示例：为 IS-IS 配置与分段路由无关的无环路替代产品
此示例显示了 IS-IS 协议与分段路由相关的拓扑无关无环路备用 （TI-LFA），该协议使用更深的标签堆栈构造备份路径，为给定故障提供与后融合路径对应的 MPLS 快速重新路由 （FRR） 备份路径。TI-LFA 提供链路故障、节点故障和命运共享故障防护。在链路故障模式下，如果链路失败，目标将得到保护。在节点保护模式下，如果连接到主链路的邻接方发生故障，目标将受到保护。要确定节点保护的融合后路径，假定离开邻接方的所有链路的成本都会增加一定数额。借助命运共享保护，在每个 PLR 上配置了命运共享组列表，每个命运共享组中的链路均由其各自的 IP 地址标识。
注意：
我们的内容测试团队已经验证并更新了此示例。
要求
此示例使用以下硬件和软件组件：
9 台 MX 系列路由器
在所有设备上运行的 Junos OS 17.4 或更高版本
-
在 Junos OS 21.1R1 版上使用 vMX 进行更新和重新验证。
-
使用 SPRING 为 IS-IS 配置 TI-LFA 路由之前，请确保配置 SPRING 或分段路由。
概述
Junos OS 允许您通过在层次结构级别配置 use-post-convergence-lfa 语句 [edit protocols isis backup-spf-options] 来为 IS-IS 启用 TI-LFA。通过在层级配置融合后 lfa 语句 [edit protocols isis interface interface-name level level] ，可以为给定接口创建融合后备份路径。
TI-LFA 提供针对链路故障、节点故障和命运共享组故障的防护。您可以使用语句启用链路保护模式post-convergence-lfa。可以为层次结构级别的给定接口[edit protocols isis interface interface-name level level post-convergence-lfa]启用node-protection模式或两fate-sharing-protection种模式。为了确保为给定的命运共享组启用命运共享保护，需要在层次结构级别配置语句use-for-post-convergence-lfa[edit routing-options fate-sharing group group-name]。
注意：
TI-LFA 支持对 IPv4 和 IPv6 前缀的路由进行保护。此示例演示了对 IPv4 前缀的路由的保护。
拓扑
配置
CLI 快速配置
要快速配置此示例中的链路保护，请复制以下命令，将其粘贴到文本文件中，删除所有换行符，更改详细信息，以便与网络配置匹配，将命令复制并粘贴到 [edit] 层次结构级别的 CLI 中，然后从配置模式进入提交。
R1
set interfaces ge-0/0/0 unit 0 description r1-to-r21 set interfaces ge-0/0/0 unit 0 family inet address 10.10.20.1/24 set interfaces ge-0/0/0 unit 0 family iso set interfaces ge-0/0/0 unit 0 family mpls set interfaces ge-0/0/1 unit 0 description r1-to-r31 set interfaces ge-0/0/1 unit 0 family inet address 10.10.30.1/24 set interfaces ge-0/0/1 unit 0 family iso set interfaces ge-0/0/1 unit 0 family mpls set interfaces ge-0/0/2 unit 0 description r1-to-r2 set interfaces ge-0/0/2 unit 0 family inet address 10.10.10.1/24 set interfaces ge-0/0/2 unit 0 family iso set interfaces ge-0/0/2 unit 0 family mpls set interfaces lo0 unit 0 family inet address 198.168.0.1/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0001.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/0.0 level 2 disable set protocols isis interface ge-0/0/0.0 point-to-point set protocols isis interface ge-0/0/1.0 level 2 disable set protocols isis interface ge-0/0/1.0 point-to-point set protocols isis interface ge-0/0/2.0 level 2 disable set protocols isis interface ge-0/0/2.0 level 1 post-convergence-lfa set protocols isis interface ge-0/0/2.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1001 set protocols isis backup-spf-options use-post-convergence-lfa maximum-labels 8 set protocols mpls interface ge-0/0/0.0 set protocols mpls interface ge-0/0/1.0 set protocols mpls interface ge-0/0/2.0 set policy-options policy-statement pplb then load-balance per-packet set routing-options forwarding-table export pplb set routing-options router-id 198.168.0.1
R 2
