TaiLieuTongHop.com---Giao Thuc Dinh Tuyen Bgp (Border Gateway Protocol)

7/28/2019 TaiLieuTongHop.com---Giao Thuc Dinh Tuyen Bgp (Border Gateway Protocol)

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LI CM N

Trc ht ti xin by t lng bit n chn thnh n Th.s Trn Quang t,

ngi tn tnh hng dn, gip v to iu kin thun li cho ti trong thi gian

thc hin ti. Xin gi li cm n chn thnh, lng bit n su sc ti cc thy c, b

m v tt c cc bn trong khoa in t vin thng - H Cng Ngh tn tnh gip

, ng vin v to iu kin ti thc hin tt ti ny.

Mc d ht sc c gng xong chc chn khng trnh khi nhng thiu st.

Em rt mong nhn c s thng cm v ch bo tn tnh ca qu thy c, cc anh ch

v tt c cc bn.

H Ni, thng 5 nm 2008.

L V Thng

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MC LC

LI CM N................................................................................................................1

CC THUT NG TING ANH................................................................................3Li gii thiu.................................................................................................................4CHNG 1...................................................................................................................5GII THIU TNG QUAN V GIAO THC BGP....................................................5

1.1 Gii thiu. .........................................................................................51.2 S dng BGP trong nh tuyn............................................................................5

CHNG 2...................................................................................................................7CC THUC TNH V THUT NG S DNG TRONG BGP.............................7

2.1 nh ngha Autonomous System (AS) ..............................................................82.2 Thuc tnh Autonomous system path (AS_PATH)..............................................9

2.3 Thuc tnh WEIGHT.........................................................................................112.4 Thuc tnh Local Preference (LOCAL_PREF)..................................................132.5 Thuc tnh Metric hay MULTI_EXIT_DISC (MED)........................................142.6 Thuc tnh ORIGIN...........................................................................................152.7 Thuc tnh NEXT_HOP.....................................................................................152.8 Thuc tnh Community......................................................................................17

CHNG 3.................................................................................................................18HOT NG CA BGP............................................................................................18

3.1 Hot ng ca EBGP ...................................................................................... 183.1.1 Kho st hot ng ca EBGP...................................................................18

3.1.2 Cu trc thng bo ca BGP.......................................................................193.2 Qung b tuyn trong BGP...............................................................................253.2.1 Qung b tuyn s dng cu lnh Network.................................................263.2.2 Qung b tuyn s dng redistribute...........................................................33

3.3 Hot ng ca IBGP .........................................................................................373.3.1 Kho st hot ng ca IBGP................................................................373.3.2 Giao din loopback trong IBGP..........................................................48

3.3.3 Route-Reflector (RR)..................................................................................523.3.4 Phn cp nh tuyn trong cc AS (Confederations).................................57

3.4 Gii thut nh tuyn trong BGP........................................................................59

3.5 S tm tt tuyn trong BGP...............................................................................613.6 Qun l lu lng trong BGP ............................................................................66KT LUN.................................................................................................................69TI LIU THAM KHO............................................................................................71

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CC THUT NG TING ANH

AGGREGATE Qu trnh tm tt tuynAS_PATH Thuc tnh AS_PATH

ATTRIBUTE Thuc tnh

AUTONOMOUS SYSTEM Vng t trBORDER GATEWAY PROTOCOL Giao thc BGP

COMMUNITY Thuc tnh COMMUNITYCONFEDERATION S phn chia AS nhm gim s tuyn

EBGP Giao thc BGP chy gia cc AS

EGPs Cc giao thc s dng gia cc ASIBGP Giao thc BGP chy trn mt AS

IGPs Cc giao thc s dng trong mt AS

LOCAL_PREF Thuc tnh LOCAL_PREF

MED Thuc tnh MED

NEXT_HOP Thuc tnh NEXT_HOP

ORIGIN Thuc tnh ORIGIN

OSPF Giao thc nh tuyn OSPF

RIP Giao thc nh tuyn RIP

ROUTE_REFLECTOR Phn x tuyn nhm lm gim s tuyn

trong BGPROUTE_REFLECTOR_CLIENT Router c mt phin TCP vi mt

router khc hot ng nh mt route-reflector-server

ROUTE_REFLECTOR_CLUSTER Mt cluster l mt nhm bao gm route-

reflector v clientsWEIGHT Thuc tnh WEIGHT

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Li gii thiu

Chng ta ang sng trong th k 21, k nguyn ca khoa hc k thut v cng

ngh hin i. Vo thi im ny, ngnh cng nghip cng ngh thng tin v chic

my vi tnh nm gi mt vai tr khng th thiu trong mi lnh vc hot ng ca conngi. Mt chic my tnh bn hot ng c lp l khng , con ngi mun lin

kt cc my tnh li vi nhau thnh mng my tnh tn dng sc mnh x l, trao

i thng tin v chia s ti nguyn. Khi mng my tnh tng ln c v quy m v s

lng, con ngi li mun lin kt cc mng my tnh ny li vi nhau. Lm th no

lin kt cc my tnh li vi nhau ? Lm th no thng tin c th c trao i

gia cc mng my tnh cch nhau hng trm cy s ? Mt bi ton cn c gii

tr li nhng cu hi trn, l bi ton nh tuyn.

nh tuyn hiu n gin l tm ng i. Trong truyn thng my tnh nh

tuyn ngha l ch ra ng i thng tin c th di chuyn t ngun n ch theo

cch tt nht. Khng th ph nhn tm quan trng ca nh tuyn trong truyn thng

my tnh. Khng c nh tuyn, cc my tnh khng th trao i thng tin vi cc

mng khc.

Thit b thc hin chc nng nh tuyn trn mng ch yu l cc Router. c

th thc hin chc nng nh tuyn, cc Router phi trao i thng tin v tuyn vi

nhau xy dng nn cc tuyn ng. Tp hp cc qui tc trao i thng tin nhtuyn gia cc thit b nh tuyn vi nhau gi l giao thc nh tuyn.

i tng nghin cu ca ti ny l giao thc nh tuyn BGP (Border

Gateway Protocol) giao thc c s dng ht sc rng ri trn mng Internet hin

nay. Mc ch ca ti l tm hiu hot ng ca giao thc nh tuyn BGP v cch

thc trin khai giao thc nh tuyn BGP trn cc Router.

Do nhng hn ch v mt thi gian v thit b, mt s ni dung lin quan khng

c a vo ti nh: S hot ng v trin khai BGP trn IPv6. Mc d ht scc gng xong ti khng trnh khi nhng thiu st v vy rt mong nhn c

kin ng gp, s ch bo tn tnh ca cc thy c v tt c cc bn.

