驗證MPLS第3層VPN轉發
簡介
本文檔介紹在MPLS第3層VPN核心網路中驗證端到端連線的過程。
必要條件
需求
思科建議您瞭解以下主題：
- 基本IP路由知識
- Cisco IOS® XE和Cisco IOS® XR命令列知識
採用元件
本文中的資訊係根據以下軟體和硬體版本：
- 使用Cisco IOS XR軟體的路由器
- 使用Cisco IOS XE軟體的路由器
本文中的資訊是根據特定實驗室環境內的裝置所建立。文中使用到的所有裝置皆從已清除（預設）的組態來啟動。如果您的網路運作中，請確保您瞭解任何指令可能造成的影響。
背景資訊
本文檔的目的是演示基本的驗證和故障排除步驟，這些步驟用於檢查透過混合使用Cisco IOS XE和Cisco IOS XR路由器作為PE（提供商邊緣）和P（提供商）路由器的MPLS第3層VPN核心網路與BGP（邊界網關協定）互連的兩台CE（客戶邊緣）路由器之間的連線和轉發。
慣例
如需文件慣例的詳細資訊，請參閱思科技術提示慣例。
拓撲
MPLS拓撲圖
疑難排解
初始資訊
源網路：192.168.1.0/24
源CE路由器：CE-EAST
目的網路：172.16.1.0/24
目的CE路由器：CE-WEST
根據初始資訊和拓撲，在路由器CE-EAST上Loopback1表示的源地址192.168.1.10和路由器CE-WEST上Loopback1表示的目的地地址172.16.1.10之間必須能夠成功連通：
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可達性和traceroute用於開始檢查這些源地址和目標地址之間的連線，但從接下來的輸出中可以看到此操作不成功：
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：在排除故障時，在連線到MPLS網路時使用跟蹤路由可能不太有效，因為某些服務提供商傾向於在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，以隱藏核心中的所有LSR（標籤交換機路由器）（但入口和出口PE路由器除外）。
在檢視源CE路由器的狀態時，由於此路由器沒有任何VRF（虛擬路由轉發）並且不支援MPLS感知，您需要驗證RIB（路由資訊庫）、CEF（思科快速轉發）和BGP。在接下來的輸出中，可以觀察到有一個路由條目，該條目透過BGP獲知到目標子網172.16.1.0/24，可透過介面GigabitEthernet0/0到達：
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#由於源CE-EAST路由器在RIB中安裝了通往目標的路由，因此檢視提供商邊緣路由器PE4（入口PE）所花的時間如拓撲所示。此時，配置了VRF和路由區分符以及路由目標導入和導出，如下面的輸出所示：
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#從先前的輸出中可以看到，VRF名稱「EAST」是使用65000：1的路由目標導入定義的，現在可以檢查VRF路由表，這有助於確定PE4是否具有通向目標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#由於此PE是思科IOS XR裝置，因此可在show route vrf <name>命令末尾使用「detail」關鍵字檢視某些其他資訊，例如由MP-BGP（多協定BGP）和源RD（路由區分器）強加的VPNv4標籤以及字首：
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#現在，我們來看一下導入到VRF中的BGP VPNv4字首，發現這與之前輸出中的標籤16相同，並且它還具有擴展社群65000：1。此外，必須注意的是，10.10.10.1是PE4為其執行路由遞迴所需的下一跳，下一個地址「來自10.10.10.6」是PE4用於學習此字首的BGP對等體（在此場景中是路由反射器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 <<<<< 透過在VRF級別使用exact-route關鍵字檢視CEF，您可以瞭解資料包的送出介面。此命令還可以提供一些重要的詳細資訊，因為它顯示強加到字首24001和16的兩個標籤，原因是標籤16來自BGP VPNv4，標籤24001來自LDP（標籤分發協定）：
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，show bgp vpnv4 unicast命令用於檢查此PE正在獲取的VPNv4路由。此輸出顯示VPNv4字首導入VRF之前的資訊，請記住，配置的RT（路由目標）(例如，導入的RT是65000：1、65001：1和65001：2)指示要導入的VRF的路由和目標：
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
在本示例中，VPNv4表可以很小，但在生產環境中，您可以使用下一個命令將驗證範圍縮小到特定RD和字首，而不是檢視所有VPNv4字首：
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此時，MP-BGP控制平面分別具有目標字首和LDP和VPNv4標籤{24001 16}，此流量的送出介面似乎是Gi0/0/0/4，需要轉發流量的下一跳是10.10.10.1。但是，是否有其他選項檢驗首選送出介面？現在是時候瞭解MPLS轉發表或LFIB（標籤轉發資訊庫）了。使用命令show mpls forwarding可顯示指向10.10.10.1目標（Pe1的Loopback0）的兩個條目，一條路徑具有傳出介面Gi0/0/0/4和下一跳10.0.0.16（路由器P5），其中強加的傳出標籤為24001，另一條路徑透過Gi0/0/0/3，其中下一跳為10.0.0.13（路由器P6），傳出標籤為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
