高級路由技術原理-bgp選路原則詳解

BGP路由選路原則詳解技術培訓中心修訂記錄修訂日期修訂版本修訂描述作者2009-09-27V1.0初稿完成。巖學習目標掌握BGP十三條選路原則的原理熟練掌握常見的BGP路由選路原則BGP路由選路原則Weight屬性Local

Preference屬性本地路由始發(fā)方式AS-Path長度Origin屬性6.MED屬性EBGP優(yōu)于IBGP到達Next-hop的代價執(zhí)行等價負載均衡EBGP路由接收的順序路由的Router-ID12.Cluster-list長度13.配置的BGP

Peer指定地址第一條:Weight屬性比較原則及配置注意事項:Cisco私有,可通過關聯(lián)Route-map方式進行配置,該值無法傳遞給其他BGPPeer,只能在本地使用.攜帶的Weight值越大,則該路由越優(yōu)先.本地始發(fā)路由的默認值是32768,從其他BGP

Peer學習過來的路由的默認值是0雖然Weight屬性是Cisco私有的,但是很多廠商也是內置該屬性(但無法顯示及修改),這樣就保證了本地始發(fā)的路由是最優(yōu)先的,因為本地始發(fā)路由的”Weight”為32768,從其他

BGP

Peer學習過來的路由的”Weight”為0.第一條:Weight屬性實驗驗證R2、R3分別通告10.0.0.0給R1R1將10.0.0.0使用network方式引入BGP10.0.0.0/810.0.0.0/810.0.0.0/8AS

1AS

2R3R1R2IBGPEBGP第一條:Weight屬性實驗驗證R1的BGP表r1#sh

ip

bgpBGP

table

version

is

2,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*i10.0.0.09.9.13.301000i*9.9.12.2002i*>0.0.0.0032768i第一條:Weight屬性實驗驗證R1對BGP

Peer應用不同的Route-map修改所學習路由的

Weight值10.0.0.0/810.0.0.0/810.0.0.0/8AS

1AS

2R3R1R2IBGPEBGProuter

bgp

1

---R1的路由策略neighbor

9.9.12.2

route-map

FROM_R2

inroute-map

FROM_R2

permit

10set

weight

65535第一條:Weight屬性實驗驗證R1的BGP表選路結果r1#sh

ip

bgpBGP

table

version

is

7,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Pathri10.0.0.09.9.13.301000ir>9.9.12.20655352

ir0.0.0.0032768iBGP路由選路原則Weight屬性Local

Preference屬性本地路由始發(fā)方式AS-Path長度Origin屬性6.MED屬性EBGP優(yōu)于IBGP到達Next-hop的代價執(zhí)行等價負載均衡EBGP路由接收的順序路由的Router-ID12.Cluster-list長度13.配置的BGP

Peer指定地址第二條:Local

Preference屬性比較原則及配置注意事項:值越大,越優(yōu)先默認情況下,本地始發(fā)的路由的LP為100,從EBGP

Peer接收的路由的LP為100.Local

Preference屬性只能在IBGP

Peer之間傳遞,不能在

EBGP

Peer之間傳遞,如果在EBGP

Peer之間收到的路由的路徑屬性中攜帶了LocalPreference,則會觸發(fā)Notifacation報文,造成會話中斷第二條:Local

Preference屬性比較原則及配置注意事項:Local

Preference通過如下三種方法進行設置:通過將IGP路由引入BGP時關聯(lián)Route-map進行設置針對IBGPPeer應用IN/OUT方向的Route-map,對從Peer接收到的或者通告給Peer的所有或部分路由進行設置針對EBGPPeer應用IN方向的Route-map,對從Peer接收到的所有或部分路由進行設置Local

