BGP影响选路的三大属性

BGP选路1.A.当指定对端ROUTER-ID作为neighborip需注意更新源要指定为loop此时需单独做一条静态路由,指向对端回环口需在运行EBGP的路由器上做一个EBGP-MULTIHOP不开启的情况下,默认为1跳。则无法达到对端回环口.邻居无法建立B.当指定对端IP做为neighborip需注意更新源也最好选择是IP接口而非回环口。控制BGP选路有众多参数修改本地优先级（默认100越高越好）,修改weight值（越高越好,cisco私有），修改MED值（类似与IGP中metric值越小越优）R1ConfigtNoipdomain-lookupLinecon0Exec-timeout00LoggsynExitIntloop0Ipadd1.1.1.1255.255.255.0NoshutInts0/0Ipadd12.1.1.1255.255.255.0NoshutInts0/1Ipadd13.1.1.1255.255.255.0NoshutExitRouterbgp1Bgprouter-id1.1.1.1NosynNoauto-summaryNeighbor12.1.1.2remote-as2Neighbor12.1.1.2update-sources0/0Neighbor13.1.1.3remote-as2Neighbor13.1.1.3update-sources0/1Network1.1.1.0mask255.255.255.0Network13.1.1.0mask255.255.255.0Network12.1.1.0mask255.255.255.0Neighbor12.1.1.2soft-reconfigurationinboundNeighbor13.1.1.3soft-reconfigurationinbound（开启记录从邻居1.3接受到的bgp通告路由）R2ConfigtNoipdomain-lookupLinecon0Exec-timeout00LoggsynExitIntloop0Ipadd2.2.2.2255.255.255.0NoshutInts0/0Ipadd12.1.1.2255.255.255.0NoshutInts0/1Ipadd24.1.1.2255.255.255.0NoshutExitRouterbgp2Bgprouter-id2.2.2.2NosynNoauto-summaryNeighbor12.1.1.1remote-as1Neighbor12.1.1.1update-sources0/0Neighbor4.4.4.4remote-as2Neighbor4.4.4.4update-sourceloop0Neighbor4.4.4.4next-hop-selfNetwork2.2.2.0mask255.255.255.0Network24.1.1.0mask255.255.255.0Network12.1.1.0mask255.255.255.0ExitRouterospf110Router-id2.2.2.2Network2.2.2.00.0.0.255a0Network12.1.1.00.0.0.255a0Network24.1.1.00.0.0.255a0ExitR3ConfigtNoipdomain-lookupLinecon0Exec-timeout00LoggsynExitIntloop0Ipadd3.3.3.3255.255.255.0NoshutInts0/1Ipadd13.1.1.3255.255.255.0NoshutIntfa0/0Ipadd34.1.1.3255.255.255.0NoshutExitRouterospf110Router-id3.3.3.3Network3.3.3.00.0.0.255a0Network34.1.1.00.0.0.255a0Network13.1.1.00.0.0.255a0ExitRouterbgp2Bgprouter-id3.3.3.3NosynNoauto-summaryNeighbor13.1.1.1remote-as1Neighbor13.1.1.1update-sources0/1Neighbor4.4.4.4remote-as2Neighbor4.4.4.4update-sourceloop0Neighbor4.4.4.4next-hop-selfNetwork3.3.3.0mask255.255.255.0Network13.1.1.0mask255.255.255.0Network34.1.1.0mask255.255.255.0ExitR4ConfigtNoipdomain-lookupLinecon0Exec-timeout00LoggsynExitIntloop0Ipadd4.4.4.4255.255.255.0NoshutIntfa0/0Ipadd34.1.1.4255.255.255.0NoshutInts0/1Ipadd24.1.1.4255.255.255.0NoshutExitRouterospf110Router-id4.4.4.4Network4.4.4.00.0.0.255a0Network24.1.1.00.0.0.255a0Network34.1.1.00.0.0.255a0ExitRouterbgp2Bgprouter-id4.4.4.4NosynNoauto-summaryNeighborGROUPpeer-groupNeighborGROUPremote-as2NeighborGROUPupdate-sourceloop0NeighborGROUPnext-hop-selfNeighbor2.2.2.2peer-groupGROUPNeighbor3.3.3.3peer-groupGROUPNetwork4.4.4.0mask255.255.255.0Network24.1.1.0mask255.255.255.0Network34.1.1.0mask255.255.255.0Exit输入以上配置后，即可完成BGP基础配置，相应的建立邻居。