Reporting Topology Changes in an Upper-Layer Network - Configuring Association Between SEP and CFM

SEP runs on devices at the access layer or aggregation layer. To enable devices running SEP to detect the topology changes in an upper-layer network, you must configure on SEP and CFM association the device connecting the lower-layer network to the upper-layer network.

When CFM detects a fault on the upper-layer network, the edge device sends a CFM packet to notify the OAM module of the fault. Then the SEP status of the interface associated with CFM on the edge device changes to Down.

The peer device (on the SEP segment) of the edge device notifies other nodes in the same SEP segment of topology changes by sending Flush-FDB packets. After a device in the SEP segment receives the Flush-FDB packet, the blocked interface on the device is unblocked, enters the Forwarding state, and sends a Flush-FDB packet to instruct other nodes in the SEP segment to refresh their MAC forwarding tables and ARP tables. Therefore, the lower-layer network can then detect the faults on the upper-layer network, ensuring reliable service transmission.

IEEE 802.1ag, also known as Connectivity Fault Management (CFM), defines OAM functions, such as continuity check (CC), link trace (LT) and loopback (LB), for Ethernet networks. CFM is network-level OAM and applies to large-scale end-to-end networking.