Preference為BGP選路策略中經常使用的一個路徑屬性第二條:Local

Preference屬性實驗一:Local

Prefenerce無法在EBGP

Peer之間傳遞R1R2AS

1AS

210.0.0.0/8EBGProuter

bgp

2network

10.0.0.0neighbor

9.9.12.1

remote-as

1neighbor

9.9.12.1

route-map

TO_R1

out!route-map

TO_R1

permit

10set

local-preference

500第二條:Local

Preference屬性實驗一:Local

Prefenerce無法在EBGP

Peer之間傳遞查看本地始發(fā)的BGP路由的LP值r2#show

ip

bgpBGP

table

version

is

2,

local

router

ID

is

9.9.0.2Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,rRIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork*>

10.0.0.0iNext

Hop Metric

LocPrf

Weight

Path0.0.0.0

0

空值?

32768r2#sh

ip

b

10.0.0.0BGP

routing

table

entry

for

10.0.0.0/8,

version2Paths:

(1

available,

best

#1,

table

Default-IP-Routing-Table)Advertised

to

non

peer-group

peers:9.9.12.1Local0.0.0.0

from

0.0.0.0

(9.9.0.2)Origin

IGP,

metric

0,

localpref

100,

weight

32768,

valid,

sourced,

local,

best第二條:Local

Preference屬性實驗一:Local

Prefenerce無法在EBGP

Peer之間傳遞R2通告給R1的BGP路由是否攜帶LP?r1#sh

ip

bgpBGP

table

version

is

2,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork*>

10.0.0.0Next

Hop Metric

LocPrf

Weight

Path9.9.12.2

0

0

2

i500沒有傳遞?r2#sh

ip

bgp

neighbors

9.9.12.1

advertised-routesBGP

table

version

is

2,

local

router

ID

is

9.9.0.2Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork*>

10.0.0.0Next

Hop Metric

LocPrf

Weight

Path0.0.0.0

0 32768

i第二條:Local

Preference屬性實驗一:Local

Prefenerce無法在EBGP

Peer之間傳遞R2通告給R1的BGP

Update報文R2通告的10.0.0.0/8前綴的路徑屬性中不包含Local

Preference屬性第二條:Local

Preference屬性實驗二:修改本地始發(fā)路由的默認LP值R1R210.0.0.0/8AS

1IBGProuter

bgp

1---R2的路由策略

bgp

default

local-preference

500network

10.0.0.0neighbor

9.9.12.1

remote-as

1第二條:Local

Preference屬性實驗二:修改本地始發(fā)路由的默認LP值r2#sh

ip

bBGP

table

version

is

2,

local

router

ID

is

10.0.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork*>

10.0.0.0NextHop Metric

LocPrf

Weight

Path0.0.0.0

0

空值?

32768

ir2#sh

ip

b

10.0.0.0BGP

routing

table

entry

for

10.0.0.0/8,

version2Paths:

(1

available,

best

#1,

table

Default-IP-Routing-Table)Advertised

to

non

peer-group

peers:9.9.12.1Local0.0.0.0

from

0.0.0.0

(10.0.0.1)Origin

IGP,

metric

0,

localpref

500,

weight

32768,

valid,

sourced,

local,

best第二條:Local

Preference屬性實驗二:修改本地始發(fā)路由的默認LP值r1#sh

ip

bBGP

table

version

is

4,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork*>i10.0.0.0NextHop Metric

