SNTP - Simple Network Time Protocol

What is SNTP?

SNTP (Simple Network Time Protocol) is a protocol used to synchronize the clocks of computers and devices over a network. It is a simplified version of NTP (Network Time Protocol) that offers less precision, making it suitable for less demanding time synchronization needs.

Why is SNTP useful?

  • Provides a simple and lightweight way to synchronize system clocks.

  • Ensures consistent timekeeping across devices in a network.

  • More efficient and less complex than NTP, ideal for systems where high precision isn’t critical.

  • Widely supported by various devices and operating systems.

How it works?

  • A client sends a request to an SNTP server, typically over UDP.

  • The server responds with the current time.

  • The client adjusts its system clock based on the response.

  • The protocol does not perform complex time correction algorithms, making it less accurate than NTP, but sufficient for most applications.

Where is SNTP used?

  • SNTP is commonly used in environments where precise time synchronization is not a priority.

  • It is typically used in consumer devices, home routers, printers, and embedded systems.

  • Often found in systems with limited processing power or where NTP’s high precision isn’t necessary.

Which OSI layer does this protocol belong to?

  • SNTP operates at the Application Layer (Layer 7) of the OSI model.

  • It uses lower layers (Transport Layer and Network Layer) for communication, typically relying on UDP at the Transport Layer.

Is SNTP Windows specific?

  • No, SNTP is not Windows-specific.

  • It is supported by a wide range of operating systems including Linux, macOS, and many embedded devices.

Is SNTP Linux specific?

  • No, SNTP is not Linux-specific.

  • It is supported by various operating systems and is commonly used in a wide range of devices across different platforms.

Which Transport Protocol is used by SNTP?

  • SNTP typically uses UDP (User Datagram Protocol) at the Transport Layer.

  • UDP is used because it provides low-latency communication, which is suitable for time synchronization.

Which Port is used by SNTP?

  • SNTP operates on UDP port 123.

  • This is the same port used by NTP, as SNTP is essentially a simplified version of it.

Is SNTP using Client-server model?

  • Yes, SNTP follows the client-server model.

  • The client sends a request to the SNTP server, and the server responds with the current time.

Topics in this section,

  • In this section, you are going to learn

  • Terminology

  • Version Info

SNTP Version

SNTP Number

Year

Core Idea / Contribution

SNTP v1

RFC 1361

1992

First formal definition of SNTP; introduced a simplified version of NTP for systems not requiring full NTP complexity.

SNTP v2

RFC 1769

1995

Updated SNTP to align with NTPv3; clarified usage in simple devices and embedded systems.

SNTP v3

RFC 2030

1996

Extended SNTP for IPv4 and introduced compatibility with NTPv3; emphasized simplicity and ease of implementation.

SNTP v4

RFC 4330

2006

Added support for IPv6 and OSI protocols; aligned with NTPv4 while maintaining simplicity; obsoleted RFC 2030 and RFC 1769.

SNTP C Code (Client-Server Model over UDP)

  • This C program demonstrates how to build a simple SNTP (Simple Network Time Protocol) server and client using UDP sockets.

    • The SNTP server (mode 4) listens on a UDP port and responds with a basic NTP packet containing the transmit timestamp.

    • The SNTP client (mode 3) sends a request to the server and reads the transmit timestamp to print the server time.

  • This setup is useful for testing SNTP communication, simulating time servers, or learning basic NTP packet structure.

  • Replace the server IP address (127.0.0.1) in the client code with your actual SNTP server address before running.

  • Step-1: Download C source code for SNTP server and client.

    Download SNTP Server Code Download SNTP Client Code

  • Step-2: Convert C code to executable files.

    test:~$gcc sntp_server.c -o sntp_server
test:~$gcc sntp_client.c -o sntp_client

  • Step-3: Run SNTP server and client.

    # Start SNTP server (may require sudo if using port 123)
test:~$sudo ./sntp_server
SNTP server listening on port 123...

# Run SNTP client
test:~$ ./sntp_client
Server time: Wed Jul 31 13:44:28 2025

  • Step-4: Wireshark Capture

    Download Wireshark capture

SNTP Client Code with Error Handling (Invalid Server IP Demonstration)

  • This C program demonstrates how an SNTP client handles network errors when provided with an invalid or unreachable NTP server IP address.

    • The client constructs a basic NTP request packet (mode 3), sends it to the specified IP, and waits for a response.

    • If the IP address is invalid, or no response is received within 3 seconds, the program prints a relevant error message.

  • This is useful for testing SNTP client robustness, network failure scenarios, or for educational purposes.

  • Step-1: Download C source code for SNTP invalid server IP test.

    Download SNTP Client (Invalid IP Test)

  • Step-2: Convert C code to executable file.

    test:~$ gcc sntp_invalid_ip_client.c -o sntp_invalid_ip_client

  • Step-3: Run SNTP client with an invalid or unreachable IP.

    test:~$ ./sntp_invalid_ip_client 192.0.2.1
Packet sent to 192.0.2.1. Waiting for response...
Receive failed: Resource temporarily unavailable

    Note

    • 192.0.2.1 is a reserved non-routable IP (TEST-NET-1) and is commonly used for documentation.

    • The client sets a 3-second receive timeout to avoid indefinite blocking.

  • Step-4: Wireshark Capture

    Download Wireshark capture

SNTP Wrong Mode Packet Injection (Mode 7 - Reserved/Private Use)

  • This C program demonstrates how to manually construct and send an SNTP/NTP packet with an invalid mode field:

    • Mode 7 (Reserved / Private) is not used in standard client-server communication and is typically rejected or ignored by NTP servers.

    • The client sets LI = 0, VN = 4, Mode = 7 and sends it to a specified NTP server over UDP.

  • This test is useful for:

    • Evaluating how NTP servers handle non-standard or malformed mode values.

    • Auditing firewalls and NTP-aware intrusion detection systems.

    • Learning how NTP mode bits work at the packet level.

  • Step-1: Download the C source code for wrong mode packet generation.

    Download SNTP Wrong Mode Code

  • Step-2: Convert the C code to an executable file.

    test:~$ gcc sntp_wrong_mode.c -o sntp_wrong_mode

  • Step-3: Run the wrong-mode SNTP client with the target NTP server IP.

    test:~$ ./sntp_wrong_mode 216.239.35.0
Wrong-mode NTP packet (mode 7) sent to 216.239.35.0

    Note

    • Replace 216.239.35.0 with your actual test NTP server IP.

    • Most compliant servers will ignore or drop mode 7 packets without replying.

  • Step-4: Wireshark Capture

    Download Wireshark capture (mode 7 test)

SNTP Delayed Response Simulation (Send and Receive Timestamped NTP Packets)

  • This C program demonstrates how to send a fully formed SNTP (Simple Network Time Protocol) request to a server and then receive and interpret the response, including transmit timestamps.

    • The client sends a well-formed NTPv4 packet using Mode 3 (Client) and a valid transmit timestamp.

    • The program sets a 2-second socket timeout to simulate how SNTP clients handle slow or unresponsive servers.

    • The received NTP packet is decoded and the transmit timestamp is converted to a human-readable date/time.

  • This is useful for:

    • Understanding client-side time parsing in SNTP.

    • Testing server responsiveness and round-trip behavior.