set interfaces ge-0/0/1 unit 0 description r2-to-r23 set interfaces ge-0/0/1 unit 0 family inet address 10.10.50.1/24 set interfaces ge-0/0/1 unit 0 family iso set interfaces ge-0/0/1 unit 0 family mpls set interfaces ge-0/0/2 unit 0 description r2-to-r1 set interfaces ge-0/0/2 unit 0 family inet address 10.10.10.2/24 set interfaces ge-0/0/2 unit 0 family iso set interfaces ge-0/0/2 unit 0 family mpls set interfaces ge-0/0/3 unit 0 description r2-to-r3 set interfaces ge-0/0/3 unit 0 family inet address 10.10.40.1/24 set interfaces ge-0/0/3 unit 0 family iso set interfaces ge-0/0/3 unit 0 family mpls set interfaces lo0 unit 0 family inet address 192.168.0.2/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0002.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/1.0 level 2 disable set protocols isis interface ge-0/0/1.0 point-to-point set protocols isis interface ge-0/0/2.0 level 2 disable set protocols isis interface ge-0/0/2.0 point-to-point set protocols isis interface ge-0/0/3.0 level 2 disable set protocols isis interface ge-0/0/3.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1002 set protocols mpls interface ge-0/0/1.0 set protocols mpls interface ge-0/0/2.0 set protocols mpls interface ge-0/0/3.0 set routing-options router-id 192.168.0.2
R3
set interfaces ge-0/0/0 unit 0 description r3-to-r24 set interfaces ge-0/0/0 unit 0 family inet address 10.10.60.1/24 set interfaces ge-0/0/0 unit 0 family iso set interfaces ge-0/0/0 unit 0 family mpls set interfaces ge-0/0/1 unit 0 description r3-to-r34 set interfaces ge-0/0/1 unit 0 family inet address 10.10.70.1/24 set interfaces ge-0/0/1 unit 0 family iso set interfaces ge-0/0/1 unit 0 family mpls set interfaces ge-0/0/3 unit 0 description r3-to-r2 set interfaces ge-0/0/3 unit 0 family inet address 10.10.40.2/24 set interfaces ge-0/0/3 unit 0 family iso set interfaces ge-0/0/3 unit 0 family mpls set interfaces lo0 unit 0 family inet address 192.168.0.3/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0003.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/0.0 level 2 disable set protocols isis interface ge-0/0/0.0 point-to-point set protocols isis interface ge-0/0/1.0 level 2 disable set protocols isis interface ge-0/0/1.0 point-to-point set protocols isis interface ge-0/0/3.0 level 2 disable set protocols isis interface ge-0/0/3.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1003 set protocols mpls interface ge-0/0/0.0 set protocols mpls interface ge-0/0/1.0 set protocols mpls interface ge-0/0/3.0 set routing-options router-id 192.168.0.3
R21
set interfaces ge-0/0/0 unit 0 description r21-to-r1 set interfaces ge-0/0/0 unit 0 family inet address 10.10.20.2/24 set interfaces ge-0/0/0 unit 0 family iso set interfaces ge-0/0/0 unit 0 family mpls set interfaces ge-0/0/1 unit 0 description r21-to-r22 set interfaces ge-0/0/1 unit 0 family inet address 10.10.80.1/24 set interfaces ge-0/0/1 unit 0 family iso set interfaces ge-0/0/1 unit 0 family mpls set interfaces lo0 unit 0 family inet address 192.168.0.21/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0021.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/0.0 level 2 disable set protocols isis interface ge-0/0/0.0 point-to-point set protocols isis interface ge-0/0/1.0 level 2 disable set protocols isis interface ge-0/0/1.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1021 set protocols mpls interface ge-0/0/0.0 set protocols mpls interface ge-0/0/1.0 set routing-options router-id 192.168.0.21
