BGP路由反射器与联盟详解（上）
为什么需要路由反射器就是为了打破BGP中从IBGP学到的路由不能再传给IBGP（防止环路），那用什么来防止环路呢？利用
Originator_ID和Cluster_List
，收到
Originator_ID和本地的Router ID，如果两个ID相同，BGP 路由器会忽略掉这条路由，不做处理。
更详细的内容请见前面
http://tangfangxiao.blog.51cto.com/2116646/646077
组网需求：
1.
R1、R2、R3、R4、R5、R6、R7处于同一AS 10
2.
R8处于AS30,R9处于AS20，它们之间通过EBGP与AS10进行通信。
3.
在R1发布汇总静态路由10.0.0.0/16至BGP、在R5发布汇总静态路由10.5.0.0/16至BGP、
在R7发布汇总静态路由10.7.0.0/16至BGP、在R8发布汇总静态路由10.8.0.0/16至BGP、
在R9发布汇总静态路由10.9.0.0/16至BGP。
4.运用RR全连接或二级路由反射解决路由反射问题。
AS10 IGP配置如下：
R1：
router ospf 1
router-id 10.0.0.1
passive-interface Ethernet0/0
network 10.0.14.0 0.0.0.3 area 0
network 10.0.16.0 0.0.0.3 area 0
network 10.0.12.0 0.0.0.3 area 0
network 10.0.13.0 0.0.0.3 area 0
network 10.0.18.0 0.0.0.3 area 0(上面拓扑写错了，是10.0.18.0/30)
network 10.0.0.1 0.0.0.0 area 0
R2:
router ospf 1
router-id 10.0.0.2
passive-interface Ethernet0/1
network 10.0.0.2 0.0.0.0 area 0
network 10.0.12.0 0.0.0.3 area 0
network 10.0.29.0 0.0.0.3 area 0
R3:
router ospf 1
router-id 10.0.0.3
network 10.0.0.3 0.0.0.0 area 0
network 10.0.13.0 0.0.0.3 area 0
R4:
router ospf 1
router-id 10.0.0.4
network 10.0.0.4 0.0.0.0 area 0
network 10.0.14.0 0.0.0.3 area 0
network 10.0.45.0 0.0.0.3 area 0
R5:
router ospf 1
router-id 10.0.0.5
network 10.0.0.5 0.0.0.0 area 0
network 10.0.45.0 0.0.0.3 area 0
R6:
router ospf 1
router-id 10.0.0.6
network 10.0.0.6 0.0.0.0 area 0
network 10.0.16.0 0.0.0.3 area 0
network 10.0.67.0 0.0.0.3 area 0
R7:
router ospf 1
router-id 10.0.0.7
network 10.0.0.7 0.0.0.0 area 0
network 10.0.67.0 0.0.0.3 area 0
现在AS内可以连通了，开始配置BGP：
在R1、R4、R6上配置成RR，R2、R3为R1的客户端，R5为R4的客户端，R7为R6的客户端，R1与R8建立EBGP，R2与R9建立EBGP。
R1：
router bgp 10
no synchronization //关闭同步
network 10.0.0.0 //静态发布BGP路由汇总
neighbor rrc peer-group //创建一个名为rrc对等组（共享同一BGP策略）
neighbor rrc remote-as 10 //指定邻居AS为10
neighbor rrc update-source Loopback0 //指定更新源为LOOP 0
neighbor rrc route-reflector-client //指定为RR的客户端RRC
neighbor rrc next-hop-self //将下一条改变为自己
neighbor 10.0.0.2 peer-group rrc //指定邻居使用对等组策略
neighbor 10.0.0.3 peer-group rrc //指定邻居使用对等组策略
neighbor 10.0.0.4 remote-as 10
neighbor 10.0.0.4 update-source Loopback0
neighbor 10.0.0.4 next-hop-self
neighbor 10.0.0.6 remote-as 10
neighbor 10.0.0.6 update-source Loopback0
neighbor 10.0.0.6 next-hop-self
neighbor 10.0.18.2 remote-as 30
no auto-summary //关闭自动汇总
ip route 10.0.0.0 255.0.0.0 Null0 //添加汇总静态路由
R2：
router bgp 10 //RRC只需在RR上配置，RRC只要配置IGBP
no synchronization
neighbor 10.0.0.1 remote-as 10
neighbor 10.0.0.1 update-source Loopback0
neighbor 10.0.0.1 next-hop-self
neighbor 10.0.29.2 remote-as 20 //配置EBGP邻居
no auto-summary
R3：
