验证MPLS第3层VPN转发
简介
本文档介绍验证跨MPLS第3层VPN核心网络的端到端连接的过程。
先决条件
要求
Cisco 建议您了解以下主题：
- 基本IP路由的相关知识
- 了解Cisco IOS® XE和Cisco IOS® XR命令行
使用的组件
本文档中的信息基于以下软件和硬件版本：
- 使用Cisco IOS XR软件的路由器
- 使用Cisco IOS XE软件的路由器
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
本文档旨在演示基本的验证和故障排除步骤，以检查通过混合使用Cisco IOS XE和Cisco IOS XR路由器作为PE（提供商边缘）和P（提供商）路由器的MPLS第3层VPN核心网络与BGP（边界网关协议）互连的两台CE（客户边缘）路由器之间的连接和转发。
规则
有关文件规则的更多信息请参见“ Cisco技术提示规则”。
拓扑
MPLS拓扑图
故障排除
初始信息
源网络：192.168.1.0/24
源CE路由器：CE-EAST
目的网络：172.16.1.0/24
目的CE路由器：CE-WEST
根据初始信息和拓扑，在路由器CE-EAST上由Loopback1表示的源地址192.168.1.10和路由器CE-WEST上由Loopback1表示的目的地地址172.16.1.10之间必须能够成功通信：
CE-EAST#show run interface loopback1
Building configuration...
Current configuration : 66 bytes
!
interface Loopback1
ip address 192.168.1.10 255.255.255.0
end
CE-WEST#show run interface loopback 1
Building configuration...
Current configuration : 65 bytes
!
interface Loopback1
ip address 172.16.1.10 255.255.255.0
endICMP可达性和traceroute用于开始检查这些源地址和目标地址之间的连接，但是从接下来的输出中可看到此操作不成功：
CE-EAST#ping 172.16.1.10 source loopback1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.10, timeout is 2 seconds:
Packet sent with a source address of 192.168.1.10
.....
Success rate is 0 percent (0/5)
CE-EAST#traceroute 172.16.1.10 source loop1 probe 1 numeric
Type escape sequence to abort.
Tracing the route to 172.16.1.10
VRF info: (vrf in name/id, vrf out name/id)
1 10.11.0.2 2 msec
2 *
3 10.10.0.2 [MPLS: Label 16 Exp 0] 9 msec
4 *
5 *
6 *
7 *
8 *
9 *
10 *
11 *
12 *
13 *
14 *
15 *
16 *
17 *
18 *
19 *
20 *
21 *
22 *
23 *
24 *
25 *
26 *
27 *
28 *
29 *
30 *
CE-EAST#
注意：在排除故障时，在连接到MPLS网络时使用traceroute可能不太有效，因为一些服务提供商倾向于在Cisco IOS XE中配置no mpls ip propagate-ttl forward命令或在Cisco IOS XR中配置mpls ip-ttl-propagate disable forwarded命令，以隐藏核心中的所有LSR（标签交换路由器）（但入口和出口PE路由器除外）。
在查看源CE路由器的状态时，由于此路由器没有任何VRF（虚拟路由转发）并且不支持MPLS感知，您需要验证RIB（路由信息库）、CEF（思科快速转发）和BGP。在接下来的输出中，可以看到有一个路由条目通过BGP获知到目标子网172.16.1.0/24，可通过接口GigabitEthernet0/0到达：
CE-EAST#show ip route 172.16.1.10
Routing entry for 172.16.1.0/24
Known via "bgp 65001", distance 20, metric 0 <<<<<
Tag 65500, type external
Last update from 10.11.0.2 3d01h ago
Routing Descriptor Blocks:
* 10.11.0.2, from 10.11.0.2, 3d01h ago
Route metric is 0, traffic share count is 1
AS Hops 2
Route tag 65500
MPLS label: none
CE-EAST#show ip cef 172.16.1.10
172.16.1.0/24
nexthop 10.11.0.2 GigabitEthernet0/0 <<<<<
CE-EAST#由于源CE-EAST路由器在RIB中安装了通往目标的路由，因此查看提供商边缘路由器PE4（入口PE）的时间较长，如拓扑所示。此时，配置了VRF和路由区分符以及路由目标导入和导出，如以下输出所示：
RP/0/0/CPU0:PE4#show run vrf EAST
Mon Sep 11 20:01:54.454 UTC
vrf EAST
address-family ipv4 unicast
import route-target 65000:1 65001:1 65001:2 ! export route-target 65001:1
!
!
!
RP/0/0/CPU0:PE4#show run router bgp
Mon Sep 11 20:06:48.164 UTC
router bgp 65500
address-family ipv4 unicast
!
address-family vpnv4 unicast
!
neighbor 10.10.10.6
remote-as 65500
update-source Loopback0
address-family vpnv4 unicast
!
!
vrf EAST
rd 65001:1
address-family ipv4 unicast
!
neighbor 10.11.0.1
remote-as 65001
address-family ipv4 unicast
route-policy PASS in
route-policy PASS out
!
!
!
!
RP/0/0/CPU0:PE4#从先前的输出中可以看到，VRF名称“EAST”是使用65000：1的路由-目标导入定义的，现在可以检查VRF路由表，这有助于确定PE4是否具有通往目标IP地址172.16.1.10的路由：
RP/0/0/CPU0:PE4#show route vrf EAST 172.16.1.10
Mon Sep 11 19:58:28.128 UTC
Routing entry for 172.16.1.0/24
Known via "bgp 65500", distance 200, metric 0
Tag 65000, type internal
Installed Sep 8 18:28:46.303 for 3d01h
Routing Descriptor Blocks
10.10.10.1, from 10.10.10.6
Nexthop in Vrf: "default", Table: "default", IPv4 Unicast, Table Id: 0xe0000000
Route metric is 0
No advertising protos.
