With features such as ease of use and low price, Ethernet has gradually become the major underlying technology for today’s local area networks (LANs). Recently, with the emergence of Gigabit Ethernet and 10-Gigabit Ethernet, Ethernet is gaining popularity in metropolitan area networks (MANs) and wide area networks (WANs) as well.

In the beginning, Ethernet is mainly used in LANs, which have low reliability and stability requirements. This is why an effective management and maintenance mechanism for Ethernet has been absent all along, hindering the usage of Ethernet in MANs and WANs. Implementing Operation, Administration and Maintenance (OAM) on Ethernet networks has now become an urgent matter.

Ethernet OAM is a tool that monitors Layer 2 link status and addresses common link-related issues on the “last mile.” You can monitor the status of the point-to-point link between two directly connected devices by enabling Ethernet OAM on them.

Major functions of Ethernet OAM

Ethernet OAM can effectively promote your management and maintenance capabilities over Ethernet networks, guaranteeing the stability of the networks. Ethernet OAM provides the following functions:

· Link performance monitoring—Monitors the performance indices of a link, including packet loss, delay, and jitter, and collects traffic statistics of various types

· Fault detection and alarm—Checks the connectivity of a link by sending OAM protocol data units (OAMPDUs) and reports to the network administrators when a link error occurs

· Remote loopback—Checks link quality and locates link errors by looping back OAMPDUs

Ethernet OAMPDUs

Ethernet OAM works on the data link layer. Ethernet OAM reports the link status by periodically exchanging OAMPDUs between devices, so that the administrator can effectively manage the network.

Ethernet OAMPDUs fall into the following types: Information, Event Notification, and Loopback Control.

Figure 1 Formats of different types of Ethernet OAMPDUs

Table 1 The fields in an OAMPDU

Field	Description
Dest addr	Destination MAC address of the Ethernet OAMPDU It is a slow protocol multicast address 0180c2000002. Because bridges cannot forward slow protocol packets, Ethernet OAMPDUs cannot be forwarded.
Source addr	Source MAC address of the Ethernet OAMPDU It is the bridge MAC address of the sending side and is a unicast MAC address.
Type	Type of the encapsulated protocol in the Ethernet OAMPDU The value is 0x8809.
Subtype	The specific protocol being encapsulated in the Ethernet OAMPDU The value is 0x03.
Flags	Status information of an Ethernet OAM entity
Code	Type of the Ethernet OAMPDU

NOTE:

Throughout this document, a port with Ethernet OAM enabled is an Ethernet OAM entity or an OAM entity.

Table 2 Functions of different types of OAMPDUs

OAMPDU type	Function
Information OAMPDU	Used for transmitting state information of an Ethernet OAM entity—including the information about the local device and remote devices, and customized information—to the remote Ethernet OAM entity, and maintaining OAM connections
Event Notification OAMPDU	Used by link monitoring to notify the remote OAM entity when it detects problems on the link in between
Loopback Control OAMPDU	Used for remote loopback control. By inserting the information used to enable/disable loopback to a loopback control OAMPDU, you can enable/disable loopback on a remote OAM entity.

How Ethernet OAM works

This section describes the working procedures of Ethernet OAM.

Ethernet OAM connection establishment

Ethernet OAM connection is the basis of all the other Ethernet OAM functions. OAM connection establishment is also known as the “Discovery phase”, where an Ethernet OAM entity discovers remote OAM entities and establishes sessions with them.

In this phase, interconnected OAM entities determine whether Ethernet OAM connections can be established, by exchanging Information OAMPDUs to notify the peer of their OAM configuration information and the OAM capabilities of the local nodes. An Ethernet OAM connection can be established between entities that have matching Loopback, link detecting, and link event settings. After an Ethernet OAM connection is established, Ethernet OAM takes effect on both sides.

For Ethernet OAM connection establishment, a device can operate in active Ethernet OAM mode or passive Ethernet OAM mode, but a switch role will be somewhat different depending on the mode.

Table 3 Active Ethernet OAM mode and passive Ethernet OAM mode

Item	Active Ethernet OAM mode	Passive Ethernet OAM mode
Initiating OAM Discovery	Available	Unavailable
Responding to OAM Discovery	Available	Available
Transmitting Information OAMPDUs	Available	Available
Transmitting Event Notification OAMPDUs	Available	Available
Transmitting Information OAMPDUs without any TLV	Available	Available
Transmitting Loopback Control OAMPDUs	Available	Unavailable
Responding to Loopback Control OAMPDUs	Available—if both sides operate in active OAM mode	Available

NOTE:

· Only OAM entities operating in active OAM mode can initiate OAM connections, and those operating in passive mode wait and respond to the connection requests sent by their peers.

