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# 31.11 IPv6

Originally Written by Aaron Kaplan. Restructured and Added by Tom Rhodes. Extended by Brad Davis.

IPv6 (also known as IPng “IP next generation”) is the new version of the well known IP protocol (also known as IPv4). Like the other current *BSD systems, FreeBSD includes the KAME IPv6 reference implementation. So your FreeBSD system comes with all you will need to experiment with IPv6. This section focuses on getting IPv6 configured and running.

In the early 1990s, people became aware of the rapidly diminishing address space of IPv4. Given the expansion rate of the Internet there were two major concerns:

- Running out of addresses. Today this is not so much of a concern anymore since RFC1918 private address space (`10.0.0.0/8`, `172.16.0.0/12`, and `192.168.0.0/16`) and Network Address Translation (NAT) are being employed.

- Router table entries were getting too large. This is still a concern today.

IPv6 deals with these and many other issues:

- 128 bit address space. In other words theoretically there are 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses available. This means there are approximately 6.67 * 10^27 IPv6 addresses per square meter on our planet.

- Routers will only store network aggregation addresses in their routing tables thus reducing the average space of a routing table to 8192 entries.

There are also lots of other useful features of IPv6 such as:

- Address autoconfiguration (RFC2462)

- Anycast addresses (“one-out-of many”)

- Mandatory multicast addresses

- IPsec (IP security)

- Simplified header structure

- Mobile IP

- IPv6-to-IPv4 transition mechanisms

For more information see:

- IPv6 overview at playground.sun.com

- KAME.net

## 31.11.1 Background on IPv6 Addresses

There are different types of IPv6 addresses: Unicast, Anycast and Multicast.

Unicast addresses are the well known addresses. A packet sent to a unicast address arrives exactly at the interface belonging to the address.

Anycast addresses are syntactically indistinguishable from unicast addresses but they address a group of interfaces. The packet destined for an anycast address will arrive at the nearest (in router metric) interface. Anycast addresses may only be used by routers.

Multicast addresses identify a group of interfaces. A packet destined for a multicast address will arrive at all interfaces belonging to the multicast group.

> Note: The IPv4 broadcast address (usually `xxx.xxx.xxx.255`) is expressed by multicast addresses in IPv6.

Table 31-2. Reserved IPv6 addresses

IPv6 address | Prefixlength (Bits) | Description | Notes
--- | --- | --- | ---
`::` | 128 bits | unspecified | cf. `0.0.0.0` in IPv4
`::1` | 128 bits | loopback address | cf. `127.0.0.1` in IPv4
`::00:xx:xx:xx:xx` | 96 bits | embedded IPv4 | The lower 32 bits are the IPv4 address. Also called “IPv4 compatible IPv6 address”
`::ff:xx:xx:xx:xx` | 96 bits | IPv4 mapped IPv6 address | The lower 32 bits are the IPv4 address. For hosts which do not support IPv6.
`fe80::` - `feb::` | 10 bits | link-local | cf. loopback address in IPv4
`fec0::` - `fef::` | 10 bits | site-local |
`ff::` | 8 bits | multicast |
`001` (base 2) | 3 bits | global unicast | All global unicast addresses are assigned from this pool. The first 3 bits are “001”.

## 31.11.2 Reading IPv6 Addresses

The canonical form is represented as: `x:x:x:x:x:x:x:x`, each “x” being a 16 Bit hex value. For example `FEBC:A574:382B:23C1:AA49:4592:4EFE:9982`

Often an address will have long substrings of all zeros therefore one such substring per address can be abbreviated by “::”. Also up to three leading “0”s per hexquad can be omitted. For example `fe80::1` corresponds to the canonical form `fe80:0000:0000:0000:0000:0000:0000:0001`.

A third form is to write the last 32 Bit part in the well known (decimal) IPv4 style with dots “.” as separators. For example `2002::10.0.0.1` corresponds to the (hexadecimal) canonical representation `2002:0000:0000:0000:0000:0000:0a00:0001` which in turn is equivalent to writing `2002::a00:1`.