    • Simulating timeout or delay handling in a lightweight SNTP implementation.

  • Step-1: Download the C source code for SNTP delayed response client.

    Download SNTP Delayed Response Code

  • Step-2: Compile the C code into an executable.

    test:~$ gcc sntp_delayed_response.c -o sntp_delayed_response

  • Step-3: Run the SNTP client and observe server response or timeout.

    test:~$ ./sntp_delayed_response 129.6.15.28
NTP request sent to 129.6.15.28. Waiting for response...
Response received in 365.73 ms
Server time: 2025-07-31 12:34:46

    Note

    • Replace 129.6.15.28 with the IP of a valid public or local NTP server.

    • If no response is received within 2 seconds, a timeout error will be shown.

  • Step-4: Wireshark Capture

    Download Wireshark capture (delayed SNTP test)

SNTP C Client Querying Multiple NTP Servers

  • This C program implements a basic SNTP client that sends an NTP request (Mode 3) to a given NTP server.

  • It constructs a 48-byte SNTP packet, sends it via UDP, waits for the response, extracts the transmit timestamp, and converts it to human-readable local time.

  • This can be used to verify synchronization accuracy across multiple public NTP servers.

  • Step-1: Download C source code for SNTP client.

    Download SNTP client code

  • Step-2: Compile the source code into an executable.

    test:~$ gcc sntp_client_1.c -o sntp_client_1

  • Step-3: Run the SNTP client with different public NTP server IPs.

    test:~$ ./sntp_client_1 129.6.15.28  #time.google.com
Server Time: Thu Jul 31 12:45:28 2025

test:~$ ./sntp_client_1 216.239.35.12 #pool.ntp.org
Server Time: Thu Jul 31 12:45:30 2025

test:~$ ./sntp_client_1 40.119.6.228  #time.windows.com
Server Time: Thu Jul 31 12:45:32 2025

  • Step-4: Analyze server time differences or round-trip delays using Wireshark.

    Download Wireshark capture

SNTP Version Mismatch Test (Version 1 Packet to NTPv4 Server)

  • This C program sends an SNTP packet using NTP Version 1, which is outdated and not typically supported by modern NTP servers (which use v3 or v4).

  • It is useful for testing how NTP servers handle requests with unsupported or mismatched protocol versions.

  • This helps in evaluating server behavior and backward compatibility with legacy clients.

  • Step-1: Download C source code for SNTP version mismatch test.

    Download C source code

  • Step-2: Compile the source code into an executable.

    test:~$ gcc sntp_version_mismatch.c -o sntp_version_mismatch

  • Step-3: Send version 1 SNTP request to an NTPv4 server.

    test:~$ ./sntp_version_mismatch 216.239.35.0
NTP packet with version 1 sent to 216.239.35.0

  • Step-4: Observe behavior:

    • No response or timeout indicates the server rejects outdated versions.

    • Use Wireshark or tcpdump to analyze network-level handling.

  • Step-5: Capture the packet exchange using Wireshark.

    Download Wireshark capture

SNTP Malformed Packet Test

  • This C program sends a malformed NTP packet (only 20 bytes, whereas a valid NTP/SNTP packet must be 48 bytes) to an NTP server.

  • The purpose of this test is to observe how the NTP server handles improperly sized or corrupted packets.

  • This can be used for robustness testing, fuzzing, or input validation verification.

  • Step-1: Download the C source code for malformed packet generation.

    Download malformed packet code

  • Step-2: Compile the source code.

    test:~$ gcc sntp_malformed.c -o sntp_malformed

  • Step-3: Run the executable against an NTP server.

    test:~$ ./sntp_malformed 216.239.35.0
Malformed packet (20 bytes) sent to 216.239.35.0

  • Step-4: Observe behavior:

    • The server may silently drop the packet.

    • Use Wireshark or tcpdump to confirm packet dispatch and any server response.

  • Step-5: Capture and analyze using Wireshark.

    Download Wireshark capture

SNTP Rapid-Fire Request Test

  • This C program sends 10 consecutive SNTP requests in rapid succession (100ms apart) to a specified NTP server.

  • It is used to simulate a burst of time requests to observe:

    • Server rate-limiting behavior.

    • Whether the server drops packets under load.

    • How responses are handled when queried at high frequency.

  • This is helpful for testing firewall rules, DoS handling, or client behavior in time-critical environments.

  • Step-1: Download the C source code for rapid-fire SNTP requests.

    Download C source code

  • Step-2: Compile the source code.

    test:~$ gcc sntp_rapid_fire.c -o sntp_rapid_fire

  • Step-3: Run the test against a reachable NTP server.

    test:~$ ./sntp_rapid_fire 216.239.35.0
Request 1 sent
Request 2 sent
Request 3 sent
Request 4 sent
Request 5 sent
Request 6 sent
Request 7 sent
Request 8 sent
Request 9 sent
Request 10 sent

  • Step-4: Observe server behavior:

    • Use Wireshark or tcpdump to verify if all packets were sent and whether responses were returned.

    • Useful for assessing tolerance to polling frequency.

  • Step-5: Capture the test using Wireshark.

    Download Wireshark capture

One-time Sync with ntpdate (SNTP Server Response Verification)

  • To ensure that the SNTP server responds correctly to time synchronization requests from an NTP client, and client can successfully update its system time using the received data.

  • Step-1: Install and Configure NTP Server (on Machine A).

    test1:~$ sudo apt update
test1:~$ sudo apt install ntp

# Edit the NTP configuration
test1:~$ sudo nano /etc/ntp.conf

# Add the following lines or update accordingly
restrict 192.168.56.0 mask 255.255.255.0 nomodify notrap
server 127.127.1.0
fudge 127.127.1.0 stratum 10
broadcast 192.168.56.255

# Comment out online pool servers if offline
# pool 0.ubuntu.pool.ntp.org iburst
# pool 1.ubuntu.pool.ntp.org iburst

# Restart the NTP service
test1:~$ sudo systemctl restart ntp
test1:~$ sudo systemctl status ntp

  • Step-2: Verify NTP Listening on Port 123 (UDP)

    test1:~$ ss -ulpn | grep :123

  • Step-3: Allow NTP Traffic via UFW (if enabled)

    test1:~$ sudo ufw status
test1:~$ sudo ufw allow 123/udp

  • Step-4: Install Client Tools on Machine B

    test2:~$ sudo apt update
test2:~$ sudo apt install ntpdate sntp

  • Step-5: One-Time Time Sync Using ntpdate

    test2:~$ sudo ntpdate -q 192.168.56.10

# Example Output:
# server 192.168.56.10, stratum 10, offset -0.000123, delay 0.02567

  • Expected Result:

    • The client should receive a valid time response from the server.

    • Output should indicate stratum and offset.

    • No errors like “no server suitable for synchronization found” should occur.

  • Step-6: Wireshark Capture

    Download wireshark capture

One-time Sync with sntp (SNTP Server Response Verification)

  • To verify that the NTP server (Machine A) responds correctly to SNTP (Simple NTP) queries and that a client (Machine B) can synchronize its time using the sntp utility.

