1、 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID1BGPBGP路由选路原则详解路由选路原则详解V1.0V1.0学习总结，个人见解，如有错误欢迎改正！2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID2学习目标学习目标 掌握BGP十三条选路原则的原理 熟练掌握常见的BGP路由选路原则 2007 Cisco Systems,Inc.All rights reserved.Cisco Confi
2、dentialPresentation_ID3BGP路由选路原则路由选路原则1.Weight1.Weight属性属性2.Local Preference2.Local Preference属性属性3.3.本地路由始发方式本地路由始发方式4.AS-Path4.AS-Path长度长度5.Origin5.Origin属性属性6.MED6.MED属性属性7.EBGP7.EBGP优于优于IBGPIBGP8.8.到达到达Next-hopNext-hop的代价的代价9.9.执行等价负载均衡执行等价负载均衡10.EBGP10.EBGP路由接收的顺序路由接收的顺序11.11.路由的路由的Router-IDRou
3、ter-ID12.Cluster-list12.Cluster-list长度长度13.13.配置的配置的BGP PeerBGP Peer指定地址指定地址 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID4第一条第一条:Weight属性属性 比较原则及配置注意事项:Cisco私有,可通过关联Route-map方式进行配置,该值无法传递给其他BGP Peer,只能在本地使用.携带的Weight值越大,则该路由越优先.本地始发路由的默认值是32768,从其他BGP Peer学习过来的路由的默认值是
4、0虽然Weight属性是Cisco私有的,但是很多厂商也是内置该属性(但无法显示及修改),这样就保证了本地始发的路由是最优先的,因为本地始发路由的”Weight”为32768,从其他BGP Peer学习过来的路由的”Weight”为0.2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID5第一条第一条:Weight属性属性 实验验证R2、R3分别通告10.0.0.0给R1R1将10.0.0.0使用network方式引入BGP10.0.0.0/810.0.0.0/810.0.0.0/8AS 1AS
5、 2R3R1R2IBGPEBGP 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID6第一条第一条:Weight属性属性 实验验证R1的BGP表r1#sh ip bgp BGP table version is 2,local router ID is 9.9.0.1Status codes:s suppressed,d damped,h history,*valid,best,i-internal,r RIB-failure,S StaleOrigin codes:i-IGP,e-EGP,?
6、-incomplete Network Next Hop Metric LocPrf Weight Path*i10.0.0.0 9.9.13.3 0 100 0 i*9.9.12.2 0 0 2 i*0.0.0.0 0 32768 i 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID7第一条第一条:Weight属性属性 实验验证R1对BGP Peer应用不同的Route-map修改所学习路由的Weight值10.0.0.0/810.0.0.0/810.0.0.0/8AS 1AS 2R3R1
7、R2IBGPEBGProuter bgp 1 -R1的路由策略的路由策略neighbor 9.9.12.2 route-map FROM_R2 inroute-map FROM_R2 permit 10 set weight 65535 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID8第一条第一条:Weight属性属性 实验验证R1的BGP表选路结果r1#sh ip bgpBGP table version is 7,local router ID is 9.9.0.1Status cod
8、es: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 Pathr i10.0.0.0 9.9.13.3 0 100 0 ir 9.9.12.2 0 65535 2 ir 0.0.0.0 0 32768 i 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresenta
9、tion_ID9BGP路由选路原则路由选路原则1.Weight1.Weight属性属性2.Local Preference2.Local Preference属性属性3.3.本地路由始发方式本地路由始发方式4.AS-Path4.AS-Path长度长度5.Origin5.Origin属性属性6.MED6.MED属性属性7.EBGP7.EBGP优于优于IBGPIBGP8.8.到达到达Next-hopNext-hop的代价的代价9.9.执行等价负载均衡执行等价负载均衡10.EBGP10.EBGP路由接收的顺序路由接收的顺序11.11.路由的路由的Router-IDRouter-ID12.Cluste
10、r-list12.Cluster-list长度长度13.13.配置的配置的BGP PeerBGP Peer指定地址指定地址 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID10第二条第二条:Local Preference属性属性 比较原则及配置注意事项:值越大,越优先默认情况下,本地始发的路由的LP为100,从EBGP Peer接收的路由的LP为100.Local Preference属性只能在IBGP Peer之间传递,不能在EBGP Peer之间传递,如果在EBGP Peer之间收到的