LocPrf

Weight

Path9.9.12.2

0

500 0

i第二條:Local

Preference屬性實驗三:將IGP中的路由引入BGP時關聯(lián)Route-map設置LPR1R2AS

110.0.0.0/8IBGProuter

bgp

1---R2的路由策略network

10.0.0.0

route-map

SET_LPneighbor

9.9.12.1

remote-as

1!route-map

SET_LP

permit

10set

local-preference

400第二條:Local

Preference屬性實驗三:將IGP中的路由引入BGP時關聯(lián)Route-map設置LPr2#sh

ip

bBGP

table

version

is

3,

local

router

ID

is

10.0.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetworkNextHopMetric

LocPrf

WeightPath*>

10.0.0.00.0.0.00 400

32768ir1#sh

ip

bBGP

table

version

is

6,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork*>i10.0.0.0Next

Hop Metric

LocPrf

Weight

Path9.9.12.2

0

400

0i第二條:Local

Preference屬性實驗四:對IBGP

Peer應用IN/OUT方向Route-mapR3單向

R6的數(shù)據(jù)流需求R1\R2對R3應用OUT方向Route-mapR1R2AS

1R3R4R5AS

2R6以該方式部署策略,對數(shù)據(jù)流控制的作用范圍10.0.0.0/811.0.0.0/8EBGP第二條:Local

Preference屬性實驗四:對IBGP

Peer應用IN/OUT方向Route-mapR4、R5正常通告R6的路由，R1、R2的BGP表R1R2AS

1R3R4R5AS

2R610.0.0.0/811.0.0.0/8EBGPr1#sh

ip

bgpNetwork Next

Hop Metric

LocPrf

Weight

Pathr2#sh

ip

bgpNetwork Next

Hop

Metric

LocPrf

Weight

Path*

10.0.0.09.9.15.502

i*

10.0.0.09.9.25.502

i*>9.9.14.402

i*>9.9.24.402

i*

11.0.0.09.9.15.502

i*

11.0.09.9.25.502

i*>9.9.14.402

i*>9.9.24.402

i第二條:Local

Preference屬性實驗四:對IBGP

Peer應用IN/OUT方向Route-mapR1、R2的路由策略router

bgp

1

-----R1的路由策略neighbor

9.9.13.3

route-map

TO_R3

outaccess-list

1

permit

10.0.0.0access-list

2

permit

11.0.0.0route-map

TO_R3

permit

10match

ip

address

1set

local-preference

500route-map

TO_R3

permit

20match

ip

address

2set

local-preference

400router

bgp

1----R2的路由策略neighbor

9.9.23.3

route-map

TO_R3

outaccess-list

1

permit

10.0.0.0access-list

2

permit

11.0.0.0route-map

TO_R3

permit

10match

ip

address

1set

local-preference

400route-map

TO_R3

permit

20match

ip

address

2set

local-preference

500R2AS

1R3R1

R4R5AS

2R610.0.0.0/811.0.0.0/8EBGP第二條:Local

Preference屬性實驗四:對IBGP

Peer應用IN/OUT方向Route-mapR3的路由選路結果r3#sh

ip

bBGP

table

version

is

6,

local

router

ID

is

9.9.0.3Status

codes:

