Create NTP Server on Linux Debian

Fig : NTP Server

1. Install the NTP Service

Debian 12 uses ntpsec by default.

• sudo apt update
• sudo apt install ntpsec -y

2. Configure NTP

Edit the configuration file:

• sudo nano /etc/ntpsec/ntp.conf

Upstream Time Servers

Replace or add U.S.-based pool servers:

• pool 0.us.pool.ntp.org iburst
• pool 1.us.pool.ntp.org iburst
• pool 2.us.pool.ntp.org iburst
• pool 3.us.pool.ntp.org iburst

Allow Your LAN Clients

For your network 192.168.32.0/19:

• restrict default kod nomodify notrap nopeer noquery
• restrict 127.0.0.1
• restrict ::1
• restrict 192.168.32.0 mask 255.255.224.0 nomodify notrap

Optional: Local Clock Fallback

• server 127.127.1.0
• fudge 127.127.1.0 stratum 10

3. Enable and Start the Service

• sudo systemctl enable ntpsec
• sudo systemctl restart ntpsec

4. Allow UDP Port 123

If you’re using iptables:

• sudo iptables -A INPUT -i ens192 -s 192.168.32.0/19 -p udp --dport 123 -j ACCEPT
• sudo netfilter-persistent save

If using nftables (Debian 12 default):

• sudo nano /etc/nftables.conf

Add:

• add rule inet filter input iif "ens192" ip saddr 192.168.32.0/19 udp dport 123 accept

Then:

• sudo systemctl restart nftables

5. Verify Server Status

Check if it’s listening:

• ss -ulpn | grep ':123 '

Check sync status:

• ntpq -pn

You should see a * next to one of the pool servers with a stratum < 16.

6. Test From a Client

Linux client:

• sudo ntpdate -q 192.168.32.76

Windows client (PowerShell):

• w32tm /stripchart /computer:192.168.32.76 /samples:5 /dataonly

7. Monitor Connected Clients

Enable monitoring in /etc/ntpsec/ntp.conf:

Then:

• sudo systemctl restart ntpsec
• ntpq -c "mrulist"