RP/0/0/CPU0:PE4#因为此PE是思科IOS XR设备，所以可在show route vrf <name>命令末尾使用“detail”关键字来查看其他一些信息，例如由MP-BGP（多协议BGP）强加的VPNv4标签和源RD（路由区分符）与前缀：
RP/0/0/CPU0:PE4#show route vrf EAST 172.16.1.10 detail
Mon Sep 11 20:21:48.492 UTC
Routing entry for 172.16.1.0/24
Known via "bgp 65500", distance 200, metric 0
Tag 65000, type internal
Installed Sep 8 18:28:46.303 for 3d01h
Routing Descriptor Blocks
10.10.10.1, from 10.10.10.6
Nexthop in Vrf: "default", Table: "default", IPv4 Unicast, Table Id: 0xe0000000
Route metric is 0
Label: 0x10 (16) <<<<<
Tunnel ID: None
Binding Label: None
Extended communities count: 0
Source RD attributes: 0x0000:65000:1 <<<<<
NHID:0x0(Ref:0)
Route version is 0x5 (5)
No local label
IP Precedence: Not Set
QoS Group ID: Not Set
Flow-tag: Not Set
Fwd-class: Not Set
Route Priority: RIB_PRIORITY_RECURSIVE (12) SVD Type RIB_SVD_TYPE_REMOTE
Download Priority 3, Download Version 36
No advertising protos.
RP/0/0/CPU0:PE4#现在，让我们看看导入到VRF中的BGP VPNv4前缀，观察到，这是从上一个输出中得到的相同标签16，并且它还具有扩展社区65000：1。此外，请注意10.10.10.1是PE4需要对其执行路由递归的下一跳，下一个地址“from 10.10.10.6”是PE4用于获取此前缀的BGP对等体（在本场景中是路由反射器P6）：
RP/0/0/CPU0:PE4#show bgp vpnv4 unicast vrf EAST 172.16.1.10
Mon Sep 11 22:42:28.114 UTC
BGP routing table entry for 172.16.1.0/24, Route Distinguisher: 65001:1
Versions:
Process bRIB/RIB SendTblVer
Speaker 48 48
Last Modified: Sep 8 18:28:46.314 for 3d04h
Paths: (1 available, best #1)
Not advertised to any peer
Path #1: Received by speaker 0
Not advertised to any peer
65000
10.10.10.1 (metric 20) from 10.10.10.6 (10.10.10.1) <<<<<
Received Label 16
Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, imported
Received Path ID 0, Local Path ID 0, version 48
Extended community: RT:65000:1 <<<<<
Originator: 10.10.10.1, Cluster list: 10.10.10.6
Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 65000:1 <<<<< 通过在VRF级别使用exact-route关键字查看CEF，您可以了解数据包的送出接口。此命令还可以提供一些重要的详细信息，因为它显示施加到前缀24001和16的两个标签，原因是标签16来自BGP VPNv4，标签24001来自LDP（标签分发协议）：
RP/0/0/CPU0:PE4#show cef vrf EAST exact-route 192.168.1.10 172.16.1.10
Mon Sep 11 22:48:15.241 UTC
172.16.1.0/24, version 36, internal 0x5000001 0x0 (ptr 0xa12dc74c) [1], 0x0 (0x0), 0x208 (0xa155b1b8)
Updated Sep 8 18:28:46.323
local adjacency 10.0.0.16
Prefix Len 24, traffic index 0, precedence n/a, priority 3
via GigabitEthernet0/0/0/4
via 10.10.10.1/32, 3 dependencies, recursive [flags 0x6000]
path-idx 0 NHID 0x0 [0xa15c3f54 0x0]
recursion-via-/32
next hop VRF - 'default', table - 0xe0000000
next hop 10.10.10.1/32 via 24010/0/21
next hop 10.0.0.16/32 Gi0/0/0/4 labels imposed {24001 16} <<<<<下一步，使用show bgp vpnv4 unicast命令检查由此PE获取的VPNv4路由。此输出显示将VPNv4前缀导入VRF之前的信息，请记住，配置的RT（路由目标）(例如，导入的RT是65000：1、65001：1、65001：2)表示导入的路由和导入的VRF：
RP/0/0/CPU0:PE4#show bgp vpnv4 unicast
Fri Sep 15 02:15:15.463 UTC
BGP router identifier 10.10.10.4, local AS number 65500
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0x0 RD version: 0
BGP main routing table version 85
BGP NSR Initial initsync version 1 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
BGP scan interval 60 secs
Status codes: s suppressed, d damped, h history, * valid, > best
i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 65000:1
*>i172.16.1.0/24 10.10.10.1 0 100 0 65000 i <<<<<
*>i172.16.2.0/24 10.10.10.1 0 100 0 65000 i
