BGP3

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1、传播范围

2、默认值

3、值大好还是小好

8、Prefer the path through the closest iGPneighbor.

11，65，环回口

R3#show ip bgp 2.2.2.0/24

BGP routing table entry for 2.2.2.0/24, version 3

Paths: (2 available, best #2, table default)

Not advertised to any peer

1.1.1.1 (metric 65) from1.1.1.1 (1.1.1.1)

Origin IGP, metric 0, localpref 100, valid, internal

4.4.4.4 (metric 11) from4.4.4.4 (4.4.4.4)

Origin IGP, metric 0, localpref 100, valid, internal, best

R3#show ip route

Codes: L - local, C - connected, S - static, R - RIP, M -mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA -OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSAexternal type 2

E1 - OSPF external type 1, E2 - OSPF externaltype 2

i - IS-IS, su - IS-IS summary, L1 - IS-ISlevel-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U -per-user static route

o - ODR, P - periodic downloaded static route, +- replicated route

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets

O 1.1.1.1 [110/65] via 13.1.1.1, 00:33:44,Serial2/0

2.0.0.0/24 is subnetted, 1 subnets

B 2.2.2.0 [200/0] via 4.4.4.4,00:06:14

3.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C 3.3.3.0/24 is directly connected, Loopback0

L 3.3.3.3/32 is directly connected, Loopback0

4.0.0.0/32 is subnetted, 1 subnets

O 4.4.4.4 [110/11] via 34.1.1.4, 00:31:22,Ethernet0/1

13.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C 13.1.1.0/24 is directly connected,Serial2/0

L 13.1.1.3/32 is directly connected,Serial2/0

34.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C 34.1.1.0/24 is directly connected,Ethernet0/1

L 34.1.1.3/32 is directly connected,Ethernet0/1

R2再增加一条路由，9.9.9.0/24, R3 访问2.2.20/24 和9.9.9.9 从R1 上走, 默认从R4上走，人为控制选路

weight值

默认weight为32768

R2#show ip bgp

BGP table version is 1, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, >best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf WeightPath

* 2.2.2.0/24 0.0.0.0 0 32768i

* 9.9.9.0/24 0.0.0.0 0 32768i

R1#show ip bgp

BGP table version is 3, local router ID is 1.1.1.1

Status codes: s suppressed, d damped, h history, * valid, >best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf WeightPath

*> 2.2.2.0/24 12.1.1.2 0 0 2i

*> 9.9.9.0/24 12.1.1.2 0 0 2i

R3(config-router)#neighbor1.1.1.1 weight 1 //默认in方向

R3#clear ip bgp *soft

weight调为1 ，从R1上走

2.2.2.0/24从r1走，9.9.9.0/24从r4走

R3上的配置

ip prefix-list 2 seq 5 permit 2.2.2.0/24

route-map W permit 10

match ip address prefix-list 2

set weight 3

route-map W permit 20

router bgp 1

no synchronization

bgp router-id 3.3.3.3

bgp log-neighbor-changes

neighbor 1.1.1.1 remote-as 1

neighbor 1.1.1.1 update-sourceLoopback0

neighbor 1.1.1.1route-map W in

neighbor 4.4.4.4 remote-as 1

neighbor 4.4.4.4 update-sourceLoopback0

no auto-summary

结果

Weight Attribute(CiscoOnly)

Local PreferenceAttribute

Path with highest localpreference value are preferred:

Local preference is used to advertise to IBGP neighbors abouthow to leave their AS.
The local preference is sent to IBGP neighbors only (that is,within the AS only).
The local preference attribute is well-known anddiscretionary.
Default value is 100

默认路由从R4上走，通过设置R1的local preference attribute，使路由从r1上走

R1(config-router)#bgp default local-preference 111

R3#show ip bgp 2.2.2.0/24

BGP routing table entry for 2.2.2.0/24, version 4

Paths: (2 available, best #1, table default)

Not advertised to any peer

1.1.1.1 (metric 65) from1.1.1.1 (1.1.1.1)

Origin IGP, metric 0, localpref 111,valid, internal, best

4.4.4.4 (metric 11) from4.4.4.4 (4.4.4.4)

Origin IGP, metric 0, localpref 100, valid, internal

1、network ???

2、ebgp ???

3、IGBP ???

4、agg ??

