IEEE 802.3ah Ethernet in First Mile

Using Ethernet in the EFM solution, you gain broadcast Internet access, and access to services such as Layer 2 transparent LAN services, voice services over Ethernet access networks, video, and multicast applications. This access is reinforced by security and quality of service to build a scalable network. The in-band management specified by this standard defines the operations, administration, and maintenance (OAM) mechanism needed for the advanced monitoring and maintenance of Ethernet links in the first mile.

802.3ah protocol in Ethernet

The 802.3ah protocol activities are classified into three layers: transport layer, connectivity layer, and service layer. The transport layer 802.3ah protocol provides single-link OAM capabilities, offering an opportunity to create the operations and OAM sub-layer in the data-link layer. The connectivity layer provides utilities for monitoring and troubleshooting Ethernet links.

The data-link layer protocol targets the last-mile applications. Service providers can use it for demarcation point OAM services. The 802.3ah protocol resolves validation and testing problems. Using the Ethernet demarcation, service providers can additionally manage the remote device without using an IP layer.

The functionality of the 802.3ah protocol is as follows:
  • Discovery: A mechanism to detect the presence of a sublayer on the remote device. During the process, information about OAM entities, capabilities and configuration are exchanged.
  • Link monitoring: A process used to detect link faults and to provide information about the number of frame errors and coding symbol errors.


    Link monitoring functionality is not supported.
  • Remote fault detection: Provides a mechanism to convey error conditions to its peer via a flag. The failure conditions are defined as follows:
    • Link Fault: This fault condition is detected when the receiver loses the signal. This condition is sent one time per second.
    • Dying Gasp: This condition is detected when the receiver goes down. The condition is considered as unrecoverable.
    • Critical Event: When a critical event occurs, the device is unavailable as a result of malfunction and must be restarted by the user. The critical events are sent immediately and continually.
    • Remote loopback: Provides a mechanism to troubleshoot networks and to isolate problem segments in a large network by sending test segments.

Feature support and limitations

Link OAM is a link-level protocol and is supported on physical interfaces.

The following functions are not supported:
  • Link monitoring functionality
  • Unidirectional support
  • SNMP MIB or traps
  • UDLD and Link OAM cannot coexist

On SLX-OS devices, Link OAM configuration is allowed on VPLS and VLL endpoints. Support for VPLS and VLL endpoints is available only when Link OAM is configured on the link between CE (passive) and PE (active).

How discovery works

When OAM is present, two connected OAM sub-layers exchange OAM Protocol Data Units (OAMPDU). OAMPDUs are standard-size untagged 802.3 frames that can be sent at a maximum rate of 10 frames per second. A combination of the destination MAC address, the Ethernet type, and subtype distinguishes OAM PDU frames from other frames.


Only Information and loopback Control OAMPDUs are supported.

Network devices are identified with their OAM configuration and capabilities in the discovery phase of the EFM-OAM. Remote loopback configuration and OAM mode (active/passive) capability are supported during this phase.



There is no prerequisite or support for configuration to consider the discovery status as unsatisfied. Any capability received from the peer is considered to be satisfied and will wait for the peer to become stable before marking the Link OAM status as up.

How remote loopback works

Remote loopback allows you to estimate if a network segment can satisfy an SLA and helps you to ensure quality of links during installation and troubleshooting. An OAM entity can put its remote entity into loopback mode using a loopback control OAMPDU. The remote-loop-back command allows you to start and stop the remote loopback on peer that is connected to the specified local ethernet interface.

device# link-oam remote-loop-back ethernet 1/1 start
device# link-oam remote-loop-back ethernet 1/1 stop


As a best practice for loopback mode, you should remove the loopback ports from the active network topology to reduce the impact of protocol flaps. In loopback mode, IP traffic is looped back with the MAC header removed.

For more information about commands, see the Extreme SLX-OS Command Reference Guide.