接下来，查看BGP路由，准备做BGP路由选路。R4上showipbgpMffshouripbgpE.4#shouripbgpBGFtableversionis12SlocalrouterIDis4.4.4.4Statuscodes:ssuppressed^ddampedjhhrsizoryj*validj》best1-internalj匸KIB-failurejSStaleOrigirLcod.es:i-IGP,e-EGP,?-incDepleteMEt矿cir± Ne:k1:Hciu 工:LuLocFrfVfEzLdrl:Fath*il.1.1.0/242.2.2.20LOO01i*>i3.3.3.30LOOa1i*>i2.2.2.0/242.2.2.20100at>i3.3.3.0/243.3.3.30LOOa_j+>4.4.4.0/240.0.0.00327C8ril2.1.1.0/243.3.3.30LOO011r>i2.2.2.20100ar±13.1.1.0/242.2.2.20100a1ir>i3.3.3.30100a*i24.1.1.0/242.2.2.20LOO0*>0.0.0.0032768*i34.1.1.0/243.3.3.30LOOa■*>0.0.0.00327CSR4#R4去往R1回环口的路由会优先从R3经过。一.我们通过BGP修改本地优先级属性，1.1.1.0/24的路由改由从R2上走。R2ConfigtIpprefix-list1permit1.1.1.0/24Route-mapTESTpermit10Matchipaddressprefix-list1Setlocal-preference111（默认为100）ExitRoute-mapTESTpermit20ExitRouterbgp2Neighbor4.4.4.4route-mapTESToutR2上面配置完成后，需要在R4上查看去往1.1.1.0/24的路由。Showipbgp M目tvfork M目xtHup 血土工让 LuuPrf Voight F®:h*>il.1.1.0/24 2.2.2.2 0 111 0 1i*i 3.3.3.3 0 100 0 1i*>i2.2.2.0/242.2.2.201000i*>13.3.3.0/243・3.3・301000i4.4.4.0/240.0.0.0032768i匸112.1.1.0/243.3.3.30100011r>i2.2.2.201000ir113.1.1.0/242.2.2.201000 1ir>i3.3.3.301000i*124.1.1.0/242.2.2.2010Q0i*>0.□.0.□0327G8i*134.1.1.0/243.3.3.301000i*>0.0.0.00327SSiR4#|以上可以发现，输入上述修改本地优先级的配置后，1.1.1.0/24的路由发生了改变，next-hop为R2.二.通过修改weight值，改变路由走向。上述基本配置不变。需要在R4上面做R4ConfigtIpprefix-list1permit1.1.1.0/24Route-mapTESTpermit10Matchipaddressprefix-list1Setweight9（默认为0，越大越优先）ExitRoute-mapTESTpermit20ExitNeighbor2.2.2.2route-mapTESTin（从2.2.2.2这个邻居通告过来的1.1.1.0/24路由进行weight值设定）在R4上showipbgp查看通往1.1.1.0/24的路由走向WetworkflextHopMetricLocfriWeightfatM*>il.1.1.0/242.2.2.20100*i3.3.3.30100*>l2.2.2.0/242.2.2.2"TTTUU"nr*>i3.3.3.0/243.3.3.301000*>4.4.4.0/240.0.0.00327S8■r112.1.1.0/243.3.3.30100011r>x2.2.2.201000r113.1.1.0/242.2.2.20100011r>i3.3.3.301000■*124.1.1.0/242.2.2.201000*>□.0.0.□032758*134.1.1.0/243.3.3.301000*>□.0.0.□0327S8R4#|此刻查看到通往1.1.1.0/24的路由next-hop为2.2.2.2选路成功三.通过修改MED值（metric值越小路径越优）这个需要在R4上做，然后通告给EBGP告诉该条路由的med值R4ConfigtIpprefix-list1permit1.1.1.0/24Route-mapTESTpermit10Matchipaddressprefix-list1Setmetric99ExitRoute-mapTESTpermit20ExitRouterbgp2Neighbor3.3.3.3route-mapTESTinExit配置完成，接下来，看看效果如何。*>il.1.1.0/24*i2.2.2.23.3.3.3(M\oo^1007□林1匕乙z.u/閃Z7乙'乙2/1UUT*>i3.3.3.0/243.3.3.