Inspecting DNS configuration

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Inspecting DNS configuration

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Available in Classic

If you do not use the DNS settings provided by NAVER Cloud Platform, normal communication with the servers provided for internal management may not be possible. If possible, do not set up DNS separately. If you set up DNS separately, you may encounter errors in the process of creating a server with a server image or setting the admin password.

CentOS

Inspect the DNS settings and file in the RedHat OS provided on NAVER Cloud Platform.

Note

Described for CentOS 7.2, CentOS 7.3, CentOS 7.8.

Check the DNS settings of NAVER Cloud Platform received from DHCP. The IPs of the DNS server provided in the Classic environment are 10.250.255.11 and 10.250.255.12.

[root@centos78 ~]# grep domain-name /var/lib/dhclient/dhclient--eth0.lease
  option domain-name-servers 10.250.255.11,10.250.255.12;
  option domain-name "ncloud.com";
  option domain-name-servers 10.250.255.11,10.250.255.12;
  option domain-name "ncloud.com";

Check the settings and content of the /etc/resolv.conf file.
- If the contents of the file differ from the following, normal communication with NAVER Cloud Platform DNS server may not be possible. However, after editing the file and rebooting the OS, it is initialized to NAVER Cloud Platform settings received from DHCP.
```
[root@centos78 ~]# cat /etc/resolv.conf
; generated by /usr/sbin/dhclient-script
search ncloud.com
nameserver 10.250.255.11
nameserver 10.250.255.12
```

Run the nslookup command to check DNS query operation.

When the query works correctly, 10.250.5.105 is displayed.

[root@centos78 ~]# nslookup repo.ncloud.com
Server:		10.250.255.11
Address:	10.250.255.11#53

Non-authoritative answer:
repo.ncloud.com	canonical name = repo.ncloud.grm.ncloud.com.
repo.ncloud.grm.ncloud.com	canonical name = kr2-init.ncloud.grm.ncloud.com.
Name:	kr2-init.ncloud.grm.ncloud.com
Address: 10.250.5.105

Ubuntu

Ubuntu 18.04 provided by NAVER Cloud Platform uses systemd-resolved. Inspect the DNS settings and files on the Ubuntu OS.

Note

Described for Ubuntu 18.04.

Check the settings and content of the /etc/resolv.conf file.

Check if the file's symbolic link exists.

root@ubuntu1804:~# ll /etc/resolv.conf
lrwxrwxrwx 1 root root 39 Sep 28  2020 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

Check if the contents of the file are the same as the following:

root@ubuntu1804:~# cat /etc/resolv.conf
# This file is managed by man:systemd-resolved(8). Do not edit.
... Omitted...
nameserver 127.0.0.53
options edns0
search ncloud.com

Check the DNS settings of NAVER Cloud Platform received from DHCP.

root@ubuntu1804:~# cat /run/systemd/resolved.conf.d/isc-dhcp-v4-eth0.conf
[Resolve]
DNS=10.250.255.11 10.250.255.12
Domains= ncloud.com

Check the configured DNS settings on the OS. The IPs of the DNS server provided in the Classic environment are 10.250.255.11 and 10.250.255.12.

root@ubuntu1804:~# cat /run/systemd/resolve/resolv.conf
... Omitted...
nameserver 10.250.255.11
nameserver 10.250.255.12
search ncloud.com

If it appears as follows, the DNS server settings are in an abnormal state.

root@ubuntu1804:~# tail -2 /run/systemd/resolve/resolv.conf

# No DNS servers known.

If applicable, handle it as follows:

root@ubuntu1804:~# cat /run/systemd/resolved.conf.d/isc-dhcp-v4-eth0.conf
[Resolve]
DNS=10.250.255.11 10.250.255.12
Domains= ncloud.com

root@ubuntu1804:~# systemctl restart systemd-resolved
root@ubuntu18:~# tail -3 /run/systemd/resolve/resolv.conf
nameserver 10.250.255.11
nameserver 10.250.255.12
search ncloud.com

Check if the systemd-resolved daemon is running and its status.

The systemd-resolved daemon must be enabled in the list of installed units so it can work properly after booting.

root@ubuntu1804:~# systemctl list-unit-files | grep systemd-resolved.service
systemd-resolved.service               enabled

The systemd-resolved daemon must be active for normal operation.

root@ubuntu1804:~# systemctl status systemd-resolved.service
● systemd-resolved.service - Network Name Resolution
   Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled)
   Active: active (running) since Sun 2023-04-09 20:27:10 KST; 14h ago
     Docs: man:systemd-resolved.service(8)
           https://www.freedesktop.org/wiki/Software/systemd/resolved
           https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
           https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
 Main PID: 687 (systemd-resolve)
   Status: "Processing requests..."
    Tasks: 1 (limit: 4622)
   CGroup: /system.slice/systemd-resolved.service
           └─687 /lib/systemd/systemd-resolved

Check the connection status of the IP address 127.0.0.53. It must be LISTEN through port 53 (nameservice port) by the systemd-resolve service.

