BGP对等组 peer-group
 
 
 
BGP对等组：
当同样的路由策略应用于多个BGP对端的时候，将对端指定为一个对等组的成员将会极大地简化一个路由器的BGP配置。可以按照下面步骤来生成一个对等组：
1）为对等组指定一个名字   neighbor xiaomu peer-group 
2）如果是内部对等组，就要先为对等组指定AS号（neighbor xiaomu remote-as 100 ）；
    如果是外部对等组，每个EBGP都要单独指定。
    neighbor x.x.x.x remote-as 200
3）将成员加入对等组中:  neighbor 2.2.2.2 peer-group xiaomu
4) 如果是内部对等组，要指定loopback , next-hop-self
     neighbor xiaomu update-source Loopback0
     neighbor xiaomu next-hop-self
5）对对等组应用策略：neighbor xiaomu filter-list 1 in
 
 

内部对等组的配置：
R1：
router bgp 100
 no synchronization
 bgp log-neighbor-changes
 network 1.1.1.0 mask 255.255.255.0
 neighbor xiaomu peer-group             //为对等体组指定一个名字
 neighbor xiaomu remote-as 100        //必须先指定内部对等组的AS号
 neighbor xiaomu update-source Loopback0 
 neighbor 2.2.2.2 peer-group xiaomu        //将对等组的成员加入对等组中
 neighbor 3.3.3.3 peer-group xiaomu
 no auto-summary
R2：
!        
router bgp 100
 no synchronization
 bgp router-id 2.2.2.2
 bgp log-neighbor-changes
 network 2.2.2.0 mask 255.255.255.0
 neighbor xiaomu peer-group
 neighbor xiaomu remote-as 100
 neighbor xiaomu update-source Loopback0
 neighbor xiaomu next-hop-self
 neighbor 1.1.1.1 peer-group xiaomu
 neighbor 3.3.3.3 peer-group xiaomu
 neighbor 172.16.4.4 remote-as 200
 no auto-summary
R3：
!        
router bgp 100
 no synchronization
 bgp router-id 3.3.3.3
 bgp log-neighbor-changes
 network 3.3.3.0 mask 255.255.255.0
 neighbor xiaomu peer-group
 neighbor xiaomu remote-as 100
 neighbor xiaomu update-source Loopback0
 neighbor xiaomu next-hop-self
 neighbor 1.1.1.1 peer-group xiaomu
 neighbor 2.2.2.2 peer-group xiaomu
 neighbor 172.16.5.5 remote-as 200
 no auto-summary

外部对等组的配置：
R2：
!
router bgp 100
 no synchronization
 bgp router-id 2.2.2.2
 bgp log-neighbor-changes
 network 2.2.2.0 mask 255.255.255.0
 neighbor xiaomu peer-group
 neighbor xiaomu remote-as 100
 neighbor xiaomu update-source Loopback0
 neighbor xiaomu next-hop-self
 neighbor out-xiaomu peer-group                 //定义一个对等组名
 neighbor 1.1.1.1 peer-group xiaomu
 neighbor 3.3.3.3 peer-group xiaomu
 neighbor 172.16.4.4 remote-as 200    //单独指定外部对等组成员的AS号
 neighbor 172.16.4.4 peer-group out-xiaomu     //将成员加入对等组中
 no auto-summary
R3：
!        
router bgp 100
 no synchronization
 bgp router-id 3.3.3.3
 bgp log-neighbor-changes
 network 3.3.3.0 mask 255.255.255.0
 neighbor xiaomu peer-group
 neighbor xiaomu remote-as 100
 neighbor xiaomu update-source Loopback0
 neighbor xiaomu next-hop-self
 neighbor out-xiaomu peer-group                          
 neighbor 1.1.1.1 peer-group xiaomu
 neighbor 2.2.2.2 peer-group xiaomu
 neighbor 172.16.5.5 remote-as 200
 neighbor 172.16.5.5 peer-group out-xiaomu
 no auto-summary
 
测试：
R2#show ip bgp peer-group
BGP peer-group is xiaomu,  remote AS 100
  BGP version 4
  Default minimum time between advertisement runs is 5 seconds
 For address family: IPv4 Unicast
  BGP neighbor is xiaomu, peer-group internal, members:
  1.1.1.1 3.3.3.3
  Index 1, Offset 0, Mask 0x2
  NEXT_HOP is always this router
  Update messages formatted 17, replicated 5
  Number of NLRIs in the update sent: max 0, min 0
         
BGP peer-group is out-xiaomu
  BGP version 4
  Default minimum time between advertisement runs is 30 seconds
 For address family: IPv4 Unicast
  BGP neighbor is out-xiaomu, peer-group external, members:
  172.16.4.4
  Index 2, Offset 0, Mask 0x4
  Update messages formatted 5, replicated 0
  Number of NLRIs in the update sent: max 0, min 0