配置思路：
1、所有的EBGP用物理口进行peer连接建立邻居
2、深圳分部内的IBGP用loop 0口建立BGP邻居，底层用ospf打通
3、默认深圳到北京走长沙，经过BGP选路用preferred-value 改变，走上海到北京。

R1:

interface GigabitEthernet0/0/0
 ip address 12.1.1.1 255.255.255.0 
#
interface GigabitEthernet0/0/1
 ip address 13.1.1.1 255.255.255.0 
#
interface GigabitEthernet0/0/2
 ip address 15.1.1.1 255.255.255.0 
 ospf enable 1 area 0.0.0.0
#
interface NULL0
#
interface LoopBack0
 ip address 11.1.1.1 255.255.255.0 
 ospf enable 1 area 0.0.0.0
#
interface LoopBack1
 ip address 192.168.1.1 255.255.255.0 
#
#
bgp 100
 router-id 1.1.1.1
 peer 12.1.1.2 as-number 200 
 peer 13.1.1.2 as-number 300 
 peer 19.1.1.1 as-number 100 
 peer 19.1.1.1 connect-interface LoopBack0
 #
 ipv4-family unicast
  undo synchronization
  peer 12.1.1.2 enable
  peer 13.1.1.2 enable
  peer 13.1.1.2 route-policy RP import
  peer 19.1.1.1 enable
  peer 19.1.1.1 next-hop-local 
#
ospf 1 
 area 0.0.0.0 
#
route-policy RP permit node 10 
 if-match ip-prefix 1 
 apply preferred-value 10
#
ip ip-prefix 1 index 10 permit 192.168.4.0 24

R5:

interface GigabitEthernet0/0/2
 ip address 15.1.1.2 255.255.255.0 
 ospf enable 1 area 0.0.0.0
#
interface NULL0
#
interface LoopBack0
 ip address 19.1.1.1 255.255.255.0 
 ospf enable 1 area 0.0.0.0
#
interface LoopBack1
 ip address 192.168.5.1 255.255.255.0 
#
bgp 100
 peer 11.1.1.1 as-number 100 
 peer 11.1.1.1 connect-interface LoopBack0
 #
 ipv4-family unicast
  undo synchronization
  network 192.168.5.0 
  peer 11.1.1.1 enable
#
ospf 1 
 area 0.0.0.0 

R2:

interface GigabitEthernet0/0/0
 ip address 12.1.1.2 255.255.255.0 
#
interface GigabitEthernet0/0/1
 ip address 24.1.1.1 255.255.255.0 
#
interface GigabitEthernet0/0/2
 ip address 192.168.1.3 255.255.255.0 
#
interface NULL0
#
bgp 200
 router-id 2.2.2.2
 peer 12.1.1.1 as-number 100 
 peer 24.1.1.2 as-number 400 
 #
 ipv4-family unicast
  undo synchronization
  peer 12.1.1.1 enable
  peer 24.1.1.2 enable

R3:

interface GigabitEthernet0/0/1
 ip address 13.1.1.2 255.255.255.0 
#
interface GigabitEthernet0/0/2
 ip address 34.1.1.1 255.255.255.0 
#
interface NULL0
#
bgp 300
 router-id 3.3.3.3
 peer 13.1.1.1 as-number 100 
 peer 34.1.1.2 as-number 400 
 #
 ipv4-family unicast
  undo synchronization
  peer 13.1.1.1 enable
  peer 34.1.1.2 enable

R4:

interface GigabitEthernet0/0/1
 ip address 24.1.1.2 255.255.255.0 
#
interface GigabitEthernet0/0/2
 ip address 34.1.1.2 255.255.255.0 
#
interface NULL0
#
interface LoopBack0
 ip address 192.168.4.1 255.255.255.0 
#
bgp 400
 router-id 4.4.4.4
 peer 24.1.1.1 as-number 200 
 peer 34.1.1.1 as-number 300 
 #
 ipv4-family unicast
  undo synchronization
  network 192.168.4.0 
  peer 24.1.1.1 enable
  peer 34.1.1.1 enable