Filter
Top Products
802.1ag | 87
Continuity Check Messages
Continuity Check Messages (CCM) are periodic hellos used to:
• 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
Continuity Check Messages (CCM) 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 processes the CCM messages originated by MEPs and construct a
MIP CCM database.
MEPs and MIPs filter CCMs from higher and lower domain levels as described in Table 5-1.
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:
1. Loss of 3 consecutive CCMs from any of the remote MEP, which indicates a network failure
2. Reception of a CCM with an incorrect CCM transmission interval, which indicates a configuration
error.
3. Reception of CCM with an incorrect MEP ID or MAID, which indicates a configuration or
cross-connect error. This could happen when different VLANs are cross-connected due to a
configuration error.
4. Reception of a CCM with an MD level lower than that of the receiving MEP, which indicates a
configuration or cross-connect error.
5. 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
any of the above errors are encountered.
Table 5-1. Continuity Check Message Processing
Frames at Frames from UP-MEP Action Down-MEP Action MIP Action
Less than my level Bridge-relay side or Wire side Drop Drop Drop
My level Bridge-relay side Consume Drop Add to MIP-DB
and forward
Wire side Drop Consume
Greater than my level Bridge-relay side or Wire side Forward Forward Forward