LPIC あずき本v5.0 ch11 ネットワークの基礎 11.4
DNSの設定
DNSの概要
- IPアドレス
- TCP/IPネットワークにおいてネットワーク上のコンピュータを識別
- 人間にとって扱いづらいので、ホスト名でコンピュータを指定できるようにしている
- 名前解決
/etc/hosts- ホスト名とIPアドレスとの対応情報が保存されているファイル
- ホストが少数・更新頻度が低いならこれでいい
- DNS: Domain Name System
- ホストが多くなったり更新頻度が高くなったりしたら必要になってくる
- 名前解決サービスを提供
- ほかにもいっぱいある
- LDAPとか
- ホスト名
DNSの設定ファイル
/etc/resolv.conf
# This file is managed by man:systemd-resolved(8). Do not edit. # # This is a dynamic resolv.conf file for connecting local clients to the # internal DNS stub resolver of systemd-resolved. This file lists all # configured search domains. # # Run "systemd-resolve --status" to see details about the uplink DNS servers # currently in use. # # Third party programs must not access this file directly, but only through the # symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way, # replace this symlink by a static file or a different symlink. # # See man:systemd-resolved.service(8) for details about the supported modes of # operation for /etc/resolv.conf. nameserver 127.0.0.53 options edns0
- 直接触っちゃだめ
# This file is managed by man:systemd-resolved(8). Do not edit.
systemd-resolved.serviceが絡んでいる(後述)
# See man:systemd-resolved.service(8) for details about the supported modes of # operation for /etc/resolv.conf.
systemctl status systemd-resolved
● systemd-resolved.service - Network Name Resolution Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled) Active: active (running) since Fri 2019-04-12 16:53:31 JST; 5 days ago ...
- ローカルの53番ポートでDNSサーバが動いている
nameserver 127.0.0.53
ss -atupn | grep LISTEN
tcp LISTEN 0 128 127.0.0.53%lo:53 0.0.0.0:* users:(("systemd-resolve",pid=624,fd=13))
tcp LISTEN 0 128 0.0.0.0:22 0.0.0.0:* users:(("sshd",pid=28294,fd=3))
tcp LISTEN 0 5 127.0.0.1:631 0.0.0.0:* users:(("cupsd",pid=10044,fd=6))
tcp LISTEN 0 128 [::]:22 [::]:* users:(("sshd",pid=28294,fd=4))
tcp LISTEN 0 5 [::1]:631 [::]:* users:(("cupsd",pid=10044,fd=5))
- 抜粋
- ループバックの53番ポート
- 53はDNSに割り当てられたwell-known port
- ループバックの53番ポート
127.0.0.53%lo:53 0.0.0.0:* users:(("systemd-resolve",pid=624,fd=13))
- 有名どころ
8.8.8.88.8.4.4
/etc/nsswitch.conf
# /etc/nsswitch.conf # # Example configuration of GNU Name Service Switch functionality. # If you have the `glibc-doc-reference' and `info' packages installed, try: # `info libc "Name Service Switch"' for information about this file. passwd: compat systemd group: compat systemd shadow: compat gshadow: files hosts: files mdns4_minimal [NOTFOUND=return] dns myhostname networks: files protocols: db files services: db files ethers: db files rpc: db files netgroup: nis
- 名前解決の問い合わせ順
hosts: files mdns4_minimal [NOTFOUND=return] dns myhostname
- 名前解決の方法はさまざま
getent hosts- 全部加味したホスト名一覧を得る
getent hosts
127.0.0.1 localhost 127.0.1.1 wand-ThinkPad-X240s 127.0.0.1 ip6-localhost ip6-loopback
systemd-resolved
- systemd採用システムにおいて名前解決に使われているサービス
/etc/systemd/resolved.conf
# This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. # # Entries in this file show the compile time defaults. # You can change settings by editing this file. # Defaults can be restored by simply deleting this file. # # See resolved.conf(5) for details [Resolve] #DNS= #FallbackDNS= #Domains= #LLMNR=no #MulticastDNS=no #DNSSEC=no #Cache=yes #DNSStubListener=yes
- systemd-resolvedサービスが使われているシステムでは...
