Path MTU Discovery
acronymnetworking
Stands for: Path MTU Discovery (PMTUD)
How a sender finds the smallest MTU along the whole route, not just the first hop.
PMTUD (RFC 1191) probes the path and shrinks packets to fit its narrowest link, avoiding fragmentation end to end. When firewalls block the ICMP messages it relies on, it fails silently, producing the classic "connects but hangs on large transfers" symptom.
Also known as: pmtud, path mtu