做路由分担，2.2.2.0/24从r1上走，9.9.9.0/24从r4上走

R1 上配置

R3访问2.2.2.0/24 网络通过r1,设置As path来实现

从出方向设置，R2发给R42.2.2..0/24path增加，

set as-path prepend 6 78

neighbor 24.1.1.4 route-map AS out

当R2把这条路由发出去之前，已经有了 6 7 8 AS号

IN方向

人为修改AS PATH弊端

容易造成EBGP环路。

prepend 自己的AS号

MEDAttribute

The path with the lowest MED(also called the metric) value are the most desirable

-MED is used t advertise toEBGP neighbors how to exit their AS to reach networks owned by thisAS.

The MED attribute is optionaland nontransitive.

通过设置MED属性，使R2去8.8.8.0/24,通过R4走。

R1上通过设置MED属性大于0，则可以使远端EBGP R2 去往8.8.8.0/24通过r4走

设置之前

设置之后

R1#debug ip bgp updates

最常用的这两个

local preference

MED

由于水平分割的问题，在IBGP中，R1发给R3的路由，R3,不会发给R4,如下图。

解决IBGP的水平分割：

1、路由反射器

2、联邦

router bgp 64512

no synchronization

bgp router-id 1.1.1.1

bgp log-neighbor-changes

bgp confederationidentifier 1

neighbor 3.3.3.3remote-as 64512

neighbor 3.3.3.3update-source Loopback0

neighbor 3.3.3.3next-hop-self

neighbor 12.1.1.2 remote-as 2

no auto-summary

router bgp 64512

no synchronization

bgp router-id 3.3.3.3

bgp log-neighbor-changes

bgp confederationidentifier 1

bgp confederationpeers 64513

neighbor 1.1.1.1remote-as 64512

neighbor 1.1.1.1 update-sourceLoopback0

neighbor 4.4.4.4 remote-as 64513

neighbor 4.4.4.4ebgp-multihop 255

neighbor 4.4.4.4 update-sourceLoopback0

no auto-summary

router bgp 64513

no synchronization

bgp router-id 4.4.4.4

bgp log-neighbor-changes

bgp confederationidentifier 1

bgp confederationpeers 64512

neighbor 3.3.3.3remote-as 64512

neighbor 3.3.3.3ebgp-multihop 255

neighbor 3.3.3.3 update-sourceLoopback0

no auto-summary

R4#show ip route bgp

Codes: L - local, C - connected, S - static, R - RIP, M -mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA -OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSAexternal type 2

E1 - OSPF external type 1, E2 - OSPF externaltype 2

i - IS-IS, su - IS-IS summary, L1 - IS-ISlevel-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U -per-user static route

o - ODR, P - periodic downloaded static route, +- replicated route

Gateway of last resort is not set

2.0.0.0/24 is subnetted, 1 subnets

B 2.2.2.0 [200/0] via 1.1.1.1, 00:03:54

R4#show ip bgp 2.2.2.2/24

BGP routing table entry for 2.2.2.0/24, version 2

Paths: (1 available, best #1, table default)

Not advertised to any peer

(64512) 2

1.1.1.1 (metric 75) from3.3.3.3 (3.3.3.3)

Origin IGP, metric 0, localpref 100, valid, confed-external, best

R4#show ip bgp

BGP table version is 2, local router ID is 4.4.4.4

Status codes: s suppressed, d damped, h history, * valid, >best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf WeightPath

*> 2.2.2.0/24 1.1.1.1 0 100 0(64512) 2 i

_____________________________________________________________________________________

社团属性:community

可选：路由器可能不识别此属性.(default)

neighbor x.x.x.x. send-community

传递;些属性只在nei的邻居有效

neighbor x.x.x.x send-community

route-map COM permit 10

set community no-advertise

router bgp 2

no synchronization

bgp router-id 2.2.2.2

bgp log-neighbor-changes

network 2.2.2.0 mask 255.255.255.0

neighbor 12.1.1.1 remote-as 1

neighbor 12.1.1.1 send-community

neighbor 12.1.1.1route-map COM out

neighbor 24.1.1.4 remote-as 1

neighbor 24.1.1.4 route-map AS out

no auto-summary

R1#show ip bgp 2.2.2.2/24

BGP routing table entry for 2.2.2.0/24, version 3

Paths: (1 available, best #1, table default, not advertised toany peer)

Not advertised to any peer

12.1.1.2 from 12.1.1.2(2.2.2.2)

Origin IGP, metric 0, localpref 100, valid, external, best

Community: no-advertise

no-advertise , 携带此属性的路由不会通知给任何给BGP邻居。

no-export:携带此属性的路由不会传出大AS

local-AS:携带此属性的路由不会传出小AS.

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