From c98efe6238660844aa2a667b8531dfa7857a5692 Mon Sep 17 00:00:00 2001 From: songshunqiang Date: Wed, 29 Aug 2018 16:41:58 +0800 Subject: [PATCH] submit tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md --- ...natomy of a Linux DNS Lookup - Part III.md | 316 ------------------ ...natomy of a Linux DNS Lookup - Part III.md | 300 +++++++++++++++++ 2 files changed, 300 insertions(+), 316 deletions(-) delete mode 100644 sources/tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md create mode 100644 translated/tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md diff --git a/sources/tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md b/sources/tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md deleted file mode 100644 index 3cac477739..0000000000 --- a/sources/tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md +++ /dev/null @@ -1,316 +0,0 @@ -pinewall is translating - -Anatomy of a Linux DNS Lookup – Part III -============================================================ - -In [Anatomy of a Linux DNS Lookup – Part I][1] I covered: - -* `nsswitch` - -* `/etc/hosts` - -* `/etc/resolv.conf` - -* `ping` vs `host` style lookups - -and in [Anatomy of a Linux DNS Lookup – Part II][2] I covered: - -* `systemd` and its `networking` service - -* `ifup` and `ifdown` - -* `dhclient` - -* `resolvconf` - -and ended up here: - -* * * - -![linux-dns-2 (2)](https://zwischenzugs.files.wordpress.com/2018/06/linux-dns-2-2.png?w=525) - - _A (roughly) accurate map of what’s going on_ - -Unfortunately, that’s not the end of the story. There’s still more things that can get involved. In Part III, I’m going to cover NetworkManager and dnsmasq and briefly show how they play a part. - -* * * - -# 1) NetworkManager - -As mentioned in Part II, we are now well away from POSIX standards and into Linux distribution-specific areas of DNS resolution management. - -In my preferred distribution (Ubuntu), there is a service that’s available and often installed for me as a dependency of some other package I install called [NetworkManager][3]. It’s actually a service developed by RedHat in 2004 to help manage network interfaces for you. - -What does this have to do with DNS? Install it to find out: - -``` -$ apt-get install -y network-manager -``` - -In my distribution, I get a config file. - -``` -$ cat /etc/NetworkManager/NetworkManager.conf -[main] -plugins=ifupdown,keyfile,ofono -dns=dnsmasq - -[ifupdown] -managed=false -``` - -See that `dns=dnsmasq` there? That means that NetworkManager will use `dnsmasq` to manage DNS on the host. - -* * * - -# 2) dnsmasq - -The dnsmasq program is that now-familiar thing: yet another level of indirection for `/etc/resolv.conf`. - -Technically, dnsmasq can do a few things, but is primarily it acts as a DNS server that can cache requests to other DNS servers. It runs on port 53 (the standard DNS port), on all local network interfaces. - -So where is `dnsmasq` running? NetworkManager is running: - -``` -$ ps -ef | grep NetworkManager -root     15048     1  0 16:39 ?        00:00:00 /usr/sbin/NetworkManager --no-daemon -``` - -But no `dnsmasq` process exists: - -``` -$ ps -ef | grep dnsmasq -$ -``` - -Although it’s configured to be used, confusingly it’s not actually installed! So you’re going to install it. - -Before you install it though, let’s check the state of `/etc/resolv.conf`. - -``` -$ cat /etc/resolv.conf -# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8) -#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN -nameserver 10.0.2.2 -search home -``` - -It’s not been changed by NetworkManager. - -If `dnsmasq` is installed: - -``` -$ apt-get install -y dnsmasq -``` - -Then `dnsmasq` is up and running: - -``` -$ ps -ef | grep dnsmasq -dnsmasq  15286     1  0 16:54 ?        