s

suppressed,

d

damped,

h

history,

*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*i10.0.0.09.9.23.2040002

i*>i9.9.13.1050002

i*>i11.0.0.09.9.23.2050002

i*

i9.9.13.1040002

iR2AS

1R3R1

R4R5AS

2R610.0.0.0/811.0.0.0/8EBGP第二條:Local

Preference屬性實驗四:對IBGP

Peer應用IN/OUT方向Route-map路由策略結果：R3到R6的實際單向數(shù)據(jù)流R1R2AS

1R3R4R5AS

2R610.0.0.0/811.0.0.0/8EBGP以該方式部署策略,對數(shù)據(jù)流控制的作用范圍第二條:Local

Preference屬性實驗五:對EBGP

Peer應用IN方向Route-mapR3單向

R6的數(shù)據(jù)流需求R1\R2分別對R4\R5應用OUT方向的Route-mapR1R2AS

1R3R4R5AS

2R6以該方式部署策略,對數(shù)據(jù)流控制的作用范圍10.0.0.0/811.0.0.0/8EBGP第二條:Local

Preference屬性實驗五:對EBGP

Peer應用IN方向Route-mapR1、R2的路由策略router

bgp

1---R1的路由策略neighbor

9.9.14.4

route-map

FROM_R4

inaccess-list

1

permit

10.0.0.0route-map

FROM_R4

permit

10match

ip

address

1set

local-preference

500route-map

FROM_R4

permit

20router

bgp

1---R2的路由策略neighbor

9.9.25.5

route-map

FROM_R5

inaccess-list

2

permit

11.0.0.0route-map

FROM_R5

permit

10match

ip

address

2set

local-preference

500route-map

FROM_R5

permit

20R1R2AS

1R3R4R5AS

2R610.0.0.0/811.0.0.0/8EBGP第二條:Local

Preference屬性實驗五:對EBGP

Peer應用IN方向Route-mapR1、R2的BGP表r1#sh

ip

bgpNetwork Next

Hop

Metric

LocPrf

Weight

Pathr2#sh

ip

bgpNetwork

Next

Hop

Metric

LocPrf

Weight

Path*

10.0.0.09.9.15.502

i*

10.0.0.09.9.25.502

i*>9.9.14.450002

i*>9.9.24.402

i*

11.0.0.09.9.14.402

i*>

11.0.0.09.9.25.550002

i*>9.9.15.502

i*9.9.24.402

iR1R2AS

1R3R4R5AS

2R610.0.0.0/811.0.0.0/8EBGP第二條:Local

Preference屬性實驗五:對EBGP

Peer應用IN方向Route-mapR3的BGP表r3#sh

ip

bgpBGP

table

version

is

10,

local

router

ID

is

9.9.0.3Status

codes:

s

suppressed,

d

damped,

h

history,

*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*i10.0.0.09.9.23.2010002

i*>i9.9.13.1050002

i*>i11.0.0.09.9.23.2050002

i*

i9.9.13.1010002

iR2AS

1R3R1

R4R5AS

2R610.0.0.0/811.0.0.0/8EBGP第二條:Local

Preference屬性實驗五:對EBGP

Peer應用IN方向Route-map路由策略結果：R3到R6的實際單向數(shù)據(jù)流R1R2AS

1R3R4R5AS

2R610.0.0.0/811.0.0.0/8以該方式部署策略,對數(shù)據(jù)流控制的作用范圍BGP路由選路原則Weight屬性Local

Preference屬性本地路由始發(fā)方式AS-Path長度Origin屬性6.MED屬性EBGP優(yōu)于IBGP到達Next-hop的代價執(zhí)行等價負載均衡EBGP路由接收的順序路由的Router-ID12.Cluster-list長度13.配置的BGP

Peer指定地址第三條:本地路由始發(fā)方式比較原則及配置注意事項該比較原則主要是指本地在進入一條IGP路由進去BGP表時，使用不同的方式比如network或redistribute等，那么這些方式之間是存在優(yōu)先順序的：network>redistribute>aggregate注意，該原則是不會作為BGP路由選路策略的第三條:本地路由始發(fā)方式實驗驗證本地分別以3種方式引入一條路由，如下配置所示interface

Loopback1ip

address

3.3.3.3

255.255.255.255router

bgp

1network

3.3.3.3

mask

255.255.255.255

route-map

Aaggregate-address

3.3.3.3

255.255.255.255

attribute-map

Credistribute

connected

route-map

Broute-map

A

permit

10set

local-preference

200route-map

B

permit

10set

local-preference

300route-map

C

permit

10set

local-preference

400第三條:本地路由始發(fā)方式實驗驗證本地BGP表中的顯示，network方式為第一選擇r3#sh

ip

bgpBGP

table

version

is

13,

local

router

ID

is

9.9.0.3Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,rRIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork*>

3.3.3.3/32Next

Hop Metric

LocPrf

Weight

Path0.0.0.0

0

200

32768i第三條:本地路由始發(fā)方式實驗驗證將network

3.3.3.3

mask

255.255.255.255刪除redistribute方式成為優(yōu)選r3#sh

ip

bBGP

table

version

is

14,

local

router

ID

is

9.9.0.3Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork*>3.3.3.3/32Next

Hop Metric

LocPrf

Weight

Path0.0.0.0

0

300

32768?BGP路由選路原則Weight屬性Local

Preference屬性本地路由始發(fā)方式AS-Path長度Origin屬性6.MED屬性EBGP優(yōu)于IBGP到達Next-hop的代價執(zhí)行等價負載均衡EBGP路由接收的順序路由的Router-ID12.Cluster-list長度13.配置的BGP

