Network Time Protocol (NTP) is a client-server protocol. A client computer periodically requests timing information from a NTP server. The server responds to requests with timing information that the client can then use for synchronization purposes. Update NTP server in Linux Application linux February 11, 2018 Leave a comment We use the NTP protocol to sync the time of servers,network devices, client PC’s with our local time zone to keep the correct time over the network. Windows has taken this into account. The Network Time Protocol (NTP) service has been built into Windows since Windows XP and Windows Server 2003, and most Unix and Linux implementations have supported NTP since they were first built. I am not interested in synchronizing my local clock with the remote server. I only want to query it and print the result. I would have assumed that there is a port of ntpq for Windows, but was unable to find any. All other NTP clients I could find, they always want to install themselves as a service or make it otherwise clear that they want to synchronize my local time.
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![]() ContentsIntroduction
This document describes the use of debugs in order to troubleshoot Network Time Protocol (NTP) issues, as well as the output from key show ntp commands.
NTP show Commands
Before you look at the cause of NTP problems, you should understand the use of and output from these commands:
Note: Use the Command Lookup Tool (registered customers only) in order to obtain more information on the commands used in this section.
Note: The Output Interpreter Tool (registered customers only) supports certain show commands. Use the Output Interpreter Tool in order to view an analysis of show command output.
show ntp association
An NTP association can be a peer association (one system is willing to synchronize to the other system or to allow the other system to synchronize to it) or a server association (only one system synchronizes to the other system and not the other way around).
This is an example of output from the show ntp association command:
show ntp association detail
This is an example of output from the show ntp association detail command: Full version windows 10 download.
Terms already defined in the show ntp association section are not repeated.
show ntp status
This is an example of output from the show ntp status command:
Terms already defined in the show ntp association section or the show ntp association details section are not repeated.
Troubleshooting NTP with Debugs
Some of the most common causes of NTP issues are:
Important debug commands that help isolate the cause of these issues include:
The next sections illustrate the use of debugs in order to resolve these common issues.
Note: Use the Command Lookup Tool (registered customers only) in order to obtain more information on the commands used in this section.
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Note: Refer to Important Information on Debug Commands before you use debug commands.
NTP Packets Not Received
Use the debug ip packet command in order to check if NTP packets are received and sent. Since debug output can be chatty, you can limit debug output with the use of Access Control Lists (ACLs). NTP uses User Datagram Protocol (UDP) port 123.
This example output indicates that packets are not being sent:
Once you confirm that NTP packets are not received, you should:
NTP Packets Not Processed
With both debug ip packet and debug ntp packets commands enabled, you can see the packets that are being received and transmitted, and you can see that NTP is acting upon those packets. For every NTP packet received (as shown by debug ip packet), there is a corresponding entry generated by debug ntp packets.
This is the debug output when the NTP process works on received packets:
This is an example where NTP does not work on received packets. Although NTP packets are received (as shown by debug ip packets), the NTP process does not act on them. For NTP packets that are sent out, a corresponding debug ntp packets output is present, because the NTP process has to generate the packet. Download eos utility mac without cd. The issue is specific to received NTP packets that are not being processed.
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Loss of Synchronization
Loss of synchronization might occur if the dispersion and/or delay value for a server goes very high. High values indicate that the packets are taking too long to get to the client from the server/peer in reference to the root of the clock. So, the local machine cannot trust the accuracy of the time present in the packet, because it does not know how long it took for the packet to get here.
NTP is meticulous about time and will not synchronize with another device it cannot trust or cannot adjust in a way so that it can be trusted.
If there is a saturated link and buffering occurs along the way, the packets get delayed as they come to the NTP client. So, the timestamp contained in a subsequent NTP packet can occasionally vary a lot, and the local client cannot really adjust for that variance.
NTP does not offer a method to turn off the validation of these packets unless you use SNTP (Simple Network Time Protocol). SNTP may not be much of an alternative because it is not widely supported in software.
