4.2 优选local preference值更高路由

local preference值缺省为100(从IBGP学习)和0(从EBGP学习),local preference只在AS内部传递,不能传递给EBGP,local preference值越大越优先。

图片[1]-4.2 优选local preference值更高路由-大赛人网
图4-2  BGP优选local preference值更高路由网络拓扑

1.R1配置OSPF

[R1]ospf 1 router-id 1.1.1.1
[R1-ospf-1]area 0
[R1-ospf-1-area-0.0.0.0]network 1.1.1.1 0.0.0.0
[R1-ospf-1-area-0.0.0.0]network 12.1.1.0 0.255.255.255

2.R2配置OSPF

[R2]ospf 1 router-id 2.2.2.2
[R2-ospf-1]area 0
[R2-ospf-1-area-0.0.0.0]network 2.2.2.2 0.0.0.0
[R2-ospf-1-area-0.0.0.0]network 12.1.1.0 0.255.255.255

3.R1配置IBGP、EBGP

[R1]bgp 12
[R1-bgp]router-id 1.1.1.1
[R1-bgp]peer 2.2.2.2 as-number 12
[R1-bgp]peer 2.2.2.2 connect-interface LoopBack 0
[R1-bgp]peer 2.2.2.2 next-hop-local
[R1-bgp]peer 13.1.1.3 as-number 300

4.R2配置IBGP、EBGP

[R2]bgp 12
[R2-bgp]router-id 2.2.2.2 
[R2-bgp]peer 1.1.1.1 as-number 12
[R2-bgp]peer 1.1.1.1 connect-interface LoopBack 0
[R2-bgp]peer 1.1.1.1 next-hop-local
[R2-bgp]peer 23.1.1.3 as-number 300

5.R3配置EBGP,宣告3.3.3.3/32到BGP

[R3]bgp 300
[R3-bgp]router-id 3.3.3.3
[R3-bgp]peer 13.1.1.1 as-number 12
[R3-bgp]peer 23.1.1.2 as-number 12
[R3-bgp]network 3.3.3.3 32

6.R1查看BGP路由信息,AR2对应LocPrf为100,AR2对应LocPrf为0(EBGP学习到条目不带local preference值)

<R1>display bgp routing-table 
 Total Number of Routes: 2
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn

 *>   3.3.3.3/32         13.1.1.3        0                     0      300i
 * i                     2.2.2.2         0          100        0      300i

7.R1查看BGP路由信息(3.3.3.3/32),从R3学习

<R1>display bgp routing-table 3.3.3.3
 BGP local router ID : 1.1.1.1
 Local AS number : 12
 Paths:   2 available, 1 best, 1 select
 BGP routing table entry information of 3.3.3.3/32:
 From: 13.1.1.3 (3.3.3.3)
 Route Duration: 00h38m12s  
 Direct Out-interface: GigabitEthernet0/0/2
 Original nexthop: 13.1.1.3
 Qos information : 0x0
 AS-path 300, origin igp, MED 0, pref-val 0, valid, external, best, select, active, pre 255
 Advertised to such 1 peers:
    2.2.2.2
 BGP routing table entry information of 3.3.3.3/32:
 From: 2.2.2.2 (2.2.2.2)
 Route Duration: 00h25m18s  
 Relay IP Nexthop: 12.1.1.2
 Relay IP Out-Interface: GigabitEthernet0/0/0
 Original nexthop: 2.2.2.2
 Qos information : 0x0
 AS-path 300, origin igp, MED 0, localpref 100, pref-val 0, valid, internal, pre 255, IGP cost 1, not preferred for peer type
 Not advertised to any peer yet

8.使用策略方法修改local preference值

[R1]ip ip-prefix dsrw.com permit 3.3.3.3 32
[R1]route-policy dsrw permit node 10
[R1-route-policy]if-match ip-prefix dsrw.com
[R1-route-policy]apply local-preference 200
[R1-route-policy]quit
[R1]route-policy dsrw permit node 20
[R1]bgp 12
[R1-bgp]peer 2.2.2.2 route-policy dsrw import 

9.查看BGP路由信息

<R1>refresh bgp all import 
<R1>display bgp routing-table 
 *>i  3.3.3.3/32         2.2.2.2         0          200        0      300i
 *                       13.1.1.3        0                     0      300i

<R1>display bgp routing-table 3.3.3.3

 BGP local router ID : 1.1.1.1
 Local AS number : 12
 Paths:   2 available, 1 best, 1 select
 BGP routing table entry information of 3.3.3.3/32:
 From: 2.2.2.2 (2.2.2.2)
 Route Duration: 00h00m30s  
 Relay IP Nexthop: 12.1.1.2
 Relay IP Out-Interface: GigabitEthernet0/0/0
 Original nexthop: 2.2.2.2
 Qos information : 0x0
 AS-path 300, origin igp, MED 0, localpref 200, pref-val 0, valid, internal, best, select, active, pre 255, IGP cost 1
 Advertised to such 1 peers:
    13.1.1.3
 BGP routing table entry information of 3.3.3.3/32:
 From: 13.1.1.3 (3.3.3.3)
 Route Duration: 00h00m30s  
 Direct Out-interface: GigabitEthernet0/0/2
 Original nexthop: 13.1.1.3
 Qos information : 0x0
 AS-path 300, origin igp, MED 0, pref-val 0, valid, external, pre 255, not preferred for Local_Pref
 Not advertised to any peer yet

10.删除使用策略方法修改local preference值方法

[R1]bgp 12
[R1-bgp]undo peer 2.2.2.2 route-policy dsrw import
[R1]undo route-policy dsrw               
[R1]undo ip ip-prefix dsrw.com
//删除使用策略方法修改local preference值方法

11.使用直接修改local preference值方法,查看BGP路由,没有从R2学习到路由

[R1]bgp 12
[R1-bgp]default local-preference 300
[R1]display bgp routing-table   
 *>   3.3.3.3/32         13.1.1.3        0                     0      300i

12.查看R2的BGP路由表,R2从R1学习到了3.3.3.3/32路由,没有再回传给R1

<R2>display bgp routing-table 
 *>i  3.3.3.3/32         1.1.1.1         0          300        0      300i
 *                       23.1.1.3        0                     0      300i
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