拓扑：
配置：
R2：
router bgp 100
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 4.4.4.4 remote-as 100
neighbor 4.4.4.4 update-source Loopback0
!
address-family vpnv4
neighbor 4.4.4.4 activate
neighbor 4.4.4.4 send-community extended
exit-address-family
!
address-family ipv4 vrf a
redistribute rip
no synchronization
exit-address-family
--------------------------------------------------
R4：
router bgp 100
no bgp default ipv4-unicast
no bgp default route-target filter
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 100
neighbor 2.2.2.2 update-source Loopback0
neighbor 192.168.45.5 remote-as 200
!
address-family vpnv4
neighbor 2.2.2.2 activate
neighbor 2.2.2.2 send-community extended
neighbor 2.2.2.2 next-hop-self
neighbor 192.168.45.5 activate
neighbor 192.168.45.5 send-community extended
exit-address-family
R5：
router bgp 200
no bgp default ipv4-unicast
no bgp default route-target filter
bgp log-neighbor-changes
neighbor 7.7.7.7 remote-as 200
neighbor 7.7.7.7 update-source Loopback0
neighbor 192.168.45.4 remote-as 100
!
address-family vpnv4
neighbor 7.7.7.7 activate
neighbor 7.7.7.7 send-community extended
neighbor 7.7.7.7 next-hop-self
neighbor 192.168.45.4 activate
neighbor 192.168.45.4 send-community extended
exit-address-family
R7：
router bgp 200
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 5.5.5.5 remote-as 200
neighbor 5.5.5.5 update-source Loopback0
!
address-family vpnv4
neighbor 5.5.5.5 activate
neighbor 5.5.5.5 send-community extended
exit-address-family
!
address-family ipv4 vrf b
redistribute rip
no synchronization
exit-address-family
分析：
从上图可看出，系统自动产生一条指向EBGP 对端的32位主机路由。
LDP为自动产生的32主机路由分配了一个标签。
从上图可以看出，从MPLS 原理来说192.168.45.5/32 在没有收到remote binding标签应该是untagging，但是这里是POP TAG ，这样做的目的是使倒数第二跳改变为R4，是LDP 标签LSP贯通整个MPBGP路径。
验证：
