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CLI-based Configuration Guide - IP Unicast Routing

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document describes the concepts and configuration procedures of IP Service features on the device, and provides the configuration examples.
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Configuring a Route Monitoring Group (Non-Down-Weight Mode)

Configuring a Route Monitoring Group (Non-Down-Weight Mode)

In a dual-device hot backup scenario, you can add network-side routes to a route monitoring group and associate access-side service modules with it so that the service modules can perform primary/backup link switchovers upon route status changes in the group. This mechanism can prevent traffic congestion or loss.

Context

To improve network reliability, most carriers implement device-level redundancy by deploying two devices. The two devices back up each other and can balance traffic loads. If one of the devices fails, the other device can take over user services.

As shown in Figure 13-1, BRAS1 and BRAS2 backs up each other. NPEs on the user side are dual-homed to two BRASs to balance traffic loads, and the two BRASs are connected to the IP core network.

Figure 13-1 Route monitoring group
On the network shown in Figure 13-1, configure a route monitoring group on each BRAS and add multiple network-side routes of the BRAS to the route monitoring group.
  • If all links on the network side fail, the RM module reports the information to the associated service modules on the BRAS to trigger a primary/backup link switchover. This allows NPEs to access the other BRAS to prevent traffic loss and service interruptions.
  • (Optional) You can set the status of routes in the route monitoring group to be of the AND relation. If a link on the network side fails, the RM module reports the information to the associated service modules on the BRAS to trigger a primary/backup link switchover. This allows NPEs to access the other BRAS to prevent network congestion arising from link faults.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run ip route-monitor-group group-name

    By default, no route monitoring groups are created.

    A route monitoring group is created, and the route monitoring group view is displayed.

  3. Run track ip route [ vpn-instance vpn-instance-name ] dest-address { mask | mask-length }

    A route is added to the route monitoring group.

    By default, no routes are added to a route monitoring group.

    To add multiple routes to the route monitoring group, repeat this step. A maximum of 16 routes can be added to a route monitoring group.

  4. (Optional) Run operator and The status of routes in the route monitoring group is set to be of the AND relation.

    After this command is run, the status of the route monitoring group is up only when all routes in the group are up. The status of the monitoring group is down as long as one route is down.

    By default, routes in a route monitoring group is of the OR relation. That is, the status of the route monitoring group is up as long as one route in the group is up. The status of the monitoring group is down if all routes in the group is down.

  5. (Optional) Run trigger-down-delay delay-value

    A delay is configured after which the RM module instructs the associated service modules to perform link switchovers.

    By default, the delay is 0s.

    During a link switchover, the RM module re-delivers routes to the forwarding table and establishes forwarding entries for the routes, which takes some time. Packet loss may occur if the RM module immediately instructs the associated service modules to perform link switchovers. To resolve this problem, run the trigger-down-delay command to configure a delay after which the RM module instructs the associated service modules to perform link switchovers.

    If the value of delay-value is set to 0, the RM module instructs the service modules to perform link switchovers immediately when the status of the route monitoring group changes to down.

  6. (Optional) Run trigger-up-delay delay-value

    A delay is configured after which the RM module instructs the associated service modules to perform link switchbacks.

    By default, the delay is 5s.

    If a route in a route monitoring group goes up again, the RM module delivers this route to the forwarding table and establishes a forwarding entry for it, which takes some time. Packet loss may occur if the RM module immediately instructs the associated service modules to perform link switchbacks. To resolve this problem, run the trigger-up-delay command to configure a delay after which the RM module instructs the associated service modules to perform link switchbacks.

    If the value of delay-value is set to 0, the RM module instructs the associated service modules to perform link switchbacks immediately when the status of the route monitoring group changes to up.

  7. Run monitor enable in the route monitoring group view

    The route monitoring group is enabled.

    By default, the route monitoring group is disabled.

    When a large number of routes are being added to or deleted from a route monitoring group, the status of the route monitoring group may change frequently, which in turn leads to service flapping of the service modules associated with the route monitoring group. To prevent such service flapping, run the undo monitor enable command in the route monitoring group view to disable the route monitoring group so that it is dissociated from all service modules. After the routes are added or deleted, run the monitor enable command in the route monitoring group to re-associate the route monitoring group with all service modules.

Verifying the Configuration

  • Run the display ip route-monitor-group [ group-name ] command to view information about all route monitoring groups or a specific one.
  • Run the display ip route-monitor-group track-route [ vpn-instance vpn-instance-name ] dest-address { mask | mask-length } command to view information about all route monitoring groups to which a route has been added.

In a dual-device hot backup scenario, you can associate specified service modules with a route monitoring group to protect specified services. This prevents traffic overload and forwarding failures when the primary link on the network side fails, improving user experience.

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Updated: 2019-08-12

Document ID: EDOC1100034072

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