BGP分解实验·11——路由聚合与条件性通告（3）

续接上（2）的实验。其拓扑如下：

路由聚合的负向也就是拆分，在有双出口的情况下，在多出口做流量分担是优选方法之一。

BGP可以根据指定来源而聚合路由，在产生该聚合路由的范围内的条目注入到本地BGP表后再向外分发出去。

实施BGP路由拆分实验，需要注意的是其本质上仍然属于条件性通告，这是Cisco IOS对条件性通告做了大量支持。之所以这种方式被称为路由拆分，是因为其特性上仅仅是对条件性通告的一个非常形象的称呼而已。

实现拆分路由的配置清单如下：

首先在iBGP与eBGP的边界上，配置前缀列表，定义需要拆分出来的明细条目；
再配置可以匹配汇总的路由前缀；
定义前缀列表边界路由器的邻居来源；
对准备要拆分出来的条目设置周知团体属性no-export以用于防环（防止传递出本AS）；
定义聚合前缀及来源；
在边界路由器的进程下对其配置iBGP邻居可传递的BGP团体属性；
最后设置注入列表的条进行通告及复制属性。（copy-attributes——将从聚合路由中复制路径属性到注入的路由条目中）

PS：//这里先把上个实验（2）的完整配置附上，如做完上个实验保存了配置可忽略以下R1~R5这个为添加拆分实验的配置。添加完成R1~R5的基本配后对上述清单做添加配置附在其后。

R1的基本配置如下：

hostname R1
!
interface Loopback0
 ip address 172.22.0.1 255.255.255.0
!
interface Loopback1
 ip address 172.22.1.1 255.255.255.0
!
interface Ethernet0/0
 ip address 10.0.12.1 255.255.255.0
 no sh
!
interface Ethernet0/1
 ip address 10.1.13.1 255.255.255.0
 no sh
!
ip prefix-list IFN3 seq 5 permit 172.22.3.0/24
!
ip prefix-list IFN3ADV seq 5 permit 172.22.0.0/22
ipv6 ioam timestamp
!
route-map IFN3ADV permit 10
 match ip address prefix-list IFN3ADV
!
route-map IFN3 permit 10
 match ip address prefix-list IFN3
!
router bgp 111
 bgp router-id 1.1.1.1
 bgp aggregate-timer 0
 network 172.22.0.0 mask 255.255.255.0
 network 172.22.1.0 mask 255.255.255.0
 aggregate-address 172.22.0.0 255.255.252.0 summary-only
 neighbor 10.0.12.2 remote-as 222
 neighbor 10.1.13.3 remote-as 345
 neighbor 10.1.13.3 advertise-map IFN3ADV exist-map IFN3
!
end

R2的基本配置如下：

hostname R2
!
interface Loopback0
 ip address 172.22.2.2 255.255.255.0
!
interface Loopback1
 ip address 172.22.3.2 255.255.255.0
!
interface Ethernet0/0
 ip address 10.0.12.2 255.255.255.0
 no sh
!
interface Ethernet0/1
 ip address 10.2.24.2 255.255.255.0
 no sh
!
ip prefix-list IFN3E seq 5 permit 172.22.3.0/24
!
route-map LEAK3 permit 10
 match ip address prefix-list IFN3E
!
router bgp 222
 bgp router-id 2.2.2.2
 bgp aggregate-timer 0
 network 172.22.2.0 mask 255.255.255.0
 network 172.22.3.0 mask 255.255.255.0
 aggregate-address 172.22.0.0 255.255.252.0 summary-only
 neighbor 10.0.12.1 remote-as 111
 neighbor 10.0.12.1 unsuppress-map LEAK3
 neighbor 10.2.24.4 remote-as 345
!
end

