Unbound
Unbound は検証をおこなったり再帰・キャッシュをする DNS リゾルバです。
目次
インストール
公式リポジトリから unbound パッケージをインストールしてください。
さらに、DNSSEC 検証をするには expat が必要です。
設定
unbound の設定は簡単です。サンプル設定ファイル /etc/unbound/unbound.conf.example が存在するので /etc/unbound/unbound.conf にコピーして、必要に応じて修正を加えるだけで、IPv4 と IPv6 の両方で動作させることができます。
アクセス制御
IP アドレスによってクエリに応答するインターフェイスを指定できます。localhost で listen するには、以下を使用:
interface: 127.0.0.1
全てのインターフェイスで listen するには、以下を使用:
interface: 0.0.0.0
access-control オプションを使うことでさらに細かくアクセスを設定できます:
access-control: subnet action
例:
access-control: 192.168.1.0/24 allow
action は deny (drop message), refuse (polite error reply), allow (recursive ok), allow_snoop (recursive and nonrecursive ok) のどれかに置き換えます。デフォルトでは、ローカルホスト以外の全てが拒否されます。
ルートヒント
アドレスがキャッシュされていないホストを問い合わせられた場合、リゾルバはサーバーツリーの一番上からルートサーバーに問い合わせて、アドレスを問い合わせることができるトップレベルドメインの場所を知る必要があります。したがって、unbound の設定ディレクトリにルートヒントファイルを配置しなければなりません。以下のコマンドを実行するのが一番シンプルな方法です:
# curl -o /etc/unbound/root.hints https://www.internic.net/domain/named.cache
ルートサーバーのリストを最新にするために、上記のコマンドは6ヶ月ごとに実行すると良いでしょう。手動で実行してもかまいませんが、cron ジョブでタスクを設定する方法もあります。
unbound から root.hints ファイルの場所を設定してください:
root-hints: "/etc/unbound/root.hints"
ローカル DNS サーバーを使うように /etc/resolv.conf を設定
/etc/resolv.conf を編集 (resolv.conf を見て下さい):
nameserver 127.0.0.1
Also if you want to be able to use the hostname of local machine names without the fully qualified domain names, then add a line with the local domain such as:
domain localdomain.com nameserver 127.0.0.1
That way you can refer to local hosts such as mainmachine1.localdomain.com as simply mainmachine1 when using the ssh command, but the drill command below still requires the fully qualified domain names in order to perform lookups.
Testing the server before making it default can be done using the drill command from the ldns package with examples from internal and external forward and reverse addresses:
$ drill @127.0.0.1 www.cnn.com $ drill @127.0.0.1 localmachine.localdomain.com $ drill @127.0.0.1 -x w.x.y.z
where w.x.y.z can be a local or external IP address and the -x option requests a reverse lookup. Once all is working, and you have /etc/resolv.conf set to use 127.0.0.1 as the nameserver then you no longer need the @127.0.0.1 in the drill command, and you can test again that it uses the default DNS server - check that the server used as listed at the bottom of the output from each of these commands shows it is 127.0.0.1 being queried.
ログ出力
If you will want logging for unbound, then create a log file which can also be in the same directory, but you can choose any location. One way is then to do as root:
# touch /etc/unbound/unbound.log # chown unbound:unbound /etc/unbound/unbound.log
Then you can include the logging parameter when you set up the main unbound.conf file as below.
DNSSEC 検証
You will need the root server trust key anchor file. It is provided by the dnssec-anchors package (already installed as a dependency), however, unbound needs read and write access to the file. The unbound.service service accomplishes this by copying the /etc/trusted-key.key file to /etc/unbound/trusted-key.key. You just need to point unbound to this file:
/etc/unbound/unbound.conf
server: ... trust-anchor-file: trusted-key.key ...
Also make sure that if a general forward to the Google servers had been in place, then comment them out otherwise DNS queries will fail. DNSSEC validation will be done if the DNS server being queried supports it.
ldns (依存パッケージとしてインストールされます) の drill を使って DNSSEC が機能しているかテストできます:
drill sigfail.verteiltesysteme.net # should return rcode: SERVFAIL drill sigok.verteiltesysteme.net # should return rcode: NOERROR
クエリの転送
If you have a local network which you wish to have DNS queries for and there is a local DNS server that you would like to forward queries to then you should include this line:
private-address: local_subnet/subnet_mask
例:
private-address: 10.0.0.0/24
To include a local DNS server for both forward and reverse local addresses a set of lines similar to these below is necessary with a forward and reverse lookup (choose the IP address of the server providing DNS for the local network accordingly by changing 10.0.0.1 in the lines below):
local-zone: "10.in-addr.arpa." transparent
This line above is important to get the reverse lookup to work correctly.
forward-zone: name: "mynetwork.com." forward-addr: 10.0.0.1 # Home DNS
forward-zone: name: "10.in-addr.arpa." forward-addr: 10.0.0.1
You can set up the localhost forward and reverse lookups with the following lines:
local-zone: "localhost." static local-data: "localhost. 10800 IN NS localhost." local-data: "localhost. 10800 IN SOA localhost. nobody.invalid. 1 3600 1200 604800 10800" local-data: "localhost. 10800 IN A 127.0.0.1" local-zone: "127.in-addr.arpa." static local-data: "127.in-addr.arpa. 10800 IN NS localhost." local-data: "127.in-addr.arpa. 10800 IN SOA localhost. nobody.invalid. 2 3600 1200 604800 10800" local-data: "1.0.0.127.in-addr.arpa. 10800 IN PTR localhost."