00:00:00 /usr/sbin/dnsmasq -x /var/run/dnsmasq/dnsmasq.pid -u dnsmasq -r /var/run/dnsmasq/resolv.conf -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new --local-service --trust-anchor=.,19036,8,2,49AAC11D7B6F6446702E54A1607371607A1A41855200FD2CE1CDDE32F24E8FB5 -``` - -And `/etc/resolv.conf` has changed again! - -``` -root@linuxdns1:~# cat /etc/resolv.conf -# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8) -#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN -nameserver 127.0.0.1 -search home -``` - -And `netstat` shows `dnsmasq` is serving on all interfaces at port 53: - -``` -$ netstat -nlp4 -Active Internet connections (only servers) -Proto Recv-Q Send-Q Local Address     Foreign Address State   PID/Program name -tcp        0      0 127.0.0.1:53      0.0.0.0:*       LISTEN  15286/dnsmasq  -tcp        0      0 10.0.2.15:53      0.0.0.0:*       LISTEN  15286/dnsmasq -tcp        0      0 172.28.128.11:53  0.0.0.0:*       LISTEN  15286/dnsmasq -tcp        0      0 0.0.0.0:22        0.0.0.0:*       LISTEN  1237/sshd -udp        0      0 127.0.0.1:53      0.0.0.0:*         15286/dnsmasq -udp        0      0 10.0.2.15:53      0.0.0.0:*               15286/dnsmasq   -udp        0      0 172.28.128.11:53  0.0.0.0:*               15286/dnsmasq   -udp        0      0 0.0.0.0:68        0.0.0.0:*               10758/dhclient -udp        0      0 0.0.0.0:68        0.0.0.0:*               10530/dhclient -udp        0      0 0.0.0.0:68        0.0.0.0:*               10185/dhclient -``` - -* * * - -# 3) Unpicking dnsmasq - -Now we are in a situation where all DNS queries are going to `127.0.0.1:53` and from there what happens? - -We can get a clue from looking again at the `/var/run` folder. The `resolv.conf` in `resolvconf` has been changed to point to where `dnsmasq` is being served: - -``` -$ cat /var/run/resolvconf/resolv.conf -# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8) -#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN -nameserver 127.0.0.1 -search home -``` - -while there’s a new `dnsmasq` folder with its own `resolv.conf`. - -``` -$ cat /run/dnsmasq/resolv.conf -nameserver 10.0.2.2 -``` - -which has the nameserver given to us by `DHCP`. - -We can reason about this without looking too deeply, but what if we really want to know what’s going on? - -* * * - -# 4) Debugging Dnsmasq - -Frequently I’ve found myself wondering what dnsmasq’s state is. Fortunately, you can get a good amount of information out of it if you set change this line in `/etc/dnsmasq.conf`: - -``` -#log-queries -``` - -to: - -``` -log-queries -``` - -and restart ​`dnsmasq` - -Now, if you do a simple: - -``` -$ ping -c1 bbc.co.uk -``` - -you will see something like this in `/var/log/syslog` (the `[...]