Changing the DNS Server

This topic explains how to change the DNS Server on your TOS nodes. We recommend performing this task during an IT change window because changing the DNS server may cause a network disruption (especially if an incorrect DNS server is entered in error).

We recommend backing up your TOS data before changing the DNS server. See Backup and Restore.

This procedure is relevant for deployments on TOS appliances and VMWare VMs.

Change DNS Address

Locate the first network interface.
```
[<ADMIN> ~]$ sudo /opt/tufinos/scripts/network_interface_by_pci_order.sh | awk -F'=' '/NET_IFS\[0\]/ { print $NF }'
```
sudo /opt/tufinos/scripts/network_interface_by_pci_order.sh | awk -F'=' '/NET_IFS\[0\]/ { print $NF }'
Run the command:

[<ADMIN> ~]$ sudo nmtui edit <First Interface Name>

sudo nmtui edit <First Interface Name>

Set the gateway and DNS Servers to the IPs used by your organization.

Restart the network service.

[<ADMIN> ~]$ sudo systemctl restart NetworkManager.service

sudo systemctl restart NetworkManager.service

To apply the changes, restart the kube-system pods:
```
[<ADMIN> ~]$ kubectl delete pod -n kube-system -l k8s-app=kube-dns
```
sudo systemctl kubectl delete pod -n kube-system -l k8s-app=kube-dns
Verify that the DNS server can resolve its own address using a reverse lookup
Run:
[<ADMIN> ~]$ sudo nslookup <DNS SERVER IP>
sudo nslookup <DNS SERVER IP>
If the name of the server appears, the DNS server can resolve its own address using a reverse lookup.

Example Output
```
[<ADMIN> ~]$ sudo nslookup  1.2.3.4
4.3.2.1.in-addr.arpa	name=EXAMPLE.company.com
```
If the name of the server does not appear, set it using a reverse lookup entry at /etc/hosts.

Example Output where 1.2.3.4 4.3.2.1.in-addr-arpa was added.
```
[<ADMIN> ~]$ sudo cat /etc/hosts 
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost6 localhost6.localdomain6
1.2.3.4 admin.company.com admin
2.3.4.5 5.4.3.2.in-addr-arpa
```