Route Distinguisher: 65001:1 (default for vrf EAST)
* i0.0.0.0/0 10.10.10.3 0 100 0 65001 i
*> 10.11.0.1 0 0 65001 i
*>i172.16.1.0/24 10.10.10.1 0 100 0 65000 i
*>i172.16.2.0/24 10.10.10.1 0 100 0 65000 i
*> 192.168.1.0/24 10.11.0.1 0 0 65001 i
*>i192.168.2.0/24 10.10.10.3 0 100 0 65001 i
*> 192.168.3.0/24 10.11.0.1 0 0 65001 i
Route Distinguisher: 65001:2
*>i0.0.0.0/0 10.10.10.3 0 100 0 65001 i
*>i192.168.2.0/24 10.10.10.3 0 100 0 65001 i
Processed 10 prefixes, 11 paths
在本例中，VPNv4表可能很小，但在生产环境中，您可以使用以下命令将验证范围缩小到特定RD和前缀，而不是查看所有VPNv4前缀：
RP/0/0/CPU0:PE4#show bgp vpnv4 unicast rd 65000:1 172.16.1.10
Mon Sep 11 22:54:04.967 UTC
BGP routing table entry for 172.16.1.0/24, Route Distinguisher: 65000:1
Versions:
Process bRIB/RIB SendTblVer
Speaker 46 46
Last Modified: Sep 8 18:28:46.314 for 3d04h
Paths: (1 available, best #1)
Not advertised to any peer
Path #1: Received by speaker 0
Not advertised to any peer
65000
10.10.10.1 (metric 20) from 10.10.10.6 (10.10.10.1)
Received Label 16
Origin IGP, metric 0, localpref 100, valid, internal, best, group-best, import-candidate, not-in-vrf
Received Path ID 0, Local Path ID 0, version 46
Extended community: RT:65000:1
Originator: 10.10.10.1, Cluster list: 10.10.10.6此时，MP-BGP控制平面具有目标前缀以及LDP和VPNv4标签{24001 16}，此流量的送出接口似乎是Gi0/0/0/4，需要转发流量的下一跳是10.10.10.1。但是，是否还有其它选项可用于检验首选送出接口？是时候了解MPLS转发表或LFIB（标签转发信息库）了。使用命令show mpls forwarding将显示指向10.10.10.1目标（来自PE1的Loopback0）的两个条目，一条路径具有传出接口Gi0/0/0/4和下一跳10.0.0.16（路由器P5），其中强加的传出标签为24001，另一条路径通过Gi0/0/0/3，下一跳10.0.13（路由器P6）和传出标签23：
RP/0/0/CPU0:PE4#show mpls forwarding
Mon Sep 11 23:28:33.425 UTC
Local Outgoing Prefix Outgoing Next Hop Bytes
Label Label or ID Interface Switched
------ ----------- ------------------ ------------ --------------- ------------
24000 Unlabelled 192.168.1.0/24[V] Gi0/0/0/0 10.11.0.1 1096
24001 Unlabelled 192.168.3.0/24[V] Gi0/0/0/0 10.11.0.1 56056
24002 Unlabelled 0.0.0.0/0[V] Gi0/0/0/0 10.11.0.1 0
24003 Pop 10.10.10.6/32 Gi0/0/0/3 10.0.0.13 7778512
24004 Pop 10.0.0.4/31 Gi0/0/0/3 10.0.0.13 0
24005 Pop 10.0.0.8/31 Gi0/0/0/3 10.0.0.13 0
24006 Pop 10.10.10.5/32 Gi0/0/0/4 10.0.0.16 3542574
24007 Pop 10.0.0.10/31 Gi0/0/0/3 10.0.0.13 0
Pop 10.0.0.10/31 Gi0/0/0/4 10.0.0.16 0
24008 Pop 10.0.0.6/31 Gi0/0/0/4 10.0.0.16 0
24009 Pop 10.0.0.0/31 Gi0/0/0/4 10.0.0.16 0
24010 23 10.10.10.1/32 Gi0/0/0/3 10.0.0.13 22316 <<<<<
24001 10.10.10.1/32 Gi0/0/0/4 10.0.0.16 42308 <<<<<
24011 18 10.10.10.2/32 Gi0/0/0/3 10.0.0.13 0
24003 10.10.10.2/32 Gi0/0/0/4 10.0.0.16 0
24012 17 10.0.0.2/31 Gi0/0/0/3 10.0.0.13 0
24005 10.0.0.2/31 Gi0/0/0/4 10.0.0.16 0
24013 Pop 10.10.10.3/32 Gi0/0/0/1 10.0.0.20 3553900
24014 Pop 10.0.0.14/31 Gi0/0/0/1 10.0.0.20 0
Pop 10.0.0.14/31 Gi0/0/0/4 10.0.0.16 0
24015 Pop 10.0.0.18/31 Gi0/0/0/1 10.0.0.20 0
Pop 10.0.0.18/31 Gi0/0/0/3 10.0.0.13 0
RP/0/0/CPU0:PE4#show mpls forwarding prefix 10.10.10.1/32
Mon Sep 11 23:30:54.685 UTC
Local Outgoing Prefix Outgoing Next Hop Bytes
Label Label or ID Interface Switched
------ ----------- ------------------ ------------ --------------- ------------
24010 23 10.10.10.1/32 Gi0/0/0/3 10.0.0.13 3188
24001 10.10.10.1/32 Gi0/0/0/4 10.0.0.16 6044
RP/0/0/CPU0:PE4#show mpls forwarding prefix 10.10.10.1/32 detail hardware egress
Mon Sep 11 23:36:06.504 UTC
