Glossary: TCP/IP in Depth, Part 1
fragmentation needed
Also written: Frag needed and DF set, need to frag, type 3 code 4
An ICMP error (type 3, code 4) from a router that had to drop a DF packet because it was too big for the next link. The error includes that link's MTU, such as 1,400, so the sender can send smaller packets.
Where the book teaches it
Related terms
path MTU discoveryDF (don't fragment)Packet Too BigPMTU black hole