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interface GigabitEthernet0
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interface GigabitEthernet1
 ip address 172.16.12.254 255.255.255.0

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router bgp 1001
 network 10.1.1.0 mask 255.255.255.0
 neighbor 172.16.12.253 remote-as 1002

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 ip address 172.16.12.253 255.255.255.0

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router bgp 1002
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RT1#sh ip route
C        10.1.1.0/24 is directly connected, GigabitEthernet0
B        10.1.2.0/24 [20/0] via 172.16.12.253, 00:52:50
C        172.16.12.0/24 is directly connected, GigabitEthernet1

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RT1#sh ip bgp neighbors
BGP neighbor is 172.16.12.253,  remote AS 1002, external link
  BGP version 4, remote router ID 172.16.23.254
  BGP state = Established, up for 01:29:06¡¡
 
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RT1#sh ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
*> 10.1.1.0/24      0.0.0.0                  0         32768 i
*> 10.1.2.0/24      172.16.12.253            0             0 1002 i

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RT4#sh ip route
B        10.1.1.0/24 [20/0] via 172.16.14.254, 00:08:40
B        10.1.2.0/24 [20/0] via 172.16.14.254, 00:04:16
B        10.1.3.0/24 [20/0] via 172.16.34.254, 00:07:23

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RT4#sh ip bgp

   Network          Next Hop            Metric LocPrf Weight Path
*  10.1.1.0/24      172.16.34.254                          0 1003 1002 1001 i
*>                  172.16.14.254            0             0 1001 i
*  10.1.2.0/24      172.16.34.254                          0 1003 1002 i
*>                  172.16.14.254                          0 1001 1002 i
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