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Packet Needs To Be Fragmented But DF Set -Reason and Solution

While testing the correct MTU size of your current network, sometimes you may receive the error message "Packet needs to be fragmented but DF set". In this tutorial let us check the reason and solution for this error message. If the MTU size you have set on the ping test is too high, you will get this message. Let us check this by an example. Here I am testing whether the MTU value 1480 is the proper value for my network. The ping command to perform this test is:

ping www.corenetworkz.com -f -l 1480

  1. Here www.corenetworkz.com is the ping test destination

  2. -l is used to switch the default ping packet size. You can learn more about it by following the link below.
    Use -l to Change Default Ping Packet Size

  3. -f ensures the packets send are not fragmented.


See the test result below.
Packet needs to be fragmented but DF set


Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\sijugk>ping www.corenetworkz.com -f -l 1480

Pinging ghs.l.google.com [74.125.200.121] with 1480 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

Ping statistics for 74.125.200.121:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\Users\sijugk>


Reasons for the Message Packet needs to be fragmented but DF set
If the packet size you have entered is too high for your network, you will get the message Packet needs to be fragmented but DF set.

Solve the Error Packet needs to be fragmented but DF set
In order to solve the error, Packet needs to be fragmented but DF set, visit the link below and follow the steps mentioned on the tutorial.
Testing Proper MTU Size Of Your Network

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Alex George
Alex George has Engineering graduation in Computer Science and an MBA in Finance. He had been working as a senior Network Engineer for ten years. His specialization is in Cisco products. Traveling is one of his hobbies and visited various places as part of his onsite work. He visited different places as part of his onsite work like New York, Dubai, London, etc. Right now Alex is a director of one of the leading career development firms in India, which trains students for UPSC, SSC, and PSC examinations. He guides a lot of students to get selection for various prestigious institutions like CBI, Income Tax Department, etc. Alex George is a stock market investor and a very active intraday trader. Engineering Background: He has a B.Tech in Computer Science and Engineering and passed different network and security courses like CCNA, CCNP (Security), CEH, and various Microsoft certifications. Finance Background: Alex has an MBA in Finance. He is an active intraday trader and a Share Market Investor. Webmaster Skills: Alex is a blogger since 2004. He has a working knowledge of HTML, CSS, PHP, and JavaScrip.

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