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配置BGP的基本功能后可以组建BGP网络。
组网需求
某个地区拥有多个AS，AS之间有相互访问的需求，因此需要AS之间相互交换本AS内部的路由。由于AS内NE数量众多，导致路由数量较大，路由变化频繁，如何高效率的在AS之间传递大量路由，并且不占用大量带宽成为一个难题。为解决上述问题，可以使用BGP协议。
如图1所示，DeviceA处于AS65008，DeviceB、DeviceC和DeviceD处于AS65009，并且这几个NE的路由数量都比较大，路由表变化频繁。在这几个NE上部署BGP协议之后，NE之间可以相互传递路由，并且当任何一个NE有路由更新时，只需发送路由更新信息给邻居NE，而无须发送整个路由表，大大节约了网络带宽。
本例中interface1，interface2，interface3分别代表GE0/1/0，GE0/2/0，GE0/3/0。
| 设备名称 | 接口 | IP地址 |
| DeviceA | Loopback 0 | 1.1.1.1/32 |
| GE 0/1/0 | 172.16.0.1/16 | |
| GE 0/2/0 | 192.168.0.1/24 | |
| DeviceB | Loopback 0 | 2.2.2.2/32 |
| GE 0/1/0 | 10.1.1.1/24 | |
| GE 0/2/0 | 192.168.0.2/24 | |
| GE 0/3/0 | 10.1.3.1/24 | |
| DeviceC | Loopback 0 | 3.3.3.3/32 |
| GE 0/2/0 | 10.1.2.1/24 | |
| GE 0/3/0 | 10.1.3.2/24 | |
| DeviceD | Loopback 0 | 4.4.4.4/32 |
| GE 0/1/0 | 10.1.1.2/24 | |
| GE 0/2/0 | 10.1.2.2/24 |
配置注意事项
在配置过程中，需注意以下事项：
建立对等体时，当所指定的对等体的IP地址为Loopback接口地址或子接口的IP地址时，需要在对等体两端同时配置命令peer connect-interface，以保证两端连接的正确性。
EBGP对等体之间不是直连的物理链路时，则必须使用peer ebgp-max-hop命令允许它们之间经过多跳建立TCP连接。
配置思路
采用如下的思路配置BGP的基本功能：
在DeviceB、DeviceC、DeviceD之间配置IBGP连接。
在DeviceA和DeviceB之间配置EBGP连接。
在DeviceA上通过network命令发布路由，查看DeviceA、DeviceB、DeviceC的路由表信息。
在DeviceB上配置BGP引入直连路由，查看DeviceA、DeviceC的路由表信息。
数据准备
为完成此配置例，需准备如下的数据：
DeviceA的Router ID以及所在的AS号。
DeviceB、DeviceC、DeviceD的Router ID以及所在的AS号。
操作步骤
- 配置各接口的IP地址，请参见配置文件
- 配置OSPF
# 配置DeviceB。
[~DeviceB] ospf 1
[*DeviceB-ospf-1] area 0
[*DeviceB-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255
[*DeviceB-ospf-1-area-0.0.0.0] network 10.1.3.0 0.0.0.255
[*DeviceB-ospf-1-area-0.0.0.0] network 2.2.2.2 0.0.0.0
[*DeviceB-ospf-1-area-0.0.0.0] commit
[~DeviceB-ospf-1-area-0.0.0.0] quit
[~DeviceB-ospf-1] quit
# 配置DeviceC。
[~DeviceC] ospf 1
[*DeviceC-ospf-1] area 0
[*DeviceC-ospf-1-area-0.0.0.0] network 10.1.2.0 0.0.0.255
[*DeviceC-ospf-1-area-0.0.0.0] network 10.1.3.0 0.0.0.255
[*DeviceC-ospf-1-area-0.0.0.0] network 3.3.3.3 0.0.0.0
[*DeviceC-ospf-1-area-0.0.0.0] commit
[~DeviceC-ospf-1-area-0.0.0.0] quit
[~DeviceC-ospf-1] quit
# 配置DeviceD。
[~DeviceD] ospf 1
[*DeviceD-ospf-1] area 0
[*DeviceD-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255
[*DeviceD-ospf-1-area-0.0.0.0] network 10.1.2.0 0.0.0.255
[*DeviceD-ospf-1-area-0.0.0.0] network 4.4.4.4 0.0.0.0
[*DeviceD-ospf-1-area-0.0.0.0] commit
[~DeviceD-ospf-1-area-0.0.0.0] quit
[~DeviceD-ospf-1] quit
- 配置IBGP连接
# 配置DeviceB。
[~DeviceB] bgp 65009
[*DeviceB-bgp] router-id 2.2.2.2
[*DeviceB-bgp] peer 3.3.3.3 as-number 65009
[*DeviceB-bgp] peer 4.4.4.4 as-number 65009
[*DeviceB-bgp] peer 3.3.3.3 connect-interface LoopBack0
[*DeviceB-bgp] peer 4.4.4.4 connect-interface LoopBack0
[*DeviceB-bgp] commit
[~DeviceB-bgp] quit
# 配置DeviceC。
[~DeviceC] bgp 65009
[*DeviceC-bgp] router-id 3.3.3.3
[*DeviceC-bgp] peer 2.2.2.2 as-number 65009
[*DeviceC-bgp] peer 4.4.4.4 as-number 65009
[*DeviceC-bgp] peer 2.2.2.2 connect-interface LoopBack0
[*DeviceC-bgp] peer 4.4.4.4 connect-interface LoopBack0
[*DeviceC-bgp] commit
[~DeviceC-bgp] quit
# 配置DeviceD。
[~DeviceD] bgp 65009
[*DeviceD-bgp] router-id 4.4.4.4
[*DeviceD-bgp] peer 2.2.2.2 as-number 65009
[*DeviceD-bgp] peer 3.3.3.3 as-number 65009
