Border Gateway Protocol ( BGP Backdoor )

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Monday, December 19, 2016

After we learned , External Border Gateway Protocol (EBGP Peering Physical Interface) On Mikrotik We will learn about BGP Backdoor. BGP Backdoor is a technique for manipulating the selection between best path routing protocol EBGP with IGP routing protocols such as OSPF, EIGRP, etc.

Border Gateway Protocol ( BGP Backdoor )

By default, the value of AD EBGP is 20, EBGP certainly would be an advantage compared with IGP protocols such as OSPF, EIGRP, etc.. With BGP Backdoor, we can manipulate so IGP routing protocol takes precedence over EBGP

We will configure BGP Peering between R1 to R3 and R2 to R3. While the link between R1 and R2, we will only configure OSPF

R1(config)#int e0/0

R1(config-if)#no sh R1(config-if)#ip add 12.12.12.1 255.255.255.0
R1(config-if)#int e0/1 R1(config-if)#no sh
R1(config-if)#ip add 13.13.13.1 255.255.255.0
R1(config-if)#int l0 R1(config-if)#ip add 1.1.1.1 255.255.255.255
R1(config-if)#router bgp 1
R1(config-router)#nei 13.13.13.3 remote-as 3
R1(config-router)#net 1.1.1.1 mask 255.255.255.255
R1(config-router)#router ospf 1
R1(config-router)#net 12.12.12.0 0.0.0.255 are 0
R1(config-router)#net 1.1.1.1 0.0.0.0 are 0

R2(config)#int e0/0
R2(config-if)#no sh
R2(config-if)#ip add 12.12.12.2 255.255.255.0
R2(config-if)#int e0/1 R2(config-if)#no sh
R2(config-if)#ip add 23.23.23.2 255.255.255.0
R2(config-if)#router bgp 2
R2(config-router)#nei 23.23.23.3 remote-as 3
R2(config-router)#router ospf 1
R2(config-router)#net 12.12.12.0 0.0.0.255 are 0

R3(config)#int e0/0
R3(config-if)#no sh
R3(config-if)#ip add 13.13.13.3 255.255.255.0
R3(config-if)#int e0/1 R3(config-if)#no sh
R3(config-if)#ip add 23.23.23.3 255.255.255.0
R3(config-if)#router bgp 3
R3(config-router)#nei 13.13.13.1 remote-as 1
R3(config-router)#nei 23.23.23.2 rempte-as 2

Now we check the routing table on R2

R2(config-router)#do sh ip ro
1.0.0.0/32 is subnetted, 1 subnets
B 1.1.1.1 [20/0] via 23.23.23.3, 00:06:15
12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 12.12.12.0/24 is directly connected, Ethernet0/0
23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 23.23.23.0/24 is directly connected, Ethernet0/1

[Note]: R2 prefer to use EBGP routing protocol to heading 1.1.1.1 than OSPF. And if using BGP, R2 R3 must pass first. Whereas if you use OSPF, should R2 can go straight to R1. Why R2 can choose BGP than OSPF ?? because the value of AD BGP is 20 while the value of OSPF is 110 AD.
In order R2 prefer use OSPF routing protocol, we can configure BGP Backdoor

R2(config)#router bgp 2

R2(config-router)#net 1.1.1.1 mask 255.255.255.255 backdoor

Now we check the routing table on R2

R2(config-router)#do sh ip ro
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/11] via 12.12.12.1, 00:00:06, Ethernet0/0
12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C
12.12.12.0/24 is directly connected, Ethernet0/0
23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks C
23.23.23.0/24 is directly connected, Ethernet0/1

Note that at this time has chosen R2 using OSPF routing protocol BGP compared to heading 1.1.1.1

Labels: JARINGAN KOMPUTER, KOMPUTER, MIKROTIK

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