在Cisco IOS XR中部署BGP软下一跳

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已更新: 2022 年 3 月 16 日

文档 ID:217744

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简介

本文档介绍Cisco IOS® XR中边界网关协议(BGP)的下一跳处^理行为。BGP要求在路由信息库(RIB)中安装路径之前，路径的下一跳(NH)是可到达的。此规则适用于所有BGP扬声器。这是下一跳验证检查。BGP软下一跳功能可确保不再需要在RIB中访问BGP下一跳。

先决条件

要求

本文档没有任何特定的要求。

使用的组件

本文档特定于Cisco IOS XR。

本文档中的信息都是基于特定实验室环境中的设备编写的。本文档中使用的所有设备最初均采用原始（默认）配置。如果您的网络处于活动状态，请确保您了解所有命令的潜在影响。

背景信息

在单个自治系统(AS)网络、多域网络或AS间场景中，如果NH未在域或自治系统之间重分布，则可能无法到达NH。

问题不仅限于前端提供商边缘(PE)路由器，还包括出口和入口PE之间的中间BGP扬声器(例如路由反射器(RR)和自治系统边界路由器(ASBR))。中间BGP扬声器在安装和传播路由之前必须具有到NH的连通性。

按需下一跳(ODN)是在路由器上安装SR策略的分段路由(SR)应用程序。连接到这些SR策略的服务路由可以是BGP路由。如果下一跳有效，则这些BGP路由只能安装在RIB和思科快速转发(CEF)表中。有无缝MPLS或AS间MPLS虚拟专用网(VPN)等设计，其中RIB中的路由不保证到网络另一部分（如另一个区域或另一个域）中BGP下一跳的可达性。如果可达性由控制器或SR路径计算元素(SR-PCE)保证，而SR路径计算元素提供对整个网络中网络元素的可达性，则这不是问题。

当前，BGP服务路由仅当BGP路由的下一跳在RIB中作为非默认路由时，才能使用SR策略。

如果具有SR策略的BGP发言者在RIB中没有路由（默认路由除外）用于BGP下一跳，则可以使用解决方法。解决方法是将特定（非默认）静态路由配置为null0，覆盖那些不可达的NH，通过BGP-LU注入路由，或在IGP域之间重分布路由。

这很麻烦，并且/或影响了可扩展性。

解决方案

PE（头端）接收有色BGP L3VPN前缀。它可以在本地学习SR策略，或为颜色和下一跳请求ODN SR策略。

如果配置了NH验证，BGP将对NH执行软验证，并在启用命令时应用NH AD/metric。对于彩色NH，AD/度量来自SR控制器。下一跳的软验证意味着不检查RIB可达性，但检查是对SR策略信息执行的。这包括SR策略路由类型、管理距离和该度量类型的度量值。

引入新命令，在头端路由器或路由反射器上执行此软下一跳验证。

为RR引入了新命令，以跳过彩色扩展通信路径的下一跳可达性验证。

为RR引入了新命令，以便SR策略不用于BGP最佳路径计算。

此功能在Cisco IOS XR版本7.3.2和7.4.1中引入。

BGP路由的下一跳不可访问

不通告具有不可访问下一跳的BGP路由。

此路由是路由反射器上的VPNv4路由。其下一跳（PE环回）不可访问，因为路由表中没有下一跳地址的路由。

RP/0/RP0/CPU0:RR#show bgp vpnv4 unicast rd 65001:2 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65001:2
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                   0            0
Last Modified: Oct 26 10:40:12.136 for 00:03:07
Paths: (1 available, no best path)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002, (Received from a RR-client)
    10.0.0.5 (inaccessible) from 10.0.0.5 (10.0.0.5)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, not-in-vrf
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: Color:101 RT:65001:101

因此，BGP VPNv4路由不会通告。

RP/0/RP0/CPU0:RR#show route 10.0.0.5
Routing entry for 0.0.0.0/0
  Known via "isis 1", distance 115, metric 20, candidate default path, type level-1
  Installed Oct 25 09:35:07.256 for 1d01h
  Routing Descriptor Blocks
    10.2.7.2, from 10.0.0.3, via GigabitEthernet0/0/0/0
      Route metric is 20
  No advertising protos.

当前的解决方法是配置一条静态路由，该路由覆盖头端路由器上的PE环回地址。这是到null0的此类静态路由的示例。

address-family ipv4 unicast
  10.0.0.0/24 Null0
 !
!

此到Null0的静态路由在RIB中为所有远程PE环回地址（BGP下一跳地址）创建可达性。此静态路由涵盖10.0.0.0 - 10.0.0.255范围内的所有地址。

下一跳通过静态路由解析。您可以使用此命令查看此内容。

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast nexthops 10.0.0.5 color 101
Nexthop: 10.0.0.5 C:101
  VRF: default
  Nexthop ID: 0x6000008, Version: 0x0
  Nexthop Flags: 0x00480002
  Nexthop Handle: 0x7fa734042e94

  RIB Related Information:
  Firsthop interface handle 0x0000000c
    Gateway TBL Id: 0xe0000000    Gateway Flags: 0x00000080
    Gateway Handle: 0x7fa7988c7ce8
    Gateway: reachable, non-Connected route, prefix length 24
    Resolving Route: 10.0.0.0/24 (static)
    Paths: 0
    RIB Nexhop ID: 0x0
    Status: [Reachable][Connected][Not Local]
    Metric: 0
    ORR afi bits: 0x0
    Registration: Synchronous, Completed: 01:22:27
    Events: Critical (0)/Non-critical (0)
    Last Received: 01:22:27 (Registration)
    Last gw update: (Crit-sync) 01:22:27(rib)
    Reference Count: 4

  Prefix Related Information
    Active Tables: [IPv4 Unicast][VPNv4 Unicast]
    Metrices: [0x0][0x0]
    Reference Counts: [0][4]
  Interface Handle: 0x0
  Attr ref-count: 7
  SR policy color 101, State: [Up]
    Not registered, bsid 24009
    Skip Reg on restart [No]
    First notif received [Yes]
    SR Policy Flags [0x2]
    BGP TE registered [No]
    ODN registered [No]

    IPv6 capability required/enabled: Yes/Yes
    Last SR policy update: 01:22:35

如果SR策略用于验证下一跳，则您会看到以下输出：

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast nexthops 10.0.0.5 color 101
Nexthop: 10.0.0.5 C:101
  VRF: default
  Nexthop ID: 0x6000008, Version: 0x0
  Nexthop Flags: 0x00480000
  Nexthop Handle: 0x7fa734042e94

  RIB Related Information:
  Firsthop interface handle 0x00000000
    Gateway TBL Id: 0xe0000000    Gateway Flags: 0x00000080
    Gateway Handle: 0x7fa7988c7ce8
    Gateway: unreachable, non-Connected route, prefix length 8192
    Resolving Route: 10.0.0.0/24 (static)
    Paths: 0
    RIB Nexhop ID: 0x0
    Status: [Unreachable]
    Metric: 4294967295
    ORR afi bits: 0x0
    Registration: Synchronous, Completed: 01:25:30
    Events: Critical (1)/Non-critical (0)
    Last Received: 00:00:43 (Critical)
    Last gw update: (Crit-notif) 00:00:43(rib)
    Reference Count: 2

