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IPv6 Auto-Configuration in Linux
======
![](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/banner_5.png?itok=3kN83IjL)
In [Testing IPv6 Networking in KVM: Part 1][1], we learned about unique local addresses (ULAs). In this article, we will learn how to set up automatic IP address configuration for ULAs.
### When to Use Unique Local Addresses
Unique local addresses use the fd00::/8 address block, and are similar to our old friends the IPv4 private address classes: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. But they are not intended as a direct replacement. IPv4 private address classes and network address translation (NAT) were created to alleviate the shortage of IPv4 addresses, a clever hack that prolonged the life of IPv4 for years after it should have been replaced. IPv6 supports NAT, but I can't think of a good reason to use it. IPv6 isn't just bigger IPv4; it is different and needs different thinking.
So what's the point of ULAs, especially when we have link-local addresses (fe80::/10) and don't even need to configure them? There are two important differences. One, link-local addresses are not routable, so you can't cross subnets. Two, you control ULAs; choose your own addresses, make subnets, and they are routable.
Another benefit of ULAs is you don't need an allocation of global unicast IPv6 addresses just for mucking around on your LAN. If you have an allocation from a service provider then you don't need ULAs. You can mix global unicast addresses and ULAs on the same network, but I can't think of a good reason to have both, and for darned sure you don't want to use network address translation (NAT) to make ULAs publicly accessible. That, in my peerless opinion, is daft.
ULAs are for private networks only and should be blocked from leaving your network, and not allowed to roam the Internet. Which should be simple, just block the whole fd00::/8 range on your border devices.
### Address Auto-Configuration
ULAs are not automatic like link-local addresses, but setting up auto-configuration is easy as pie with radvd, the router advertisement daemon. Before you change anything, run `ifconfig` or `ip addr show` to see your existing IP addresses.
You should install radvd on a dedicated router for production use, but for testing you can install it on any Linux PC on your network. In my little KVM test lab, I installed it on Ubuntu, `apt-get install radvd`. It should not start after installation, because there is no configuration file:
```
$ sudo systemctl status radvd
● radvd.service - LSB: Router Advertising Daemon
Loaded: loaded (/etc/init.d/radvd; bad; vendor preset: enabled)
Active: active (exited) since Mon 2017-12-11 20:08:25 PST; 4min 59s ago
Docs: man:systemd-sysv-generator(8)
Dec 11 20:08:25 ubunut1 systemd[1]: Starting LSB: Router Advertising Daemon...
Dec 11 20:08:25 ubunut1 radvd[3541]: Starting radvd:
Dec 11 20:08:25 ubunut1 radvd[3541]: * /etc/radvd.conf does not exist or is empty.
Dec 11 20:08:25 ubunut1 radvd[3541]: * See /usr/share/doc/radvd/README.Debian
Dec 11 20:08:25 ubunut1 radvd[3541]: * radvd will *not* be started.
Dec 11 20:08:25 ubunut1 systemd[1]: Started LSB: Router Advertising Daemon.
```
It's a little confusing with all the start and not started messages, but radvd is not running, which you can verify with good old `ps|grep radvd`. So we need to create `/etc/radvd.conf`. Copy this example, replacing the network interface name on the first line with your interface name:
```
interface ens7 {
AdvSendAdvert on;
MinRtrAdvInterval 3;
MaxRtrAdvInterval 10;
prefix fd7d:844d:3e17:f3ae::/64
{
AdvOnLink on;
AdvAutonomous on;
};
};
```
The prefix defines your network address, which is the first 64 bits of the address. The first two characters must be `fd`, then you define the remainder of the prefix, and leave the last 64 bits empty as radvd will assign the last 64 bits. The next 16 bits after the prefix define the subnet, and the remaining bits define the host address. Your subnet size must always be /64. RFC 4193 requires that addresses be randomly generated; see [Testing IPv6 Networking in KVM: Part 1][1] for more information on creating and managing ULAs.
### IPv6 Forwarding
IPv6 forwarding must be enabled. This command enables it until restart:
```
$ sudo sysctl -w net.ipv6.conf.all.forwarding=1
```
Uncomment or add this line to `/etc/sysctl.conf` to make it permanent:
```
net.ipv6.conf.all.forwarding = 1
```
Start the radvd daemon:
```
$ sudo systemctl stop radvd
$ sudo systemctl start radvd
```
This example reflects a quirk I ran into on my Ubuntu test system; I always have to stop radvd, no matter what state it is in, and then start it to apply any changes.
