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Feature Description - MPLS 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Feature Description - MPLS
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Loopback Detection for a Static Bidirectional Co-Routed CR-LSP

Loopback Detection for a Static Bidirectional Co-Routed CR-LSP

Loopback detection for a specified static bidirectional co-routed CR-LSP locates faults if a few packets are dropped or bit errors occur on links along the CR-LSP.

Background

On a network with a static bidirectional co-routed CR-LSP used to transmit services, if a few packets are dropped or bit errors occur on links, no alarms indicating link or LSP failures are generated, which poses difficulties in locating the faults. To locate the faults, loopback detection can be enabled for the static bidirectional co-routed CR-LSP.

Implementation

To implement loopback detection for a specified static bidirectional co-routed CR-LSP, a transit node temporarily connects the forward CR-LSP to the reverse CR-LSP and generates a forwarding entry for the loop so that the transit node can loop all traffic back to the ingress. A professional monitoring device connected to the ingress monitors data packets that the ingress sends and receives and checks whether a fault occurs on the link between the ingress and transit node.

The dichotomy method is used to perform loopback detection by reducing the range of nodes to be monitored before locating a faulty node. For example, in Figure 4-38, loopback detection is enabled for a static bidirectional co-routed CR-LSP established between PE1 (ingress) and PE2 (egress). The process of using loopback detection to locate a fault is as follows:

  1. Loopback is enabled on P1 to loop data packets back to the ingress. The ingress checks whether the sent packets match the received ones.

    • If the packets do not match, a fault occurs on the link between PE1 and P1. Loopback detection can then be disabled on P1.

    • If the packets match, the link between PE1 and P1 is working properly. The fault location continues.

  2. Loopback is disabled on P1 and enabled on P2 to loop data packets back to the ingress. The ingress checks whether the sent packets match the received ones.

    • If the packets do not match, a fault occurs on the link between P1 and P2. Loopback detection can then be disabled on P2.

    • If the packets match, a fault occurs on the link between P2 and PE2. Loopback detection can then be disabled on P2.

Figure 4-38 Loopback detection for a static bidirectional co-routed CR-LSP
NOTE:

Loopback detection information is not saved in a configuration file after loopback detection is enabled. A loopback detection-enabled node loops traffic back to the ingress through a temporary loop. Loopback alarms can then be generated to prompt users that loopback detection is performed. After loopback detection finishes, it can be manually or automatically disabled. Loopback detection configuration takes effect only on a main control board. After a master/slave main control board switchover is performed, loopback detection is automatically disabled.

Benefits

Loopback detection for a static bidirectional co-routed CR-LSP helps rapidly local faults, such as minor packet loss or bit errors, and improve network operation and maintenance efficiency.

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Updated: 2019-01-14

Document ID: EDOC1100058933

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