32.9. IPv6

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

IPv6 is the new version of the well known IP protocol, also known as IPv4. IPv6 provides several advantages over IPv4 as well as many new features:

FreeBSD includes the http://www.kame.net/ IPv6 reference implementation and comes with everything needed to use IPv6. This section focuses on getting IPv6 configured and running.

32.9.1. Background on IPv6 Addresses

There are three different types of IPv6 addresses:


A packet sent to a unicast address arrives at the interface belonging to the address.


These 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 router interface. Anycast addresses are only used by routers.


These addresses identify a group of interfaces. A packet destined for a multicast address will arrive at all interfaces belonging to the multicast group. The IPv4 broadcast address, usually xxx.xxx.xxx.255, is expressed by multicast addresses in IPv6.

When reading an IPv6 address, the canonical form is represented as x:x:x:x:x:x:x:x, where each x represents a 16 bit hex value. An example is FEBC:A574:382B:23C1:AA49:4592:4EFE:9982.

Often, an address will have long substrings of all zeros. A :: (double colon) can be used to replace one substring per address. Also, up to three leading 0s per hex value 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 bits using the well known IPv4 notation. For example, 2002:: corresponds to the hexadecimal canonical representation 2002:0000:0000:0000:0000:0000:0a00:0001, which in turn is equivalent to 2002::a00:1.

To view a FreeBSD system's IPv6 address, use ifconfig(8):

# 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

In this example, the rl0 interface is using fe80::200:21ff:fe03:8e1%rl0, an auto-configured link-local address which was automatically generated from the MAC address.

Some IPv6 addresses are reserved. A summary of these reserved addresses is seen in Table 32.3, “Reserved IPv6 Addresses”:

Table 32.3. Reserved IPv6 Addresses
IPv6 addressPrefixlength (Bits)DescriptionNotes
::128 bitsunspecifiedEquivalent to in IPv4.
::1128 bitsloopback addressEquivalent to in IPv4.
::00:xx:xx:xx:xx96 bitsembedded IPv4The lower 32 bits are the compatible IPv4 address.
::ff:xx:xx:xx:xx96 bitsIPv4 mapped IPv6 addressThe lower 32 bits are the IPv4 address for hosts which do not support IPv6.
fe80::/1010 bitslink-localEquivalent to in IPv4.
fc00::/77 bitsunique-localUnique local addresses are intended for local communication and are only routable within a set of cooperating sites.
ff00::8 bitsmulticast 
2000::-3fff:: 3 bitsglobal unicastAll global unicast addresses are assigned from this pool. The first 3 bits are 001.

For further information on the structure of IPv6 addresses, refer to RFC3513.

32.9.2. Configuring IPv6

To configure a FreeBSD system as an IPv6 client, add these two lines to rc.conf:

ifconfig_rl0_ipv6="inet6 accept_rtadv"

The first line enables the specified interface to receive router advertisement messages. The second line enables the router solicitation daemon, rtsol(8).

If the interface needs a statically assigned IPv6 address, add an entry to specify the static address and associated prefix length:

ifconfig_rl0_ipv6="inet6 2001:db8:4672:6565:2026:5043:2d42:5344 prefixlen 64"

To assign a default router, specify its address:


32.9.3. Connecting to a Provider

In order to connect to other IPv6 networks, one must have a provider or a tunnel that supports IPv6:

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

  • Hurricane Electric offers tunnels with end-points all around the globe.


Install the net/freenet6 package or port for a dial-up connection.

This section demonstrates how to take the directions from a tunnel provider and convert them into /etc/rc.conf settings that will persist through reboots.

The first /etc/rc.conf entry creates the generic tunneling interface gif0:


Next, configure that interface with the IPv4 addresses of the local and remote endpoints. Replace MY_IPv4_ADDR and REMOTE_IPv4_ADDR with the actual IPv4 addresses:

create_args_gif0="tunnel MY_IPv4_ADDR REMOTE_IPv4_ADDR"

To apply the IPv6 address that has been assigned for use as the IPv6 tunnel endpoint, add this line, replacing MY_ASSIGNED_IPv6_TUNNEL_ENDPOINT_ADDR with the assigned address:

ifconfig_gif0_ipv6="inet6 MY_ASSIGNED_IPv6_TUNNEL_ENDPOINT_ADDR"

Then, set the default route for the other side of the IPv6 tunnel. Replace MY_IPv6_REMOTE_TUNNEL_ENDPOINT_ADDR with the default gateway address assigned by the provider:


If the FreeBSD system will route IPv6 packets between the rest of the network and the world, enable the gateway using this line:


32.9.4. 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:


It is important to specify the interface on which to do IPv6 router advertisement. For example, to tell rtadvd(8) to use rl0:


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


Replace rl0 with the interface to be used and 2001:db8:1f11:246:: 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.

32.9.5. 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:


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 administrators.

All FreeBSD documents are available for download at https://download.freebsd.org/ftp/doc/

Questions that are not answered by the documentation may be sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.