從先前的輸出可以清楚地看到，流量可以在兩個路徑選項中進行負載均衡，但是有幾種方法可以幫助確定哪一條是首選路徑。一種方式是使用show cef exact-route <source IP> <destination IP>命令，增加來自源PE的Loopback0和來自目標PE的Loopback0。如下一個輸出所示，首選路徑是透過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}另一個選項是首先驗證LIB（標籤資訊庫）並透過使用show mpls ldp bindings <prefix/mask>命令獲取目標Loopback0（屬於出口PE的10.10.10.1）的LDP繫結，從該輸出中找到本地繫結標籤後，使用命令show mpls forwarding exact-route label <label> ipv4 <source IP> <destination IP> detail 中的標籤值查詢首選路徑：
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)接下來，務必檢查資料平面中的下一跳路由器，在本例中，要檢驗的路由器是P5（介面為10.0.0.16）。首先要瞭解的是MPLS轉發表，其中字首10.10.10.1的本地標籤必須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#從先前的輸出中可以看到，字首10.10.10.1/32的LFIB條目顯示「Pop」作為傳出標籤，這意味著此路由器是倒數第二跳躍點(PHP)。它還顯示流量必須根據LFIB資訊透過Gi0/0/0/1傳送，這也可以透過檢視CEF進行驗證。下一個CEF exact-route輸出顯示隱式Null標籤作為強加的標籤，這同樣是由於在Gi0/0/0/1連線的下一跳是標籤交換機路徑中的最後一個路由器，也是面向目標站點(CE-WEST)的PE。這也是為什麼路由器P5會刪除資料包而不對資料包施加其他標籤的原因，由於此過程，出口路由器PE1將接收不帶LDP標籤的資料包：
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} <<<<<檢驗標籤交換機路徑的最後一點是PE1。在檢視MPLS轉發表時，可以注意到LFIB中沒有字首10.10.10.1/32的條目：
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正如您已經瞭解的那樣，此行為的原因是字首(10.10.10.1/32)屬於PE1，並且路由器也為此連線的字首分配了一個隱式null標籤。這可以透過show mpls ldp bindings命令進行驗證：
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由於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>有助於辨識和確認透過MP-BGP正確瞭解目標字首172.16.1.0/24。這些命令的輸出顯示了導出後的字首：
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類似地，檢視VRF中的BGP VPNv4字首，即CE-WEST接收的字首，使用命令show bgp vpnv4 unicast vrf <name> <prefix>，輸出顯示一直傳輸到入口PE4的MP-BGP標籤16以及配置的RT導出65000：1：
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上要檢查的最後一個資訊是到目標IP的VRF級別的RIB和CEF條目，與在PE4上看到的條目相比，RIB上沒有字首172.16.1.0/24的標籤，原因是這是來自CE的路由，透過eBGP獲知並在將此字首導出到VPNv4之前插入VRF路由表中。這可以透過使用命令show ip route vrf <name> <prefix>和show ip cef vrf <name> <prefix>進行驗證，如下所示：
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此時，已確認流量CE (CE-EAST)的源已正確獲知目標字首172.16.1.0/24，該字首已透過MP-BGP正確傳播，並且已跨標籤交換機路徑獲知來自PE和Ps環回的標籤。但是，源/目標之間的可達性仍然不成功，並且還有最後一台路由器需要檢驗CE-WEST。要在此路由器中檢查的第一件事是路由表，請記住，源IP字首192.168.1.0/24應出現在其中：
CE-WEST#show ip route 192.168.1.10
% Network not in table CE-WEST#「Network not in table」顯然是問題，BGP表也可以驗證，但在查詢字首後它也不存在：
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#下一步，您可以驗證此提供商邊緣路由器(PE1)是否正在向eBGP鄰居CE-WEST通告字首，這可以透過使用命令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根據上一步驟，可以確認PE1路由器已正確將字首通告給CE-WEST，因此現在應該檢視CE端的BGP鄰居：
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 先前的輸出顯示有應用於名為「FILTER」的傳入通告的路由對映，在檢視路由對映配置後，它顯示了一個指向192.168.0.0/16的permit語句的字首清單的匹配子句，但是這是不正確的，因為prefix-list僅允許該特定字首，而不是可以包含在此範圍中的所有字首：
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對字首清單配置稍作更改後，到達192.168.1.10的路由現在已安裝在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驗證
現在，源和目標之間的可接通性是成功的，並且可以確認traceroute是否透過與MPLS網路相同的標籤交換路徑：
轉發路徑
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驗證命令
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>Cisco IOS XR驗證命令
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]相關資訊
修訂記錄
| 修訂 | 發佈日期 | 意見 |
|---|---|---|
1.0 |
21-Sep-2023 |
初始版本 |
意見