  Prefix Related Information
    Active Tables: [IPv4 Unicast][VPNv4 Unicast]
    Metrices: [0xffffffff][0xffffffff]
    Reference Counts: [0][2]
  Interface Handle: 0x0
  Attr ref-count: 5
  SR policy color 101, State: [Up]
    Not registered, bsid 24009
    Skip Reg on restart [No]
    First notif received [Yes]
    SR Policy Flags [0x2]
    BGP TE registered [No]
    ODN registered [No]

    IPv6 capability required/enabled: Yes/Yes
    Last SR policy update: 01:25:38

配置

以下配置命令是新命令：

nexthop validation color-extcomm sr-policy
nexthop validation color-extcomm disable
bgp bestpath igp-metric sr-policy
bgp bestpath sr-policy prefer
bgp bestpath sr-policy force
nexthop validation color-extcomm disable

BGP ODN AS NextHop软验证命令

在PE(HE)上：

RP/0/RP0/CPU0:PE1(config)#router bgp 65001
RP/0/RP0/CPU0:PE1(config-bgp)#nexthop ?
  mpls        Configure next-hop related items for mpls
  resolution  Configure next-hop related items for resolution
  validation  Configure next-hop reachability validation

RP/0/RP0/CPU0:PE1(config-bgp)#nexthop validation ?
  color-extcomm  Configure next-hop reachability validation for color-extcomm paths

RP/0/RP0/CPU0:PE1(config-bgp)#nexthop validation color-extcomm ?
  disable    Disable next-hop reachability validation for color-extcomm paths
  sr-policy  Enable BGP next-hop reachability validation by SR Policy for color-extcomm paths

RP/0/RP0/CPU0:PE1(config-bgp)#nexthop validation color-extcomm sr-policy 
RP/0/RP0/CPU0:PE1(config-bgp)#commit

以下是主命令：它打开BGP软下一跳行为。如果SR策略为下一跳和颜色启用，则不执行RIB验证。

BGP ODN AS下一跳硬验证命令

BGP硬下一跳是默认行为。

此命令是恢复为此行为的命令：no nexthop validation color-extcomm。

考虑SR策略路径度量的BGP最佳路径选择

当我们有到NH的内部网关协议(IGP)可达性，且算法在BGP最佳路径选择过程中达到步骤8时，首选BGP路径是到下一跳距离最低(IGP)的路径。这是默认行为。请参阅BGP最佳路径选择算法。

除非配置了bgp bestpath igp-metric ignore命令，否则此情况为真。在这种情况下，根本不考虑IGP开销。

目前，仅考虑到BGP NH的IGP度量；不是SR策略路径提供的度量。这仍是默认行为，但有命令指示BGP使用SR策略路径度量，而不是BGP最佳路径选择算法的IGP度量。

RP/0/RP0/CPU0:PE1(config)#router bgp 65001
RP/0/RP0/CPU0:PE1(config-bgp)#bgp bestpath igp-metric ?
  ignore     Ignore IGP metric during path comparison
  sr-policy  Use next-hop admin/metric from SR policy at Next Hop metric compareson stage

RP/0/RP0/CPU0:PE1(config-bgp)#bgp bestpath igp-metric sr-policy 
RP/0/RP0/CPU0:PE1(config-bgp)#commit

此命令将启用PCE/路径管理和度量值的考虑。只有在SR策略启用时，这些管理员/度量值才能传递到BGP。此命令使BGP算法能够根据SR策略中下一跳的管理和度量来选择最佳路径。如果没有此命令，默认行为是仅考虑下一跳的IGP度量。这称为“下一跳的RIB验证”。

BGP最佳路径选择优先选择SR策略路径

有些平台不支持具有本地下一跳或SR策略下一跳的路径混合。该平台可能不支持在两种路径类型上进行转发时混合使用这一功能。考虑到使用等价多路径(ECMP)或不等价多路径(UCMP)或备份路径，这一点非常重要。任何类型的路径都可以是BGP的最佳路径。默认行为是仅考虑与BGP最佳路径具有相同下一跳类型的BGP路径。

此命令指示BGP在路由器执行最佳路径计算时首选具有颜色/下一跳SR策略的路由。这意味着在最佳路径计算过程中不考虑SR策略关闭或没有SR策略的路径。

bgp bestpath sr-policy {force |首选}

必须配置两个关键字之一。

RP/0/RP0/CPU0:PE1(config-bgp)#bgp bestpath sr-policy ?
  force   Consider only paths over SR Policy for bestpath selection, eBGP no-color ineligible
  prefer  Consider only paths over SR Policy for bestpath selection, eBGP no-color eligible

如果配置首选选项，则无颜色的eBGP路径将标记为符合条件（因此可以成为最佳路径的一部分）。如果不需要此行为，您可以向eBGP路径添加虚拟SR策略。否则，您可以配置此命令的force选项，以使没有颜色的eBGP路由不符合要求。

如图所示，参考网络。

Network Diagram

从路由器PE1到网络10.99.99.99/32有三条可能的路径。前缀10.99.99.99/32由R8和CE路由器通告。

BGP有3条路由10.99.99.99/32的路径：2个iBGP（PE2和PE3是BGP下一跳路由器）和1个eBGP路径（来自R8）。

iBGP路径具有下一跳10.0.0.5和10.0.0.6。eBGP路径具有下一跳10.1.8.8。

配置没有此命令bgp bestpath sr-policy。

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.9.9.9/32
BGP routing table entry for 10.9.9.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 474          474
    Local Label: 24005
Last Modified: Nov 29 09:04:07.948 for 00:00:49
Paths: (3 available, best #3)
  Advertised to PE peers (in unique update groups):
    10.0.0.4        10.0.0.3       
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24007) (admin 20) (metric 23) from 10.0.0.3 (10.0.0.5)
      Received Label 24018
      Origin IGP, metric 0, localpref 100, valid, internal, group-best, imported
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24007
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2
  Path #2: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.6 from 10.0.0.4 (10.0.0.6)
      Received Label 24004
      Origin IGP, metric 0, localpref 100, valid, internal, imported
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: RT:65001:101
      Originator: 10.0.0.6, Cluster list: 10.0.0.4
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:3
  Path #3: Received by speaker 0
  Advertised to PE peers (in unique update groups):
    10.0.0.4        10.0.0.3       
  65003
    10.1.8.8 from 10.1.8.8 (10.0.0.8)
      Origin IGP, metric 0, localpref 100, valid, external, best, group-best, import-candidate
      Received Path ID 0, Local Path ID 1, version 474
      Extended community: RT:65001:101
      Origin-AS validity: (disabled)

