【正文】 network R1sh ip bgp BGP table version is 2, local router ID is Status codes: s suppressed, d damped, h history, * valid, best, i internal, r RIBfailure, S StaleOrigin codes: i IGP, e EGP, ? inplete Network Next Hop Metric LocPrf Weight Path* 0 32768 iR2sh ip bgp BGP table version is 10, local router ID is Status codes: s suppressed, d damped, h history, * valid, best, i internal, r RIBfailure, S StaleOrigin codes: i IGP, e EGP, ? inplete Network Next Hop Metric LocPrf Weight Path* 100 0 iR3sh ip bgp BGP table version is 7, local router ID is Status codes: s suppressed, d damped, h history, * valid, best, i internal, r RIBfailure, S StaleOrigin codes: i IGP, e EGP, ? inplete Network Next Hop Metric LocPrf Weight Path* 0 0 1R3sh ip routeCodes: C connected, S static, R RIP, M mobile, B BGP D EIGRP, EX EIGRP external, O OSPF, IA OSPF inter area N1 OSPF NSSA external type 1, N2 OSPF NSSA external type 2 E1 OSPF external type 1, E2 OSPF external type 2 i ISIS, su ISIS summary, L1 ISIS level1, L2 ISIS level2 ia ISIS inter area, * candidate default, U peruser static route o ODR, P periodic downloaded static routeGateway of last resort is to network , 2 subnetsC is directly connected, Serial1/0S is directly connected, Serial1/0B* [20/0] via , 00:02:117:理解IBGP的防環(huán)機制及理解同步原則從IBGP學習路由時必須考慮的下一條可達IGp路由表同步(同步原則)R1router bgp 2 no synchronization bgp logneighborchanges network mask neighbor remoteas 1 no autosummaryR2!router bgp 1 no synchronization bgp logneighborchanges network mask neighbor remoteas 1 neighbor remoteas 2 no autosummary!R3!router bgp 1 no synchronization bgp logneighborchanges neighbor remoteas 1 no autosummary! R2 BGP轉(zhuǎn)發(fā)表和路由表里的情況R1sh ip bgp BGP table version is 3, local router ID is Status codes: s suppressed, d damped, h history, * valid, best, i internal, r RIBfailure, S StaleOrigin codes: i IGP, e EGP, ? inplete Network Next Hop Metric LocPrf Weight Path* * R1sh ip routeCodes: C connected, S static, R RIP, M mobile, B BGP D EIGRP, EX EIGRP external, O OSPF, IA OSPF inter area N1 OSPF NSSA external type 1, N2 OSPF NSSA external type 2 E1 OSPF external type 1, E2 OSPF external type 2 i ISIS, su ISIS summary, L1 ISIS level1, L2 ISIS level2 ia ISIS inter area, * candidate default, U peruser static route o ODR, P periodic downloaded static routeGateway of last resort is not set , 1 subnetsC is directly connected, Loopback0 , 1 subnetsB [20/0] via , 00:04:09 , 2 subnetsC is directly connected, FastEthernet0/0C is directly connected, Serial1/1r2sh ip bgp BGP table version is 2, local router ID is Status codes: s suppressed, d damped, h history, * valid, best, i internal, r RIBfailure, S StaleOrigin codes: i IGP, e EGP, ? inplete Network Next Hop Metric LocPrf Weight Path** r2sh ip bgp BGP routing table entry for , version 0Paths: (1 available, no best path) Not advertised to any peer 2 (inaccessible) from () Origin IGP, metric 0, localpref 100, valid, internalr2sh ip routeCodes: C connected, S static, R RIP, M mobile, B BGP D EIGRP, EX EIGRP external, O OSPF, IA OSPF inter area N1 OSPF NSSA external type 1, N2 OSPF NSSA external type 2 E1 OSPF external type 1, E2 OSPF external type 2 i ISIS, su ISIS summary, L1 ISIS level1, L2 ISIS level2 ia ISIS inter area, * candidate default, U peruser static route o ODR, P periodic downloaded static routeGateway of last resort is not set , 1 subnetsB [200/0] via , 00:10:22 , 1 subnetsC is directly connected, Serial1/0這里R2學不到R3的路由第一個原因是下一跳不可達,為了使得R2學到R3的路由必須使得R2把R1當作到達該路由的下一跳,所以要加上如下配置.R1(configrouter)nei nexthopself配置完畢后再觀察R3路由表r2sh ip bgp BGP table version is 3, local router ID is Status codes: s suppressed, d damped, h history, * valid, best, i internal, r RIBfailure, S StaleOrigin codes: i IGP, e EGP, ? inplete Network Next Hop Metric LocPrf Weight Path**r2sh ip routeCodes: C connected, S static, R RIP, M mobile, B BGP D EIGRP, EX EIGRP external, O OSPF, IA OSPF inter area N1 OSPF NSSA external type 1, N2 OSPF NSSA external type 2 E1 OSPF external type 1, E2 OSPF external type 2 i ISIS, su ISIS summary, L1 ISIS level1, L2 ISIS level2 ia ISIS inter area, * candidate default, U peruser static route o ODR, P periodic downloaded static routeGateway of last resort is not set , 1 subnetsB [200/0] via , 00:14:07 , 1 subnetsB [200/0] via , 00:00:34 , 1 subnetsC is directly connected, Serial1/0我們發(fā)現(xiàn)在R2只所以不學習IBGP對等體公告的EBGP路由是因為R2覺得下一跳不可達,這個還不是同步原則,我們把BGP的同步規(guī)則打開.Synchronization 打開R1 R2 的同步規(guī)則觀察R1 R2 BGP轉(zhuǎn)發(fā)表和路由表R1sh ip bgp BGP table version is 3, local router ID is Status codes: s suppressed, d damped, h history, * valid, best, i internal, r RIBfailure, S StaleOrigin codes: i IGP, e EGP, ? inplete Network Next Hop Metric LocPrf Weight Path*