(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 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin 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 i
r>i2.2.2.2/32 23.1.1.2 0 100 0 i
*> 3.3.3.3/32 0.0.0.0 0 32768 i
R3#
(2)基本配置如下 R1配置:
interface Loopback1
ip address 1.1.1.1 255.255.255.255
interface FastEthernet0/0
ip address 12.1.1.1 255.255.255.0
duplex auto
speed auto
router 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 234
R2(config-router)#neighbor 23.1.1.3 next-hop-self
R3#sh ip bgp
BGP table version is 6, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin 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 i
r>i2.2.2.2/32 23.1.1.2 0 100 0 i
*> 3.3.3.3/32 0.0.0.0 0 32768 i
R3#
(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