  • Step-1: Ensure SNTP is Installed on the Client (Machine B)

    test2:~$ sudo apt update
test2:~$ sudo apt install sntp

  • Step-2: Query the NTP Server Using SNTP

    test2:~$ sntp 192.168.56.10

# Example Output:
# 2025-08-04 13:15:07.123456 (+0000) +0.001234 +/- 0.005678 secs

  • Interpretation:

    • The client successfully queried the NTP server.

    • The output includes: - The current timestamp - Time offset (e.g., +0.001234) - Estimated error bounds (+/-)

    • Note: sntp by default does not set the system time; it only queries.

  • Step-4: Ensure Server is Listening (Run on Server - Machine A)

    test1:~$ ss -ulpn | grep :123

  • Expected Result:

    • The SNTP client should successfully contact the server and display the timestamp, offset, and delay.

    • No error messages such as “no server suitable for synchronization found”.

  • Step-5: Wireshark Capture

    Download wireshark capture

Time Sync Validation via ntpdate

  • To verify the system time on the client machine before and after synchronization using ntpdate, and confirm time alignment with the NTP server.

  • Requirements:

    • Machine B (Client – test2) must have ntpdate installed.

    • Machine A (Server – test1) must be running and accessible on 192.168.56.10.

    • sudo privileges available on the client.

  • Step-1: Check Current Time on Client (Before Sync)

    test2:~$ date

# Example Output:
# Mon Aug  4 13:24:10 UTC 2025

    • Note the time. You may observe it differs from the actual/current time if the system is out of sync.

  • Step-2: Synchronize Time with NTP Server

    test2:~$ sudo ntpdate 192.168.56.10

# Example Output:
# 4 Aug 13:25:10 ntpdate[1234]: adjust time server 192.168.56.10 offset -0.345678 sec

    • This indicates that the system clock was adjusted by the reported offset.

  • Step-3: Check Time Again on Client (After Sync)

    test2:~$ date

# Example Output:
# Mon Aug  4 13:25:10 UTC 2025

    • Compare this with the time noted in Step 1. It should now reflect the correct time based on the server’s clock.

  • Step-4 (Optional): Check NTP Sync Status via timedatectl

    test2:~$ timedatectl status

    • Example output might include:

      • NTP enabled: no (if only manual sync is used)

      • System clock synchronized: yes

      • Accurate Local time and Universal time

  • Step-5: Wireshark Capture

    Download wireshark capture

Time Sync with Deliberately Skewed System Clock

  • To verify that ntpdate can successfully correct the system clock on the client when the clock is significantly incorrect.

  • Requirements:

    • Machine B (Client – test2) must have ntpdate installed.

    • Machine A (Server – test1) must be running NTP and accessible at 192.168.56.10.

    • sudo access is required on the client machine.

  • Step-1: Manually Skew the System Clock on Client

    test2:~$ sudo date -s "2020-01-01 12:00:00"
test2:~$ date

# Example Output:
# Wed Jan  1 12:00:00 UTC 2020

* This sets the system clock far in the past.

  • Step-2: Synchronize Time with NTP Server

    test2:~$ sudo ntpdate 192.168.56.10

# Example Output:
# 4 Aug 13:32:15 ntpdate[5678]: adjust time server 192.168.56.10 offset +176490745.123456 sec

    • A large offset indicates a significant correction has been made.

  • Step-3: Confirm System Time is Corrected

    test2:~$ date

# Example Output:
# Mon Aug  4 13:32:16 UTC 2025

    • The time should now match the correct date/time from the NTP server.

  • Expected Result:

    • The system clock is reset from the incorrect manual value to the correct time.

    • No synchronization errors should appear in the output.

  • Step-4: Wireshark Capture

    Download wireshark capture

Verbose SNTP Query for Debugging

  • To view detailed NTP response fields using sntp in debug mode. This is useful for troubleshooting and analyzing time synchronization behavior at the protocol level.

  • Requirements:

    • Machine B (Client – test2) must have sntp installed.

    • Machine A (Server – test1) must be running and accessible at 192.168.56.10.

  • Step-1: Run SNTP in Debug Mode from Client

    test2:~$ sntp -d 192.168.56.10

# Example Output:
# sntp 4.2.8p15@1.3728-o (1)
# 2025-08-04 13:40:00.123456 (+0000) +0.000123 +/- 0.001234 secs
# server 192.168.56.10, port 123
# stratum 10, precision -23, leap 00, trust 000
# refid [127.127.1.0], delay 0.02567, dispersion 0.00345
# transmitted 2025-08-04 13:40:00.123456
# received   2025-08-04 13:40:00.125678

  • Expected Output Details:

    • Server IP and port used

    • Stratum level of the server

    • Offset and estimated delay

    • Leap indicator

    • Reference ID

    • Dispersion and precision

    • Timestamps for transmit/receive events

  • This mode is especially useful for debugging synchronization issues, analyzing NTP behavior, or validating server response fields manually.

  • Step-2: Wireshark Capture

    Download wireshark capture

DNS Resolution Failure Handling

  • To verify how sntp behaves when provided with an invalid or non-existent hostname, and confirm that proper DNS resolution errors are shown.

  • Requirements:

    • Machine B (Client – test2) must have sntp installed.

    • No specific NTP server is required, since the test targets DNS failure handling.

  • Step-1: Attempt to Query an Invalid Hostname

    test2:~$ sntp thisdoesnotexist.local

# Expected Output:
# sntp: Name or service not known

  • Expected Result:

    • The command should fail with a clear DNS resolution error.

    • No query attempt is made to any server.

    • Helpful for testing fallback or error handling mechanisms in time sync scripts.

  • This test confirms graceful failure and diagnostic output in cases of unreachable or misconfigured DNS names.

  • Step-2: Wireshark Capture (Optional — likely empty of NTP packets)

    Download wireshark capture

Sync with Multiple NTP Servers (Fallback Behavior)

  • To verify that sntp correctly handles multiple server inputs by skipping unreachable ones and falling back to the next available server.

  • Requirements:

    • Machine B (Client – test2) must have sntp installed.

    • Machine A (Server – test1) must be running NTP at 192.168.56.10.

    • At least one unreachable IP (e.g., 192.168.99.99) is included in the test.

  • Step-1: Run SNTP with Multiple Servers (First Invalid, Second Valid)

    test2:~$ sudo sntp -s 192.168.99.99 192.168.56.10

# Example Output:
# sntp: no response received from 192.168.99.99
# (then silently succeeds using 192.168.56.10)

  • Step-2: Check Time After Sync

    test2:~$ date

# Output should show correct current time synced from the valid server.

  • Expected Result:

    • sntp should attempt to contact 192.168.99.99 first.

    • Upon failure, it should continue to 192.168.56.10 and perform time sync.

    • No critical failure occurs; only a warning for the first server.

  • This test validates fallback behavior and fault tolerance when using multiple servers in SNTP.

  • Step-3: Wireshark Capture

    Download wireshark capture

  • Setup

Symmetric Active Packet

#

Protocol Packets

Description

Size(bytes)

1

Symmetric Active

A peer initiates the connection and sends requests.

48

LI (Leap Indicator)

Warns of an impending leap second.

2(bits)

VN (Version Number)

NTP version (e.g., 4 for NTPv4).

3(bits)

Mode

Set to 1 for symmetric active.

3(bits)

Stratum

Indicates the distance from the reference clock.

1

Poll

Maximum interval between messages (in log2 seconds).

