4
packets (using protocol 41), in order to traverse IPv4-only networks and for
example, allow transit of IPv6 thru ISPs that only offer IPv4 service.

In principle, it requires a public IPv4 address.

According to RFC3056 there are two ways a router could support the 6to4
transition mechanism.

The first is called 6to4 Router and the second 6to4 Relay Router.

1) 6to4 Router: An IPv6 router supporting a 6to4 pseudo-interface. It is
normally the border router between an IPv6 site and a wide-area IPv4

For example, think in an isolated IPv6 cloud. This cloud could use 6to4
addresses and get connected to other IPv6 nodes through the 6to4 router.

2) 6to4 Relay Router: A 6to4 router configured to support transit routing
between 6to4 addresses and native IPv6 addresses.

The main difference with the 6to4 Router is that the Relay router is
connected to the native IPv6 world. Or what is the same, they announce the
2002::/16 prefix to their routing peers.

Note that an isolated host could be configured as 6to4 router just to
obtain IPv6 connectivity (this is called a 6to4 router/host). This
configuration is automatic in many operating systems, and in practice, in
means that when a host has IPv6 enabled and a public IPv4 address, if it
supports 6to4, it will gain automatic access to IPv6 even if the ISP doesn't
provide the service.

The 6to4 addresses use the prefix 2002::/16

For the automatic configuration of the 6to4 hosts in order to reach a 6to4
relay, the 6to4 relays need to use an anycast address, which is
More info on this in RFC3068.

More information and pictures are available at:

The IPv6 Portal: http://www.ipv6tf.org

Bye 6Bone. Hi, IPv6 !

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