11、路由的路径属性中携带了Local Preference,则会触发Notifacation报文,造成会话中断 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID11第二条第二条:Local Preference属性属性 比较原则及配置注意事项:Local Preference通过如下三种方法进行设置:通过将IGP路由引入BGP时关联Route-map进行设置针对IBGP Peer应用IN/OUT方向的Route-map,对从Peer接收到的或者通告给Peer的所有或部分路由进行设置针对EBGP
12、Peer应用IN方向的Route-map,对从Peer接收到的所有或部分路由进行设置Local Preference为BGP选路策略中经常使用的一个路径属性 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID12第二条第二条:Local Preference属性属性 实验一:Local Prefenerce无法在EBGP Peer之间传递R1R2AS 1AS 210.0.0.0/8EBGProuter bgp 2 network 10.0.0.0 neighbor 9.9.12.1 remot
13、e-as 1 neighbor 9.9.12.1 route-map TO_R1 out!route-map TO_R1 permit 10 set local-preference 500 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID13第二条第二条:Local Preference属性属性 实验一:Local Prefenerce无法在EBGP Peer之间传递查看本地始发的BGP路由的LP值r2#show ip bgp BGP table version is 2,local ro
14、uter ID is 9.9.0.2Status 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*10.0.0.0 0.0.0.0 0 32768 i空值空值?r2#sh ip b 10.0.0.0BGP routing table entry for 10.0.0.0/8,version 2Paths:(1 avail
15、able,best#1,table Default-IP-Routing-Table)Advertised to non peer-group peers:9.9.12.1 Local 0.0.0.0 from 0.0.0.0(9.9.0.2)Origin IGP,metric 0,localpref 100,weight 32768,valid,sourced,local,best 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID14第二条第二条:Local Preference属性属性
16、实验一:Local Prefenerce无法在EBGP Peer之间传递R2通告给R1的BGP路由是否携带LP?r1#sh ip bgp BGP table version is 2,local router ID is 9.9.0.1Status 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*10.0.0.0 9.9
17、.12.2 0 0 2 i500500没有传递没有传递?r2#sh ip bgp neighbors 9.9.12.1 advertised-routes BGP table version is 2,local router ID is 9.9.0.2Status 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*10.
18、0.0.0 0.0.0.0 0 32768 i 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID15第二条第二条:Local Preference属性属性 实验一:Local Prefenerce无法在EBGP Peer之间传递R2通告给R1的BGP Update报文R2通告的通告的10.0.0.0/8前缀的路径属性中不包含前缀的路径属性中不包含Local Preference属性属性 2007 Cisco Systems,Inc.All rights reserved.Cisco Conf
19、identialPresentation_ID16第二条第二条:Local Preference属性属性 实验二:修改本地始发路由的默认LP值R1R2AS 110.0.0.0/8IBGProuter bgp 1-R2的路由策略的路由策略 bgp default local-preference 500 network 10.0.0.0 neighbor 9.9.12.1 remote-as 1 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID17第二条第二条:Local Preference
20、属性属性 实验二:修改本地始发路由的默认LP值r2#sh ip b BGP table version is 2,local router ID is 10.0.0.1Status 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*10.0.0.0 0.0.0.0 0 32768 i空值空值?r2#sh ip b 10.0
21、.0.0BGP routing table entry for 10.0.0.0/8,version 2Paths:(1 available,best#1,table Default-IP-Routing-Table)Advertised to non peer-group peers:9.9.12.1 Local 0.0.0.0 from 0.0.0.0(10.0.0.1)Origin IGP,metric 0,localpref 500,weight 32768,valid,sourced,local,best 2007 Cisco Systems,Inc.All rights reser