Peer指定地址第四條:AS-Path長度比較原則及配置注意事項優(yōu)選長度小的AS-Path列表其他AS-Path比較原則：在做聚合路由時，使用as-set后產生的AS-Path列表中的{}里的AS號長度只算一個AS號的長度在內的AS-Path列表中的()的AS號長度不做計算依據(jù)當向EBGP

Peer

通告路由時，將自己的AS號加在AS-Path列表的最左端，向IBGP

Peer通告路由時，不會對AS-Path列表做任何修改第四條:AS-Path長度比較原則及配置注意事項修改AS-Path列表的方法：可以通過對EBGP

Peer使用IN/OUT方向的Route-map，使用setas-path

prepend命令來添加AS號。注意，上述操作只能對EBGPPeer，對IBGP

Peer無法生效?？梢栽贐GP進程下使用bgpbestpathas-pathignore命令來跳過AS-Path的長度比較修改AS-Path長度可作為BGP選路策略的一種。第四條:AS-Path長度實驗一：使用OUT方向的Route-map來修改AS-PathR3

R4的單向數(shù)據(jù)流需求R1R3R4AS1AS210.0.0.0/8R2以該方式部署策略,對數(shù)據(jù)流控制的作用范圍第四條:AS-Path長度實驗一：使用OUT方向的Route-map來修改AS-PathR1、R2的路由策略(R1保持默認)router

bgp

2----R2的路由策略neighbor

9.9.23.3

route-map

TO_R3

outroute-map

TO_R3

permit

10set

as-path

prepend

5

5

5R1R2R3AS1AS2R410.0.0.0/8第四條:AS-Path長度實驗一：使用OUT方向的Route-map來修改AS-PathR3的BGP表選路結果r3#sh

ip

bBGP

table

version

is

2,

local

router

ID

is

9.9.0.3Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetworkNext

HopMetric

LocPrf

Weight

Path*

10.0.0.09.9.23.20 2

5

5

5

i*>9.9.13.10

2

i第四條:AS-Path長度實驗二：使用IN方向的Route-map來修改AS-PathR3

R4的單向數(shù)據(jù)流需求R1R3R4AS1AS210.0.0.0/8R2以該方式部署策略,對數(shù)據(jù)流控制的作用范圍第四條:AS-Path長度實驗二：使用IN方向的Route-map來修改AS-PathR3的路由策略router

bgp

1---R3的路由策略neighbor

9.9.23.2

route-map

FROM_R2

inroute-map

FROM_R2

permit

10set

as-path

prepend

5

5

5R1R2R3AS1AS2R410.0.0.0/8第四條:AS-Path長度實驗二：使用IN方向的Route-map來修改AS-PathR3的BGP表選路結果r3#sh

ip

bgpBGP

table

version

is

2,

local

router

ID

is

9.9.0.3Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,rRIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetworkNext

HopMetric

LocPrf

Weight

Path*

10.0.0.09.9.23.20

5

5

5

2

i*>9.9.13.10

2

i不同方向的route-map對于的AS號的位置是不同的BGP路由選路原則Weight屬性Local

Preference屬性本地路由始發(fā)方式AS-Path長度Origin屬性6.MED屬性EBGP優(yōu)于IBGP到達Next-hop的代價執(zhí)行等價負載均衡EBGP路由接收的順序路由的Router-ID12.Cluster-list長度13.配置的BGP

Peer指定地址第五條:Origin屬性比較原則及配置注意事項三種不同的Origin屬性的優(yōu)先順序:IGP>EGP>Origin屬性會一直在BGP路由中攜帶Origin屬性配置方法：–將IGP路由引入BGP時關聯(lián)Route-map進行設置plete默認情況下，network方式產生的BGP路由的Origin屬性為IGP，而redistribute方式產生的BGP路由的Origin屬性為“？”–對BGP

