首先来介绍下网络拓扑图：路由器r1、r2、r3属于 AS 100并且内部运行ospf协议。r4属于AS 200。r5、6、7属于AS 300并且内部运行ospf协议。

本例中a路径：1.1.1.1 访问172.16.10.1 走 r1-r2-r4-r5-r7。b路径:1.1.1.1 访问172.16.20.1 走路径r1-r3-r4-r6-r7。介绍完拓扑图后接下来将为大家依次介绍每个路由器的配置！

路由器r1的核心配置：

#

interface GigabitEthernet0/0/0

ip address 10.0.12.1 255.255.255.0

#

interface GigabitEthernet0/0/1

ip address 10.0.13.1 255.255.255.0

#

interface GigabitEthernet0/0/2

#

interface NULL0

#

interface LoopBack0

ip address 1.1.1.1 255.255.255.255

#

interface LoopBack10

ip address 192.168.10.1 255.255.255.0

#

interface LoopBack20

ip address 192.168.20.1 255.255.255.0

#

bgp 100

router-id 1.1.1.1

peer 10.0.12.2 as-number 100

peer 10.0.13.3 as-number 100

#

ipv4-family unicast

undo synchronization

network 1.1.1.1 255.255.255.255

network 192.168.10.0

network 192.168.20.0

peer 10.0.12.2 enable

peer 10.0.13.3 enable

#

ospf 1 router-id 1.1.1.1

area 0.0.0.0

network 1.1.1.1 0.0.0.0

network 10.0.12.0 0.0.0.255

network 10.0.13.0 0.0.0.255

#

路由器r2的核心配置：

#

interface GigabitEthernet0/0/0

ip address 10.0.12.2 255.255.255.0

#

interface GigabitEthernet0/0/1

ip address 10.0.24.2 255.255.255.0

#

interface GigabitEthernet0/0/2

#

interface NULL0

#

interface LoopBack0

ip address 2.2.2.2 255.255.255.255

#

bgp 100

router-id 2.2.2.2

peer 10.0.12.1 as-number 100

peer 10.0.24.4 as-number 200

#

ipv4-family unicast

undo synchronization

network 2.2.2.2 255.255.255.255

peer 10.0.12.1 enable

peer 10.0.24.4 enable

#

ospf 1 router-id 2.2.2.2

area 0.0.0.0

network 2.2.2.2 0.0.0.0

network 10.0.12.0 0.0.0.255

network 10.0.24.0 0.0.0.255

#

路由器r3的核心配置：

#

interface GigabitEthernet0/0/0

ip address 10.0.34.3 255.255.255.0

#

interface GigabitEthernet0/0/1

ip address 10.0.13.3 255.255.255.0

#

interface GigabitEthernet0/0/2

#

interface NULL0

#

interface LoopBack0

ip address 3.3.3.3 255.255.255.255

#

bgp 100

router-id 3.3.3.3

peer 10.0.13.1 as-number 100

peer 10.0.34.4 as-number 200

#

ipv4-family unicast

undo synchronization

network 3.3.3.3 255.255.255.255

peer 10.0.13.1 enable

peer 10.0.34.4 enable

#

ospf 1 router-id 3.3.3.3

area 0.0.0.0

network 3.3.3.3 0.0.0.0

network 10.0.13.0 0.0.0.255

network 10.0.34.0 0.0.0.255

#

路由器r4的核心配置：

#

interface GigabitEthernet0/0/0

ip address 10.0.34.4 255.255.255.0

#

interface GigabitEthernet0/0/1

ip address 10.0.24.4 255.255.255.0

#

interface GigabitEthernet4/0/0

ip address 10.0.46.4 255.255.255.0

#

interface GigabitEthernet4/0/1

ip address 10.0.45.4 255.255.255.0

#

interface LoopBack0

ip address 4.4.4.4 255.255.255.255

#

bgp 200

router-id 4.4.4.4

peer 10.0.24.2 as-number 100

peer 10.0.34.3 as-number 100

peer 10.0.45.5 as-number 300

peer 10.0.46.6 as-number 300

#

ipv4-family unicast

undo synchronization

network 4.4.4.4 255.255.255.255

peer 10.0.24.2 enable

peer 10.0.24.2 route-policy med10 export

peer 10.0.24.2 advertise-community

peer 10.0.34.3 enable

peer 10.0.34.3 route-policy med20 export

peer 10.0.34.3 advertise-community

peer 10.0.45.5 enable

peer 10.0.45.5 route-policy 10 import

peer 10.0.46.6 enable

peer 10.0.46.6 route-policy 10 import

#

route-policy 10 permit node 10

if-match community-filter 10

apply ip-address next-hop 10.0.45.5

#

route-policy 10 permit node 20

if-match community-filter 20

apply ip-address next-hop 10.0.46.6

#

route-policy med10 permit node 10

if-match community-filter 10

apply cost 100

#

route-policy med10 permit node 20

if-match community-filter 20

apply cost 200

#

route-policy med20 permit node 10

if-match community-filter 20

apply cost 100

#

route-policy med20 permit node 20

if-match community-filter 10

apply cost 200

#

ip community-filter 10 permit 300:100