[*DeviceD-bgp] peer 2.2.2.2 connect-interface LoopBack0
[*DeviceD-bgp] peer 3.3.3.3 connect-interface LoopBack0
[*DeviceD-bgp] commit
[~DeviceD-bgp] quit
- 配置EBGP
# 配置DeviceA。
[~DeviceA] bgp 65008
[*DeviceA-bgp] router-id 1.1.1.1
[*DeviceA-bgp] peer 192.168.0.2 as-number 65009
[*DeviceA-bgp] commit
[~DeviceA-bgp] quit
# 配置DeviceB。
[~DeviceB] bgp 65009
[*DeviceB-bgp] peer 192.168.0.1 as-number 65008
[*DeviceB-bgp] commit
[~DeviceB-bgp] quit
# 查看BGP对等体的连接状态。
[~DeviceB] display bgp peer
BGP local router ID : 2.2.2.2
Local AS number : 65009
Total number of peers : 3 Peers in established state : 3
Peer V AS MsgRcvd MsgSent OutQ Up/Down State PrefRcv
3.3.3.3 4 65009 5 5 0 00:44:58 Established 0
4.4.4.4 4 65009 4 4 0 00:40:54 Established 0
192.168.0.1 4 65008 3 3 0 00:44:03 Established 0
可以看出，DeviceB到其他NE的BGP连接均已建立（连接状态为“Established”）。
- 配置DeviceA发布路由172.16.0.0/16
# 配置DeviceA发布路由。
[~DeviceA] bgp 65008
[*DeviceA-bgp] ipv4-family unicast
[*DeviceA-bgp-af-ipv4] network 172.16.0.0 255.255.0.0
[*DeviceA-bgp-af-ipv4] commit
[~DeviceA-bgp-af-ipv4] quit
[~DeviceA-bgp] quit
# 查看DeviceA路由表信息。
[~DeviceA] display bgp routing-table
BGP Local router ID is 1.1.1.1
Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V - valid, I - invalid, N - not-found
Total Number of Routes: 1
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 172.16.0.0 0.0.0.0 0 0 i
# 显示DeviceB的路由表。
[~DeviceB] display bgp routing-table
BGP Local router ID is 2.2.2.2
Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V - valid, I - invalid, N - not-found
Total Number of Routes: 1
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 172.16.0.0 192.168.0.1 0 0 65008i
# 显示DeviceC的路由表。
[~DeviceC] display bgp routing-table
BGP Local router ID is 3.3.3.3
Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V - valid, I - invalid, N - not-found
Total Number of Routes: 1
Network NextHop MED LocPrf PrefVal Path/Ogn
i 172.16.0.0 192.168.0.1 0 100 0 65008i
从路由表可以看出，DeviceC虽然学到了AS65008中的172.16.0.0的路由，但因为下一跳192.168.0.1不可达，所以也不是有效路由。
- 配置BGP引入直连路由
# 配置DeviceB。
[~DeviceB] bgp 65009
[*DeviceB-bgp] ipv4-family unicast
[*DeviceB-bgp-af-ipv4] import-route direct
[*DeviceB-bgp-af-ipv4] commit
[~DeviceB-bgp-af-ipv4] quit
[~DeviceB-bgp] quit
# 显示DeviceA的BGP路由表。
[~DeviceA] display bgp routing-table
BGP Local router ID is 1.1.1.1
Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete RPKI validation codes: V - valid, I - invalid, N - not-found
Total Number of Routes: 8
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 2.2.2.2/32 192.168.0.2 0 0 65009?
*> 172.16.0.0 0.0.0.0 0 0 i
*> 10.1.1.0/24 192.168.0.2 0 0 65009?
*> 10.1.1.2/32 192.168.0.2 0 0 65009?
*> 10.1.3.0/24 192.168.0.2 0 0 65009?
*> 10.1.3.2/32 192.168.0.2 0 0 65009?
* 192.168.0.0 192.168.0.2 0 0 65009?
* 192.168.0.1/32 192.168.0.2 0 0 65009?
# 显示DeviceC的路由表。
[~DeviceC] display bgp routing-table
BGP Local router ID is 3.3.3.3
Status codes: * - valid, > - best, d - damped, x - best external, a - add path,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete RPKI validation codes: V - valid, I - invalid, N - not-found
Total Number of Routes: 8
Network NextHop MED LocPrf PrefVal Path/Ogn
i 2.2.2.2/32 2.2.2.2 0 100 0 ?
