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NE40E V800R010C10SPC500 Configuration Guide - IP Routing 01

This is NE40E V800R010C10SPC500 Configuration Guide - IP Routing
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Configuring OSPF IP FRR

Configuring OSPF IP FRR

If a link fails, an OSPF IP FRR-capable device can fast switch traffic to a backup link, which protects traffic and improves OSPF network reliability.

Usage Scenario

As networks develop, services such as Voice over IP (VoIP) and on-line video services require high-quality real-time transmission. Nevertheless, if an OSPF fault occurs, traffic can be switched to a new link only after the fault detection that lasts milliseconds, fault notification to the routing control plane that lasts milliseconds, new topology information generation and flooding that lasts milliseconds, Shortest Path First (SPF) calculation that lasts tens of milliseconds, and new route notification and adding that lasts hundreds of milliseconds. As a result, it takes much more than 50 ms, the maximum convergence time tolerable for VoIP and on-line video services, which cannot meet the requirement for real-time services on the network.

With OSPF IP FRR that calculates a backup link in advance, devices can fast switch traffic to the backup link without interrupting traffic if the primary link fails, which protects traffic and improves OSPF network reliability.

As shown in Figure 5-4, traffic flows from Router S to Router D. The preceding inequality is met. Router S switches the traffic to the backup link if the primary link fails.

Figure 5-4 OSPF IP FRR link protection

NOTE:

OSPF IP FRR also applies to node protection. For details, see "OSPF" in HUAWEI NetEngine40E Feature Description.

OSPF IP FRR is applicable to services that are sensitive to packet delay and packet loss.

The NE40E supports OSPF IP FRR that uses LFA or Remote LFA as the algorithm.

LFA Auto FRR cannot be used to calculate alternate links on large-scale networks, especially on ring networks. To address this problem, enable Remote LFA Auto FRR. Remote LFA takes effect only when LFA has been enabled.

Both OSPF LFA FRR and OSPF remote LFA FRR use the SPF algorithm to calculate the shortest path to the destination node, with each neighbor that provides a backup link as the root node. The backup next hop is node-based, which applies to single-source routing scenarios. As networks are increasingly diversified, two ABRs or ASBRs are deployed to improve network reliability. In this case, OSPF FRR in a multi-source routing scenario is needed. In Figure 5-5, Device B and Device C function as ABRs to forward area 0 and area 1 routes. Device E advertises an intra-area route. Upon receipt of the route, Device B and Device C translate it to a Type 3 LSA and flood the LSA to area 0. After OSPF FRR is enabled on Device A, Device A considers Device B and Device C as its neighbors. Without a fixed neighbor as the root node, Device A fails to calculate FRR backup next hop. To address this problem, a virtual node is simulated between Device B and Device C and used as the root node of Device A, and Device A uses the LFA or remote LFA algorithm to calculate the backup next hop. This solution converts multi-source routing into single-source routing.

Figure 5-5 OSPF FRR in a multi-source routing scenario

After OSPF IP FRR is configured, the lower layer needs to fast respond to a link change so that traffic can be fast switched to the backup link. After FRR and BFD are bound, link failures can be detected rapidly so that traffic is rapidly switched to the backup link if the primary link fails.

Pre-configuration Tasks

Before configuring OSPF IP FRR, complete the following tasks:

  • Configure a link layer protocol.

  • Configure IP addresses for interfaces to ensure that neighboring nodes are reachable at the network layer.

  • Configure basic OSPF functions.

  • Before you configure remote LFA FRR, configure LDP LSPs to be iterated hop by hop between the source node and PQ node. That is, configure a local LDP session between each pair of directly connected nodes along the link from the source node to PQ node.

Configuration Procedures

Figure 5-6 Flowchart for configuring OSPF IP FRR

Enabling OSPF IP FRR

With OSPF IP FRR and loop-free backup links, a device can switch traffic to a backup link immediately if the primary link fails.

Context

Perform the following steps on the router:

Procedure

  1. Run system-view

    The system view is displayed.

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

    An 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, and a loop-free backup link is generated.

    NOTE:

    OSPF can generate a loop-free backup link only when the OSPF IP FRR traffic protection inequality is met. For detailed description of OSPF IP FRR, see HUAWEI NetEngine40E Feature Description- OSPF IP FRR.

  5. (Optional) Run frr-policy route { route-policy route-policy-name | route-filter route-filter-name }

    An OSPF IP FRR filtering policy is configured.

    After the OSPF IP FRR filtering policy is configured, only the OSPF backup routes that match the filtering conditions of the policy can be added to the forwarding table.

  6. If you want to configure remote LFA Auto FRR, perform the following steps:
    1. Run remote-lfa tunnel ldp [ maximum-reachable-cost cost-value ]

      Remote LFA Auto FRR is enabled.

    2. (Optional) Run remote-lfa available-tunnel-destination ip-prefix ip-prefix-name

      A filtering policy is configured to filter PQ nodes.

      Only the PQ node that matches the filtering policy can be used as the next hop of an LFA link.

    3. (Optional) Run avoid-microloop frr-protected

      The OSPF anti-microloop is enabled.

    4. (Optional) Run avoid-microloop frr-protected rib-update-delay rib-update-delay

      The delay after which OSPF delivers routes is configured.

