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NE40E V800R010C10SPC500 Feature Description - Network Reliability 01

This is NE40E V800R010C10SPC500 Feature Description - Network Reliability
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VRRP Tracking CFM

VRRP Tracking CFM

Principles

Virtual Router Redundancy Protocol (VRRP) tracking Ethernet in the First Mile (EFM) effectively facilitates link fault detection on a network on which UPEs do not support Bidirectional Forwarding Detection (BFD). However, EFM can detect faults only on single-hop links. As shown in Figure 5-20, EFM cannot detect faults on the link between UPE2 and NPE1 or between UPE2 and NPE2.

Figure 5-20 VRRP networking diagram

Connectivity fault management (CFM) defined in 802.1ag provides functions, such as point-to-point connectivity fault detection, fault notification, fault verification, and fault locating. CFM can monitor the connectivity of an entire network and locate connectivity faults. CFM can also be used together with switchover techniques to improve network reliability. VRRP tracking CFM enables a VRRP backup group to rapidly perform a master/backup VRRP switchover when CFM detects a link fault. This implementation minimizes the service interruption time.

Implementation

NOTE:

CFM can detect only local link failures. If the link between UPE2 and NPE1 fails, NPE2 cannot detect the failure. NPE2 has to wait three VRRP Advertisement packet transmission intervals before it switches to the Master state. During this period, upstream service traffic is interrupted. To speed up master/backup VRRP switchovers and minimize the service interruption time, configure VRRP also to track the peer BFD session.

Figure 5-21 shows a network on which VRRP tracks CFM and the peer BFD session.
Figure 5-21 VRRP tracking CFM
  • NPE1 and NPE2 are configured to belong to a VRRP backup group.
  • A peer BFD session is configured to detect the faults on the two NPEs and on the link between the two NPEs.
  • A CFM session is configured between UPE2 and NPE1 and between UPE2 and NPE2 to detect the faults on UPE2 and the NPEs and on links between UPE2 and the NPEs.
The implementation is as follows:
  1. In normal circumstances, NPE1 periodically sends VRRP Advertisement packets to inform NPE2 that NPE1 works properly. NPE1 and NPE2 both track the CFM and peer BFD session status.
  2. If NPE1 or the link between UPE2 and NPE1 fails, the status of the CFM session between UPE2 and NPE1 changes to Down, the status of the peer BFD session changes to Down, and the status of the CFM session between UPE2 and NPE2 changes to Up. NPE1's VRRP status directly changes from Master to Initialize, and NPE2's VRRP status directly changes from Backup to Master.
  3. After NPE1 or the link between UPE2 and NPE1 recovers, the status of the peer BFD session changes to Up, and the status of the CFM session between UPE2 and NPE1 changes to Up. If the preemption function is configured on NPE1, NPE1 changes back to the Master state after VRRP negotiation, and NPE2 changes back to the Backup state.
    NOTE:
    In normal circumstances, if the link between UPE2 and NPE2 fails, NPE1 remains in the Master state and continues to forward upstream traffic. However, NPE2's VRRP status changes to Master if NPE2 detects the Down state of the peer BFD session before it detects the Down state of the link between itself and UPE2. After NPE2 detects the Down state of the link between itself and UPE2, NPE2's VRRP status changes from Master to Initialize.
Figure 5-22 shows the state machine for VRRP tracking CFM.
Figure 5-22 State machine for VRRP tracking CFM

Benefits

VRRP tracking CFM prevents service interruptions caused by dual master devices in a VRRP backup group and facilitates master/slave VRRP switchovers.

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Updated: 2019-01-03

Document ID: EDOC1100055045

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