You won't see any output on a successful start, and often not on a failure either, so run `sudo systemctl radvd status`. If there are errors, systemctl will tell you. The most common errors are syntax errors in `/etc/radvd.conf`.
A cool thing I learned after complaining on Twitter: when you run ` journalctl -xe --no-pager` to debug systemctl errors, your output lines will wrap, and then you can actually read your error messages.
Now check your hosts to see their new auto-assigned addresses:
```
$ ifconfig
ens7 Link encap:Ethernet HWaddr 52:54:00:57:71:50
[...]
inet6 addr: fd7d:844d:3e17:f3ae:9808:98d5:bea9:14d9/64 Scope:Global
[...]
```
And there it is! Come back next week to learn how to manage DNS for ULAs, so you can use proper hostnames instead of those giant IPv6 addresses.
Learn more about Linux through the free ["Introduction to Linux" ][2]course from The Linux Foundation and edX.
--------------------------------------------------------------------------------
via: https://www.linux.com/learn/intro-to-linux/2017/12/ipv6-auto-configuration-linux
作者：[Carla Schroder][a]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]:https://www.linux.com/users/cschroder
[1]:https://www.linux.com/learn/intro-to-linux/2017/11/testing-ipv6-networking-kvm-part-1
[2]:https://training.linuxfoundation.org/linux-courses/system-administration-training/introduction-to-linux

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在 Linux 中自动配置 IPv6 地址
======
![](https://www.linux.com/sites/lcom/files/styles/rendered_file/public/banner_5.png?itok=3kN83IjL)
在 [ KVM 中测试 IPv6 网络：第 1 部分][1] 一文中，我们学习了关于唯一本地地址（ULAs）的相关内容。在本文中，我们将学习如何为 ULAs 自动配置 IP 地址。
### 何时使用唯一本地地址
唯一本地地址使用 fd00::/8 地址块，它类似于我们常用的 IPv4 的私有地址：10.0.0.0/8、172.16.0.0/12、以及 192.168.0.0/16。但它们并不能直接替换。IPv4 的私有地址分类和网络地址转换（NAT）功能是为了缓解 IPv4 地址短缺的问题，这是个明智的解决方案，它延缓了本该被替换的 IPv4 的生命周期。IPv6 也支持 NAT，但是我想不出使用它的理由。IPv6 的地址数量远远大于 IPv4；它是不一样的，因此需要做不一样的事情。
那么，ULAs 存在的意义是什么呢？尤其是在我们已经有了本地链路地址（fe80::/10）时，到底需不需要我们去配置它们呢？它们之间（译者注：指的是唯一本地地址和本地链路地址）有两个重要的区别。一是，本地链路地址是不可路由的，因此，你不能跨子网使用它。二是，ULAs 是你自己管理的；你可以自己选择它用于子网的地址范围，并且它们是可路由的。
使用 ULAs 的另一个好处是，如果你只是在局域网中“混日子”的话，你不需要为它们分配全局单播 IPv6 地址。当然了，如果你的 ISP 已经为你分配了 IPv6 的全局单播地址，就不需要使用 ULAs 了。你也可以在同一个网络中混合使用全局单播地址和 ULAs，但是，我想不出这样使用的一个好理由，并且要一定确保你不使用网络地址转换以使 ULAs 可公共访问。在我看来，这是很愚蠢的行为。
ULAs 是仅为私有网络使用的，并且它会阻塞所有流出你的网络的数据包，不允许进入因特网。这很简单，在你的边界设备上只要阻止整个 fd00::/8 范围的 IPv6 地址即可实现。
### 地址自动配置
ULAs 不像本地链路地址那样自动配置的，但是使用 radvd 设置自动配置是非常容易的，radva 是路由器公告守护程序。在你开始之前，运行 `ifconfig` 或者 `ip addr show` 去查看你现有的 IP 地址。
在生产系统上使用时，你应该将 radvd 安装在一台单独的路由器上，如果只是测试使用，你可以将它安装在你的网络中的任意 Linux PC 上。在我的小型 KVM 测试实验室中，我使用 `apt-get install radvd` 命令把它安装在 Ubuntu 上。安装完成之后，我先不启动它，因为它还没有配置文件：
```
$ sudo systemctl status radvd
● radvd.service - LSB: Router Advertising Daemon
Loaded: loaded (/etc/init.d/radvd; bad; vendor preset: enabled)
Active: active (exited) since Mon 2017-12-11 20:08:25 PST; 4min 59s ago
Docs: man:systemd-sysv-generator(8)
Dec 11 20:08:25 ubunut1 systemd[1]: Starting LSB: Router Advertising Daemon...