R22
set interfaces ge-0/0/0 unit 0 description r22-to-r23 set interfaces ge-0/0/0 unit 0 family inet address 10.10.90.1/24 set interfaces ge-0/0/0 unit 0 family iso set interfaces ge-0/0/0 unit 0 family mpls set interfaces ge-0/0/1 unit 0 description r22-to-r21 set interfaces ge-0/0/1 unit 0 family inet address 10.10.80.2/24 set interfaces ge-0/0/1 unit 0 family iso set interfaces ge-0/0/1 unit 0 family mpls set interfaces lo0 unit 0 family inet address 192.168.0.22/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0022.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/0.0 level 2 disable set protocols isis interface ge-0/0/0.0 point-to-point set protocols isis interface ge-0/0/1.0 level 2 disable set protocols isis interface ge-0/0/1.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1022 set protocols mpls interface ge-0/0/0.0 set protocols mpls interface ge-0/0/1.0 set routing-options router-id 192.168.0.22
R23
set interfaces ge-0/0/0 unit 0 description r23-to-r22 set interfaces ge-0/0/0 unit 0 family inet address 10.10.90.2/24 set interfaces ge-0/0/0 unit 0 family iso set interfaces ge-0/0/0 unit 0 family mpls set interfaces ge-0/0/1 unit 0 description r23-to-r2 set interfaces ge-0/0/1 unit 0 family inet address 10.10.50.2/24 set interfaces ge-0/0/1 unit 0 family iso set interfaces ge-0/0/1 unit 0 family mpls set interfaces ge-0/0/2 unit 0 description r23-to-r24 set interfaces ge-0/0/2 unit 0 family inet address 10.10.100.1/24 set interfaces ge-0/0/2 unit 0 family iso set interfaces ge-0/0/2 unit 0 family mpls set interfaces lo0 unit 0 family inet address 192.168.0.23/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0023.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/0.0 level 2 disable set protocols isis interface ge-0/0/0.0 point-to-point set protocols isis interface ge-0/0/1.0 level 2 disable set protocols isis interface ge-0/0/1.0 point-to-point set protocols isis interface ge-0/0/2.0 level 2 disable set protocols isis interface ge-0/0/2.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1023 set protocols mpls interface ge-0/0/0.0 set protocols mpls interface ge-0/0/1.0 set protocols mpls interface ge-0/0/2.0 set routing-options router-id 192.168.0.23
R24
set interfaces ge-0/0/0 unit 0 description r24-to-r3 set interfaces ge-0/0/0 unit 0 family inet address 10.10.60.2/24 set interfaces ge-0/0/0 unit 0 family iso set interfaces ge-0/0/0 unit 0 family mpls set interfaces ge-0/0/2 unit 0 description r24-to-r23 set interfaces ge-0/0/2 unit 0 family inet address 10.10.100.2/24 set interfaces ge-0/0/2 unit 0 family iso set interfaces ge-0/0/2 unit 0 family mpls set interfaces lo0 unit 0 family inet address 192.168.0.24/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0024.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/0.0 level 2 disable set protocols isis interface ge-0/0/0.0 point-to-point set protocols isis interface ge-0/0/2.0 level 2 disable set protocols isis interface ge-0/0/2.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1024 set protocols mpls interface ge-0/0/0.0 set protocols mpls interface ge-0/0/2.0 set routing-options router-id 192.168.0.24
