IPv6: Obtaining IP Addresses

Orignally the only way to get connected to the test IPv6 network was to find someone who was willing to tunnel IPv6 packets over the existing IPv4 network. They would allocate you a part of their network range for your testing. This made it difficult to just get up and going since finding someone to get these tunnels from isn't exactly easy. To resolve this issue they invented a new addresses scheme called 6to4 which is described below.

6to4 Addresses

• The 6to4 address allocation scheme is definied in RFC3068

All 6to4 address are in the 2002::/16 network range. The next 32 bits contain the IP address of the IPv4 gateway, this is the gateway that packets this IPv6 address range should be tunneled to - ie your IPv4 IP address.

So a 6to4 address consists of:

• 16 bits 6to4 prefix: 2002:
• 32 bits IPv4 gateway address: Example: c0a8:0001:
• 80 bits for user networks and hosts.

And since host addresses are normally 64 bits, this is usually allocated as:

• 16 bits 6to4 prefix: 2002:
• 32 bits IPv4 gateway address: Example: c0a8:0001:
• 16 bits for user networks.
• 64 bits for user hosts

Example 6in4 usage

The host egwene6.twibble.org uses the 6to4 gateway charon.twibble.org, is in subnet 0 and is host 1. This gateway has the IP address of 203.217.29.134 and this address cb.d9.1d.86 in hex. This gives us:

• 16 bits 6to4 prefix: 2002:
• 32 bits IPv4 gateway address: cbd9:1d86:
• 16 bits user network: 0
• 64 bits user host: 1

Any traffic for

• 2002:cbd9:1d86::/48

will be routed to charon.twibble.org via a tunnel, and from there charon can route the packet as it likes (using the remaining 80 bits). The full IP address for egwene.twibble.org will be:

• 2002:cbd9:1d86:0000:0000:0000:0000:0001

which can be shortend by replacing all the longest set of 0's with :: to:

• 2002:cbd9:1d86::1

Tunneling

Any IPv6 hosts, that also an IPv4 address, can send traffic directly to sites in the 2002::/16 subnet by simply extracting the IPv4 gateway address from the packet and tunneling it. Not all hosts support 6to4 though (they may be IPv6 only for example, or may not configured to support 6to4) in which case the traffic will be routed to the nearest 6to4 gateway before being tunneled.

For sending traffic back to the IPv6 internet there are two options availble for the 6to4 router:

1. If the destination address is in the 2002::/16 then we can tunnel the packets directly to the gateway for target host (since the gateway IPv4 address is encoded in the IPv6 address); or
2. For all other packets we need to tunnel them to a gateway which is connected to the IPv6 internet and will accept tunneled packets from 6to4 hosts.

The RFC defines the gateway address to be 192.88.99.1. This is not a single machine, but rather a specific address that gateways are expected to advertise (via BPG) as part of their network. So in theory this should connect to the nearest (in BPG route terms) gateway. Currently for here in melbourne this routes to a site in switzerland, even though AARNET have a machine configured with the same IP address. The AARNET one is either not being advertised at all via BPG, is not reaching the ISP's I have access to or is only being advertised privately within AARNET.

This list: http://www.kfu.com/~nsayer/6to4/ is a list of other public gateway sites. Not all of them work and I'm not sure how up-to-date this list is.

AARNET are also running a 6to4 gateway on ipv6.broadway.aarnet.net.au - I've verified that this one currently works. (Found at http://www.aarnet.edu.au/engineering/resources/ipv6/)

Examples

The following is example traceroute to a host in the 2002:/16 network. This is tunneled directly to the target site:

   [egwene][ 7:38PM]~#> traceroute6 6to4.ipv6.aarnet.net.au
   traceroute to 6to4.ipv6.aarnet.net.au (2002:c0e7:d405::1) from 2002:cbd9:1d86::1, 30 hops max, 16 byte packets
   1  2002:c0e7:d405::1 (2002:c0e7:d405::1)  41.939 ms  42.228 ms  43.685 ms

The following is example traceroute to a host not in the 2002:/16 network. This needs to be tunneled to a gateway site.

   [egwene][ 7:38PM]~#> traceroute6 trumpet-vbns.hay.vbns.net
   traceroute to trumpet-vbns.hay.vbns.net (3ffe:28ff:ffff:3::101) from 2002:cbd9:1d86::1, 30 hops max, 16 byte  packets
   1  swi6T1-F0-1.switch.ch (2001:620:0:20::6)  368.506 ms  368.679 ms  369.221 ms
   2  sprint-gw2.us.ipv6.aorta.net (2001:730::1:65)  532.344 ms *  532.344 ms
   3  vbns-ipls.abilene.ucaid.edu (2001:468:ff:dc1::2)  497.63 ms  495.779 ms  496.829 ms
   4  cs-v6-atm0-2.hay.vbns.net (3ffe:28ff:ffff:1::)  577.896 ms  575.9 ms  573.975 ms
   5  trumpet-vbns.hay.vbns.net (3ffe:28ff:ffff:3::101)  840.332 ms  816.861 ms  793.008 ms

Here's the previous trace again, this time using ipv6.broadway.aarnet.net.au instead of 192.88.99.1 for the 6to4 relay:

  [egwene][ 7:50PM]~#> traceroute6 trumpet-vbns.hay.vbns.net
  traceroute to trumpet-vbns.hay.vbns.net (3ffe:28ff:ffff:3::101) from 2002:cbd9:1d86::1, 30 hops max, 16 byte packets
   1  2002:c0e7:d405::1 (2002:c0e7:d405::1)  45.244 ms  43.255 ms  44.733 ms
   2  6plains-janet.abilene.ucaid.edu (2001:468:ff:1dc2::1)  360.138 ms  357.592 ms  358.306 ms
   3  ipls-6plains.abilene.ucaid.edu (2001:468:ff:61d::1)  386.066 ms  386.872 ms  383.49 ms
   4  chinng-iplsng.abilene.ucaid.edu (2001:468:ff:f12::1)  382.296 ms  386.615 ms  384.969 ms
   5  nycmng-chinng.abilene.ucaid.edu (2001:468:ff:f15::2)  383.284 ms  385.662 ms  384.228 ms
   6  washng-nycmng.abilene.ucaid.edu (2001:468:ff:1518::2)  385.992 ms  386.667 ms  388.417 ms
   7  vbns-ipls.abilene.ucaid.edu (2001:468:ff:dc1::2)  389.188 ms  390.183 ms  389.177 ms
   8  cs-v6-atm0-2.hay.vbns.net (3ffe:28ff:ffff:1::)  467.52 ms  469.81 ms  471.334 ms
   9  trumpet-vbns.hay.vbns.net (3ffe:28ff:ffff:3::101)  685.429 ms  684.485 ms  697.09 ms

Other options?

So you don't want 6to4 address, would prefer real ones? Take a look here:

• http://tunnelbroker.net/

Address prefixes

The current address prefixes that will be seen are:

• 2002::/16 These are the 6to4 addresses.
• 2001::/16 These are the production addressess, allocated by the registration authorities and allocated to ISPs to allocate to their customers.
• 3ffe::/16 These are the 6bone addresses. These were allocated early in the development of IPv6 for testing. There are plans afoot to remove these addresses from use sometime in the next 2-3 years.