43、BGP配置實驗之聚合aggregate-address

1、實驗拓撲

2、基礎配置

R1配置

interface Loopback0

 ip address 1.1.1.1 255.255.255.0

interface Serial0/0

 ip address 13.1.1.1 255.255.255.0

interface FastEthernet1/0

 ip address 124.1.1.1 255.255.255.0

router ospf 110

 log-adjacency-changes

 network 1.1.1.0 0.0.0.255 area 0

 network 124.1.1.0 0.0.0.255 area 0

router bgp 1

 no synchronization

 bgp router-id 1.1.1.1

 neighbor 2.2.2.2 remote-as 1

 neighbor 2.2.2.2 update-source Loopback0

 neighbor 2.2.2.2 next-hop-self

 neighbor 13.1.1.3 remote-as 3

 no auto-summary

R2配置

interface Loopback0

 ip address 2.2.2.2 255.255.255.0

interface FastEthernet1/0

 ip address 124.1.1.2 255.255.255.0

router ospf 110

 log-adjacency-changes

 network 2.2.2.0 0.0.0.255 area 0

 network 124.1.1.0 0.0.0.255 area 0

router bgp 1

 no synchronization

 bgp router-id 2.2.2.2

 bgp log-neighbor-changes

 neighbor 1.1.1.1 remote-as 1

 neighbor 1.1.1.1 update-source Loopback0

 neighbor 124.1.1.4 remote-as 4

 no auto-summary

R3配置

interface Loopback0

 ip address 3.3.3.3 255.255.255.0        

interface Loopback16

 ip address 202.1.16.3 255.255.255.0

interface Loopback17

 ip address 202.1.17.3 255.255.255.0

interface Loopback18

 ip address 202.1.18.3 255.255.255.0

interface Loopback19

 ip address 202.1.19.3 255.255.255.0

interface Serial0/0

 ip address 13.1.1.3 255.255.255.0

router bgp 3

 no synchronization

 bgp router-id 3.3.3.3

 bgp log-neighbor-changes

 network 3.3.3.0 mask 255.255.255.0

 network 202.1.16.0

 network 202.1.17.0

 network 202.1.18.0

 network 202.1.19.0

 neighbor 13.1.1.1 remote-as 1

 no auto-summary

R4配置

interface Loopback0

 ip address 4.4.4.4 255.255.255.0

interface FastEthernet1/0

 ip address 124.1.1.4 255.255.255.0

router bgp 4

 no synchronization

 bgp router-id 4.4.4.4

 bgp log-neighbor-changes

 network 4.4.4.0 mask 255.255.255.0

 neighbor 124.1.1.2 remote-as 1

 no auto-summary

3、配置聚合

BGP聚合可以使用兩種方法：

方法一:手動寫一條指向空接口的靜態匯總路由，再在BGP路由進程匯總發布該匯總路由

方法二：先在BGP路由進程中network所有的明細路由，在用aggregate-address 202.1.16.0 255.255.252.0 做聚合，此時會將聚合路由和明細路由都通告出去，aggregate-address 202.1.16.0 255.255.252.0 summary-only將會抑制明細路由，標識為s，且不發給其他BGP鄰居。

此外我們也可以指定不通告特定路由，基本步驟如下：

ip prefix-list 1 permit 202.1.16.0/23 ge 24 le 24

route-map YZ permit 10

match ip address prefix-list 1

router bgp 3

aggregate-address 202.1.16.0 255.255.252.0 suppress-map YZ

方法二是在發送方做聚合，如果在接收方做聚合，接收方生成聚合路由后會反傳給發送方，此時將會產生丟包現象，所以不應該讓聚合路由回傳。為達到不會傳的目的，我們采用BGP的水平分割技術，在聚合路由上加入明細路由的屬性，這樣當發送方收到聚合路由后，由于聚合路由攜帶有自身的AS號而不接受該路由，aggregate-address 202.1.16.0 255.255.252.0 summary-only as-set。

方法一：

R3配置

ip route 202.1.16.0 255.255.252.0 null0

router bgp 3

no network 202.1.16.0

no network 202.1.17.0

no network 202.1.18.0

no network 202.1.19.0

network 202.1.16.0 mask 255.255.252.0

方法二：

R3配置

no ip route 202.1.16.0 255.255.252.0 null0

router bgp 3

no network 202.1.16.0 mask 255.255.252.0

 network 202.1.16.0

 network 202.1.17.0

 network 202.1.18.0

 network 202.1.19.0

 aggregate-address 202.1.16.0 255.255.252.0

aggregate-address 202.1.16.0 255.255.252.0 summary-only將會抑制明細路由，標識為s，且不發給其他BGP鄰居。

router bgp 3

aggregate-address 202.1.16.0 255.255.252.0 summary-only

清除R3上的聚合，將聚合做在R1上。

router bgp 3

no aggregate-address 202.1.16.0 255.255.252.0 summary-only

router bgp 1

no aggregate-address 202.1.16.0 255.255.252.0 summary-only

router bgp 1

no aggregate-address 202.1.16.0 255.255.252.0 summary-only as-set

R1不再將聚合路由通告給R3。