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Simple Network Time Protocol (SNTP) is a simplified version of Network Time Protocol(NTP). This module describes how to configure Simple Network Time Protocol on Cisco devices.
Simple Network Time Protocol (SNTP) and Network Time Protocol (NTP) cannot coexist on the same machine as they use the same port. This means that these two services cannot be configured on the system at the same time.
Support for IPv6 addresses is available only if the image supports IPv6 addressing.
Simple Network Time Protocol (SNTP) is a simplified, client-only version of NTP. SNTP can receive only the time from NTP servers; it cannot be used to provide time services to other systems.
SNTP typically provides time within 100 milliseconds of the accurate time, but it does not provide the complex filtering and statistical mechanisms of NTP. In addition, SNTP does not authenticate traffic, although you can configure extended access lists to provide some protection. An SNTP client is more vulnerable to servers that have unexpected behavior than an NTP client, and should be used only in situations where strong authentication is not required.
You can configure SNTP to request and accept packets from configured servers or to accept NTP broadcast packets from any source. When multiple sources are sending NTP packets, the server with the best stratum is selected. (See the Network Time Protocol section on page 3 for a description of strata.) If multiple servers are at the same stratum, a configured server is preferred over a broadcast server. If multiple servers pass both tests, the first one to send a time packet is selected. SNTP will choose a new server only if it stops receiving packets from the currently selected server, or if a better server (according to the criteria described) is discovered.
Simple Network Time Protocol (SNTP) is a simplified version of Network Time Protocol (SNTP). This module describes how to configure SNTP on Cisco devices.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
enable Example: |
Enables privileged EXEC mode.
|
|
Step 2 |
configure terminal Example: |
Enters global configuration mode. |
|
Step 3 |
sntp authenticate Example: |
Enables the SNTP Authentication feature. |
|
Step 4 |
sntp authentication-key number md5 key Example: |
Defines authentication keys.
|
|
Step 5 |
sntp trusted-key key-number [- end-key] Example: |
Defines trusted authentication keys.
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|
Step 6 |
sntp server ip-address key key-id Example: |
Allows the software clock to be synchronized by an SNTP time server. |
|
Step 7 |
end Example: |
Exits global configuration mode and returns to privileged EXEC mode. |
To verify and troubleshoot Simple Network Time Protocol configuration, use the following commands.
|
Step 1 |
enable Example:Enables privileged EXEC mode.
|
|
Step 2 |
debug sntp packets [detail] Example:Displays the NTP packet sent and received along with the SNTP packet fields. |
|
Step 3 |
debug sntp select Example:Displays the SNTP server selection for IPv4 and IPv6 servers. |
|
Step 4 |
show sntp Example:Displays information about SNTP available in Cisco devices. |
clock timezone PST -8
clock summer-time PDT recurring
sntp update-calendar
sntp server 192.168.13.57
sntp server 192.168.11.58
interface Ethernet 0/0
sntp broadcast|
Related Topic |
Document Title |
|---|---|
|
Basic System Management commands |
|
|
NTP4 in IPv6 |
Cisco IOS Basic System Management Guide |
|
IP extended access lists |
Cisco IOS IP Addressing Configuration Guide |
|
IPX extended access lists |
Novell IPX Configuration Guide |
|
NTP package vulnerability |
Network Time Protocol Package Remote Message Loop Denial of Service Vulnerability |
|
Cisco IOS and NX-OS software releases |
White Paper: Cisco IOS and NX-OS Software Reference Guide |
|
Standard/RFCs |
Title |
|---|---|
|
RFC 1305 |
Network Time Protocol (Version 3) Specification, Implementation and Analysis |
|
Description |
Link |
|---|---|
|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.|
Feature Name |
Releases |
Feature Information |
|---|---|---|
|
Simple Network Time Protocol |
Simple Network Time Protocol (SNTP) is a simplified version of Network Time Protocol(NTP). This module describes how to configure Simple Network Time Protocol on Cisco devices. The following commands were introduced or modified: sntp server, sntp authenticate, sntp authentication-key, sntp multicast, sntp trusted-key . |
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