      If OSPF remote LFA FRR is enabled and the primary link fails, traffic is switched to the backup link. If route convergence occurs again, traffic is switched from the backup link to a new primary link. During the switchover, microloop may occur. To prevent this problem, OSPF anti-microloop is enabled and delays the switching. To configure the delay, run the avoid-microloop frr-protected rib-update-delay command. After the command is run, OSPF does not switch traffic to the backup link until the delay elapses.

      NOTE:
      OSPF anti-microloop applies only to OSPF remote LFA FRR.

  7. (Optional) Run tiebreaker { node-protecting | lowest-cost | ldp-sync hold-max-cost } preference preference

    The solution of selecting a backup path for OSPF IP FRR is set.

    By default, the solution of selecting a backup path for OSPF IP FRR is node-protection path first. In some cases, the solution needs to be changed to smallest-cost path first because of data forwarding capacity or link cost consideration. In Figure 5-7, the primary path is Link-1 (Device S -> Device E -> Device D), and Link-2 and Link-3 (Device S -> Device N -> Device D) are backup path candidates. By default, Link-3 is selected as the backup path. To change the solution of selecting a backup path for OSPF IP FRR to smallest-cost path first, run the tiebreaker command. After the command is run, Link-2 is selected as the backup path.
    Figure 5-7 Solution of selecting a backup path for OSPF IP FRR
    Figure 5-8 shows an inter-board scenario, where Link-1 (Device A -> Device D) is the primary path, and Link-2 (Device A -> Device E -> Device D) is the backup path. If Link-1 fails, Link-2 functions as the new primary path, and Link-3 (Device A->Device B->Device C->Device D) functions as the new backup path. If Link-1 goes Up again but the LDP session has not gone Up, OSPF enters the Hold-max-cost state. Consequently, the primary path is still Link-2, and the backup path is still Link-3. If the LDP session goes Up but ldp-sync hold-max-cost is not configured, OSPF exits from the Hold-max-cost state when the timer used to delay sending an LDP session Up message expires. In this case, OSPF switches the primary path back to Link-1. Because the upstream and downstream entries reside on different boards and the downstream entry has not been updated when downstream traffic arrives, packet loss occurs. To resolve the problem, configure ldp-sync hold-max-cost so that OSPF preferentially selects the path with the maximum cost set by LDP-IGP synchronization when OSPF is in the Hold-max-cost state. Then OSPF switches the backup path to Link-1 and delivers the backup forwarding entry in advance. When the timer used to delay sending an LDP session Up message expires, OSPF exits from the Hold-max-cost state and switches the primary path to Link-1. Because the downstream backup entry is available, no packet loss occurs.
    Figure 5-8 Maximum-cost (set by LDP-IGP synchronization) path first solution

  8. Run commit

    The configuration is committed.

(Optional) Binding IP FRR and BFD

Binding IP FRR and BFD enables the lower layer to fast respond to a link change so that traffic can be rapidly switched to the backup link if the primary link fails.

Context

After the parameter frr-binding is set to bind the BFD status to the link status of an interface, link failures can be detected rapidly. This ensures that traffic is rapidly switched to the backup link if the primary link fails.

Perform the following steps on the router where IP FRR and BFD need to be bound:

Procedure

  • Bind IP FRR and BFD in an OSPF process.
    1. Run system-view

      The system view is displayed.

    2. Run ospf

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

    3. Run bfd all-interfaces frr-binding

      IP FRR and BFD are bound in the OSPF process.

    4. Run commit

      The configuration is committed.

  • Bind IP FRR and BFD on a specified OSPF interface.
    1. Run system-view

      The system view is displayed.

    2. Run interface interface-type interface-number

      The interface view is displayed.

    3. Run ospf bfd frr-binding

      IP FRR and BFD are bound on the interface.

      NOTE:

      The BFD configuration on an interface takes precedence over that in an OSPF process.

    4. Run commit

      The configuration is committed.

(Optional) Disabling OSPF IP FRR on an Interface

If an interface runs key services, ensure that the backup path does not pass through this interface so that services will not be affected after FRR calculation.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run interface interface-type interface-number

    The view of an OSPF interface on which FRR is enabled is displayed.

  3. Run ospf frr block

    FRR is blocked on the OSPF interface.

  4. (Optional) Run ospf remote-lfa disable

    Interfaces of the specified level are disabled from being calculated as the Remote LFA next hop.

  5. Run commit

    The configuration is committed.

Verifying the Configuration of OSPF IP FRR

After configuring OSPF IP FRR, you can view the information about the backup next hop.

Prerequisites

OSPF IP FRR has been configured.

Procedure

  • Run the display ospf [ process-id ] routing command to check the information about the primary and backup links after configuring OSPF IP FRR.

Example

View the routes to a specified OSPF router, including information about the backup next hop.

<HUAWEI> display ospf routing 10.1.1.1
         OSPF Process 1 with Router ID 1.1.1.1

 Destination    : 10.1.1.0/24                  
 AdverRouter    : 10.1.1.1             Area             : 0.0.0.0
 Cost           : 1                    Type             : Transit
 NextHop        : 10.1.1.2             Interface        : GE1/0/0
 Priority       : High                 Age              : 09h20m11s
 Backup NextHop : 10.1.1.3             Backup Interface : GE1/0/1
 Backup Type    : LFA LINK             Tunnel Destination  : 3.3.3.3
 Tunnel Type    : LDP
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Updated: 2019-01-03

Document ID: EDOC1100055018

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