· No OAM connection can be established between OAM entities operating in passive OAM mode.

After an Ethernet OAM connection is established, the Ethernet OAM entities on both sides exchange Information OAMPDUs at a specified interval—handshake packet transmission interval—to check whether the Ethernet OAM connection is normal. If an Ethernet OAM entity receives no Information OAMPDU within the Ethernet OAM connection timeout time, the Ethernet OAM connection is considered disconnected.

Link monitoring

Error detection in an Ethernet is difficult, especially when the physical connection in the network is not disconnected but network performance is degrading gradually. Link monitoring is used to detect and indicate link faults in various environments. Ethernet OAM implements link monitoring through the exchange of Event Notification OAMPDUs. When detecting one of the link error events listed in Table 4, the local OAM entity sends an Event Notification OAMPDU to notify the remote OAM entity. With the log information, network administrators can keep track of network status promptly.

Table 4 Ethernet OAM link error events

Ethernet OAM link events	Description
Errored symbol event	An errored symbol event occurs when the number of detected symbol errors during a specified detection interval exceeds the predefined threshold.
Errored frame event	An errored frame event occurs when the number of detected error frames during a specified interval exceeds the predefined threshold.
Errored frame period event	An errored frame period event occurs if the number of frame errors in specified number of received frames exceeds the predefined threshold.
Errored frame seconds event	An errored frame seconds event occurs when the number of error frame seconds detected on a port during a specified detection interval reaches the error threshold.

NOTE:

· The system transforms the period of detecting errored frame period events into the maximum number of 64-byte frames that a port can send in the specified period. The system takes the maximum number of frames sent as the period. The maximum number of frames sent is calculated using this formula: the maximum number of frames = interface bandwidth (bps) × errored frame period event detection period (in ms)/(64 × 8 × 1000)

· A second in which errored frames appear is called an “errored frame second”.

Remote fault detection

Information OAMPDUs are exchanged periodically among Ethernet OAM entities across established OAM connections. In a network where traffic is interrupted due to device failures or unavailability, the flag field defined in information OAMPDUs allows an Ethernet OAM entity to send error information—the critical link event type—to its peer. You can use the log information to track ongoing link status and troubleshoot problems promptly.

Table 5 Critical link events

Type	Description	OAMPDU transmission frequencies
Link Fault	Peer link signal is lost.	Once per second
Dying Gasp	An unexpected fault, such as power failure, occurred.	Non-stop
Critical Event	An undetermined critical event happened.	Non-stop

NOTE:

· The switching engine on a WX3000E wireless switch is able to receive information OAMPDUs carrying the critical link events listed in Table 5.

· Only the Gigabit fiber ports are able to send information OAMPDUs carrying link fault events.

· The switching engine on a WX3000E Series Wireless Switches is able to send information OAMPDUs carrying Dying Gasp events when the device is rebooted or relevant ports are manually shut down.

· The switching engine on a WX3000E Series Wireless Switches is unable to send information OAMPDUs carrying Critical Events.

Remote loopback

Remote loopback is available only after the Ethernet OAM connection is established. With remote loopback enabled, the Ethernet OAM entity operating in active Ethernet OAM mode sends non-OAMPDUs to its peer. After receiving these frames, the peer does not forward them according to their destination addresses. Instead, it returns them to the sender along the original path.

Remote loopback enables you to check the link status and locate link failures. Performing remote loopback periodically helps to detect network faults promptly. Furthermore, performing remote loopback by network segments helps to locate network faults.

Standards and protocols

Ethernet OAM is defined in IEEE 802.3ah (Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications.

Ethernet OAM configuration task list

Complete the following tasks to configure Ethernet OAM:

Task		Remarks
Configuring basic Ethernet OAM functions		Required
Configuring the Ethernet OAM connection detection timers		Required
Configuring link monitoring	Configuring errored symbol event detection	Optional
	Configuring errored frame event detection	Optional
	Configuring errored frame period event detection	Optional
	Configuring errored frame seconds event detection	Optional
Configuring Ethernet OAM remote loopback		Optional

Configuring basic Ethernet OAM functions

For Ethernet OAM connection establishment, an Ethernet OAM entity operates in active mode or passive mode. Only an Ethernet OAM entity in active mode can initiate connection establishment. After Ethernet OAM is enabled on an Ethernet port, according to its Ethernet OAM mode, the Ethernet port establishes an Ethernet OAM connection with its peer port.