R31
set interfaces ge-0/0/0 unit 0 description r31-to-r34 set interfaces ge-0/0/0 unit 0 family inet address 10.10.110.1/24 set interfaces ge-0/0/0 unit 0 family iso set interfaces ge-0/0/0 unit 0 family mpls set interfaces ge-0/0/1 unit 0 description r31-to-r1 set interfaces ge-0/0/1 unit 0 family inet address 10.10.30.2/24 set interfaces ge-0/0/1 unit 0 family iso set interfaces ge-0/0/1 unit 0 family mpls set interfaces lo0 unit 0 family inet address 198.162.0.31/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0031.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/0.0 level 1 metric 500 set protocols isis interface ge-0/0/0.0 level 2 disable set protocols isis interface ge-0/0/0.0 point-to-point set protocols isis interface ge-0/0/1.0 level 1 metric 10 set protocols isis interface ge-0/0/1.0 level 2 disable set protocols isis interface ge-0/0/1.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1031 set protocols mpls interface ge-0/0/1.0 set protocols mpls interface ge-0/0/0.0 set routing-options router-id 198.162.0.31
R34
set interfaces ge-0/0/0 unit 0 description r34-to-r31 set interfaces ge-0/0/0 unit 0 family inet address 10.10.110.2/24 set interfaces ge-0/0/0 unit 0 family iso set interfaces ge-0/0/0 unit 0 family mpls set interfaces ge-0/0/1 unit 0 description r34-to-r3 set interfaces ge-0/0/1 unit 0 family inet address 10.10.70.2/24 set interfaces ge-0/0/1 unit 0 family iso set interfaces ge-0/0/1 unit 0 family mpls set interfaces lo0 unit 0 family inet address 192.168.0.34/32 set interfaces lo0 unit 0 family iso address 49.0000.2222.0034.00 set interfaces lo0 unit 0 family mpls set protocols isis interface ge-0/0/0.0 level 1 metric 500 set protocols isis interface ge-0/0/0.0 level 2 disable set protocols isis interface ge-0/0/0.0 point-to-point set protocols isis interface ge-0/0/1.0 level 1 metric 10 set protocols isis interface ge-0/0/1.0 level 2 disable set protocols isis interface ge-0/0/1.0 point-to-point set protocols isis interface fxp0.0 disable set protocols isis interface lo0.0 passive set protocols isis source-packet-routing node-segment ipv4-index 1034 set protocols mpls interface ge-0/0/0.0 set protocols mpls interface ge-0/0/1.0 set routing-options router-id 192.168.0.34
配置 R1
逐步过程
以下示例要求您在配置层次结构中的各个级别上导航。有关导航 CLI 的信息，请参阅《Junos OS CLI 用户指南》中的在配置模式下使用 CLI 编辑器。
要配置设备 R1：
-
配置接口。
[edit interfaces] user@R1# set ge-0/0/0 unit 0 description r1-to-r21 user@R1# set ge-0/0/0 unit 0 family inet address 10.10.20.1/24 user@R1# set ge-0/0/0 unit 0 family iso user@R1# set ge-0/0/0 unit 0 family mpls user@R1# set ge-0/0/1 unit 0 description r1-to-r31 user@R1# set ge-0/0/1 unit 0 family inet address 10.10.30.1/24 user@R1# set ge-0/0/1 unit 0 family iso user@R1# set ge-0/0/1 unit 0 family mpls user@R1# set ge-0/0/2 unit 0 description r1-to-r2 user@R1# set ge-0/0/2 unit 0 family inet address 10.10.10.1/24 user@R1# set ge-0/0/2 unit 0 family iso user@R1# set ge-0/0/2 unit 0 family mpls user@R1# set lo0 unit 0 family inet address 198.168.0.1/32 user@R1# set lo0 unit 0 family iso address 49.0000.2222.0001.00 user@R1# set lo0 unit 0 family mpls
