The network-monitor (also referred to as the monitor in this chapter) is a fault manager daemon (fmd) transport module utility that you use to perform network diagnostics on your Oracle Solaris system. The utility monitors network resources and reports conditions that might lead to limited or degraded network functionality. When the monitor utility detects an abnormal network condition, an alert is generated. You can retrieve information about alerts by using the fmadm command. See Obtaining Information About the Active FMA Alerts on a System. The monitor utility does not perform any further diagnosis of the error condition, nor does it perform any additional recovery actions. For more information, see the network-diagnostics(5) man page.
You control the monitor utility by setting property values that are stored in the svc:/network/diagnostics SMF service instance. For more information, see Controlling the Use of Probes Through the svc:/network/diagnostics SMF Service.
This error condition occurs when there is a mismatch between the MTUs of 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 utility attempts to detect any datalinks on the local system with MTUs that are set too high. Datalinks are verified 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 utility 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.
VLANs are used to group end-system hosts into the same broadcast domain. The hosts on a VLAN might not reside on the same LAN, but even if they do, each host can communicate with another host by using Layer 2 (L2) protocols. Conversely, hosts that reside on the same LAN but different VLANs cannot communicate by using L2 protocols. Each host that resides on a VLAN uses a network interface to communicate with the other hosts on the VLAN. VLANs are identified by VLAN identifiers (VIDs) that are exported by LLDP daemons over the relevant network interfaces to their peers. These peers are typically network devices, for example, switches that use a VID to forward data packets to respective hosts.
Hosts might not receive the intended packets if the VIDs are not configured correctly on the relevant network interfaces. The monitor utility captures this type of VLAN ID mismatch because it verifies the VLAN ID information periodically and whenever the VLAN information is modified at system boot time. If the VLAN ID for an interface changes, the appropriate alerts are generated. Because the VLAN information is verified by using LLDP packets, the peer host needs to have the LLDP service enabled. For information about LLDP, see Chapter 7, Exchanging Network Connectivity Information With Link Layer Discovery Protocol in Managing Network Datalinks in Oracle Solaris 11.4.