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1、BGP路由选路原则详解V1.0,学习总结，个人见解，如有错误欢迎改正！,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,BGP路由选路原则,1.Weight属性,2.Local Preference属性,3.本地路由始发方式,4.AS-Path长度,5.Origin属性,6.MED属性,7.EBGP优于IBGP,8.到达Next-hop的代价,9.执行等价负载均衡,10.EBGP路由接收的顺序,11.路由的Router-ID,12.Cluster-list长度,13.配置的BGP Peer指定地址,第一条:Weight属性,实验验证 R2、R3分别通告10.0.0.
2、0给R1 R1将10.0.0.0使用network方式引入BGP,10.0.0.0/8,10.0.0.0/8,10.0.0.0/8,AS 1,AS 2,R3,R1,R2,IBGP,EBGP,第一条:Weight属性,实验验证 R1的BGP表,r1#sh ip bgp BGP table version is 2, local router ID is 9.9.0.1 Status codes: s suppressed, d damped, h history, * valid, best, i - internal, r RIB-failure, S Stale Origin codes:
3、i - IGP, e - EGP, ? - 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,第一条:Weight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,10.0.0.0/8,10.0.0.0/8,10.0.0.0/8,AS 1,AS 2,R3,R1,R2,IBGP,EBGP,router bgp 1 -R1的路由策略 neighbor 9.
4、9.12.2 route-map FROM_R2 in route-map FROM_R2 permit 10 set weight 65535,第一条:Weight属性,实验验证 R1的BGP表选路结果,r1#sh ip bgp BGP table version is 7, local router ID is 9.9.0.1 Status codes: s suppressed, d damped, h history, * valid, best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP,
5、? - incomplete Network Next Hop Metric LocPrf Weight Path r i10.0.0.0 9.9.13.3 0 100 0 i r 9.9.12.2 0 65535 2 i r 0.0.0.0 0 32768 i,BGP路由选路原则,1.Weight属性,2.Local Preference属性,3.本地路由始发方式,4.AS-Path长度,5.Origin属性,6.MED属性,7.EBGP优于IBGP,8.到达Next-hop的代价,9.执行等价负载均衡,10.EBGP路由接收的顺序,11.路由的Router-ID,12.Cluster-li
6、st长度,13.配置的BGP Peer指定地址,第二条:Local Preference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,第二条:Local Preference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
7、: 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 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,第二条:Local Preference属性,实验一:Local Prefenerce无法在EBGP Peer之间传递,R1,R2,AS 1,AS 2,10.0.0.0/8,EBGP,router bgp 2 network 10.0
8、.0.0 neighbor 9.9.12.1 remote-as 1 neighbor 9.9.12.1 route-map TO_R1 out ! route-map TO_R1 permit 10 set local-preference 500,第二条:Local Preference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 router ID is 9.9.0.2 Status codes: s suppressed, d d
9、amped, 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 * 10.0.0.0 0.0.0.0 0 32768 i,空值?,r2#sh ip b 10.0.0.0 BGP routing table entry for 10.0.0.0/8, version 2 Paths: (1 available, best #1, table D
10、efault-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,第二条:Local Preference属性,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
11、 2, local router ID is 9.9.0.1 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 * 10.0.0.0 9.9.12.2 0 0 2 i,500没有传递?,r2#sh ip bgp neighbors 9.9.12.1 advertise
12、d-routes BGP table version is 2, local router ID is 9.9.0.2 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 * 10.0.0.0 0.0.0.0 0 32768 i,第二条:Local Preference
13、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10.0.0.0/8前缀的路径属性中不包含Local Preference属性,第二条:Local Preference属性,实验二:修改本地始发路由的默认LP值,R1,R2,AS 1,10.0.0.0/8,IBGP,router bgp 1 -R2的路由策略 bgp default local-preference 500 network 10.0.0.0 neighbor 9.9.12.1 remote-as 1,第二条:Local Preference属性,
14、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 10.0.0.1 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 * 10.0.0.0 0.0.0.0 0 32768
15、i,空值?,r2#sh ip b 10.0.0.0 BGP routing table entry for 10.0.0.0/8, version 2 Paths: (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,第二条:Local Preference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 9.9.0.1 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