Local Outgoing Prefix Outgoing Next Hop Bytes
Label Label or ID Interface Switched
------ ----------- ------------------ ------------ --------------- ------------
24010 23 10.10.10.1/32 Gi0/0/0/3 10.0.0.13 N/A
Updated: Sep 8 20:27:26.596
Version: 39, Priority: 3
Label Stack (Top -> Bottom): { 23 }
NHID: 0x0, Encap-ID: N/A, Path idx: 0, Backup path idx: 0, Weight: 0
MAC/Encaps: 14/18, MTU: 1500
Outgoing Interface: GigabitEthernet0/0/0/3 (ifhandle 0x000000a0)
Packets Switched: 0
24001 10.10.10.1/32 Gi0/0/0/4 10.0.0.16 N/A
Updated: Sep 8 20:27:26.596
Version: 39, Priority: 3
Label Stack (Top -> Bottom): { 24001 }
NHID: 0x0, Encap-ID: N/A, Path idx: 1, Backup path idx: 0, Weight: 0
MAC/Encaps: 14/18, MTU: 1500
Outgoing Interface: GigabitEthernet0/0/0/4 (ifhandle 0x000000c0)
Packets Switched: 0
从前面的输出可以清楚地看到，流量可以负载均衡的路径选项有两个，但是有几种方法可以帮助确定哪一个是首选路径。一种方式是使用show cef exact-route <source IP> <destination IP>命令，方法是添加源PE的Loopback0和目标PE的Loopback0。如下一个输出所示，首选路径是通过Gi0/0/0/4：
RP/0/0/CPU0:PE4#show cef exact-route 10.10.10.4 10.10.10.1
Mon Sep 11 23:49:44.558 UTC
10.10.10.1/32, version 39, internal 0x1000001 0x0 (ptr 0xa12dbdbc) [1], 0x0 (0xa12c18c0), 0xa28 (0xa185307c)
Updated Sep 8 20:27:26.596
local adjacency 10.0.0.16
Prefix Len 32, traffic index 0, precedence n/a, priority 3
via GigabitEthernet0/0/0/4
via 10.0.0.16/32, GigabitEthernet0/0/0/4, 9 dependencies, weight 0, class 0 [flags 0x0] <<<<<
path-idx 1 NHID 0x0 [0xa16765bc 0x0]
next hop 10.0.0.16/32
local adjacency
local label 24010 labels imposed {24001}另一个选项是首先验证LIB（标签信息库）并通过使用show mpls ldp bindings <prefix/mask>命令获取目标Loopback0 （属于出口PE的10.10.10.1）的LDP绑定，然后从该输出中找到本地绑定标签后，使用该标签值在show mpls forwarding exact-route label <label> ipv4 <source IP> <destination IP> detail命令中查找首选路径：
RP/0/0/CPU0:PE4#show mpls ldp bindings 10.10.10.1/32
Wed Sep 13 17:18:43.007 UTC
10.10.10.1/32, rev 29
Local binding: label: 24010 <<<<<
Remote bindings: (3 peers)
Peer Label
----------------- ---------
10.10.10.3:0 24
10.10.10.5:0 24001
10.10.10.6:0 23
RP/0/0/CPU0:PE4#show mpls forwarding exact-route label 24010 ipv4 10.10.10.4 10.10.10.1 detail
Wed Sep 13 17:20:06.342 UTC
Local Outgoing Prefix Outgoing Next Hop Bytes
Label Label or ID Interface Switched
------ ----------- ------------------ ------------ --------------- ------------
24010 24001 10.10.10.1/32 Gi0/0/0/4 10.0.0.16 N/A <<<<<
Updated: Sep 12 14:15:37.009
Version: 198, Priority: 3
Label Stack (Top -> Bottom): { 24001 }
NHID: 0x0, Encap-ID: N/A, Path idx: 1, Backup path idx: 0, Weight: 0
Hash idx: 1
MAC/Encaps: 14/18, MTU: 1500
Outgoing Interface: GigabitEthernet0/0/0/4 (ifhandle 0x000000c0)
Packets Switched: 0
Via: Gi0/0/0/4, Next Hop: 10.0.0.16
Label Stack (Top -> Bottom): { 24001 }
NHID: 0x0, Encap-ID: N/A, Path idx: 1, Backup path idx: 0, Weight: 0
Hash idx: 1
MAC/Encaps: 14/18, MTU: 1500
Outgoing Interface: GigabitEthernet0/0/0/4 (ifhandle 0x000000c0)接下来，必须检查数据平面中的下一跳路由器，在本例中，要验证的路由器是P5（即接口为10.0.0.16）。首先要了解的是MPLS转发表，其中前缀10.10.10.1的本地标签必须24001：
RP/0/0/CPU0:P5#show mpls forwarding
Thu Sep 14 20:07:16.455 UTC
Local Outgoing Prefix Outgoing Next Hop Bytes
Label Label or ID Interface Switched
------ ----------- ------------------ ------------ --------------- ------------
24000 Pop 10.10.10.6/32 Gi0/0/0/2 10.0.0.11 361906
24001 Pop 10.10.10.1/32 Gi0/0/0/1 10.0.0.0 361002 <<<<<
24002 Pop 10.0.0.4/31 Gi0/0/0/1 10.0.0.0 0
Pop 10.0.0.4/31 Gi0/0/0/2 10.0.0.11 0
24003 Pop 10.10.10.2/32 Gi0/0/0/0 10.0.0.6 360940
24004 Pop 10.0.0.8/31 Gi0/0/0/0 10.0.0.6 0
Pop 10.0.0.8/31 Gi0/0/0/2 10.0.0.11 0
24005 Pop 10.0.0.2/31 Gi0/0/0/0 10.0.0.6 0
Pop 10.0.0.2/31 Gi0/0/0/1 10.0.0.0 0
24006 Pop 10.10.10.4/32 Gi0/0/0/4 10.0.0.17 361230
24007 Pop 10.0.0.12/31 Gi0/0/0/2 10.0.0.11 0
Pop 10.0.0.12/31 Gi0/0/0/4 10.0.0.17 0
24008 Pop 10.10.10.3/32 Gi0/0/0/3 10.0.0.15 361346
24009 Pop 10.0.0.20/31 Gi0/0/0/3 10.0.0.15 0
Pop 10.0.0.20/31 Gi0/0/0/4 10.0.0.17 0
24010 Pop 10.0.0.18/31 Gi0/0/0/2 10.0.0.11 0
Pop 10.0.0.18/31 Gi0/0/0/3 10.0.0.15 0
RP/0/0/CPU0:P5#show mpls forwarding labels 24001
Thu Sep 14 20:07:42.584 UTC
Local Outgoing Prefix Outgoing Next Hop Bytes
Label Label or ID Interface Switched
------ ----------- ------------------ ------------ --------------- ------------
24001 Pop 10.10.10.1/32 Gi0/0/0/1 10.0.0.0 361060
RP/0/0/CPU0:P5#从先前的输出中可以看到，前缀10.10.10.1/32的LFIB条目显示“Pop”作为传出标签，这意味着此路由器是倒数第二跳跳跳跃(PHP)。它还显示必须根据LFIB信息通过Gi0/0/0/1发送流量，在查看CEF时也可以进行验证。下一个CEF exact-route输出显示隐式空标签作为强加的标签，这同样是因为在Gi0/0/0/1连接的下一跳是标签交换机路径中的最后一个路由器，也是面向目标站点(CE-WEST)的PE。这也是路由器P5删除数据包且不向数据包施加其他标签的原因，由于此过程，出口路由器PE1将接收不带LDP标签的数据包：
RP/0/0/CPU0:P5#show cef exact-route 10.10.10.4 10.10.10.1
Thu Sep 14 20:25:57.269 UTC
10.10.10.1/32, version 192, internal 0x1000001 0x0 (ptr 0xa1246394) [1], 0x0 (0xa122b638), 0xa20 (0xa155b550)
Updated Sep 12 14:15:38.009
local adjacency 10.0.0.0
Prefix Len 32, traffic index 0, precedence n/a, priority 3
via GigabitEthernet0/0/0/1
via 10.0.0.0/32, GigabitEthernet0/0/0/1, 9 dependencies, weight 0, class 0 [flags 0x0]
path-idx 0 NHID 0x0 [0xa166e280 0xa166e674]
next hop 10.0.0.0/32
local adjacency
local label 24001 labels imposed {ImplNull} <<<<<检验标签交换机路径的最后一点是PE1。在查看MPLS转发表时，可以注意到LFIB中没有前缀10.10.10.1/32的条目：
PE1#show mpls forwarding-table
Local Outgoing Prefix Bytes Label Outgoing Next Hop
Label Label or Tunnel Id Switched interface
16 No Label 172.16.1.0/24[V] 12938 Gi3 10.10.0.1
17 No Label 172.16.2.0/24[V] 0 Gi3 10.10.0.1
18 Pop Label 10.0.0.6/31 0 Gi1 10.0.0.1
Pop Label 10.0.0.6/31 0 Gi2 10.0.0.3
19 Pop Label 10.0.0.8/31 0 Gi2 10.0.0.3
Pop Label 10.0.0.8/31 0 Gi4 10.0.0.5
20 Pop Label 10.0.0.10/31 0 Gi1 10.0.0.1
Pop Label 10.0.0.10/31 0 Gi4 10.0.0.5
21 Pop Label 10.0.0.12/31 0 Gi4 10.0.0.5
22 Pop Label 10.0.0.14/31 0 Gi1 10.0.0.1
23 Pop Label 10.0.0.16/31 0 Gi1 10.0.0.1
24 Pop Label 10.0.0.18/31 0 Gi4 10.0.0.5
25 24009 10.0.0.20/31 0 Gi1 10.0.0.1
22 10.0.0.20/31 0 Gi4 10.0.0.5
26 Pop Label 10.10.10.2/32 0 Gi2 10.0.0.3
27 24008 10.10.10.3/32 0 Gi1 10.0.0.1
24 10.10.10.3/32 0 Gi4 10.0.0.5
28 24006 10.10.10.4/32 0 Gi1 10.0.0.1
25 10.10.10.4/32 0 Gi4 10.0.0.5
29 Pop Label 10.10.10.5/32 0 Gi1 10.0.0.1
Local Outgoing Prefix Bytes Label Outgoing Next Hop
Label Label or Tunnel Id Switched interface
30 Pop Label 10.10.10.6/32 0 Gi4 10.0.0.5
31 [T] Pop Label 1/1[TE-Bind] 0 drop
[T] Forwarding through a LSP tunnel.
View additional labelling info with the 'detail' option如您所知，此行为的原因在于前缀(10.10.10.1/32)属于PE1，并且路由器还为此连接的前缀分配了一个隐式null标签。这可以通过使用show mpls ldp bindings命令进行验证：
PE1#show run interface loopback 0
Building configuration...
