31.9. IPv6
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## 31.9. 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:

- Its 128-bit address space allows for 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses. This addresses the IPv4 address shortage and eventual IPv4 address exhaustion.

- Routers only store network aggregation addresses in their routing tables, thus reducing the average space of a routing table to 8192 entries. This addresses the scalability issues associated with IPv4, which required every allocated block of IPv4 addresses to be exchanged between Internet routers, causing their routing tables to become too large to allow efficient routing.

- Address autoconfiguration (RFC2462).

- Mandatory multicast addresses.

- Built-in IPsec (IP security).

- Simplified header structure.

- Support for mobile IP.

- IPv6-to-IPv4 transition mechanisms.

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.

### 31.9.1. IPv6 位址的背景知識

There are three different types of IPv6 addresses:

Unicast

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

Anycast

  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.

Multicast

  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 `0`s 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::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`.

To view a FreeBSD system's IPv6 address, use 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

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 表格 31.3, “已保留的 IPv6 位址”:

表格 31.3. 已保留的 IPv6 位址

IPv6 address | Prefixlength (Bits) | 說明 | 說明
--- | --- | --- | ---
`::` | 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::/10` | 10 bits | link-local | Equivalent to 169.254.0.0/16 in IPv4.
`fc00::/7` | 7 bits | unique-local | Unique local addresses are intended for local communication and are only routable within a set of cooperating sites.
`ff00::` | 8 bits | multicast |
`2000::-3fff::` | 3 bits | global unicast | All 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.

### 31.9.2. 設定 IPv6

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

    ifconfig_rl0_ipv6="inet6 accept_rtadv"
    rtsold_enable="YES"

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:

    ipv6_defaultrouter="2001:db8:4672:6565::1"

### 31.9.3. 連線到 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.

### 注意:

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``:

    cloned_interfaces="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:

    ipv6_defaultrouter="MY_IPv6_REMOTE_TUNNEL_ENDPOINT_ADDR"

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

    ipv6_gateway_enable="YES"

### 31.9.4. Router Advertisement 與 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 advertisement. For example, to tell rtadvd(8) to use `rl0`:

    rtadvd_interfaces="rl0"

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

    rl0:\
    	:addrs#1:addr="2001:db8:1f11:246::":prefixlen#64:tc=ether:

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.

### 31.9.5. IPv6 與 IPv6 位址對應表

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 administrators.

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