CISCO MPLS *** 标签转发表项
注，在该案例研究中，我们全程关注私网路由4.4.4.4/32。在公网中，需要关注公网路由2.2.2.2/32 1、Ingress-PE1)、VRP路由表：show ip route vrf <vrf>
Routing Table: ***1
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
4.0.0.0/32 is subnetted, 1 subnets
B 4.4.4.4 via 2.2.2.2, 00:28:54
5.0.0.0/32 is subnetted, 1 subnets
B 5.5.5.5 via 172.16.35.5, 00:29:38
172.17.0.0/24 is subnetted, 1 subnets
B 172.17.24.0 via 2.2.2.2, 00:30:55
172.16.0.0/24 is subnetted, 2 subnets
C 172.16.35.0 is directly connected, FastEthernet1/0.1
B 172.16.24.0 via 2.2.2.2, 00:30:55
2)、私网标签：show ip bgp ***v4 vrf <vrf> labels
C3600-R3#show ip bgp ***v4 vrf ***1 labels
Network Next Hop In label/Out label
Route Distinguisher: 65000:300 (***1)
4.4.4.4/32 2.2.2.2 nolabel/22
5.5.5.5/32 172.16.35.5 21/nolabel
172.16.24.0/24 2.2.2.2 nolabel/20
172.16.35.0/24 172.16.35.5 20/nolabel
0.0.0.0 20/aggregate(***1)
172.17.24.0/24 2.2.2.2 nolabel/21
只显示私网标签，为了了解转发过程的完整性，可以根据下一跳进一步查找公网标签
3)、公网标签：show mpls forwarding-table
C3600-R3#show mpls forwarding-table
LocalOutgoing Prefix Bytes tagOutgoing Next Hop
tag tag or VC or Tunnel> 17 Pop tag 1.1.1.1/32 0 Fa0/0 172.16.13.1
18 16 2.2.2.2/32 0 Fa0/0 172.16.13.1
19 Pop tag 172.16.12.0/24 0 Fa0/0 172.16.13.1
20 Aggregate 172.16.35.0/24 1164
21 Untagged 5.5.5.5/32 0 Fa1/0.1 172.16.35.5
主要关注到2.2.2.2/32的标签，结合2)、3)命令的输出，可以看出到私网路由4.4.4.4/32的公网标签为16，私网标签为22。即，标签栈为{16，22}，到该私网目的地址的数据包会打上两层标签{16,22}
4)、私网 cef：show ip cef vrf <vrf> <dest ip>
该命令的好处就是，可以看到完整的标签栈
C3600-R3#show ip cef vrf ***1 4.4.4.4
4.4.4.4/32, version 13, epoch 0, cached adjacency 172.16.13.1
0 packets, 0 bytes
tag information set
local tag: ***-route-head
fast tag rewrite with Fa0/0, 172.16.13.1, tags imposed: {16 22}
via 2.2.2.2, 0 dependencies, recursive
next hop 172.16.13.1, FastEthernet0/0 via 2.2.2.2/32
valid cached adjacency
tag rewrite with Fa0/0, 172.16.13.1, tags imposed: {16 22}
输出结果和2)、 3)命令得出的结果是一致的，但是使用更方便
2、P
1)、公网标签转发表：show mpls forwarding-table
C3600-R1#show mpls forwarding-table
LocalOutgoing Prefix Bytes tagOutgoing Next Hop
tag tag or VC or Tunnel> 16 Pop tag 2.2.2.2/32 73 Fa0/0 172.16.12.2
18 Pop tag 3.3.3.3/32 11751 Fa1/0 172.16.13.3
关注到2.2.2.2/32的表项，入标签(Local Tag)和1.4)中的公网标签一致。出标签执行Pop操作（倒数第二跳弹出）。
3、Egress-PE
1)、VRF路由表
C3600-R2#show ip route vrf ***1
Routing Table: ***1
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
4.0.0.0/32 is subnetted, 1 subnets
B 4.4.4.4 via 172.16.24.4, 01:17:52
5.0.0.0/32 is subnetted, 1 subnets
B 5.5.5.5 via 3.3.3.3, 01:18:16
172.17.0.0/24 is subnetted, 1 subnets
C 172.17.24.0 is directly connected, FastEthernet1/0.2
172.16.0.0/24 is subnetted, 2 subnets
B 172.16.35.0 via 3.3.3.3, 01:19:31
C 172.16.24.0 is directly connected, FastEthernet1/0.1
2)、私网标签：show ip bgp ***v4 vrf <vrf> labels
C3600-R2#show ip bgp ***v4 vrf ***1 labels
Network Next Hop In label/Out label
Route Distinguisher: 65000:100 (***1)
4.4.4.4/32 172.17.24.4 22/nolabel
172.16.24.4 22/nolabel
5.5.5.5/32 3.3.3.3 nolabel/21
172.16.24.0/24 172.17.24.4 20/nolabel
172.16.24.4 20/nolabel
0.0.0.0 20/aggregate(***1)
172.16.35.0/24 3.3.3.3 nolabel/20
172.17.24.0/24 172.17.24.4 21/nolabel
172.16.24.4 21/nolabel
0.0.0.0 21/aggregate(***1)
到私网路由4.4.4.4/32的入标签为22，和Ingress- PE打的私网标签一致。无出标签，转为IP转发。
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