23.1.9 Notes on using CFM

(1) Devices that do not run CFM

When you use the CFM functionality, you do not need to use it on all the switches in a domain. However, CFM PDUs must be transparent on the switches on which the functionality is not used.

Except for the Switch, you need to configure the switches on which the CFM functionality is not used so that the frames described in the following table are transparent.

If the CFM functionality is not used, the Switch makes all CFM PDUs transparent.

(2) About coexistence with other functions

(3) About CFM PDU Burst-Receive

When there are 96 or more remote MEPs to be monitored continuously by the CC functionality, the Switch might receive CFM PDUs in a burst if the timing for sending CFM PDUs from remote MEPs is accidentally the same. In such case, the Switch might discard CFM PDUs and might detect a failure incorrectly.

If this problem occurs often, adjust the timing for sending CFM PDUs on all switches so that there is no timing overlap.

(4) MEP setting on MA with the same primary VLAN in the same domain

In MAs in which the same primary VLAN is set within the same domain (including the same MA), you cannot set two or more MEPs on the same port. If you do so, the CFM functionality does not operate correctly on the applicable MEPs.

(5) About Collecting Route Info in Linktrace

The linktrace functionality determines the destination port for forwarding linktrace messages by referencing the MIP CCM database or the MAC address table. However, correct routing information cannot be collected because the destination port cannot be determined until the CC functionality sends or receives a CCM when link-up is detected (including a second link-up after a link failure) or after a change of the route when a Spanning Tree Protocol is used.

(6) Timing When CFM Does Not Work in Up MEP and MIP

The CFM functionality does not work on the ports for up MEPs and MIPs for which link-up has not yet occurred after any of the events below has occurred. The functionality is able to operate if link-up occurred once.

• Switch startup (including restarting of the switch)

• Application of the configuration file to a running configuration

• Executing the restart vlan operation command

• Execution of the restart cfm operation command

(7) Understanding When a MIP Does Not Respond to Loopback,Linktrace on a Blocked Port

If you configure a MIP on a blocked port and perform one of the following operations for the port, the MIP might not respond to the loopback functionality and the linktrace functionality.

• Executing the Spanning Tree Protocol (PVST+, single) to use the loop guard functionality

• When the Spanning Tree Protocol (MSTP) is used, configuring the access VLAN or the native VLAN as the primary VLAN

• Using LLDP

• Using OADP

(8) About CC Operation in a Redundant Configuration

When a CC is operated on a network that has a redundant Layer 2 configuration (spanning tree, Ring Protocol, etc.), MEP of the local switch may receive CCM sent to detect ErrorCCM when a communication path is switched. This failure is corrected after the communication route becomes stable.