1

Precision

Precision of the system clock (in log2 seconds).

1

Root Delay

Total round-trip delay to the reference clock.

4

Root Dispersion

Maximum error relative to the reference clock.

4

Reference ID

Identifier of the reference clock.

4

Reference Timestamp

Time when the system clock was last set or corrected.

8

Originate Timestamp

Time at which the request departed the client.

8

Receive Timestamp

Time at which the request arrived at the server.

8

Transmit Timestamp

Time at which the reply left the server.

8

Symmetric Passive Packet

#

Protocol Packets

Description

Size(bytes)

2

Symmetric Passive

A peer listens and responds to symmetric active requests.

48

LI (Leap Indicator)

Indicates if a leap second is to be inserted or deleted.

2(bits)

VN (Version Number)

NTP version number (e.g., 4 for NTPv4).

3(bits)

Mode

Set to 2 for symmetric passive.

3(bits)

Stratum

Indicates the distance from the reference clock.

1

Poll

Maximum interval between messages (log2 seconds).

1

Precision

Precision of the system clock (log2 seconds).

1

Root Delay

Total round-trip delay to the reference clock.

4

Root Dispersion

Maximum error relative to the reference clock.

4

Reference ID

Identifier of the reference clock.

4

Reference Timestamp

Time when the system clock was last set or corrected.

8

Originate Timestamp

Time at which the request left the client (copied from the request).

8

Receive Timestamp

Time at which the request was received by the server.

8

Transmit Timestamp

Time at which the reply left the server.

8

Client Packet

#

Protocol Packets

Description

Size(bytes)

3

Client

used when a device (the client) sends a request to a time server to synchronize its clock.

48

LI (Leap Indicator)

Warns of an upcoming leap second. Usually set to 0 by the client.

2(bits)

VN (Version Number)

NTP version number (e.g., 4 for NTPv4).

3(bits)

Mode

Set to 3 for client mode.

3(bits)

Stratum

Set to 0 by the client (server fills this in the response).

1

Poll

Maximum interval between messages (log2 seconds).

1

Precision

Precision of the client clock (log2 seconds).

1

Root Delay

Set to 0 by the client (server fills this in the response).

4

Root Dispersion

Set to 0 by the client (server fills this in the response).

4

Reference ID

Set to 0 by the client (server fills this in the response).

4

Reference Timestamp

Set to 0 by the client (server fills this in the response).

8

Originate Timestamp

Time when the client sent the request.

8

Receive Timestamp

Set to 0 by the client (server fills this in the response).

8

Transmit Timestamp

Time when the client sends the request .

8

Server Packet

#

Protocol Packets

Description

Size(bytes)

4

Server

used when a time server responds to a client’s request.

48

LI (Leap Indicator)

Indicates if a leap second is to be added or subtracted.

2(bits)

VN (Version Number)

NTP version number (e.g., 4 for NTPv4).

3(bits)

Mode

Set to 4 for server mode.

3(bits)

Stratum

Indicates the server’s distance from the reference clock (1 = primary server).

1

Poll

Maximum interval between successive messages (log2 seconds).

1

Precision

Precision of the server clock (log2 seconds).

1

Root Delay

Total round-trip delay to the reference clock.

4

Root Dispersion

Maximum error relative to the reference clock.

4

Reference ID

Identifier of the reference clock (e.g., IP address or ASCII code).

4

Reference Timestamp

Time when the server clock was last set or corrected.

8

Originate Timestamp

Copied from the client’s transmit timestamp (when the request was sent).

8

Receive Timestamp

Time when the server received the client’s request.

8

Transmit Timestamp

Time when the server sent the response back to the client.

8

Broadcast Packet

#

Protocol Packets

Description

Size(bytes)

5

Broadcast

The server sends time updates to a broadcast address.

48

LI (Leap Indicator)

Indicates if a leap second is to be inserted or deleted.

2(bits)

VN (Version Number)

NTP version number (e.g., 4 for NTPv4).

3(bits)

Mode

Set to 5 for broadcast mode.

3(bits)

Stratum

Indicates the servers distance from the reference clock.

1

Poll

Maximum interval between messages (log2 seconds).

1

Precision

Precision of the server clock (log2 seconds).

1

Root Delay

Total round-trip delay to the reference clock.

4

Root Dispersion

Maximum error relative to the reference clock.

4

Reference ID

Identifier of the reference clock.

4

Reference Timestamp

Time when the server clock was last set or corrected.

8

Originate Timestamp

Set to 0 in broadcast mode (no client request).

8

Receive Timestamp

Set to 0 in broadcast mode (no client request).

8

Transmit Timestamp

Time when the server sends the broadcast packet.

8

SNTP Control Message Packet

#

Protocol Packets

Description

Size(bytes)

6

NTP Control Message

used for monitoring, configuration, and control of NTP servers and peers

~24

LI (Leap Indicator)

Same as in standard NTP packets.

2(bits)

VN (Version Number)

NTP version number.

3(bits)

Mode

Set to 6 for control messages.

3(bits)

Response Bit (R)

Set to 1 if the message is a response.

1(bit)

Error Bit (E)

Set to 1 if an error occurred.

1(bit)

More Bit (M)

Set to 1 if more data follows in additional packets.

1(bit) Remaining 5 bits are reserved

Operation Code (OpCode)

Specifies the type of control operation (e.g., read status, write variables).

1

Sequence Number

Used to match requests and responses.

2

Status

Server status word (e.g., stratum, leap indicator, etc.).

2

Association ID

Identifies the peer association (0 for system variables).

2

Offset

Offset into the data field (for fragmented messages).

2

count

Number of octets in the data field.

2

S.no

Use Case

Description

1

IoT Devices

SNTP is ideal for Internet of Things (IoT) devices like smart thermostats, sensors, and home automation systems that need basic time synchronization without the overhead of full NTP.

2

Consumer Electronics

Devices such as smart TVs, DVRs, and gaming consoles use SNTP to maintain accurate time for logs, updates, and scheduled recordings.

3

Embedded Systems

Microcontrollers and embedded systems with limited resources use SNTP for lightweight time synchronization.

4

Small Office Networks

In small networks without a dedicated time server, SNTP provides sufficient accuracy for basic coordination and logging.

5

Routers and Network Devices

Many routers and switches use SNTP to timestamp logs and events, aiding in diagnostics and monitoring.

6

Digital Signage Systems

SNTP ensures that digital displays show accurate time and synchronize scheduled content playback.

7

Point of Sale (POS) Systems

Retail systems use SNTP to timestamp transactions accurately, which is crucial for auditing and reporting.

8

Industrial Automation

SNTP is used in factory equipment and control systems where approximate time accuracy is sufficient for operations.

S.no

Feature

Description

1

Simplicity

SNTP is a lightweight protocol with minimal configuration, making it easy to implement in devices with limited resources.

2

Time Synchronization

Provides basic synchronization of system clocks with a reference time source, ensuring devices maintain reasonably accurate time.

3

UDP-Based Communication

Uses UDP (port 123) for communication, which is faster and requires fewer resources than TCP.

4

Low Overhead

Designed for environments where full NTP functionality is unnecessary, reducing processing and memory requirements.

5

Compatibility with NTP Servers

SNTP clients can communicate with standard NTP servers, allowing integration into existing time synchronization infrastructures.