22、ved.Cisco ConfidentialPresentation_ID18第二条第二条:Local Preference属性属性 实验二:修改本地始发路由的默认LP值r1#sh ip b BGP table version is 4,local router ID is 9.9.0.1Status 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 LocP
23、rf Weight Path*i10.0.0.0 9.9.12.2 0 500 0 i 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID19第二条第二条:Local Preference属性属性 实验三:将IGP中的路由引入BGP时关联Route-map设置LPR1R2AS 110.0.0.0/8IBGProuter bgp 1 -R2的路由策略的路由策略 network 10.0.0.0 route-map SET_LP neighbor 9.9.12.1 remote-as 1!rout
24、e-map SET_LP permit 10 set local-preference 400 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID20第二条第二条:Local Preference属性属性 实验三:将IGP中的路由引入BGP时关联Route-map设置LPr2#sh ip b BGP table version is 3,local router ID is 10.0.0.1Status codes:s suppressed,d damped,h history,*valid,
25、best,i-internal,r RIB-failure,S StaleOrigin codes:i-IGP,e-EGP,?-incomplete Network Next Hop Metric LocPrf Weight Path*10.0.0.0 0.0.0.0 0 400 32768 ir1#sh ip bBGP table version is 6,local router ID is 9.9.0.1Status codes:s suppressed,d damped,h history,*valid,best,i-internal,r RIB-failure,S StaleOrig
26、in codes:i-IGP,e-EGP,?-incomplete Network Next Hop Metric LocPrf Weight Path*i10.0.0.0 9.9.12.2 0 400 0 i 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID21第二条第二条:Local Preference属性属性 实验四:对IBGP Peer应用IN/OUT方向Route-mapR3单向访问R6的数据流需求R1R2对R3应用OUT方向Route-mapR1AS 1R2R3R4R5R6AS
27、 2以该方式部署策略以该方式部署策略,对对数据流控制的作用范围数据流控制的作用范围10.0.0.0/811.0.0.0/8EBGP 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID22第二条第二条:Local Preference属性属性 实验四:对IBGP Peer应用IN/OUT方向Route-mapR4、R5正常通告R6的路由，R1、R2的BGP表R1AS 1R2R3R4R5R6AS 210.0.0.0/811.0.0.0/8EBGPr1#sh ip bgp Network Next
28、Hop Metric LocPrf Weight Path*10.0.0.0 9.9.15.5 0 2 i*9.9.14.4 0 2 i*11.0.0.0 9.9.15.5 0 2 i*9.9.14.4 0 2 ir2#sh ip bgp Network Next Hop Metric LocPrf Weight Path*10.0.0.0 9.9.25.5 0 2 i*9.9.24.4 0 2 i*11.0.0 9.9.25.5 0 2 i*9.9.24.4 0 2 iIBGPIBGPIBGPIBGP 2007 Cisco Systems,Inc.All rights reserved.Ci
29、sco ConfidentialPresentation_ID23第二条第二条:Local Preference属性属性 实验四:对IBGP Peer应用IN/OUT方向Route-mapR1、R2的路由策略router bgp 1 -R1的路由策略的路由策略 neighbor 9.9.13.3 route-map TO_R3 outaccess-list 1 permit 10.0.0.0access-list 2 permit 11.0.0.0route-map TO_R3 permit 10 match ip address 1 set local-preference 500route
30、-map TO_R3 permit 20 match ip address 2 set local-preference 400router bgp 1 -R2的路由策略的路由策略 neighbor 9.9.23.3 route-map TO_R3 outaccess-list 1 permit 10.0.0.0access-list 2 permit 11.0.0.0route-map TO_R3 permit 10 match ip address 1 set local-preference 400route-map TO_R3 permit 20 match ip address 2
