一、实验需求

除R5的5.5.5.0环回外，其他所有的环回均可互相一访问。

二、实验步骤

1.配置ip

2.建立邻居关系

2.1 R1和R2建立直连的EBGP邻居关系

[r1]bgp 1

[r1-bgp]router-id 1.1.1.1

[r1-bgp]peer 12.1.1.2 as-number 2

要建的话双方都要建下面配置R2

[r2]bgp 2
[r2-bgp]router-id 2.2.2.2
[r2-bgp]peer 12.1.1.1 as-number 1

2.2 R2和R3建立IGBP

[r2]bgp 2
[r2-bgp]router-id 2.2.2.2
[r2-bgp]peer 3.3.3.3 as-number 2
[r2-bgp]peer 3.3.3.3 connect-interface LoopBack 0
[r2-bgp]peer 4.4.4.4 as-number 2
[r2-bgp]peer 4.4.4.4 connect-interface LoopBack 0

[r3]bgp 2
[r3-bgp]router-id 3.3.3.3
[r3-bgp]peer 2.2.2.2 as-number 2
[r3-bgp]peer 2.2.2.2 connect-interface LoopBack 0
[r3-bgp]peer 4.4.4.4 as-number 2
[r3-bgp]peer 4.4.4.4 connect-interface LoopBack 0

[r4]bgp 2
[r4-bgp]router-id 4.4.4.4
[r4-bgp]peer 3.3.3.3 as-number 2
[r4-bgp]peer 3.3.3.3 connect-interface LoopBack 0
[r4-bgp]peer 2.2.2.2 as-number 2
[r4-bgp]peer 2.2.2.2 connect-interface LoopBack 0

2.3 R4和R5之间配置EBGP

1.配置静态路由

[r4]undo ip route-static 5.5.5.0 24 45.1.1.2
[r4]ip route-static 5.5.5.5 32 45.1.1.2

[r5]undo ip route-static 4.4.4.0 24 45.1.1.1
[r5]ip route-static 4.4.4.4 32 45.1.1.1

2.建立EBGP邻居关系

[r4]bgp 2
[r4-bgp]peer 5.5.5.5 as-number 3
[r4-bgp]peer 5.5.5.5 connect-interface LoopBack 0
[r5]bgp 3
[r5-bgp]router-id 5.5.5.5
[r5-bgp]peer 4.4.4.4 as-number 2
[r5-bgp]peer 4.4.4.4 connect-interface LoopBack 0

3.更改TTL值

[r4-bgp]peer 4.4.4.4 ebgp-max-hop 2

[r5-bgp]peer 5.5.5.5 ebgp-max-hop 2

3.BGP宣告

AS1：

R1
[r1]bgp 1
[r1-bgp]network 1.1.1.0 24

[r1-bgp]network 12.1.1.0 24

AS2：

R2
[r2]bgp 2
[r2-bgp]network 2.2.2.0 24

[r2-bgp]network 12.1.1.0 24
[r2-bgp]network 23.1.1.0 24

R3
[r3]bgp 2
[r3-bgp]network 3.3.3.0 24

[r3-bgp]network 23.1.1.0 24
[r3-bgp]network 34.1.1.0 24

R4

[r4]bgp 2
[r4-bgp]network 4.4.4.0 24

[r4-bgp]network 34.1.1.0 24
[r4-bgp]network 45.1.1.0 24
[r4-bgp]network 54.1.1.0 24

AS3：

R5

[r5]bgp 3
[r5-bgp]network 5.5.5.0 24

[r5-bgp]network 45.1.1.0 24
[r5-bgp]network 54.1.1.0 24

4.选路问题

4.1 R3学习到R1/R5路由不优

需要将R2与R4将路由条目传递给下一个邻居时，修改下一跳为本地地址

R2

[r2]bgp 2
[r2-bgp]peer 3.3.3.3 next-hop-local
[r2-bgp]peer 4.4.4.4 next-hop-local

R4

[r4]bgp 2
[r4-bgp]peer 2.2.2.2 next-hop-local
[r4-bgp]peer 3.3.3.3 next-hop-local