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CHNG 1

GII THIU TNG QUAN V GIAO THC BGP

1.1 Gii thiu.

BGP, vit tt ca t ting Anh Border Gateway Protocol, l giao thc nh tuynnng ct trn Internet. N hot ng da trn vic cp nht mt bng cha cc a chmng v cho bit mi lin kt gia cc h t tr. BGP l giao thc vector ng i(path vector). Khc vi cc giao thc nh tuyn khc nh RIP (vector di), OSPF(trng thi lin kt), BGP nh tuyn bng mt tp cc chnh sch v lut. Phin bnBGP hin nay l phin bn 4, da trn RFC 4271. BGP h tr nh tuyn lin vng philp (CIDR Classless Inter-Domain Routing) v dng k thut kt hp tuyn gim

kch thc bng nh tuyn (v d nu mt mng chim 255 a ch lp C t203.162.0.0/24 - 203.162.254.0/24 th ch dng 1 a ch 203.162.0.0/16 nh danhmng). Ngoi vic s dng BGP gia cc AS, BGP cng c th c s dng trongcc mng ring quy m ln do OSPF khng p ng c. Mt l do khc l dngBGP h tr kt ni n nhiu nh cung cp dch v. a s ngi s dng Internetthng khng s dng BGP mt cch trc tip. Ch c cc nh cung cp dch vInternet s dng BGP trao i ng i. BGP l mt trong nhng giao thc quantrng nht m bo tnh kt ni ca Internet.

Nh ni trn BGP l mt giao thc kh phc tp c dng nhiu trnInternet v trong cc cng ty a quc gia. Mc ch chnh ca BGP l kt ni ccmng rt ln hoc cc Autonomous-System. Cc cng ty ln c th dng BGP nh lmt kt ni gia cc mng cc quc gia khc nhau. BGP l giao thc khng ch tmra mt tuyn i v mt mng no m cn cho php ngi qun tr tm ra cc AS cacc mng. Cc giao thc nh EIGRP, RIP, OSPF v ISIS s tm ra tuyn m ngiqun tr cn.

1.2 S dng BGP trong nh tuyn

La chn giao thc nh tuyn ph hp cho mt mng l vic quan trng v nggp vo s n nh ca h thng. Khi quyt nh s dng BGP cho vic nh tuynngi qun tr cn gii p c mt s cu hi ht sc cn thit

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http://vi.wikipedia.org/wiki/Ti%E1%BA%BFng_Anhhttp://vi.wikipedia.org/wiki/Giao_th%E1%BB%A9chttp://vi.wikipedia.org/wiki/Internethttp://vi.wikipedia.org/wiki/RIPhttp://vi.wikipedia.org/w/index.php?title=OSPF&action=edit&redlink=1http://tools.ietf.org/html/4271http://vi.wikipedia.org/wiki/Ti%E1%BA%BFng_Anhhttp://vi.wikipedia.org/wiki/Giao_th%E1%BB%A9chttp://vi.wikipedia.org/wiki/Internethttp://vi.wikipedia.org/wiki/RIPhttp://vi.wikipedia.org/w/index.php?title=OSPF&action=edit&redlink=1http://tools.ietf.org/html/4271


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Cu hi u tin cn c cc nh qun tr t ra l: S dng BGP cho vic nhtuyn khi no ?

Mt h thng mng n gin l mt h thng mng d dng qun l v bo tr.

Mc d BGP l giao thc phc tp tuy nhin cc trng hp di y c khuynco cho vic s dng giao thc BGP nh tuyn :

- Mt AS cho php chuyn tip gi tin qua n n cc AS khc

- Mt AS c nhiu kt ni n AS khc

- Lu lng thng tin vo ra trn AS cn c x l

Cc khuyn co trn c rt ra t cc c tnh m BGP s dng nh tuyn.Cc c tnh s c trnh by k chng sau.

trnh vic s dng khng hiu qu giao thc nh tuyn BGP cu hi th haim cc nh qun tr cn quan tm l: Khng nn s dng BGP cho vic nh tuyn khino ? BGP l mt giao thc kh phc tp v c s dng trn internet v trong cccng ty ln. V l d BGP c khuyn co l khng nn s dng khi tn ti mttrong cc iu kin di y :

- Ch c mt kt ni n n Internet hoc n AS khc

- Chnh sch nh tuyn v la chn tuyn khng lin quan g n AS cangi s dng

- Ti nguyn mng l c gii hn: ti nguyn v b nh v kh nng x l caCPU trn router.

- Qun tr mng thiu kinh nghim, hiu bit i vi giao thc BGP trong vicchn, lc tuyn

- Bng thng gia cc AS l thp v cc ph tn cho nh tuyn s nh hngn qu trnh chuyn d liu. Gii php x l vn khi khng s dng BGP nh tuyn l s dng tuyn tnh (static route)

Vic tr li tt hai cu hi trn s gp phn gip cho cc nh qun tr la chn vs dng hiu qu giao thc BGP trong vic nh tuyn cho h thng mng ca mnh

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CHNG 2

CC THUC TNH V THUT NG S DNG TRONG BGP

Cc giao thc nh tuyn IGPs qung b mt mng vi cc tham s nh tuyn:metric,cost. Mi giao thc IGPs c mt tham s la chn tuyn ng ti ch khcnhau (RIP s dng m s hop, OSPF s dng tham s cost = 100000000/BW).

Nu c nhiu ng dn n ch vi metric hoc cost khc nhau th ng dn vimetric hoc cost thp nht phi c la chn. BGP khng phi l giao thc ngoi lv cng cn cc tham s la chn tuyn tt nht n ch. Cc tham s trong BGPc gi l thuc tnh (Attributes).

BGP nh tuyn bng cch s dng cc thuc tnh. Vic s dng cc thuc tnh

m ch n vic s dng cc bin trong qu trnh chn la ng i trong BGP. Ccthuc tnh ca BGP khng ch l danh sch cc bin m qua tuyn c chn la.Mt vi thng tin c mang trong cc thng ip cp nht l quan trng hn ccthng tin khc. Mt s thng tin khc l rt quan trng cho hot ng ca BGP, v vycc thng tin ny phi c mang n tt c cc router BGP trong mng. Qu trnhnh tuyn da trn nhng thuc tnh v cc gi tr ca n. Cc thuc tnh c chiathnh 4 nhm: nhm well-known mandatory , well-known discretionary, optionaltransitive v optional nontrasitive. Cc thuc tnh c m t k trong bng

di y :

Nhm M T

Well-known mandatoryCc thuc tnh ny l bt buc v c cng nhn bi tt ccc router BGP

Well-known DiscretionaryKhng yu cu cc thuc tnh ny tn ti trong cc cp nhtnhng nu chng tn ti, tt c cc router s cng nhn vs c hnh ng tng ng da trn thng tin c cha

bn trong thuc tnh ny.

Optional Transitive

Router c th khng cng nhn cc thuc tnh ny nhngnu router nhn c thuc tnh ny, n s nh du v giy cp nht ny n router k tip. Cc thuc tnh skhng thay i khi i qua router nu thuc tnh ny khngc cng nhn bi router.

Optional Nontransitive

Cc thuc tnh ny b loi b nu cp nht mang thuc tnhny i vo router m router khng hiu hoc khng cngnhn thuc tnh. Cc thuc tnh ny s khng truyn ti ccBGP.

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Bn nhm trn m t mt cch tng qut cc thuc tnh ca BGP. ng vi minhm ta s i su nghin cu cc c tnh c th ca tng loi thuc tnh trong

nhm .

