当一个AS包含多个IBGP对等体时，路由反射器非常有用。因为IBGP客户只需要和路由反射器建立邻居关系，从而降低了IBGP的连接数量。路由反射器和它的客户合称为一个簇。路由反射是克服IBGP水平分割的重要手段。

RR的反射规则如下：
1.如果路由是从非客户的IBGP邻居学来的，则RR只将它反射给客户
2.如果路由是从客户学来的，RR会将它反射给所有的非客户和客户(除了发起该路由的客户)
3.如果路由是从EBGP邻居学来的，RR会将它反射给所有的非客户和客户

1.ORIGINATOR_ID: 由路由反射器生成，是本AS内路由创造者的路由器ID
2.CLUSTER_ID: 一个AS内的每个簇必须用一个唯一的4个字节的簇ID来标识，如果簇内只有一个RR，则簇ID就是RR的路由器ID。当RR收到一个更新消息的时候，它检查CLUSTER_LIST，如果发现在列表中有自己的簇ID，就知道出现了路由环路。

1.路由反射器
2.层次化的RR
3.BGP联邦
4.BGP团体属性Community
5.过滤私有AS号
6.BGP后门路由
7.BGP路由标记

enable
conf t
no ip do lo
enable pass cisco
line con 0
logg sync
exec-t 0 0
exit
line vty 0 4
pass cisco
logg sync
exit
host

1.路由反射器
-------------------------------------------------------------------------------------

R1:
int f0/0
ip add 12.1.1.1 255.255.255.0
no shut
exit
int l0
ip add 11.1.1.1 255.255.255.0
exit
router bgp 100
neighbor 12.1.1.2 remote-as 200
network 11.1.1.0 mask 255.255.255.0
exit

R2:
int f0/0
ip add 12.1.1.2 255.255.255.0
no shut
exit
int f1/0
ip add 23.1.1.2 255.255.255.0
no shut
exit
int l0
ip add 22.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 22.1.1.0 0.0.0.255
network 23.1.1.0 0.0.0.255
exit

router bgp 200
bgp router-id 22.1.1.1
neighbor 12.1.1.1 remote-as 100
neighbor 33.1.1.1 remote-as 200
neighbor 33.1.1.1 update-source l0
neighbor 33.1.1.1 next-hop-self
exit

R3:
int f0/0
ip add 23.1.1.3 255.255.255.0
no shut
exit
int f1/0
ip add 34.1.1.3 255.255.255.0
no shut
exit
int l0
ip add 33.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 23.1.1.0 0.0.0.255
network 33.1.1.0 0.0.0.255
network 34.1.1.0 0.0.0.255
exit

router bgp 200
bgp router-id 33.1.1.1
neighbor 22.1.1.1 remote-as 200
neighbor 22.1.1.1 update-source l0
neighbor 22.1.1.1 next-hop-self
neighbor 44.1.1.1 remote-as 200
neighbor 44.1.1.1 update-source l0
neighbor 44.1.1.1 next-hop-self
exit

R4:
int f0/0
ip add 34.1.1.4 255.255.255.0
no shut
exit
int l0
ip add 44.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 34.1.1.0 0.0.0.255
network 44.1.1.0 0.0.0.255
exit

router bgp 200
bgp router-id 44.1.1.1
neighbor 33.1.1.1 remote-as 200
neighbor 33.1.1.1 update-source l0
neighbor 33.1.1.1 next-hop-self
exit

----------------------------------------------
R3:
end
show ip bgp
show ip bgp neighbors 44.1.1.1 advertised-routes
conf t

router bgp 200
neighbor 44.1.1.1 route-reflector-client
neighbor 22.1.1.1 route-reflector-client
exit

end
show ip bgp
show ip bgp neighbors 44.1.1.1 advertised-routers
show ip bgp neighbors 44.1.1.1
show ip bgp 11.1.1.0
conf t

R4:
end
show ip bgp 11.1.1.0
conf t

R3:
router bgp 200
bgp cluster-id 3.3.3.3

R4:
end
show ip bgp 11.1.1.0
conf t

2.层次化的RR
-----------------------------------------------------------------------------------------

