Linux resolv conf domain

🌐 Как сделать постоянными изменения DNS в resolv.conf на Linux

Прочтите это руководство, чтобы узнать, как внести постоянные изменения DNS в resolv.conf на Linux.

Согласно man resolv.conf, resolv.conf – это файл конфигурации резолвера.

Resolver – это набор процедур в библиотеке C, которые обеспечивают доступ к системе доменных имен Интернета (DNS).

Файл предназначен для чтения человеком и содержит список ключевых слов со значениями, которые предоставляют различные типы информации о резолвере.

Файл конфигурации считается надежным источником информации DNS (например, информация о битах AD DNSSEC будет возвращена из этого источника без изменений).

Если этот файл не существует, будет опрошен только сервер имен (nameserver) на локальном компьютере, а список search будет содержать имя локального домена, определенное по имени хоста.

Внесем постоянные изменения DNS в resolv.conf

Внесем постоянные изменения DNS в resolv.conf

Любые изменения, внесенные вручную в файл конфигурации /etc/resolv.conf, обязательно будут перезаписаны при изменениях в сети или перезагрузке системы.

Согласно комментариям, сделанным в файле, файл является динамическим. «DO NOT EDIT THIS FILE BY HAND — YOUR CHANGES WILL BE OVERWRITTEN».

Итак, возьмем, к примеру, если вы хотите добавить DNS-сервер в свой Linux-сервер, вы обычно обновляете этот файл, указывая IP-адрес сервера имен, который должен запрашивать резолвер.

См. Приведенную ниже команду, которая обновляет файл resolv.conf общедоступным первичным DNS-сервером Google DNS, выполнив такую команду:

Использование фреймворка Resolvconf

Resolvconf – это платформа для обновления системной информации о серверах DNS.

Он настраивается как посредник между программами, которые предоставляют эту информацию (такими как ifup и ifdown, DHCP-клиенты, демон PPP и локальные серверы имен) и программами, которые используют эту информацию, такими как кэши DNS и библиотеки resolver).

В дистрибутивах Ubuntu/Debian вы можете установить resolvconf, выполнив команду ниже;

После установки фреймворк стартует и запускается при загрузке системы.

Затем отредактируйте файл конфигурации /etc/resolvconf/resolv.conf.d/base и введите настройки DNS.

Затем обновите файл /etc/resolv.conf, чтобы внести постоянные изменения в DNS:

Обновление настроек DNS-сервера в dhclient.conf

Если вы используете DHCPd для автоматического назначения IP-адреса, отредактируйте файл /etc/dhcp/dhclient.conf и добавьте следующую строку;

supersede domain-name-servers IP1, IP2;

Замените IP1 и IP2 соответствующими IP-адресами DNS:

Сохраните файл и выйдите.

Теперь, если вы запустите dhclient, ваш /etc/resolv.conf будет обновлен с использованием серверов DNS, определенных в dhclient.conf.

Вы можете использовать опцию prepend вместо supersede, чтобы добавить дополнительные IP-адреса к IP-адресу по умолчанию, предоставленному интернет-провайдером.

Как уcтановить IP-адрес сервера имен в настройках вашего интерфейса.

Отредактируйте файл конфигурации сетевого интерфейса и добавьте адрес сервера имен.

В Ubuntu 18.04/20.04 вы должны обновить файл конфигурации Netplan, например:

Мы устанавили DNS на публичный адрес DNS-сервера Google, 8.8.8.8.

В вашем случае все может быть иначе.

Перезапустите сеть, чтобы изменения вступили в силу;

На CentOS и аналогичных производных отредактируйте соответствующий интерфейс следующим образом.

Замените INTERFACE своим именем интерфейса.

Также отключите управление сетевым интерфейсом с помощью демона NetworkManager.

Теперь у вас должен быть установлен статический DNS.

Источник

Setup DNS Resolution With “resolv.conf” in Examples

The /etc/resolv.conf configuration file contains information that allows a computer to convert alpha-numeric domain names into the numeric IP addresses.

The process of converting domain names to IP addresses is called resolving.

When using DHCP, dhclient usually rewrites resolv.conf with information received from the DHCP server.

How do I edit the “/etc/resolv.conf” file?

Use text editor such as vi or gedit from Linux desktop:

There are three main configuration directives in /etc/resolv.conf :

The “nameserver” directive

The nameserver directive points out to the IP address of a Name Server.

It can be your own Name Server, some public Name Server or the Name Server of your’s ISP.

Note: Up to 3 name servers may be listed.

The “domain” directive

Local domain name.

How the “domain” directive in the “resolv.conf” file works?

You can use domain directive for resolving short host-names – e.g. test .
So if you have the following in your /etc/resolv.conf :

Then your computer will try to resolve test.example.com .

The “search” directive

Search list for hostname lookup. The search list is normally determined from the local domain name but it can be set to a list of domains.

How the “search” directive in the “resolv.conf” file works?