-
配置路由器 ID。
[edit routing-options] user@R1# set router-id 198.168.0.1
-
配置 MPLS。
[edit protocols] user@R1# set mpls interface ge-0/0/0.0 user@R1# set mpls interface ge-0/0/1.0 user@R1# set mpls interface ge-0/0/2.0
-
配置 IS-IS。
[edit protocols] user@R1# set isis interface ge-0/0/0.0 level 2 disable user@R1# set isis interface ge-0/0/0.0 point-to-point user@R1# set isis interface ge-0/0/1.0 level 2 disable user@R1# set isis interface ge-0/0/1.0 point-to-point user@R1# set isis interface ge-0/0/2.0 level 2 disable user@R1# set isis interface ge-0/0/2.0 point-to-point user@R1# set isis interface lo0.0 passive user@R1# set isis interface fxp0.0 disable
-
配置为在接口 ge-0/0/2 上沿链路保护后融合路径安装备份路由。
[edit protocols] user@R1# set isis interface ge-0/0/2.0 level 1 post-convergence-lfa
-
配置分段路由路由路径的最大标签数，以保护备份最短路径优先属性。
[edit protocols] user@R1# set isis backup-spf-options use-post-convergence-lfa maximum-labels 8
-
为 IS-IS 协议的分段路由中的节点分段配置 IPv4 索引和索引范围。
[edit protocols] user@R1# set isis source-packet-routing node-segment ipv4-index 1001
-
（可选）在接口 ge-0/0/2 上启用节点保护。
[edit protocols] user@R1# set isis interface ge-0/0/2 level 2 post-convergence-lfa node-protection cost 2000
-
（可选）配置命运共享组成本。
[edit routing-options] user@R1# set fate-sharing group fs-group-1 cost 3000
-
（可选）配置命运共享组以指示从设备 R1 到设备 R2 的链路，以及从设备 R21 到设备 R22 的链路共享命运，并允许用于后融合-lfa。
[edit routing-options] user@R1# set fate-sharing group fs-group-1 from 10.10.10.1 to 10.10.10.2 user@R1# set fate-sharing group fs-group-1 from 10.10.80.1 to 10.10.80.2 user@R1# set fate-sharing group fs-group-1 use-for-post-convergence-lfa
-
（可选）为设备 R1 上的 ge-0/0/2 启用命运共享保护。
[edit protocols] user@R1# set isis interface ge-0/0/2 level 2 post-convergence-lfa fate-sharing-protection
-
为 TI-LFA 配置按数据包负载均衡策略，确保更快融合。
[edit] user@R1# set policy-options policy-statement pplb then load-balance per-packet
-
应用策略，将路由导出到转发表。
[edit] user@R1# set routing-options forwarding-table export pplb
结果
在配置模式下，输入 、 show protocols 和 show routing-options 命令，show interfaces以确认您的配置。如果输出未显示预期的配置，请重复此示例中的说明，以更正配置。
user@R1# show interfaces
ge-0/0/0 {
unit 0 {
description r1-to-r21;
family inet {
address 10.10.20.1/24;
}
family iso;
family mpls;
}
}
ge-0/0/1 {
unit 0 {
description r1-to-r31;
family inet {
address 10.10.30.1/24;
}
family iso;
family mpls;
}
}
ge-0/0/2 {
unit 0 {
description r1-to-r2;
family inet {
address 10.10.10.1/24;
}
family iso;
family mpls;
}
}
lo0 {
unit 0 {
family inet {
address 198.168.0.1/32;
}
family iso {
address 49.0000.2222.0001.00;
}
family mpls;
}
}
user@R1# show routing-options
router-id 198.168.0.1;
forwarding-table {
export pplb;
}
user@R1# show policy-options
policy-statement pplb {
then {
load-balance per-packet;
}
}
user@R1# show protocols
isis {
interface ge-0/0/0.0 {
level 2 disable;
point-to-point;
}
interface ge-0/0/1.0 {
level 2 disable;
point-to-point;
}
interface ge-0/0/2.0 {
level 2 disable;
level 1 {
post-convergence-lfa;
}
point-to-point;
}
interface fxp0.0 {
disable;
}
interface lo0.0 {
passive;
}
source-packet-routing {
node-segment ipv4-index 1001;
}
backup-spf-options {
use-post-convergence-lfa maximum-labels 8;