If you experience loss of synchronization, you should check the links:
Monitor the reach value from the show ntp associations detail command. The highest value is 377. If the value is 0 or low, NTP packets are being received intermittently, and the local client goes out of sync with the server.
debug ntp validity
The debug ntp validity command indicates whether the NTP packet failed sanity or validity checks and reveals the reason for the failure. Compare this output to the sanity tests specified in RFC1305 that are used in order to test the NTP packet received from a server. Eight tests are defined:
This is sample output of from the debug ntp validity command:
debug ntp packets
You can use the debug ntp packets command in order to see the time that the peer/server gives you in the received packet. The time local machine also tells the time it knows to the peer/server in the transmitted packet.
In this sample output, the time stamps in the received packet from the server and the packet sent to another server are the same, which indicates that the client NTP is in sync.
This is an example of output when the clocks are not in sync. Notice the time difference between the xmit packet and the rcv packet. The peer dispersion will be at the max value of 16000, and the reach for the peer will show 0.
debug ntp sync and debug ntp events
The debug ntp sync command produces one-line outputs that show whether the clock has synced or the sync has changed. The command is generally enabled with debug ntp events.
The debug ntp events command shows any NTP events that occur, which helps you determine if a change in the NTP triggered an issue such as clocks going out of sync. (In other words, if your happily synced clocks suddenly go crazy, you know to look for a change or trigger!)
This is an example of both debugs. Initially, the client clocks were synced. The debug ntp events command shows that an NTP peer stratum change occurred, and the clocks then went out of sync.
NTP clock-period Manually SetTime Ntp Server List
The Cisco.com website warns that:
'The ntp clock-period command is automatically generated to reflect the constantly changing correction factor when the copy running-configuration startup-configuration command is entered to save the configuration to NVRAM. Do not attempt to manually use the ntp clock-period command. Ensure that you remove this command line when copying configuration files to other devices.'
The clock-period value is dependent on the hardware, so it differs for every device.
The ntp clock-period Seriale turcesti online subtitrate. command automatically appears in the configuration when you enable NTP. The command is used in order to adjust the software clock. The 'adjustment value' compensates for the 4 msec tick interval, so that, with the minor adjustment, you have 1 second at the end of the interval.
If the device has calculated that its system clock is losing time (perhaps there needs to be a frequency compensation from the base level of the router), it automatically adds this value to the system clock in order to maintain its synchronicity.
Note: This command should not be changed by the user.
The default NTP clock-period for a router is 17179869 and is essentially used in order to start the NTP process.
The conversion formula is 17179869 * 2^(-32) = 0.00399999995715916156768798828125, or approximately 4 milliseconds.
For example, the system clock for the Cisco 2611 routers (one of the Cisco 2600 Series Routers) was found to be slightly out-of-sync and could be resynchronized with this command:
This equals 17208078 * 2^(-32) = 0.0040065678767859935760498046875, or a little over 4 milliseconds.
Cisco recommends that you let the router run for a week or so in normal network conditions and then use the wr mem command in order to save the value. This gives you an accurate figure for next reboot and allows NTP to synchronize more quickly.
Use the no ntp clock-period command when you save the configuration for use on another device because this command drops the clock-period back to the default of that particular device. The true value will be recalculated (but will reduce the accuracy of the system clock during that recalculation time period).
Remember that this value is hardware dependent, so if you copy a configuration and use it on different devices, you can cause problems. Cisco plans to replace NTP version 3 with version 4 in order to resolve this issue.
If you are not aware of these issues, you may decide to manually tinker with this value. In order to migrate from one device to another, you may decide to copy the old configuration and paste it on the new device. Unfortunately, because the ntp clock-period command appears in the running-config and startup-config, NTP clock-period is pasted on the new device. When this happens, NTP on the new client always goes out of sync with the server with a high peer dispersion value.
Instead, clear the NTP clock-period with the no ntp clock-period command, then save the configuration. The router eventually calculates a clock-period appropriate for itself.
The ntp clock-period command is no longer available in Cisco IOS software Version 15.0 or later; the parser now rejects the command with the error:
So, you are not allowed to configure the clock-period manually, and the clock-period is not allowed in the running-config. Since the parser rejects the command if it was in the start-up config (in earlier Cisco IOS versions such as 12.4), the parser rejects the command when it copies the start-up config to the running-config on boot-up.
The new, replacement command is ntp clear drift.
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