6

Support for IPv4 and IPv6

Modern SNTP versions support both IPv4 and IPv6, ensuring compatibility with current network standards.

7

One-Way Communication

Typically uses a simple request-response model without complex clock discipline algorithms.

8

Periodic Updates

Devices can periodically query SNTP servers to maintain time accuracy over long periods.

Simplicity - Testcases

#

Test Case

Description

Expected Result

1

Start SNTP client with default config

Minimal setup

Time synchronized

2

Start SNTP client with IP address

Direct server IP

Time synchronized

3

Start SNTP client with hostname

DNS resolution

Time synchronized

4

Use SNTP on embedded device

Limited resources

Time synchronized

5

Use SNTP on microcontroller

No OS

Time synchronized

6

Use SNTP on IoT sensor

Low-power device

Time synchronized

7

Use SNTP on smart plug

Minimal firmware

Time synchronized

8

Use SNTP on smart light

Lightweight stack

Time synchronized

9

Use SNTP on Raspberry Pi

Simple Linux setup

Time synchronized

10

Use SNTP on Arduino with Ethernet

Basic connectivity

Time synchronized

11

Use SNTP on ESP32

Wi-Fi microcontroller

Time synchronized

12

Use SNTP with no authentication

Basic SNTP

Time synchronized

13

Use SNTP with no encryption

Lightweight protocol

Time synchronized

14

Use SNTP with UDP

Default transport

Time synchronized

15

Use SNTP with IPv4

Standard IP

Time synchronized

16

Use SNTP with IPv6

Modern IP

Time synchronized

17

Use SNTP with single server

One source

Time synchronized

18

Use SNTP with fallback server

Primary fails

Secondary used

19

Use SNTP with DHCP option 42

Auto server config

Time synchronized

20

Use SNTP with static IP config

Manual setup

Time synchronized

21

Use SNTP with minimal memory

Low RAM usage

Time synchronized

22

Use SNTP with minimal CPU

Low processing power

Time synchronized

23

Use SNTP with no logging

Silent operation

Time synchronized

24

Use SNTP with basic logging

Simple output

Time synchronized

25

Use SNTP with no GUI

CLI or headless

Time synchronized

26

Use SNTP with no config file

Hardcoded server

Time synchronized

27

Use SNTP with config file

Simple format

Time synchronized

28

Use SNTP with retry logic

Server unreachable

Retry succeeds

29

Use SNTP with timeout

No response

Retry or fail

30

Use SNTP with low bandwidth

Constrained network

Time synchronized

31

Use SNTP with high latency

Satellite link

Time synchronized

32

Use SNTP with packet loss

Unreliable network

Retry succeeds

33

Use SNTP with firewall open

Port 123 open

Time synchronized

34

Use SNTP with firewall blocked

Port 123 closed

Sync fails

35

Use SNTP with SNTP server simulator

Test environment

Time synchronized

36

Use SNTP with public NTP server

e.g., pool.ntp.org

Time synchronized

37

Use SNTP with local NTP server

LAN sync

Time synchronized

38

Use SNTP with no DNS

IP-only config

Time synchronized

39

Use SNTP with DNS

Hostname resolution

Time synchronized

40

Use SNTP with system clock drift

Inaccurate clock

Time corrected

41

Use SNTP after reboot

Cold start

Time synchronized

42

Use SNTP after network reconnect

Interface up

Time synchronized

43

Use SNTP with scheduled sync

Periodic update

Time synchronized

44

Use SNTP with manual trigger

On-demand sync

Time synchronized

45

Use SNTP with logging to serial

Microcontroller debug

Time output logged

46

Use SNTP with minimal firmware

Tiny footprint

Time synchronized

47

Use SNTP with real-time OS

RTOS support

Time synchronized

48

Use SNTP with Linux busybox

Lightweight distro

Time synchronized

49

Use SNTP with Windows IoT

Embedded Windows

Time synchronized

50

Use SNTP with no user interaction

Fully automated

Time synchronized

Time Synchronization - Testcases

#

Test Case

Description

Expected Result

1

Sync with public SNTP server

Use pool.ntp.org

Time synchronized

2

Sync with local SNTP server

LAN-based server

Time synchronized

3

Sync with stratum 1 server

High-accuracy source

Time synchronized

4

Sync with stratum 2 server

Intermediate source

Time synchronized

5

Sync with unreachable server

Server offline

Sync fails

6

Sync with invalid server address

Malformed hostname

Sync fails

7

Sync with fallback server

Primary fails

Secondary used

8

Sync with GPS-based NTP server

Hardware time source

Time synchronized

9

Sync with DHCP-provided server

Option 42

Time synchronized

10

Sync with static IP server

Manual config

Time synchronized

11

Sync with IPv4 server

Standard IP

Time synchronized

12

Sync with IPv6 server

Modern IP

Time synchronized

13

Sync over Wi-Fi

Wireless network

Time synchronized

14

Sync over Ethernet

Wired network

Time synchronized

15

Sync over mobile network

4G/5G

Time synchronized

16

Sync over satellite link

High latency

Time synchronized

17

Sync with high latency

Delayed response

Time adjusted

18

Sync with packet loss

Unreliable network

Retry succeeds

19

Sync with firewall open

Port 123 open

Time synchronized

20

Sync with firewall blocked

Port 123 closed

Sync fails

21

Sync after reboot

Cold start

Time synchronized

22

Sync after network reconnect

Interface up

Time synchronized

23

Sync after long offline period

Clock drifted

Time corrected

24

Sync with system clock drift

Hardware inaccuracy

Time corrected

25

Sync with scheduled interval

Periodic update

Time synchronized

26

Sync with manual trigger

On-demand sync

Time synchronized

27

Sync with SNTP client on Linux

Lightweight daemon

Time synchronized

28

Sync with SNTP client on Windows

Built-in or third-party

Time synchronized

29

Sync with SNTP client on macOS

System time service

Time synchronized

30

Sync with SNTP client on IoT device

Embedded system

Time synchronized

31

Sync with SNTP client on microcontroller

Minimal firmware

Time synchronized

32

Sync with SNTP client on VM

Virtualized environment

Time synchronized

33

Sync with SNTP client on container

Docker/LXC

Time synchronized

34

Sync with SNTP client on mobile device

Smartphone

Time synchronized

35

Sync with SNTP client on smart TV

Consumer device

Time synchronized

36

Sync with SNTP client on smart meter

Utility device

Time synchronized

37

Sync with SNTP client on smart camera

Surveillance device

Time synchronized

38

Sync with SNTP client on POS terminal

Retail system

Time synchronized

39

Sync with SNTP client on ATM

Banking system

Time synchronized

40

Sync with SNTP client on SCADA system

Industrial control

Time synchronized

41

Sync with SNTP client on wearable

Smartwatch

Time synchronized

42

Sync with SNTP client on e-reader

Kindle or similar

Time synchronized

43

Sync with SNTP client on smart display

Google Nest, Echo Show

Time synchronized

44

Sync with SNTP client on firewall appliance

Security device

Time synchronized

45

Sync with SNTP client on load balancer

Network appliance

Time synchronized

46

Sync with SNTP client on NAS

Storage device

Time synchronized

47

Sync with SNTP client on printer

Network printer

Time synchronized

48

Sync with SNTP client on router

