Ubuntu как изменить dns

Domain Name Service (DNS) is an Internet service that maps IP addresses and fully qualified domain names (FQDN) to one another. In this way, DNS alleviates the need to remember IP addresses. Computers that run DNS are called name servers. Ubuntu ships with BIND (Berkley Internet Naming Daemon), the most common program used for maintaining a name server on Linux.

Installation

At a terminal prompt, enter the following command to install dns:

sudo apt install bind9

A very useful package for testing and troubleshooting DNS issues is the dnsutils package. Very often these tools will be installed already, but to check and/or install dnsutils enter the following:

sudo apt install dnsutils

Configuration

There are many ways to configure BIND9. Some of the most common configurations are a caching nameserver, primary server, and secondary server.

• When configured as a caching nameserver BIND9 will find the answer to name queries and remember the answer when the domain is queried again.

• As a primary server, BIND9 reads the data for a zone from a file on its host and is authoritative for that zone.

• As a secondary server, BIND9 gets the zone data from another nameserver that is authoritative for the zone.

Overview

The DNS configuration files are stored in the /etc/bind directory. The primary configuration file is /etc/bind/named.conf, which in the layout provided by the package just includes these files.

• /etc/bind/named.conf.options: global DNS options
• /etc/bind/named.conf.local: for your zones
• /etc/bind/named.conf.default-zones: default zones such as localhost, its reverse, and the root hints

The root nameservers used to be described in the file /etc/bind/db.root. This is now provided instead by the /usr/share/dns/root.hints file shipped with the dns-root-data package, and is referenced in the named.conf.default-zones configuration file above.

It is possible to configure the same server to be a caching name server, primary, and secondary: it all depends on the zones it is serving. A server can be the Start of Authority (SOA) for one zone, while providing secondary service for another zone. All the while providing caching services for hosts on the local LAN.

Caching Nameserver

The default configuration acts as a caching server. Simply uncomment and edit /etc/bind/named.conf.options to set the IP addresses of your ISP’s DNS servers:

forwarders {
    1.2.3.4;
    5.6.7.8;
};

Note

Replace 1.2.3.4 and 5.6.7.8 with the IP Addresses of actual nameservers.

To enable the new configuration, restart the DNS server. From a terminal prompt:

sudo systemctl restart bind9.service

See dig for information on testing a caching DNS server.

Primary Server

In this section BIND9 will be configured as the Primary server for the domain example.com. Simply replace example.com with your FQDN (Fully Qualified Domain Name).

Forward Zone File

To add a DNS zone to BIND9, turning BIND9 into a Primary server, first edit /etc/bind/named.conf.local:

zone "example.com" {
    type master;
    file "/etc/bind/db.example.com";
};

Note

If bind will be receiving automatic updates to the file as with DDNS, then use /var/lib/bind/db.example.com rather than /etc/bind/db.example.com both here and in the copy command below.

Now use an existing zone file as a template to create the /etc/bind/db.example.com file:

sudo cp /etc/bind/db.local /etc/bind/db.example.com

Edit the new zone file /etc/bind/db.example.com and change localhost. to the FQDN of your server, leaving the additional . at the end. Change 127.0.0.1 to the nameserver’s IP Address and root.localhost to a valid email address, but with a . instead of the usual @ symbol, again leaving the . at the end. Change the comment to indicate the domain that this file is for.

Create an A record for the base domain, example.com. Also, create an A record for ns.example.com, the name server in this example:

;
; BIND data file for example.com
;
$TTL    604800
@       IN      SOA     example.com. root.example.com. (
                              2         ; Serial
                         604800         ; Refresh
                          86400         ; Retry
                        2419200         ; Expire
                         604800 )       ; Negative Cache TTL

@       IN      NS      ns.example.com.
@       IN      A       192.168.1.10
@       IN      AAAA    ::1
ns      IN      A       192.168.1.10

You must increment the Serial Number every time you make changes to the zone file. If you make multiple changes before restarting BIND9, simply increment the Serial once.

Now, you can add DNS records to the bottom of the zone file. See Common Record Types for details.

Note

Many admins like to use the last date edited as the serial of a zone, such as 2020012100 which is yyyymmddss (where ss is the Serial Number)

Once you have made changes to the zone file BIND9 needs to be restarted for the changes to take effect:

sudo systemctl restart bind9.service

Reverse Zone File

Now that the zone is setup and resolving names to IP Addresses, a Reverse zone needs to be added to allows DNS to resolve an address to a name.

Edit /etc/bind/named.conf.local and add the following:

zone "1.168.192.in-addr.arpa" {
    type master;
    file "/etc/bind/db.192";
};

Note

Replace 1.168.192 with the first three octets of whatever network you are using. Also, name the zone file /etc/bind/db.192 appropriately. It should match the first octet of your network.

Now create the /etc/bind/db.192 file:

sudo cp /etc/bind/db.127 /etc/bind/db.192

Next edit /etc/bind/db.192 changing the same options as /etc/bind/db.example.com:

;
; BIND reverse data file for local 192.168.1.XXX net
;
$TTL    604800
@       IN      SOA     ns.example.com. root.example.com. (
                              2         ; Serial
                         604800         ; Refresh
                          86400         ; Retry
                        2419200         ; Expire
                         604800 )       ; Negative Cache TTL
;
@       IN      NS      ns.
10      IN      PTR     ns.example.com.

The Serial Number in the Reverse zone needs to be incremented on each change as well. For each A record you configure in /etc/bind/db.example.com, that is for a different address, you need to create a PTR record in /etc/bind/db.192.

After creating the reverse zone file restart BIND9:

sudo systemctl restart bind9.service

Secondary Server

Once a Primary Server has been configured a Secondary Server is highly recommended in order to maintain the availability of the domain should the Primary become unavailable.

First, on the Primary server, the zone transfer needs to be allowed. Add the allow-transfer option to the example Forward and Reverse zone definitions in /etc/bind/named.conf.local:

zone "example.com" {
    type master;
    file "/etc/bind/db.example.com";
    allow-transfer { 192.168.1.11; };
};
    
zone "1.168.192.in-addr.arpa" {
    type master;
    file "/etc/bind/db.192";
    allow-transfer { 192.168.1.11; };
};

Note

Replace 192.168.1.11 with the IP Address of your Secondary nameserver.

Restart BIND9 on the Primary server:

sudo systemctl restart bind9.service

Next, on the Secondary server, install the bind9 package the same way as on the Primary. Then edit the /etc/bind/named.conf.local and add the following declarations for the Forward and Reverse zones:

zone "example.com" {
    type secondary;
    file "db.example.com";
    masters { 192.168.1.10; };
};        
          
zone "1.168.192.in-addr.arpa" {
    type secondary;
    file "db.192";
    masters { 192.168.1.10; };
};

Note

Replace 192.168.1.10 with the IP Address of your Primary nameserver.