Then to use specific servers for default forward zones that are outside of the local machine and outside of the local network (i.e. all other queries will be forwarded to them, and then cached) add this to the configuration file (and in this example the first two addresses are the fast google DNS servers):
forward-zone: name: "." forward-addr: 8.8.8.8 forward-addr: 8.8.4.4 forward-addr: 208.67.222.222 forward-addr: 208.67.220.220
This will make unbound use Google and OpenDNS servers as the forward zone for external lookups.
使用方法
Unbound の起動
unbound パッケージには unbound.service が入っているので、起動してください。ブート時に起動させたいときは有効化します。
Unbound の遠隔操作
unbound には unbound-control ユーティリティが付いており、リモートの unbound サーバーを管理することができます。pdnsd の pdnsd-ctl コマンドに似ています。
unbound-control の設定
使用する前に、以下の設定が必要です:
1) まず、以下のコマンドを実行してください:
# unbound-control-setup
自己署名証明書とサーバーとクライアントの秘密鍵が生成されます。これらのファイルは /etc/unbound ディレクトリに保存されます。
2) その後、/etc/unbound/unbound.conf を編集して以下の内容を記述してください。control-enable: yes オプションは必須ですが、他のオプションは必要に応じて変更できます。
remote-control:
# Enable remote control with unbound-control(8) here.
# set up the keys and certificates with unbound-control-setup.
control-enable: yes
# what interfaces are listened to for remote control.
# give 0.0.0.0 and ::0 to listen to all interfaces.
control-interface: 127.0.0.1
# port number for remote control operations.
control-port: 8953
# unbound server key file.
server-key-file: "/etc/unbound/unbound_server.key"
# unbound server certificate file.
server-cert-file: "/etc/unbound/unbound_server.pem"
# unbound-control key file.
control-key-file: "/etc/unbound/unbound_control.key"
# unbound-control certificate file.
control-cert-file: "/etc/unbound/unbound_control.pem"
unbound-control を使う
unbound-control で使用できるコマンドの例:
- 再設定しないで統計を出力
# unbound-control stats_noreset
- キャッシュを標準出力にダンプ
# unbound-control dump_cache
- キャッシュを消去して設定をリロード
# unbound-control reload
詳しくは man 8 unbound-control を参照してください。
Adding an authoritative DNS server
For users who wish to run both a validating, recursive, caching DNS server as well as an authoritative DNS server on a single machine then it may be useful to refer to the wiki page nsd which gives an example of a configuration for such a system. Having one server for authoritative DNS queries and a separate DNS server for the validating, recursive, caching DNS functions gives increased security over a single DNS server providing all of these functions. Many users have used bind as a single DNS server, and some help on migration from bind to the combination of running nsd and bind is provided in the nsd wiki page.
WAN と DNS
It is also possible to change the configuration files and interfaces on which the server is listening so that DNS queries from machines outside of the local network can access specific machines within the LAN. This is useful for web and mail servers which are accessible from anywhere, and the same techniques can be employed as has been achieved using bind for many years, in combination with suitable port forwarding on firewall machines to forward incoming requests to the right machine.
num-threads の問題
The man page for unbound.conf mentions:
outgoing-range: <number>
Number of ports to open. This number of file descriptors can be opened per thread.
and some sources suggest that the num-threads parameter should be set to the number of cpu cores. The sample unbound.conf.example file merely has:
# number of threads to create. 1 disables threading.
# num-threads: 1
However it is not possible to arbitrarily increase num-threads above 1 without causing unbound to start with warnings in the logs about exceeding the number of file descriptors. In reality for most users running on small networks or on a single machine it should be unnecessary to seek performance enhancement by increasing num-threads above 1. If you do wish to do so then refer to official documentation and the following rule of thumb should work:
- Set
num-threadsequal to the number of CPU cores on the system. E.g. for 4 CPUs with 2 cores each, use 8.
Set the outgoing-range to as large a value as possible, see the sections in the referred web page above on how to overcome the limit of 1024 in total. This services more clients at a time. With 1 core, try 950. With 2 cores, try 450. With 4 cores try 200. The num-queries-per-thread is best set at half the number of the outgoing-range.
Because of the limit on outgoing-range thus also limits num-queries-per-thread, it is better to compile with libevent, so that there is no 1024 limit on outgoing-range. If you need to compile this way for a heavy duty DNS server then you will need to compile the programme from source instead of using the unbound package.