BGP-20190320-next-hop-self

（1）本实验主要论述了 BGP协议中、next-hop-self 的根本原因、如上图 R3学习到R1 的1.1.1.1/32路由的下一跳是R1 的接口f0/0 的IP地址 12.1.1.1、为什么？R

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（1）本实验主要论述了 BGP协议中、next-hop-self 的根本原因、如上图 R3学习到R1 的1.1.1.1/32路由的下一跳是R1 的接口f0/0 的IP地址 12.1.1.1、为什么？

R3#sh ip bgp BGP table version is 4, local router ID is 3.3.3.3Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,              r RIB-failure, S StaleOrigin codes: i - IGP, e - EGP, ? - incomplete   Network          Next Hop            Metric LocPrf Weight Path* i1.1.1.1/32       12.1.1.1                 0    100      0 1 ir>i2.2.2.2/32       23.1.1.2                 0    100      0 i*> 3.3.3.3/32       0.0.0.0                  0         32768 iR3#

（2）基本配置如下
R1配置：

interface Loopback1 ip address 1.1.1.1 255.255.255.255interface FastEthernet0/0 ip address 12.1.1.1 255.255.255.0 duplex auto speed autorouter bgp 1 no synchronization bgp log-neighbor-changes network 1.1.1.1 mask 255.255.255.255 neighbor 12.1.1.2 remote-as 234 no auto-summary

R2配置：

interface Loopback2 ip address 2.2.2.2 255.255.255.255!interface FastEthernet0/0 ip address 12.1.1.2 255.255.255.0 duplex auto speed auto!interface FastEthernet0/1 ip address 23.1.1.2 255.255.255.0 duplex auto speed auto!router ospf 1 log-adjacency-changes network 2.2.2.2 0.0.0.0 area 0 network 23.1.1.2 0.0.0.0 area 0!router bgp 234 no synchronization bgp log-neighbor-changes network 2.2.2.2 mask 255.255.255.255 neighbor 12.1.1.1 remote-as 1 neighbor 23.1.1.3 remote-as 234 no auto-summary!

R3配置：

interface Loopback3 ip address 3.3.3.3 255.255.255.255!interface FastEthernet0/0 no ip address shutdown duplex auto speed auto!interface FastEthernet0/1 ip address 23.1.1.3 255.255.255.0 duplex auto speed auto!router ospf 1 log-adjacency-changes network 3.3.3.3 0.0.0.0 area 0 network 23.1.1.3 0.0.0.0 area 0!router bgp 234 no synchronization bgp log-neighbor-changes network 3.3.3.3 mask 255.255.255.255 neighbor 23.1.1.2 remote-as 234 no auto-summary!

（3）配置next-hop-self之后效果：

R2(config)#router bgp 234R2(config-router)#neighbor 23.1.1.3 next-hop-self 

R3#sh ip bgp BGP table version is 6, local router ID is 3.3.3.3Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,              r RIB-failure, S StaleOrigin codes: i - IGP, e - EGP, ? - incomplete   Network          Next Hop            Metric LocPrf Weight Path*>i1.1.1.1/32       23.1.1.2                 0    100      0 1 ir>i2.2.2.2/32       23.1.1.2                 0    100      0 i*> 3.3.3.3/32       0.0.0.0                  0         32768 iR3#

（4）原因分析：
记得我在讲解BGP概述时候曾经跟学生讲过、BGP这个EGP协议是工作在AS by AS之间的、BGP着眼的边界是AS、那么从这个角度来看我们应该把一个AS号内的设备逻辑当成是一台
大的路由器、

R1 看成是一台大的路由器1 、R2和R3看成是一台大的路由器2 、2收到1的路由、下一跳默认自然指向1的接口IP地址 12.1.1.1/24

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