Restart BIND9 on the Secondary server:

sudo systemctl restart bind9.service

In /var/log/syslog you should see something similar to the following (some lines have been split to fit the format of this document):

client 192.168.1.10#39448: received notify for zone '1.168.192.in-addr.arpa'
zone 1.168.192.in-addr.arpa/IN: Transfer started.
transfer of '100.18.172.in-addr.arpa/IN' from 192.168.1.10#53:
 connected using 192.168.1.11#37531
zone 1.168.192.in-addr.arpa/IN: transferred serial 5
transfer of '100.18.172.in-addr.arpa/IN' from 192.168.1.10#53:
 Transfer completed: 1 messages, 
6 records, 212 bytes, 0.002 secs (106000 bytes/sec)
zone 1.168.192.in-addr.arpa/IN: sending notifies (serial 5)

client 192.168.1.10#20329: received notify for zone 'example.com'
zone example.com/IN: Transfer started.
transfer of 'example.com/IN' from 192.168.1.10#53: connected using 192.168.1.11#38577
zone example.com/IN: transferred serial 5
transfer of 'example.com/IN' from 192.168.1.10#53: Transfer completed: 1 messages, 
8 records, 225 bytes, 0.002 secs (112500 bytes/sec)

Note

Note: A zone is only transferred if the Serial Number on the Primary is larger than the one on the Secondary. If you want to have your Primary DNS notifying other Secondary DNS Servers of zone changes, you can add also-notify { ipaddress; }; to /etc/bind/named.conf.local as shown in the example below:

zone "example.com" {
    type master;
    file "/etc/bind/db.example.com";
    allow-transfer { 192.168.1.11; };
    also-notify { 192.168.1.11; }; 
};

zone "1.168.192.in-addr.arpa" {
    type master;
    file "/etc/bind/db.192";
    allow-transfer { 192.168.1.11; };
    also-notify { 192.168.1.11; }; 
};
    

Note

The default directory for non-authoritative zone files is /var/cache/bind/. This directory is also configured in AppArmor to allow the named daemon to write to it. For more information on AppArmor see Security — AppArmor.

Troubleshooting

This section covers diagnosing problems with DNS and BIND9 configurations.

Testing

resolv.conf

The first step in testing BIND9 is to add the nameserver’s IP Address to a hosts resolver. The Primary nameserver should be configured as well as another host to double check things. Refer to DNS client configuration for details on adding nameserver addresses to your network clients. In the end your nameserver line in /etc/resolv.conf should be pointing at 127.0.0.53 and you should have a search parameter for your domain. Something like this:

nameserver  127.0.0.53
search example.com

To check which DNS server your local resolver is using, run:

systemd-resolve --status

Note

You should also add the IP Address of the Secondary nameserver to your client configuration in case the Primary becomes unavailable.

dig

If you installed the dnsutils package you can test your setup using the DNS lookup utility dig:

• After installing BIND9 use dig against the loopback interface to make sure it is listening on port 53. From a terminal prompt:

  dig -x 127.0.0.1
  

  You should see lines similar to the following in the command output:

  ;; Query time: 1 msec
  ;; SERVER: 192.168.1.10#53(192.168.1.10)
  

• If you have configured BIND9 as a Caching nameserver “dig” an outside domain to check the query time:

  dig ubuntu.com
  

  Note the query time toward the end of the command output:

  ;; Query time: 49 msec
  

  After a second dig there should be improvement:

  ;; Query time: 1 msec
  

ping

Now to demonstrate how applications make use of DNS to resolve a host name use the ping utility to send an ICMP echo request:

ping example.com

This tests if the nameserver can resolve the name ns.example.com to an IP Address. The command output should resemble:

PING ns.example.com (192.168.1.10) 56(84) bytes of data.
64 bytes from 192.168.1.10: icmp_seq=1 ttl=64 time=0.800 ms
64 bytes from 192.168.1.10: icmp_seq=2 ttl=64 time=0.813 ms

named-checkzone

A great way to test your zone files is by using the named-checkzone utility installed with the bind9 package. This utility allows you to make sure the configuration is correct before restarting BIND9 and making the changes live.

• To test our example Forward zone file enter the following from a command prompt:

  named-checkzone example.com /etc/bind/db.example.com
  

  If everything is configured correctly you should see output similar to:

  zone example.com/IN: loaded serial 6
  OK
  

• Similarly, to test the Reverse zone file enter the following:

  named-checkzone 1.168.192.in-addr.arpa /etc/bind/db.192
  

  The output should be similar to:

  zone 1.168.192.in-addr.arpa/IN: loaded serial 3
  OK
  

Note

The Serial Number of your zone file will probably be different.

Quick temporary query logging

With the rndc tool, you can quickly turn query logging on and off, without restarting the service or changing the configuration file.

To turn query logging on, run:

sudo rndc querylog on

Likewise, to turn it off, run:

sudo rndc querylog off

The logs will be sent to syslog and will show up in /var/log/syslog by default:

Jan 20 19:40:50 new-n1 named[816]: received control channel command 'querylog on'
Jan 20 19:40:50 new-n1 named[816]: query logging is now on
Jan 20 19:40:57 new-n1 named[816]: client @0x7f48ec101480 192.168.1.10#36139 (ubuntu.com): query: ubuntu.com IN A +E(0)K (192.168.1.10)

Note

The amount of logs generated by enabling querylog could be huge!

Logging

BIND9 has a wide variety of logging configuration options available, but the two main ones are channel and category, which configure where logs go, and what information gets logged, respectively.

If no logging options are configured the default configuration is:

logging {
     category default { default_syslog; default_debug; };
     category unmatched { null; };
};

Let’s instead configure BIND9 to send debug messages related to DNS queries to a separate file.

We need to configure a channel to specify which file to send the messages to, and a category. In this example, the category will log all queries. Edit /etc/bind/named.conf.local and add the following:

logging {
    channel query.log {
        file "/var/log/named/query.log";
        severity debug 3;
    };
    category queries { query.log; };
};

Note

The debug option can be set from 1 to 3. If a level isn’t specified, level 1 is the default.

• Since the named daemon runs as the bind user the /var/log/named directory must be created and the ownership changed:

  sudo mkdir /var/log/named
  sudo chown bind:bind /var/log/named
  

• Now restart BIND9 for the changes to take effect:

  sudo systemctl restart bind9.service
  

You should see the file /var/log/named/query.log fill with query information. This is a simple example of the BIND9 logging options. For coverage of advanced options see More Information.

References

Common Record Types

This section covers some of the most common DNS record types.

