BGP选路原则彻底理解!(中)

第三条 :LP值用于as多出口,离开as最佳的路由
查看r4路由表:
<R4>dis bgp routing-table 
 Total Number of Routes: 11
 BGP Local router ID is 4.4.4.4 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
     Network            NextHop         MED        LocPrf     PrefVal Path/Ogn
 *>i 1.1.1.1/32         2.2.2.2         0          100        0       100i
 * i                    3.3.3.3         0          100        0       100i
   i 2.2.2.2/32         2.2.2.2         0          100        0       i
 * i                    3.3.3.3         3124       100        0       ?
 * i 3.3.3.3/32         2.2.2.2         3124       100        0       ?
   i                    3.3.3.3         0          100        0       i
 *>  4.4.4.4/32         0.0.0.0         0                     0       i
 * i                    2.2.2.2         1562       100        0       ?
 * i                    3.3.3.3         1562       100        0       ?
 * i 24.24.24.0/24      3.3.3.3         3124       100        0       ?
 * i 34.34.34.0/24      2.2.2.2         3124       100        0       ?
R4上的路由优选的ROUTER ID最小的,见第十二条!
LP值默认为100,无比较价值,修改r2的lp值
[R2-bgp]default local-preference 2222
<R4>dis bgp routing-table 
 Total Number of Routes: 11
 BGP Local router ID is 4.4.4.4 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
     Network            NextHop         MED        LocPrf     PrefVal Path/Ogn
 *>i 1.1.1.1/32         2.2.2.2         0          2222       0       100i
 * i                    3.3.3.3         0          100        0       100i
   i 2.2.2.2/32         2.2.2.2         0          2222       0       i
 * i                    3.3.3.3         3124       100        0       ?
 * i 3.3.3.3/32         2.2.2.2         3124       2222       0       ?
   i                    3.3.3.3         0          100        0       i
 *>  4.4.4.4/32         0.0.0.0         0                     0       i
 * i                    2.2.2.2         1562       2222       0       ?
 * i                    3.3.3.3         1562       100        0       ?
 * i 24.24.24.0/24      3.3.3.3         3124       100        0       ?
 * i 34.34.34.0/24      2.2.2.2         3124       2222       0       ?
来在R2的路由lp值都变成了2222,优选lp值大的路由离开as
在R4上加入三条换回口并且宣告
[R4-bgp]network 40.1.1.1 32
[R4-bgp]network 40.2.2.2 32  
[R4-bgp]network 40.3.3.3 32 
在R3上做聚合aggregate 40.0.0.0 255.0.0.0
查看R3的路由表:[R3]dis ip routing-table 40.0.0.0
Routing Table : Public
Summary Count : 1
Destination/Mask    Proto  Pre  Cost         NextHop         Interface
40.0.0.0/8          BGP    130  0            127.0.0.1       NULL0
优先级只有130,普通的bgp路由优先级都是255,优选优先级数值小的路由!
为了看到实验现象,在R2上使用路由策略,是aspash变长
[R2]dis acl 2000
Basic ACL  2000, named -none-, 1 rule,
ACL's step is 5
 rule 0 permit source 4.4.4.4 0 (8 times matched) 使用acl匹配4.4.4.4/32的路由
[R2]dis cu conf ro
#
route-policy as permit node 10
 if-match acl 2000
 apply as-path 200 300 400
route-policy as permit node 20使用路由策略改变aspash的属性
#
peer 12.12.12.1 route-policy as export
 peer 10.0.12.1 route-policy as export将策略是以在出方向上
查看R1上的4.4.4.4路由:
*>  4.4.4.4/32         13.13.13.3      1562                  0       200?
 *                      12.12.12.2      1562                  0       200 200
                                                                      300 400?
 *                      10.0.12.2       1562                  0       200 200
                                                                      300 400?
优选了来自R3的4.4.4.4,因为aspash最短!
第四条 实验方法和思想与第五条类似,不罗嗦重复
med其实和igp中的metric类似,比如ospf的cost,用于一个as多入口选路,选择med小的路由,注意:仅仅在两个as之间传播
将R3的med改的很小:[R3-bgp]default med 1
查看R1bgp路由表:<R1>dis bgp routing-table 
 Total Number of Routes: 13
 BGP Local router ID is 1.1.1.1 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
     Network            NextHop         MED        LocPrf     PrefVal Path/Ogn
 *>  1.1.1.1/32         0.0.0.0         0                     0       i
 *>  2.2.2.2/32         10.0.12.2       0                     0       200i
 *                      13.13.13.3      1                     0       200?
 *                      12.12.12.2      0                     0       200i
 *>  3.3.3.3/32         13.13.13.3      1                     0       200i
 *                      12.12.12.2      3124                  0       200?
 *                      10.0.12.2       3124                  0       200?
 *>  4.4.4.4/32         13.13.13.3      1                     0       200?
 *                      12.12.12.2      1562                  0       200?
 *                      10.0.12.2       1562                  0       200?
 *>  24.24.24.0/24      13.13.13.3      1                     0       200?
 *>  34.34.34.0/24      10.0.12.2       3124                  0       200?
 *                      12.12.12.2      3124                  0       200?
:在R3上改变下cost,R4有限R3来的路由
[R1]dis bgp r
 Total Number of Routes: 13
 BGP Local router ID is 1.1.1.1 
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
     Network            NextHop         MED        LocPrf     PrefVal Path/Ogn
 *>  1.1.1.1/32         0.0.0.0         0                     0       i
 *>  2.2.2.2/32         10.0.12.2       0                     0       200i
 *                      13.13.13.3      1563                  0       200?
 *                      12.12.12.2      0                     0       200i
 *>  3.3.3.3/32         13.13.13.3      0                     0       200i
 *                      12.12.12.2      3124                  0       200?
 *                      10.0.12.2       3124                  0       200?
 *>  4.4.4.4/32         13.13.13.3      1                     0       200?
 *                      12.12.12.2      1562                  0       200?
 *                      10.0.12.2       1562                  0       200?
 *>  24.24.24.0/24      13.13.13.3      1563                  0       200?
 *>  34.34.34.0/24      10.0.12.2       3124                  0       200?
 *                      12.12.12.2      3124                  0       200?
剩下的几条,回头再写

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