Tag Archives: Packets

NTP client time out of Sync?

Published / by Chen Ye / 3 Comments on NTP client time out of Sync?

Starter:

We know NTP is used to synchronize time from authorized time server to the client to keep the client local time consistent with standard time.

However, what if we successfully set up the NTP servers, but the client is still out of sync with NTP server time to time which causes authentication issue? We need to know how to troubleshoot the related issue.

 

Knowledge Prerequisite:

Before troubleshooting the NTP related issues, you should have following knowledge:

  • What is a reference clock?
  • How will NTP use a reference clock?
  • How will NTP know about Time Sources?
  • What happens if the Reference Time changes?
  • How is Time synchronized?
  • Which Network Protocols are used by NTP?
  • When are the Servers polled?
  • How frequently will the System Clock be updated?
  • How frequently are Correction Values updated?

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What is MTU and How to use it to locate network issues

Published / by Chen Ye / Leave a Comment

 

It is normal to see the TCP retransmission most of time which will cause lots of different network issue, packet drop etc. Today let’s have a short discussion about improper size of MTU caused packet drop during the transmission.

 

Definition

PDU Protocol Data Unit (describes a message at some protocol layer; sometimes used interchangeably and informally with packet, frame, datagram, segment, or message)

MTU Maximum Transmission unitThere is a limit on the size of the frame available for carrying the PDUs of higher-layer protocols in many link-layer networks such as Ethernet. For the Ethernet, usually limits the number of payload bytes to about 1500.

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