This specifies the largest datalink-level frame the node will ever receive on any of its links, with WAN links' reserved internal trailer space not counted toward this figure. An admin connecting equipment that sends larger frames than this configured maximum, for instance after enabling jumbo frames somewhere upstream, would see those oversized frames rejected or fragmented at this node. For example, leaving this at a legacy default of 1500 bytes while upstream equipment starts sending 4000-byte frames would cause this node to reject or mishandle those larger frames.