在运行IBGP时，内部路由器一般都要运行IGP路由协议，建立邻居关系时用loopback口作为更新源，在运行EBGP时，也是用loopback口作为更新源，而且还要建立一条到对端路由器loopback口的路由，一般是静态，因为BGP默认路由只传播一跳，所以EBGP没有IGP传播路由，所以要特别指定EBGP多跳，BGP建立邻居关系后，并不能传播路由，需要把与对等体组相连的网络通告。BGP的边界路由器和内部对等体建立邻居关系时，要指明next-hop-self
指向自己，这样内部BGP对等体才能通告自己去往其他的AS。
R1配置
interface
Loopback0
ip
address 1.1.1.1 255.255.255.255
interface
FastEthernet0/0
ip
address 12.12.12.1 255.255.255.0
interface
FastEthernet0/1
ip
address 13.13.13.1 255.255.255.0!
router rip
version
2
network
1.0.0.0
network
12.0.0.0
network
13.0.0.0
no
auto-summary
router bgp 65535
no
synchronization
network 12.12.12.0 mask
255.255.255.0
network 13.13.13.0
mask 255.255.255.0
neighbor 2.2.2.2
remote-as 65535
neighbor 2.2.2.2
update-source Loopback0
neighbor 3.3.3.3
remote-as 65535
neighbor 3.3.3.3
update-source Loopback0
no
auto-summary
R2配置
interface
Loopback0
ip
address 2.2.2.2 255.255.255.255
interface
FastEthernet0/0
ip
address 12.12.12.2 255.255.255.0
interface
FastEthernet0/1
ip
address 24.24.24.1 255.255.255.0
interface
FastEthernet1/0
ip
address 23.23.23.1 255.255.255.0
router rip
version
2
network
2.0.0.0
network
12.0.0.0
network
23.0.0.0
no
auto-summary
router bgp 65535
no
synchronization
bgp default
local-preference 200
//在全局下配置本地优先级，影响本地
network 12.12.12.0 mask
255.255.255.0
network 23.23.23.0
mask 255.255.255.0
network 24.24.24.0
mask 255.255.255.0
neighbor INTER
peer-group
//运用对等体组配置BGP，简化了配置
neighbor INTER
remote-as 65535
neighbor INTER
update-source Loopback0
neighbor INTER
next-hop-self
neighbor 1.1.1.1
peer-group INTER
neighbor 3.3.3.3
peer-group INTER
neighbor 4.4.4.4
remote-as 100
neighbor 4.4.4.4
ebgp-multihop 2
neighbor 4.4.4.4
update-source Loopback0
neighbor 4.4.4.4
route-map LOCAL_PRE_200 in
no
auto-summary
ip route
4.4.4.4 255.255.255.255 24.24.24.2
access-list 10 permit 200.200.200.0 0.0.0.255
route-map LOCAL_PRE_200 permit 10
match ip address
10
set local-preference
1500
运用rout-map指明特定的网络从哪个路由器通过，对本地的成员出去起作用
R3路由器配置
interface
Loopback0
ip
address 3.3.3.3 255.255.255.255
interface
FastEthernet0/0
ip
address 13.13.13.2 255.255.255.0
interface
FastEthernet0/1
ip
address 34.34.34.1 255.255.255.0
interface
FastEthernet1/0
ip
address 23.23.23.2 255.255.255.0
router rip
version
2
network
3.0.0.0
network
13.0.0.0
network
23.0.0.0
no
auto-summary
router bgp 65535
no
synchronization
bgp default
local-preference 500
network 13.13.13.0 mask
255.255.255.0
network 23.23.23.0
mask 255.255.255.0
network 34.34.34.0
mask 255.255.255.0
neighbor INTER
peer-group
neighbor INTER
remote-as 65535
neighbor INTER
update-source Loopback0
neighbor INTER
next-hop-self
neighbor 1.1.1.1
peer-group INTER
neighbor 2.2.2.2
peer-group INTER
neighbor 4.4.4.4
remote-as 100
neighbor 4.4.4.4
ebgp-multihop 2
neighbor 4.4.4.4
update-source Loopback0
no
auto-summary
ip route
4.4.4.4 255.255.255.255 34.34.34.2
R4路由器配置
interface
Loopback0
ip
address 4.4.4.4 255.255.255.255
interface
Loopback100
ip
address 100.100.100.1 255.255.255.0
interface
Loopback200
ip
address 200.200.200.1 255.255.255.0
interface
FastEthernet0/0
ip
address 24.24.24.2 255.255.255.0
interface
FastEthernet0/1
ip
address 34.34.34.2 255.255.255.0
router bgp
100
no
synchronization
bgp
log-neighbor-changes
network 24.24.24.0
mask 255.255.255.0
network 34.34.34.0
mask 255.255.255.0
network 100.100.100.0
mask 255.255.255.0
network
200.200.200.0
neighbor EBGP
peer-group
neighbor EBGP
remote-as 65535
neighbor EBGP
ebgp-multihop 2
neighbor EBGP
update-source Loopback0
neighbor 2.2.2.2
peer-group EBGP
neighbor 3.3.3.3
peer-group EBGP
no
auto-summary
ip route
3.3.3.3 255.255.255.255 34.34.34.1
BGP的路径操作有
权重(weight)，权重越大越优先。neighbor PEERROUTER weight
权重值，权重值只影响当前的路由器，对其他路由器权重值不影响，但是会影响其他路由的路径
本地优先级(local-preference):
优先级越大越优先，上面配置运用到了。
AS路由(as-path):通告路由映射图设置，可以手动指定到某个网络经过哪些AS。
MED多路径鉴别器，当本AS的两个或两个以上路由器连接到其他ASS时，影响外部网络到内部网络要经过的路由器，可以在路由配置全局指定，也可以用路由映射图指定特定的网络的MED。
BGP还有一些团体属性和路由反射器功能。
