Introduction to OAM Link Fault Management (LFM)
This section describes the Operation, Administration, and Management (OAM) of link fault management (LFM).
Use Feature Explorer to confirm platform and release support for specific features.
Review the Platform-Specific OAM LFM Behavior section for notes related to your platform.
IEEE 802.3ah OAM Link Fault Management Overview
Junos OS supports IEEE 802.3ah link-fault management. Junos OS enables routers and switches to support the IEEE 802.3ah OAM standard for Ethernet interfaces in access networks. The standard defines OAM LFM. You can configure IEEE 802.3ah OAM LFM on point-to-point Ethernet links that are connected either directly or through Ethernet repeaters. The IEEE 802.3ah standard meets the requirement for OAM capabilities as Ethernet moves from being solely an enterprise technology to being a WAN and access technology, as well as being backward-compatible with existing Ethernet technology.
Ethernet OAM provides tools that network management software and network managers can use to determine how a network of Ethernet links is functioning. Ethernet OAM should:
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Rely only on the media access control (MAC) address or virtual LAN identifier for troubleshooting.
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Work independently of the actual Ethernet transport and function over physical Ethernet ports or a virtual service such as a pseudowire.
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Isolate faults over a flat (or single-operator) network architecture or nested or hierarchical (or multiprovider) networks.
The features of LFM are:
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Discovery and Link Monitoring
The discovery process is triggered automatically when OAM is enabled on the interface. The discovery process permits Ethernet interfaces to discover and monitor the peer on the link if it also supports the IEEE 802.3ah standard. You can specify the discovery mode used for IEEE 802.3ah OAM support. In active mode, the interface discovers and monitors the peer on the link if the peer also supports IEEE 802.3ah OAM functionality. In passive mode, the peer initiates the discovery process. After the discovery process has been initiated, both sides participate in the process. The router performs link monitoring by sending periodic OAM protocol data units (PDUs) to advertise OAM mode, configuration, and capabilities.
You can specify the number of OAM PDUs that an interface can skip before the link between peers is considered down.
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Remote Fault Detection
Remote fault detection uses flags and events. Flags are used to convey the following:
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Link Fault means a loss of signal
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Dying Gasp means an unrecoverable condition such as a power failure. In this condition, the local peer informs the remote peer about the failure state. When the remote peer receives a dying-gasp PDU, it takes an action corresponding to the action profile configured with the link-adjacency-loss event.
When LFM is configured on an interface, a dying-gasp PDU is generated for the interface on the following failure conditions:
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Power failure
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Packet Forwarding Engine panic or a crash
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Critical Event means an unspecified vendor-specific critical event.
You can specify the interval at which OAM PDUs are sent for fault detection.
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Remote Loopback Mode
Remote loopback mode ensures link quality between the router and a remote peer during installation or troubleshooting. In this mode, when the interface receives a frame that is not an OAM PDU or a PAUSE frame, it sends it back on the same interface on which it was received. The link appears to be in the active state. You can use the returned loopback acknowledgement to test delay, jitter, and throughput.
If a remote data terminal equipment (DTE) supports remote loopback mode, Junos OS can place the remote DTE into loopback mode. When you place a remote DTE into loopback mode, the interface receives the remote loopback request and puts the interface into remote loopback mode. When the interface is in remote loopback mode, all frames except OAM PDUs and PAUSE frames are looped back. No changes are made to the frames. OAM PDUs continue to be sent and processed.
The Ethernet link fault management daemon (lfmd) runs on the backup Routing Engine when graceful Routing Engine switchover (GRES) is configured.
Aggregated Ethernet member links use the physical MAC address as the source MAC address in 802.3ah OAM packets.
Configure Ethernet 802.3ah OAM
The IEEE 802.3ah standard for Operation, Administration, and Management (OAM) provides a specification for Ethernet in the first mile (EFM) connectivity. EFM defines how Ethernet can be transmitted over new media types using new Ethernet physical layer (PHY) interfaces. You can configure IEEE 802.3ah OAM on Ethernet point-to-point direct links or links across Ethernet repeaters. The IEEE 802.3ah OAM standard meets the requirement for OAM capabilities as Ethernet moves from being solely an enterprise technology to being a WAN and access technology, as well as being backward-compatible with existing Ethernet technology.
For Ethernet interfaces capable of running at 100 Mbps or faster, the IEEE 802.3ah OAM standard is supported on numerous Juniper Networks routers and switches. This topic describes configuration support for IEEE 802.3ah OAM features on routers.
To configure 802.3ah OAM support for Ethernet interfaces, include the
oam statement at the [edit protocols]
hierarchy level:
oam {
ethernet {
link-fault-management {
interfaces {
interface-name {
pdu-interval interval;
link-discovery (active | passive);
pdu-threshold count;
}
}
}
}
}
You can configure threshold values for fault events that trigger the sending of link
event TLVs when the values exceed the threshold. To set threshold values for fault
events on an interface, include the event-thresholds statement at
the [edit protocols oam ethernet link-fault-management interface]
hierarchy level.
You can also configure OAM threshold values within an action profile and apply the
action profile to multiple interfaces. To create an action profile, include the
action-profile statement at the [edit protocols oam
ethernet link-fault-management] hierarchy level.
You can configure LFM on an aggregate Ethernet interface (aex), on its member links, or on both. When you configure LFM on both the aex and its member links, the member link configuration takes precedence over the aex configuration. In addition, when LFM is configured on a member link, parameters that are not explicitly configured on that member link use their default values and do not inherit values configured on the aex. To avoid unexpected behavior, explicitly configure any aex LFM parameters on the member links.
For example, if you configure pdu-interval
100 on aggregate Ethernet interface
ae0 and configure LFM on member link
et-0/0/4:0 using only the pdu-threshold
5 statement, the member link uses its
default pdu-interval value of 1000 instead of the
ae0 value of 100. To ensure consistent behavior, configure
pdu-interval 100 on
et-0/0/4:0.
To view OAM statistics, use the show oam ethernet
link-fault-management operational mode command. To clear OAM
statistics, use the clear oam ethernet link-fault-management
statistics operational mode command. To clear link-fault management
state information and restart the link discovery process on Ethernet interfaces, use
the clear oam ethernet link-fault-management state operational mode
command. For more information about these commands, see the CLI Explorer.
To enable IEEE 802.3ah OAM support, include the interface statement
at the [edit protocols oam ethernet link-fault-management]
hierarchy level:
[edit protocols oam ethernet link-fault-management interface interface-name]
When you enable IEEE 802.3ah OAM on a physical interface, the discovery process is automatically triggered.
Platform-Specific OAM LFM Behavior
Use Feature Explorer to confirm platform and release support for specific features.
Use the following table to review platform-specific behaviors for your platform.
| Platform | Difference |
|---|---|
|
ACX Series |
|
|
MX Series |
|
|
PTX Series |
|
Change History Table
Feature support is determined by the platform and release you are using. Use Feature Explorer to determine if a feature is supported on your platform.