R1:
int f0/0
ip add 12.1.1.1 255.255.255.0
no shut
exit
int l0
ip add 11.1.1.1 255.255.255.0
exit
router bgp 100
neighbor 12.1.1.2 remote-as 200
network 11.1.1.0 mask 255.255.255.0
exit

R2:
int f0/0
ip add 12.1.1.2 255.255.255.0
no shut
exit
int f1/0
ip add 23.1.1.2 255.255.255.0
no shut
exit
int l0
ip add 22.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 22.1.1.0 0.0.0.255
network 23.1.1.0 0.0.0.255
exit

router bgp 200
bgp router-id 22.1.1.1
neighbor 12.1.1.1 remote-as 100
neighbor 33.1.1.1 remote-as 200
neighbor 33.1.1.1 update-source l0
neighbor 33.1.1.1 next-hop-self
exit

R3:
int f0/0
ip add 23.1.1.3 255.255.255.0
no shut
exit
int f1/0
ip add 34.1.1.3 255.255.255.0
no shut
exit
int l0
ip add 33.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 23.1.1.0 0.0.0.255
network 33.1.1.0 0.0.0.255
network 34.1.1.0 0.0.0.255
exit

router bgp 200
bgp router-id 33.1.1.1
neighbor 22.1.1.1 remote-as 200
neighbor 22.1.1.1 update-source l0
neighbor 22.1.1.1 next-hop-self
neighbor 44.1.1.1 remote-as 200
neighbor 44.1.1.1 update-source l0
neighbor 44.1.1.1 next-hop-self
exit

R4:
int f0/0
ip add 34.1.1.4 255.255.255.0
no shut
int f1/0
ip add 45.1.1.4 255.255.255.0
no shut
exit
int l0
ip add 44.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 34.1.1.0 0.0.0.255
network 44.1.1.0 0.0.0.255
network 45.1.1.0 0.0.0.255
exit

router bgp 200
bgp router-id 44.1.1.1
neighbor 33.1.1.1 remote-as 200
neighbor 33.1.1.1 update-source l0
neighbor 33.1.1.1 next-hop-self
neighbor 55.1.1.1 remote-as 200
neighbor 55.1.1.1 update-source l0
neighbor 55.1.1.1 next-hop-self
exit

R5:
int f0/0
ip add 45.1.1.5 255.255.255.0
no shut
int l0
ip add 55.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 45.1.1.0 0.0.0.255
network 55.1.1.0 0.0.0.255
exit

router bgp 200
bgp router-id 55.1.1.1
neighbor 44.1.1.1 remote-as 200
neighbor 44.1.1.1 update-source l0
neighbor 44.1.1.1 next-hop-self
exit

----------------------------------------------
R3:
router bgp 200
neighbor 44.1.1.1 route-reflector-client
neighbor 22.1.1.1 route-reflector-client
exit

R4:
router bgp 200
neighbor 55.1.1.1 route-reflector-client
exit

3.BGP联邦

IBGP邻居并不把路由信息从一个IBGP邻居传播给另一个IBGP邻居。如果全互联，这将产生一个规模与费用的问题。BGP联邦克服了IBGP引起的规模问题。把AS划分为多个子自治系统。但在联邦内部，仍然需要IBGP的full-mesh，或者在联邦内部使用RR。联邦之间的BGP连接就像一个EBGP对等体，但是他们在交换路由信息的时候，就如在使用IBGP，同时保留了下一跳、度量和本地优先级等属性。
------------------------------------------------------------------------------------------------------

R1:
int f0/0
ip add 12.1.1.1 255.255.255.0
no shut
exit
int l0
ip add 11.1.1.1 255.255.255.0
exit
router bgp 100
bgp router-id 11.1.1.1
neighbor 12.1.1.2 remote-as 200
network 11.1.1.0 mask 255.255.255.0
exit

R2:
int f0/0
ip add 12.1.1.2 255.255.255.0
no shut
exit
int f1/0
ip add 23.1.1.2 255.255.255.0
no shut
int f2/0
ip add 27.1.1.2 255.255.255.0
no shut
exit
int l0
ip add 22.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 22.1.1.0 0.0.0.255
network 23.1.1.0 0.0.0.255
network 27.1.1.0 0.0.0.255
exit

router bgp 65001
bgp router-id 22.1.1.1
bgp confederation identifier 200
bgp confederation peers 65002
neighbor 12.1.1.1 remote-as 100
neighbor 33.1.1.1 remote-as 65002
neighbor 33.1.1.1 update-source l0
neighbor 33.1.1.1 next-hop-self
neighbor 33.1.1.1 ebgp-multihop
neighbor 77.1.1.1 remote-as 65001
neighbor 77.1.1.1 update-source l0
neighbor 77.1.1.1 next-hop-self
exit