ip community-filter 20 permit 300:200

#

路由器r5核心配置：

#

interface GigabitEthernet0/0/1

ip address 10.0.45.5 255.255.255.0

#

interface GigabitEthernet0/0/2

ip address 10.0.57.5 255.255.255.0

#

interface NULL0

#

interface LoopBack0

ip address 5.5.5.5 255.255.255.255

#

bgp 300

router-id 5.5.5.5

peer 10.0.45.4 as-number 200

peer 10.0.57.7 as-number 300

#

ipv4-family unicast

undo synchronization

network 5.5.5.5 255.255.255.255

peer 10.0.45.4 enable

peer 10.0.45.4 advertise-community

peer 10.0.57.7 enable

#

ospf 1 router-id 5.5.5.5

area 0.0.0.0

network 5.5.5.5 0.0.0.0

network 10.0.45.0 0.0.0.255

network 10.0.57.0 0.0.0.255

#

路由器r6核心配置：

#

interface GigabitEthernet0/0/0

ip address 10.0.46.6 255.255.255.0

#

interface GigabitEthernet0/0/1

ip address 10.0.67.6 255.255.255.0

#

interface LoopBack0

ip address 6.6.6.6 255.255.255.255

#

bgp 300

router-id 6.6.6.6

peer 10.0.46.4 as-number 200

peer 10.0.67.7 as-number 300

#

ipv4-family unicast

undo synchronization

network 6.6.6.6 255.255.255.255

peer 10.0.46.4 enable

peer 10.0.46.4 advertise-community

peer 10.0.67.7 enable

#

ospf 1 router-id 6.6.6.6

area 0.0.0.0

network 6.6.6.6 0.0.0.0

network 10.0.46.0 0.0.0.255

network 10.0.67.0 0.0.0.255

#

路由器r7核心配置：

#

interface GigabitEthernet0/0/1

ip address 10.0.67.7 255.255.255.0

#

interface GigabitEthernet0/0/2

ip address 10.0.57.7 255.255.255.0

#

interface NULL0

#

interface LoopBack0

ip address 7.7.7.7 255.255.255.255

#

interface LoopBack10

ip address 172.16.10.1 255.255.255.0

#

interface LoopBack20

ip address 172.16.20.1 255.255.255.0

#

bgp 300

router-id 7.7.7.7

peer 10.0.57.5 as-number 300

peer 10.0.67.6 as-number 300

#

ipv4-family unicast

undo synchronization

network 7.7.7.7 255.255.255.255

network 172.16.10.0 255.255.255.0 route-policy com10

network 172.16.20.0 255.255.255.0 route-policy com20

peer 10.0.57.5 enable

peer 10.0.57.5 advertise-community

peer 10.0.67.6 enable

peer 10.0.67.6 advertise-community

#

ospf 1 router-id 7.7.7.7

area 0.0.0.0

network 7.7.7.7 0.0.0.0

network 10.0.57.0 0.0.0.255

network 10.0.67.0 0.0.0.255

#

route-policy com10 permit node 10

apply community 300:100

#

route-policy com20 permit node 10

apply community 300:200

#

配置好所有设备后我们在r4上查看172.16.10.0和172.16.20.0网段的community值：

ar4dis bgp routing-table 172.16.10.1

BGP local router ID : 4.4.4.4

Local AS number : 200

Paths: 2 available, 1 best, 1 select

BGP routing table entry information of 172.16.10.0/24:

From: 10.0.45.5 (5.5.5.5)

Route Duration: 01h13m49s

Direct Out-interface: GigabitEthernet4/0/1

Original nexthop: 10.0.45.5

Qos information : 0x0

Community:300:100

AS-path 300, origin igp, pref-val 0, valid, external, best, select, active, pre

255

Advertised to such 4 peers:

10.0.45.5

10.0.46.6

10.0.24.2

10.0.34.3

BGP routing table entry information of 172.16.10.0/24:

From: 10.0.46.6 (6.6.6.6)

Route Duration: 01h13m39s

Relay IP Nexthop: 0.0.0.0

Relay IP Out-Interface: GigabitEthernet4/0/1

Original nexthop: 10.0.45.5

Qos information : 0x0

Community:300:100

通过上面输出的信息可以看到172.16.10.1的Community属性值是300:100！

最后我们在r1上使用tracert命令查看路径是否如我们所设置的那样：

ar1tracert -a 1.1.1.1 172.16.10.1

traceroute to 172.16.10.1(172.16.10.1), max hops: 30 ,packet length: 40,press

CTRL_C to break

1 10.0.12.2 20 ms 20 ms 20 ms

2 10.0.24.4 20 ms 30 ms 30 ms

3 10.0.45.5 30 ms 30 ms 30 ms

4 10.0.57.7 30 ms 40 ms 40 ms

ar1tr

ar1tracert -a 1.1.1.1 172.16.20.1

traceroute to 172.16.20.1(172.16.20.1), max hops: 30 ,packet length: 40,press

CTRL_C to break

1 10.0.13.3 20 ms 20 ms 20 ms

2 10.0.34.4 20 ms 30 ms 20 ms

3 10.0.46.6 30 ms 30 ms 40 ms

4 10.0.67.7 30 ms 20 ms 30 ms

输出结果与路由器的输出结果路线均正确，配置成功！