eBGP路径没有颜色或SR策略。这是最佳路径。

如果eBGP路由确实有颜色，但没有SR策略，则仍会选择它作为最佳路径。

如果eBGP路由确实有颜色和SR策略，则选择它作为最佳路径。

这是另一个例子。eBGP路由没有颜色，并且没有配置SR策略和bgp bestpath sr-policy prefer命令。

注意：eBGP邻居在VRF内。这意味着您必须在VRF下配置bgp bestpath sr-policy prefer命令。

router bgp 65001
 nexthop validation color-extcomm sr-policy
 bgp unsafe-ebgp-policy
 bgp bestpath igp-metric sr-policy
 address-family vpnv4 unicast
 !
 neighbor 10.0.0.3
  remote-as 65001
  update-source Loopback0
  address-family vpnv4 unicast
  !
 !
 neighbor 10.0.0.4
  remote-as 65001
  update-source Loopback0
  address-family vpnv4 unicast
  !
 !
 neighbor 10.0.0.7
  remote-as 65001
  shutdown
  update-source Loopback0
  address-family vpnv4 unicast
  !
 !
 vrf one
  rd 65000:1
  bgp unsafe-ebgp-policy
  bgp bestpath sr-policy prefer
  address-family ipv4 unicast
   redistribute connected
  !
  neighbor 10.1.8.8
   remote-as 65003
   address-family ipv4 unicast
   !
  !
 !
!

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.9.9.9/32 bestpath-compare 
BGP routing table entry for 10.9.9.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 579          579
    Local Label: 24004 (no rewrite);
    Flags: 0x01343001+0x00020000;
Last Modified: Nov 30 07:36:55.948 for 00:03:05
Paths: (3 available, best #3)
  Advertised to PE peers (in unique update groups):
    10.0.0.4        10.0.0.3       
  Path #1: Received by speaker 0
  Flags: 0x2000000001020005, import: 0x080
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24007) (admin 20) (metric 23) from 10.0.0.3 (10.0.0.5), if-handle 0x00000000
      Received Label 24018
      Origin IGP, metric 0, localpref 100, valid, internal, group-best, imported
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24007
      best of AS 65002
      An iBGP path, whereas best path (path #3) is an eBGP path
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2
  Path #2: Received by speaker 0
  Flags: 0x2000000000020005, import: 0x0a0
  Not advertised to any peer
  65002
    10.0.0.6 from 10.0.0.4 (10.0.0.6), if-handle 0x00000000
      Received Label 24004
      Origin IGP, metric 0, localpref 100, valid, internal, imported
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: RT:65001:101
      Originator: 10.0.0.6, Cluster list: 10.0.0.4
      Non SR-policy path is ignored due to config knob
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:3
  Path #3: Received by speaker 0
  Flags: 0x300000000d040003, import: 0x31f
  Advertised to PE peers (in unique update groups):
    10.0.0.4        10.0.0.3       
  65003
    10.1.8.8 from 10.1.8.8 (10.0.0.8), if-handle 0x00000000
      Origin IGP, metric 0, localpref 100, valid, external, best, group-best, import-candidate
      Received Path ID 0, Local Path ID 1, version 579
      Extended community: RT:65001:101
      Origin-AS validity: (disabled)
      best of AS 65003, Overall best

eBGP路径是最佳路径，即使它没有颜色。如果不希望eBGP路由不带颜色作为最佳路径，则使用force选项配置bgp bestpath sr-policy命令。

注意：本地路径和重分发的路径始终符合最佳路径计算的条件。

使用此命令检查平台是否支持通过SR策略转发和本地下一跳的混合。

RP/0/RP0/CPU0:R1#show bgp process detail | include native
Platform support mix of sr-policy and native nexthop: No

注意：路由器NCS55xx和NCS560/NCS540显示no，而ASR9000显示yes。

BGP最佳路径选择强制SR策略路径

该命令指示BGP在执行最佳路径计算时首选具有SR策略下一跳的路由，但不包括无颜色的eBGP路径。

RP/0/RP0/CPU0:PE1(config-bgp)#bgp bestpath sr-policy ?
  force   Consider only paths over SR Policy for bestpath selection, eBGP no-color ineligible
RP/0/RP0/CPU0:PE1(config-bgp)#bgp bestpath sr-policy force ?

禁用颜色扩展通信路径的下一跳可达性验证

这通常用于路由反射器(RR)。

在RR上：

RP/0/RP0/CPU0:RR1(config-bgp)#nexthop validation color-extcomm disable 
RP/0/RP0/CPU0:RR1(config-bgp)#commit

禁用颜色扩展通信路径的下一跳可达性验证。这与SR策略的状态或存在无关。

概述

头端和RR上的行为由下一跳验证命令和bgp best path igp-metric sr-policy命令的配置驱动。有4种方案。每个场景都有两个配置命令的组合。

默认行为

适用于头端路由器和路由反射器。

配置:

no nexthop validation color-extcomm sr-policy
no bgp bestpath igp-metric sr-policy

功能:

Perform RIB validation (hard next-hop).  
Do not use admin/metric from the sr-policy.

使用SR策略度量进行RIB相关验证

适用于头端路由器和路由反射器。

配置:

no nexthop validation color-extcomm sr-policy
bgp bestpath igp-metric sr-policy

功能:

Perform RIB validation (hard next-hop).       
If NH is reachable in RIB:
 If policy is up: 
  Use policy metric
 If policy is down:
  Use RIB metric

SR策略相关验证与RIB度量

这是默认行为。

适用于头端路由器。

配置:

nexthop validation color-extcomm sr-policy
no bgp bestpath igp-metric sr-policy

功能:

Do not perform RIB validation (soft next-hop). 
Do not use admin/metric from the SR policy.
The RIB metric might not be available.

SR策略相关验证与SR策略度量

适用于头端路由器。

配置:

nexthop validation color-extcomm sr-policy
bgp bestpath igp-metric sr-policy

功能:

Do not perform RIB validation (soft next-hop).  RIB reachability is not needed.
If policy is up: 
 Use policy metric and validation, even if RIB reachability is present
If policy is down:
 Use RIB validation and metric if available. If not available, the route is not installed.

SR策略相关验证，RIB度量和SR策略不用于最佳路径计算

适用于RR路由器。

配置:

nexthop validation color-extcomm disable
no bgp bestpath igp-metric sr-policy

功能:

Use RIB metric if the next-hop is in the RIB. Else, use the gateway metric (the next-hop IGP metric) 0.
Do not use SR policy for bestpath calculation. Do not use admin/metric from the SR policy.

SR策略相关验证，使用RIB度量和SR策略进行最佳路径计算

适用于RR路由器。

配置:

nexthop validation color-extcomm disable
bgp bestpath igp-metric sr-policy

功能:

Use RIB metric if the next-hop is in the RIB. Else, use the gateway metric 0.
Use sr-policy for bestpath calculation.