router bgp 10 //RRC只需在RR上配置，RRC只要配置IGBP
no synchronization
neighbor 10.0.0.1 remote-as 10
neighbor 10.0.0.1 update-source Loopback0
neighbor 10.0.0.1 next-hop-self
no auto-summary
R4：
router bgp 10 //配置成RR，客户端为R5
no synchronization
neighbor rrc peer-group
neighbor rrc remote-as 10
neighbor rrc update-source Loopback0
neighbor rrc route-reflector-client
neighbor rrc next-hop-self
neighbor 10.0.0.1 remote-as 10
neighbor 10.0.0.1 update-source Loopback0
neighbor 10.0.0.1 next-hop-self
neighbor 10.0.0.5 peer-group rrc
no auto-summary
R5：
router bgp 10
no synchronization
network 10.5.0.0 mask 255.255.0.0 //发布路由到BGP
neighbor 10.0.0.4 remote-as 10
neighbor 10.0.0.4 update-source Loopback0
neighbor 10.0.0.4 next-hop-self
no auto-summary
ip route 10.5.0.0 255.255.0.0 Null0 //添加汇总静态路由
R6：
router bgp 10 //配置成RR，RRC为R7
no synchronization
neighbor rrc peer-group
neighbor rrc remote-as 10
neighbor rrc update-source Loopback0
neighbor rrc route-reflector-client
neighbor rrc next-hop-self
neighbor 10.0.0.1 remote-as 10
neighbor 10.0.0.1 update-source Loopback0
neighbor 10.0.0.1 next-hop-self
neighbor 10.0.0.7 peer-group rrc
no auto-summary
R７：
router bgp 10
no synchronization
network 10.7.0.0 mask 255.255.0.0 //发布到BGP
neighbor 10.0.0.6 remote-as 10
neighbor 10.0.0.6 update-source Loopback0
neighbor 10.0.0.6 next-hop-self
no auto-summary
ip route 10.7.0.0 255.255.0.0 Null0 //添加汇总静态路由
R8：
router bgp 30 //配置EBGP
no synchronization
network 10.8.0.0 mask 255.255.0.0
neighbor 10.0.18.1 remote-as 10 //发布到BGP中
no auto-summary
ip route 10.8.0.0 255.255.0.0 Null0 //添加汇总静态路由
R9：
router bgp 20
no synchronization
network 10.9.0.0 mask 255.255.0.0 //发布到BGP中
neighbor 10.0.29.1 remote-as 10
no auto-summary
ip route 10.9.0.0 255.255.0.0 Null0 //添加汇总静态路由
现在我们可以看到R9能够学习到所有路由，R８也一样：
Network Next Hop Metric LocPrf Weight Path
*> 10.0.0.0 10.0.29.1 0 10 i
*> 10.5.0.0/16 10.0.29.1 0 10 i
*> 10.7.0.0/16 10.0.29.1 0 10 i
*> 10.8.0.0/16 10.0.29.1 0 10 30 i
*> 10.9.0.0/16 0.0.0.0 0 32768 i
我们来分析一下10.7.0.0/16路由是怎么传播到R９的：
R7： Network Next Hop Metric LocPrf Weight Path
*>i10.0.0.0 10.0.0.1 0 100 0 i
*> 10.7.0.0/16 0.0.0.0 0 32768 i
*>i10.8.0.0/16 10.0.0.1 0 100 0 30 i
*>i10.9.0.0/16 10.0.0.2 0 100 0 20 i
首先由R7始发路由，所以下一跳为0.0.0.0,本地始发Weight为32768
然后传播到R6,其它的路由都是由RR反射过来的,
这里显示从RRC10.0.0.7学习到的路由，下一跳开销为101跟OSPF里的值一样，Origin为IGP，由静态发布IGP到BGP中的，MED值默认为0,本地优先级（localpref）默认为100,此路由是有效的，域内的，最优的
从RRC学习到的路由，传播给它的非客户端R1，
由RR反射过来的路由，不会改变下一跳等信息，起源ID为AS始发路由器ID 10.0.0.7，簇列表为RR的ROUTER-ID10.0.0.6，只经过了一个RR反射！
现在我们看一下R4的路由表：
Network Next Hop Metric LocPrf Weight Path