root@ubuntu1804:~# netstat -anp | grep 127.0.0.53
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      687/systemd-resolve 
udp        0      0 127.0.0.53:53           0.0.0.0:*                           687/systemd-resolve

Check the DNS settings in the systemd-resolve service.
- Use the following command to verify the DNS server information that sends queries.
```
root@ubuntu1804:~# systemd-resolve --status
Global
     DNS Servers: 10.250.255.11
                  10.250.255.12
 ... Omitted...
```
Check the permissions of the /etc/hosts file.
- Other User in the /etc/hosts file must have the read permission for the systemd-resolved daemon to operate properly. By default, the /etc/hosts file has permission set to 644.
```
root@ubuntu1804:~# ls -l /etc/hosts
-rw-r--r-- 1 root root 189 Sep 28  2020 /etc/hosts
```

Run the nslookup command to check DNS query operation.

When the query works correctly, 10.250.5.105 is displayed.

root@ubuntu1804:~# nslookup repo.ncloud.com
Server:		127.0.0.53
Address:	127.0.0.53#53

Non-authoritative answer:
repo.ncloud.com	canonical name = repo.ncloud.grm.ncloud.com.
repo.ncloud.grm.ncloud.com	canonical name = kr2-init.ncloud.grm.ncloud.com.
Name:	kr2-init.ncloud.grm.ncloud.com
Address: 10.250.5.105

Changing the Fade-out DNS server

If the confirmed DNS server settings are 125.209.192.12 or 125.209.192.13, changing DNS server settings is required.
Check if it should be changed and if so, proceed with changing the DNS server.

Linux

Caution

The relevant guide target equipment only falls under some VMs of Classic. Do not run the action if it does not need to be changed.

Run the DNS server configuration change file and change the DNS server for the resolv.conf configuration.

[root@centos78 ~]# curl -sSL -k https://kr.object.ncloudstorage.com/dns-tools/resolv-change.sh | /bin/bash

Note

When you run the file, the DNS server automatically changes and a test is conducted to see if questioning is normally performed.

Caution

DNS servers other than 125.209.192.12 and 125.209.192.13 are not changed by the job.

Note

If changing the DNS server fails, the operation result displays Change failed as follows. If applicable, contact Customer support.

[root@centos78 ~]# curl -sSL -k https://kr.object.ncloudstorage.com/dns-tools/resolv-change.sh | /bin/bash

Task result: change failed
Failed to change resolv.conf settings. The required nameserver(s) not found.

Windows

The following describes how to set DNS on Windows servers:

Connect to the Windows server.
- For more information on how to connect to the server, see Access Windows server.
Click , then click Settings > Network & Internet > Change adapter options, in order.
- Alternatively, you can enter ncpa.cpl on the Run command window.
On the list that appears, find the network you are using, right-click it and then click Properties.
- In the Internet Protocol Version 4 (TCP/IPv4) Properties, edit Use the following DNS server addresses at the bottom to 10.250.255.11, 10.250.255.12.

Caution

If you are operating your own DNS, such as Active Directory or DNS Server, check and change it as necessary.

Q. The following isc_socket_bind error occurs when querying DNS. What should I do?

[root@ncp-server ~]# nslookup repo.ncloud.com
Server:		10.250.255.11
Address:	10.250.255.11#53

Non-authoritative answer:
repo.ncloud.com	canonical name = repo.ncloud.grm.ncloud.com.
repo.ncloud.grm.ncloud.com	canonical name = kr2-init.ncloud.grm.ncloud.com.
Name:	kr2-init.ncloud.grm.ncloud.com
Address: 10.250.5.105
nslookup: isc_socket_bind: address in use

The issue occurs when the ip_local_port_range value is too small for the customer service network environment, or when there are too many socket ports currently in use.
You can check the ip_local_port_range as follows. By default, the minimum port is 32768, and the maximum port is 60999.

[root@ncp-server ~]# sysctl net.ipv4.ip_local_port_range
net.ipv4.ip_local_port_range = 32768    60999

If the server can be rebooted, reboot in the OS. If it cannot be rebooted, check the number of currently used sockets and organize the unnecessary sockets or increase the ip_local_port_range value.
DNS query in normal status is output as follows:

[root@ncp-server ~]# nslookup repo.ncloud.com
Server:		10.250.255.11
Address:	10.250.255.11#53

Non-authoritative answer:
repo.ncloud.com	canonical name = repo.ncloud.grm.ncloud.com.
repo.ncloud.grm.ncloud.com	canonical name = kr1-init.ncloud.grm.ncloud.com.
Name:	kr1-init.ncloud.grm.ncloud.com
Address: 10.101.86.18

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What's Next

Force stopping and terminating

Table of contents

CentOS
Ubuntu
Changing the Fade-out DNS server
FAQ related to DNS

Inspecting DNS configuration

CentOS

Ubuntu

Changing the Fade-out DNS server

Linux

Windows

FAQ related to DNS

Q. The following isc_socket_bind error occurs when querying DNS. What should I do?

What's Next