If policy is up: 
 Use policy metric and validation, even if RIB reachability is present
If policy is down
 Use RIB validation and metric if available
 If RIB validation and metric is not available:
  use the gateway metric 0

确认

这是验证哪种下一跳验证处于活动状态以及SR策略的管理距离/度量是否在最佳路径计算期间使用的方式。

RP/0/RP0/CPU0:PE1#show bgp process detail | i Nexthop   
Use SR-Policy admin/metric of color-extcomm Nexthop during path comparison: enabled
ExtComm Color Nexthop validation: SR-Policy then RIB

这是默认设置。

这是SR策略相关验证的示例，其中RIB度量和SR策略不用于最佳路径计算。

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast process detail | in Nexthop
Use SR-Policy admin/metric of color-extcomm Nexthop during path comparison: disabled
ExtComm Color Nexthop validation: RIBExtComm Color Nexthop validation: RIB

这是附加到BGP路由的管理距离/度量的示例。

RP/0/RP0/CPU0:PE1#show bgp vrf VRF1002 ipv4 unicast 10.77.2.0 
BGP routing table entry for 10.77.2.0/24, Route Distinguisher: 18522:1002
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker            5232243     5232243
Paths: (1 available, best #1)
  Advertised to CE peers (in unique update groups):
    10.11.2.11      10.15.2.2     
  Path #1: Received by speaker 0
  Advertised to CE peers (in unique update groups):
    10.11.2.11      10.15.2.2     
  16611 770
    10.1.1.33 C:1129 (bsid:27163) (admin 20) (metric 25) from 10.1.1.100 (10.1.1.33)
      Received Label 24007
      Origin IGP, localpref 100, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 1, Local Path ID 1, version 5232243
      Extended community: Color:1129 RT:17933:1002 RT:18522:1002
      Originator: 10.1.1.33, Cluster list: 10.1.1.100
      SR policy color 1129, up, registered, bsid 27163, if-handle 0x200053dc
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 18522:3002

检查策略是打开还是关闭

这是验证SR策略是打开还是关闭的方式。

RP/0/RP0/CPU0:PE1#show segment-routing traffic-eng pcc lsp
PCC's SR policy database:
-------------------------
Symbolic Name: cfg_ODN-policy-1_discr_100
 LSP[0]:
  Source 10.0.0.1, Destination 10.0.0.5, Tunnel ID 3, LSP ID 8
  State: Admin up, Operation up
  Setup type: SR
  Binding SID: 24005

验证是否使用策略

使用BGP show命令查看路由。

如果有绑定网段IDentifier(BSID)，则此路由使用SR策略。

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  89           89
Last Modified: Oct 28 13:21:57.714 for 00:00:30
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24004) from 10.0.0.3 (10.0.0.5)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 87
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24004
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2

绑定SID是此处的MPLS标签。此标签链接到一个SR策略。

RP/0/RP0/CPU0:PE1#show mpls forwarding labels 24004
Local  Outgoing    Prefix             Outgoing     Next Hop        Bytes
Label  Label       or ID              Interface                    Switched
------ ----------- ------------------ ------------ --------------- ------------
24004  Pop         No ID              srte_c_101_e point2point     0

Show BGP Nexthops命令

您可以使用show bgp nexthops命令查看终端的颜色、管理和度量。

RP/0/RP0/CPU0:RR#show bgp nexthops wide
Total Nexthop Processing
  Time Spent: 0.000 secs

Maximum Nexthop Processing
  Received: 00:21:57
  Bestpaths Deleted: 0
  Bestpaths Changed: 31
  Time Spent: 0.000 secs

Last Notification Processing
  Received: 00:01:22
  Time Spent: 0.000 secs

Gateway Address Family: IPv4 Unicast
Table ID: 0xe0000000
Gateway Reference Count: 8
Gateway AF Bits : 0x8011
Nexthop Count: 6
Critical Trigger Delay: 3000msec
Non-critical Trigger Delay: 10000msec

Nexthop Version: 1, RIB version: 1
EPE Table Version: 1, EPE Label version: 1
EPE Downloaded Version: 1, EPE Standby Version: 0

Status codes: R/UR Reachable/Unreachable
              C/NC Connected/Not-connected
              L/NL Local/Non-local
              PR   Pending Registration
              I    Invalid (Policy drop)

Next Hop                                Status          Metric           Tbl-ID                  Notf      LastRIBEvent             RefCount
10.0.0.1                                [R][NC][NL]         30         e0000000                   6/0    00:01:22 (Cri)                  0/5
10.0.0.3                                [R][NC][NL]         20         e0000000                   6/0    00:01:22 (Cri)                 0/34
10.0.0.4                                [R][NC][NL]         30         e0000000                   6/0    00:01:22 (Cri)                 0/34
10.0.0.5                                [UR]        4294967295         e0000000                   2/0    00:01:22 (Cri)                  0/4
10.0.0.5 T:101                          [UR]        4294967295         e0000000                   2/0    00:01:22 (Cri)                  0/3
10.0.0.6                                [UR]        4294967295         e0000000                   2/0    00:01:22 (Cri)                  0/3

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast nexthops 10.0.0.5 color 101
Nexthop: 10.0.0.5 C:101
  VRF: default
  Nexthop ID: 0x6000006, Version: 0x0
  Nexthop Flags: 0x00480002
  Nexthop Handle: 0x7efc84043624
  RIB Related Information:
  Firsthop interface handle 0x0000000c
    Gateway TBL Id: 0xe0000000    Gateway Flags: 0x00000080
    Gateway Handle: 0x7efcadee6e98
    Gateway: reachable, non-Connected route, prefix length 8
    Resolving Route: 10.0.0.0/8 (static)
    Paths: 0
    RIB Nexhop ID: 0x0
    Status: Reachable via SR-TE
    Status: [Reachable][Connected][Not Local]
    Metric: 0 (SR-TE metric 333)
    ORR afi bits: 0x0
    Registration: Asynchronous, Completed: 2d05h
    Events: Critical (14)/Non-critical (0)
    Last Received: 02:15:15 (Critical)
    Last gw update: (Crit-notif) 02:15:15(rib)
    Reference Count: 2

  Prefix Related Information
    Active Tables: [IPv4 Unicast][VPNv4 Unicast]
    Metrices: [0x0][0x0]
    Reference Counts: [0][2]
  Interface Handle: 0x0
  Attr ref-count: 5
  SR policy color 101, State: [Up]
    Not registered, bsid 24004
    Skip Reg on restart [No]
    First notif received [Yes]
    SR Policy Flags [0x2]
    BGP TE registered [No]
    ODN registered [No]
    End-point admin/metric: 30/333
    IPv6 capability required/enabled: Yes/Yes
    Last SR policy update: 00:55:07