Attribute Name Attribute Type Description

AS_PATH Well-knownmandatory

Danh sch cc AS m tuyn c qung bthng qua n

WEIGHT Cisco definedattribute

c s dng nh tuyn trong BGP

LOCAL_PREF Well-known

discretionary

c s dng chn tuyn, thng c

s dng trong mt ASMULTI_EXIT_DISC Optional

nontransitivec s dng chn tuyn, thng cs dng gia cc AS

ORIGIN Well-knownmandatory

Ch ra cc tuyn BGP c hc nh th noIGP T cu lnh NetworkEGP T EBGP hng xmIncomplete T redistribution

NEXT_HOP Well-known

mandatory

EBGP a ch ca giao din c s

dng truyn thng vi hng xm bnkhcIBGP EBGP next hop c gi v khngthay i khi ti cc IBGP hng xm.

Community Optional transitive Mt s c s dng cho vic p mt chnhsch n mt nhm cc tuyn.

2.1 nh ngha Autonomous System (AS)

L mt tp hp cc mng c cng chnh sch nh tuyn v thng thuc quynqun l, khai thc ca mt ch th. Mi nh cung cp dch v internet (ISP) c th coil mt AS.Vic kt ni gia cc AS ny thng c s dng BGP

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Hnh 1: Kt ni gia cc AS

2.2 Thuc tnh Autonomous system path (AS_PATH)

Thuc tnh ny c s dng cho vic chn tuyn v chng loop trong BGP.AS_PATH thuc vo nhm well-known mandatory, cn c qung b v hiu bi ttc cc router hng xm. Mi nh cung cp dch v u c gn mt s nh danh

duy nht autonomous system (AS) trong khong t 1 n 64511. Cc s AS ny c ng k v gn tng t nh vic cung cp cc di a ch IP . Cc nh cung cpdch v cng c th nh ngha cc vng t tr AS bng cch s dng cc s AS ringc phm vi cho php trong khong 64512 n 65534. Tuy nhin cc s AS ring nykhng c qung b ra internet v ch c s dng trong vng AS to ra n. CcAS ring tng t nh a ch IP ring

Chng ta xt mt v d di y vi cc nh cung cp dch v c gn cc sAS 1, 2, 3 v 4. Nh cung cp dch v vi AS bng 1 qung b mng v netmask ca

mng 156.26.32.0/24 n nh cung cp dch v 2 vi AS l 2.

Hnh 2: thuc tnh AS_PATH

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Khi tuyn c qung b c nhn bi AS 2, AS 2 bit mng 156.26.32.0 nmtrong AS 1 bi v ch c 1 s AS duy nht nm trong thuc tnh AS_PATH v ct bng 1. Khi AS 2 qung b tuyn 156.26.32.0/24 n AS 3, AS 2 s c b xungv c t vo AS_PATH. Kt qu sau khi nhn c qung b t AS 2 thuc tnh

AS_PATH s c gi tr l 2 1 vi du cch gia cc s AS. AS 3 cng bit rng mngc qung b nm trong AS 1 (do s cui trong thuc tnh AS_PATH c t bng1 ) v mng c qung b thng qua AS 2. AS 3 b xung s AS ca n vo thuctnh AS_PATH v qung b tuyn n AS 4. AS 4 nhn thuc tnh qung b viAS_PATH l 3 2 1 cho mng 156.26.32.0/24

Nu tt c c thuc tnh khc ca BGP l bng nhau, router vi AS_PATH ngnnht s c s dng lm tham s la chn tuyn. Trong v d trn ta ch qung bcho mng 156.26.32.0/24 v mc nh n s c ng dn ti u n ch. Nu c

nhiu tuyn, thuc tnh AS_PATH s c s dng la chn tuyn tt nht ti ch.Di y l mt v d. Trong hnh 3, AS 4 nhn 2 s qung b cho mng156.26.32.0/24. Qung b t AS 3 c di AS l 3 v t AS 5 c di l 2. V thAS 4 ch quan tm n tuyn thng qua AS 5 v la chn n l tuyn tt nht nch. Tuyn tt nht ny s c t trong bng nh tuyn.

Hnh 3: La chn tuyn thng qua thuc tnh AS_PATH

AS_PATH l danh sch cc s AS c qung b . Tham s ny tng t vicm s hop trong RIP v s AS cng c s dng quyt nh tuyn tt nht nch (tng t nh hop count).

Ngoi vic AS_PATH c s dng cho vic la chn tuyn tt nht n ch.BGP cn s dng thuc tnh AS_PATH chng loop.

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Trong hnh 4, AS 4 qung b tuyn tt nht cho mng 156.26.32.0/24 n AS 6.AS 6 qung b tuyn ny n AS 1 vi AS_PATH l 6 4 5 1 . Khi AS 1 nhn qung bt AS 6 tuyn ny s b t chi v AS 1 nm trong AS_PATH. Cc BGP routers tchi bt k s qung b no m cha ng s AS ca chng.

Hnh 4: BGP chng loop s dng thuc tinh AS_PATH

2.3 Thuc tnh WEIGHT

Weight l thuc tnh khng c ch nh trong BGP . N l thuc tnh c bitc pht trin trn cc thit b ca cisco v l thuc tnh do cisco nh ngha. Tham

s ny cng l mt trong cc thuc tnh c s dng quyt nh tuyn tt nht tich. Trong hnh 5, AS 2 nhn 2 s qung b cho mng 156.26.32.0/24. Qung b tAS 3 c AS_PATH di l 3 v qung b t AS 1 c di l 2. AS 2 s la chntuyn thng qua AS 1 v qua AS_PATH s l ngn nht.

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Hnh 5 : AS 2 la chn ng n 156.26.32.0/24 thng qua AS 1 v n c thuc tnhAS_PATH tt nht

Tuy nhin nu mun router trong AS 2 s dng tuyn thng qua AS 3 thay thcho AS 1 ta s dng thuc tnh weight. Weight l thuc tnh c biu din bng 16

bit v gi tr trong khong 0 n 65535. Router c s dng thuc tnh Weight chnh tuyn ti ch. Vic la chn ny thng c s dng khi c nhiu ng dntt nht n cng 1 ch. Trng s Weight s c u tin hn

Hinh 6 : Chn tuyn thng qua thuc tnh weight

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Thuc tnh weight ch c gi tr trn router v khng qung b ra cc routerhng xm chy BGP. Cc tuyn BGP c weight mc nh l 32768

2.4 Thuc tnh Local Preference (LOCAL_PREF)

LOCAL_PREF l thuc tnh tng t nh weight. Khi c nhiu hn mt tuynti mt ch, tuyn c thuc tnh LOCAL_PREF cao nht (khi cc weight bng nhau)s c la chn l tuyn tt nht. Mc nh LOCAL_PREF c gi tr 100 v gi trcao hn s c u tin s dng l tham s quyt nh tuyn ti ch (khi weight bngnhau). LOCAL_PREF l mt s 32 bit c gi tr t 0 4294967295.

