Network Engineering Stack Exchange is a question and answer site for network engineers. It only takes a minute to sign up.
Sign up to join this community
I'm writing a socket application that is running on Linux. My server machine is connected to a switch that is connected to a network. There are also other servers connected to the switch.
My client application sends 10 messages, each of the messages is 105 bytes. I build the whole packet and write it to the socket. Since 105*10=1050 < MTU, I assume it will not get fragmented while it is going to the target.
Am I wrong? Can the network devices on the path fragment my packet for a reason?
Thanks
YES. If the MTU somewhere along the path is smaller than your packet size, it will be fragmented.
This may not apply in your simple network, but it's possible in the real world.
One thing isn't clear from your description: sockets are stream-oriented. The stack will handle the fragmenting/defragmenting for you. I'm not sure why you're concerned.
Can the network devices on the path fragment my packet for a reason?
If it is IPv4, and the DF bit is clear, then yes, your packets can be fragmented in the path. The fragmentation and reassembly will be transparent to your application. Packets can get fragmented in the path, then the destination host will reassemble them at IPv4 before passing the packet up to the transport protocol.
If the DF bit is set and the packet needs fragmentation, then the packet is dropped. An ICMP message should be sent back telling you that the packet is too big.
IPv6 has eliminated path fragmentation, requiring every link in the path to have a minimum MTU of 1280, and it uses PMTUD.
