The Nokia layer 2 switch must enable Ethernet Connectivity Fault Management (ETH-CFM) to protect against one-way connections.

In topologies where fiber optic interconnections are used, physical misconnections can occur that allow a link to appear to be up when there is a mismatched set of transmit/receive pairs. When such a physical misconfiguration occurs, protocols such as Spanning Tree Protocol (STP) can cause network instability.

Enabling ETH-CFM is the standard and most effective way to protect a layer 2 service against one-way (unidirectional) connections on a Nokia 7750 SR. The constant, bidirectional exchange of Continuity Check Messages (CCMs) provides an "always-on" monitoring system. It ensures that connectivity is healthy in both directions, detecting silent failures that would be missed by on-demand tests such as a loopback (ping).

Verify the ETH-CFM configuration for the service access point (SAP) in the virtual private local area network service (VPLS) appears as shown in the example below.

- show service id 10 sap 1/1/c3/10 detail

Eth-Cfm MEP Configuration Information

Md-index : 3 Direction : Down Ma-index : 1 Admin : Enabled MepId : 10 CCM-Enable : Enabled

If ETH-CFM is not configured to protect against one-way connections, this is a finding.

Configure the ETH-CFM maintenance domain and bind the Maintenance Endpoint (MEP) to the SAP to be monitored. Use the CCMs to detect possible unidirectional issues.

Configure ETH-CFM domain information:

- configure eth-cfm domain <domain id> format none level <level> - association 1 format icc-based name <name> - bridge-identifier bridge-name <vpls service name> - back - remote-mepid <mep id>

Apply to the SAP within VPLS:

- configure service vpls <id> - sap <sap id> eth-cfm mep <mep id> domain <domain id> association <index> - ccm-enable - no shutdown