You need to use search directive for resolving short host-names – e.g. test .
So if you have the following in your /etc/resolv.conf :

Then your computer will try to resolve test.example.com followed by test.company.net . It will return the first query that was successful.

7 Replies to “Setup DNS Resolution With “resolv.conf” in Examples”

Can you add an example for option: ndot:n

does it matter in which order those name-value pairs are mentioned in the file?
search / domain / nameserver key-value pairs…

Hi, this is very helpful 🙂

One question: As you stated domain is overwriten if DHCP Client is used. I’m having two ethernet interfaces, one with fixed IP and one running on dhcp. Is it possible to force a domain in this configuration?

How can we use resolv.conf to redirect all dns requests to local ip address?

If DHCP is being used, the default behavior in Red Hat and its derivatives (CentOS, etc) is to inherit the DNS information from the DHCP server. However, this can be disabled by defining PEERDNS=no in your network configuration file located at
/etc/sysconfig/network-scripts/ifcfg-ens192 .

Keep in mind that ‘ifcfg-ens192’ may vary depending on the network card type on your system.

Here is an example:

cat /etc/sysconfig/network-scripts/ifcfg-ens192
TYPE=Ethernet
NAME=ens192
DEVICE=ens192
ONBOOT=yes
BOOTPROTO=dhcp
DEFROUTE=yes
PEERDNS=no
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
IPV6_AUTOCONF=no
NM_CONTROLLED=no
USERCTL=no
MTU=”1500″

Other options like DOMAIN= and SEARCH= can be applied globally by defining them on this file.

Источник

Domain name resolution

In general, a domain name represents an IP address and is associated to it in the Domain Name System (DNS). This article explains how to configure domain name resolution and resolve domain names.

Contents

Name Service Switch

This article or section needs expansion.

The Name Service Switch (NSS) facility is part of the GNU C Library ( glibc ) and backs the getaddrinfo(3) API, used to resolve domain names. NSS allows system databases to be provided by separate services, whose search order can be configured by the administrator in nsswitch.conf(5) . The database responsible for domain name resolution is the hosts database, for which glibc offers the following services:

Systemd provides three NSS services for hostname resolution:

• nss-resolve(8) — a caching DNS stub resolver, described in systemd-resolved
• nss-myhostname(8) — provides local hostname resolution without having to edit /etc/hosts , described in Network configuration#Local hostname resolution
• nss-mymachines(8) — provides hostname resolution for the names of local systemd-machined(8) containers

Resolve a domain name using NSS

NSS databases can be queried with getent(1) . A domain name can be resolved through NSS using:

Glibc resolver

The glibc resolver reads /etc/resolv.conf for every resolution to determine the nameservers and options to use.

resolv.conf(5) lists nameservers together with some configuration options. Nameservers listed first are tried first, up to three nameservers may be listed. Lines starting with a number sign ( # ) are ignored.

Overwriting of /etc/resolv.conf

Network managers tend to overwrite /etc/resolv.conf , for specifics see the corresponding section:

To prevent programs from overwriting /etc/resolv.conf , it is also possible to write-protect it by setting the immutable file attribute:

Limit lookup time

If you are confronted with a very long hostname lookup (may it be in pacman or while browsing), it often helps to define a small timeout after which an alternative nameserver is used. To do so, put the following in /etc/resolv.conf .

Hostname lookup delayed with IPv6

If you experience a 5 second delay when resolving hostnames it might be due to a DNS-server/Firewall misbehaving and only giving one reply to a parallel A and AAAA request.[1] You can fix that by setting the following option in /etc/resolv.conf :

Local domain names

To be able to use the hostname of local machine names without the fully qualified domain name, add a line to /etc/resolv.conf with the local domain such as:

That way you can refer to local hosts such as mainmachine1.example.org as simply mainmachine1 when using the ssh command, but the drill command still requires the fully qualified domain names in order to perform lookups.

Lookup utilities

To query specific DNS servers and DNS/DNSSEC records you can use dedicated DNS lookup utilities. These tools implement DNS themselves and do not use NSS.

ldns provides drill(1) , which is a tool designed to retrieve information out of the DNS.

For example, to query a specific nameserver with drill for the TXT records of a domain:

Unless a DNS server is specified, drill will use the nameservers defined in /etc/resolv.conf .

Resolver performance

The Glibc resolver does not cache queries. To implement local caching, use systemd-resolved or set up a local caching DNS server and use it as the name server by setting 127.0.0.1 and ::1 as the name servers in /etc/resolv.conf or in /etc/resolvconf.conf if using openresolv.

Privacy and security

The DNS protocol is unencrypted and does not account for confidentiality, integrity or authentication, so if you use an untrusted network or a malicious ISP, your DNS queries can be eavesdropped and the responses manipulated. Furthermore, DNS servers can conduct DNS hijacking.

