ra#sh run
interface Loopback0
ip address 1.1.1.1 255.255.255.0
interface Serial1/0
ip address 10.1.1.1 255.255.255.0
serial restart-delay 0
clock rate 64000
router bgp 10
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.1.1.0 mask 255.255.255.0
neighbor 10.1.1.2 remote-as 10
no auto-summary

rb#sh run
interface Loopback0
ip address 2.2.2.2 255.255.255.0
!
interface Ethernet0/0
ip address 30.1.1.1 255.255.255.0
!
interface Serial1/0
ip address 20.1.1.1 255.255.255.0
serial restart-delay 0
clock rate 64000
!
interface Serial2/0
ip address 10.1.1.2 255.255.255.0
serial restart-delay 0
!
router bgp 10
no synchronization
bgp router-id 2.2.2.2
bgp log-neighbor-changes
network 2.2.2.0 mask 255.255.255.0
neighbor 3.3.3.0 remote-as 20
neighbor 3.3.3.0 update-source Loopback0
neighbor 3.3.3.0 next-hop-self
neighbor 10.1.1.1 remote-as 10
no auto-summary
ip route 3.3.3.3 255.255.255.255 20.1.1.2
ip route 3.3.3.3 255.255.255.255 30.1.1.2
rc#sh run
Building configuration...
     
!
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface Ethernet0/0
ip address 30.1.1.2 255.255.255.0
!
interface Serial1/0
ip address 40.1.1.1 255.255.255.0
serial restart-delay 0
clock rate 64000
!
interface Serial2/0
ip address 20.1.1.2 255.255.255.0
serial restart-delay 0
!
router bgp 20
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
network 3.3.3.0 mask 255.255.255.0
neighbor 2.2.2.2 remote-as 10
neighbor 2.2.2.2 ebgp-multihop 2
neighbor 2.2.2.2 update-source Loopback0
neighbor 2.2.2.2 next-hop-self
neighbor 40.1.1.2 remote-as 20
no auto-summary
!
ip classless
ip route 2.2.2.2 255.255.255.255 20.1.1.1
ip route 2.2.2.2 255.255.255.255 30.1.1.1

rd#sh run
        
!
interface Loopback0
ip address 4.4.4.4 255.255.255.0
interface Serial2/0
ip address 40.1.1.2 255.255.255.0
serial restart-delay 0
!
router bgp 20
no synchronization
bgp router-id 4.4.4.4
bgp log-neighbor-changes
network 4.4.4.0 mask 255.255.255.0
neighbor 40.1.1.1 remote-as 20
no auto-summary
在EBGP上面建立邻居的话，只要在IBGP建立邻居的基础上改一下TTL值就可以了，怎么我在RB上面输入这条命令的时候提示出错，
rb(config)#router bgp 10
rb(config-router)#nei 3.3.3.3 e
rb(config-router)#nei 3.3.3.3 ebgp-multihop 2
% Specify remote-as or peer-group commands first
而我在RC上面配置的时候又一切正常
rc(config)#router bgp 20
rc(config-router)#nei 2.2.2.2 e  
rc(config-router)#nei 2.2.2.2 ebgp-multihop 2
RB和RC的邻居状态只能保持在ACTIVE，clear ip bgp *后又从ldle转换为ACTIVE

neighbor 3.3.3.0 remote-as 20
neighbor 3.3.3.0 update-source Loopback0
neighbor 3.3.3.0 next-hop-self

这是你设置上的问题,应该能连上的,好好去检查一下