Peer應用IN/OUT方向的Route-map進行設置很少使用設置Origin屬性作為BGP路由選路策略第五條:Origin屬性實驗1：設置Origin屬性R1\R2\R3分別以network方式引入路由，R1\R3關聯(lián)不同的Route-map設置不同的Origin屬性11.0.0.0/813.0.0.0/812.0.0.0/8AS

1AS

2R3R1R2IBGPEBGProuter

bgp

1---R3的路由策略network

13.0.0.0

route-map

SET_Originroute-map

SET_Origin

permit

10set

origin

pleterouter

bgp

1---R1的路由策略network

11.0.0.0

route-map

SET_Originroute-map

SET_Origin

permit

10set

origin

egp第五條:Origin屬性實驗1：設置Origin屬性R1的BGP表r1#

sh

ipbgpBGP

table

version

is

4,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*>

11.0.0.00.0.0.0032768e*>

12.0.0.09.9.12.2002

i*>i13.0.0.09.9.13.301000?第五條:Origin屬性實驗1：設置Origin屬性R1對R3應用IN方向的Route-map修改Origin屬性，R2對R1使用OUT方向的Route-map修改Origin屬性11.0.0.0/813.0.0.0/812.0.0.0/8AS

1AS

2R3R1R2IBGPEBGProuter

bgp

1---R1的路由策略neighbor

9.9.13.3

route-map

FROM_R3

inroute-map

FROM_R3

permit

10set

origin

igprouter

bgp

2---R2的路由策略neighbor

9.9.12.1

route-map

TO_R1

outroute-map

TO_R1

permit

10set

origin

plete第五條:Origin屬性實驗1：設置Origin屬性R1的BGP表r1#sh

ip

bgpBGP

table

version

is

6,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*>

11.0.0.00.0.0.0032768e*>

12.0.0.09.9.12.2002?*>i13.0.0.09.9.13.301000i第五條:Origin屬性10.0.0.0/810.0.0.0/8實驗2：不同Origin屬性之間的優(yōu)先順序AS

1R3R1R2IBGPIBGPR410.0.0.0/8IBGProuter

bgp

1---R3的路由策略network

10.0.0.0

route-map

SET_Originroute-map

SET_Origin

permit

10set

origin

pleteR2僅使用network方式引入10.0.0.0router

bgp

1---R4的路由策略network

10.0.0.0

route-map

SET_Originroute-map

SET_Origin

permit

10set

origin

egp第五條:Origin屬性實驗2：不同Origin屬性之間的優(yōu)先順序R1的BGP表路由選路結果r1#sh

ip

bgpBGP

table

version

is

2,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,rRIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*i10.0.0.09.9.14.401000e*

i9.9.13.301000?*>i9.9.12.201000i第五條:Origin屬性實驗2：不同Origin屬性之間的優(yōu)先順序斷開R1與R2的連接,R1的BGP表路由選路結果r1#sh

ip

bBGP

table

version

is

3,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*i10.0.0.09.9.14.401000e*>i9.9.13.301000?BGP路由選路原則Weight屬性Local

Preference屬性本地路由始發(fā)方式AS-Path長度Origin屬性6.MED屬性EBGP優(yōu)于IBGP到達Next-hop的代價執(zhí)行等價負載均衡EBGP路由接收的順序路由的Router-ID12.Cluster-list長度13.配置的BGP

Peer指定地址第六條:MED屬性比較原則及配置注意事項MED值越小,越優(yōu)先.默認情況下，只比較來自同一鄰居AS的BGP路由的MED值MED設置方法:將IGP路由引入BGP時關聯(lián)Route-map進行設置對BGP