Trong hnh 7, Router A v Router B c 2 ng n mng 156.26.32.0/24.Router A s dng gi tr LOCAL_PREF mc nh l 100. Router B c thit lp gi

tr LOCAL_PREF l 200 v th Router B s la chn tuyn qua AS 3. Khng gingnh thuc tnh weight LOCAL_PREF c qung b trong 1 AS. Router A nhnqung b cho mng 156.26.32.0/24 t Router B vi LOCAL_PREF l 200. V thRouter A s dng tuyn thng qua AS 3 t ti mng 156.26.32.0/24

Hnh 7: Thuc tnh LOCAL_PREF

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2.5 Thuc tnh Metric hay MULTI_EXIT_DISC (MED)

Thuc tnh Weight c s dng quyt nh tuyn t mt router.LOCAL_PREF c s dng la chn tuyn ri khi 1 autonomous system. Thuc

tnh MULTI_EXIT_DISC (Multi-exit discriminator hay MED) c s dng quytnh tuyn gia cc AS. MED cng l mt s c gi tr 32 bit tuy nhin thuc tnh nyc mt im khc bit vi thuc tnh LOCAL_PREF l gi tr thp hn s c utin thay v gi tr cao s c u tin chn tuyn nh trong LOCAL_PREF.

Di y l mt v d ch ra vic la chn tuyn dng MED. Trong Hnh 8, AS 5qung b mng 156.26.32.0/24 v c 2 ng ti c mng 156.26.32.0/24 t AS1. AS 5 mun AS 1 s dng tuyn bn phi cho lu lng t AS 1 n AS 5. AS 5thit lp MED bn tri c gi tr cao hn gi tr mc nh l 0 v qung b gi tr nyn AS 1

Hnh 8 : S dng thuc tnh MED chn tuyn

Nu tt c cc thuc tnh khc ca BGP l bng nhau. AS 1 s la chn tuynbn phi n AS 5 v n c gi tr MED thp hn. u tin ca cc thuc tnh trongBGP c quyt nh ln lt l WEIGHT, LOCAL_PREF,AS_PATH v cui cngl MED.

Khi 3 tham s trn l bng nhau MED s c s dng chn tuyn tt nhtn ch

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2.6 Thuc tnh ORIGIN

Thuc tnh ORIGIN ch ra kiu ti nguyn ca BGP trong bng BGP routing. Cba cch gip cho BGP c th hc tuyn, trong cc thit b ca cisco ba cch l :

S dng cu lnh network

T EBGP hng xm

Thng qua redistribution

Cu lnh network c s dng qung b tuyn trong bng nh tuyn n ccBGP hng xm. Cc tuyn hc c thng qua cu lnh network c thuc tnhORIGIN t l IGP v ch ra rng tuyn l tuyn nm trong cng AS.

C hai kiu kt ni BGP. Kiu th nht l kiu kt ni gia c router chy BGPtrong cng 1 AS. Kiu ny c gi l Internal BGP (IBGP). Kiu kt ni th 2 lkiu kt ni gia cc autonomous-system khc nhau. Kiu ny c gi l ExternalBGP (EBGP)

Hnh 9 : Cc tuyn IBGP v EBGP

Cc tuyn c hc t EBGP hng xm c thuc tnh ORIGIN l EGP. Cctuyn redistributed trong BGP c thuc tnh ORIGIN l incomplete. Cc tuyn IGP

c u tin thng qua cc tuyn EGP v cc tuyn EGP c u tin thng cc cctuyn incomplete. Ni cch khc cc tuyn EBGP c u tin, s dng thng qua cctuyn IBGP

2.7 Thuc tnh NEXT_HOP

Khi mt router qung b mt tuyn n router EBGP hng xm, thuc tnhNEXT_HOP c t l a ch IP ca giao din kt ni n hng xm . c bitnu router qung b mt tuyn c hc thng qua EBGP n IBGP hng xm, thuc

tnh NEXT_HOP s khng c thay i.

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Hnh 10 : Thuc tnh NEXT_HOP

Khi mt router nhn mt tuyn t mt BGP hng xm, thuc tnh u tin nkiu tra l NEXT_HOP. Nu NEXT_HOP khng t c ( khng nm trong bng

nh tuyn), tuyn s b t chi. EBGP s dng kt ni vt l trc tip trn cc giaodin vt l v th NEXT_HOP s c t trong bng routing ging nh giao din ktni trc tip. Cc IBGP hng xm khng c kt ni trc tip. Trong v d hnh 10router B chp nhn tuyn t router A v NEXT_HOP l mng kt ni trc tip vi n.Router C s chp nhn tuyn t router B nu mng NEXT_HOP c trong bng nhtuyn ca router C.

Khi BGP khai bo mt mng, router t nh r bn thn router nh l NEXT_HOP. Tuy nhin, nu router gi thng ip update cho mt router hng xm khc

trong cng mt AS th n li tip tc dng router ngoi AS lm NEXT_HOP. Do taphi cu hnh cho cc router cn li trong AS bit c chnh router bin cng ASvi n l router Next Hop ch khng phi l router khc AS.

Hnh 11: Hot ng ca router vi thuc tnh NEXT_HOP

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Xt v d hot ng ca router vi thuc tnh NEXT_HOP trong hnh 11

Bc 1: Router A gi cp nht v mng 192.33.33.0

Bc 2: Router D nhn update v truyn. Tuy nhin nu router D thay i a chngun thnh a ch ca chnh n, s c mt s nhm ln xy ra v trong mi trng atruy cp, mi router s cng b n l NEXT_HOP. trnh tnh hung ny, a chngun ca thng tin cp nht tuyn khng thay i.

Bc 3: Router B bit router A l NEXT_HOP ca mng 192.33.33.0

Do tnh cht ny m bt buc cc IBGP hng xm phi c tuyn n mngNEXT_HOP trong bng nh tuyn

2.8 Thuc tnh Community

y l mt thuc tnh khng bt buc. Thuc tnh ny c dng cung cpchnh sch cho mt nhm cc router i qua cc AS. Do cc router ny c cng mttnh cht v c chung chnh sch. Nu mt router nhn c mt thng ip thng tincp nht nh tuyn vi thuc tnh Community c thit lp, n s x l thng ipny mt cch hp l. Nu n khng hiu thng ip ny th s gi thuc tnh chorouter hng xm x l. (Tuy nhin, nu n hiu th s khng bao gi gi thuc tnh cho router hng xm tr khi c ch nh lm thm iu g ).

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CHNG 3

HOT NG CA BGP

3.1 Hot ng ca EBGP

3.1.1 Kho st hot ng ca EBGP

Cc router BGP ( EBGP ) l hng xm ca nhau c kt ni trc tip. Chng ta cth thit lp cu hnh gia cc router A v B v kim tra s hot ng gia cc router. Xt s hot ng ca 2 router di y :

Hnh 12: Cu hnh hot ng EBGP

Trc tin chng ta s thit lp cc giao din loopback trn cc router. Ging nhtrong OSPF a ch IP c gn trn giao din loopback c s dng nh l ID cacc router chy BGP

Router A

interface Loopback0

ip address 172.16.15.254 255.255.255.255

Router B

interface Loopback0

ip address 172.16.16.254 255.255.255.255

Cc cu lnh trn gip thit lp a ch IP trn giao din loopback. Bc tip theo lbc quan trng v cho php khi to mt qu trnh BGP trn cc router.

