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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 12

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Principles

Principles

This section describes the implementation of EFM.

Basic Concepts

OAM PDUs

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 11-92 shows the OAMPDU format and common types of OAMPDUs. Table 11-31 lists and describes fields in an OAMPDU.

Figure 11-92 OAMPDU format
Table 11-31 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.

Type

Slow protocol type, which has a fixed value of 0x8809.

Subtype

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

Flags

Status of an EFM entity.
  • Remote Stable

  • Remote Evaluating

  • Local Stable

  • Local Evaluating

  • Critical Event

  • Dying Gasp

  • Link Fault

Code

OAMPDU type.
  • 0X00: Information OAMPDU

  • 0X01: Event Notification OAMPDU

  • 0X04: Loopback Control OAMPDU

Table 11-32 lists common types of OAMPDUs.

Table 11-32 OAMPDU types

OAMPDU Type

Description

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 a Flags field of an Information OAMPDU sent by the remote EFM entitythe local EFM entity sends an Information OAMPDU to notify the remote EFM entity of the event.

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 11-33 lists capabilities for processing OAMPDUs in the two modes.

Table 11-33 Capabilities for processing OAMPDUs in active and passive modes

Capability

Active Mode

Passive Mode

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

Supported

Not supported

Respond to a connection request during the discovery process

Supported

Supported

Send Information OAMPDUs

Supported

Supported

Send Event Notification OAMPDUs

Supported

Supported

Send Loopback Control OAMPDUs

Supported

Not supported

Respond to Loopback Control OAMPDUs

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

Supported

Basic Functions

EFM supports the following functions: OAM discovery, link monitoring, fault notification, and remote loopback. The following example illustrates EFM implementation on the network shown in Figure 11-93. The SwitchA is an access layer device and SwitchB is an aggregation layer device. EFM is used to monitor the link connecting the SwitchA to SwitchB, allowing an operator to monitor link connectivity and quality.

Figure 11-93 Typical EFM network
EFM Discovery
During the discovery process, a local EFM entity discovers and establishes a stable EFM connection with a remote EFM entity. Figure 11-94 shows the discovery process.
NOTE:

Two OAM entities both working in passive mode cannot establish an EFM connection between them.

Figure 11-94 EFM discovery

EFM entities at both ends of an EFM connection periodically exchange Information OAMPDUs to monitor link connectivity. The interval at which Information OAMPDUs are sent is also known as an interval between handshakes. If an EFM entity does not receive any Information OAMPDU from the remote EFM entity within the connection timeout interval, the EFM entity considers the connection interrupted. Establishing an EFM connection is a way to monitor physical link connectivity automatically.

Link Monitoring

Monitoring Ethernet links is difficult if network performance deteriorates while traffic is being transmitted over physical links. To resolve this problem, configure the EFM link monitoring function that detects data link layer faults in various environments. EFM entities that are enabled with link monitoring exchange Event Notification OAMPDUs to monitor links.

If an EFM entity receives a link event listed in Table 11-34, it sends an Event Notification OAMPDU to notify the remote EFM entity of the event.

Table 11-34 Minor link events

Minor Link Event

Description

Usage Scenario

Errored Symbol Period Event

If the number of symbol errors that occur on a device interface during a specified period of time reaches a specified upper limit, the device generates an errored symbol period event, advertises the event to the remote device.

This event helps the device detect code errors during data transmission at the physical layer.

Errored Frame Event

If the number of frame errors that occur on a device interface during a specified period of time reaches a specified upper limit, the device generates an errored frame event, advertises the event to the remote device.

This event helps the device detect frame errors that occur during data transmission at the data link layer.

Errored Frame Seconds Summary Event

An errored frame second is a one-second interval wherein at least one frame error is detected. If the number of errored frame that occur during a specified period of time reaches a specified upper limit on an interface of a device, the device generates an errored frame second summary event, advertises the event to the remote device.

This event helps the device detect errored frame seconds that occur during data transmission at the data link layer.

Fault Notification

After the OAM discovery process finishes, two EFM entities at both ends of an EFM connection exchange Information OAMPDUs to monitor link connectivity. When traffic is interrupted because the remote EFM entity fails or becomes unavailable, the faulty EFM entity will send an Information OAMPDU carrying a critical link event listed in Table 11-35 to the local EFM entity.

Table 11-35 Critical link event

Critical Link Event

Description

Link fault

If a loss of signal (LoS) error occurs because a physical link fails.

Dying gasp

If an unexpected status change or event occurs because a remote device is powered off.

Link Loss

If a loss of signal (LoS) error occurs because the interval at which OAMPDUs are sent elapses.

Remote Loopback

Figure 11-95 demonstrates the implementation of remote loopback. When a local interface sends non-OAMPDUs to a remote interface, the remote interface loops the non-OAMPDUs back to the local interface, not to the destination addresses of the non-OAMPDUs. This is remote loopback. An EFM connection must be established to implement remote loopback.

NOTE:

An OAM entity that initiates a loopback request must work in active mode.

Figure 11-95 Implementation of remote loopback

After remote loopback is enabled, the device discards all the non-OAMPDUs, causing service interruption. It is recommended that you enable remote loopback to check link connectivity and quality before a new network is used or a link fault is rectified. The results help an operator take measures to minimize the remote loopback impact on services.

The local device computes communication quality parameters such as the packet loss ratio on the current link based on the number of sent packets and the number of received packets. Figure 11-96 shows the remote loopback process.

Figure 11-96 Remote loopback process

If the local device attempts to stop remote loopback, it sends a message to instruct the remote device to disable remote loopback. After receiving the message, the remote device disables remote loopback.

If remote loopback is left enabled, the remote device keeps looping back service data, causing a service interruption. To prevent this problem, a capability can be configured to disable remote loopback automatically after a specified timeout interval. After the timeout interval expires, the local device automatically sends a message to instruct the remote device to disable remote loopback.

EFM Enhancements

EFM enhancements in compliance with EFM standards are extended EFM functions, including an association between EFM.

Association Between EFM and Interfaces

A device carrying IP services is usually dual-homed to an IP network to improve network robustness and service reliability. As shown in Figure 11-97, SwitchA is dual-homed to SwitchB and SwitchC. If the active link between SwitchA and SwitchC fails, traffic switches to the standby link between SwitchA and SwitchB,minimizing the service interruption time.

Association between EFM and EFM interfaces that connect SwitchB and SwitchC to SwitchA allows traffic to switch from the active link to the standby link if EFM detects a link fault or link quality deterioration. EFM detects faults on the link between SwitchA and SwitchC on the network shown in Figure 11-97. Association between EFM and EFM interfaces can set the status of Port1 to EFM down and trigger an active/standby link switchover, improving transmission quality and reliability.

Figure 11-97 Association between EFM and interfaces
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Updated: 2019-08-09

Document ID: EDOC1000041694

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