• A record: This record maps an IP Address to a hostname.

  www      IN    A      192.168.1.12
  

• CNAME record: Used to create an alias to an existing A record. You cannot create a CNAME record pointing to another CNAME record.

  web     IN    CNAME  www
  

• MX record: Used to define where email should be sent to. Must point to an A record, not a CNAME.

  @       IN    MX  1   mail.example.com.
  mail    IN    A       192.168.1.13
  

• NS record: Used to define which servers serve copies of a zone. It must point to an A record, not a CNAME. This is where Primary and Secondary servers are defined.

  @       IN    NS     ns.example.com.
  @       IN    NS     ns2.example.com.
  ns      IN    A      192.168.1.10
  ns2     IN    A      192.168.1.11
  

More Information

• Upstream BIND9 Documentation

• DNS and BIND is a popular book now in it’s fifth edition. There is now also a DNS and BIND on IPv6 book.

• A great place to ask for BIND9 assistance, and get involved with the Ubuntu Server community, is the #ubuntu-server IRC channel on freenode.

Ubuntu ships with a number of graphical utilities to configure your network devices. This document is geared toward server administrators and will focus on managing your network on the command line.

Ethernet interfaces

Ethernet interfaces are identified by the system using predictable network interface names. These names can appear as eno1 or enp0s25. However, in some cases an interface may still use the kernel eth# style of naming.

Identify Ethernet interfaces

To quickly identify all available Ethernet interfaces, you can use the ip command as shown below.

ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:16:3e:e2:52:42 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.102.66.200/24 brd 10.102.66.255 scope global dynamic eth0
       valid_lft 3257sec preferred_lft 3257sec
    inet6 fe80::216:3eff:fee2:5242/64 scope link
       valid_lft forever preferred_lft forever

Another application that can help identify all network interfaces available to your system is the lshw command. This command provides greater details around the hardware capabilities of specific adapters. In the example below, lshw shows a single Ethernet interface with the logical name of eth4 along with bus information, driver details and all supported capabilities.

sudo lshw -class network
  *-network
       description: Ethernet interface
       product: MT26448 [ConnectX EN 10GigE, PCIe 2.0 5GT/s]
       vendor: Mellanox Technologies
       physical id: 0
       bus info: pci@0004:01:00.0
       logical name: eth4
       version: b0
       serial: e4:1d:2d:67:83:56
       slot: U78CB.001.WZS09KB-P1-C6-T1
       size: 10Gbit/s
       capacity: 10Gbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm vpd msix pciexpress bus_master cap_list ethernet physical fibre 10000bt-fd
       configuration: autonegotiation=off broadcast=yes driver=mlx4_en driverversion=4.0-0 duplex=full firmware=2.9.1326 ip=192.168.1.1 latency=0 link=yes multicast=yes port=fibre speed=10Gbit/s
       resources: iomemory:24000-23fff irq:481 memory:3fe200000000-3fe2000fffff memory:240000000000-240007ffffff

Ethernet Interface logical names

Interface logical names can also be configured via a Netplan configuration. If you would like control which interface receives a particular logical name use the match and set-name keys. The match key is used to find an adapter based on some criteria like MAC address, driver, etc. The set-name key can be used to change the device to the desired logical name.

network:
  version: 2
  renderer: networkd
  ethernets:
    eth_lan0:
      dhcp4: true
      match:
        macaddress: 00:11:22:33:44:55
      set-name: eth_lan0

Ethernet Interface settings

ethtool is a program that displays and changes Ethernet card settings such as auto-negotiation, port speed, duplex mode, and Wake-on-LAN. The following is an example of how to view the supported features and configured settings of an Ethernet interface.

sudo ethtool eth4
Settings for eth4:
    Supported ports: [ FIBRE ]
    Supported link modes:   10000baseT/Full
    Supported pause frame use: No
    Supports auto-negotiation: No
    Supported FEC modes: Not reported
    Advertised link modes:  10000baseT/Full
    Advertised pause frame use: No
    Advertised auto-negotiation: No
    Advertised FEC modes: Not reported
    Speed: 10000Mb/s
    Duplex: Full
    Port: FIBRE
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: off
    Supports Wake-on: d
    Wake-on: d
    Current message level: 0x00000014 (20)
                   link ifdown
    Link detected: yes

IP addressing

The following section describes the process of configuring your system’s IP address and default gateway needed for communicating on a local area network and the Internet.

Temporary IP address assignment

For temporary network configurations, you can use the ip command which is also found on most other GNU/Linux operating systems. The ip command allows you to configure settings which take effect immediately – however they are not persistent and will be lost after a reboot.

To temporarily configure an IP address, you can use the ip command in the following manner. Modify the IP address and subnet mask to match your network requirements.

sudo ip addr add 10.102.66.200/24 dev enp0s25

The ip can then be used to set the link up or down.

ip link set dev enp0s25 up
ip link set dev enp0s25 down

To verify the IP address configuration of enp0s25, you can use the ip command in the following manner:

ip address show dev enp0s25
10: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:16:3e:e2:52:42 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.102.66.200/24 brd 10.102.66.255 scope global dynamic eth0
       valid_lft 2857sec preferred_lft 2857sec
    inet6 fe80::216:3eff:fee2:5242/64 scope link
       valid_lft forever preferred_lft forever6

To configure a default gateway, you can use the ip command in the following manner. Modify the default gateway address to match your network requirements.

sudo ip route add default via 10.102.66.1

You can also use the ip command to verify your default gateway configuration, as follows:

ip route show
default via 10.102.66.1 dev eth0 proto dhcp src 10.102.66.200 metric 100
10.102.66.0/24 dev eth0 proto kernel scope link src 10.102.66.200
10.102.66.1 dev eth0 proto dhcp scope link src 10.102.66.200 metric 100 

If you require DNS for your temporary network configuration, you can add DNS server IP addresses in the file /etc/resolv.conf. In general, editing /etc/resolv.conf directly is not recommended, but this is a temporary and non-persistent configuration. The example below shows how to enter two DNS servers to /etc/resolv.conf, which should be changed to servers appropriate for your network. A more lengthy description of the proper (persistent) way to do DNS client configuration is in a following section.

nameserver 8.8.8.8
nameserver 8.8.4.4

If you no longer need this configuration and wish to purge all IP configuration from an interface, you can use the ip command with the flush option:

ip addr flush eth0

Note
Flushing the IP configuration using the ip command does not clear the contents of /etc/resolv.conf. You must remove or modify those entries manually (or re-boot), which should also cause /etc/resolv.conf, which is a symlink to /run/systemd/resolve/stub-resolv.conf, to be re-written.

