Basically if the frame size of a packet is more than the MTU size configured in the router (which is an intermediate hop) the packet is dropped. Since IP does not have any ARQ mechanism, is there a method to know at source that packets are being dropped? What is the thing to do in this scenario. Does the network operator ensure manually this does not happen?

  • Besides Ron's answer, look up PMTUD. Fragmentation is built into IPv4, but IPv6 has eliminated it.
    – Ron Maupin
    Commented Mar 26, 2017 at 15:50

1 Answer 1


If the MTU of the outgoing interface is smaller than the packet, the router will fragment the packet unless the DF flag is set. In that case the router will drop the packet and send an ICMP packet too big message back to the sender.

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