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Configuration Guide - IP Routing 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 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 IS-IS Auto FRR

Configuring IS-IS Auto FRR

This section describes how to configure IS-IS Auto FRR.

Usage Scenario

Single-source routing scenario

As networks develop, voice over IP (VoIP) and online video services pose increasingly higher requirements for real-time transmission. Nevertheless, if an IS-IS fault occurs, multiple operations, including fault detection, LSP updating, LSP flooding, route calculation, and forwarding information base (FIB) entry delivery, must be performed to switch traffic to a new link. These operations take a long time, much longer than 50 ms, the minimum delay to which users are sensitive. As a result, user experience is affected.

With IS-IS Auto FRR, devices can rapidly switch traffic from a faulty link to an alternate one without interrupting the traffic, which significantly improves IS-IS network reliability.

IS-IS Auto FRR is suitable for IP services that are sensitive to delay and packet loss.

In Figure 9-3, the link cost satisfies the traffic protection inequality: Distance_opt (B, D) < Distance_opt (B, A) + Distance_opt (A, D), in which Distance_opt (X, Y) specifies the shortest distance from node X to node Y. After IS-IS Auto FRR is configured, if the link between Device A and Device C fails, traffic forwarded by Device A is rapidly switched to the alternate link.
Figure 9-3 Networking with IS-IS Auto FRR

The NE supports IS-IS Auto 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.

Multi-source routing scenario

IS-IS LFA FRR uses 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. With the diversification of networks, multi-source routing scenarios appear, where multiple nodes advertise the same route. Such multi-source routing scenarios do not meet single-source LFA conditions. As a result, the backup next hop cannot be calculated. IS-IS FRR for multi-source routing scenarios can address this problem by using a routing source to protect the primary routing source and improve network reliability.

Figure 9-4 Networking with IS-IS FRR in a multi-source routing scenario

In Figure 9-4 (a), the cost of the link between Device A and Device B is 5, whereas the cost of the link between Device A and Device C is 10. Both Device B and Device C advertise the route 10.1.1.0/24. IS-IS FRR is enabled on Device A. However, single-source LFA conditions are not met. As a result, Device A fails to calculate the backup next hop of the route 10.1.1.0/24. IS-IS FRR for multi-source routing scenarios can address this problem.

In Figure 9-4 (b), a virtual node is simulated between Device B and Device C and is connected to Device B and Device C. The cost of the link from Device B or Device C to the virtual node is 0, whereas the cost of the link from the virtual node to Device B or Device C is the maximum value. After the virtual node advertises the route 10.1.1.0/24, Device A uses the LFA algorithm to calculate the backup next hop of the virtual node. Then the route 10.1.1.0/24 inherits the backup next hop from the virtual node. In this example, the primary link to the virtual node is the one from Device A to Device B, and the backup link is the one from Device A to Device C.

Pre-configuration Tasks

Before configuring IS-IS Auto FRR, complete the following tasks:

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

  • Configure basic IPv4 IS-IS 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.

Procedure

  1. Run system-view

    The system view is displayed.

  2. Run isis [ process-id ]

    The IS-IS process is enabled, and the IS-IS view is displayed.

    By default, an IS-IS process runs in a public network instance.

  3. Run frr

    The IS-IS FRR view is displayed.

    By default, FRR is not enabled.

  4. Run loop-free-alternate [ level-1 | level-2 | level-1-2 ]

    LFA is enabled for IS-IS Auto FRR.

    If no IS-IS level is specified, LFA is enabled for both Level-1 and Level-2 IS-IS Auto FRR.

    For details about IS-IS Auto FRR, see Feature Description - IP Routing.

    NOTE:

    IS-IS can calculate the loop-free alternate route only if the interface cost meets the traffic protection inequality of IS-IS Auto FRR.

  5. (Optional) Run frr-policy route route-policy route-policy-name

    A route-policy is configured to filter IS-IS alternate routes.

    By default, all calculated IS-IS alternate routes are added to the routing table, which consumes a large number of memory resources and complicates network optimization. To address this problem, configure a route-policy to allow the device to add only the IS-IS alternate routes that match the policy to the routing 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 ] [ level-1 | level-2 | level-1-2 ]

      Remote LFA Auto FRR is enabled.

