IP fragmentation explained in Wireshark in under 10 minutes!

In this video I explain IP fragmentation and how it works in Wireshark

[rubo]

For the questions up above.

1) To test the MTU of your own system and to reproduce this behaviour from a host, the ping command has an option to set the payload. Based on OS the payload may include the ICMP header or exclusively the ICMP payload.

By setting the DF bit on the ping command you can sweep through packet sizes to see the MTU that gets through (use a capture tool to remove any doubt as to what is going on the line).

2) To produce this behaviour in GNS3, on a particular link set each endpoints interface MTU via a command. The quickest way to do this would be between a link that has a router on each end. Hop on the respective interfaces and set the MTU to 1200. Then ping from host to host that is forced to cross that particular link in the network path.


The commands to run on routers, or your host are VERY easily found on an internet search.

[BroddeB]

It is 1480 bytes. Not bits. The offset counts 8-byte blocks

[CharusheelaIngole-qu]

I want to understand why only 20 bytes as a header is considered in fragmentation and why an ethernet header is not included/calculated when a data packet is sent

Example: MTU is 1500 so we will send 1480 bytes of data + 20 bytes =1500 bytes but each fragmented packet has headers as frame, Ethernet that will be an add-on header (8 bytes) to the limit specified.

[АлександърАндреев-цт]

guys i ping a random site and it apears only ICMP protocols.There are no IPv4's and no fragments.How can i see those fragments and get to appear on my screen IPV4 protocols like those in the video

[ramanha]

But how did you get packets fragmented? can I do that via command line manually?

[azherqadirshah]

Make a lab how we get these fragments via gns3 lab