31、set local-preference 500R1AS 1R2R3R4R5R6AS 210.0.0.0/811.0.0.0/8EBGPIBGPIBGPIBGPIBGP 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID24第二条第二条:Local Preference属性属性 实验四:对IBGP Peer应用IN/OUT方向Route-mapR3的路由选路结果r3#sh ip b BGP table version is 6,local router ID is 9.9.0.3Status
32、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*i10.0.0.0 9.9.23.2 0 400 0 2 i*i 9.9.13.1 0 500 0 2 i*i11.0.0.0 9.9.23.2 0 500 0 2 i*i 9.9.13.1 0 400 0 2 iR1AS 1R2R3R4R5R6AS 210.0.0.0/8
33、11.0.0.0/8EBGPIBGPIBGPIBGPIBGP 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID25第二条第二条:Local Preference属性属性 实验四:对IBGP Peer应用IN/OUT方向Route-map路由策略结果：R3到R6的实际单向数据流R1AS 1R2R3R4R5R6AS 210.0.0.0/811.0.0.0/8EBGP以该方式部署策略以该方式部署策略,对对数据流控制的作用范围数据流控制的作用范围 2007 Cisco Systems,Inc.All
34、 rights reserved.Cisco ConfidentialPresentation_ID26第二条第二条:Local Preference属性属性 实验五:对EBGP Peer应用IN方向Route-mapR3单向访问R6的数据流需求R1R2分别对R4R5应用OUT方向的Route-mapR1AS 1R2R3R4R5R6AS 2以该方式部署策略以该方式部署策略,对对数据流控制的作用范围数据流控制的作用范围10.0.0.0/811.0.0.0/8EBGP 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPres
35、entation_ID27第二条第二条:Local Preference属性属性 实验五:对EBGP Peer应用IN方向Route-mapR1、R2的路由策略router bgp 1 -R1的路由策略的路由策略 neighbor 9.9.14.4 route-map FROM_R4 inaccess-list 1 permit 10.0.0.0route-map FROM_R4 permit 10 match ip address 1 set local-preference 500route-map FROM_R4 permit 20router bgp 1-R2的路由策略的路由策略 ne
36、ighbor 9.9.25.5 route-map FROM_R5 inaccess-list 2 permit 11.0.0.0route-map FROM_R5 permit 10 match ip address 2 set local-preference 500route-map FROM_R5 permit 20R1AS 1R2R3R4R5R6AS 210.0.0.0/811.0.0.0/8EBGPIBGPIBGPIBGPIBGP 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID
37、28第二条第二条:Local Preference属性属性 实验五:对EBGP Peer应用IN方向Route-mapR1、R2的BGP表r1#sh ip bgp Network Next Hop Metric LocPrf Weight Path*10.0.0.0 9.9.15.5 0 2 i*9.9.14.4 500 0 2 i*11.0.0.0 9.9.14.4 0 2 i*9.9.15.5 0 2 ir2#sh ip bgp Network Next Hop Metric LocPrf Weight Path*10.0.0.0 9.9.25.5 0 2 i*9.9.24.4 0 2 i
38、*11.0.0.0 9.9.25.5 500 0 2 i*9.9.24.4 0 2 iR1AS 1R2R3R4R5R6AS 210.0.0.0/811.0.0.0/8EBGPIBGPIBGPIBGPIBGP 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID29第二条第二条:Local Preference属性属性 实验五:对EBGP Peer应用IN方向Route-mapR3的BGP表r3#sh ip bgp BGP table version is 10,local router ID i
39、s 9.9.0.3Status 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*i10.0.0.0 9.9.23.2 0 100 0 2 i*i 9.9.13.1 0 500 0 2 i*i11.0.0.0 9.9.23.2 0 500 0 2 i*i 9.9.13.1 0 100 0 2 iR1AS 1R2R3R4R5
40、R6AS 210.0.0.0/811.0.0.0/8EBGPIBGPIBGPIBGPIBGP 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID30第二条第二条:Local Preference属性属性 实验五:对EBGP Peer应用IN方向Route-map路由策略结果：R3到R6的实际单向数据流R1AS 1R2R3R4R5R6AS 210.0.0.0/811.0.0.0/8以该方式部署策略以该方式部署策略,对对数据流控制的作用范围数据流控制的作用范围 2007 Cisco Systems
