29.11 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:

IPv6 deals with these and many other issues:

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

For more information see:

29.11.1 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 29-2. Reserved IPv6 addresses

IPv6 address Prefixlength (Bits) Description Notes
:: 128 bits unspecified cf. in IPv4
::1 128 bits loopback address cf. 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”.

29.11.2 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:: 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
         inet netmask 0xffffff00 broadcast
         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.

29.11.3 Getting Connected

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

29.11.4 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:


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.

29.11.5 Applying the needed changes to /etc/rc.conf 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:


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


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" 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:


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:


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" 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:


29.11.6 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:


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


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


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.

This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.