Dell PowerSwitch S4820T 9.50.1 Configuration Guide for the S4820T System - Page 90

Continuity Check Messages Continuity check messages (CCM) are periodic hellos. Continuity check messages: • discover MEPs and MIPs within a maintenance domain • detect loss of connectivity between MEPs • detect misconfiguration, such as VLAN ID mismatch between MEPs • to detect unauthorized MEPs in a maintenance domain CCMs are multicast Ethernet frames sent at regular intervals from each MEP. They have a destination address based on the MD level (01:80:C2:00:00:3X where X is the MD level of the transmitting MEP from 0 to 7). All MEPs must listen to these multicast MAC addresses and process these messages. MIPs may optionally process the CCM messages the MEPs originate and construct a MIP CCM database. MEPs and MIPs filter CCMs from higher and lower domain levels as described in the following table. Table 4. Continuity Check Message Processing Frames at Frames from UP-MEP Action Less than my level Bridge-relay side or Drop Wire side My level Bridge-relay side Consume My level Wire side Drop Greater than my level Bridge-relay side or Forward Wire side Down-MEP Action MIP Action Drop Drop Drop Consume Forward Add to MIP-DB and forward add to MIP-DB and forward Forward All the remote MEPs in the maintenance domain are defined on each MEP. Each MEP then expects a periodic CCM from the configured list of MEPs. A connectivity failure is then defined as: • Loss of three consecutive CCMs from any of the remote MEP, which indicates a network failure. • Reception of a CCM with an incorrect CCM transmission interval, which indicates a configuration error. • Reception of a CCM with an incorrect MEP ID or MAID, which indicates a configuration or cross- connect error. This error could happen when different VLANs are cross-connected due to a configuration error. • Reception of a CCM with an MD level lower than the receiving MEP, which indicates a configuration or cross-connect error. • Reception of a CCM containing a port status/interface status TLV, which indicates a failed bridge or aggregated port. The continuity check protocol sends fault notifications (Syslogs, and SNMP traps, if enabled) whenever you encounter any of the these errors. 90 802.1ag