An MPLS MTU can be configured on an interface to determine the maximum number of bytes in an MPLS packet that an interface can forward without fragmenting the packet.
Path MTU auto discovery allows BGP to discover the smallest MTU value on a path so that BGP messages are transmitted based on the path MTU. This function improves transmission efficiency and BGP performance.
MTU is the largest packet of data that can be transmitted on a network, expressed in bytes. MTU is determined by data link layer protocols, and MTU values vary with networks. A proper MTU is a prerequisite for normal communication between network devices.