NOTE:

To change the Ethernet OAM mode on an Ethernet OAM-enabled port, you need to first disable Ethernet OAM on the port.

Follow these steps to configure basic Ethernet OAM functions:

To do…	Use the command…	Remarks
Enter system view	System-view	—
Enter Layer 2 Ethernet port view	interface interface-type interface-number	—
Set the Ethernet OAM mode	oam mode { active \| passive }	Optional The default is active Ethernet OAM mode.
Enable Ethernet OAM on the current port	oam enable	Required Ethernet OAM is disabled by default.

Configuring the Ethernet OAM connection detection timers

By adjusting the handshake packet transmission interval and the connection timeout timer, you can change the detection time resolution for Ethernet OAM connections.

Follow these steps to configure the Ethernet OAM connection detection timers:

To do…	Use the command…	Remarks
Enter system view	System-view	—
Configure the Ethernet OAM handshake packet transmission interval	oam timer hello interval	Optional 1000 millisecond by default.
Configure the Ethernet OAM connection timeout timer	oam timer keepalive interval	Optional 5000 milliseconds by default.

CAUTION:

After the timeout timer of an Ethernet OAM connection expires, the local OAM entity ages out its connection with the peer OAM entity, causing the OAM connection to be disconnected. H3C recommends that you set the connection timeout timer at least fives times the handshake packet transmission interval, ensuring the stability of Ethernet OAM connections.

Configuring link monitoring

NOTE:

After Ethernet OAM connections are established, the link monitoring periods and thresholds configured in this section take effect on all Ethernet ports automatically.

Configuring errored symbol event detection

Follow these steps to configure errored symbol event detection:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Configure the errored symbol event detection interval	oam errored-symbol period period-value	Optional 1 second by default.
Configure the errored symbol event triggering threshold	oam errored-symbol threshold threshold-value	Optional 1 by default.

Configuring errored frame event detection

Follow these steps to configure errored frame event detection:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Configure the errored frame event detection interval	oam errored-frame period period-value	Optional 1 second by default.
Configure the errored frame event triggering threshold	oam errored-frame threshold threshold-value	Optional 1 by default.

Configuring errored frame period event detection

Follow these steps to configure errored frame period event detection:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Configure the errored frame period event detection period	oam errored-frame-period period period-value	Optional 1000 milliseconds by default.
Configure the errored frame period event triggering threshold	oam errored-frame-period threshold threshold-value	Optional 1 by default.

Configuring errored frame seconds event detection

Follow these steps to configure errored frame seconds event detection:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Configure the errored frame seconds event detection interval	oam errored-frame-seconds period period-value	Optional 60 second by default.
Configure the errored frame seconds event triggering threshold	oam errored-frame-seconds threshold threshold-value	Optional 1 by default.

CAUTION:

Make sure the errored frame seconds triggering threshold is less than the errored frame seconds detection interval. Otherwise, no errored frame seconds event can be generated.

Configuring Ethernet OAM remote loopback

When you enable Ethernet OAM remote loopback on a port, the port sends Loopback Control OAMPDUs to a remote port, and the remote port enters the loopback state. The port then sends test frames to the remote port. By observing how many of these test frames return, you can calculate the packet loss ratio on the link and evaluate the link performance.

Follow these steps to enable Ethernet OAM remote loopback:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Enter Ethernet interface view	interface interface-type interface-number	—
Enable Ethernet OAM remote loopback	oam loopback	Required Disabled by default.

CAUTION:

Use this function with caution, because enabling Ethernet OAM remote loopback impacts other services.

NOTE:

· Ethernet OAM remote loopback is available only after the Ethernet OAM connection is established and can be performed only by Ethernet OAM entities operating in active Ethernet OAM mode.

· Remote loopback is available only on full-duplex links that support remote loopback at both ends.

· Ethernet OAM remote loopback must be supported by both the remote port and the sending port.

· Enabling Ethernet OAM remote loopback interrupts data communications. After Ethernet OAM remote loopback is disabled, all the ports involved will shut down and then come up. Ethernet OAM remote loopback can be disabled by any of the following events: executing the undo oam enable command to disable Ethernet OAM, executing the undo oam loopback command to disable Ethernet OAM remote loopback, and Ethernet OAM connection timing out.

· Ethernet OAM remote loopback is only applicable to individual links. It is not applicable to link aggregation member ports. In addition, do not assign ports where Ethernet OAM remote loopback is being performed to link aggregation groups. For more information about link aggregation groups, see the Layer 2 Configuration Guide.

· Enabling internal loopback test on a port in remote loopback test can terminate the remote loopback test. For more information about loopback test, see the Layer 2 Configuration Guide.