R3:
int f0/0
ip add 23.1.1.3 255.255.255.0
no shut
exit
int f1/0
ip add 34.1.1.3 255.255.255.0
no shut
exit
int l0
ip add 33.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 23.1.1.0 0.0.0.255
network 33.1.1.0 0.0.0.255
network 34.1.1.0 0.0.0.255
exit

router bgp 65002
bgp router-id 33.1.1.1
bgp confederation identifier 200
bgp confederation peers 65001
neighbor 22.1.1.1 remote-as 65001
neighbor 22.1.1.1 update-source l0
neighbor 22.1.1.1 ebgp-multihop
neighbor 44.1.1.1 remote-as 65002
neighbor 44.1.1.1 update-source l0
exit

R4:
int f0/0
ip add 34.1.1.4 255.255.255.0
no shut
int f1/0
ip add 45.1.1.4 255.255.255.0
no shut
exit
int l0
ip add 44.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 34.1.1.0 0.0.0.255
network 44.1.1.0 0.0.0.255
network 45.1.1.0 0.0.0.255
exit

router bgp 65002
bgp router-id 44.1.1.1
bgp confederation identifier 200
bgp confederation peers 65003
neighbor 33.1.1.1 remote-as 65002
neighbor 33.1.1.1 update-source l0
neighbor 55.1.1.1 remote-as 65003
neighbor 55.1.1.1 update-source l0
neighbor 55.1.1.1 ebgp-multihop
exit

R5:
int f0/0
ip add 45.1.1.5 255.255.255.0
no shut
int f1/0
ip add 56.1.1.5 255.255.255.0
no shut
int l0
ip add 55.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 45.1.1.0 0.0.0.255
network 55.1.1.0 0.0.0.255
network 56.1.1.0 0.0.0.255
exit

router bgp 65003
bgp router-id 55.1.1.1
bgp confederation identifier 200
bgp confederation peers 65002
neighbor 44.1.1.1 remote-as 65002
neighbor 44.1.1.1 update-source l0
neighbor 44.1.1.1 next-hop-self
neighbor 44.1.1.1 ebgp-multihop
neighbor 56.1.1.6 remote-as 300
exit

R6:
int f0/0
ip add 56.1.1.6 255.255.255.0
no shut
int l0
ip add 66.1.1.1 255.255.255.0
exit

router bgp 300
bgp router-id 66.1.1.1
neighbor 56.1.1.5 remote-as 200
exit

R7:
int f0/0
ip add 27.1.1.7 255.255.255.0
no shut
int l0
ip add 77.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 27.1.1.0 0.0.0.255
network 77.1.1.0 0.0.0.255
exit

router bgp 65001
bgp router-id 77.1.1.1
bgp confederation identifier 200
neighbor 22.1.1.1 remote-as 65001
neighbor 22.1.1.1 update-source l0
exit

----------------------------------------------
R2:
router bgp 65001
bgp default local-pre 200
exit

show ip bgp
show ip bgp 11.1.1.0

R3:
show ip bgp

R5:
show ip bgp

R6:
show ip bgp

4.BGP团体属性Community

Community主要用来控制路由的传播范围；
团体属性，也叫做共同体属性，是可选传递属性，可选意味着并不是所有的路由器都能识别这个团体属性；
团体属性类似于tag标记，它允许路由器能够使用一个指示符来标记路由，并且允许其它路由器根据这个标记做出相应的决定，可以简化策略的执行。它是Cisco的一个专有属性，现在在RFC1997中已被标准化；
一条路由可以设置多个团体属性，也就是说可以同时打上多个标记，还可以利用团体属性实现一些扩展的功能，比如在MPLS-VPN中RT属性；
默认情况下团体属性不会传递给邻居，必须有以下命令才行：neighbor 1.1.1.1 send-community;团体属性只会传给指定的邻居，并且只在该邻居上生效
Community值可以自己定义，此外有几个已经定义好的团体属性：
NO_ADVERTISE：携带该值的路由不能公布给EBGP和IBGP邻居
NO_EXPORT：携带该值的路由公布给任何真正的EBGP对等体
LOCAL_AS：携带该值的路由不能公布给任何EBGP对等体，包括联邦内部子系统EBGP对等体

