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Configuration Guide - Reliability

S1720, S2700, S5700, and S6720 V200R010C00

This document describes the configuration of BFD, DLDP, VRRP, SmartLink, CFM, EFM, Y.1731 and MAC swap loopback to ensure reliability on the device.

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Basic Concepts

Basic Concepts


EFM works at the data link layer and uses protocol packets called OAM Protocol Data Units (PDUs). EFM devices periodically exchange OAMPDUs to report the link status, helping network administrators effectively manage networks. Figure 8-2 shows the format of an OAMPDU as well as the common types of OAMPDUs.

Figure 8-2  OAMPDU format

Table 8-1 describes fields in an OAMPDU.

Table 8-1  Fields in an OAMPDU
Field Description

Destination addr

Destination MAC address, which is a slow protocol multicast address 0x0180-C200-0002. Network bridges cannot forward slow protocol packets. EFM OAMPDUs cannot be forwarded over multiple devices, even if OAM is supported or enabled on the devices.

Source addr

Source address, which is a unicast MAC address of a port on the transmit end. If no port MAC address is specified on the transmit end, the bridge MAC address of the transmit end is used.


Slow protocol type that has the fixed value of 0x8809.


Subtype of a slow protocol. The value is 0x03, indicating that the slow subprotocol is EFM.


EFM entity status:
  • Remote Stable

  • Remote Evaluating

  • Local Stable

  • Local Evaluating

  • Critical Event

  • Dying Gasp

  • Link Fault


OAMPDU type:
  • 0X00: Information OAMPDU

  • 0X01: Event Notification OAMPDU

  • 0X04: Loopback Control OAMPDU

Table 8-2 describes OAMPDU types.

Table 8-2  OAMPDU types



Information OAMPDU

  • Used to discover a remote EFM entity, initiate a handshake process, and establish an EFM connection. After the EFM connection is established, both EFM entities periodically exchange Information OAMPDUs to monitor link connectivity.

  • Used to advertise fault information. Upon receiving a critical link event carried in the Flags field of an Information OAMPDU sent by the remote EFM entity, the local EFM entity sends a trap to the NMS.

Event Notification OAMPDU

Used to monitor links. If an errored frame event, errored code period event, or errored frame second event occurs on an interface, the interface sends an Event Notification OAMPDU to notify the remote interface of the event.

Loopback Control OAMPDU

Used to enable or disable the remote loopback function.

Connection Modes

EFM supports two connection modes: active and passive. An EFM connection can only be initiated by an OAM entity working in active mode. An OAM entity working in passive mode waits to receive a connection request from its peer entity. Table 8-3 lists capabilities for processing OAMPDUs in the two connection modes.

Table 8-3  Capabilities for processing OAMPDUs in active and passive modes


Active Mode

Passive Mode

Initiate a connection request by sending an Information OAMPDU during the discovery process


Not supported

Respond to a connection request during the discovery process



Send Information OAMPDUs



Send Event Notification OAMPDUs



Send Loopback Control OAMPDUs


Not supported

Respond to Loopback Control OAMPDUs

Supported (The remote EFM entity must work in active mode.)


Updated: 2019-12-28

Document ID: EDOC1000141941

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