BGP跟踪

show bgp trace输出中的某些条目引用SR策略。注意管理员/度量的存在。

default-bgp/spkr-tr2-sr 0/RP0/CPU0 t8885 [SR]:1323: SR-policy hdlr for reg nh with XTC af 0, reg/unreg flag 1
default-bgp/spkr-tr2-sr 0/RP0/CPU0 t8885 [SR]:3394: SR-policy XTC nexthop 10.0.0.5/32 T:, color 101, register 1 with XTC done, v6-cap 1, rc 'Success', flags 0x480000
default-bgp/spkr-tr2-sr 0/RP0/CPU0 t8885 [SR]:3394: SR-policy XTC nexthop 10.0.0.6/32 T:, color 101, register 1 with XTC done, v6-cap 0, rc 'Success', flags 0x480000
default-bgp/spkr-tr2-sr 0/RP0/CPU0 t8885 [SR]:2424: SR-policy XTC notif NH end-point color,gw_afi 0, [C:101][10.0.0.5] admin/metric 100/2147483647
default-bgp/spkr-tr2-sr 0/RP0/CPU0 t8885 [SR]:2424: SR-policy XTC notif NH end-point color,gw_afi 0, [C:101][10.0.0.5] admin/metric 100/2147483647
default-bgp/spkr-tr2-sr 0/RP0/CPU0 t8885 [SR]:2424: SR-policy XTC notif NH end-point color,gw_afi 0, [C:101][10.0.0.5] admin/metric 20/30
default-bgp/spkr-tr2-sr 0/RP0/CPU0 t8881 [SR]:1379: SR-policy trigger XTC for nh reg af 0, reg/unreg flag 1
default-bgp/spkr-tr2-nh 0/RP0/CPU0 t8885 [NH]:7370: nexthop walk for AFI:'VPNv4 Unicast' start
default-bgp/spkr-tr2-nh 0/RP0/CPU0 t8885 [NH]:7425: nexthop walk for AFI:'VPNv4 Unicast', paths deleted: 0, recalculated bestpaths: 2, color nh trigger for 2 nets, 0 msec

注意：思科IOS XR流量控制器(XTC)是指SR控制器。

BGP跟踪中的某些条目指与下一跳处理相关的配置更改。

default-bgp/spkr-tr2-prog 0/RP0/CPU0 t9036 [PROG]:724: 'Done VRF cfg notif init', name default iid 0
default-bgp/spkr-tr2-prog 0/RP0/CPU0 t9036 [PROG]:792: 'Done cfg init', name default iid 0
default-bgp/spkr-tr2-gen 0/RP0/CPU0 t9048 [GEN]:17871: nh cfg change 2 sense 1
default-bgp/spkr-tr2-gen 0/RP0/CPU0 t9048 [GEN]:17920: nh cfg change 1 sense 1

管理距离和度量

管理距离(admin)由SR策略中的度量类型确定。可以在头端路由器上设置度量类型。

RP/0/RP0/CPU0:PE1#conf t
RP/0/RP0/CPU0:PE1(config)#segment-routing
RP/0/RP0/CPU0:PE1(config-sr)#traffic-eng
RP/0/RP0/CPU0:PE1(config-sr-te)#policy ODN-policy-1
RP/0/RP0/CPU0:PE1(config-sr-te-policy)#color 101 end-point ipv4 10.0.0.5
RP/0/RP0/CPU0:PE1(config-sr-te-policy)#candidate-paths
RP/0/RP0/CPU0:PE1(config-sr-te-policy-path)#preference 100
RP/0/RP0/CPU0:PE1(config-sr-te-policy-path-pref)#dynamic
RP/0/RP0/CPU0:PE1(config-sr-te-pp-info)#metric ?
  margin     Metric margin
  sid-limit  SID limit
  type       Metric type configuration
  <cr>

RP/0/RP0/CPU0:PE1(config-sr-te-pp-info)#metric type ?
  hopcount  Hopcount metric type
  igp       IGP metric type
  latency   Latency metric type
  te        TE metric type

管理员值

这些是默认SR策略管理员值。

延迟10
TE 20
IGP（默认）30
hopcount 40
NONE/UNKNOWN度量类型（对于显式段列表策略）100

如果度量类型为none，则度量值为1。

管理员值越低，通向BGP的路径越优先。

度量越低，如果管理员具有相同值，则路径越首选BGP。

验证ODN中的管理和度量类型

RP/0/RP0/CPU0:PE1#show segment-routing traffic-eng policy color 101 endpoint ipv4 10.0.0.5

SR-TE policy database
---------------------

Color: 101, End-point: 10.0.0.5
  Name: srte_c_101_ep_10.0.0.5
  Status:
    Admin: up  Operational: up for 01:01:00 (since Oct 28 15:22:36.012)
  Candidate-paths:
    Preference: 100 (configuration) (active)
      Name: ODN-policy-1
      Requested BSID: dynamic
      PCC info:
        Symbolic name: cfg_ODN-policy-1_discr_100
        PLSP-ID: 4
        Protection Type: protected-preferred
        Maximum SID Depth: 10
      Dynamic (pce 10.0.0.7) (valid)
        Metric Type: IGP,   Path Accumulated Metric: 30
          16002 [Prefix-SID, 10.0.0.2]
          24009 [Adjacency-SID, 10.2.3.2 - 10.2.3.3]
          16005 [Prefix-SID, 10.0.0.5]
  Attributes:
    Binding SID: 24004
    Forward Class: Not Configured
    Steering labeled-services disabled: no
    Steering BGP disabled: no
    IPv6 caps enable: yes
    Invalidation drop enabled: no

有效指标

有效度量强制配置此命令的策略的类型和度量。

RP/0/RP0/CPU0:PE1#conf t
RP/0/RP0/CPU0:PE1(config)#segment-routing
RP/0/RP0/CPU0:PE1(config-sr)#traffic-eng
RP/0/RP0/CPU0:PE1(config-sr-te)#policy ODN-policy-1
RP/0/RP0/CPU0:PE1(config-sr-te-policy)#candidate-paths
RP/0/RP0/CPU0:PE1(config-sr-te-policy-path)#preference 100
RP/0/RP0/CPU0:PE1(config-sr-te-policy-path-pref)#effective-metric ?
  value  Metric value, advertised to other protocols
  <cr>

RP/0/RP0/CPU0:PE1(config-sr-te-policy-path-pref)#effective-metric value 333 ?
  type  Metric type, advertised to other protocols
  <cr>

RP/0/RP0/CPU0:PE1(config-sr-te-policy-path-pref)#effective-metric value 333 type ?
  hopcount  HOPCOUNT metric type
  igp       IGP metric type
  latency   LATENCY metric type
  te        TE metric type

RP/0/RP0/CPU0:PE1(config-sr-te-policy-path-pref)#effective-metric value 333 type igp ?
  <cr>

RP/0/RP0/CPU0:PE1(config-sr-te-policy-path-pref)#effective-metric value 333 type igp
RP/0/RP0/CPU0:PE1(config-sr-te-policy-path-pref)#commit

RP/0/RP0/CPU0:PE1#show run segment-routing traffic-eng policy ODN-policy-1
segment-routing
 traffic-eng
  policy ODN-policy-1
   color 101 end-point ipv4 10.0.0.5
   candidate-paths
    preference 100
     dynamic
      pcep
      !
      metric
       type igp
      !
     !
     effective-metric
      value 333 type igp