*>i10.0.0.0 10.0.0.1 0 100 0 i
*>i10.5.0.0/16 10.0.0.5 0 100 0 i
*>i10.8.0.0/16 10.0.0.1 0 100 0 30 i
*>i10.9.0.0/16 10.0.0.2 0 100 0 20 i
很显然没有10.7.0.0/16这条路由。因为从非客户端学习到的路由只会传给RRC，同理RR、R7没有10.5.0.0/16这条路由。
解决方法：1.统一由R1做RR，AS内其它路由器都作为R1的客户端
2.RR之间全连接
3.二级路由反射，R4,R6作为R1的客户端
4.用联盟
方法-：容易造成单点故障，当核心节点失效后，整个网络将不能互访
配置如下（R2、R3配置不变）：
R1：
no router bgp 10 //清除前面的配置
router bgp 10
no synchronization
network 10.0.0.0
neighbor rrc peer-group
neighbor rrc remote-as 10
neighbor rrc update-source Loopback0
neighbor rrc route-reflector-client
neighbor rrc next-hop-self
neighbor 10.0.0.2 peer-group rrc
neighbor 10.0.0.4 peer-group rrc
neighbor 10.0.0.3 peer-group rrc
neighbor 10.0.0.5 peer-group rrc
neighbor 10.0.0.6 peer-group rrc
neighbor 10.0.0.7 peer-group rrc
neighbor 10.0.18.2 remote-as 30
no auto-summary
R4：
no router bgp 10 //清除前面的配置
router bgp 10
no synchronization
neighbor 10.0.0.1 remote-as 10
neighbor 10.0.0.1 update-source Loopback0
neighbor 10.0.0.1 next-hop-self
no auto-summary
R5：
no router bgp 10 //清除前面的配置
router bgp 10
no synchronization
bgp log-neighbor-changes
network 10.5.0.0 mask 255.255.0.0
neighbor 10.0.0.1 remote-as 10
neighbor 10.0.0.1 update-source Loopback0
neighbor 10.0.0.1 next-hop-self
no auto-summary
R6：
no router bgp 10 //清除前面的配置
router bgp 10
neighbor 10.0.0.1 remote-as 10
neighbor 10.0.0.1 update-source Loopback0
neighbor 10.0.0.1 next-hop-self
no auto-summary
R7：
no router bgp 10 //清除前面的配置
router bgp 10
no synchronization
network 10.7.0.0 mask 255.255.0.0
neighbor 10.0.0.1 remote-as 10
neighbor 10.0.0.1 update-source Loopback0
neighbor 10.0.0.1 next-hop-self
no auto-summary
Network Next Hop Metric LocPrf Weight Path
*>i10.0.0.0 10.0.0.1 0 100 0 i
*>i10.5.0.0/16 10.0.0.5 0 100 0 i
*> 10.7.0.0/16 0.0.0.0 0 32768 i
*>i10.8.0.0/16 10.0.0.1 0 100 0 30 i
*>i10.9.0.0/16 10.0.0.2 0 100 0 20 i
现在在R7上看有整个网络的路由了！
方法二：很简单，在R4和R6之间再建立一个IBGP，路由器多的时候就有得忙了
在原来的配置上再加入以下配置：
R4：
neighbor 10.0.0.6 remote-as 10
neighbor 10.0.0.6 update-source loop 0
neighbor 10.0.0.6 next-hop-self
R6:
neighbor 10.0.0.4 remote-as 10
neighbor 10.0.0.4 update-source loop 0
neighbor 10.0.0.4 next-hop-self
这个方法简单吧
方法三：也很简单，用得也比较多
neighbor 10.0.0.4 remote-as 10 //也可以直接加在前面那个对等组里，就更简单了
neighbor 10.0.0.4 update-source Loopback0 //方便大家理解就写多点
neighbor 10.0.0.4 route-reflector-client
neighbor 10.0.0.4 next-hop-self
neighbor 10.0.0.6 remote-as 10
neighbor 10.0.0.6 update-source Loopback0
neighbor 10.0.0.6 route-reflector-client
neighbor 10.0.0.6 next-hop-self
就这么简单没了
由于字数限制，所以只能发在下一篇
http://tangfangxiao.blog.51cto.com/2116646/647835
本文出自 “凡人世界” 博客，谢绝转载！