Overview of Ethernet OAM

Ethernet OAM provides the tools that network management software and network managers can use to determine how a network of Ethernet links is functioning. OAM can provide simple link-level information, provide performance statistics, or track end-to-end connectivity across the network. Simple link fault management (LFM) for Ethernet links is defined in IEEE 802.3ah. The most complete connectivity fault management (CFM) is defined in IEEE 802.1ag. This chapter emphasizes the use of CFM in a Metro Ethernet environment.

CFM can be used to monitor an Ethernet network at a per-service level, unlike LFM, which functions at the physical link level. The service monitored could be a virtual local area network (VLAN), concatenation of VLANs or a virtual private LAN service (VPLS) instance.

The major features of CFM are:

• Fault monitoring using the continuity check protocol
• Path discovery and fault verification using the linktrace protocol
• Fault isolation using the loopback protocol

CFM partitions the service network into various administrative domains. For example, operators, providers, and customers may be part of different administrative domains. Each administrative domain is mapped into one maintenance domain providing enough information to perform its own management, thus avoiding security breaches and making end-to-end monitoring possible. Each maintenance domain is associated with a level. Level allocation is based on the network hierarchy, where outermost domains are assigned a higher level than the innermost domains. In a CFM maintenance domain, each service instance is called a maintenance association. A maintenance association can be thought as a full mesh of maintenance endpoints (MEPs) having similar characteristics. MEPs are active CFM entities generating and responding to CFM protocol messages. The following examples below use CFM to monitor connectivity over a VPLS and bridge network.

In all the examples in this chapter, CFM can be used at two levels:

• By the service provider to check the connectivity among its provider edge (PE) routers
• By the customer to check the connectivity among its customer edge (CE) routers

  Note: The configured customer CFM level must be greater than service provider CFM level.

Note: The configurations in this chapter are only partial examples of complete and functional router configurations. Do not copy these configurations and use them directly on an actual system.