Dynamic IP address assignment (DHCP client)

To configure your server to use DHCP for dynamic address assignment, create a Netplan configuration in the file /etc/netplan/99_config.yaml. The following example assumes you are configuring your first Ethernet interface identified as enp3s0.

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      dhcp4: true

The configuration can then be applied using the netplan command:

sudo netplan apply

Static IP address assignment

To configure your system to use static address assignment, create a netplan configuration in the file /etc/netplan/99_config.yaml. The example below assumes you are configuring your first Ethernet interface identified as eth0. Change the addresses, routes, and nameservers values to meet the requirements of your network.

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses:
        - 10.10.10.2/24
      routes:
        - to: default
          via: 10.10.10.1
      nameservers:
          search: [mydomain, otherdomain]
          addresses: [10.10.10.1, 1.1.1.1]

The configuration can then be applied using the netplan command.

sudo netplan apply

NOTE
netplan in Ubuntu Bionic 18.04 LTS doesn’t understand the “to: default” syntax to specify a default route, and should use the older gateway4: 10.10.10.1 key instead of the whole routes: block.

The loopback interface is identified by the system as lo and has a default IP address of 127.0.0.1. It can be viewed using the ip command.

ip address show lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever

Name resolution

Name resolution (as it relates to IP networking) is the process of mapping hostnames to IP addresses, and vice-versa, making it easier to identify resources on a network. The following section will explain how to properly configure your system for name resolution using DNS and static hostname records.

DNS client configuration

Traditionally, the file /etc/resolv.conf was a static configuration file that rarely needed to be changed, or it automatically changed via DCHP client hooks. systemd-resolved handles nameserver configuration, and it should be interacted with through the systemd-resolve command. Netplan configures systemd-resolved to generate a list of nameservers and domains to put in /etc/resolv.conf, which is a symlink:

/etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

To configure the resolver, add the IP addresses of the appropriate nameservers for your network to the netplan configuration file. You can also add optional DNS suffix search-lists to match your network domain names. The resulting file might look like the following:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s25:
      addresses:
        - 192.168.0.100/24
      routes:
        - to: default
          via: 192.168.0.1
      nameservers:
          search: [mydomain, otherdomain]
          addresses: [1.1.1.1, 8.8.8.8, 4.4.4.4]

The search option can also be used with multiple domain names so that DNS queries will be appended in the order in which they are entered. For example, your network may have multiple sub-domains to search; a parent domain of example.com, and two sub-domains, sales.example.com and dev.example.com.

If you have multiple domains you wish to search, your configuration might look like the following:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s25:
      addresses:
        - 192.168.0.100/24
      routes:
        - to: default
          via: 192.168.0.1
      nameservers:
          search: [example.com, sales.example.com, dev.example.com]
          addresses: [1.1.1.1, 8.8.8.8, 4.4.4.4]

If you try to ping a host with the name server1, your system will automatically query DNS for its Fully Qualified Domain Name (FQDN) in the following order:

1. server1.example.com

2. server1.sales.example.com

3. server1.dev.example.com

If no matches are found, the DNS server will provide a result of notfound and the DNS query will fail.

Static hostnames

Static hostnames are locally defined hostname-to-IP mappings located in the file /etc/hosts. Entries in the hosts file will have precedence over DNS by default. This means that if your system tries to resolve a hostname and it matches an entry in /etc/hosts, it will not attempt to look up the record in DNS. In some configurations, especially when Internet access is not required, servers that communicate with a limited number of resources can be conveniently set to use static hostnames instead of DNS.

The following is an example of a hosts file where a number of local servers have been identified by simple hostnames, aliases and their equivalent Fully Qualified Domain Names (FQDN’s):

127.0.0.1   localhost
127.0.1.1   ubuntu-server
10.0.0.11   server1 server1.example.com vpn
10.0.0.12   server2 server2.example.com mail
10.0.0.13   server3 server3.example.com www
10.0.0.14   server4 server4.example.com file

Note
In this example, notice that each of the servers were given aliases in addition to their proper names and FQDN’s. Server1 has been mapped to the name vpn, server2 is referred to as mail, server3 as www, and server4 as file.

Name Service Switch (NSS) configuration

The order in which your system selects a method of resolving hostnames to IP addresses is controlled by the Name Service Switch (NSS) configuration file /etc/nsswitch.conf. As mentioned in the previous section, typically static hostnames defined in the systems /etc/hosts file have precedence over names resolved from DNS. The following is an example of the line responsible for this order of hostname lookups in the file /etc/nsswitch.conf.

hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4

• files first tries to resolve static hostnames located in /etc/hosts.

• mdns4_minimal attempts to resolve the name using Multicast DNS.

• [NOTFOUND=return] means that any response of notfound by the preceding mdns4_minimal process should be treated as authoritative and that the system should not try to continue hunting for an answer.

• dns represents a legacy unicast DNS query.

• mdns4 represents a multicast DNS query.

To modify the order of these name resolution methods, you can simply change the hosts: string to the value of your choosing. For example, if you prefer to use legacy unicast DNS versus multicast DNS, you can change the string in /etc/nsswitch.conf as shown below:

hosts:          files dns [NOTFOUND=return] mdns4_minimal mdns4

Bridging multiple interfaces

Bridging is a more advanced configuration, but is very useful in multiple scenarios. One scenario is setting up a bridge with multiple network interfaces, then using a firewall to filter traffic between two network segments. Another scenario is using bridge on a system with one interface to allow virtual machines direct access to the outside network. The following example covers the latter scenario:

Configure the bridge by editing your netplan configuration found in /etc/netplan/, entering the appropriate values for your physical interface and network:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      dhcp4: no
  bridges:
    br0:
      dhcp4: yes
      interfaces:
        - enp3s0

Now apply the configuration to enable the bridge:

sudo netplan apply

The new bridge interface should now be up and running. The brctl provides useful information about the state of the bridge, controls which interfaces are part of the bridge, etc. See man brctl for more information.

networkd-dispatcher for hook scripts

Users of the former ifupdown may be familiar with using hook scripts (e.g., pre-up, post-up) in their interfaces file. Netplan configuration does not currently support hook scripts in its configuration definition.

Instead, to achieve this functionality with the networkd renderer, users can use networkd-dispatcher. The package provides both users and packages with hook points when specific network states are reached, to aid in reacting to network state.

Note:
If you are on Desktop (not Ubuntu Server) the network is driven by Network Manager — in that case you need NM Dispatcher scripts instead.

The Netplan FAQ has a great table that compares event timings between ifupdown/systemd-networkd/network-manager.

It is important to be aware that these hooks run asynchronously; i.e. they will not block transition into another state.

The Netplan FAQ also has an example on converting an old ifupdown hook to networkd-dispatcher.