Network device

Time synchronized

49

Sync with SNTP client on switch

Layer 2 device

Time synchronized

50

Sync with SNTP client on server

General-purpose system

Time synchronized

UDP-Based Communication - Testcases

#

Test Case

Description

Expected Result

1

Sync with public SNTP server

Use pool.ntp.org

Time synchronized

2

Sync with local SNTP server

LAN-based server

Time synchronized

3

Sync with stratum 1 server

High-accuracy source

Time synchronized

4

Sync with stratum 2 server

Intermediate source

Time synchronized

5

Sync with unreachable server

Server offline

Sync fails

6

Sync with invalid server address

Malformed hostname

Sync fails

7

Sync with fallback server

Primary fails

Secondary used

8

Sync with GPS-based NTP server

Hardware time source

Time synchronized

9

Sync with DHCP-provided server

Option 42

Time synchronized

10

Sync with static IP server

Manual config

Time synchronized

11

Sync with IPv4 server

Standard IP

Time synchronized

12

Sync with IPv6 server

Modern IP

Time synchronized

13

Sync over Wi-Fi

Wireless network

Time synchronized

14

Sync over Ethernet

Wired network

Time synchronized

15

Sync over mobile network

4G/5G

Time synchronized

16

Sync over satellite link

High latency

Time synchronized

17

Sync with high latency

Delayed response

Time adjusted

18

Sync with packet loss

Unreliable network

Retry succeeds

19

Sync with firewall open

Port 123 open

Time synchronized

20

Sync with firewall blocked

Port 123 closed

Sync fails

21

Sync after reboot

Cold start

Time synchronized

22

Sync after network reconnect

Interface up

Time synchronized

23

Sync after long offline period

Clock drifted

Time corrected

24

Sync with system clock drift

Hardware inaccuracy

Time corrected

25

Sync with scheduled interval

Periodic update

Time synchronized

26

Sync with manual trigger

On-demand sync

Time synchronized

27

Sync with SNTP client on Linux

Lightweight daemon

Time synchronized

28

Sync with SNTP client on Windows

Built-in or third-party

Time synchronized

29

Sync with SNTP client on macOS

System time service

Time synchronized

30

Sync with SNTP client on IoT device

Embedded system

Time synchronized

31

Sync with SNTP client on microcontroller

Minimal firmware

Time synchronized

32

Sync with SNTP client on VM

Virtualized environment

Time synchronized

33

Sync with SNTP client on container

Docker/LXC

Time synchronized

34

Sync with SNTP client on mobile device

Smartphone

Time synchronized

35

Sync with SNTP client on smart TV

Consumer device

Time synchronized

36

Sync with SNTP client on smart meter

Utility device

Time synchronized

37

Sync with SNTP client on smart camera

Surveillance device

Time synchronized

38

Sync with SNTP client on POS terminal

Retail system

Time synchronized

39

Sync with SNTP client on ATM

Banking system

Time synchronized

40

Sync with SNTP client on SCADA system

Industrial control

Time synchronized

41

Sync with SNTP client on wearable

Smartwatch

Time synchronized

42

Sync with SNTP client on e-reader

Kindle or similar

Time synchronized

43

Sync with SNTP client on smart display

Google Nest, Echo Show

Time synchronized

44

Sync with SNTP client on firewall appliance

Security device

Time synchronized

45

Sync with SNTP client on load balancer

Network appliance

Time synchronized

46

Sync with SNTP client on NAS

Storage device

Time synchronized

47

Sync with SNTP client on printer

Network printer

Time synchronized

48

Sync with SNTP client on router

Network device

Time synchronized

49

Sync with SNTP client on switch

Layer 2 device

Time synchronized

50

Sync with SNTP client on server

General-purpose system

Time synchronized

Low Overhead - Testcases

#

Test Case

Description

Expected Result

1

Run SNTP on low-memory device

256KB RAM microcontroller

Time synchronized

2

Run SNTP on embedded Linux

BusyBox environment

Time synchronized

3

Run SNTP on battery-powered device

Energy-efficient sync

Time synchronized

4

Run SNTP on real-time OS

RTOS like FreeRTOS

Time synchronized

5

Run SNTP on headless device

No GUI or shell

Time synchronized

6

Run SNTP on minimal firmware

No OS, bare-metal

Time synchronized

7

Run SNTP on constrained IoT node

Low CPU and RAM

Time synchronized

8

Run SNTP on sensor module

Periodic sync

Time synchronized

9

Run SNTP on BLE device

Bluetooth-only comms

Time synchronized

10

Run SNTP on Zigbee device

Mesh network

Time synchronized

11

Run SNTP on LoRaWAN device

Long-range, low-power

Time synchronized

12

Run SNTP on solar-powered device

Limited energy budget

Time synchronized

13

Run SNTP on e-ink display

Low refresh rate

Time synchronized

14

Run SNTP on wearable

Smartwatch or band

Time synchronized

15

Run SNTP on smart tag

Asset tracking

Time synchronized

16

Run SNTP on smart plug

Home automation

Time synchronized

17

Run SNTP on smart bulb

Minimal firmware

Time synchronized

18

Run SNTP on smart thermostat

HVAC control

Time synchronized

19

Run SNTP on smart lock

Secure sync

Time synchronized

20

Run SNTP on smart speaker

Voice assistant

Time synchronized

21

Run SNTP on smart camera

Motion detection

Time synchronized

22

Run SNTP on smart meter

Utility monitoring

Time synchronized

23

Run SNTP on smart fridge

Appliance sync

Time synchronized

24

Run SNTP on smart oven

Cooking timer

Time synchronized

25

Run SNTP on smart irrigation system

Scheduled watering

Time synchronized

26

Run SNTP on smart mirror

Display time

Time synchronized

27

Run SNTP on smart scale

Health tracking

Time synchronized

28

Run SNTP on smart toothbrush

Usage logging

Time synchronized

29

Run SNTP on smart toy

Interactive play

Time synchronized

30

Run SNTP on smart glasses

AR overlay

Time synchronized

31

Run SNTP on smart pen

Note timestamping

Time synchronized

32

Run SNTP on smart wallet

Anti-theft sync

Time synchronized

33

Run SNTP on smart helmet

Safety alerts

Time synchronized

34

Run SNTP on smart bike computer

Ride tracking

Time synchronized

35

Run SNTP on smart doorbell

Event logging

Time synchronized

36

Run SNTP on smart vacuum

Cleaning schedule

Time synchronized

37

Run SNTP on smart projector

Auto power-on

Time synchronized

38

Run SNTP on smart coffee machine

Brew timer

Time synchronized

39

Run SNTP on smart fan

Climate control

Time synchronized

40

Run SNTP on smart bed

Sleep tracking

Time synchronized

41

Run SNTP on smart pet feeder

Feeding schedule

Time synchronized

42

Run SNTP on smart aquarium

Lighting/tank control

Time synchronized

43

Run SNTP on smart air purifier

Filter cycle

Time synchronized

44

Run SNTP on smart curtain

Light automation

Time synchronized

45

Run SNTP on smart switch

Power control

Time synchronized

46

Run SNTP on smart router

Network sync

Time synchronized

47

Run SNTP on smart TV

Display clock

Time synchronized

48

Run SNTP on smart printer

Job timestamping

Time synchronized

49

Run SNTP on smart NAS

File sync

Time synchronized

50

Run SNTP on smart server

Lightweight sync

Time synchronized

Compatibility with NTP servers - Testcases