    2. (Optional) Run remote-lfa available-tunnel-destination ip-prefix ip-prefix-name [ level-1 | level-2 | level-1-2 ]

      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 IS-IS anti-microloop is enabled.

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

      The delay after which IS-IS delivers routes is configured.

      If IS-IS 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, IS-IS anti-microloop is enabled by default and delays the switching. To configure the delay, run the avoid-microloop frr-protected rib-update-delay command. After the command is run, IS-IS does not switch traffic to the backup link until the delay elapses.

      By default, the delay is 100 ms. Keeping the default delay is recommended.

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

  7. (Optional) Run tiebreaker { node-protecting | lowest-cost } preference preference [ level-1 | level-2 | level-1-2 ]

    The solution of selecting a backup path for IS-IS Auto FRR is set.

    By default, the solution of selecting a backup path for IS-IS Auto FRR is node-protection path first.

    By default, the solution of selecting a backup path for IS-IS Auto 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 9-5, the primary path is Link-1 (DeviceS -> DeviceE -> DeviceD), and Link-2 and Link-3 (DeviceS -> DeviceN -> DeviceD) are backup path candidates. By default, Link-3 is selected as the backup path. To change the solution of selecting a backup path for IS-IS Auto FRR to smallest-cost path first, run the tiebreaker command. After the command is run, Link-2 is selected as the backup path.
    Figure 9-5 Solution of selecting a backup path for IS-IS Auto FRR

  8. (Optional) After the preceding steps are performed, all IS-IS interfaces will be calculated to select an LFA next hop. If you want to disable an interface from being calculated as an LFA next hop, perform the following steps:
    1. Run quit

      Return to the IS-IS view.

    2. Run quit

      Return to the system view.

    3. Run interface interface-type interface-number

      The interface view is displayed.

    4. Run undo isis lfa-backup [ level-1 | level-2 | level-1-2 ]

      The interface is disabled from being calculated as an LFA or Remote LFA next hop.

      By default, an IS-IS interface can participate in LFA calculation.

  9. (Optional) Run isis remote-lfa disable [ level-1 | level-2 | level-1-2 ]

    The system is prevented from calculating a remote LFA next hop for the IS-IS route whose outbound interface is the current interface.

  10. Run commit

    The configuration is committed.

Checking the Configurations

After configuring IS-IS Auto FRR, check the configurations.

  • Run the display isis route [ level-1 | level-2 ] [ process-id ] [ verbose ] command to check information about the primary and alternate links after IS-IS Auto FRR is enabled.

  • Run the display isis spf-tree [ [ level-1 | level-2 ] | verbose ] * [ process-id | vpn-instance vpn-instance-name ] command to check SPT topology.

Enable IS-IS Auto FRR and check information about the outbound interface and next hop of the alternate route with destination address 100.1.1.0/24.

<HUAWEI> display isis route verbose
                                                                                
                         Route information for ISIS(1)                          
                         -----------------------------                          
                                                                                
                        ISIS(1) Level-1 Forwarding Table                        
                        --------------------------------                        
                                                                                
 IPV4 Dest  : 100.1.1.0/24       Int. Cost : 30            Ext. Cost : NULL     
 Admin Tag  : -                  Src Count : 1             Flags     : A/-/L/-/-
 Priority   : Medium
 NextHop    :                    Interface :               ExitIndex :          
      1.0.0.2                            GE0/1/0                   0x00000003   
     (B)2.0.0.2                         GE0/2/0                   0x00000004
                                                                                
     Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, U-Up/Down Bit Set   
                                                                                
                                                                                
                        ISIS(1) Level-2 Forwarding Table                        
                        --------------------------------                        
                                                                                
 IPV4 Dest  : 100.1.1.0/24       Int. Cost : 30            Ext. Cost : NULL     
 Admin Tag  : -                  Src Count : 3             Flags     : -/-/-/-/-
 Priority   : Medium
 NextHop    :                    Interface :               ExitIndex :          
      1.0.0.2                            GE0/1/0                   0x00000003   
 Remote LFA:
  Interface  : GE0/3/0      NextHop   : 2.0.0.2  
  Tunnel Type: LDP        Tunnel Destination Address: 2.2.2.2
                                                                                
     Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
                                 U-Up/Down Bit Set   
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Updated: 2019-01-14

Document ID: EDOC1100058916

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