R1:
int l100
ip add 100.1.1.1 255.255.255.0
exit
router bgp 100
network 100.1.1.0 mask 255.255.255.0
exit

ip prefix-list 100.1 permit 100.1.1.0/24
route-map COMMUNITY permit 10
match ip add prefix-list 100.1
set community local-as
exit
route-map COMMUNITY permit 9999
exit

router bgp 100
neighbor 12.1.1.2 route-map COMMUNITY out
neighbor 12.1.1.2 send-community
exit

R2:
show ip bgp 100.1.1.0

R3/R7:
show ip bgp

-------------------------------------------------------
R1:
int l101
ip add 101.1.1.1 255.255.255.0
exit
router bgp 100
network 101.1.1.0 mask 255.255.255.0
exit

ip prefix-list 101.1 permit 101.1.1.0/24
route-map COMMUNITY permit 20
match ip add prefix-list 101.1
set community no-advertise
exit

clear ip bgp * soft out

R2:
show ip bgp 101.1.1.0

R3/R7:
show ip bgp

----------------------------------------------------------
R2:
int l200
ip add 200.1.1.1 255.255.255.0
exit

route-map NO-EXPORT permit 10
set community no-export
exit

router bgp 65001
network 200.1.1.0 mask 255.255.255.0 route-map NO-EXPORT
exit

show ip bgp 200.1.1.0

ip prefix-list 101.1 permit 101.1.1.0/24
route-map COMMUNITY permit 20
match ip add prefix-list 101.1
set community no-advertise
exit

R1/R3/R7:
show ip bgp

5.过滤私有AS号
--------------------------------------------------------------------------

R1:
int f0/0
ip add 12.1.1.1 255.255.255.0
no shut
exit
int l0
ip add 11.1.1.1 255.255.255.0
exit

router bgp 65000
router-id 11.1.1.1
neighbor 12.1.1.2 remote-as 100
network 11.1.1.0 mask 255.255.255.0
exit

R2:
int f0/0
ip add 12.1.1.2 255.255.255.0
no shut
exit
int f1/0
ip add 23.1.1.2 255.255.255.0
no shut
exit
int l0
ip add 22.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 23.1.1.0 0.0.0.255
network 22.1.1.0 0.0.0.255
exit

router bgp 100
bgp router-id 22.1.1.1
neighbor 33.1.1.1 remote-as 100
neighbor 33.1.1.1 update-source l0
neighbor 33.1.1.1 next-hop-self
neighbor 12.1.1.1 remote-as 65000
exit

R3:
int f0/0
ip add 34.1.1.3 255.255.255.0
no shut
exit
int f1/0
ip add 23.1.1.3 255.255.255.0
no shut
exit
int l0
ip add 33.1.1.1 255.255.255.0
exit

router eigrp 1
no auto-summary
network 23.1.1.0 0.0.0.255
network 33.1.1.0 0.0.0.255
exit

router bgp 100
bgp router-id 33.1.1.1
neighbor 22.1.1.1 remote-as 100
neighbor 22.1.1.1 update-source l0
neighbor 22.1.1.1 next-hop-self
neighbor 34.1.1.4 remote-as 200
exit

R4:
int f0/0
ip add 34.1.1.4 255.255.255.0
no shut
exit
int l0
ip add 44.1.1.1 255.255.255.0
exit

router bgp 200
bgp router-id 44.1.1.1
neighbor 34.1.1.3 remote-as 100
exit

R4:
show ip bgp

R3:
router bgp 100
neighbor 34.1.1.4 remove-private-as
exit

R4:
clear ip bgp * in
show ip bgp

6.BGP后门路由
---------------------------------------------------------------------------------