#

Test Case

Description

Expected Result

1

Connect to NTPv3 server

Legacy server compatibility

Time synchronized

2

Connect to NTPv4 server

Modern server compatibility

Time synchronized

3

Connect to pool.ntp.org

Public NTP pool

Time synchronized

4

Connect to time.google.com

Google NTP server

Time synchronized

5

Connect to time.windows.com

Microsoft NTP server

Time synchronized

6

Connect to time.apple.com

Apple NTP server

Time synchronized

7

Connect to time.cloudflare.com

Cloudflare NTP server

Time synchronized

8

Connect to stratum 1 NTP server

High-precision source

Time synchronized

9

Connect to stratum 2 NTP server

Intermediate source

Time synchronized

10

Connect to ISP-provided NTP server

Local provider

Time synchronized

11

Connect to university NTP server

Academic network

Time synchronized

12

Connect to government NTP server

National time authority

Time synchronized

13

Connect to corporate NTP server

Enterprise environment

Time synchronized

14

Connect to NTP server via IPv4

Standard IP

Time synchronized

15

Connect to NTP server via IPv6

Modern IP

Time synchronized

16

Connect to NTP server with DNS name

Hostname resolution

Time synchronized

17

Connect to NTP server with static IP

Direct IP access

Time synchronized

18

Connect to NTP server with authentication

Secure mode

Time synchronized

19

Connect to NTP server without authentication

Open mode

Time synchronized

20

Connect to NTP server with leap second support

Time accuracy

Time synchronized

21

Connect to NTP server with jitter

Network instability

Time synchronized

22

Connect to NTP server with delay

Latency tolerance

Time synchronized

23

Connect to NTP server with offset

Time correction

Time synchronized

24

Connect to NTP server with packet loss

Retry mechanism

Time synchronized

25

Connect to NTP server with firewall open

Port 123 open

Time synchronized

26

Connect to NTP server with firewall blocked

Port 123 blocked

Sync fails

27

Connect to NTP server on LAN

Local network

Time synchronized

28

Connect to NTP server on WAN

Internet-based

Time synchronized

29

Connect to NTP server on VPN

Encrypted tunnel

Time synchronized

30

Connect to NTP server on proxy

Indirect routing

Time synchronized

31

Connect to NTP server on cloud

AWS/GCP/Azure

Time synchronized

32

Connect to NTP server on hybrid cloud

Mixed infra

Time synchronized

33

Connect to NTP server on edge device

Edge computing

Time synchronized

34

Connect to NTP server on container

Dockerized service

Time synchronized

35

Connect to NTP server on VM

Virtual machine

Time synchronized

36

Connect to NTP server on physical server

Bare-metal

Time synchronized

37

Connect to NTP server on mobile device

Smartphone/tablet

Time synchronized

38

Connect to NTP server on IoT device

Embedded system

Time synchronized

39

Connect to NTP server on Windows

OS compatibility

Time synchronized

40

Connect to NTP server on Linux

OS compatibility

Time synchronized

41

Connect to NTP server on macOS

OS compatibility

Time synchronized

42

Connect to NTP server on BSD

OS compatibility

Time synchronized

43

Connect to NTP server on router

Network device

Time synchronized

44

Connect to NTP server on switch

Layer 2 device

Time synchronized

45

Connect to NTP server on firewall

Security appliance

Time synchronized

46

Connect to NTP server on NAS

Storage device

Time synchronized

47

Connect to NTP server on printer

Peripheral device

Time synchronized

48

Connect to NTP server on SCADA system

Industrial control

Time synchronized

49

Connect to NTP server on ATM

Banking system

Time synchronized

50

Connect to NTP server on POS terminal

Retail system

Time synchronized

Support for IPv4 and IPv6 - Testcases

#

Test Case

Description

Expected Result

1

Sync using IPv4 address

Direct IPv4 server

Time synchronized

2

Sync using IPv6 address

Direct IPv6 server

Time synchronized

3

Sync using dual-stack server

Supports both IP versions

Time synchronized

4

Sync using IPv4 DNS resolution

Hostname resolves to IPv4

Time synchronized

5

Sync using IPv6 DNS resolution

Hostname resolves to IPv6

Time synchronized

6

Sync using IPv4-only client

No IPv6 stack

Time synchronized

7

Sync using IPv6-only client

No IPv4 stack

Time synchronized

8

Sync using NAT IPv4

Behind NAT

Time synchronized

9

Sync using NAT64 IPv6

IPv6 to IPv4 translation

Time synchronized

10

Sync using IPv4 over VPN

Encrypted IPv4 tunnel

Time synchronized

11

Sync using IPv6 over VPN

Encrypted IPv6 tunnel

Time synchronized

12

Sync using IPv4 over proxy

Indirect routing

Time synchronized

13

Sync using IPv6 over proxy

Indirect routing

Time synchronized

14

Sync using IPv4 on LAN

Local IPv4 network

Time synchronized

15

Sync using IPv6 on LAN

Local IPv6 network

Time synchronized

16

Sync using IPv4 on WAN

Internet IPv4

Time synchronized

17

Sync using IPv6 on WAN

Internet IPv6

Time synchronized

18

Sync using IPv4 on mobile network

4G IPv4

Time synchronized

19

Sync using IPv6 on mobile network

5G IPv6

Time synchronized

20

Sync using IPv4 on satellite link

High latency

Time synchronized

21

Sync using IPv6 on satellite link

High latency

Time synchronized

22

Sync using IPv4 with packet loss

Retry mechanism

Time synchronized

23

Sync using IPv6 with packet loss

Retry mechanism

Time synchronized

24

Sync using IPv4 with firewall open

Port 123 open

Time synchronized

25

Sync using IPv6 with firewall open

Port 123 open

Time synchronized

26

Sync using IPv4 with firewall blocked

Port 123 blocked

Sync fails

27

Sync using IPv6 with firewall blocked

Port 123 blocked

Sync fails

28

Sync using IPv4 on Windows

OS compatibility

Time synchronized

29

Sync using IPv6 on Windows

OS compatibility

Time synchronized

30

Sync using IPv4 on Linux

OS compatibility

Time synchronized

31

Sync using IPv6 on Linux

OS compatibility

Time synchronized

32

Sync using IPv4 on macOS

OS compatibility

Time synchronized

33

Sync using IPv6 on macOS

OS compatibility

Time synchronized

34

Sync using IPv4 on IoT device

Embedded IPv4 stack

Time synchronized

35

Sync using IPv6 on IoT device

Embedded IPv6 stack

Time synchronized

36

Sync using IPv4 on VM

Virtualized IPv4

Time synchronized

37

Sync using IPv6 on VM

Virtualized IPv6

Time synchronized

38

Sync using IPv4 on container

Docker IPv4

Time synchronized

39

Sync using IPv6 on container

Docker IPv6

Time synchronized

40

Sync using IPv4 on router

Network device

Time synchronized

41

Sync using IPv6 on router

Network device

Time synchronized

42

Sync using IPv4 on NAS

Storage device

Time synchronized

43

Sync using IPv6 on NAS

Storage device

Time synchronized

44

Sync using IPv4 on smart TV

Consumer device

Time synchronized

45

Sync using IPv6 on smart TV

Consumer device

Time synchronized

46

Sync using IPv4 on printer

Peripheral device

Time synchronized

47

Sync using IPv6 on printer

Peripheral device

Time synchronized

48

Sync using IPv4 on firewall appliance

Security device

Time synchronized

49

