OSPF and BGP Basic SetupWord文件下载.docx

OSPF and BGP Basic SetupWord文件下载.docx

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area<

areanumber>

"

OSPFworksthroughbroadcast.Areaislikepartitiontoseperatedifferentbroadcastdomain.

AboveisexamplefromCisco,thereare3areasconnectedthroughArea0.Area0isreservedasbackbone.Thebackbonehastobeatthecenterofallotherareas,i.e.allareashavetobephysicallyconnectedtothebackbone.

ForsmallLANenviroment,oneareaisenough.Forourexample,wewillsetasfollowing:

core_a:

router 

ospf 

10

network 

192.168.1.1 

0.0.0.0 

area 

100

access_a:

192.168.1.2 

Toseeifitworksornot,wecantrytoseeiftheyfoundtheirneighbour.

core_a#show 

ip 

neighbor

Neighbor 

ID 

Pri 

State 

Dead 

Time 

Address 

Interface

1 

FULL/DR 

00:

29 

FastEthernet0/0

core_a#

ButcurrentlyitonlyexchangeOSPFroutes.NormallywewantOSPFtoredistributeconnectedandstaticroutesforus.Soweneedtoadd:

redistribute 

connected 

metric-type 

subnets

static 

Nowletmeaddastaticrouteataccess_a,wecanseeatcore_a

access_a（config）#ip 

route 

1.1.1.1 

255.255.255.255 

null0

route

Codes:

C 

- 

connected, 

S 

static, 

R 

RIP, 

M 

mobile, 

B 

BGP

D 

EIGRP, 

EX 

EIGRP 

external, 

O 

OSPF, 

IA 

OSPF 

inter 

area

N1 

NSSA 

external 

type 

1, 

N2 

2

E1 

E2 

i 

IS-IS, 

su 

IS-IS 

summary, 

L1 

level-1, 

L2 

level-2

ia 

area, 

* 

candidate 

default, 

U 

per-user 

o 

ODR, 

P 

periodic 

downloaded 

Gateway 

of 

last 

resort 

is 

not 

set

1.0.0.0/32 

subnetted, 

[110/21] 

via 

192.168.1.2, 

00, 

192.168.1.0/24 

directly 

DefaultRoute

Bydefault,itwillnotredistributeanydefaultroute.Inordertoletitredistribute,weneedtouse"

default-informationoriginate"

command.

!

default-information 

originate 

metric 

3 

1

Now 

access_a 

learn 

the 

default 

route:

access_a#show 

to 

0.0.0.0

Null0

O*E1 

0.0.0.0/0 

110/11

192.168.1.1, 

07, 

access_a#

Security

AsOSPFwilllearnpeersthemselves,itisbettertoaddauthenticationkeyforsecuritypurpose.

interface 

XXXX

message-digest-key 

<

keyid>

md5 

key>

XX

area-id>

authentication 

message-digest

Example:

10 

7 

096B6B273C363E21

100 

CostControl

OSPFcalculatethecostbyinterfacebandwidth.Defaultis（100M/interfacebandwidth）.Sothecostwillincreaseby1iftheconnectionisoverFastEthernetinterface,whilethecostwillincreaseby64iftheconnectionisoveraT1link.Thecostaccumulateuntilitreachthedestination.

Intheaboveexample,thecostforAtoreachEwillbe（1+10）=11or（1+1+2）=4.OSPFwillthenchoosethepaththroughCandDwhichhaslowercost.

TherearetwobasicwaytocontrolOSPFcost:

∙Use"

ipospfcostxx"

underinterface.NotethisonlyaffectOSPFroutereceived.

1.1.1.1

Routing 

entry 

for 

1.1.1.1/32

Known 

10"

distance 

110, 

21, 

extern 

Last 

update 

from 

on 

FastEthernet0/0, 

05:

10:

43 

ago

Descriptor 

Blocks:

ago, 

Route 

traffic 

share 

count 

Metric 

= 

（redistribution 

cost 

20） 

+ 

（100M/100M） 

21

If 

we 

apply 

under 

30, 

03 

Interface 

forced 

10. 

Total 

30.

metric"

parameterduringtheredistribution

Continue 

above 

example:

09 

Change 

redistribution 

at 

to:

50 

60, 

02 

now 

become 

50） 

60

AdvanceControl

Route-maporaccess-listcanbeusetocontrolroutereceive/redistribution.

distribute-list 

access-list>

in/out>

subnets 

route-map 

name>

rf--OSPF-REDISTRIBUTE-CONNECTED

rf--OSPF-REDISTRIBUTE-STATIC

BGP

BGP（BorderGatewayProtocol）isroutingprotocolwidelyusebetweenISPs.UnlikeOSPF,itispeertopeerbasedinsteadofbroadcast.

BGPCaseStudies

BGP:

ConfiguringBGP

PathSelection

BGPuseAS（AutonomousSystems）numberstoindicatethepathtodestination.Eachparty（e.g.ISP）hastheirownASnumber.ASnumber,likeIPaddress,needtoapplyfromrelatedNIC（e.g.APNIC,CNNIC,TWNIC）.AlsolikeprivateIPaddress,therearearangeofASnumberreservedforprivateuse.IANAhasreservedAS64512throughtoAS65535tobeusedasprivateASnumbers.

Whenannoucing/redistributingroutestotheirpeers,theirASnumberisprependtotheroutes.Themoretheroutesredistributeamongdifferentparties,thelongertheASpath.

Intheaboveexample,therearetwopathsforAS100tonetworkbroadcastfromAS300:

∙ASpath:

200300

400500300

TherouterwillchoosetheshorterASpathasbestroute.

core_b,f0/0:

192.168.2.1/24

access_b,f0/0:

192.168.2.2/24

core_a,s1/0:

10.10.10.1/30

core_b,s1/0:

10.10.10.2/30

core_a&

access_a,core_b&

access_bhasOSPFrunning

BGPusespeertopeersetupandonerouteronlyuseoneASnumber.Hereistheminimumconfiguration:

bgp 

AS 

number>

neighbor 

remote 

peer 

IP>

remote-as 

xx.xx.xx.xx 

mask 

yy.yy.yy.yy

Usuallyweuse"

networkxx.xx.xx.xx"

commandtoannouceourIPrangetoremotepeer,insteadofredistributeconnected/static/OSPFroutes.AlsowhenworkingwithISP,theminimumIPsegmentisClassC（/24）.

Assume 

have 

two 

ISP 

A 

and 

B, 

which 

has 

AS100 

AS200 

respectively. 

（Use 

private 

when 

working 

client 

CPE 

if 

they 

don'

t 

their 

own 

AS）

10.10.10.2 

200

192.168.1.0 

255.255.255.0

core_b:

10.10.10.1 

192.168.2.0 

Inthisexample,core_aisusingAS100andcore_bisusingAS200.WeannouncethecorrespondingLANIPtoremotenetwork.

summary

BGP 

identifier 

local 

number 

table 

version 

3, 

main 

routing 

3

2 

entries 

using 

234 

bytes 

memory

path 

104 

3/2 

path/bestpath 

attribute 

372 

AS-PATH 

24 

0 

cache 

filter-lis