Current configuration : 66 bytes
!
interface Loopback0
ip address 10.10.10.1 255.255.255.255
end
PE1#show mpls ldp bindings 10.10.10.1 32
lib entry: 10.10.10.1/32, rev 24
local binding: label: imp-null
remote binding: lsr: 10.10.10.6:0, label: 23
remote binding: lsr: 10.10.10.5:0, label: 24001
remote binding: lsr: 10.10.10.2:0, label: 24000由于PE1是Cisco IOS XE路由器，使用命令show bgp vpnv4 unicast all或show bgp vpnv4 unicast rd <value> <destination IP>有助于识别和确认是否通过MP-BGP正确获取了目标前缀172.16.1.0/24。导出后，这些命令的输出会显示前缀：
PE1#show bgp vpnv4 unicast all
BGP table version is 61, local router ID is 10.10.10.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path, L long-lived-stale,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 65000:1 (default for vrf WEST)
*>i 0.0.0.0 10.10.10.3 0 100 0 65001 i
*bi 10.10.10.4 0 100 0 65001 i
*> 172.16.1.0/24 10.10.0.1 0 0 65000 i <<<<<
*> 172.16.2.0/24 10.10.0.1 0 0 65000 i
*>i 192.168.1.0 10.10.10.4 0 100 0 65001 i
*>i 192.168.2.0 10.10.10.3 0 100 0 65001 i
*>i 192.168.3.0 10.10.10.4 0 100 0 65001 i
Route Distinguisher: 65001:1
*>i 0.0.0.0 10.10.10.4 0 100 0 65001 i
*>i 192.168.1.0 10.10.10.4 0 100 0 65001 i
*>i 192.168.3.0 10.10.10.4 0 100 0 65001 i
Route Distinguisher: 65001:2
Network Next Hop Metric LocPrf Weight Path
*>i 0.0.0.0 10.10.10.3 0 100 0 65001 i
*>i 192.168.2.0 10.10.10.3 0 100 0 65001 i
PE1#show bgp vpnv4 unicast rd 65000:1 172.16.1.10
BGP routing table entry for 65000:1:172.16.1.0/24, version 2
Paths: (1 available, best #1, table WEST)
Additional-path-install
Advertised to update-groups:
6
Refresh Epoch 2
65000
10.10.0.1 (via vrf WEST) from 10.10.0.1 (172.16.2.10) <<<<<
Origin IGP, metric 0, localpref 100, valid, external, best
Extended Community: RT:65000:1 , recursive-via-connected <<<<<
mpls labels in/out 16/nolabel
rx pathid: 0, tx pathid: 0x0
Updated on Sep 15 2023 18:27:23 UTC类似地，查看VRF上的BGP VPNv4前缀，即CE-WEST接收的前缀，使用命令show bgp vpnv4 unicast vrf <name> <prefix>时，输出显示一直传输到入口PE4的MP-BGP标签16以及配置了65000：1的RT导出：
PE1#show bgp vpnv4 unicast vrf WEST 172.16.1.10
BGP routing table entry for 65000:1:172.16.1.0/24, version 2
Paths: (1 available, best #1, table WEST)
Additional-path-install
Advertised to update-groups:
6
Refresh Epoch 2
65000
10.10.0.1 (via vrf WEST) from 10.10.0.1 (172.16.2.10)
Origin IGP, metric 0, localpref 100, valid, external, best
Extended Community: RT:65000:1 , recursive-via-connected <<<<<
mpls labels in/out 16/nolabel <<<<<
rx pathid: 0, tx pathid: 0x0
Updated on Sep 15 2023 18:27:23 UTC
PE1#show run vrf WEST
Building configuration...
Current configuration : 478 bytes
vrf definition WEST
rd 65000:1
route-target export 65000:1 <<<<<
route-target import 65000:1
route-target import 65001:1
route-target import 65001:2
!
address-family ipv4
exit-address-family
!
!
interface GigabitEthernet3
vrf forwarding WEST
ip address 10.10.0.2 255.255.255.252
negotiation auto
no mop enabled
no mop sysid
!
router bgp 65500
!
address-family ipv4 vrf WEST
neighbor 10.10.0.1 remote-as 65000
neighbor 10.10.0.1 activate
exit-address-family
!
end在此PE上要检查的最后信息是到目标IP的VRF级别的RIB和CEF条目，与在PE4上看到的条目相比，RIB上没有前缀172.16.1.0/24的标签，原因是这是来自CE的路由，并且通过eBGP获知该路由并将其插入到VRF路由表中，然后将此前缀导出到VPNv4。这可以通过使用show ip route vrf <name> <prefix>和show ip cef vrf <name> <prefix>（如下所示）命令进行验证：
PE1#show ip route vrf WEST 172.16.1.10
Routing Table: WEST
Routing entry for 172.16.1.0/24
Known via "bgp 65500", distance 20, metric 0
Tag 65000, type external
Last update from 10.10.0.1 1w0d ago
Routing Descriptor Blocks:
* 10.10.0.1, from 10.10.0.1, 1w0d ago, recursive-via-conn
opaque_ptr 0x7F8B4E3E1D50
Route metric is 0, traffic share count is 1
AS Hops 1
Route tag 65000
MPLS label: none
PE1#show ip cef vrf WEST 172.16.1.10
172.16.1.0/24
nexthop 10.10.0.1 GigabitEthernet3这时，已确认目的地前缀172.16.1.0/24是由流量CE (CE-EAST)的源正确获知的，它通过MP-BGP正确传播，并且来自PE和Ps环回的标签也是在标签交换机路径上获知的。但是，源/目标之间的可达性仍然不成功，而且还有最后一个路由器用于检验CE-WEST。要在此路由器中检查的第一件事是路由表，请记住，源IP前缀192.168.1.0/24应显示在此表中：
CE-WEST#show ip route 192.168.1.10
% Network not in table CE-WEST#“Network not in table”显然是个问题，BGP表也可以验证，但在查找前缀后同样不存在：
CE-WEST#show ip bgp
BGP table version is 41, local router ID is 172.16.2.10
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*> 172.16.1.0/24 0.0.0.0 0 32768 i
*> 172.16.2.0/24 0.0.0.0 0 32768 i
CE-WEST#后退一步，您可以验证此提供商边缘路由器(PE1)是否正在向eBGP邻居CE-WEST通告前缀，这可以使用命令show bgp vpnv4 unicast vrf <name> neighbors <neighbor IP> advertised-routes完成，如下所示：
