LAB: BGP Backdoor

- Shutdown the BGP peering link between AS 100 and AS 300
- Create a new Loopback1 interface in SW1 with the IP address 150.1.77.77/24 and advertise it into BGP.
- Configure R1 and R4 so that they prefer reaching the new subnet via EIGRP as opposed to eBGP.

configuration:

SW1:

interface Loopback1
ip address 150.1.77.77 255.255.255.0

!

router eigrp 1
 network 150.1.0.0
 network 155.1.0.0
!
router bgp 300
 no synchronization
 bgp log-neighbor-changes
 network 150.1.77.0 mask 255.255.255.0
 neighbor 155.1.37.3 remote-as 200
 neighbor 155.1.67.6 remote-as 100
 neighbor 155.1.67.6 shutdown
 neighbor 155.1.79.9 remote-as 300
 no auto-summary

R1 & R4:

router bgp 100
network 150.1.77.0 mask 255.255.255.0 backdoor

verification:

before applying the backdoor command.

Rack1R1#show ip route 150.1.77.0
Routing entry for 150.1.77.0/24
  Known via "bgp 100", distance 20, metric 0
  Tag 200, type external
  Last update from 155.1.13.3 00:03:22 ago
  Routing Descriptor Blocks:
  * 155.1.13.3, from 155.1.13.3, 00:03:22 ago
      Route metric is 0, traffic share count is 1
      AS Hops 2
      Route tag 200

after applying the backdoor command:

Rack1R1#show ip route 150.1.77.0
*Mar  1 01:00:32.839: %SYS-5-CONFIG_I: Configured from console by console
Rack1R1#show ip route 150.1.77.0
Routing entry for 150.1.77.0/24
  Known via "eigrp 1", distance 90, metric 158720, type internal
  Redistributing via eigrp 1
  Last update from 155.1.146.6 on FastEthernet0/0, 00:00:19 ago
  Routing Descriptor Blocks:
  * 155.1.146.6, from 155.1.146.6, 00:00:19 ago, via FastEthernet0/0
      Route metric is 158720, traffic share count is 1
      Total delay is 5200 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2

Rack1R1#show ip bgp 150.1.77.0 
BGP routing table entry for 150.1.77.0/24, version 65
Paths: (2 available, best #2, table Default-IP-Routing-Table, RIB-failure(17))
Multipath: iBGP
  Advertised to update-groups:
     1        
  200 300, (Received from a RR-client)
    155.1.45.5 (metric 2172416) from 155.1.146.4 (150.1.4.4)
      Origin IGP, metric 0, localpref 100, valid, internal
  200 300
    155.1.13.3 from 155.1.13.3 (150.1.3.3)
      Origin IGP, localpref 100, valid, external, best
Rack1R1#