*>i 172.16.0.0 192.168.0.1 0 100 0 65008i
*>i 10.1.1.0/24 2.2.2.2 0 100 0 ?
*>i 10.1.1.2/32 2.2.2.2 0 100 0 ?
* i 10.1.3.0/24 2.2.2.2 0 100 0 ?
* i 10.1.3.2/32 2.2.2.2 0 100 0 ?
*>i 192.168.0.0 2.2.2.2 0 100 0 ?
*>i 192.168.0.1/32 2.2.2.2 0 100 0 ?
可以看出，到172.16.0.0的路由变为有效路由，下一跳为DeviceA的地址。
# 使用Ping进行验证。
[~DeviceC] ping 172.16.0.1
PING 172.16.0.1: 56 data bytes, press CTRL_C to break
Reply from 172.16.0.1: bytes=56 Sequence=1 ttl=254 time=31 ms
Reply from 172.16.0.1: bytes=56 Sequence=2 ttl=254 time=47 ms
Reply from 172.16.0.1: bytes=56 Sequence=3 ttl=254 time=31 ms
Reply from 172.16.0.1: bytes=56 Sequence=4 ttl=254 time=16 ms
Reply from 172.16.0.1: bytes=56 Sequence=5 ttl=254 time=31 ms
--- 172.16.0.1 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 16/31/47 ms
配置文件
DeviceA的配置文件
#
sysname DeviceA
#
interface GigabitEthernet0/1/0
undo shutdown
ip address 172.16.0.1 255.255.0.0
#
interface GigabitEthernet0/2/0
undo shutdown
ip address 192.168.0.1 255.255.255.0
#
interface LoopBack0
ip address 1.1.1.1 255.255.255.255
#
bgp 65008
router-id 1.1.1.1
peer 192.168.0.2 as-number 65009
#
ipv4-family unicast
undo synchronization
network 172.16.0.0 255.255.0.0
peer 192.168.0.2 enable
#
return
DeviceB的配置文件
sysname DeviceB
#
interface GigabitEthernet0/1/0
undo shutdown
ip address 10.1.1.1 255.255.255.0
#
interface GigabitEthernet0/2/0
undo shutdown
ip address 192.168.0.2 255.255.255.0
#
interface GigabitEthernet0/3/0
undo shutdown
ip address 10.1.3.1 255.255.255.0
#
interface LoopBack0
ip address 2.2.2.2 255.255.255.255
#
bgp 65009
router-id 2.2.2.2
peer 3.3.3.3 as-number 65009
peer 3.3.3.3 connect-interface LoopBack0
peer 4.4.4.4 as-number 65009
peer 4.4.4.4 connect-interface LoopBack0
peer 192.168.0.1 as-number 65008
#
ipv4-family unicast
undo synchronization
import-route direct
peer 3.3.3.3 enable
peer 4.4.4.4 enable
peer 192.168.0.1 enable
#
ospf 1
area 0.0.0.0
network 2.2.2.2 0.0.0.0
network 10.1.1.0 0.0.0.255
network 10.1.3.0 0.0.0.255
#
return
DeviceC的配置文件
#
sysname DeviceC
#
interface GigabitEthernet0/2/0
undo shutdown
ip address 10.1.2.1 255.255.255.0
#
interface GigabitEthernet0/3/0
undo shutdown
ip address 10.1.3.2 255.255.255.0
#
interface LoopBack0
ip address 3.3.3.3 255.255.255.255
#
bgp 65009
router-id 3.3.3.3
peer 2.2.2.2. as-number 65009
peer 2.2.2.2 connect-interface LoopBack0
peer 4.4.4.4 as-number 65009
peer 4.4.4.4 connect-interface LoopBack0
#
ipv4-family unicast
undo synchronization
peer 2.2.2.2 enable
peer 4.4.4.4 enable
#
ospf 1
area 0.0.0.0
network 3.3.3.3 0.0.0.0
network 10.1.2.0 0.0.0.255
network 10.1.3.0 0.0.0.255
#
return
DeviceD的配置文件
#
sysname DeviceD
#
interface GigabitEthernet0/1/0
undo shutdown
ip address 10.1.1.2 255.255.255.0
#
interface GigabitEthernet0/2/0
undo shutdown
ip address 10.1.2.2 255.255.255.0
#
interface LoopBack0
ip address 4.4.4.4 255.255.255.255
#
bgp 65009
router-id 4.4.4.4
peer 2.2.2.2 as-number 65009
peer 2.2.2.2 connect-interface LoopBack0
peer 3.3.3.3 as-number 65009
peer 3.3.3.3 connect-interface LoopBack0
#
ipv4-family unicast
undo synchronization
peer 2.2.2.2 enable
peer 3.3.3.3 enable
#
ospf 1
area 0.0.0.0
network 4.4.4.4 0.0.0.0
network 10.1.1.0 0.0.0.255
network 10.1.2.0 0.0.0.255
#
return
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