您可以以这种方式验证应用的有效度量类型（管理距离）和度量值。

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 131          131
Last Modified: Oct 28 15:22:35.714 for 00:03:42
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24004) (admin 30) (metric 333) from 10.0.0.7 (10.0.0.5)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 130
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.7, 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24004
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2

BGP路径比较

默认情况下，BGP路径的比较不会更改。

如果配置了bgp bestpath igp-metric sr-policy命令，则SR策略的管理距离和度量在BGP最佳路径选择算法中使用。

SR策略的管理距离和度量与SR策略关联。这是本地配置或通过PCEP（路径计算元素协议）从SR-PCE接收的。这意味着，如果路由反射器比较路径，它看不到管理距离和度量，因为它没有ODN的头端功能。因此，它没有到SR PCE的PCEP会话。

此示例显示一个远程PE路由器通告的前缀。这是配置。

segment-routing
 global-block 16000 23999
 traffic-eng
  logging
   policy status
  !
  policy ODN-policy-1
   color 101 end-point ipv4 10.0.0.5
   candidate-paths
    preference 100
     dynamic
      pcep
      !
      metric
       type te
      !
     !
    !
    preference 200
     dynamic
      pcep
      !
      metric
       type te
      !

度量类型为TE。

此头端路由器看到带有颜色的前缀两次，且具有相同的TE度量，因为它对于两条路径是相同的BGP下一跳。

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast rd 65001:2 10.0.0.9/32 bestpath-compare
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65001:2
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                   8            8
    Flags: 0x00040001+0x00010000;
Last Modified: Nov  2 09:21:55.948 for 00:00:32
Paths: (2 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0xa000000025060005, import: 0x31f
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24018) (admin 20) (metric 23) from 10.0.0.3 (10.0.0.5), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, not-in-vrf
      Received Path ID 0, Local Path ID 1, version 8
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24018
      best of AS 65002, Overall best
  Path #2: Received by speaker 0
  Flags: 0x2000000024020005, import: 0x000
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24018) (admin 20) (metric 23) from 10.0.0.4 (10.0.0.5), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, import-candidate, not-in-vrf
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.4, 10.0.0.7, 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24018
      Longer cluster length than best path (path #1)

由于管理距离和度量对于两条路径都相同，因此在BGP最佳路径选择算法中，将进一步决定哪条路径是最佳路径。

此示例显示两个远程PE路由器通告的前缀。一条路径的下一跳为10.0.0.5，另一条路径的下一跳为10.0.0.6。前缀的颜色为101，来自两个远程PE路由器。头端路由器PE1对此颜色有两个ODN策略。

segment-routing
 global-block 16000 23999
 traffic-eng
  logging
   policy status
  !
  policy ODN-policy-1
   color 101 end-point ipv4 10.0.0.5
   candidate-paths
    preference 100
     dynamic
      pcep
      !
      metric
       type igp
      !
     !
    !
    preference 200
     dynamic
      pcep
      !
      metric
       type te
      !
     !
    !
   !
  !
  policy ODN-policy-2
   color 101 end-point ipv4 10.0.0.6
   candidate-paths
    preference 100
     dynamic
      pcep
      !
      metric
       type igp
      !

终端10.0.0.5的策略使用度量类型TE，而终端10.0.0.6的策略使用度量类型IGP。

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast vrf one 10.0.0.9/32 bestpath-compare
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  25           25
    Flags: 0x00043001+0x00000000;
Last Modified: Nov  1 11:42:28.948 for 00:43:41
Paths: (2 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0xa000000005060005, import: 0x080
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24007) (admin 20) (metric 30) from 10.0.0.4 (10.0.0.5), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, weight 65000, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 25
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.4, 10.0.0.7, 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24007
      best of AS 65002, Overall best
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2
  Path #2: Received by speaker 0
  Flags: 0x2000000000020005, import: 0x0a0
  Not advertised to any peer
  65002
    10.0.0.6 C:101 (bsid:24012) (admin 30) (metric 30) from 10.0.0.4 (10.0.0.6), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, weight 65000, valid, internal, imported
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.6, Cluster list: 10.0.0.4
      SR policy color 101, up, not-registered, bsid 24012
      Higher nexthop admin distance than best path (path #1)
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:3

最佳路径是第一条，因为它的管理距离比第二条路径的管理距离低。度量类型TE的管理距离低于度量类型IGP的管理距离。

ODN-policy-1的SR策略优先级为200,ODN-policy-2的SR策略优先级为100。

RP/0/RP0/CPU0:PE1#show segment-routing traffic-eng pcc lsp detail

PCC's SR policy database:
-------------------------
Symbolic Name: cfg_ODN-policy-1_discr_100
 LSP[0]:
  Source 10.0.0.1, Destination 10.0.0.5, Tunnel ID 1, LSP ID 0
  State: Admin up, Operation down
  Setup type: SR
  Bandwidth: requested 0, used 0
  LSP object:
    PLSP-ID 0x1, flags: D:0 S:0 R:0 A:1 O:0 C:0
  Metric type: IGP, Accumulated Metric 30
  ERO:
    SID[0]: Node, Label 16004, NAI: 10.0.0.4
    SID[1]: Node, Label 16005, NAI: 10.0.0.5
Symbolic Name: cfg_ODN-policy-1_discr_200
 LSP[0]:
  Source 10.0.0.1, Destination 10.0.0.5, Tunnel ID 1, LSP ID 4
  State: Admin up, Operation up
  Binding SID: 24007
  Setup type: SR
  Bandwidth: requested 0, used 0
  LSP object:
    PLSP-ID 0x2, flags: D:0 S:0 R:0 A:1 O:1 C:0
  Metric type: TE, Accumulated Metric 30
  ERO:
    SID[0]: Adj, Label 24001, NAI: local 10.1.2.1 remote 10.1.2.2
    SID[1]: Adj, Label 24003, NAI: local 10.2.3.2 remote 10.2.3.3
    SID[2]: Node, Label 16005, NAI: 10.0.0.5
Symbolic Name: cfg_ODN-policy-2_discr_100
 LSP[0]:
  Source 10.0.0.1, Destination 10.0.0.6, Tunnel ID 2, LSP ID 2
  State: Admin up, Operation up
  Binding SID: 24012
  Setup type: SR
  Bandwidth: requested 0, used 0
  LSP object:
    PLSP-ID 0x3, flags: D:0 S:0 R:0 A:1 O:1 C:0
  Metric type: IGP, Accumulated Metric 30
  ERO:
    SID[0]: Node, Label 16004, NAI: 10.0.0.4
    SID[1]: Node, Label 16006, NAI: 10.0.0.6

