【正文】 Origin codes: i IGP, e EGP, ? inplete Network Next Hop Metric LocPrf Weight Path* 0 100 0 1 i 的下一條是R2 ，如下顯示R1sh ip route ospf , 1 subnetsO [110/65] via , 00:06:01, Serial1/1 , 1 subnetsO [110/129] via , 00:06:01, Serial1/1 , 1 subnetsO [110/193] via , 00:06:01, Serial1/1 , 3 subnetsO [110/192] via , 00:06:01, Serial1/1O [110/128] via , 00:06:01, Serial1/1所以又將數(shù)據(jù)包發(fā)向了R2 ，那么這就已經(jīng)產(chǎn)生了環(huán)路，R2 又發(fā)給R1 R1 又發(fā)給R2 如此循環(huán)。所以這里的解決方法就是在R1通過(guò)BGP通告網(wǎng)絡(luò)給R2 時(shí)，因該不改變 下一條，這樣R2 可以直接通過(guò)IGP路由表把去往R4 ，這樣環(huán)路就避免了，也避免了次優(yōu)路徑。R1(configrouter)nei nexthopunchangedR2sh ip bgpBGP 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 2 1 iR2traceroute ipTarget IP address: Source address: Numeric display [n]: Timeout in seconds [3]: Probe count [3]: Minimum Time to Live [1]: Maximum Time to Live [30]: Port Number [33434]: Loose, Strict, Record, Timestamp, Verbose[none]: Type escape sequence to abort.Tracing the route to 1 504 msec 772 msec 72 msec 2 556 msec * 376 msec環(huán)路避免，實(shí)驗(yàn)結(jié)束。9:理解BGP 自動(dòng)匯總BGP的自動(dòng)匯總是關(guān)閉的當(dāng)自動(dòng)匯總開(kāi)啟時(shí),如果你使用NETWORK 語(yǔ)句進(jìn)行網(wǎng)絡(luò)通告時(shí),如果你宣告的是主網(wǎng)地址,那么BGP會(huì)查看本地的路由表查看是否有該主網(wǎng)的子網(wǎng),如果有說(shuō)明是有明細(xì)子網(wǎng)的主網(wǎng)信息,就可以直接將主網(wǎng)宣告出去,. BGP基本的匯總概念R1!interface Loopback0 ip address !interface Loopback1 ip address !interface Loopback2 ip address !router bgp 1 no synchronization bgp logneighborchanges neighbor remoteas 1 no autosummary!!interface Serial1/1 ip address no sh!EndR2!router bgp 1 no synchronization bgp logneighborchanges neighbor remoteas 1 no autosummary!interface Serial1/0 ip address no sh!R1sh ip protocols Routing Protocol is bgp 1 Outgoing update filter list for all interfaces is not set Ining update filter list for all interfaces is not set IGP synchronization is disabled Automatic route summarization is disabled Neighbor(s): Address FiltIn FiltOut DistIn DistOut Weight RouteMap Maximum path: 1 Routing Information Sources: Gateway Distance Last Update Distance: external 20 internal 200 local 200默認(rèn)時(shí)只要你使用了NET命令都必須匹配網(wǎng)絡(luò)掩碼,可以進(jìn)行匯總的宣告及不一定非要匹配路由表?xiàng)l目.NETWORK 我們發(fā)現(xiàn)R1 R2 轉(zhuǎn)發(fā)表都為空R1SHOW IP BGP因?yàn)樵摼W(wǎng)絡(luò)不在路由表內(nèi)如果想宣告你可以做一個(gè)NULL0路由R1(config)ip route null 0R1(config)endR1sh 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 , 4 subnets, 2 masksS , Null0C , Loopback0C , Loopback1C , Loopback2 , 1 subnetsC is directly connected, Serial1/1R1R1R1sh *May 9 16:54:: %SYS5CONFIG_I: Configured from console by consoleR1sh 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 i但如果不加該默認(rèn)路由可以打開(kāi)自動(dòng)匯總，那么只要不匹配路由表他會(huì)以匯總路由方式發(fā)送 重分發(fā)時(shí)的自動(dòng)匯總R3 EnableConf tHost R1No ip do lo Line cons 0Logg syncNo exect!!!interface Loopback0 ip address !interface FastEthernet0/0 ip address duplex half!router rip version 2 network network no autosummary!R1!interface FastEthernet0/0 ip address !interface Serial1/1 ip address !router rip version 2 network no autosummary!router bgp 1 no synchronization bgp logneighborchanges neighbor remoteas 1 no autosummary!EndR2!interface Serial1/0 ip address !router bgp 1 no synchronization bgp logneighborchanges neighbor remoteas 1 no autosummary!EndR1sh 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 subnetsR [120/1] via , 00:00:25, FastEthernet0/0 , 2 subnetsC is directly connected, FastEthernet0/0C is directly connected, Serial1/1作重分發(fā)R1sh ip protocols Routing Protocol is rip Sending updates every 30 seconds, next due in 13 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is not set Ining update filter list for all interfaces is not set Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Keychain FastEthernet0/0 2 2 Serial1/1 2 2 Automatic network summarization is not in effect Maximum path: 4 Routing for