Forwarding-adjacency
MPLS TE 的一个 feature，可以让 IGP 将 TE LSP 看做一条链路，TE tunnel 首端路由器上的 IGP 将 TE LSP 关联上一个特定的 IGP cost（自己指定）后以链路的形式将其通告出去。这样一来，同一个区域中的任何路由器在执行 SPF 算法的时候都将会包含这条链路。同样 IGP 将只会以一条链路的形式看待 TE tunnel 的整个路径
其配置说明：
必须在一对 LSR 之间配置两条 TE tunnel（每个方向上一条），并且必须在每一条上都启用邻接转发。这样做的原因是虽然只是在隧道的一个方向上配置邻接转发链路就会被通告，但是只有当两个方向上都能够看到这条链路的时候才会在 SPF 算法中包含该邻接关系的链路
r2(config-if)#ip ospf cost 10
r2(config-if)#isis metric 5（运行 ISIS 的修改方式）
r1#show ip route
Codes: L - local, 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, + - replicated route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/11] via 12.1.1.2, 00:00:18, Ethernet0/0.12
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/21] via 12.1.1.2, 00:00:18, Ethernet0/0.12
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/31] via 12.1.1.2, 00:00:18, Ethernet0/0.12
5.0.0.0/32 is subnetted, 1 subnets
O 5.5.5.5 [110/41] via 12.1.1.2, 00:00:18, Ethernet0/0.12
12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 12.1.1.0/24 is directly connected, Ethernet0/0.12
L 12.1.1.1/32 is directly connected, Ethernet0/0.12
--More--
r2(config-if)#tunnel mpls traffic-eng forwarding-adjacency（添加该命令后首端路由器就能感知 tunnel）
r1#show ip route
Codes: L - local, 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, + - replicated route
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/11] via 12.1.1.2, 00:01:37, Ethernet0/0.12
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/21] via 12.1.1.2, 00:01:37, Ethernet0/0.12
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/21] via 12.1.1.2, 00:00:25, Ethernet0/0.12
5.0.0.0/32 is subnetted, 1 subnets
O 5.5.5.5 [110/31] via 12.1.1.2, 00:00:25, Ethernet0/0.12
12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 12.1.1.0/24 is directly connected, Ethernet0/0.12
L 12.1.1.1/32 is directly connected, Ethernet0/0.12
--More--
TE Tunnel 中任何动作只对首端路由器生效，要想让对端感知 tunnel，需要加上参数 Forwarding-adjacency
因为 tunnel 之间是“标签隧道”，所以在上述拓扑中 r2 <--> r4 之间是建立不起 OSPF 邻居关系，即使 tunnel 的链路类型是 point-to-point
r2(config)#interface tunnel 24
r2(config-if)#ip ospf 100 area 0
r4(config)#interface tunnel 42
r4(config-if)#ip ospf 100 area 0
r2#show ip ospf interface tunnel 24
Tunnel24 is up, line protocol is up
Interface is unnumbered. Using address of Loopback0 (2.2.2.2), Area 0
Process ID 100, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 10
Topology-MTID Cost Disabled Shutdown Topology Name
0 10 no no Base
Enabled by interface config, including secondary ip addresses
Transmit Delay is 1 sec, State POINT_TO_POINT
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
No Hellos (Passive interface)
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 4/4, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 0, maximum is 0
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)