Resources

• The Ubuntu Wiki Network page has links to articles covering more advanced network configuration.

• The Netplan website has additional examples and documentation.

• The Netplan man page has more information on Netplan.

• The systemd-resolved man page has more information on systemd-resolved service.

• For more information on bridging see the netplan.io examples page

В статье мы расскажем, как изменить настройки DNS-серверов на популярных ОС: Ubuntu, Debian, Centos и Windows Server.

Самые распространённые причины смены DNS-серверов:

• увеличение скорости загрузки сайта в браузере,
• настройка родительского контроля (чтобы дети не просматривали нежелательный контент),
• защита от фишинга и другие.

Ubuntu 18.04

Изменить DNS-серверы поможет служба netplan. С её помощью нужно отредактировать её конфигурационный файл 01-netcfg.yaml.

Чтобы внести изменения:

Ubuntu 20.04/Debian

Чтобы сменить DNS-серверы:

CentOS

Чтобы сменить DNS-серверы:

Windows

Чтобы сменить DNS-серверы:

Introduction

The Domain Name System (DNS) translates text-based domain names to numeric IP addresses. By default, most networks are configured to work with DNS servers supplied by the internet service provider. However, users are free to change the DNS nameservers.

This tutorial will show you how to change DNS nameservers on your Ubuntu machine using GUI or the command line.

Prerequisites

• Ubuntu 20.04 (both methods also work on Ubuntu 18.04 and later)
• Access to the terminal
• Sudo privileges

Change DNS Nameserver via GUI

Use Ubuntu Settings to complete all the steps to change DNS addresses via the graphical user interface.

1. Launch Settings and click the Network tab in the menu on the left.

2. Click the cogwheel next to the connection you wish to set up.

3. Go to the IPv4 tab.

4. Disable automatic DNS configuration by turning off the switch next to the DNS field.

5. Type new DNS addresses in the field. The example shows Google’s public DNS nameservers.

6. Click Apply.

The system is now configured to work with the new DNS servers.

Change DNS Nameserver via Config File

If you do not use a GUI, change DNS settings with the command line Netplan tool.

1. Go to the Netplan directory:

cd /etc/netplan

2. List the directory contents with ls to see the name of the yaml file containing network configuration.

Open the file in a text editor. Your file may have a different name.

sudo nano 01-network-manager.yaml

Ethernet connections are listed in the ethernets section of the file. If there are any wireless connections, you can find them in the wifis section. Netplan stores the current DNS configuration parameters in nameservers subsections of each section.

Replace the addresses located in the file with the DNS addresses you want to use. You can enter more than two addresses. Save the changes and exit.

3. Apply the changes you made in the config file:

sudo netplan apply

If the operation is successful, there is no output. To check if the system successfully applied the changes, type:

systemd-resolve --status | grep 'DNS Servers' -A2

The output lists your current DNS servers:

Why Change DNS Nameserver on Ubuntu?

In most cases, your default DNS settings offer optimal performance. However, there are scenarios in which you should consider switching to a third-party DNS provider:

• Large companies with better infrastructure are usually more capable of providing uninterrupted DNS service. If your ISP is unreliable and you experience frequent downtimes, switching the DNS provider may be the solution.
• Third-party DNS servers can be faster than those provided to you by your ISP.

• Some DNS providers offer filters that prevent phishing sites from reaching your computer. The same mechanism is also used to block sensitive content on the internet. Businesses often employ this DNS feature.
• Internet Service Providers sometimes block content on the DNS level, so switching to another DNS nameserver may help you access some geo-restricted websites.

Conclusion

This tutorial showed you how to set your DNS nameservers on Ubuntu, either using a graphical user interface or the command line.

To learn more about DNS, read What Is a Domain Name System & How Does it Work?

Краткое описание руководства

Требования к системе

$ sudo lshw -C network

ubuntu@ubuntu:~$ sudo lshw -C network
  *-network               
       description: Ethernet interface                             # Тип устройства 
       product: L2 100 Mbit Ethernet Adapter                       # Название адаптера
       vendor: Attansic Technology Corp.                           # Производитель устройства
       physical id: 0
       bus info: pci@0000:03:00.0
       logical name: eth0                                          # Имя сетевого интерфейса
       version: a0
       serial: 00:00:00:00:00:00                                   # Физический адрес устройства (mac-адрес)
       size: 100MB/s
       capacity: 100MB/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vpd bus_master cap_list 
ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes 
                      driver=atl2                                  # Используемый драйвер
                      driverversion=2.2.3                          # Версия драйвера
                      duplex=full firmware=L2 ip=192.168.0.5 latency=0 
                      link=yes                                     # Наличие линка
                      module=atl2 multicast=yes port=twisted pair 
                      speed=100MB/s                                # Текущая скорость подключения.

       logical name: eth0 

Настройка проводной сети

Настройка IP-адреса, шлюза по умолчанию, маски подсети

$ sudo nano /etc/network/interfaces 

iface eth0 inet static 
address 192.168.0.1 
netmask 255.255.255.0 
gateway 192.168.0.254
dns-nameservers 192.168.0.254 8.8.8.8
auto eth0 

$ ip addr

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# Моя проводная сеть.
iface eth0 inet static 
address 192.168.0.1 
netmask 255.255.255.0 
gateway 192.168.0.254 
dns-nameservers 192.168.0.254 8.8.8.8
auto eth0 

iface eth0 inet dhcp
auto eth0 

Временная настройка IP-адреса и маски подсети

$ sudo ip addr add 192.168.0.1/24 dev eth0

Настройка DNS

iface eth0 inet static 
address 192.168.0.1 
netmask 255.255.255.0 
gateway 192.168.0.254 
dns-nameservers 8.8.8.8 192.168.0.254
auto eth0 

Ubuntu до версии 12.04

$ sudo gedit /etc/resolv.conf

nameserver 192.168.0.100
nameserver 192.168.0.200

Настройка соединений ppp

За создание соединений типа «точка-точка» в Ubuntu отвечает демон pppd, более подробная информация о котором доступна в документации. В рамках данного руководства будут рассмотрены примеры создания PPPoE подключения через DSL модем, подключения PPTP (VPN-подключения) и DIAL-UP подключения через обычный модем.

