Path MTU Discovery (PMTUD) is a standardized technique in computer networking for determining the maximum transmission unit (MTU) size on the network path between two Internet Protocol (IP) hosts, usually with the goal of avoiding IP fragmentation.
This can result in connections that complete the TCP three-way handshake correctly but then hang when attempting to transfer data.
[7] Some implementations of PMTUD attempt to circumvent this problem by inferring that large payload packets have been dropped due to MTU rather than link congestion.
One such scheme is standardized under RFC 8899, Datagram Packetization Layer Path MTU Discovery (DPLPMTUD).
[8] However, in order for transport layer protocols to operate most efficiently, ICMP Unreachable messages (type 3) should still be permitted.
Some routers, including the Linux kernel[9] and Cisco,[10] provide an option to reduce the maximum segment size (MSS) advertised in the TCP handshake as a workaround.