What does a router do if the MTU is too small for the packet.txt

What does a router do if the MTU is too small for the packet.txt

packet fragmentation, but you can talk about MSS and PMTUD

IP fragmentation is an Internet Protocol (IP) process that breaks datagrams into smaller pieces (fragments), so that packets may be formed that can pass through a link with a smaller maximum transmission unit (MTU) than the original datagram size. The fragments are reassembled by the receiving host.

Path MTU Discovery (PMTUD) is a standardized |Internet |Engineering Task Force| (IETF) technique for determining an acceptable |Maximum Transmission Unit (MTU) between two IP network connections. |The goal of this technique is to discover the largest size datagram |that does not require fragmentation anywhere along the path between |the source and destination. This discovered datagram size is known |as the Path Maximum Transmission Unit (PMTU).

 usually with the goal of avoiding IP fragmentation