R1:
int f1/0
ip add 12.1.1.1 255.255.255.0
no shut
exit
int s0/0
ip add 13.1.1.1 255.255.255.0
no shut
exit

router ospf 1
router-id 11.1.1.1
network 12.1.1.0 0.0.0.255 area 0
exit

router bgp 100
bgp router-id 11.1.1.1
neighbor 13.1.1.3 remote-as 300
exit

R2:
int f1/0
ip add 12.1.1.2 255.255.255.0
no shut
exit
int s0/0
ip add 23.1.1.2 255.255.255.0
no shut
exit

router ospf 1
router-id 22.1.1.1
network 12.1.1.0 0.0.0.255 area 0
exit

router bgp 200
bgp router-id 22.1.1.1
neighbor 23.1.1.3 remote-as 300
exit

R3:
int s0/0
ip add 13.1.1.3 255.255.255.0
no shut
exit
int s0/1
ip add 23.1.1.3 255.255.255.0
no shut
exit

router bgp 300
bgp router-id 33.1.1.1
neighbor 13.1.1.1 remote-as 100
neighbor 23.1.1.2 remote-as 200
exit

R1:
int l0
ip add 11.1.1.1 255.255.255.0
exit
router ospf 1
network 11.1.1.0 0.0.0.255 area 0
exit

int l0
ip ospf network point-to-point
exit

R2:
show ip route

R1:
router bgp 100
network 11.1.1.0 mask 255.255.255.0
exit

R2:
show ip route

以上表示当11.1.1.0/24这条路由同时从EBGP邻居和OSPF邻居学习到的时候，会选择从BGP邻居学习到的路由，因为EBGP路由的AD值为20.
要想让R2优选从OSPF学习的路由，需要在R2上做BGP后门路由配置。

R2:
router bgp 200
network 11.1.1.0 mask 255.255.255.0 backdoor
exit

show ip route

int f1/0
shutdown
exit

show ip route

7.BGP路由标记
---------------------------------------------------------------------------------

R1:
int f0/0
ip add 12.1.1.1 255.255.255.0
no shut
exit

router bgp 100
bgp router-id 11.1.1.1
neighbor 12.1.1.2 remote-as 300
exit

R2:
int f0/0
ip add 12.1.1.2 255.255.255.0
no shut
exit
int f1/0
ip add 23.1.1.2 255.255.255.0
no shut
exit

router ospf 1
router-id 22.1.1.1
network 23.1.1.0 0.0.0.255 area 0
exit

router bgp 300
bgp router-id 22.1.1.1
neighbor 12.1.1.1 remote-as 100
exit

R3:
int f1/0
ip add 23.1.1.3 255.255.255.0
no shut
exit
int f0/0
ip add 34.1.1.3 255.255.255.0
no shut
exit

router ospf 1
router-id 33.1.1.1
network 23.1.1.0 0.0.0.255 area 0
exit

router bgp 300
bgp router-id 33.1.1.1
neighbor 34.1.1.4 remote-as 200
exit

R4:
int f0/0
ip add 34.1.1.4 255.255.255.0
no shut
exit

router bgp 200
bgp router-id 44.1.1.1
neighbor 34.1.1.3 remote-as 300
exit

R1:
int l0
ip add 11.1.1.1 255.255.255.0
exit

router bgp 100
network 11.1.1.0 mask 255.255.255.0
exit

默认情况下R4不能学到此路由，因为R2与R3之间并没有BGP邻居关系，需要在OSPF之间进行重分布才能学到。

R2:
router ospf 1
redistribute bgp 300 subnets
exit

R3:
router bgp 300
redistribute ospf 1 match external 2
exit

R4:
show ip bgp

能够看到11.1.1.0/24这条路由，但是不能看到这条路由的起源AS号100.产生此问题的原因是该路由被R3学到之前已经过了OSPF区域的重发布，而OSPF协议是无法理解AS路径属性的。解决的办法是在R2上从BGP向OSPF发布路由时利用route-map将AS路径属性转为路由标记，这样就可以携带在OSPF路由中，然后在R3上从OSPF发布回BGP时，再次利用route-map，将路由标记转回AS路径属性。

R2:
route-map TAG permit 10
set automatic-tag
exit
router bgp 300
table-map TAG
exit

R3:
route-map TAG permit 10
set as-path tag
exit
router bgp 300
redistribute ospf 1 route-map TAG
exit

R4:
show ip bgp

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