Соединение PPPoE

$ sudo pppoeconf

$ sudo pon dsl-provider # Для подключения
или
$ sudo poff dsl-provider # Для отключения

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

$ sudo /etc/init.d/networking restart

$ sudo /etc/init.d/NetworkManager restart

Соединение PPTP

$ sudo nano /etc/ppp/peers/my-provider

persist # При разрыве соединения - переподключаться снова.
maxfail 0 # Максимальное количество неудачных попыток подключения. 0 - бесконечно.
mtu 1476 # Значение MTU
name {логин} # Ваш логин.
#nodefaultroute # Не быть шлюзом по умолчанию
defaultroute # Быть шлюзом по умолчанию
replacedefaultroute # Заменить шлюз по умолчанию если он был
remotename {vpn} # Имя удаленного сервера (для нас), может быть любым.
pty "pptp {адрес_сервера} --nolaunchpppd" # Команда запуска pptp. 
# Адрес сервера - может быть как IP адресом, так и доменным именем, например vpn.foo.bar

{логин} {vpn} {пароль}

$ sudo pon my-provider # Для подключения
или
$ sudo poff my-provider # Для отключения

Настройка DIAL-UP подключения

Для настройки модемного соединения можно использовать встроенный конфигуратор pppd — pppconfig или специальную утилиту wvdial .

При помощи pppconfig

$ sudo pppconfig

$ sudo pon my-provider # Для подключения
или
$ sudo poff my-provider # Для отключения

При помощи wvdial

$ sudo apt-get install wvdial

$ sudo wvdialconf

ubuntu@ubuntu:~$ sudo wvdialconf
[sudo] password for ubuntu: 
Editing `/etc/wvdial.conf'.

Scanning your serial ports for a modem.

Modem Port Scan<*1>: S0   S1   S2   S3   
WvModem<*1>: Cannot get information for serial port.
ttyACM0<*1>: ATQ0 V1 E1 -- OK
ttyACM0<*1>: ATQ0 V1 E1 Z -- OK
ttyACM0<*1>: ATQ0 V1 E1 S0=0 -- OK
ttyACM0<*1>: ATQ0 V1 E1 S0=0 &C1 -- OK
ttyACM0<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 -- OK
ttyACM0<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK
ttyACM0<*1>: Modem Identifier: ATI -- Manufacturer: QUALCOMM INCORPORATED
ttyACM0<*1>: Speed 4800: AT -- OK
ttyACM0<*1>: Speed 9600: AT -- OK
ttyACM0<*1>: Speed 19200: AT -- OK
ttyACM0<*1>: Speed 38400: AT -- OK
ttyACM0<*1>: Speed 57600: AT -- OK
ttyACM0<*1>: Speed 115200: AT -- OK
ttyACM0<*1>: Speed 230400: AT -- OK
ttyACM0<*1>: Speed 460800: AT -- OK
ttyACM0<*1>: Max speed is 460800; that should be safe.
ttyACM0<*1>: ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0 -- OK

Found an USB modem on /dev/ttyACM0.
Modem configuration written to /etc/wvdial.conf.
ttyACM0<Info>: Speed 460800; init "ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0"

$ sudo nano /etc/wvdial.conf

[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Modem Type = USB Modem
ISDN = 0
Idle Seconds = 0
New PPPD = yes
Dial Attempts = 0
Phone = #777
Modem = /dev/ttyACM0
Username = mobile
Password = internet
Baud = 460800
Idle Seconds = 0 # Время простоя соединения, 
# после которого нужно будет его разорвать. Значение 0 - никогда.
Dial Attempts = 0 # Количество попыток дозвона. 0 - бесконечно.
[Dialer pulse]
Dial Command = ATDP # Команда набора номера (P - импульсный, T - тональный). Имеет смысл для набора номера в импульсном режиме на старых АТС.

$ sudo wvdial

$ sudo wvdial pulse

Автоматическое подключение

$ sudo nano /etc/network/interfaces 

iface ppp0 inet ppp
provider my-provider
auto ppp0 

iface ppp0 inet wvdial
provider wvdial
auto ppp0 

Ручная настройка роутинга

$ sudo nano /etc/ppp/ip-up.local

$ sudo nano /etc/ppp/ip-up.d/routing

#! /bin/sh
#
route del default
route add default ppp0 # Имя ppp-подключения.
# тут - необходимые маршруты, например:
route add -net 192.168.0.0 netmask 255.255.255.0 gw 192.168.0.1 dev eth0

$ sudo chmod ug+x /etc/ppp/ip-up.local

$ sudo chmod ug+x /etc/ppp/ip-up.d/routing

Установка MTU и TTL

auto eth0
iface eth0 inet static
address 192.168.1.5
netmask 255.255.255.0
mtu 600

$ sudo su
затем
# echo "128" > /proc/sys/net/ipv4/ip_default_ttl

Настройка WiFi

Настройка Wi-Fi при помощи wpa-supplicant и /etc/network/interfaces

Замечания

Подготовка

$ sudo apt-get install wpasupplicant wireless-tools

$ iwconfig

ubuntu@ubuntu:~$ iwconfig
lo        no wireless extensions.

eth0      no wireless extensions.

wmaster0  no wireless extensions.

wlan0     IEEE 802.11bg  ESSID:""  
          Mode:Managed  Frequency:2.412 GHz  Access Point: Not-Associated   
          Tx-Power=27 dBm   
          Retry min limit:7   RTS thr:off   Fragment thr=2352 B   
          Power Management:off
          Link Quality:0  Signal level:0  Noise level:0
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

$ iwlist <имя интерфейса> scan

ubuntu@ubuntu:~$ iwlist wlan0 scan

wlan0     Scan completed :
          Cell 01 - Address: 00:00:00:00:00:00
                    ESSID:"ubuntuessid"
                    Mode:Master
                    Channel:8
                    Frequency:2.447 GHz (Channel 8)
                    Quality=7/100  Signal level:-99 dBm  Noise level=-104 dBm
                    Encryption key:on
                    Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
                              24 Mb/s; 36 Mb/s; 54 Mb/s; 6 Mb/s; 9 Mb/s
                              12 Mb/s; 48 Mb/s
                    Extra:tsf=0000001d57e98bf6
                    Extra: Last beacon: 388ms ago

wlan0	Failed to read scan data : Network is down

sudo ip link set dev wlan0 up

sudo ip link set dev wlan0 down

Настройка

$ sudo gedit /etc/network/interfaces

iface wlan0 inet dhcp
wpa-driver wext
wpa-ssid <имя_точки_доступа>
wpa-ap-scan 1
wpa-proto RSN
wpa-pairwise CCMP
wpa-group CCMP
wpa-key-mgmt WPA-PSK
wpa-psk <hex_ключ> [ВАЖНО - см. Генерация ключей]
auto wlan0

Генерация ключей

$ wpa_passphrase <имя_точки_доступа> <ascii_ключ>

network={
ssid="test"
#psk="12345678"
psk=fe727aa8b64ac9b3f54c72432da14faed933ea511ecab1 5bbc6c52e7522f709a
}

