Network devices employ Internet Control Message Protocol (ICMP) to gather communications-related information. ICMP is capable of sending error messages but also delivers operational information. Ping and TraceRoute both send ICMP messages to provide connectivity information including latency and network hops.
Most devices have a default MTU that is configurable and remains at the defined value. PowerScale OneFS determines the MTU specific to each transaction. After the initial TCP handshake, the PowerScale node sends an ICMP message for Path MTU Discovery (PMTUD), RFC 1191, gathering the maximum supported MTU. If for any reason ICMP is disabled, or PMTUD is not supported, this causes OneFS to default the MTU to 536 bytes, which typically leads to performance degradation.