Displaying and maintaining Ethernet OAM configuration

To do…	Use the command…	Remarks
Display global Ethernet OAM configuration	display oam configuration [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Display the statistics on critical events after an Ethernet OAM connection is established	display oam critical-event [ interface interface-type interface-number ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Display the statistics on Ethernet OAM link error events after an Ethernet OAM connection is established	display oam link-event { local \| remote } [ interface interface-type interface-number ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Display the information about an Ethernet OAM connection	display oam { local \| remote } [ interface interface-type interface-number ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Clear statistics on Ethernet OAM packets and Ethernet OAM link error events	reset oam [ interface interface-type interface-number ]	Available in user view only

Ethernet OAM configuration example

Network requirements

On the network shown in Figure 2, perform the following operations:

· Enable Ethernet OAM on Device A and Device B to auto-detect link errors between the two devices

· Monitor the performance of the link between Device A and Device B by collecting statistics about the error frames received by Device A

Figure 2 Network diagram for Ethernet OAM configuration

Configuration procedure

1. Configure Device A

# Configure GigabitEthernet 1/0/1 to operate in passive Ethernet OAM mode and enable Ethernet OAM for it.

<DeviceA> system-view

[DeviceA] interface gigabitethernet 1/0/1

[DeviceA-GigabitEthernet1/0/1] oam mode passive

[DeviceA-GigabitEthernet1/0/1] oam enable

[DeviceA-GigabitEthernet1/0/1] quit

# Set the errored frame detection interval to 20 seconds and set the errored frame event triggering threshold to 10.

[DeviceA] oam errored-frame period 20

[DeviceA] oam errored-frame threshold 10

2. Configure Device B

# Configure GigabitEthernet 1/0/1 to operate in active Ethernet OAM mode (the default) and enable Ethernet OAM for it.

<DeviceB> system-view

[DeviceB] interface gigabitethernet 1/0/1

[DeviceA-GigabitEthernet1/0/1] oam mode active

[DeviceB-GigabitEthernet1/0/1] oam enable

[DeviceB-GigabitEthernet1/0/1] quit

3. Verify the configuration

Use the display oam configuration command to display the Ethernet OAM configuration. For example:

# Display the Ethernet OAM configuration on Device A.

[DeviceA] display oam configuration

Configuration of the link event window/threshold :

--------------------------------------------------------------------------

Errored-symbol Event period(in seconds) : 1

Errored-symbol Event threshold : 1

Errored-frame Event period(in seconds) : 20

Errored-frame Event threshold : 10

Errored-frame-period Event period(in ms) : 1000

Errored-frame-period Event threshold : 1

Errored-frame-seconds Event period(in seconds) : 60

Errored-frame-seconds Event threshold : 1

Configuration of the timer :

--------------------------------------------------------------------------

Hello timer(in ms) : 1000

Keepalive timer(in ms) : 5000

The output shows that the detection period of errored frame events is 20 seconds, the detection threshold is 10 seconds, and all the other parameters use the default values.

You can use the display oam critical-event command to display the statistics of Ethernet OAM critical link events. For example:

# Display the statistics of Ethernet OAM critical link events on all the ports of Device A.

[DeviceA] display oam critical-event

Port : GigabitEthernet1/0/1

Link Status : Up

Event statistic :

-------------------------------------------------------------------------

Link Fault :0 Dying Gasp : 0 Critical Event : 0

The output shows that no critical link event occurred on the link between Device A and Device B.

You can use the display oam link-event command to display the statistics of Ethernet OAM link error events. For example:

# Display Ethernet OAM link event statistics of the remote end of Device B.

[DeviceB] display oam link-event remote

Port :GigabitEthernet1/0/1

Link Status :Up

OAMRemoteErrFrameEvent : (ms = milliseconds)

---------------------------------------------------------------------

Event Time Stamp : 5789 Errored FrameWindow : 10(100ms)

Errored Frame Threshold : 1 Errored Frame : 3

Error Running Total : 35 Event Running Total : 17

The output shows that 35 errors occurred since Ethernet OAM is enabled on Device A, 17 of which are caused by error frames. The link is instable.

07-High Availability Configuration Guide

Ethernet OAM configuration

Ethernet OAMPDUs

How Ethernet OAM works

Ethernet OAM connection establishment

Link monitoring

Remote loopback

Ethernet OAM configuration task list

Configuring the Ethernet OAM connection detection timers

Configuring link monitoring

Configuring Ethernet OAM remote loopback

Network requirements

Configuration procedure

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