BGP路径选择的控制——局部偏爱属性案例.doc

操纵BGP路径选择---local?preference属性案例 HYPERLINK /showpic.html \l blogid=56fdccdb0100075jurl=/orignal/56fdccdbe506e09720ab8 \t _blank 本地优先级（local pref）属性是分配给路由的一种优先级度量，用于和到同一目的地的其他路由相比较。这是BGP路由处理中的第二优先属性（WEIGHT是第一优先属性）。Local Pref属性只在本AS内部有效，不会被传送到EBGP邻居上。本地优先级越高，路由优先级越高。 ? 以上案例中，我们通过对R3的配置，设置从R1学到的的本地优先级（Localpref）设置为200，由于缺省的值为100，AS200中所有的路由器都会选择R3到达。 ? ? //// r1 //// int f2/0 ? ip ad ? int f3/0 ? ip ad ? int lo0 ? ip ad ? int lo1 ? ip ad ? router bgp 100 ? no syn ? neighbor remote-as 200 ? neighbor remote-as 200 ? network ? network ? ? ? //// r2 //// int f2/0 ? ip ad ? int f4/0 ? ip ad ? router os 1 ? netw 55 a 0 ? passive-interface f2/0 ? router bgp 200 ? no syn ? neighbor remote-as 100 ? neighbor remote-as 200 ? neighbor remote-as 200 ? neighbor next-hop-self ? ? //// r3 //// int f3/0 ? ip ad ? int f5/0 ? ip ad ? router os 1 ? netw 55 a 0 ? passive-interface f3/0 ? router bgp 200 ? no syn ? neighbor remote-as 100 ? neighbor remote-as 200 ? neighbor next-hop-self ? neighbor remote-as 200 ? neighbor route-map localpref in ? access-list 1 permit 55 ? route-map localpref permit 10 ? match ip ad 1 ? set local-pref 200 route-map localpref permit 20 ? set local-pref 100 ? //// r4 //// int f4/0 ? ip ad ? int f5/0 ? ip ad ? int lo0 ? ip ad ? router os 1 ? netw 55 a 0 ? router bgp 200 ? no syn ? neighbor remote-as 200 ? neighbor remote-as 200 ? netw ? ? ? ? 验证： //// r4 //// r4#sh ip bgp?? Network????????? Next Hop??????????? Metric LocPrf Weight Path*i????????? ??????????????? 0??? 200????? 0 100 i* i????????? ??????????????? 0??? 100????? 0 100 i*i???????????????? ??????????????? 0??? 100????? 0 100 i* ????????? ????????????????? 0???????? 32768 i ? ? r4#sh ip roB??? /8 [200/0] via , 00:02:20B??? /8 [200/0] via , 00:02:24???? /24 is subnetted, 1 subnetsC?????? is directly connected, Loopback0O??? /24 [110/128] via , 00:04:35, Serial5/0O??? /24 [110/128] via , 00:04:35, Serial4/0C??? /24 is directly connected, Serial5/0