Sync using IPv6 on firewall appliance

Security device

Time synchronized

50

Sync using IPv4 and IPv6 fallback

One fails, other used

Time synchronized

One-Way Communication - Testcases

#

Test Case

Description

Expected Result

1

Send SNTP request to NTP server

Basic one-way query

Time received

2

Receive SNTP response

Server reply received

Time updated

3

No response from server

Timeout scenario

Sync fails

4

Delayed response from server

High latency

Time adjusted

5

Response with invalid timestamp

Corrupted data

Sync fails

6

Response with future timestamp

Time ahead

Time adjusted

7

Response with past timestamp

Time behind

Time adjusted

8

Response with zero timestamp

Invalid data

Sync fails

9

Response with leap second flag

Special case

Time synchronized

10

Response with stratum 0

Invalid source

Sync rejected

11

Response with stratum 1

High-accuracy source

Time synchronized

12

Response with stratum 15

Low-accuracy source

Time synchronized

13

Response with mode 4 (server)

Valid mode

Time synchronized

14

Response with mode 5 (broadcast)

Ignored by client

No sync

15

Response with mode 3 (client)

Invalid response

Sync fails

16

Response with root delay > threshold

High delay

Sync rejected

17

Response with root dispersion > threshold

Unstable source

Sync rejected

18

Response with valid originate timestamp

Request matched

Time synchronized

19

Response with mismatched originate timestamp

Spoofed response

Sync rejected

20

Response with correct version number

SNTP v4

Time synchronized

21

Response with unsupported version

SNTP v1

Sync fails

22

Response with correct transmit timestamp

Valid time

Time synchronized

23

Response with missing transmit timestamp

Incomplete packet

Sync fails

24

Response with correct reference ID

Valid server

Time synchronized

25

Response with invalid reference ID

Unknown source

Sync rejected

26

Response with symmetric mode

Not expected

Sync ignored

27

Response with broadcast mode

Not supported

Sync ignored

28

Response with kiss-o’-death code

Rate limited

Sync paused

29

Response with authentication not required

Open server

Time synchronized

30

Response with authentication required

No key

Sync fails

31

Response with MAC mismatch

Integrity check failed

Sync rejected

32

Response with valid MAC

Integrity verified

Time synchronized

33

Response with spoofed IP

Source mismatch

Sync rejected

34

Response with duplicate packet

Retransmission

Time synchronized

35

Response with reordered packets

Out-of-order

Time synchronized

36

Response with dropped packet

No reply

Retry triggered

37

Response with malformed packet

Parsing error

Sync fails

38

Response with correct UDP checksum

Valid packet

Time synchronized

39

Response with incorrect UDP checksum

Corrupted packet

Sync rejected

40

Response with correct port (123)

Standard port

Time synchronized

41

Response from non-standard port

Unexpected source

Sync rejected

42

Response with valid delay calculation

Round-trip delay

Time adjusted

43

Response with invalid delay calculation

Negative delay

Sync rejected

44

Response with valid offset calculation

Clock offset

Time adjusted

45

Response with invalid offset calculation

Out-of-range

Sync rejected

46

Response with server timestamp drift

Minor drift

Time adjusted

47

Response with server timestamp jump

Major drift

Sync rejected

48

Response with server reboot

New reference ID

Time synchronized

49

Response with server under load

Delayed response

Time adjusted

50

Response with server in maintenance

No response

Sync fails

Periodic Updates - Testcases

#

Test Case

Description

Expected Result

1

Periodic sync every 1 minute

High-frequency updates

Time synchronized

2

Periodic sync every 5 minutes

Frequent updates

Time synchronized

3

Periodic sync every 15 minutes

Moderate frequency

Time synchronized

4

Periodic sync every 1 hour

Standard interval

Time synchronized

5

Periodic sync every 6 hours

Low frequency

Time synchronized

6

Periodic sync every 24 hours

Daily update

Time synchronized

7

Periodic sync with random jitter

Avoid sync storms

Time synchronized

8

Periodic sync with exponential backoff

On failure

Time synchronized

9

Periodic sync with retry on failure

Resilient sync

Time synchronized

10

Periodic sync with fallback server

Primary fails

Secondary used

11

Periodic sync with time drift correction

Gradual adjustment

Time corrected

12

Periodic sync with leap second handling

Special case

Time synchronized

13

Periodic sync with daylight saving change

Time zone shift

Time adjusted

14

Periodic sync with network loss

Offline period

Sync resumes

15

Periodic sync after reboot

Cold start

Time synchronized

16

Periodic sync after sleep mode

Wake-up event

Time synchronized

17

Periodic sync after firmware update

System restart

Time synchronized

18

Periodic sync with low battery

Power-saving mode

Time synchronized

19

Periodic sync with high CPU load

Background task

Time synchronized

20

Periodic sync with low memory

Lightweight operation

Time synchronized

21

Periodic sync on mobile network

4G/5G

Time synchronized

22

Periodic sync on Wi-Fi

Wireless LAN

Time synchronized

23

Periodic sync on Ethernet

Wired LAN

Time synchronized

24

Periodic sync on satellite link

High latency

Time synchronized

25

Periodic sync on VPN

Encrypted tunnel

Time synchronized

26

Periodic sync on proxy

Indirect routing

Time synchronized

27

Periodic sync on IPv4

Standard IP

Time synchronized

28

Periodic sync on IPv6

Modern IP

Time synchronized

29

Periodic sync on dual-stack

IPv4/IPv6 fallback

Time synchronized

30

Periodic sync on container

Dockerized app

Time synchronized

31

Periodic sync on VM

Virtual machine

Time synchronized

32

Periodic sync on IoT device

Embedded system

Time synchronized

33

Periodic sync on mobile device

Smartphone/tablet

Time synchronized

34

Periodic sync on smart TV

Consumer device

Time synchronized

35

Periodic sync on smart meter

Utility device

Time synchronized

36

Periodic sync on smart camera

Surveillance device

Time synchronized

37

Periodic sync on POS terminal

Retail system

Time synchronized

38

Periodic sync on ATM

Banking system

Time synchronized

39

Periodic sync on SCADA system

Industrial control

Time synchronized

40

Periodic sync on NAS

Storage device

Time synchronized

41

Periodic sync on router

Network device

Time synchronized

42

Periodic sync on firewall

Security appliance

Time synchronized

43

Periodic sync on printer

Peripheral device

Time synchronized

44

Periodic sync on wearable

Smartwatch

Time synchronized

45

Periodic sync on e-reader

Kindle or similar

Time synchronized

46

Periodic sync on smart display

Google Nest, Echo Show

Time synchronized

47

Periodic sync on load balancer

Network appliance

Time synchronized

48

Periodic sync on server

General-purpose system

Time synchronized

49

Periodic sync with logging enabled

Track sync events

Logs updated

50

Periodic sync with alert on failure

Notification triggered

Alert sent

  • Reference links