You need to trust your DNS server to treat your queries confidentially. DNS servers are provided by ISPs and third-parties. Alternatively you can run your own recursive name server, which however takes more effort. If you use a DHCP client in untrusted networks, be sure to set static name servers to avoid using and being subject to arbitrary DNS servers. To secure your communication with a remote DNS server you can use an encrypted protocol, like DNS over TLS (RFC 7858), DNS over HTTPS (RFC 8484), or DNSCrypt, provided that both the upstream server and your resolver support the protocol. An alternative can be a dedicated software to encrypt and decrypt the communication, such as stunnel. To verify that responses are actually from authoritative name servers, you can validate DNSSEC, provided that both the upstream server(s) and your resolver support it.

Application-level DNS

Be aware that some client software, such as major web browsers[2][3], are starting to implement DNS over HTTPS. While the encryption of queries may often be seen as a bonus, it also means the software sidetracks queries around the system resolver configuration.[4]

Firefox provides configuration options to enable or disable DNS over HTTPS and select a DNS server.

Chromium will examine the user’s system resolver and enable DNS over HTTPS if the system resolver addresses are known to also provide DNS over HTTPS. See this blog post for more information and how DNS over HTTPS can be disabled.

Mozilla has proposed universally disabling application-level DNS if the system resolver cannot resolve the domain use-application-dns.net . Currently, this is only implemented in Firefox.

Oblivious DNS

Oblivious DNS is a system which addresses a number of DNS privacy concerns. See Cloudflare’s article for more information.

Third-party DNS services

There are various third-party DNS services available, some of which also have dedicated software:

You can use dnsperftest to test the performance of the most popular DNS resolvers from your location. dnsperf.com provides global benchmarks between providers.

DNS servers

DNS servers can be authoritative and recursive. If they are neither, they are called stub resolvers and simply forward all queries to another recursive name server. Stub resolvers are typically used to introduce DNS caching on the local host or network. Note that the same can also be achieved with a fully-fledged name server. This section compares the available DNS servers, for a more detailed comparison, refer to Wikipedia:Comparison of DNS server software.

This article or section needs expansion.

Name	Package	Capabilities				resolvconf	Supported protocols
		Authoritative	Recursive	Cache	Validates DNSSEC		DNS	DNSCrypt	DNS over TLS	DNS over HTTPS
BIND	bind	Yes	Yes	Yes	Yes	Yes	Yes	No	stunnel#DNS over TLS	No
CoreDNS	corednsAUR or coredns-binAUR	?	?	?	?	?	?	?	Yes	?
Deadwood (MaraDNS recursor)	maradnsAUR	No	Yes	Yes	No	No	Yes	No	No	No
dnscrypt-proxy	dnscrypt-proxy	No	No	Yes	No	No	Server	Resolver	No	Yes
dnsmasq	dnsmasq	Partial 1	No	Yes	Yes	Yes	Yes	No	No	No
Knot Resolver	knot-resolver	No	Yes	Yes	Yes	No	Yes	No	Yes	Server
pdnsd	pdnsd	Yes	Yes	Permanent	No	Yes	Yes	No	No	No
PowerDNS Recursor	powerdns-recursor	No	Yes	Yes	Yes	Yes	Yes	No	No	No
Rescached	rescached-gitAUR	No	No	Yes	No	Yes	Yes	No	No	Limited 2
SmartDNS	smartdns	No	No	Yes	No	?	Yes	No	Resolver	Resolver
Stubby	stubby	No	No	No	Yes	No	Server	No	Resolver	No
systemd-resolved	systemd	No	No	Yes	Yes	Yes	Resolver and limited server	No	Resolver	No
Unbound	unbound	Partial	Yes	Yes 3	Yes	Yes	Yes	Server	Yes	Server

1. From Wikipedia: dnsmasq has limited authoritative support, intended for internal network use rather than public Internet use.
2. Only forwards using DNS over HTTPS when Rescached itself is queried using DNS over HTTPS.[5]
3. The Redis backend can be used to provide a persistent cache for Unbound.

Authoritative-only servers

Name	Package	DNSSEC	Geographic balancing
gdnsd	gdnsd	No	Yes
Knot DNS	knot	Yes	Yes
MaraDNS	maradns AUR	No	?
NSD	nsd	No	No
PowerDNS	powerdns	Yes	Yes

Conditional forwarding

It is possible to use specific DNS resolvers when querying specific domain names. This is particularly useful when connecting to a VPN, so that queries to the VPN network are resolved by the VPN’s DNS, while queries to the internet will still be resolved by your standard DNS resolver. It can also be used on local networks.

To implement it, you need to use a local resolver because glibc does not support it.

In a dynamic environment (laptops and to some extents desktops), you need to configure your resolver based on the network(s) you are connected to. The best way to do that is to use openresolv because it supports multiple subscribers. Some network managers support it, either through openresolv, or by configuring the resolver directly. NetworkManager supports conditional forwarding without openresolv.

Источник