Peer應用IN/OUT方向的Route-map進行設置非Route-map(自動)方式:使用network或redistribute方式將IGP路由引入BGP時,MED將繼承IGP路由的Metric(直聯(lián)路由的Metric為0)使用aggregate-address方式引入路由,則MED為空第六條:MED屬性比較原則及配置注意事項本地在將一條BGP路由通告給EBGP

Peer時,是否攜帶MED值,需要根據(jù)以下條件進行判斷(不對EBGP

Peer使用Route-map):如果該BGP路由是本地始發(fā)(network或redistribute)的,則攜帶MED值發(fā)送給EBGPPeer(如果MED為空,則設置為0)如果該BGP路由是從其他BGPPeer學習過來的，那么將該路由通告給EBGPPeer時不攜帶MED本地在將一條BGP路由通告給IBGP

Peer時，一定會攜帶

MED值如果接收或產生的路由的MED為空,那么在向IBGP

Peer通告時,將MED設置為0第六條:MED屬性比較原則及配置注意事項其他MED相關配置命令(BGP進程下):bgp

pare-medbgp

bestpath

med

missing-as-worstbgp

deterministic-medbgp

bestpath

med

confedMED為BGP選路策略中經常使用的一個路徑屬性第六條:MED屬性11.0.0.0/812.0.0.0/8實驗1:MED繼承IGP的MetricR1使用network方式將11.0.0.0引入BGP,使用redistribute方式將12.0.0.0引入BGPAS

1R3R1R2IBGPOSPFCost100router

bgp

1---R1的路由策略network

11.0.0.0redistribute

ospf

1第六條:MED屬性實驗1:MED繼承IGP的MetricR1的路由表R1的BGP表r1#sh

ip

ro…9.0.0.0/8

is

variably

subnetted,

3

subnets,

2

masksC

9.9.0.1/32

is

directly

connected,

Loopback0C

9.9.12.0/24

is

directly

connected,

FastEthernet0/0.12C

9.9.13.0/24

is

directly

connected,

FastEthernet0/0.13C

11.0.0.0/8

is

directly

connected,

Loopback1O

12.0.0.0/8

[110/101]

via

9.9.12.2,

00:01:59,

FastEthernet0/0.12r1#sh

ip

bgpBGP

table

version

is

4,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*>

9.9.12.0/240.0.0.0032768?*>

11.0.0.00.0.0.0032768i*>

12.0.0.09.9.12.210132768?第六條:MED屬性實驗2:MED屬性的傳遞范圍R2\R3分別使用network方式引入直連路由進入BGP,并關聯(lián)Route-map,將MED設置為10013.0.0.0/812.0.0.0/8AS

1AS

2R3R1R2IBGPEBGProuter

bgp

1---R3的路由策略

network

13.0.0.0

route-map

SET_MEDroute-map

SET_MED

permit

10set

metric

100router

bgp

2---R2的路由策略

network

12.0.0.0

route-map

SET_MEDroute-map

SET_MED

permit

10set

metric

100R4IBGP第六條:MED屬性實驗2:MED屬性的傳遞范圍R3的BGP表R1的BGP表R2的BGP表r3#sh

ip

bgp…NetworkNext

HopMetric

LocPrf

Weight

Path*i12.0.0.09.9.12.210010002

i*>

13.0.0.00.0.0.010032768ir1#sh

ip

bgp…NetworkNext

HopMetric

LocPrf

Weight

Path*>

12.0.0.09.9.12.210002

i*>i13.0.0.09.9.13.31001000ir2#

sh

ip

bgp…NetworkNext

HopMetric

LocPrf

Weight

Path*>12.0.0.00.0.0.010032768i*>

13.0.0.09.9.12.101

i第六條:MED屬性實驗2:MED屬性的傳遞范圍R2的BGP表(詳細)R4的BGP表r2#sh

ip

bgp

13.0.0.0BGP

routing

table

entry

for

13.0.0.0/8,

version3Paths:

(1

available,

best

#1,

table

Default-IP-Routing-Table)Not

advertised

to

any

peer19.9.12.1

from

9.9.12.1

(9.9.0.1)Origin

IGP,

localpref

100,

valid,

external,

bestr4#sh

ip

bBGP

table

version

is

3,

local

router

ID

is

9.9.0.4Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*>i12.0.0.09.9.24.21001000i*>i13.0.0.09.9.12.1010001

i第六條:MED屬性實驗3:對EBGP

Peer應用IN\OUT方向Route-mapR3單向

R6的數(shù)據(jù)流需求R4\R5分別對R1\R2應用OUT方向Route-mapR1R2AS

1R3R4R5AS

2R6以該方式部署策略,對數(shù)據(jù)流控制的作用范圍10.0.0.0/811.0.0.0/8EBGP第六條:MED屬性實驗3:對EBGP

Peer應用IN\OUT方向Route-mapR4\R5的路由策略router

bgp

2---R4的路由策略neighbor

9.9.14.1

route-map

TO_R1

outneighbor

9.9.24.2

route-map

TO_R2

outaccess-list

1

permit

10.0.0.0access-list

2

permit

11.0.0.0route-map

TO_R2

permit

10set

metric

200route-map

TO_R1

permit

10match

ip

address

1set

metric

100route-map

TO_R1

permit

20match

ip

address

2set

metric

300router

bgp

2---R5的路由策略neighbor

9.9.15.1

route-map

TO_R1

outneighbor

9.9.25.2

route-map

TO_R2

outaccess-list

1

permit

10.0.0.0access-list

2

permit

11.0.0.0route-map

TO_R2

permit

10match

ip

address

1set

metric

300route-map

TO_R2

permit

20match

ip

address

2set

metric

100route-map

TO_R1

permit10set

metric

200第六條:MED屬性實驗3:對EBGP

Peer應用IN\OUT方向Route-mapR1\R2的BGP表r1#sh

ip

bgpBGP

table

version

is

9,

local

router

ID

is

9.9.0.1Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*

10.0.0.09.9.15.520002i*>9.9.14.410002i*

11.0.0.09.9.14.430002i*>9.9.15.520002ir2#sh

ip

bgpBGP

table

version

is

10,

local

router

ID

is

9.9.0.2Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*>

10.0.0.09.9.24.420002

i*9.9.25.530002

i*>

11.0.0.09.9.25.510002

i*9.9.24.420002

i第六條:MED屬性實驗3:對EBGP

Peer應用IN\OUT方向Route-mapR3的BGP表路由選路結果r3#sh

ip

bgpBGP

table

version

is

10,

local

router

ID

is

9.9.0.3Status

codes:

s

suppressed,

d

damped,

h

history,*

valid,

>

best,

i

-

internal,r

RIB-failure,

S

StaleOrigin

codes:

i

-

IGP,

e

-

EGP,

?

-

pleteNetwork Next

Hop Metric

LocPrf

Weight

Path*i10.0.0.09.9.23.220010002

i*>i9.9.13.110010002

i*

i11.0.0.09.9.13.120010002

i*>i9.9.23.210010002

i第六條:MED屬性實驗4:對IBGP

Peer應用IN\OUT方向Route-mapR3單向

R6的數(shù)據(jù)流需求R1\R2分別對R3應用OUT方向Route-mapR1R2AS

1R3R4R5AS

2R6以該方式部署策略,對數(shù)據(jù)流控制的作用范圍10.0.0.0/811.0.0.0/8EBGP第六條:MED屬性實驗4:對IBGP

Peer應用IN\OUT方向Route-mapR1\R2的路由策略router

bgp

1---R1的路由策略neighbor

9.9.13.3

route-map

TO_R3

outaccess-list

1

permit

10.0.0.0access-list

2

permit11.0.0.0route-map

TO_R3

permit

10match

ip

address

1set

metric

100route-map

TO_R3

permit

20match

ip

address

2set

metric

200router

bgp

1---R