Dec 11 20:08:25 ubunut1 radvd[3541]: Starting radvd:
Dec 11 20:08:25 ubunut1 radvd[3541]: * /etc/radvd.conf does not exist or is empty.
Dec 11 20:08:25 ubunut1 radvd[3541]: * See /usr/share/doc/radvd/README.Debian
Dec 11 20:08:25 ubunut1 radvd[3541]: * radvd will *not* be started.
Dec 11 20:08:25 ubunut1 systemd[1]: Started LSB: Router Advertising Daemon.
```
这些所有的消息有点让人困惑，实际上 radvd 并没有运行，你可以使用经典命令 `ps|grep radvd` 来验证这一点。因此，我们现在需要去创建 `/etc/radvd.conf` 文件。拷贝这个示例，将第一行的网络接口名替换成你自己的接口名字：
```
interface ens7 {
AdvSendAdvert on;
MinRtrAdvInterval 3;
MaxRtrAdvInterval 10;
prefix fd7d:844d:3e17:f3ae::/64
{
AdvOnLink on;
AdvAutonomous on;
};
};
```
前缀定义了你的网络地址，它是地址的前 64 位。前两个字符必须是 `fd`，前缀接下来的剩余部分你自己定义它，最后的 64 位留空，因为 radvd 将去分配最后的 64 位。前缀后面的 16 位用来定义子网，剩余的地址定义为主机地址。你的子网必须总是 /64。RFC 4193 要求地址必须随机生成；查看 [在 KVM 中测试 IPv6 Networking：第 1 部分][1] 学习创建和管理 ULAs 的更多知识。
### IPv6 转发
IPv6 转发必须要启用。下面的命令去启用它，重启后生效：
```
$ sudo sysctl -w net.ipv6.conf.all.forwarding=1
```
取消注释或者添加如下的行到 `/etc/sysctl.conf` 文件中，以使它永久生效：
```
net.ipv6.conf.all.forwarding = 1
```
启动 radvd 守护程序：
```
$ sudo systemctl stop radvd
$ sudo systemctl start radvd
```
这个示例在我的 Ubuntu 测试系统中遇到了一个怪事；radvd 总是停止，我查看它的状态却没有任何问题，做任何改变之后都需要重新启动 radvd。
启动成功后没有任何输出，并且失败也是如此，因此，需要运行 `sudo systemctl radvd status` 去查看它的运行状态。如果有错误，systemctl 会告诉你。一般常见的错误都是 `/etc/radvd.conf` 中的语法错误。
在 Twitter 上抱怨了上述问题之后，我学到了一件很酷的技巧：当你运行 ` journalctl -xe --no-pager` 去调试 systemctl 错误时，你的输出将被封装打包，然后，你就可以看到错误信息。
现在检查你的主机，查看它们自动分配的新地址：
```
$ ifconfig
ens7 Link encap:Ethernet HWaddr 52:54:00:57:71:50
[...]
inet6 addr: fd7d:844d:3e17:f3ae:9808:98d5:bea9:14d9/64 Scope:Global
[...]
```
本文到此为止，下周继续学习如何为 ULAs 管理 DNS，这样你就可以使用一个合适的主机名来代替这些长长的 IPv6 地址。
通过来自 Linux 基金会和 edX 的 ["Linux 入门" ][2] 免费课程学习更多 Linux 的知识。
--------------------------------------------------------------------------------
via: https://www.linux.com/learn/intro-to-linux/2017/12/ipv6-auto-configuration-linux
作者：[Carla Schroder][a]
译者：[qhwdw](https://github.com/qhwdw)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]:https://www.linux.com/users/cschroder
[1]:https://www.linux.com/learn/intro-to-linux/2017/11/testing-ipv6-networking-kvm-part-1
[2]:https://training.linuxfoundation.org/linux-courses/system-administration-training/introduction-to-linux