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Configuration Guide - IP Unicast Routing

S7700 and S9700 V200R010C00

This document describes IP Unicast Routing configurations supported by the switch, including the principle and configuration procedures of IP Routing Overview, Static Route, RIP, RIPng, OSPF, OSPFv3, IS-IS(IPv4), IS-IS(IPv6), BGP, Routing Policy ,and PBR, and provides configuration examples.
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Enabling OSPF IP FRR

Enabling OSPF IP FRR

This section describes how to enable OSPF IP FRR to generate a loop-free backup link. If the primary link fails, OSPF can fast switch traffic to the backup link.

Procedure

  1. Run:

    system-view

    The system view is displayed.

  2. Run:

    ospf [ process-id | router-id router-id | vpn-instance vpn-instance-name ] *

    The OSPF process is started, and the OSPF view is displayed.

  3. Run:

    frr

    The OSPF IP FRR view is displayed.

  4. Run:

    loop-free-alternate

    OSPF IP FRR is enabled to generate a loop-free backup link.

    By default, this function is disabled.OSPF can generate the loop-free backup link only when the OSPF IP FRR traffic protection inequality is met.

    NOTE:
    In the following description, Distance_opt(X, Y) indicates the shortest link from X to Y. S stands for a source node, E for the faulty node, N for a node along a backup link, and D for a destination node.
    • Link protection takes effect when the traffic to be protected flows along a specified link and the link costs meet the inequality: Distance_opt(N, D) < Distance_opt(N, S) + Distance_opt(S, D).

    • Node-and-link protection takes effect when the traffic to be protected flows along a specified link and node and the following conditions are met:

      • The link costs meet the inequality: Distance_opt(N, D) < Distance_opt(N, S) + Distance_opt(S, D).
      • The interface costs meet the inequality: Distance_opt(N, D) < Distance_opt(N, E) + Distance_opt(E, D).

  5. (Optional) Run:

    frr-priority static low

    The Loop-Free Alternates (LFA) algorithm is used to calculate the nexthop and outbound interface for a backup link.

    The nexthop and outbound interface of an OSPF loop-free backup link can be obtained using either of the following methods:

    • For a static backup link, after IP FRR is enabled using the ip frr command in the system view or VPN instance view, configure a nexthop and an outbound interface for the static backup link.
    • For a dynamic backup link, after OSPF IP FRR is enabled using the loop-free-alternate command, enable the device to use the LFA algorithm to calculate the nexthop and outbound interface for the dynamic backup link.

    By default, static backup links take preference over dynamic backup links during route selection. However, static backup links are less flexible than dynamic backup links. If a link failure occurs, static backup links cannot update automatically, but dynamic backup links can. Therefore, to ensure automatic link updates, run the frr-priority static low command to enable dynamic backup links to take preference over static backup links so that the LFA algorithm is used to calculate the nexthop and outbound interface.

  6. (Optional) Run:

    frr-policy route route-policy route-policy-name

    OSPF IP FRR filtering policies are configured.

    After OSPF IP FRR filtering policies are configured, only the OSPF backup routes that match the filtering conditions can be delivered to the forwarding table. To protect the traffic over a specific OSPF route, you can configure a filtering policy that matches the OSPF route to ensure that the route can be added to the forwarding table. If this route fails, OSPF can fast switch the traffic to a backup link.

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Updated: 2019-08-21

Document ID: EDOC1000141900

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