Дополнительно

$ sudo chmod o=-r /etc/network/interfaces

Примеры конфигураций

iface wlan0 inet static
address 192.168.168.40
gateway 192.168.168.230
dns-nameservers 192.168.168.230
netmask 255.255.255.0
wpa-driver wext
wpa-ssid <имя_точки_доступа>
wpa-ap-scan 2
wpa-proto RSN
wpa-pairwise CCMP
wpa-group CCMP
wpa-key-mgmt WPA-PSK
wpa-psk <hex_ключ> [ВАЖНО - см. Генерация ключа]
auto wlan0

iface wlan0 inet dhcp
wpa-driver wext
wpa-ssid <имя_точки_доступа>
wpa-ap-scan 1
wpa-proto WPA
wpa-pairwise TKIP
wpa-group TKIP
wpa-key-mgmt WPA-PSK
wpa-psk <hex_ключ> [ВАЖНО - см. Генерация ключа] 
auto wlan0

iface wlan0 inet dhcp
wpa-driver wext
wpa-ssid <имя_точки_доступа>
wpa-ap-scan 1
wpa-proto WPA RSN
wpa-pairwise TKIP CCMP
wpa-group TKIP CCMP
wpa-key-mgmt WPA-PSK
wpa-psk <hex_ключ> [ВАЖНО - см. Генерация ключа]
auto wlan0

iface wlan0 inet dhcp
wpa-driver wext
wpa-ssid <имя_точки_доступа>
wpa-ap-scan 1
wpa-eap LEAP
wpa-key-mgmt IEEE8021X
wpa-identity <имя_пользователя>
wpa-password <пароль>
auto wlan0

iface wlan0 inet dhcp
wpa-driver wext
wpa-ssid <имя_точки_доступа>
wpa-ap-scan 1
wpa-proto RSN
wpa-pairwise CCMP
wpa-group CCMP
wpa-eap PEAP
wpa-key-mgmt WPA-EAP
wpa-identity <наш_identity>
wpa-password <пароль>
auto wlan0

iface wlan0 inet dhcp
wpa-driver wext
wpa-ssid <имя_точки_доступа>
wpa-ap-scan 1
wpa-eap TTLS
wpa-key-mgmt IEEE8021X
wpa-anonymous-identity <anonymous_identity>
wpa-identity <наш_identity>
wpa-password <наш_password>
wpa-phase2 auth=PAP [Также: CHAP, MSCHAP, MSCHAPV2]
auto wlan0

Другие способы работы Wi-Fi оборудования

При помощи Wi-Fi адаптера также возможно установить децентрализованную сеть ad-hoc или сделать из компьютера под управлением Ubuntu точку доступа. Поскольку описание данных способов Wi-Fi подключения выходит за рамки этого руководства — обратитесь к соответствующим разделам. Ссылки на эти разделы см. в разделе Cсылки.

Решение проблем

Не устанавливается соединение по Wi-Fi/Ethernet с точкой доступа/маршрутизатором

sudo ifdown wlan0
sudo ifup wlan0

Listening on LPF/wlan0/00-02-2A-E1-E0-6C
Sending on   LPF/wlan0/00-02-2A-E1-E0-6C
Sending on   Socket/fallback
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 8
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 8
DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 15
No DHCPOFFERS received.
No working leases in persistent database - sleeping.

Иногда наглухо пропадает соединение по Wi-Fi с точкой доступа/маршрутизатором

auto wlan0
...
wireless-channel 6

auto wlan0
...
#wireless-channel 6

Перезапуск сети

$ sudo /etc/init.d/networking restart

FAQ по сетям

Как зайти на мой компьютер извне (через интернет)?

Мне кажется, у меня слишком медленно работает сеть!

Измерьте скорость сети между двумя компьютера с помощью iperf. Можно воспользоваться этой инструкцией. В ней предлагают скомпиллировать программу из исходников, но можно просто установить её из репозитория. Если iperf покажет значение немного меньшее, чем ожидаемое, то с сетью всё в порядке, проблема может быть в железе (жёсткий диск/процессор не могут обеспечить большую скорость), в способе передачи (например, scp и ftp весьма неторопливы), в настройках (скорость может быть ограничена, например, настройками FTP-сервера) или в чём-то ещё. Если iperf показал величину, которая в разы меньше желаемой, то да — с сетью проблемы. Стоит посмотреть, в нужном ли режиме работает карта (например, с помощью ethtool), проверить наличие «errors» в выводе ifconfig и протестировать скорость подключения к какому-нибудь третьему компьютеру.

Как узнать, какие программы слушают порты на моём компьютере?

sudo netstat -nlpA inet,inet6

sudo netstat -nlpA inet,inet6 | grep :80

ps aux | grep 2671

Как присвоить два IP-адреса одной сетевой карте?

sudo ip addr add 192.168.1.1/24 dev eth0

#исправить строку auto
auto eth0 eth0:1

# добавить алиас
iface eth0:1 inet static
  address 192.168.1.1
  netmask 255.255.255.0

Как пробросить порт?

iptables -t nat -A PREROUTING -p tcp -d внешний_ір --dport 8081 -j DNAT --to-destination внутренний_ір:8081
iptables -t nat -A POSTROUTING -p tcp --dst внутренний_ір --dport 8081 -j SNAT --to-source внешний_ір

iptables -t filter -A FORWARD -m conntrack --ctstate DNAT -j ACCEPT

Ссылки

Changing the DNS server on Ubuntu is an easy task, but needs to be done carefully.

This article shows you how to do it easily.

Step 1: Check your current DNS Server

The first step is to always check, and note down the currently used DNS Servers – in case the change in DNS Server does not result in intended changes.

To show the current DNS servers that are being used per interface, use the ‘resolvectl’ command:

resolvectl status

For systems running Ubuntu 20.04 or newer, please use the following command:

systemd-resolve --status

Running either of these commands will show you the DNS server(s) being used by each network interface.

Let us see the output of the ‘resolvectl’ command on my computer:

$ resolvectl status
Global
       Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub

Link 2 (enp1s0)
    Current Scopes: DNS
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 8.8.8.8
       DNS Servers: 8.8.8.8 8.4.4.8

As evident from the output, my current DNS provider is Google.

I’d like to change that to something else, maybe Cloudflare.

Step 2: Temporarily change DNS (to test it out)

Before you change the DNS settings permanently, it is best to change it temporarily and see the results.

If there is regression, no need to revert as this is only a temporary change. If the results are as expected, we will make it permanent.

To temporarily change the DNS server, edit the /etc/resolv.conf file.

In /etc/resolv.conf, the line which starts with the keyword nameserver deals with DNS Servers.