By now the reader should be able to understand the following:

    # ifconfig

    rl0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
             inet 10.0.0.10 netmask 0xffffff00 broadcast 10.0.0.255
             inet6 fe80::200:21ff:fe03:8e1%rl0 prefixlen 64 scopeid 0x1
             ether 00:00:21:03:08:e1
             media: Ethernet autoselect (100baseTX )
             status: active

`fe80::200:21ff:fe03:8e1%rl0` is an auto configured link-local address. It is generated from the MAC address as part of the auto configuration.

For further information on the structure of IPv6 addresses see RFC3513.

## 31.11.3 Getting Connected

Currently there are four ways to connect to other IPv6 hosts and networks:

- Contact your Internet Service Provider to see if they offer IPv6 yet.

- SixXS offers tunnels with end-points all around the globe.

- Tunnel via 6-to-4 (RFC3068)

- Use the `net/freenet6` port if you are on a dial-up connection.

## 31.11.4 DNS in the IPv6 World

There used to be two types of DNS records for IPv6. The IETF has declared A6 records obsolete. AAAA records are the standard now.

Using AAAA records is straightforward. Assign your hostname to the new IPv6 address you just received by adding:

    MYHOSTNAME           AAAA    MYIPv6ADDR

To your primary zone DNS file. In case you do not serve your own DNS zones ask your DNS provider. Current versions of bind (version 8.3 and 9) and `dns/djbdns` (with the IPv6 patch) support AAAA records.

## 31.11.5 Applying the needed changes to `/etc/rc.conf`

### 31.11.5.1 IPv6 Client Settings

These settings will help you configure a machine that will be on your LAN and act as a client, not a router. To have rtsol(8) autoconfigure your interface on boot all you need to add is:

    ipv6_enable="YES"

To statically assign an IP address such as `2001:471:1f11:251:290:27ff:fee0:2093`, to your `fxp0` interface, add:

    ipv6_ifconfig_fxp0="2001:471:1f11:251:290:27ff:fee0:2093"

To assign a default router of `2001:471:1f11:251::1` add the following to `/etc/rc.conf`:

    ipv6_defaultrouter="2001:471:1f11:251::1"

### 31.11.5.2 IPv6 Router/Gateway Settings

This will help you take the directions that your tunnel provider has given you and convert it into settings that will persist through reboots. To restore your tunnel on startup use something like the following in `/etc/rc.conf`:

List the Generic Tunneling interfaces that will be configured, for example `gif0`:

    gif_interfaces="gif0"

To configure the interface with a local endpoint of `MY_IPv4_ADDR` to a remote endpoint of `REMOTE_IPv4_ADDR`:

    gifconfig_gif0="MY_IPv4_ADDR REMOTE_IPv4_ADDR"

To apply the IPv6 address you have been assigned for use as your IPv6 tunnel endpoint, add:

    ipv6_ifconfig_gif0="MY_ASSIGNED_IPv6_TUNNEL_ENDPOINT_ADDR"

Then all you have to do is set the default route for IPv6. This is the other side of the IPv6 tunnel:

    ipv6_defaultrouter="MY_IPv6_REMOTE_TUNNEL_ENDPOINT_ADDR"

### 31.11.5.3 IPv6 Tunnel Settings

If the server is to route IPv6 between the rest of your network and the world, the following `/etc/rc.conf` setting will also be needed:

    ipv6_gateway_enable="YES"

## 31.11.6 Router Advertisement and Host Auto Configuration

This section will help you setup rtadvd(8) to advertise the IPv6 default route.

To enable rtadvd(8) you will need the following in your `/etc/rc.conf`:

    rtadvd_enable="YES"

It is important that you specify the interface on which to do IPv6 router solicitation. For example to tell rtadvd(8) to use `fxp0`:

    rtadvd_interfaces="fxp0"

Now we must create the configuration file, `/etc/rtadvd.conf`. Here is an example:

    fxp0:\
        :addrs#1:addr="2001:471:1f11:246::":prefixlen#64:tc=ether:

Replace `fxp0` with the interface you are going to be using.

Next, replace `2001:471:1f11:246::` with the prefix of your allocation.

If you are dedicated a `/64` subnet you will not need to change anything else. Otherwise, you will need to change the `prefixlen#` to the correct value.

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