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Split Horizon 법칙, 해결 3가지 방법

   Jan 11, 2023     5 min read

Split Horizon 법칙



iBGP로 광고받은 네트워크는 iBGP로 광고하지 못한다.
bgp 는 neighbor 구성이 되어도 bgp 3대 조건을 만족하지 않으면 정상적으로 라우팅 정보가 교환되지 않는다.
-> 3대 조건을 만족하면 정상적으로 라우팅 정보가 교환된다.


해결 01. Full Mesh 설정 (모든 라우터와 neighbor 구성)



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기본 구성.

R1)

router bgp 100
bgp router-id 1.1.1.1
neighbor 1.1.12.2 remote-as 100
network 1.1.1.0 mask 255.255.255.0



R2)

router bgp 100
bgp router-id 2.2.2.2
neighbor 1.1.12.1 remote-as 100
neighbor 1.1.23.3 remote-as 100
network 1.1.2.0 mask 255.255.255.0



R3)

router bgp 100
bgp router-id 1.1.3.3
neighbor 1.1.23.2 remote-as 100
neighbor 1.1.34.4 remote-as 100
network 1.1.3.0 mask 255.255.255.0



R4)

router bgp 100
bgp router-id 1.1.4.4
neighbor 1.1.34.3 remote-as 100
network 1.1.4.0 mask 255.255.255.0



Split Horizon 법칙

  • BGP 정상 작동 요건
    bgp는 neighbor 구성이 되어도 bgp 3대 조건을 만족하지 않으면 정상적으로 라우팅 정보가 교환되지 않는다.→ 3대 조건을 만족하면 정상적으로 라우팅 정보가 교환된다.

Ex. Split Horizon

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방법 - BGP AS 100

R1)

router bgp 100
bgp router-id 1.1.1.1
neighbor 1.1.12.2 remote-as 100
network 1.1.1.0 mask 255.255.255.0



R2)

router bgp 100
bgp router-id 1.1.2.2
neighbor 1.1.12.1 remote-as 100
neighbor 1.1.23.3 remote-as 100
network 1.1.2.0 mask 255.255.255.0



R3)

router bgp 100
bgp router-id 1.1.3.3
neighbor 1.1.23.2 remote-as 100
neighbor 1.1.34.4 remote-as 100
netowrk 1.1.3.0 mask 255.255.255.0



R4)

router bgp 100
bgp router-id 1.1.4.4
neighbor 1.1.34.4 remote-as 100
network 1.1.4.0 mask 255.255.255.0



Split Horizon 법칙

ex. 1.1.1.1을 본다고 가정해보자.

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  • 상대 원칙 : 같은 AS내에서의 문제.

해결하는 방법.

  1. Full Mesh 설정
  2. Route Reflector
  3. Confederation

Full Mesh 설정

  • 모든 라우터 간 neighbor를 다 맺어 주는 것.

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잘 모르겠다.ㅋ

Route Reflector

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Confederation

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방법 - no router bgp 100

R1)

router bgp 10
bgp confederation identifier 100
bgp confederation peers 20
neighbor 1.1.12.2 remote-as 20
network 1.1.1.0 mask 255.255.255.0



R2)

router bgp 20
bgp confederation identifier 100
bgp confederation peers 10 30
neighbor 1.1.12.1 remote-as 10
neighbor 1.1.23.3 remote-as 30
network 1.1.2.0 mask 255.255.255.0



R3)

router bgp 30
bgp confederation identifier 100
bgp confederation peers 20 40
neighbor 1.1.23.2 remote-as 20
neighbor 1.1.34.4 remote-as 40
network 1.1.3.0 mask 255.255.255.0



R4)

router bgp 40
bgp confederation identifier 100
bgp confederation peers 30
neighbor 1.1.34.3 remote-as 30
network 1.1.4.0 mask 255.255.255.0



  • 결과

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Ex.

Full Mesh

R1)

router bgp 100
bgp router-id 1.1.1.1
neighbor 1.1.12.2 remote-as 100
network 192.168.10.0 mask 255.255.255.0
neighbor 1.1.23.3 remote-as 100



R2)

router bgp 100
bgp router-id 2.2.2.2
neighbor 1.1.12.1 remote-as 100
neighbor 1.1.23.3 remote-as 100
network 192.168.20.0 mask 255.255.255.0



R3)

router bgp 100
bgp router-id 3.3.3.3
neighbor 1.1.23.2 remote-as 100
neighbor 4.4.12.6 remote-as 200
network 192.168.30.0 mask 255.255.255.0
neighbor 1.1.12.1 remote-as 100



Router Reflector

R4)

router bgp 200
bgp router-id 4.4.4.4
neighbor 2.2.12.5 remote-as 200
neighbor 5.5.12.7 remote-as 300
network 192.168.60.0 mask 255.255.255.0



R5)

router bgp 200
bgp router-id 5.5.5.5
neighbor 2.2.12.4 remote-as 200
neighbor 2.2.23.6 remote-as 200
network 192.168.50.0 mask 255.255.255.0
neighbor 2.2.12.4 route-reflector-client
neighbor 2.2.23.6 route-reflector-client



R6)

router bgp 200
bgp router-id 6.6.6.6
neighbor 2.2.23.5 remote-as 200
neighbor 4.4.12.3 remote-as 100
network 192.168.40.0 mask 255.255.255.0



Confederation

R7)

router bgp 10
bgp confederation identifier 300
bgp confederation peers 20
neighbor 3.3.12.8 remote-as 20
neighbor 5.5.12.4 remote-as 200
network 192.168.70.0 mask 255.255.255.0



R8)

router bgp 20
bgp confederation identifier 300
bgp confederation peers 10 30
neighbor 3.3.12.7 remote-as 10
neighbor 3.3.34.9 remote-as 30
network 192.168.80.0 mask 255.255.255.0



R9)

router bgp 30
bgp confederation identifier 300
bgp confederation peers 20
neighbor 3.3.34.8 remote-as 20
network 192.168.90.0 mask 255.255.255.0



  • 결과

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