配置BGP负载分担
如下图所示，四台路由器配置BGP协议，要求R1通过R2与R3共同访问R4；
配置接口IP地址：
[r1]int g0/0/0
[r1-GigabitEthernet0/0/0]ip address 12.1.1.1 24
配置类似，不做阐述；
配置BGP：
[r1]bgp 1
[r1-bgp]router-id 1.1.1.1
[r1-bgp]peer 12.1.1.2 as-number 2
[r1-bgp]peer 13.1.1.2 as-number 2
[r2]bgp 2
[r2-bgp]router-id 2.2.2.2
[r2-bgp]peer 12.1.1.1 as-number 1
[r2-bgp]peer 24.1.1.2 as-number 3
[r3]bgp 2
[r3-bgp]router-id 3.3.3.3
[r3-bgp]peer 13.1.1.1 as-number 1
[r3-bgp]peer 34.1.1.2 as-number 3
[r4]bgp 3
[r4-bgp]router-id 4.4.4.4
[r4-bgp]peer 24.1.1.1 as-number 2
[r4-bgp]peer 34.1.1.1 as-number 2
配置R4引入路由信息：
[r4-bgp]ipv4-family unicast
[r4-bgp-af-ipv4]network 4.4.4.4 255.255.255.0
配置BGP负载分担：
[r1]bgp 1
[r1-bgp]ipv4-family unicast
[r1-bgp-af-ipv4]maximum load-balancing ?
INTEGER<1-8> Specify maximum equal cost routes
ebgp EBGP routes as equal cost route
ibgp IBGP routes as equal cost route
[r1-bgp-af-ipv4]maximum load-balancing 2
查看配置结果：
[r1]display bgp routing-table
BGP Local router ID is 1.1.1.1
Status codes: * - valid, > - best, d - damped,
h - history, i - internal, s - suppressed, S - Stale
Origin : i - IGP, e - EGP, ? - incomplete
Total Number of Routes: 2
Network NextHop MED LocPrf PrefVal Path/Ogn
*> 4.4.4.0/24 12.1.1.2 0 2 3i
* 13.1.1.2 0 2 3i
[r1]display ip routing-table protocol bgp
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : BGP
Destinations : 1 Routes : 2
BGP routing table status : <Active>
Destinations : 1 Routes : 2
Destination/Mask Proto Pre Cost Flags NextHop Interface
4.4.4.0/24 EBGP 255 0 D 13.1.1.2 GigabitEthernet0/0/1
EBGP 255 0 D 12.1.1.2 GigabitEthernet0/0/0
BGP routing table status : <Inactive>
Destinations : 0 Routes : 0
[r1]display bgp routing-table 4.4.4.4
BGP local router ID : 1.1.1.1
Local AS number : 1
Paths: 2 available, 1 best, 2 select
BGP routing table entry information of 4.4.4.0/24:
From: 12.1.1.2 (2.2.2.2)
Route Duration: 00h00m06s
Direct Out-interface: GigabitEthernet0/0/0
Original nexthop: 12.1.1.2
Qos information : 0x0
AS-path 2 3, origin igp, pref-val 0, valid, external, best, select, active, pre 255
Advertised to such 2 peers:
12.1.1.2
13.1.1.2
BGP routing table entry information of 4.4.4.0/24:
From: 13.1.1.2 (3.3.3.3)
Route Duration: 00h00m06s
Direct Out-interface: GigabitEthernet0/0/1
Original nexthop: 13.1.1.2
Qos information : 0x0
AS-path 2 3, origin igp, pref-val 0, valid, external, select, active, pre 255, not preferred for router ID
Not advertised to any peer yet