This error condition occurs when there is a mismatch in the maximum transmission unit (MTU) between two peer datalinks. This type of mismatch can result in dropped frames because one datalink might transmit frames that are larger than the peer datalink can receive. The monitor attempts to detect any datalinks on the local system with MTUs that are set too high. Datalinks are verified once upon system start-up and then again when an MTU change occurs.
MTU verification is performed by using either the Link-Layer Discovery Protocol (LLDP) or the Internet Control Message Protocol (ICMP) probe method. A peer host that has the LLDP service enabled can include MTU details in the information exchange. The utility performs MTU verification by extracting peer MTU information. When LLDP information is unavailable, the monitor attempts to verify the MTU by transmitting a series of ICMP probes of different sizes until the datalink MTU is reached. A mismatch is flagged if the utility consistently fails to reach a target by using maximum-sized probes.