Ethernet Operations, Administration, and Maintenance

• Rely only on the media access control (MAC) address or virtual local area network (VLAN) identifier for troubleshooting
• Work independently of the actual Ethernet transport and function over physical Ethernet ports, or a virtual service such as pseudowire, and so on.
• Isolate faults over a flat (or single operator) network architecture or a nested or hierarchical (or multi-provider) networks.

OAM can provide simple link-level information, provide performance statistics, or track end-to-end connectivity across the network. Simple link fault management (LFM) for Ethernet links is defined in IEEE 802.3ah.

• Fault detection and notification (provided by continuity check messages)
• Path discovery (provided by the linktrace protocol)
• Fault isolation, verification, and recovery (isolation and verification are provided by a combination of protocols, while recovery is the function of protocols such as spanning tree)

The loopback protocol used in Ethernet OAM is modeled on the standard IP ping. After a fault is detected, the loopback protocol performs fault verification and isolation under the direction of a network operator. The loopback is performed using request and response message pairs. A unicast loopback message is generated by a MEP and a loopback reply is generated by the destination MIP or MEP. The target MAC address is learned by the continuity check protocol or linktrace protocol. The loopback message's packet is always forwarded to a unique port by the originating MEP, as determined by a MAC table lookup or the MEP interface MAC address. The target MIP or MEP generates a unicast loopback reply in response to the received loopback message. The loopback message follows the same path as a data packet, and intermediate bridges simply forward the packet to the destination MIP or MEP.