The PMTU discovery feature enables the source node to dynamically discover the PMTU for a topology, which ensures optimal usage of network resources. PMTU discovery dynamically discovers the MTU of a path so that the packet can be sent with a size that is equal to the PMTU of the path, not a size that is equal to the IPv6 minimum link MTU. The source node assumes that the PMTU of a path is the MTU of the first hop in that path, so the node sends the packet with the assumed size. If any node along the path is not able to forward the packets due to a large size, that node discards the packet and returns ICMPv6 Packet-Too-Big messages. The source node reduces the assumed PMTU based on the MTU of the constricting node, and resends the packets. This process is iterated until an acceptable PMTU value is derived.
These procedures show how to configure PMTU discovery: