PE-ASBR对等体之间建立单跳的MP-EBGP邻接体，传递×××-IPV4路由，不运行IGP和LDP。
PE-ASBR对等体之间传递私网路由时，因为EBGP邻居关系，需要改变路由的下一跳，所以需要交换内层标签。
接收端PE-ASBR，可以使用next-hop-local命令，强制修改路由的下一跳，同时再次交换内层标签，通告给MP-IBGP邻居。如果没有配置next-hop-local命令，需要把direct路由重分布（import-route）到IGP中。
PE-ASBR路由器上需要保存所有域间的私网路由。对于ASBR路由器来说，压力较大。
和VRF-VRF方式相比，具有更好的扩展性。
实验拓扑图：
说明：IGP运行OSPF，R2和R3之间运行MBGP，R5和R6上的lo0口作为测试接口
路由器配置：
R1：
hostname R1
!
!
ip vrf r5
rd 1:1
route-target export 1:1
route-target import 1:1
!
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
!
interface FastEthernet0/0
ip address 12.1.1.1 255.255.255.0
duplex auto
speed auto
mpls ip
!
!
interface FastEthernet0/1
ip vrf forwarding r5
ip address 15.1.1.1 255.255.255.0
duplex auto
speed auto
!
!
router ospf 2 vrf r5
log-adjacency-changes
redistribute bgp 12 subnets
network 15.1.1.1 0.0.0.0 area 0
!
router ospf 1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 12.1.1.1 0.0.0.0 area 0
!
router bgp 12
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 12
neighbor 2.2.2.2 update-source Loopback0
!
address-family ipv4
no synchronization
no auto-summary
exit-address-family
!
address-family ***v4
neighbor 2.2.2.2 activate
neighbor 2.2.2.2 send-community extended
exit-address-family
!
address-family ipv4 vrf r5
no synchronization
redistribute ospf 2 vrf r5 match internal external 1 external 2
exit-address-family
!
ip forward-protocol nd
no ip http server
no ip http secure-server
!
!
R2配置：
hostname R2
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
!
interface FastEthernet0/0
ip address 12.1.1.2 255.255.255.0
duplex auto
speed auto
mpls ip
!
!
interface FastEthernet0/1
ip address 23.1.1.2 255.255.255.0
duplex auto
speed auto
mpls bgp forwarding
!
!
router ospf 1
log-adjacency-changes
passive-interface FastEthernet0/1
network 2.2.2.2 0.0.0.0 area 0
network 12.1.1.2 0.0.0.0 area 0
network 23.1.1.2 0.0.0.0 area 0
!
router bgp 12
no bgp default ipv4-unicast
no bgp default route-target filter
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 12
neighbor 1.1.1.1 update-source Loopback0
neighbor 23.1.1.3 remote-as 34
!
address-family ipv4
no synchronization
no auto-summary
exit-address-family
!
address-family ***v4
neighbor 1.1.1.1 activate
neighbor 1.1.1.1 send-community extended
neighbor 1.1.1.1 next-hop-self
neighbor 23.1.1.3 activate
neighbor 23.1.1.3 send-community extended
exit-address-family
!
R3配置：
hostname R3
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
!
interface FastEthernet0/0
ip address 34.1.1.3 255.255.255.0
duplex auto
speed auto
mpls ip
!
!
interface FastEthernet0/1
ip address 23.1.1.3 255.255.255.0
duplex auto
speed auto
mpls bgp forwarding
!
!
router ospf 1
log-adjacency-changes
passive-interface FastEthernet0/1
network 3.3.3.3 0.0.0.0 area 0
network 23.1.1.3 0.0.0.0 area 0
network 34.1.1.3 0.0.0.0 area 0
!
router bgp 34
no bgp default ipv4-unicast
no bgp default route-target filter
bgp log-neighbor-changes
neighbor 4.4.4.4 remote-as 34
neighbor 4.4.4.4 update-source Loopback0
neighbor 23.1.1.2 remote-as 12
!
address-family ipv4
no synchronization
no auto-summary
exit-address-family
!
address-family ***v4
neighbor 4.4.4.4 activate
neighbor 4.4.4.4 send-community extended
neighbor 4.4.4.4 next-hop-self
neighbor 23.1.1.2 activate
neighbor 23.1.1.2 send-community extended
exit-address-family
!
R4配置：
hostname R4
!
!
ip vrf r6
rd 2:2
route-target export 1:1
route-target import 1:1
!
!
interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
!
interface FastEthernet0/0
ip address 34.1.1.4 255.255.255.0
duplex auto
speed auto
mpls ip
!
!
interface FastEthernet0/1
ip vrf forwarding r6
ip address 46.1.1.4 255.255.255.0
duplex auto
speed auto
!
!
router ospf 2 vrf r6
log-adjacency-changes
redistribute bgp 34 subnets
network 46.1.1.4 0.0.0.0 area 0
!
router ospf 1
log-adjacency-changes
network 4.4.4.4 0.0.0.0 area 0
network 34.1.1.4 0.0.0.0 area 0
!
router bgp 34
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 3.3.3.3 remote-as 34
neighbor 3.3.3.3 update-source Loopback0
!
address-family ipv4
no synchronization
no auto-summary
exit-address-family
!
address-family ***v4
neighbor 3.3.3.3 activate
neighbor 3.3.3.3 send-community extended
exit-address-family
!
address-family ipv4 vrf r6
no synchronization
redistribute ospf 2 vrf r6 match internal external 1 external 2
exit-address-family
!
R5配置：
hostname R5
!
interface Loopback0
ip address 5.5.5.5 255.255.255.255
!
!
interface FastEthernet0/1
ip address 15.1.1.5 255.255.255.0
duplex auto
speed auto
!
!
router ospf 1
log-adjacency-changes
network 5.5.5.5 0.0.0.0 area 0
network 15.1.1.5 0.0.0.0 area 0
!
R6配置：
hostname R6
!
interface Loopback0
ip address 6.6.6.6 255.255.255.255
!
!
interface FastEthernet0/1
ip address 46.1.1.6 255.255.255.0
duplex auto
speed auto
!
!
router ospf 1
log-adjacency-changes
network 6.6.6.6 0.0.0.0 area 0
network 46.1.1.6 0.0.0.0 area 0
!
测试：
R6#ping 5.5.5.5 source 6.6.6.6
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 5.5.5.5, timeout is 2 seconds:
Packet sent with a source address of 6.6.6.6
!!!!.
Success rate is 80 percent (4/5), round-trip min/avg/max = 84/110/128 ms
R6#traceroute 5.5.5.5 source 6.6.6.6
Type escape sequence to abort.
Tracing the route to 5.5.5.5
1 46.1.1.4 36 msec 52 msec 52 msec
2 34.1.1.3 [MPLS: Label 20 Exp 0] 100 msec 92 msec 92 msec
3 23.1.1.2 [MPLS: Label 18 Exp 0] 148 msec 116 msec 76 msec
4 15.1.1.1 [MPLS: Label 18 Exp 0] 96 msec 136 msec 88 msec
5 *
15.1.1.5 108 msec 96 msec