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Router A

router bgp 1

neighbor 172.16.15.162 remote-as 2

Router B

router bgp 2


Cc cu lnh router bgp as-numbercho php thc thi mt tin trnh BGP trnrouter. Ch mt s AS c th c gn ti nh cung cp dch v, v th ch mt tintrnh BGP c thit lp trn mt router. Cu lnh neighbor neighbor-ip-address cho

php BGP hot ng trn giao din . Giao din chy BGP c quyt nh bi bngIP routing. Bng ny quyt nh giao din c s dng c th t ti c a chIP ca hng xm. Vi EBGP cc hng xm c kt ni trc tip vi nhau v th giaodin c s dng ch c mt kt ni trc tip n hng xm ca n.

3.1.2 Cu trc thng bo ca BGP

Cc giao thc RIP, IGRP, EIGRP v OSPF s dng cu lnh network thc

hin cu hnh cho php nh tuyn, qung b mng, netmask. Ngoi ra n cn chophp cc giao thc IGPs khm ph, nhn bit cc router hng xm. Tuy nhin vi

EBGP do ch r cc router hng xm nn khng cn phi c bc tm, nhn bit

hng xm nh cc giao thc IGPs na. V th c th thit lp mt mi quan h hng

xm m khng cn qung b bt k tuyn no . Khi EBGP c cho php chy trn

mt giao din, cc router s c gng thc hin mt tin trnh thit lp mi quan h theo

cc bc di y :

Idle State: trng thi ny router s khi to mt kt ni TCP vi BGP hngxm

Connect State : Giai on ny router khi to s ch cho kt ni TCP c

thc hin vi router BGP hng xm. Nu mt kt ni TCP c thc hin , router s

gi mt thng bo OPEN v chuyn sang trng thi OpenSent. Nu ht thi gian ch

router vn khng thit lp c kt ni n s chuyn tip sang trng thi Active

Active State: giai on ny router vn ch cho mt kt ni c thc hin

vi router hng xm. Nu kt ni c thc hin n s chuyn sang trng thi Connect

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OpenSent State : giai on ny router s ch mt thng bo OPEN t BGP

hng xm. Nu xy ra li n s chuyn sang ch Idle State. Nu mt thng bo

OPEN c nhn t router BGP hng xm th n s chuyn sang trng thi

OpenConfirm.

OpenConfirm State: Giai on ny router ch mt thng bo KEEPALIVE t

BGP hng xm. Khi mt KEEPALIVE c nhn n s chuyn sang trng thi

Established.

Established State: Giai on ny cc router s trao i thng tin nh tuyn

vi nhau

nh dng chung phn tiu ca thng bo BGP bao gm cc trng thng tin

sau : trng nh du 16 byte, trng di 2 byte v trng kiu 1 byte.

Hnh 13: nh dng chung phn tiu ca thng boBGP

Ty tng kiu thng bo m c th c hoc khng c phn d liu sau phn tiu

. V d thng bo KEEPALIVE khng cha d liu m ch cha phn tiu

- Trng nh du (Marker field): Trng ny c di 16 byte c s dng

cho mc ch chng thc cc thng bo BGP n hoc d tm s mt ng b gia

2 hng xm. Trng ny c th c 1 hoc 2 dng :

+ Nu kiu thng bo ca BGP l OPEN hoc OPEN khng s dng chng

thc th trng nh du ny phi c t tt c bng 1

+ Ngc li trng ny s c t da vo vic tnh ton cc k thut s

dng chng thc

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- Trng di length (length field): Trng ny c di 2 byte ch ra tng

di ca thng bo BGP bao gm c phn tiu . V th trong BGP di ti thiu ca

1 thng bo l 19 byte (16 + 2 + 1) v ti a khng ln hn 4096 byte.

- Trng kiu : Trng ny c di mt byte cho php biu din cc kiu thngbo trong giao thc BGP. Cc kiu thng bo l OPEN, UPDATE, KEEPALIVE,

NOTIFICATION. Cc thng bo c th trong cc giai on nh sau :

Trong giai on Connection, mt router BGP gi mt thng bo OPEN n

router hng xm. Thng bo OPEN nh danh router vi hng xm. Ngoi ra thng

bo OPEN cn gip cho cc router thc hin qu trao i cc tham s di y :

- S phin bn (version number): Phin bn BGP hin ti l 4

- S AS (AS number)- Hold time :thi gian mt BGP router s ch trc khi khai bo rng hng

xm mt lin kt

- BGP router ID

- Opt parm len: Trng ny ch ra di ca trng Optional parameters

- Trng Optional parameters: Trng ny ch ra danh sch cc tham s c

s dng cc hng xm tha thun phin BGP vi nhau

Hnh 14: Thng bo OPEN

Sau khi BGP router gi mt thng bo OPEN ti hng xm ca n, router s

chuyn sang trng thi OpenSent v ch nhn mt thng bo OPEN t hng xm. Khi

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router nhn c thng bo OPEN t hng xm Router s chuyn tip sang trng thi

OpenConfirm State, v ch mt thng bo KEEPALIVE . Mc nh KEEPALIVE

c gi 60s v c s dng xc nhn trng thi ca router. Sau khi nhn c

KEEPALIVE router s chuyn sang trng thi Established v trao i KEEPALIVE,

UPDATE v thng bo NOTIFICATION.

Mt thng bo NOTIFICATION c s dng khi c li xut hin khin cho

phin BGP kt thc. Trong qu trnh thc hin BGP c th c nhiu li xy ra

Thng bo NOTIFICATION c nh dng nh sau:

Hnh 15 : Thng bo NOTIFICATION

Trong cc trng c m t trong bng di y :

Cc m li ca BGPError Code Error Subcode

1Message header error 1Connection Not Synchronized2Bad Message Length

3Bad Message Type

2OPEN message error 1Unsupported Version Number

2Bad Peer AS

3Bad BGP Identifier4Unsupported Optional Parameter

5Authentication Failure

6Unacceptable Hold Timer

7Unsupported Capability

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3UPDATE message error 1Malformed Attribute List

2Unrecognized Well-Known Attribute

3Missing Well-Known Attribute

4Attribute Flags Error

5Attribute Length Error

6Invalid Origin Attribute

7AS Routing Loop

8Invalid NEXT_HOP Attribute

9Optional Attribute Error

10Invalid Network Field

11Malformed AS_PATH

4Hold Timer ex ired N/A5Finite State Machine N/A

6Cease for fatal errors N/A

Mt thng bo UPDATE qung b mng ang c. Thng bo UPDATE s qung

b:

- Cc thng tin lin quan n mng ch: a ch, netmask..