R3的基本配置如下：

hostname R3
!
interface Loopback3
 ip address 192.168.3.3 255.255.255.255
!
interface Ethernet0/0
 ip address 10.1.13.3 255.255.255.0
 no sh
!
interface Ethernet0/1
 ip address 10.3.35.3 255.255.255.0
 no sh
!
router eigrp 5
 network 0.0.0.0
 passive-interface Ethernet0/0
!
router bgp 345
 bgp router-id 3.3.3.3
 neighbor IBGP peer-group
 neighbor IBGP remote-as 345
 neighbor IBGP update-source Loopback3
 neighbor IBGP next-hop-self
 neighbor 10.1.13.1 remote-as 111
 neighbor 192.168.4.4 peer-group IBGP
 neighbor 192.168.5.5 peer-group IBGP
!
end

R4的基本配置如下：

hostname R4
!
interface Loopback4
 ip address 192.168.4.4 255.255.255.255
!
interface Ethernet0/0
 ip address 10.2.24.4 255.255.255.0
 no sh
!
interface Ethernet0/1
 ip address 10.3.45.4 255.255.255.0
 no sh
!
router eigrp 5
 network 0.0.0.0
 passive-interface Ethernet0/0
!
router bgp 345
 bgp router-id 4.4.4.4
 neighbor IBGP peer-group
 neighbor IBGP remote-as 345
 neighbor IBGP update-source Loopback4
 neighbor IBGP next-hop-self
 neighbor 10.2.24.2 remote-as 222
 neighbor 192.168.3.3 peer-group IBGP
 neighbor 192.168.5.5 peer-group IBGP
!
end

R5的基本配置如下：

hostname R5
!
interface Loopback3
 ip address 172.23.3.5 255.255.255.0
!
interface Loopback5
 ip address 192.168.5.5 255.255.255.255
!
interface Ethernet0/0
 ip address 10.3.35.5 255.255.255.0
 no sh
!
interface Ethernet0/1
 ip address 10.3.45.5 255.255.255.0
 no sh
!
router eigrp 5
 network 0.0.0.0
 passive-interface default
 no passive-interface Ethernet0/0
 no passive-interface Ethernet0/1
!
route-map REDCONN permit 10
 match interface Loopback3
!
router bgp 345
 bgp router-id 5.5.5.5
 bgp listen range 192.168.0.0/21 peer-group IBGP
 redistribute connected route-map REDCONN
 neighbor IBGP peer-group
 neighbor IBGP remote-as 345
 neighbor IBGP update-source Loopback5
!
end

以上添加完成R1~R5的基本配后对上述清单做添加配置如下：

注释：定义前缀列表的名称——LONG是相对掩码较长的定义；SHORT是聚合后变短的定义；LS是Left Source，即此拓扑图左侧邻居的路由来源；RS则是Right Source，右侧邻居的来源。

R3添加的配置如下：

ip prefix-list LONG seq 5 permit 172.22.1.0/24
!
ip prefix-list SHORT seq 5 permit 172.22.0.0/22
!
ip prefix-list LS seq 5 permit 10.1.13.1/32
!
route-map LONG permit 10
 set ip address prefix-list LONG
 set community no-export
!
route-map SHORT permit 10
 match ip address prefix-list SHORT
 match ip route-source prefix-list LS
!
router bgp 345
 bgp inject-map LONG exist-map SHORT copy-attributes
 neighbor IBGP send-community
!
end

R4添加的配置如下：

ip prefix-list LONG seq 5 permit 172.22.3.0/24
!
ip prefix-list SHORT seq 5 permit 172.22.0.0/22
!
ip prefix-list RS seq 5 permit 10.2.24.2/32
!
route-map LONG permit 10
 set ip address prefix-list LONG
 set community no-export
!
route-map SHORT permit 10
 match ip address prefix-list SHORT
 match ip route-source prefix-list RS
!
router bgp 345
 bgp inject-map LONG exist-map SHORT copy-attributes
 neighbor IBGP send-community
!
end

添加完成以上配置查看注入的BGP表和邻居来源的表项如下：