Dell EMC Configuration Guide for the S3100 Series 9.14.2.4

The size of the packet that can be sent across each hop in the network path without being fragmented is called the path maximum transmission unit (PMTU). The PMTU value might differ for the same route between two devices, mainly over a public network, depending on the network load and speed, and it is not a consistent value. The MTU size can also be different for various types of traffic sent from one host to the same endpoint.

Path MTU discovery (PMTD) identifies the path MTU value between the sender and the receiver, and uses the determined value to transmit the packets across the network. Path MTU, in accordance with RFC 1981, defines the largest packet size that can traverse a transmission path without suffering fragmentation. Path MTU for IPv6 uses ICMPv6 Type-2 messages to discover the largest MTU along the path from source to destination and avoid the need to fragment the packet. The recommended MTU for IPv6 is 1280. Greater MTU settings increase the processing efficiency because each packet carries more data while protocol overheads (for example, headers) or underlying per-packet delays remain fixed.