- Cc thuc tnh BGP

- Cc tuyn khng c kh nng thc hin nh tuyn v b loi b trong bngrouting

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Thng bo UPDATE c cu trc nh sau :

Hinh 16: Thng bo UPDATE

Khi cc EBGP hng xm t c trng thi Established qu trnh trao i thng

tin nh tuyn s c thc hin. Khi ta s thy c trng thi ca router c dng

nh sau :

A#show ip bgp neighbors

BGP neighbor is 172.16.15.162, remote AS 2, external

link

BGP version 4, remote router ID 172.16.16.254

BGP state = Established, up for 02:02:11

!Output omitted for brevity

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3.2 Qung b tuyn trong BGP

Cc EBGP hng xm khi t c trng thi Estabished cng c th khng

qung b tuyn. iu ny hi khc so vi cc giao thc IGPs khi vic qung b v

nhn din hng xm c mi lin h rng buc ln nhau v u s dng cu lnh

network. Vi giao thc BGP chy trn cc thit b ca Cisco c ba cch a ch

mng c th c qung b vo trong bng nh tuyn BGP (BGP routing table).

Ba phng thc c s dng l :

- Cu lnh Network

- Qua s phn phi tuyn (Route redistribution)

- T mt BGP hng xm

Hnh 17 minh ha cc phng thc c s dng qung b tuyn BGP

Hnh 17 : Cc phng thc qung b tuyn trong BGP

Tip theo chng ta s i nghin cu c th tng phng thc c s dng qung b cc tuyn BGP

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3.2.1 Qung b tuyn s dng cu lnh Network

y l phng thc u tin mt tuyn c th c qung b vo trong

bng nh tuyn BGP. Cu lnh Network c s dng chuyn cc tuyn t bng

nh tuyn (routing table) ti bng nh tuyn BGP ging nh l cc tuyn chy BGP.

Cc tuyn trong bng routing table c hc t cc giao thc nh tuyn ni nh RIP,

IGRP, EIGRP, OSPF hoc IS-IS. Hay cc tuyn tnh, cc tuyn c kt ni trc tip.

Di y l bng nh tuyn ch c cc tuyn kt ni trc tip ca router A

A#show ip route

Codes: C - connected, S - static, I - IGRP, 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 NSSA external

type 2

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

- EGP

i - IS-IS, L1 - IS-IS level-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

Gateway of last resort is not set

172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks

C 172.16.15.160/30 is directly connected,

Serial0/0


Ethernet0/0


Loopback0


Ethernet0/1

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S hot ng ca cu lnh Network ph thuc vo vic t tm tt tuyn trong cc

tin trnh BGP. Mc nh qu trnh t tm tt (autosummariztion) tuyn c cho php

hot ng v th ta phi kho st trng hp ny . nh dng ca cu lnh network nh

sau:

network prefix mask subnet-mask

Tham s subnet-mask l tham s la chn. Nusubnet-maskkhng s dng

BGP s gi thit s dng tham s vi cc ch mc nh ty thuc lp mng . Vi

vic mc nh qu trnh t tm tt c hot ng. Cu lnh networkc s dng

qung b cc tuyn vi tham ssubnet-maskmc nh trong bng nh tuyn BGP. V

th cn phi c t nht mt tuyn vi tuyn subnet dng classful trong bng nh tuyn.

Bng nh tuyn trn router A cha subnets 172.16.0.0/16 do vy qung b tuyn

ny c th s dng cu lnh :

router bgp 1

network 172.16.0.0


Khi bng nh tuyn BGP ca router A s nh sau :

A#show ip bgp

BGP table version is 8, local router ID is 172.16.15.254

Status codes: s suppressed, d damped, h history, *

valid, > best, i - internal

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

Network Next Hop Metric LocPrf

Weight Path

*> 172.16.0.0 0.0.0.0 0

32768 i

Trong v d trn next hop l 0.0.0.0 v thuc tnh AS path l trng ch ra rng

mng 172.16.0.0 bt ngun trn router A. Ta cng c th thy MED l 0 v thuc tnh

Weight c gi tr mc nh l 32768. Sau khi mt tuyn hp l c t trong bng

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nh tuyn BGP , tuyn s c qung b ti router B . Kt qu trong bng nh

tuyn BGP l :

B#show ip bgp






Weight Path

*> 172.16.0.0 172.16.15.161 00 1 i

Mng 172.16.0.0 c qung b thnh cng ti router B. Thuc tnh

NEXT_HOP c t bng giao din c s dng qung b tuyn n router B.

Thuc tnh AS_PATH c t bng 1, MED v Weight c gi tr bng 0. Sau mt

tuyn BGP hp l s c chuyn ti bng nh tuyn trn router B.

B#show ip route

Codes: C - connected, S - static, I - IGRP, 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 NSSA external

type 2

E1 - OSPF external type 1, E2 - OSPF external type 2,E - EGP

i - IS-IS, L1 - IS-IS level-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

Gateway of last resort is not set

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Serial0/1

C 172.16.15.160/30 is directly connected,Serial0/0


Loopback0

B 172.16.0.0/16 [20/0] via 172.16.15.161, 00:09:41

T bng nh tuyn ta c th nhn thy administrative distance (AD) ca EBGP

l 20 v cost hoc metric ca tuyn BGP l 0. BGP khng s dng cost tnh ton

ng i ngn nht m s dng cc thuc tnh BGP nh: Weight, LOCAL_PREF,AS_PATH, MED v ORIGIN thay th.

Mc nh trn cc thit b ca hng Cisco cho php t tm tt tuyn. Tuy nhin

cisco khuyn ngh rng nn hy b ch ny khi s dng BGP. Vic hy b ny

c thc hin bng cch s dng cu lnh: no auto-summary trong cu hnh BGP.

Trn 2 router A v B ta c th cu hnh nh sau :

Router A

router bgp 1

network 172.16.0.0


no auto-summary

Router B

router bgp 2


no auto-summary

Sau khi hy b ch t ng tm tt tuyn mt vn c t ra. l tuyn

172.16.0.0/16 c c qung b hay khng ? Nu kho st bng BGP ca hai router A

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*> 172.16.15.128/27 0.0.0.0 0

32768 i

*> 172.16.15.160/30 0.0.0.0 0

32768 i

*> 172.16.15.254/32 0.0.0.0 0

32768 I

Di y l bng BGP ca router B

B#show ip bgp






Weight Path

*> 172.16.15.64/27 172.16.15.161 0

0 1 i

*> 172.16.15.128/27 172.16.15.161 0

0 1 i

*> 172.16.15.160/30 172.16.15.161 0

0 1 i

*> 172.16.15.254/32 172.16.15.161 0

0 1 i

Bng nh tuyn ca router B s cho ta thy c cc tuyn c qung b t

router A

B#show ip route



Serial0/1


Serial0/0

B 172.16.15.128/27 [20/0] via 172.16.15.161,

00:02:36

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B 172.16.15.254/32 [20/0] via 172.16.15.161,

00:02:36


Loopback0

B 172.16.15.64/27 [20/0] via 172.16.15.161,

00:02:36

3.2.2 Qung b tuyn s dng redistribute

y l phng thc th hai qung b tuyn t bng nh tuyn vo bng nh

tuyn BGP. Phng thc ny cho php qung b cc tuyn kt ni trc tip trn router

vo bng nh tuyn BGP. Tnh cht t ng tm tt tuyn tng t nh trong phn s

dng cu lnh networktc l nu khng hy b ch ny cc tuyn s c tm tt

thnh cc tuyn c a ch v mask mc nh.