PE1#show bgp vpnv4 unicast vrf WEST neighbors 10.10.0.1 advertised-routes
BGP table version is 61, local router ID is 10.10.10.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path, L long-lived-stale,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 65000:1 (default for vrf WEST)
*>i 0.0.0.0 10.10.10.3 0 100 0 65001 i
*>i 192.168.1.0 10.10.10.4 0 100 0 65001 i <<<<<
*>i 192.168.2.0 10.10.10.3 0 100 0 65001 i
*>i 192.168.3.0 10.10.10.4 0 100 0 65001 i
Total number of prefixes 4根据之前步骤，可以确认PE1路由器正在向CE-WEST正确通告前缀，因此是时候查看CE端的BGP邻居了：
CE-WEST#show ip bgp neighbors
BGP neighbor is 10.10.0.2, remote AS 65500, external link
BGP version 4, remote router ID 10.10.10.1
BGP state = Established, up for 1w4d
Last read 00:00:40, last write 00:00:43, hold time is 180, keepalive interval is 60 seconds
Neighbor sessions:
1 active, is not multisession capable (disabled)
Neighbor capabilities:
Route refresh: advertised and received(new)
Four-octets ASN Capability: advertised and received
Address family IPv4 Unicast: advertised and received
Enhanced Refresh Capability: advertised and received
Multisession Capability:
Stateful switchover support enabled: NO for session 1
Message statistics:
InQ depth is 0
OutQ depth is 0
Sent Rcvd
Opens: 1 1
Notifications: 0 0
Updates: 3 17
Keepalives: 19021 18997
Route Refresh: 2 0
Total: 19029 19019
Do log neighbor state changes (via global configuration)
Default minimum time between advertisement runs is 30 seconds
For address family: IPv4 Unicast
Session: 10.10.0.2
BGP table version 41, neighbor version 41/0
Output queue size : 0
Index 3, Advertise bit 0
3 update-group member
Inbound path policy configured
Route map for incoming advertisements is FILTER <<<<<
Slow-peer detection is disabled
Slow-peer split-update-group dynamic is disabled
Sent Rcvd
Prefix activity: ---- ----
Prefixes Current: 2 0
Prefixes Total: 4 23
Implicit Withdraw: 2 13
Explicit Withdraw: 0 10
Used as bestpath: n/a 0
Used as multipath: n/a 0
Used as secondary: n/a 0
Outbound Inbound
Local Policy Denied Prefixes: -------- -------
route-map: 0 4
Bestpath from this peer: 18 n/a
Total: 18 4
Number of NLRIs in the update sent: max 2, min 0
Last detected as dynamic slow peer: never
Dynamic slow peer recovered: never
Refresh Epoch: 3
Last Sent Refresh Start-of-rib: 4d23h
Last Sent Refresh End-of-rib: 4d23h
Refresh-Out took 0 seconds
Last Received Refresh Start-of-rib: 4d23h
Last Received Refresh End-of-rib: 4d23h
Refresh-In took 0 seconds
Sent Rcvd
Refresh activity: ---- ----
Refresh Start-of-RIB 1 2
Refresh End-of-RIB 1 2
Address tracking is enabled, the RIB does have a route to 10.10.0.2
Route to peer address reachability Up: 1; Down: 0
Last notification 1w5d
Connections established 3; dropped 2
Last reset 1w4d, due to Peer closed the session of session 1
External BGP neighbor configured for connected checks (single-hop no-disable-connected-check)
Interface associated: GigabitEthernet0/3 (peering address in same link)
Transport(tcp) path-mtu-discovery is enabled
Graceful-Restart is disabled
SSO is disabled
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 1
Local host: 10.10.0.1, Local port: 179
Foreign host: 10.10.0.2, Foreign port: 39410
Connection tableid (VRF): 0
Maximum output segment queue size: 50
Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0x4D15FD56):
Timer Starts Wakeups Next
Retrans 19027 1 0x0
TimeWait 0 0 0x0
AckHold 19012 18693 0x0
SendWnd 0 0 0x0
KeepAlive 0 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
Linger 0 0 0x0
ProcessQ 0 0 0x0
iss: 1676751051 snduna: 1677112739 sndnxt: 1677112739
irs: 2109012892 rcvnxt: 2109374776
sndwnd: 16061 scale: 0 maxrcvwnd: 16384
rcvwnd: 15890 scale: 0 delrcvwnd: 494
SRTT: 1000 ms, RTTO: 1003 ms, RTV: 3 ms, KRTT: 0 ms
minRTT: 0 ms, maxRTT: 1000 ms, ACK hold: 200 ms
uptime: 1036662542 ms, Sent idletime: 40725 ms, Receive idletime: 40925 ms
Status Flags: passive open, gen tcbs
Option Flags: nagle, path mtu capable
IP Precedence value : 6
Datagrams (max data segment is 1460 bytes):
Rcvd: 37957 (out of order: 0), with data: 19014, total data bytes: 361883
Sent: 37971 (retransmit: 1, fastretransmit: 0, partialack: 0, Second Congestion: 0), with data: 19027, total data bytes: 361687
Packets received in fast path: 0, fast processed: 0, slow path: 0
fast lock acquisition failures: 0, slow path: 0
