[理论说明]BGP选路原则第三条:优先选择本地产生的BGP路径；而本地产生的BGP有三种方式：1.通过network命令发布的 2.通过aggregate命令汇聚产生的3.通过redistribute命令重发布进来的。
那么当同一路径通过多种方式产生该选择谁呢？CISCO给出的原则是这样的:
Local paths that are sourced by the network or redistribute commands are preferred over local aggregates that are sourced by the aggregate-address command.
[分解实验1]
验证the local path from the network command is prefer to the local path from the aggregate command
基本配置:
R1:
interface Loopback0
ip address 1.1.0.1 255.255.255.0 secondary
ip address 1.1.1.1 255.255.255.0
!
interface f0/0
ip address 12.1.1.1 255.255.255.0
!
router bgp 12
no synchronization
bgp router-id 1.1.1.1
network 1.1.0.0 mask 255.255.252.0
network 1.1.0.0 mask 255.255.255.0
aggregate-address 1.1.0.0 255.255.252.0
neighbor 12.1.1.2 remote-as 12
no auto-summary
!
ip classless
ip route 1.1.0.0 255.255.252.0 Null0
R2:
interface f0/0
ip address 12.1.1.2 255.255.255.0
!
router bgp 12
no synchronization
bgp router-id 2.2.2.2
neighbor 12.1.1.1 remote-as 12
no auto-summary
在R1上查看BGP路由表
R1#sh ip bg
BGP table version is 5, local router ID is 1.1.1.1
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 &am p;nb sp; Metric LocPrf Weight Path
*> 1.1.0.0/24 0.0.0.0 0 32768 i
*> 1.1.0.0/22 0.0.0.0 0 32768 i
* 0.0.0.0 32768 i
R1#sh ip bg 1.1.0.0 255.255.252.0
BGP routing table entry for 1.1.0.0/22, version 5
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
12.1.1.2
Local
0.0.0.0 from 0.0.0.0 (1.1.1.1)
Origin IGP, metric 0, localpref 100, weight 32768, valid, sourced, local, best
Local, (aggregated by 12 1.1.1.1)
0.0.0.0 from 0.0.0.0 (1.1.1.1)
Origin IGP, localpref 100, weight 32768, valid, aggregated, local, atomic-aggregate
可以看到优先选择了network命令发布的条目,由此证明:network>aggregate-address
[分解实验2]验证the local path from the redistribute command is prefer to the local path from the aggregate command
在R1上删除netwok命令，重发布静态进入BGP表
R1(config)#router bg 12
R1(config-router)#no network 1.1.0.0 mask 255.255.252.0
R1(config-router)#redistribute connected static
这样你可以看到最终的效果如下
R1#sh ip bg
BGP table version is 10, local router ID is 1.1.1.1
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 &am p;nb sp; Metric LocPrf Weight Path
*> 1.1.0.0/24 0.0.0.0 0 32768 i
*> 1.1.0.0/22 0.0.0.0 0 32768 ?
* 0.0.0.0 32768 i
R1#sh ip bg 1.1.0.0 255.255.252.0
BGP routing table entry for 1.1.0.0/22, version 8
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
12.1.1.2
Local
0.0.0.0 from 0.0.0.0 (1.1.1.1)
Origin incomplete, metric 0, localpref 100, weight 32768, valid, sourced, best
Local, (aggregated by 12 1.1.1.1)
0.0.0.0 from 0.0.0.0 (1.1.1.1)
Origin IGP, localpref 100, weight 32768, valid, aggregated, local, atomic-aggregate
由此可以看出redistribute>aggregate-address
综上所述: network/redistribute>aggregate-address
注意:当同时起源于local时,network和redistribute是不用比较的，两者不能共存，如上述实验，R1不把 network删除，就重发布静态，redistribute是没有效果的。关于这个问题的补充我会尽快回帖说明