以下是管理距离相同但度量不同的示例。

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast vrf one 10.0.0.9/32 bestpath-compare
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  57           57
    Flags: 0x00043001+0x00010000;
Last Modified: Nov  2 07:54:20.948 for 00:00:04
Paths: (2 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0xa000000005060005, import: 0x080
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24007) (admin 30) (metric 23) from 10.0.0.4 (10.0.0.5), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, weight 65000, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 39
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.4, 10.0.0.7, 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24007
      best of AS 65002, Overall best
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2
  Path #2: Received by speaker 0
  Flags: 0x2000000004020005, import: 0x080
  Not advertised to any peer
  65002
    10.0.0.6 C:101 (bsid:24012) (admin 30) (metric 30) from 10.0.0.4 (10.0.0.6), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, weight 65000, valid, internal, import-candidate, imported
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.6, Cluster list: 10.0.0.4
      SR policy color 101, up, not-registered, bsid 24012
      Higher IGP metric than best path (path #1)
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:3

这是带有metric-type hopcount的示例。

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast vrf one 10.0.0.9/32 bestpath-compare
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  99           99
    Flags: 0x00043001+0x00010000;
Last Modified: Nov  2 08:21:19.948 for 00:00:41
Paths: (2 available, best #2)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Flags: 0x2000000004020005, import: 0x080
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24007) (admin 40) (metric 4) from 10.0.0.4 (10.0.0.5), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, weight 65000, valid, internal, import-candidate, imported
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.4, 10.0.0.7, 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24007
      Higher IGP metric than best path (path #2)
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2
  Path #2: Received by speaker 0
  Flags: 0xa000000005060005, import: 0x080
  Not advertised to any peer
  65002
    10.0.0.6 C:101 (bsid:24010) (admin 40) (metric 3) from 10.0.0.4 (10.0.0.6), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, weight 65000, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 95
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.6, Cluster list: 10.0.0.4
      SR policy color 101, up, not-registered, bsid 24010
      best of AS 65002, Overall best
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:3

两个不同终端有两条相互竞争的BGP路径。BGP决定哪条路径成功并安装到路由表中。这进而根据颜色和终端确定要将流量转发到BGP VPNv4前缀而安装的SR策略。

比较BGP路径是否带颜色

在场景4中，在头端路由器上启用软下一跳验证，它接收两个BGP路径，一条是带前缀，一条是不带颜色。如果没有下一跳的路由，则无颜色的路径不可访问下一跳，并且不考虑进行安装。

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast | include 10.0.0.9/32
*>i10.0.0.9/32        10.0.0.5 C:101           0    100      0 65002 i
*>i10.0.0.9/32        10.0.0.5 C:101           0    100      0 65002 i
* i10.0.0.9/32        10.0.0.6                 0    100      0 65002 i

最后一个BGP路径没有>，因此下一跳不可访问。

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast rd 65001:3 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65001:3
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  31           31
Last Modified: Nov  2 10:08:44.948 for 00:08:11
Paths: (2 available, no best path)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.6 (inaccessible) from 10.0.0.3 (10.0.0.6)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, not-in-vrf
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: RT:65001:101
      Originator: 10.0.0.6, Cluster list: 10.0.0.3, 10.0.0.7, 10.0.0.4
  Path #2: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.6 (inaccessible) from 10.0.0.4 (10.0.0.6)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, not-in-vrf
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: RT:65001:101
      Originator: 10.0.0.6, Cluster list: 10.0.0.4

使用带SR策略的BGP路径。

但是，如果由于RIB中的路由而解析下一跳10.0.0.6，则此路径可被选为最佳路径。如果它没有颜色，则不能用于ODN，SR策略将关闭。但是，此路由的管理距离是100，因此它比带有颜色的路径高得多。

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.0.0.9/32 bestpath-compare
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  47           47
    Flags: 0x00043001+0x00000000;
Last Modified: Nov  2 10:30:55.948 for 00:00:21
Paths: (2 available, best #1)
  Advertised to CE peers (in unique update groups):
    10.1.8.8
  Path #1: Received by speaker 0
  Flags: 0xa000000005060005, import: 0x080
  Advertised to CE peers (in unique update groups):
    10.1.8.8
  65002
    10.0.0.5 C:101 (bsid:24021) (admin 20) (metric 23) from 10.0.0.3 (10.0.0.5), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 40
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24021
      best of AS 65002, Overall best
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2
  Path #2: Received by speaker 0
  Flags: 0x2000000000020005, import: 0x0a0
  Not advertised to any peer
  65002
    10.0.0.6 from 10.0.0.4 (10.0.0.6), if-handle 0x00000000
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, imported
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: RT:65001:101
      Originator: 10.0.0.6, Cluster list: 10.0.0.4
      Higher nexthop admin distance than best path (path #1)
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:3

使用show命令更详细地了解场景

默认行为

适用于头端路由器和路由反射器。

配置:

no nexthop validation color-extcomm sr-policy
no bgp bestpath igp-metric sr-policy

功能:

执行RIB验证（硬下一跳）。

BGP不使用SR策略中的管理员/度量。

对服务路由的下一跳执行RIB验证。

如果下一跳没有比默认路由更具体的路由，则服务路由具有无法访问的下一跳。

If the RIB metric is available:
 RIB metric is used. Route is installed.
  If policy is up:
   Policy is used.
  If policy is not up:
   Policy is not used.
If the RIB metric is not available:
 Route is not installed.

RP/0/RP0/CPU0:PE1#show bgp vpnv4 unicast rd 65001:2 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65001:2
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  31           31
Last Modified: Oct 26 14:21:56.714 for 00:01:32
Paths: (1 available, no best path)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24005) (inaccessible) from 10.0.0.3 (10.0.0.5)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, not-in-vrf
      Received Path ID 0, Local Path ID 0, version 0
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24005

这也导致服务路由未导入到VRF。

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  37           37
Last Modified: Oct 26 14:24:36.714 for 00:00:03
Paths: (0 available, no best path)
  Not advertised to any peer

如果在头端路由器上添加非默认静态路由，覆盖服务路由的下一跳，可缓解此问题。ODN网络中通常使用此功能。

此静态路由包含下一跳10.0.0.5，不是默认路由。

router static
 address-family ipv4 unicast
  10.0.0.0/24 Null0
 !
!

它解决了ODN无法访问的下一跳。

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  27           27
Last Modified: Oct 26 14:19:06.714 for 00:00:26
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24005) from 10.0.0.3 (10.0.0.5)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 22
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24005
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2

RR也是如此：如果服务路由的下一跳不可访问，则该路由不会反映在其他iBGP扬声器中。非默认静态路由的解决方法同样适用于RR。

使用SR策略度量进行RIB相关验证

适用于头端路由器和路由反射器。

配置:

no nexthop validation color-extcomm sr-policy
bgp bestpath igp-metric sr-policy

功能:

PCE/路径管理和度量值将传递到BGP，并用于最佳路径计算。

Perform RIB validation (hard next-hop).       
If NH is reachable in RIB:
 If policy is up: 
  Use policy metric.
 If policy is down:
  Use RIB metric.

