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Configuration Guide - Reliability

CloudEngine 8800, 7800, 6800, and 5800 V200R005C10

This document describes the configurations of Reliability, including BFD Configuration, VRRP Configuration, DLDP Configuration, Smart Link and Monitor Link Configuration, EFM Configuration, and CFM Configuration.
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EFM Fundamentals

EFM Fundamentals

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 6-3. SwitchA is an access layer device and SwitchB is an aggregation layer device. EFM is used to monitor the link connecting SwitchA to SwitchB, allowing an operator to monitor link connectivity and quality.

Figure 6-3 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 6-4 shows the discovery process.
NOTE:

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

Figure 6-4 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 6-4, it sends an Event Notification OAMPDU to notify the remote EFM entity of the event.

Table 6-4 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 Period Event

If the number of errored frames among a specified number of received frames exceeds the specified threshold, the device generates an errored frame period event, advertises the event to the remote device.

This event helps the device detect frame period 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 frames 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 6-5 to the local EFM entity.

Table 6-5 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 6-5 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 6-5 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 6-6 shows the remote loopback process.

Figure 6-6 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.

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Updated: 2019-04-03

Document ID: EDOC1100075366

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