Fault Information Advertisement Between CFM and Other Modules

Fault Information Advertisement Between CFM and Detection Modules

An OAMMGR module associates CFM with detection modules. A detection module can be EFM, CFM, BFD. Fault information advertisement between CFM and detection modules enables a device to delete ARP or MAC address entries once a fault is detected. Figure 1 shows the network on which fault information is advertised between CFM and detection modules.

Figure 1 Networking for fault information advertisement between CFM and detection modules

The following example illustrates fault information advertisement between CFM and detection modules over a path UPE1 -> PE2 -> PE4 -> PE6 -> PE8 on the network shown in Table 1.

**Table 1** Fault information advertisement between CFM and detection modules
Function Deployment	Issue to Be Resolved	Solution
CFM is used to monitor the link between UPE1 and PE4.	Although CFM detects a fault in the link between UPE1 and PE4, CFM cannot notify PE6 of the fault. As a result, PE6 still forwards network traffic to PE4, causing a traffic interruption. Although port 1 on PE4 goes Down, port 1 cannot notify CE1 of the fault. As a result, CE1 still forwards user traffic to PE4, causing a traffic interruption.	CFM can be associated with port 1. If CFM detects a fault, it instructs the OAMMGR module to disconnect port 1 intermittently. This operation allows other modules to detect the fault. If port 1 goes Down, it instructs the OAMMGR module to notify CFM of the fault. After receiving the notification, CFM notifies PE6 of the fault. The association between CFM and a port is used to detect faults in an active link of a link aggregation group or in the link aggregation group in 1:1 active/standby mode. If a fault is detected, a protection switchover is triggered.
EFM is used to monitor the direct link between CE1 and UPE1, and CFM is used to monitor the link between UPE1 and PE4.	Although CFM detects a fault, CFM cannot notify CE1 of the fault. As a result, CE1 still forwards user traffic to PE4, causing a traffic interruption.	The EFM module can be associated with the CFM module. If the EFM module detects a fault, it instructs the OAMMGR module to notify the CFM module of the fault. If the CFM module detects a fault, it instructs the OAMMGR module to notify the EFM module of the fault. The association allows a module to notify another associated module of a fault and to send an alarm to an NMS. A network administrator analyzes alarm information and takes measures to rectify the fault.
CFM is configured to monitor the links between UPE1 and PE4 and between PE4 and PE8.	Although CFM detects a fault in the link between PE4 and PE8, it cannot notify UPE1 of the fault. As a result, UPE1 still forwards user traffic to PE4 through PE2, causing a traffic interruption. Although CFM detects a fault in the link between UPE1 and PE4, it cannot notify PE8 of the fault. As a result, PE8 still forwards network traffic to PE4 through PE6, causing a traffic interruption.	Two CFM modules can be associated with each other. If a CFM module detects a fault, it instructs the OAMMGR module to notify the other CFM module of the fault and sends an alarm to an NMS. A network administrator analyzes alarm information and takes measures to rectify the fault. CFM can be associated with MAC or ARP entry clearing. If CFM detects a fault, it instructs an interface to clear MAC or ARP entries, triggering traffic to be switched to a backup link.
CFM is used to monitor the link between UPE1 and PE4. BFD can be used to monitor the non-Ethernet link between PE4 and PE8.	Although CFM detects a fault in the link between UPE1 and PE4, it cannot notify PE8 of the fault. As a result, PE8 still forwards network traffic to PE4 through PE6, causing a traffic interruption. Although BFD detects a fault, BFD cannot notify UPE1 of the fault. As a result, UPE1 still forwards user traffic to PE4 through PE2, causing a traffic interruption.	The CFM module can be associated with the BFD module. If the CFM module detects a fault, it instructs the OAMMGR module to notify the BFD module of the fault. If the BFD module detects a fault, it instructs the OAMMGR module to notify the CFM module of the fault. The association allows a module to notify another associated module of a fault and to send an alarm to an NMS. A network administrator analyzes alarm information and takes measures to rectify the fault.

Fault Information Advertisement Between CFM and Application Modules

The OAMMGR module associates a CFM module with application modules, such as a Virtual Router Redundancy Protocol (VRRP) module.

Figure 2 shows the network on which a CFM module advertises fault information to a VRRP module. Figure 3 shows the network on which a VRRP module advertises fault information to a CFM module.

Figure 2 Fault information advertisement by a CFM module to a VRRP module

Figure 3 Fault information advertisement by a CFM module to a VRRP module

Table 2 describes fault information advertisement between CFM and VRRP modules.

**Table 2** Fault information advertisement between CFM and VRRP modules
Function Deployment	Issue to Be Resolved	Solution
A VRRP backup group is configured to determine the master/backup status of network provider edges (NPEs). CFM is used to monitor links between NPEs and PE-AGGs.	If a fault occurs on the link between NPE1 (the master) and PE-AGG1, NPE2 cannot receive VRRP packets within a period of three times the interval at which VRRP packets are sent. NPE2 then preempts the Master state. As a result, two master devices coexist in a VRRP backup group, and the UPE receives double copies of network traffic.	CFM can be associated with the VRRP module on NPEs. If CFM detects a fault in the link between PE-AGG1 and NPE1, it instructs the OAMMGR module to notify the VRRP module of the fault. After receiving the notification, the VRRP module triggers a master/backup VRRP switchover. NPE1 then changes its VRRP status to Initialize. NPE2 changes its VRRP status from Backup to Master after a period of three times the interval at which VRRP packets are sent. This process prevents two master devices from coexisting in the VRRP backup group.
A VRRP backup group is configured to determine the master/backup status of NPEs. CFM is used to monitor links between NPEs and PE-AGGs. PW redundancy is configured to determine the active/standby status of PWs.	If a fault occurs on the backbone network, it triggers a master/backup VRRP switchover but cannot trigger an active/standby PW switchover. As a result, the CE still transmits user traffic to the previous master NPE, causing a traffic interruption.	When VRRP status changes on NPEs, the VRRP module notifies PE-AGGs' CFM modules of VRRP status changes. The CFM module on each PE-AGG notifies the PW module of the status change and triggers an active/standby PW switchover. Each PE-AGG notifies its associated UPE of the PW status change. After the UPE receives the notification, it determines the primary/backup status of PWs.