/etc/resolv.confは/run/以下ファイルへのシンボリックリンクだったりする- systemd-resolved管理下なので直接編集してはいけない
ls -l /etc/resolv.conf
lrwxrwxrwx 1 root root 39 2月 24 02:11 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf
DNS管理コマンド
hostコマンド
host localhost
localhost has address 127.0.0.1 localhost has IPv6 address ::1
- 詳細
host -v localhost
Trying "localhost" ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31899 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;localhost. IN A ;; ANSWER SECTION: localhost. 0 IN A 127.0.0.1 Received 43 bytes from 127.0.0.53#53 in 0 ms Trying "localhost" ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16144 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;localhost. IN AAAA ;; ANSWER SECTION: localhost. 0 IN AAAA ::1 Received 55 bytes from 127.0.0.53#53 in 0 ms Trying "localhost" ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27054 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;localhost. IN MX Received 27 bytes from 127.0.0.53#53 in 0 ms
- 逆引き
host 127.0.0.1
1.0.0.127.in-addr.arpa domain name pointer localhost.
digコマンド
- DNS interrogating の意？たぶん
dig [オプション] [@DNSサーバ名] ホストまたはドメイン名 [検索タイプ]
- 正引き
- デフォルトAレコード
- Address
- IPv4アドレス
- デフォルトAレコード
dig @8.8.8.8 google.co.jp
# dig @8.8.8.8 google.co.jp a # おなじ
; <<>> DiG 9.11.3-1ubuntu1.5-Ubuntu <<>> @8.8.8.8 google.co.jp ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44089 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 512 ;; QUESTION SECTION: ;google.co.jp. IN A ;; ANSWER SECTION: google.co.jp. 68 IN A 216.58.197.195 ;; Query time: 37 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Wed Apr 17 21:29:54 JST 2019 ;; MSG SIZE rcvd: 57
dig @8.8.8.8 google.co.jp aaaa
; <<>> DiG 9.11.3-1ubuntu1.5-Ubuntu <<>> @8.8.8.8 google.co.jp aaaa ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22624 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 512 ;; QUESTION SECTION: ;google.co.jp. IN AAAA ;; ANSWER SECTION: google.co.jp. 299 IN AAAA 2404:6800:4004:80a::2003 ;; Query time: 43 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Wed Apr 17 21:33:58 JST 2019 ;; MSG SIZE rcvd: 69
- メールサーバ
dig @8.8.8.8 google.co.jp mx
; <<>> DiG 9.11.3-1ubuntu1.5-Ubuntu <<>> @8.8.8.8 google.co.jp mx ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53306 ;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 512 ;; QUESTION SECTION: ;google.co.jp. IN MX ;; ANSWER SECTION: google.co.jp. 599 IN MX 20 alt1.aspmx.l.google.com. google.co.jp. 599 IN MX 10 aspmx.l.google.com. google.co.jp. 599 IN MX 40 alt3.aspmx.l.google.com. google.co.jp. 599 IN MX 30 alt2.aspmx.l.google.com. google.co.jp. 599 IN MX 50 alt4.aspmx.l.google.com. ;; Query time: 42 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Wed Apr 17 21:34:20 JST 2019 ;; MSG SIZE rcvd: 159
- ネームサーバ
dig @8.8.8.8 google.co.jp ns
; <<>> DiG 9.11.3-1ubuntu1.5-Ubuntu <<>> @8.8.8.8 google.co.jp ns ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51256 ;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 512 ;; QUESTION SECTION: ;google.co.jp. IN NS ;; ANSWER SECTION: google.co.jp. 21599 IN NS ns3.google.com. google.co.jp. 21599 IN NS ns4.google.com. google.co.jp. 21599 IN NS ns1.google.com. google.co.jp. 21599 IN NS ns2.google.com. ;; Query time: 41 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Wed Apr 17 21:34:47 JST 2019 ;; MSG SIZE rcvd: 123
- ぜんぶ
dig @8.8.8.8 google.co.jp any
; <<>> DiG 9.11.3-1ubuntu1.5-Ubuntu <<>> @8.8.8.8 google.co.jp any ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57342 ;; flags: qr rd ra; QUERY: 1, ANSWER: 14, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 512 ;; QUESTION SECTION: ;google.co.jp. IN ANY ;; ANSWER SECTION: google.co.jp. 299 IN A 172.217.161.35 google.co.jp. 299 IN AAAA 2404:6800:4004:80a::2003 google.co.jp. 599 IN MX 20 alt1.aspmx.l.google.com. google.co.jp. 599 IN MX 50 alt4.aspmx.l.google.com. google.co.jp. 299 IN TXT "v=spf1 -all" google.co.jp. 59 IN SOA ns1.google.com. dns-admin.google.com. 243963248 900 900 1800 60 google.co.jp. 21599 IN CAA 0 issue "pki.goog" google.co.jp. 599 IN MX 30 alt2.aspmx.l.google.com. google.co.jp. 599 IN MX 10 aspmx.l.google.com. google.co.jp. 21599 IN NS ns3.google.com. google.co.jp. 21599 IN NS ns2.google.com. google.co.jp. 21599 IN NS ns4.google.com. google.co.jp. 21599 IN NS ns1.google.com. google.co.jp. 599 IN MX 40 alt3.aspmx.l.google.com. ;; Query time: 40 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Wed Apr 17 21:35:08 JST 2019 ;; MSG SIZE rcvd: 372
-xオプション- 逆引き
