1.组网需求

  Switch A、Switch B和Switch C属于同一IS-IS路由域，通过IS-IS协议实现网络互连。要求当Switch A和Switch B之间的链路出现故障时，业务可以快速切换到链路B上。

     

2.配置步骤

  1）配置各交换机接口的IP地址和IS-IS协议

  配置各交换机之间采用IS-IS协议进行互连，确保Switch A、Switch B和Switch C之间能够在网络层互通，并且各交换机之间能够借助IS-IS协议实现动态路由更新。

  2）配置IS-IS快速重路由

  IS-IS支持快速重路由配置有两种配置方法，一种是通过LFA（Loop Free Alternate）算法选取备份下一跳，另一种是在路由策略中指定备份下一跳

  方法一：使能Switch A和Switch B的IS-IS协议的自动计算快速重路由能力  

SW A
[SwitchA] isis 1
[SwitchA-isis-1] address-family ipv4
[SwitchA-isis-1-ipv4] fast-reroute lfa

SW B
[SwitchB] isis 1
[SwitchB-isis-1] address-family ipv4
[SwitchB-isis-1-ipv4] fast-reroute lfa

  方法二：使能Switch A和Switch B的IS-IS协议的指定路由策略快速重路由能力  

SW A
[SwitchA] ip prefix-list abc index 10 permit 4.4.4.4 32
[SwitchA] route-policy frr permit node 10
[SwitchA-route-policy-frr-10] if-match ip address prefix-list abc
[SwitchA-route-policy-frr-10] apply fast-reroute backup-interface vlan-interface 100 backup-nexthop 12.12.12.2
[SwitchA-route-policy-frr-10] quit
[SwitchA] isis 1
[SwitchA-isis-1] address-family ipv4
[SwitchA-isis-1-ipv4] fast-reroute route-policy frr

SW B
[SwitchB] ip prefix-list abc index 10 permit 1.1.1.1 32
[SwitchB] route-policy frr permit node 10
[SwitchB-route-policy-frr-10] if-match ip address prefix-list abc
[SwitchB-route-policy-frr-10] apply fast-reroute backup-interface vlan-interface 101 backup-nexthop 24.24.24.2
[SwitchB-route-policy-frr-10] quit
[SwitchB] isis 1
[SwitchB-isis-1] address-family ipv4
[SwitchB-isis-1-ipv4] fast-reroute route-policy frr

3.配置验证  

# 在Switch A上查看4.4.4.4/32路由，可以看到备份下一跳信息。

[SwitchS] display ip routing-table 4.4.4.4 verbose
Summary count : 1
Destination: 4.4.4.4/32
   Protocol: IS_L1
 Process ID: 1
  SubProtID: 0x1                    Age: 04h20m37s
       Cost: 10              Preference: 10
      IpPre: N/A             QosLocalID: N/A
        Tag: 0                    State: Active Adv
  OrigTblID: 0x0                OrigVrf: default-vrf
    TableID: 0x2                 OrigAs: 0
      NibID: 0x26000002          LastAs: 0
     AttrID: 0xffffffff        Neighbor: 0.0.0.0
      Flags: 0x1008c        OrigNextHop: 13.13.13.2
      Label: NULL           RealNextHop: 13.13.13.2
    BkLabel: NULL             BkNextHop: 12.12.12.2
    SRLabel: NULL             BkSRLabel: NULL
   SIDIndex: NULL               InLabel: NULL
  Tunnel ID: Invalid          Interface: Vlan-interface200
BkTunnel ID: Invalid        BkInterface: Vlan-interface100
   FtnIndex: 0x0           TrafficIndex: N/A
  Connector: N/A                 PathID: 0x0
   LinkCost: 0               MicroSegID: 0

# 在Switch B上查看1.1.1.1/32路由，可以看到备份下一跳信息。略