31.10. IPv6
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## 31.10. 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. FreeBSD includes the KAME IPv6 reference implementation. FreeBSD comes with everything needed to use 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, since RFC1918 private address space (`10.0.0.0/8`, `172.16.0.0/12`, and `192.168.0.0/16`) and 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 by providing the following:

- 128 bit address space which allows for 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses. This means there are approximately 6.67 * 10^27 IPv6 addresses per square meter on the planet.

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

There are other useful features of IPv6:

- 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:

- KAME.net

### 31.10.1. 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 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 | Equivalent to `0.0.0.0` in IPv4.
`::1` | 128 bits | loopback address | Equivalent to `127.0.0.1` in IPv4.
`::00:xx:xx:xx:xx` | 96 bits | embedded IPv4 | The lower 32 bits are the compatible IPv4 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 | Equivalent to the 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”.

### 31.10.2. Reading IPv6 Addresses

The canonical form is represented as: `x:x:x:x:x:x:x:x`, with 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. One such substring per address can be abbreviated by “::”. Also, up to three leading “0”s per hex quad 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 `2002::a00:1`.

Here is a sample entry from ifconfig(8):

`#` `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.

### 31.10.3. Getting Connected

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

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

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

- Tunnel via 6-to-4 as described in RFC3068.

- Use the `net/freenet6` port for a dial-up connection.

### 31.10.4. DNS in the IPv6 World

There used to be two types of DNS records for IPv6. The IETF has declared AAAA records as the current standard.

Using AAAA records is straightforward. Assign the hostname to the IPv6 address in the primary zone DNS file:

MYHOSTNAME AAAA MYIPv6ADDR

Current versions of named(8) and `dns/djbdns` support AAAA records.

### 31.10.5. Applying the Needed Changes to `/etc/rc.conf`

#### 31.10.5.1. IPv6 Client Settings

These settings configure a machine on a LAN which acts as a client, not a router. To instruct rtsol(8) to autoconfigure the interface on boot on FreeBSD 9.`x` and later, add this line to `rc.conf`:

ipv6_prefer="YES"

For FreeBSD 8.`x`, add:

ipv6_enable="YES"

To statically assign the IPv6 address, `2001:471:1f11:251:290:27ff:fee0:2093`, to `fxp0`, add the following for FreeBSD 9.`x`:

ifconfig_fxp0_ipv6="inet6 2001:471:1f11:251:290:27ff:fee0:2093 prefixlen `64`"

### Note:

Be sure to change `prefixlen 64` to the appropriate value for the subnet.

For FreeBSD 8`x`, 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"

#### 31.10.5.2. IPv6 Router/Gateway Settings

This section demonstrates how to take the directions from a tunnel provider and convert it into settings that will persist through reboots. To restore the tunnel on startup, add the following lines to `/etc/rc.conf`.

The first entry lists the generic tunneling interfaces to be configured. This example configures one interface, `gif0`:

gif_interfaces="gif0"

To configure that 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 that has been assigned for use as the IPv6 tunnel endpoint, add the following line for FreeBSD 9.`x` and later:

ifconfig_gif0_ipv6="inet6 `MY_ASSIGNED_IPv6_TUNNEL_ENDPOINT_ADDR`"

For FreeBSD 8.`x`, add:

ipv6_ifconfig_gif0="`MY_ASSIGNED_IPv6_TUNNEL_ENDPOINT_ADDR`"

Then, set the default route for IPv6. This is the other side of the IPv6 tunnel:

ipv6_defaultrouter="`MY_IPv6_REMOTE_TUNNEL_ENDPOINT_ADDR`"

#### 31.10.5.3. IPv6 Tunnel Settings

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

ipv6_gateway_enable="YES"

### 31.10.6. Router Advertisement and Host Auto Configuration

This section demonstrates how to setup rtadvd(8) to advertise the IPv6 default route.

To enable rtadvd(8), add the following to `/etc/rc.conf`:

rtadvd_enable="YES"

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

rtadvd_interfaces="fxp0"

Next, create the configuration file, `/etc/rtadvd.conf` as seen in this example:

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

Replace `fxp0` with the interface to be used and `2001:471:1f11:246::` with the prefix of the allocation.

For a dedicated `/64` subnet, nothing else needs to be changed. Otherwise, change the `prefixlen#` to the correct value.

### 31.10.7. IPv6 and IPv6 Address Mapping

When IPv6 is enabled on a server, there may be a need to enable IPv4 mapped IPv6 address communication. This compatibility option allows for IPv4 addresses to be represented as IPv6 addresses. Permitting IPv6 applications to communicate with IPv4 and vice versa may be a security issue.

This option may not be required in most cases and is available only for compatibility. This option will allow IPv6-only applications to work with IPv4 in a dual stack environment. This is most useful for third party applications which may not support an IPv6-only environment. To enable this feature, add the following to `/etc/rc.conf`:

ipv6_ipv4mapping="YES"

Reviewing the information in RFC 3493, section 3.6 and 3.7 as well as RFC 4038 section 4.2 may be useful to some adminstrators.

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