41、,Inc.All rights reserved.Cisco ConfidentialPresentation_ID31BGP路由选路原则路由选路原则1.Weight1.Weight属性属性2.Local Preference2.Local Preference属性属性3.3.本地路由始发方式本地路由始发方式4.AS-Path4.AS-Path长度长度5.Origin5.Origin属性属性6.MED6.MED属性属性7.EBGP7.EBGP优于优于IBGPIBGP8.8.到达到达Next-hopNext-hop的代价的代价9.9.执行等价负载均衡执行等价负载均衡10.EBGP10.EBGP路
42、由接收的顺序路由接收的顺序11.11.路由的路由的Router-IDRouter-ID12.Cluster-list12.Cluster-list长度长度13.13.配置的配置的BGP PeerBGP Peer指定地址指定地址 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID32第三条第三条:本地路由始发方式本地路由始发方式 比较原则及配置注意事项 该比较原则主要是指本地在进入一条IGP路由进去BGP表时，使用不同的方式比如network或redistribute等，那么这些方式之间是存在优
43、先顺序的：networkredistributeaggregate注意，该原则是不会作为BGP路由选路策略的 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID33第三条第三条:本地路由始发方式本地路由始发方式 实验验证 本地分别以3种方式引入一条路由，如下配置所示interface Loopback1 ip address 3.3.3.3 255.255.255.255router bgp 1 network 3.3.3.3 mask 255.255.255.255 route-map A
44、aggregate-address 3.3.3.3 255.255.255.255 attribute-map C redistribute connected route-map Broute-map A permit 10 set local-preference 200route-map B permit 10 set local-preference 300route-map C permit 10 set local-preference 400 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresenta
45、tion_ID34第三条第三条:本地路由始发方式本地路由始发方式 实验验证 本地BGP表中的显示，network方式为第一选择r3#sh ip bgpBGP table version is 13,local router ID is 9.9.0.3Status 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*3.3.3
46、.3/32 0.0.0.0 0 200 32768 i 2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID35第三条第三条:本地路由始发方式本地路由始发方式 实验验证 将network 3.3.3.3 mask 255.255.255.255 删除redistribute方式成为优选r3#sh ip bBGP table version is 14,local router ID is 9.9.0.3Status codes:s suppressed,d damped,h history,*v
47、alid,best,i-internal,r RIB-failure,S StaleOrigin codes:i-IGP,e-EGP,?-incomplete Network Next Hop Metric LocPrf Weight Path*3.3.3.3/32 0.0.0.0 0 300 32768?2007 Cisco Systems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID36BGP路由选路原则路由选路原则1.Weight1.Weight属性属性2.Local Preference2.Local Prefere
48、nce属性属性3.3.本地路由始发方式本地路由始发方式4.AS-Path4.AS-Path长度长度5.Origin5.Origin属性属性6.MED6.MED属性属性7.EBGP7.EBGP优于优于IBGPIBGP8.8.到达到达Next-hopNext-hop的代价的代价9.9.执行等价负载均衡执行等价负载均衡10.EBGP10.EBGP路由接收的顺序路由接收的顺序11.11.路由的路由的Router-IDRouter-ID12.Cluster-list12.Cluster-list长度长度13.13.配置的配置的BGP PeerBGP Peer指定地址指定地址 2007 Cisco Sys
49、tems,Inc.All rights reserved.Cisco ConfidentialPresentation_ID37第四条第四条:AS-Path长度长度 比较原则及配置注意事项优选长度小的AS-Path列表其他AS-Path比较原则：在做聚合路由时，使用as-set后产生的AS-Path列表中的里的AS号长度只算一个AS号的长度在联盟内的AS-Path列表中的()的AS号长度不做计算依据当向EBGP Peer 通告路由时，将自己的AS号加在AS-Path列表的最左端，向IBGP Peer通告路由时，不会对AS-Path列表做任何修改 2007 Cisco Systems,Inc.A
50、ll rights reserved.Cisco ConfidentialPresentation_ID38第四条第四条:AS-Path长度长度 比较原则及配置注意事项修改AS-Path列表的方法：可以通过对EBGP Peer使用IN/OUT方向的Route-map，使用set as-path prepend命令来添加AS号。注意，上述操作只能对EBGP Peer，对IBGP Peer无法生效。可以在BGP进程下使用bgp bestpath as-path ignore命令来跳过AS-Path的长度比较修改AS-Path长度可作为BGP选路策略的一种。2007 Cisco Systems,In
