DF Don’t Fragment Field in the IPv4 Header

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We will try to understand DF Don’t Fragment Field in the IPv4 Header in this class.

We have already discussed the concepts of Identification, MF, and Fragment Offset in our previous

DF Don’t Fragment Field in the IPv4 Header

To understand this concept, we will consider the image below.

Assume that sender A transmitted 1000 Bytes packet in the network and is received at the router.

The sender has set the DF Do not Fragment field to 1.

Now the router has to fragment the packet to 500 Bytes because the MTU of the network is 500 Bytes.

But the DF field in the header is set to 1, so the router cannot fragment it further.

The router will send an ICMP packet stating that I have received a packet with DF set to 1, but i need the packet to be fragmented to 500 Bytes.

The sender will now fragment the packet to 500 Bytes based on the response.