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Suppose transport layer get the segment 4000 bytes from application layer at sender site. But we know maximum MTU in layer2(Ethernet) is 1500 bytes.

My question is so fragmentation is happening at sender site?

But I read in many context even in wikipedia router gets the packet of size more than 1500 bytes for example 4000 bytes etc, then doing fragmentation according to their MTU.

My question is router never get the packet of size more than 1500 bytes because at sender never possible to generate the frame of size more than 1500 bytes?

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Do not confuse fragmentation with segmentation. Most companies now reject fragmented packets to prevent fragmentation attacks. TCP, which is used for HTTP/HTTPS (web traffic) will segment the data stream into segments that fit into the MSS advertised by the receiver during the connection handshake.

TCP segmentation is not IP fragmentation. Fragmentation is practically deprecated now because so many companies simply drop received packet fragments, and IPv6 does not even have in-path fragmentation the way IPv4 does. Today, we have PMTUD, which is required for IPv6, although optional for IPv4.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Ron Maupin
    Mar 11 at 21:27
  • You said "When a transport protocol is installed in the OS, the OS will modify the network protocol table so that IP knows that a protocol number". But how layer4 will know about destination application port number?
    – Alok Maity
    Mar 11 at 21:34
  • The system flagged this for all the comments. Please use the chat link.
    – Ron Maupin
    Mar 11 at 21:35

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