Vic phn phi, qung b quan vic redistribute ny c thc hin qua cu lnhredistribute connected.

Trn Router A qu trnh c thc hin bi cc lnh :

Router A

router bgp 1

redistribute connected


no auto-summary

Tng t nh phn 2.1 ta s thy bng nh tuyn BGP v nh tuyn ca 2

router A v B (xt trng hp hy b ch t ng tm tt tuyn ) nh sau :

A#show ip bgp





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Network Next Hop Metric LocPrf Weight

Path

*> 172.16.15.64/27 0.0.0.0 0

32768 ?

*> 172.16.15.128/27 0.0.0.0 0

32768 ?

*> 172.16.15.160/30 0.0.0.0 0

32768 ?

*> 172.16.15.254/32 0.0.0.0 0

32768 ?

B#show ip bgp

BGP table version is 21, local router ID is

172.16.16.254





Weight Path

*> 172.16.15.64/27 172.16.15.161 0

0 1 ?

*> 172.16.15.128/27 172.16.15.161 0

0 1 ?

*> 172.16.15.160/30 172.16.15.161 0

0 1 ?

*> 172.16.15.254/32 172.16.15.161 00 1 ?

B#show ip route

172.16.0.0/16 is variably subnetted, 6 subnets, 3

masks


Serial0/1

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Serial0/0

B 172.16.15.128/27 [20/0] via 172.16.15.161,

00:01:44

B 172.16.15.254/32 [20/0] via 172.16.15.161,

00:01:44


Loopback0

B 172.16.15.64/27 [20/0] via 172.16.15.161,

00:01:44

Ta ch rng khi s dng phng thc ny cc tuyn redistribute c thuc tnh

ORIGIN c t du ? trong bng BGP ca cc router

3.2.3 S dng EBGP qung b tuyn

Phng thc cui cng qung b tuyn BGP vo bng BGP l t BGP

chnh n. Xt topo mng di y

Hnh 18 : Qa trnh s dng EBGP qung b tuyn

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Bng vic s dng cc cu lnh

Router B

router bgp 2



no auto-summary

Router C

router bgp 3


Cho php router mi thm vo nhn din c hng xm vi n l router B v

router B cng nhn din c hng xm ca n l router C. Qu trnh qung b tuyn

din ra gia router B, C cho php router B qung b cc tuyn c trn router A . Kt

qu trong bng nh tuyn v BGP routing ca router C c cc tuyn cn t ti trn

router A

C#show ip bgp






Weight Path

*> 172.16.15.64/27 172.16.16.165

0 2 1 ?

*> 172.16.15.128/27 172.16.16.165

0 2 1 ?

*> 172.16.15.160/30 172.16.16.165

0 2 1 ?

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*> 172.16.15.254/32 172.16.16.165

0 2 1 ?

C#show ip route



Serial0/1

B 172.16.15.160/30 [20/0] via 172.16.16.165,

00:12:21

B 172.16.15.128/27 [20/0] via 172.16.16.165,

00:12:21

B 172.16.15.254/32 [20/0] via 172.16.16.165,

00:12:21


Loopback0


Ethernet0/0

B 172.16.15.64/27 [20/0] via 172.16.16.165,

00:12:21

Thuc tnh AS_PATH trn router C c gi tr 2 1 l cc AS phi i qua t ti

cc tuyn trn router A. V d ny chng minh rng router EBGP qung b tuyn hc

c t mt EBGP hng xm ti mt hng xm khc

3.3 Hot ng ca IBGP

3.3.1 Kho st hot ng ca IBGP

kho st s hot ng ca IBGP ta kho st topo di y

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Hnh 19 : Kt ni IBGP v EBGP

Vic cu hnh EBGP v IBGP cho vic qung b tuyn tng i ging nhau trn

cc thit b ca cisco. Tuy nhin s hot ng ca EBGP v IBGP c phn khc nhau.

kho st ta xem xt cc thng tin trn router D v E khi E qung b cc tuyn kt

ni trc tip vi n:

Router D

router bgp 1


no auto-summary

Router E

router bgp 2

redistribute connected


no auto-summary

Kho st bng routing table v bng BGP routing table ca router D ta thu c

kt qu

D#show ip bgp




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Weight Path

*> 172.16.15.160/30 172.16.15.162 0

0 2 ?*> 172.16.16.164/30 172.16.15.162 0

0 2 ?

*> 172.16.16.254/32 172.16.15.162 0

0 2 ?

D#show ip route


masks

B 172.16.16.164/30 [20/0] via 172.16.15.162,00:27:23


Serial0/0


Ethernet0/0


Loopback0

B 172.16.16.254/32 [20/0] via 172.16.15.162,

00:27:23


Ethernet0/1

Vic thit lp s hot ng ca IBGP gia cc router trong AS 1 tng i ging

so vi vic thit lp s hot ng ca EBGP ngoi tr vic thay i s AS. Trong topo

trn thit lp s hot ng ca IBGP gia router C v D ta s dng cu hnh sau :

Router C

router bgp 1


no auto-summary

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Router D

router bgp 1



no auto-summary

Sau khi thit lp c s hot ng ca IBGP trong AS 1 gia router D v C tao

c th xc nhn quan h gia chng l IBGP. Cc thng tin ch ra bi router D cho

chng ta thy r iu ny:

D#show ip bgp neighbors 172.16.15.129

BGP neighbor is 172.16.15.129, remote AS 1, internal

link

BGP version 4, remote router ID 172.16.15.253


Last read 00:00:24, hold time is 180, keepalive interval is

60 seconds

!Output omitted for brevity

Cc thng tin u ra trn cho thy router C v router D tn ti mi quan h

IBGP hng xm. Thut ng internal link trong thng tin u ra ch r mi quan h

ny. Cc tuyn c qung b t router E n router C qua router D nh sau :

C#show ip bgp


Status codes: s suppressed, d damped, h history, * valid, >

best, i - internal

i - IGP, e - EGP, ? - incomplete


Path

* i172.16.15.160/30 172.16.15.162 0 100

0 2 ?

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* i172.16.16.164/30 172.16.15.162 0 100

0 2 ?

* i172.16.16.254/32 172.16.15.162 0 100

0 2 ?

Tip tc kho st bng nh tuyn trn router C ta nhn thy :

C#show ip route


masks


Ethernet2/0


Loopback0


Ethernet0/0

C 172.16.9.0/30 is directly connected, Serial0/1


FastEthernet1/0

Da vo thng tin trong bng nh tuyn trn ta nhn thy mt s tuyn trong

bng BGP trn router khng c chuyn vo bng nh tuyn trn router C. Tuy

nhin kho st k bng nh tuyn BGP trn router C v D ta thy :

Router D

*> 172.16.15.160/30 172.16.15.162 0

0 2 ?