` indicates that the line’s start is the same as the previous one): - -``` -Jul  3 19:56:07 ubuntu-xenial dnsmasq[15372]: query[A] bbc.co.uk from 127.0.0.1 -[...] forwarded bbc.co.uk to 10.0.2.2 -[...] reply bbc.co.uk is 151.101.192.81 -[...] reply bbc.co.uk is 151.101.0.81 -[...] reply bbc.co.uk is 151.101.64.81 -[...] reply bbc.co.uk is 151.101.128.81 -[...] query[PTR] 81.192.101.151.in-addr.arpa from 127.0.0.1 -[...] forwarded 81.192.101.151.in-addr.arpa to 10.0.2.2 -[...] reply 151.101.192.81 is NXDOMAIN -``` - -which shows what `dnsmasq` received, where the query was forwarded to, and what reply was received. - -If the query is returned from the cache (or, more exactly, the local ‘time-to-live’ for the query has not expired), then it looks like this in the logs: - -``` -[...] query[A] bbc.co.uk from 127.0.0.1 -[...] cached bbc.co.uk is 151.101.64.81 -[...] cached bbc.co.uk is 151.101.128.81 -[...] cached bbc.co.uk is 151.101.192.81 -[...] cached bbc.co.uk is 151.101.0.81 -[...] query[PTR] 81.64.101.151.in-addr.arpa from 127.0.0.1 -``` - -and if you ever want to know what’s in your cache, you can provoke dnsmasq into sending it to the same log file by sending the `USR1` signal to the dnsmasq process id: - -``` -$ kill -SIGUSR1 <(cat /run/dnsmasq/dnsmasq.pid) -``` - -and the output of the dump looks like this: - -``` -Jul  3 15:08:08 ubuntu-xenial dnsmasq[15697]: time 1530630488                                                                                                                                  -[...] cache size 150, 0/5 cache insertions re-used unexpired cache entries.                                                                            -[...] queries forwarded 2, queries answered locally 0                                                                                                  -[...] queries for authoritative zones 0                                                                                                                -[...] server 10.0.2.2#53: queries sent 2, retried or failed 0                                                                                          -[...] Host           Address        Flags      Expires                             -[...] linuxdns1      172.28.128.8   4FRI   H                                                                 -[...] ip6-localhost  ::1            6FRI   H                                                                 -[...] ip6-allhosts   ff02::3         6FRI   H                                                                 -[...] ip6-localnet     fe00::         6FRI   H                                                                 -[...] ip6-mcastprefix  ff00::         6FRI   H                                                                 -[...] ip6-loopback     :               6F I   H                                                                 -[...] ip6-allnodes    ff02:           6FRI   H                                                                 -[...] bbc.co.uk        151.101.64.81  4F         Tue Jul  3 15:11:41 2018                                      -[...] bbc.co.uk        151.101.192.81 4F         Tue Jul  3 15:11:41 2018                                      -[...] bbc.co.uk        151.101.0.81    4F         Tue Jul  3 15:11:41 2018                                      -[...] bbc.co.uk        151.101.128.81 4F         Tue Jul  3 15:11:41 2018                                      -[...]                  151.101.64.81  4 R  NX    Tue Jul  3 15:34:17 2018                                      -[...] localhost        127.0.0.1      4FRI   H                                                                 -[...]           19036   8   2  SF I                                                                     -[...] ip6-allrouters   ff02::2        6FRI   H         -``` - -In the above output, I believe (but don’t know, and ‘?’ indicates a relatively wild guess on my part) that: - -* ‘4’ means IPv4 - -* ‘6’ means IPv6 - -* ‘H’ means address was read from an `/etc/hosts` file - -* ‘I’ ? ‘Immortal’ DNS value? (ie no time-to-live value?) - -* ‘F’ ? - -* ‘R’ ? - -* ‘S’? - -* ‘N’? - -* ‘X’ - -#### Alternatives to dnsmasq - -`dnsmasq` is not the only option that can be passed to dns in NetworkManager. There’s `none` which does nothing to `/etc/resolv,conf`, `default`, which claims to ‘update `resolv.conf`  to reflect currently active connections’, and `unbound`, which communicates with the `unbound` service and `dnssec-triggerd`, which is concerned with DNS security and is not covered here. - -* * * - -### End of Part III - -That’s the end of Part III, where we covered the NetworkManager service, and its `dns=dnsmasq` setting. - -Let’s briefly list some of the things we’ve come across so far: - -* `nsswitch` - -* `/etc/hosts` - -* `/etc/resolv.conf` - -* `/run/resolvconf/resolv.conf` - -* `systemd` and its `networking` service - -* `ifup` and `ifdown` - -* `dhclient` - -* `resolvconf` - -* `NetworkManager` - -* `dnsmasq` - --------------------------------------------------------------------------------- - -via: https://zwischenzugs.com/2018/07/06/anatomy-of-a-linux-dns-lookup-part-iii/ - -作者：[ZWISCHENZUGS][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://zwischenzugs.com/ -[1]:https://zwischenzugs.com/2018/06/08/anatomy-of-a-linux-dns-lookup-part-i/ -[2]:https://zwischenzugs.com/2018/06/18/anatomy-of-a-linux-dns-lookup-part-ii/ -[3]:https://en.wikipedia.org/wiki/NetworkManager diff --git a/translated/tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md b/translated/tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md new file mode 100644 index 0000000000..4e5b8628d4 --- /dev/null +++ b/translated/tech/20180706 Anatomy of a Linux DNS Lookup - Part III.md @@ -0,0 +1,300 @@ +Linux DNS 查询剖析（第三部分） +============================================================ + +在 [Linux DNS 查询剖析（第一部分）][1]中，我们介绍了： + +* `nsswitch` +* `/etc/hosts` +* `/etc/resolv.conf` +* `ping` 与 `host` 查询方式的对比 + +and in [Linux DNS 查询剖析（第二部分）][2]，我们介绍了： + +* `systemd` 和对应的 `networking` 服务 +* `ifup` 和 `ifdown` +* `dhclient` +* `resolvconf` + +剖析进展如下： + +* * * + +![linux-dns-2 (2)][4] + + _（大致）准确的关系图_ + +很可惜，故事还没有结束，还有不少东西也会影响 DNS 查询。在第三部分中，我将介绍 `NetworkManager` 和 `dnsmasq`，简要说明它们如何影响 DNS 查询。 + +* * * + +### 1) NetworkManager + +在第二部分已经提到，我们现在介绍的内容已经偏离 POSIX 标准，涉及的 DNS 解析管理部分在各个发行版上形式并不统一。 + +在我使用的发行版 （Ubuntu）中，有一个名为 [NetworkManager][3] 的服务，它通常作为一些其它软件包的依赖被安装而且处于激活available状态。它实际上是 RedHat 在 2004 年开发的一个服务，用于帮助你管理网络接口。 + +它与 DNS 查询有什么关系呢？让我们安装这个服务并找出答案： + +``` +$ apt-get install -y network-manager +``` + +对于 Ubuntu，在软件包安装后，你可以发现一个新的配置文件： + +``` +$ cat /etc/NetworkManager/NetworkManager.conf +[main] +plugins=ifupdown,keyfile,ofono +dns=dnsmasq + +[ifupdown] +managed=false +``` + +看到 `dns=dnsmasq` 了吧？这意味着 `NetworkManager` 将使用 `dnsmasq` 管理主机上的 DNS。 + +* * * + +### 2) dnsmasq + +`dnsmasq` 程序是我们很熟悉的程序：只是 `/etc/resolv.conf` 之上的又一个间接层。 + +理论上，`dnsmasq` 有多种用途，但主要被用作 DNS 缓存服务器，缓存到其它 DNS 服务器的请求。`dnsmasq` 在本地所有网络接口上监听 53 端口（标准的 DNS 端口）。 + +那么 `dnsmasq` 运行在哪里呢？`NetworkManager` 的运行情况如下： + +``` +$ ps -ef | grep NetworkManager +root     15048     1  0 16:39 ?        00:00:00 /usr/sbin/NetworkManager --no-daemon +``` + +但并没有找到 `dnsmasq` 相关的进程： + +``` +$ ps -ef | grep dnsmasq +$ +``` + +令人迷惑的是，虽然 `dnsmasq` 被配置用于管理 DNS，但其实并没有安装在系统上！