TCP Semaphore 0x0F3194AC FREE 前面的输出显示，有一个路由映射应用于名为“FILTER”的传入通告，查看路由映射配置后，它显示了一个指向192.168.0.0/16上带有permit语句的前缀列表的match子句，但这是不正确的，因为prefix-list仅允许该特定前缀，而不允许该范围内可以包含的所有前缀：
CE-WEST#show route-map FILTER
route-map FILTER, permit, sequence 10
Match clauses:
ip address prefix-lists: FILTER
Set clauses:
Policy routing matches: 0 packets, 0 bytes
CE-WEST#show ip prefix-list FILTER
ip prefix-list FILTER: 1 entries
seq 5 permit 192.168.0.0/16 <<<<<
CE-WEST#show run | i ip prefix-list
ip prefix-list FILTER seq 5 permit 192.168.0.0/16通过对前缀列表配置进行细微更改，指向192.168.1.10的路由现在已安装到RIB中：
CE-WEST#show run | i ip prefix-list
ip prefix-list FILTER seq 5 permit 192.168.0.0/16 le 32 <<<<<
CE-WEST#show ip bgp
BGP table version is 44, local router ID is 172.16.2.10
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
t secondary path,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*> 172.16.1.0/24 0.0.0.0 0 32768 i
*> 172.16.2.0/24 0.0.0.0 0 32768 i
*> 192.168.1.0 10.10.0.2 0 65500 65001 i <<<<<
*> 192.168.2.0 10.10.0.2 0 65500 65001 i
*> 192.168.3.0 10.10.0.2 0 65500 65001 i
CE-WEST#show ip route 192.168.1.10
Routing entry for 192.168.1.0/24 <<<<<
Known via "bgp 65000", distance 20, metric 0
Tag 65500, type external
Last update from 10.10.0.2 00:00:37 ago
Routing Descriptor Blocks:
* 10.10.0.2, from 10.10.0.2, 00:00:37 ago
Route metric is 0, traffic share count is 1
AS Hops 2
Route tag 65500
MPLS label: none确认
现在，源和目标之间的可达性是成功的，并且可以确认traceroute通过与MPLS网络中跟踪的同一标签交换机路径：
转发路径
CE-EAST#ping 172.16.1.10 source loopback 1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.1.10, timeout is 2 seconds: Packet sent with a source address of 192.168.1.10 !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 7/7/9 ms <<<<< CE-EAST#traceroute 172.16.1.10 source loop1 probe 1 numeric Type escape sequence to abort. Tracing the route to 172.16.1.10 VRF info: (vrf in name/id, vrf out name/id) 1 10.11.0.2 2 msec 2 10.0.0.16 [MPLS: Labels 24001/16 Exp 0] 9 msec 3 10.10.0.2 [MPLS: Label 16 Exp 0] 8 msec 4 10.10.0.1 9 msecRP/0/0/CPU0:P5#show ipv4 interface brief Wed Sep 20 18:23:47.158 UTC Interface IP-Address Status Protocol Vrf-Name Loopback0 10.10.10.5 Up Up default MgmtEth0/0/CPU0/0 unassigned Shutdown Down default GigabitEthernet0/0/0/0 10.0.0.7 Up Up default GigabitEthernet0/0/0/1 10.0.0.1 Up Up default <<<<< GigabitEthernet0/0/0/2 10.0.0.10 Up Up default GigabitEthernet0/0/0/3 10.0.0.14 Up Up default GigabitEthernet0/0/0/4 10.0.0.16 Up Up default <<<<< RP/0/0/CPU0:P5#
Cisco IOS XE验证命令
MPLS/LDP
show mpls interfaces
show mpls forwarding-table
show mpls ldp bindings [destination prefix]
show mpls ldp neighbor [neighbor address]
clear mpls ldp neighbor [neighbor address|*]
RIB and CEF show ip vrf [detail]
show run vrf
show ip route [destination prefix]
show ip route vrf <name> [destination prefix]
show ip cef vrf <name> [destination prefix]
show ip cef exact-route <source IP> <destination IP>
show ip cef vrf <name> exact-route <source IP> <destination IP>
BGP/VPNv4 show ip bgp [neighbors] <neighbor address>
show bgp vpnv4 unicast all [summary|destination prefix]
show bgp vpnv4 unicast all neighbor <neighbor address> advertised-routes
show bgp vpnv4 unicast vrf <name> neighbors <neighbor IP> advertised-routes
show bgp vpnv4 unicast vrf <name> <prefix>
show bgp vpnv4 unicast rd <value> <destination IP>思科IOS XR验证命令
MPLS/LDP show mpls interfaces
show mpls forwarding
show mpls ldp bindings [destination prefix/mask]
show mpls ldp neighbor [neighbor address]
show mpls forwarding prefix [destination prefix/mask]
show mpls forwarding prefix [destination prefix/mask] detail hardware egress
clear mpls ldp neighbor [neighbor address]
RIB and CEF show vrf [name|all]
show run vrf [name]
show route [destination prefix]
show route vrf <name> [destination prefix]
show cef vrf <name> [destination prefix]
show cef exact-route <source IP> <destination IP>
show cef vrf <name> exact-route <source IP> <destination IP>
BGP/VPNv4 show bgp vpnv4 unicast [summary|destination prefix/mask]
show bgp vpnv4 unicast neighbors <neighbor address> advertised-routes
show bgp vpnv4 unicast vrf <name> [prefix]
show bgp vrf <name> neighbors <neighbor IP> advertised-routes
show bgp vpnv4 unicast rd [value|all] [destination IP]相关信息
修订历史记录
| 版本 | 发布日期 | 备注 |
|---|---|---|
1.0 |
21-Sep-2023 |
初始版本 |
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