📘 CCNA 200-301 v1.1

4.2 Configure and verify NTP operating in a client and server mode

1. What is NTP?

• NTP (Network Time Protocol) is a protocol used to synchronize the clocks of devices (routers, switches, servers, etc.) in a network.
• Time synchronization is important in IT for:
  • Logging events accurately
  • Security (timestamps in authentication)
  • Network troubleshooting (matching logs from different devices)
  • Scheduling tasks or automation

In networks, devices can act as:

1. NTP Server: Provides the accurate time to other devices.
2. NTP Client: Receives time from an NTP server and synchronizes its clock.

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2. NTP Modes in Networks

1. Server Mode:
   • The device provides time to other devices.
   • Example: A data center router can act as an NTP server for all internal devices.
2. Client Mode:
   • The device synchronizes its clock with an NTP server.
   • Example: A branch office switch receives time from a central office router configured as NTP server.
3. Peer/Stratum:(optional for CCNA exam understanding)
   • Servers can synchronize with other NTP servers for redundancy.
   • Devices are categorized by stratum levels (stratum 1 = most accurate, stratum 2 = synced to stratum 1, etc.)

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3. Configuring NTP on Cisco Devices

Step 1: Configuring an NTP Server

• Use a router or switch as the NTP server.
• You can configure it to sync with an external time source (like an internet NTP server) or provide its own local time.

Commands:

Router> enable
Router# configure terminal
Router(config)# ntp master 1

Explanation:

• ntp master 1 → This makes the router act as an NTP server.
• The number 1 is the stratum level of the server (how accurate/trusted the time is).

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Step 2: Configuring an NTP Client

• A client syncs its clock with a server.

Commands:

Router> enable
Router# configure terminal
Router(config)# ntp server 192.168.1.1

Explanation:

• ntp server <IP> → Sets the IP address of the NTP server the device should sync with.

TIP: NTP works over UDP port 123, so ensure routing and firewall allow this traffic.

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Step 3: Verifying NTP Configuration

1. Check if the device is syncing correctly:

Router# show ntp status

• Key things to look for:
  • Clock is synchronized → YES means client is synced
  • Stratum number → Shows how far from the primary time source

2. Check which servers are used:

Router# show ntp associations

• Displays:
  • IP addresses of NTP servers
  • Status of synchronization

3. Check the clock:

Router# show clock

• Displays the current device time
• Should match the NTP server time after syncing

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4. Summary for CCNA Exam

1. NTP is used to sync time across network devices.
2. Devices can be NTP servers (provide time) or clients (receive time).
3. NTP configuration commands:
   • ntp master <stratum> → server
   • ntp server <IP> → client
4. Verification commands:
   • show ntp status → check sync
   • show ntp associations → check server connections
   • show clock → check device time

Remember: For CCNA, focus on basic NTP client/server setup and verification, not complex NTP hierarchy.

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