Add one or two lines that begin with nameserver and specify the IP address next to it. Below is what it should look like (if I want Cloudflare as my DNS provider):

nameserver 1.1.1.2
nameserver 1.0.0.2

The first line is your primary DNS server and second line is the fall-back DNS server. The fall-back DNS server is used when [for some reason] the primary DNS server is unavailable.

Once these two lines are added to your /etc/resolv.conf file, you should immediately see the results.

You can verify if the DNS server changed with the help of dig command.

$ dig google.com | grep SERVER
;; SERVER: 1.1.1.2#53(1.1.1.2) (UDP)

Grep-ing the output, we see that Cloudflare’s DNS servers are being used. That confirms that the temporary change in DNS server was in effect immediately.

After temporarily switching DNS, if you do not like the change, remove the lines that you had added and uncomment the nameserver 127.0.0.53 line.

Available DNS Providers

In case you are not aware of IP addresses for DNS servers, below is the table of a few popular DNS providers, and their primary and fall-back addresses:

To use Cloudflare (with malware blocking) as my DNS provider, I will use the 1.1.1.2 and 1.0.0.2 IP addresses.

Step 3: Permanently change DNS

After temporarily changing your DNS provider, if you are satisfied with the results, it is time to make this change permanent.

Method 1: The easy way

To permanently change your DNS server, install the resolvconf package using the following command:

sudo apt-get install resolvconf

Once that is installed, edit the /etc/resolvconf/resolv.conf.d/head file and add the same nameserver lines to it like so (assuming Cloudflare as DNS provider):

nameserver 1.1.1.2
nameserver 1.0.0.2

Once that is done, start the resolvconf.service with the following command:

sudo systemctl enable --now resolvconf.service

That is all!

Method 2: The not-so-easy way

One way to permanently change your DNS server is to edit the YAML file that resides in the /etc/netplan/ directory.

Before that, note down the name of your network interface beforehand. You can do so using the ip command:

ip addr

That will list various network interfaces. Locate the interface and note it down.

Usually, there is only one file in /etc/netplan/ directory, but the name is mostly different. If there are multiple files, grep all files for your interface name. That should narrow down the candidate file to one.

grep -H INTERFACE_NAME *.*

Once you know the filename, open it for editing. You should see something similar to my output:

network:
  ethernets:
    enp1s0:
      dhcp4: true
  version: 2

My network interface is called ‘enp1s0’, yours might be different.

Under my interface, I will add the nameservers field (below, not under dhcp), and another filed called addresses under it as well. I will specify the address in a bracket, separated by commas, like so:

network:
  ethernets:
    enp1s0:
      dhcp4: true
      nameservers:
        addresses: [1.1.1.2, 1.0.0.2]
  version: 2

Once that is done, save changes and exit.

Then, run the following command to make changes effective:

sudo netplan apply

Done! You have now permanently changed your DNS server

Let’s learn the GUI and a command-line way to set the DNS server address in your Ubuntu 22.04 LTS Jammy JellyFish.

Well, whenever we visit some website such as how2shout.com in a browser, to find the website the browser needs the Ip-address of it. Here, the DNS comes into the picture. The Domain Name System, or DNS for short, is a system that converts Internet addresses or computer names into IP addresses and vice versa.

A browser request for the IP address will be sent to the DNS server. For private individuals, this is usually the case with the associated Internet provider. The DNS server then returns the IP address.

There are numerous DNS servers connected and always inform each other about changes. If a DNS server does not find a name or an IP address, it asks the other DNS server.

The DNS is therefore responsible and necessary for us to be able to access websites via Internet addresses or IP addresses.

Steps to change the DNS Nameserver on Ubuntu 22.04 LTS Linux

Although the DNS server address supplied by your internet service provider automatically gets configured, however, if you want to change it manually then follow this guide.

#1st Method Using GUI

1. Open Ubuntu Settings

On your Ubuntu 22.04, click on the Power icon given on the right top side of the Taskbar. A pop-up will appear there select the “Settings” option to open it.

2. Go to Network Settings

Once you are on the Settings page, go to the Network menu given on the left sidebar and then click on the Gear icon given for Wired or Wireless connection.

3. Set DNS Server on Ubuntu 22.04

Now, you will have a window to configure IP addresses and other settings related to the network. However, to configure DNS Server Ip-address, select IPV4 Tab and then click on the Toggle button given in front of DNS. This will disable the automatic fetching of DNS Server addresses from your Internet provider. After that enter the IP address of the DNS server you want to set on your Ubuntu 22.04. Here we are using the address of the Google DNS server to perform this tutorial, you can set whatever you want to. After that click on the “Apply” button to save the configuration.

From now onwards to resolve some domain names, the system will check it with the Google DNS server or the one you have set.

Note: Don’t forget to Turn the Network Off and On to get the immediate effect or else the same will reflect on your next system boot-up.

#2nd method using CLI

4. Open Command terminal

Those who are not using the GUI Desktop of Ubuntu 22.04 or prefer to use the command line, can go for the Netplan configuration file. First, open the command terminal, those who are on the server version already have terminal access, whereas the Desktop user can use the keyboard shortcut – Ctrl+Alt+T.

5.  Edit Netplan Confgiuration file

Ubuntu has a command-line Netplan tool that uses a YAML configuration file; we can use it to set our network configuration.

Switch to Netplan directory:

cd /etc/netplan

List the available file:

ls

Edit it:

Before editing the file, find out your ethernet adapter name and also the IP address of the PC in your network range. To find it, you can use the command ip a

sudo nano 01-network-manager.yaml

Add the following lines, however, make sure the space should be as given in the block of code because YAML is an indent-sensitive language. And don’t forget to replace ens160 with your adapter and Ip-address + Gateway as well. After that move to the nameservers section and set whatever DNS server address you want on your system to use for resolving domain names.

network:
  version: 2
  renderer: NetworkManager
  ethernets:
    ens160:
      dhcp4: no
      addresses:
        - 192.168.17.100/24
      gateway4: 192.168.17.2
      nameservers:
          addresses: [1.1.1.1, 8.8.8.8, 4.4.4.4]

Save the file by pressing Ctlr+O, hitting the Enter key, and then exiting using Ctrl+X.

Before applying your Netplan configuration file, let’s test it by issuing the following command:

sudo netplan try

Hit the Enter key, if the Configuration you have done in the Netplan file is valid, you will have an output saying-  Configuration accepted.

Now, Apply the configuration:

sudo netplan apply

If you want also want to see what is happening while applying the new Netplan configuration, use:

sudo netplan --debug apply

With the help of the Domain Name System, the assignments between IP addresses and domain names can be resolved in the outward and backward directions. Since DNS is very important for the functioning of an IP network, there are numerous security extensions such as DNSSEC, DNS over TLS, or DNS over HTTPS.

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