头端路由器

如果下一跳在RIB中不可达，则服务路由的下一跳将不可访问，且未安装。

如果下一跳可到达（可能通过使用静态路由），则安装服务路由，现在带有管理和度量值。

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  43           43
Last Modified: Oct 26 14:42:54.714 for 00:00:03
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24005) (admin 20) (metric 30) from 10.0.0.3 (10.0.0.5)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 43
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24005
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2

政策已经启动。

如果策略关闭，而RIB有下一跳路由，则安装服务路由。但是，服务路由未在CEF表中解析。SR策略不再提供到达终端的连接（MPLS标签堆栈）。

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                  57           57
Last Modified: Oct 26 15:13:46.714 for 00:01:39
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.5 from 10.0.0.3 (10.0.0.5)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 48
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2

该路由已安装，但没有SR策略，CEF未解析为此服务路由。

RP/0/RP0/CPU0:PE1#show cef vrf one 10.0.0.9/32
10.0.0.9/32, version 36, drop adjacency, internal 0x5000001 0x30 (ptr 0xe3abf78) [1], 0x600 (0xe54a068), 0xa08 (0xec42558)
 Updated Oct 26 15:13:47.003
 Prefix Len 32, traffic index 0, precedence n/a, priority 3
  gateway array (0xe3b26b8) reference count 2, flags 0x3a, source rib (7), 0 backups
                [3 type 1 flags 0x88401 (0xec85888) ext 0x0 (0x0)]
  LW-LDI[type=1, refc=1, ptr=0xe54a068, sh-ldi=0xec85888]
  gateway array update type-time 3 Oct 26 15:16:24.524
 LDI Update time Oct 26 14:42:54.404
 LW-LDI-TS Oct 26 15:13:47.003
   via 10.0.0.5/32, 0 dependencies, recursive [flags 0x6000]
    path-idx 0 NHID 0x0 [0xd649400 0x0]
    recursion-via-/32
    next hop VRF - 'default', table - 0xe0000000
    unresolved
     labels imposed {24002}

    Load distribution: 0 (refcount 3)

    Hash  OK  Interface                 Address
    0     Y   recursive                 drop

RR路由器：

如果SR策略为up或not，并且RIB可达性存在，则RR通告服务路由。

SR策略相关验证与RIB度量

适用于头端路由器。

配置:

nexthop validation color-extcomm sr-policy
no bgp bestpath igp-metric sr-policy

功能:

PCE/路径管理和度量值不会传递给BGP。

If the RIB metric is available:
 RIB metric is used. Route is installed.
  If policy is up:
   Policy is used.
  If policy is not up:
   Policy is not used.

If the RIB metric is not available:
 Route is not installed.

SR策略相关验证与SR策略度量

适用于头端路由器。

配置:

nexthop validation color-extcomm sr-policy
bgp bestpath igp-metric sr-policy

功能:

Do not perform RIB validation (soft next-hop).  RIB reachability is not needed.
If policy is up: 
 Use policy metric and validation, even if RIB reachability is present.
If policy is down:
 Use RIB validation and metric if available. If not available, the route is not installed.

如果SR策略可用：

RP/0/RP0/CPU0:PE1#show bgp vrf one 10.0.0.9/32
BGP routing table entry for 10.0.0.9/32, Route Distinguisher: 65000:1
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker                 101          101
Last Modified: Oct 28 13:32:24.714 for 00:25:39
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  65002
    10.0.0.5 C:101 (bsid:24008) (admin 30) (metric 30) from 10.0.0.3 (10.0.0.5)
      Received Label 24002
      Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 99
      Extended community: Color:101 RT:65001:101
      Originator: 10.0.0.5, Cluster list: 10.0.0.3
      SR policy color 101, up, not-registered, bsid 24008
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65001:2

SR策略相关验证，RIB度量和SR策略不用于最佳路径计算

适用于RR路由器。

配置:

nexthop validation color-extcomm disable
no bgp bestpath igp-metric sr-policy

功能:

第一个命令表示禁用颜色扩展通信路径的下一跳可达性验证。下一跳可达性有硬性检查。可禁用软下一跳可达性的验证检查，因为此路由器是RR，仅反映BGP服务路由。RR不为其安装SR策略。如果没有此命令，将执行软检查。如果路由表中没有用于下一跳的路由比默认路由更多，则下一跳将无法访问。然后，路由不会反映。

第二个命令表示SR策略不用于BGP最佳路径计算。因此，不使用SR策略中的管理员/度量。如果下一跳在RIB中，则使用RIB度量。否则，使用网关度量0（下一跳IGP度量）。

SR策略相关验证，使用RIB度量和SR策略进行最佳路径计算

适用于RR路由器。

配置:

nexthop validation color-extcomm disable
bgp bestpath igp-metric sr-policy

功能:

第一个命令表示禁用颜色扩展通信路径的下一跳可达性验证。下一跳可达性有硬性检查。可禁用软下一跳可达性的验证检查，因为这是RR，并且仅反映BGP服务路由。RR不为其安装SR策略。如果没有此命令，将执行软检查。如果路由表中没有用于下一跳的路由比默认路由更多，则下一跳将无法访问。然后，路由不会反映。

第二个命令表示SR策略用于BGP最佳路径计算。

If policy is up: 
 Use policy metric and validation, even if RIB reachability is present
If policy is down
 Use RIB validation and metric if available
 If RIB validation and metric is not available:
  use the gateway metric 0

修订历史记录

版本	发布日期	备注
1.0	16-Mar-2022	初始版本

由思科工程师提供

Luc De Ghein
思科技术领导

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在Cisco IOS XR中部署BGP软下一跳

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非歧视性语言

关于此翻译

目录

简介

先决条件

使用的组件

背景信息

解决方案

BGP路由的下一跳不可访问

配置

BGP ODN AS NextHop软验证命令

BGP ODN AS下一跳硬验证命令

考虑SR策略路径度量的BGP最佳路径选择

BGP最佳路径选择优先选择SR策略路径

BGP最佳路径选择强制SR策略路径

概述

默认行为

使用SR策略度量进行RIB相关验证

SR策略相关验证与RIB度量

SR策略相关验证与SR策略度量

SR策略相关验证，RIB度量和SR策略不用于最佳路径计算

SR策略相关验证，使用RIB度量和SR策略进行最佳路径计算

确认

检查策略是打开还是关闭

验证是否使用策略

Show BGP Nexthops命令

BGP跟踪

管理距离和度量

管理员值

验证ODN中的管理和度量类型

有效指标

BGP路径比较

比较BGP路径是否带颜色

使用show命令更详细地了解场景

默认行为

使用SR策略度量进行RIB相关验证

SR策略相关验证与RIB度量

SR策略相关验证与SR策略度量

SR策略相关验证，RIB度量和SR策略不用于最佳路径计算

SR策略相关验证，使用RIB度量和SR策略进行最佳路径计算

修订历史记录

由思科工程师提供

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