因而，你需要自己安装它。 + +安装之前，让我们查看一下 `/etc/resolv.conf` 文件的内容： + +``` +$ cat /etc/resolv.conf +# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8) +#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN +nameserver 10.0.2.2 +search home +``` + +可见，并没有被 `NetworkManager` 修改。 + +如果安装 `dnsmasq`: + +``` +$ apt-get install -y dnsmasq +``` + +这时，`dnsmasq` 已经启动运行： + +``` +$ ps -ef | grep dnsmasq +dnsmasq  15286     1  0 16:54 ?        00:00:00 /usr/sbin/dnsmasq -x /var/run/dnsmasq/dnsmasq.pid -u dnsmasq -r /var/run/dnsmasq/resolv.conf -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new --local-service --trust-anchor=.,19036,8,2,49AAC11D7B6F6446702E54A1607371607A1A41855200FD2CE1CDDE32F24E8FB5 +``` + +然后，`/etc/resolv.conf` 文件内容又改变了！ + +``` +root@linuxdns1:~# cat /etc/resolv.conf +# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8) +#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN +nameserver 127.0.0.1 +search home +``` + +运行 `netstat` 命令，可以看出 `dnsmasq` 在所有网络接口上监听 53 端口： + +``` +$ netstat -nlp4 +Active Internet connections (only servers) +Proto Recv-Q Send-Q Local Address     Foreign Address State   PID/Program name +tcp        0      0 127.0.0.1:53      0.0.0.0:*       LISTEN  15286/dnsmasq  +tcp        0      0 10.0.2.15:53      0.0.0.0:*       LISTEN  15286/dnsmasq +tcp        0      0 172.28.128.11:53  0.0.0.0:*       LISTEN  15286/dnsmasq +tcp        0      0 0.0.0.0:22        0.0.0.0:*       LISTEN  1237/sshd +udp        0      0 127.0.0.1:53      0.0.0.0:*         15286/dnsmasq +udp        0      0 10.0.2.15:53      0.0.0.0:*               15286/dnsmasq   +udp        0      0 172.28.128.11:53  0.0.0.0:*               15286/dnsmasq   +udp        0      0 0.0.0.0:68        0.0.0.0:*               10758/dhclient +udp        0      0 0.0.0.0:68        0.0.0.0:*               10530/dhclient +udp        0      0 0.0.0.0:68        0.0.0.0:*               10185/dhclient +``` + +* * * + +### 3) 分析 dnsmasq + +在目前的情况下，所有的 DNS 查询都会使用 `127.0.0.1:53` 这个 DNS 服务器，下一步会发生什么呢？ + +我再次查看 `/var/run` 目录，可以发现一个线索： +`resolvconf` 目录下 `resolv.conf` 文件中的配置也相应变更，变更为 `dnsmasq` 对应的 DNS 服务器： + +``` +$ cat /var/run/resolvconf/resolv.conf +# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8) +#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN +nameserver 127.0.0.1 +search home +``` + +同时，出现了一个新的 `dnsmasq` 目录，也包含一个 `resolv.conf` 文件： + +``` +$ cat /run/dnsmasq/resolv.conf +nameserver 10.0.2.2 +``` + +（LCTT 译注：这里依次提到了 `/var/run` 和 `/run`，使用 Ubuntu 16.04 LTS 验证发现，`/var/run` 其实是指向 `/run/` 的软链接） + +该文件包含我们从 `DHCP` 获取的 `nameserver`。 + +虽然可以推导出这个结论，但如何查看具体的调用逻辑呢？ + +* * * + +### 4) 调试 dnsmasq + +我经常思考 `dnsmasq` （在整个过程中）的功能定位。幸运的是，如果你将 `/etc/dnsmasq.conf` 中的一行做如下调整，你可以获取大量 `dnsmasq` 状态的信息： + +``` +#log-queries +``` + +修改为： + +``` +log-queries +``` + +然后重启 `dnsmasq`。 + +接下来，只要运行一个简单的命令： + +``` +$ ping -c1 bbc.co.uk +``` + +你就可以在 `/var/log/syslog` 中找到类似的内容（其中 `[...]` 表示行首内容与上一行相同）： + +``` +Jul  3 19:56:07 ubuntu-xenial dnsmasq[15372]: query[A] bbc.co.uk from 127.0.0.1 +[...] forwarded bbc.co.uk to 10.0.2.2 +[...] reply bbc.co.uk is 151.101.192.81 +[...] reply bbc.co.uk is 151.101.0.81 +[...] reply bbc.co.uk is 151.101.64.81 +[...] reply bbc.co.uk is 151.101.128.81 +[...] query[PTR] 81.192.101.151.in-addr.arpa from 127.0.0.1 +[...] forwarded 81.192.101.151.in-addr.arpa to 10.0.2.2 +[...] reply 151.101.192.81 is NXDOMAIN +``` + +可以清晰看出 `dnsmasq` 收到的查询、查询被转发到了哪里以及收到的回复。 + +如果查询被缓存命中（或者说，本地的查询结果还在存活时间time-to-live内，并未过期），日志显示如下： + +``` +[...] query[A] bbc.co.uk from 127.0.0.1 +[...] cached bbc.co.uk is 151.101.64.81 +[...] cached bbc.co.uk is 151.101.128.81 +[...] cached bbc.co.uk is 151.101.192.81 +[...] cached bbc.co.uk is 151.101.0.81 +[...] query[PTR] 81.64.101.151.in-addr.arpa from 127.0.0.1 +``` + +如果你想了解缓存中有哪些记录，可以向 `dnsmasq` 进程 id 发送 `USR1` 信号，这样 `dnsmasq` 会将缓存记录导出并写入到相同的日志文件中： + +``` +$ kill -SIGUSR1 $(cat /run/dnsmasq/dnsmasq.pid) +``` + +（LCTT 译注：原文中命令执行报错，已变更成最接近且符合作者意图的命令） + +导记录对应如下输出： + +``` +Jul  3 15:08:08 ubuntu-xenial dnsmasq[15697]: time 1530630488 +[...] cache size 150, 0/5 cache insertions re-used unexpired cache entries. +[...] queries forwarded 2, queries answered locally 0 +[...] queries for authoritative zones 0 +[...] server 10.0.2.2#53: queries sent 2, retried or failed 0 +[...] Host           Address        Flags      Expires +[...] linuxdns1      172.28.128.8   4FRI   H +[...] ip6-localhost  ::1            6FRI   H +[...] ip6-allhosts   ff02::3         6FRI   H +[...] ip6-localnet     fe00::         6FRI   H +[...] ip6-mcastprefix  ff00::         6FRI   H +[...] ip6-loopback     :               6F I   H +[...] ip6-allnodes    ff02:           6FRI   H +[...] bbc.co.uk        151.101.64.81  4F         Tue Jul  3 15:11:41 2018 +[...] bbc.co.uk        151.101.192.81 4F         Tue Jul  3 15:11:41 2018 +[...] bbc.co.uk        151.101.0.81    4F         Tue Jul  3 15:11:41 2018 +[...] bbc.co.uk        151.101.128.81 4F         Tue Jul  3 15:11:41 2018 +[...]                  151.101.64.81  4 R  NX    Tue Jul  3 15:34:17 2018 +[...] localhost        127.0.0.1      4FRI   H +[...]           19036   8   2  SF I +[...] ip6-allrouters   ff02::2        6FRI   H +``` + +在上面的输出中，我猜测（并不确认，`?` 代表我比较疯狂的猜测）如下： + +* `4` 代表 IPv4 +* `6` 代表 IPv6 +* `H` 代表从 `/etc/hosts` 中读取 IP 地址 +* `I` ？ “永生”的 DNS 记录 ？ (例如，没有设置存活时间数值 ？) +* `F` ？ +* `R` ？ +* `S` ？ +* `N` ？ +* `X` + +（LCTT 译注：查看 `dnsmasq` 的源代码 [`cache.c`][5] 可知，`4` 代表 `IPV4`，`6` 代表 `IPV6`，`C` 代表 `CNAME`，`S` 代表 `DNSSEC`，`F` 代表 `FORWARD`，`R` 代表 `REVERSE`，`I` 代表 `IMMORTAL`，`N` 代表 `NEG`，`X` 代表 `NXDOMAIN`，`H` 代表 `HOSTS`。更具体的含义需要查看代码或相关文档） + +#### dnsmasq 的替代品 + +`NetworkManager` 配置中的 `dns` 字段并不是只能使用 `dnsmasq`，可选项包括 `none`，`default`，`unbound` 和 `dnssec-triggered` 等。使用 `none` 时，`NetworkManager` 不会改动 `/etc/resolv.conf`；使用 `default` 时，`NetworkManager` 会根据当前的活跃连接active connections更新 `resolv.conf`；使用 `unbound` 时，`NetworkManager` 会与 `unbound` 服务通信；`dnssec-triggered` 与 DNS 安全相关，不在本文讨论范围。 + +* * * + +### 第三部分总结 + +第三部分到此结束，其中我们介绍了 `NetworkManager` 服务及其 `dns=dnsmasq` 的配置。 + +下面简要罗列一下我们已经介绍过的全部内容： + +* `nsswitch` +* `/etc/hosts` +* `/etc/resolv.conf` +* `/run/resolvconf/resolv.conf` +* `systemd` 及对应的 `networking` 服务 +* `ifup` 和 `ifdown` +* `dhclient` +* `resolvconf` +* `NetworkManager` +* `dnsmasq` + +-------------------------------------------------------------------------------- + +via: https://zwischenzugs.com/2018/07/06/anatomy-of-a-linux-dns-lookup-part-iii/ + +作者：[ZWISCHENZUGS][a] +译者：[pinewall](https://github.com/pinewall) +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://zwischenzugs.com/ +[1]:https://linux.cn/article-9943-1.html +[2]:https://linux.cn/article-9949-1.html +[3]:https://en.wikipedia.org/wiki/NetworkManager +[4]:https://zwischenzugs.files.wordpress.com/2018/06/linux-dns-2-2.png?w=525 +[5]:https://github.com/imp/dnsmasq/blob/master/src/cache.c