}
}
mpls {
interface ge-0/0/0.0;
interface ge-0/0/1.0;
interface ge-0/0/2.0;
}
完成设备配置后，请从配置模式进入 commit 。
验证
确认配置工作正常。
使用节点 SID 验证 TI-LFA 路由
目的
验证设备 R1 的接口 ge-0/0/2 上的主要下一跃点的链路保护备份路径，并验证是否已创建达到 192.168.0.3/32 的备份路径并具有正确的标签堆栈。
行动
在操作模式下，运行 show route 192.168.0.3 命令以显示路由表信息。
user@R1> show route 192.168.0.3
inet.0: 38 destinations, 38 routes (38 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
192.168.0.3/32 *[IS-IS/15] 09:52:56, metric 20
> to 10.10.10.2 via ge-0/0/2.0
inet.3: 8 destinations, 8 routes (8 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
192.168.0.3/32 *[L-ISIS/14] 05:45:40, metric 20
> to 10.10.10.2 via ge-0/0/2.0, Push 801003
to 10.10.20.2 via ge-0/0/0.0, Push 801003, Push 801024(top)
意义
要达到 198.168.0.3/32（对应于设备 R3）的主路径通过接口 ge-0/0/2，标签为 801003，与设备 R3 的节点 SID 相对应。如果接口 ge-0/0/2 出现故障，则使用接口 ge-0/0/0（使用标签堆栈 [801024，801003] 的备份路径将变为活动状态。链路保护的融合后路径是 R1-R21-R22-R23-R24-R3。标签堆栈上的顶部标签是801024，与到达 R24 的节点 SID 相对应。801003标签与 R23 上的节点 SID 相对应，以在最短路径 R23-R2-R3 上到达 R3。
验证邻接 SID
验证与设备 R1 具有 IS-IS 邻接的设备的邻接 SID。
注意：
在配置设置中，SID 值可能会有所不同。
行动
在操作模式下，运行 show isis adjacency detail 命令以显示设备 R1 上的邻接信息。
user@R1> show isis adjacency detail R21 Interface: ge-0/0/0.0, Level: 1, State: Up, Expires in 19 secs Priority: 0, Up/Down transitions: 3, Last transition: 07:06:07 ago Circuit type: 1, Speaks: IP, IPv6 Topologies: Unicast Restart capable: Yes, Adjacency advertisement: Advertise IP addresses: 10.10.20.2 Level 1 IPv4 Adj-SID: 299840 R31 Interface: ge-0/0/1.0, Level: 1, State: Up, Expires in 22 secs Priority: 0, Up/Down transitions: 3, Last transition: 07:06:07 ago Circuit type: 1, Speaks: IP, IPv6 Topologies: Unicast Restart capable: Yes, Adjacency advertisement: Advertise IP addresses: 10.10.30.2 Level 1 IPv4 Adj-SID: 299808 R2 Interface: ge-0/0/2.0, Level: 1, State: Up, Expires in 24 secs Priority: 0, Up/Down transitions: 3, Last transition: 07:06:07 ago Circuit type: 1, Speaks: IP, IPv6 Topologies: Unicast Restart capable: Yes, Adjacency advertisement: Advertise IP addresses: 10.10.10.2 Level 1 IPv4 Adj-SID: 299776
意义
邻接 SID 被分配给分段路由域中设备 R1 的每个邻接：
- 设备 R21 - 299840
- 设备 R31 - 299808
- 设备 R2 - 299776
邻接 SID 具有本地意义，可用于沿着特定传出接口引导流量。如果不配置邻接 SID，系统就会使用默认（或配置）SRGB 范围以外的值动态分配这些 SID。
使用邻接 SID 验证 TI-LFA 路由
目的
提高从 R1 到 R3 的后融合路径的成本，并使用邻接 SID 验证 TI-LFA 路由，以避免使用到达目标的主要路径（设备 R3）。
行动
在配置模式下，增加连接设备 R22 和 R23、ge-0/0/0 的接口成本。
[edit protocols] user@R22# set protocols isis interface ge-0/0/0.0 level 1 metric 1000 user@R22# commit
在操作模式下，再次运行 show route 192.168.0.3 命令。
user@R1> show route 192.168.0.3
inet.0: 38 destinations, 38 routes (38 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
192.168.0.3/32 *[IS-IS/15] 10:44:56, metric 20
> to 10.10.10.2 via ge-0/0/2.0
inet.3: 8 destinations, 8 routes (8 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
192.168.0.3/32 *[L-ISIS/14] 00:00:31, metric 20
> to 10.10.10.2 via ge-0/0/2.0, Push 801003
to 10.10.30.2 via ge-0/0/1.0, Push 801003, Push 299808(top)
意义
TI-LFA 备份路径现在使用邻接 SID（在此案例中为299808）而非节点 SID （801003） 到达设备 R3。这是因为节点 SID 始终使用两个节点之间的最短路径，而当 R22-R23 链路成本上升时，R1 的最短路径会与主路径重叠。由于 TI-LFA 无法采用主路径到达目标，因此邻接 SID 会采用 R31-R34 作为到达设备 R3 的新融合后路径。