Router C

* i172.16.15.160/30 172.16.15.162 0 100

0 2 ?

Cc tuyn c cng next hop cho mng 172.16.15.160/30 nhng router D xem

tuyn l mt tuyn hp l v l tuyn tt nht (* >) cn router C cng coi tuyn

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l tuyn hp l ( * ) nhng khng phi l tuyn tt nht. Cc thng tin u ra di y

trn router C cho ta thy iu ny

C#show ip bgp 172.16.15.160

BGP routing table entry for 172.16.15.160/30, version 0

Paths: (1 available, no best path)

Not advertised to any peer 2

172.16.15.162 (inaccessible) from 172.16.15.130

(172.16.15.254)

rigin incomplete, metric 0, localpref 100, valid,

internal, not synchronized

a ch mng 172.16.15.160 v cc a ch khc c nhn t router D l khng

th truy cp. iu ny c ngha l router C khng bit lm th no t c n

NEXT_HOP do BGP khng thay i NEXT_HOP khi thng tin c nhn v qung

b t cc EBGP hng xm ti mt IBGP router. Router D khng thay i NEXT_HOP

172.16.15.162 khi tuyn 172.16.15.160 c qung b ti router C. Tuyn c

xem nh khng th truy cp v n khng tn ti trong bng routing table. gii quyt

vn ny ta c th s dng mt giao thc IGP cho khng nhng cho vic qung b

NEXT_HOP m cn qung b tt c cc mng thuc v AS 1. Trong v d ny ta c

th s dng mt vng n trn router A, B, C, D. C th xy dng mt vng OSPF v

nh danh vng AS 1 s dng cu hnh sau qung b NEXT_HOP :

router ospf 1

network 172.16.0.0 0.0.255.255 area 51

Sau khi gii quyt vn qung b NEXT_HOP. Cc thng tin trong bngnh tuyn, bng BGP s thay i nh sau :

C#show ip route | include 172.16.15.160

O 172.16.15.160/30 [110/74] via 172.16.15.130,

00:05:45, Ethernet2/0

C#show ip bgp 172.16.15.160


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Paths: (1 available, best #1, table Default-IP-Routing-

Table)

Not advertised to any peer 2

172.16.15.162 (metric 74) from 172.16.15.130

(172.16.15.254)

Origin incomplete, metric 0, localpref 100, valid,

internal, synchronized, best

Tip cc tuyn BGP c chuyn vo bng routing table :

C#show ip route

172.16.0.0/16 is variably subnetted, 12 subnets, 3masks

O 172.16.15.160/30 [110/74] via 172.16.15.130,

00:08:45, Ethernet2/0

O 172.16.15.164/30 [110/50] via 172.16.15.97,

00:08:45, FastEthernet1/0

C 172.16.15.128/27 is directly connected, Ethernet2/0

O 172.16.15.251/32 [110/3] via 172.16.15.97,00:08:45, FastEthernet1/0

O 172.16.15.254/32 [110/11] via 172.16.15.130,

00:08:45, Ethernet2/0

C 172.16.15.253/32 is directly connected, Loopback0

O 172.16.15.252/32 [110/2] via 172.16.15.97,


C 172.16.15.32/27 is directly connected, Ethernet0/0

O 172.16.15.0/27 [110/2] via 172.16.15.97, 00:08:46,

FastEthernet1/0

C 172.16.9.0/30 is directly connected, Serial0/1


FastEthernet1/0

O 172.16.15.64/27 [110/12] via 172.16.15.97,


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Mng 172.16.15.160 trong bng routing table l mt tuyn OSPF. Mt cu hi

c t ra l ti sao tuyn khng phi l mt tuyn IBGP ? Cu tr li l do router

C hc v tuyn 172.16.15.160 thng qua OSPF v IBGP tuy nhin OSPF c

Administrative distance (AD) l 110 cn IBGP l 200 v th tuyn OSPF c s dng

. Nhn vo bng routing table ta khng thy bt c tuyn BGP no tuy nhin khi quan

st thng tin u ra trn bng BGP ca router C ta nhn thy :

C#show ip bgp


tatus codes: s suppressed, d damped, h history, * valid,

> best, i - internal



Weight Path

*>i172.16.15.160/30 172.16.15.162 0 100

0 2 ?

* i172.16.16.164/30 172.16.15.162 0 100

0 2 ?

* i172.16.16.254/32 172.16.15.162 0 100

0 2 ?

Tuyn 172.16.15.160, 172.16.16.164, 172.16.16.254 l cc tuyn hp l tuy

nhin 2 tuyn 172.16.16.164 v 172.16.16.254 khng phi l cc tuyn c ng ti

u. Nhn nh trn c kim chng vi tuyn 172.16.16.164 .

C#show ip bgp 172.16.16.164


Paths: (1 available, no best path)

Not advertised to any peer

2

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172.16.15.162 (metric 74) from 172.16.15.130

(172.16.15.254)

Origin incomplete, metric 0, localpref 100, valid,

internal, not synchronized

Cc tuyn khng hp l trn l cc tuyn khng c ng b. ng b l mtc tnh ca IBGP. Lut ng b qui nh mt tuyn BGP nhn t mt IBGP hng

xm khng c coi l hp l nu nh tuyn khng nm trong bng nh tuyn.

Tuyn 172.16.15.160 trong topo trn c ng b bi tuyn nm trong

bng IP routing table vi vai tr ca mt tuyn OSPF. Cc tuyn BGP 172.16.16.164

v 172.16.16.254 khng nm trong bng nh tuyn v th chng c xem l khng

ng b. ni r hn v lut ng b ny ta kho st topo di y

Hnh 20 : ng b trong IBGP

Router A v B thc hin mt kt ni EBGP, Router A qung b tuyn172.16.1.0/24 n router B. Trong AS 2 mt ng kt ni vt l tn ti gia router B

v D thng qua router C. IBGP khng yu cu mt kt ni vt l v cc Router B, D

thc hin c mt kt ni IBGP. Cc thng tin trao i gia router B v D c

thc hin qua kt ni vt l vi router C tuy nhin router C khng bit c nhng ni

dung ca thng tin trao i ny .

Router B v D phi bit c lm cch no c th n c cc tuyn khc. AS 2

chy OSPF qung b tt c cc tuyn trong AS 2. Tt c nhng iu trn nhm thc

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hin mt kt ni IBGP gia cc hai router. Gi s ng b khng phi l c tnh ca

IBGP chng ta kho st cc s kin sau :

1, Router A qung b tuyn 172.16.1.0/24 n router B thng qua EBGP

2, Router B chp nhn tuyn v n bit NEXT_HOP (NEXT_HOP c bitdo tuyn c kt ni trc tip ). Tip tuyn c t vo trong bng routing trn

router B.

3, Router B qung b tuyn n router D thng qua IBGP m khng thay i

NEXT_HOP.

4, Router D chp nhn tuyn v NEXT_HOP c bit thong qua OSPF.

5, Router D qung b tuyn 172.16.1.0/24 n router E trong AS 3.

6, Router E chp nhn tuyn v bit NEXT_HOP v t tuyn ny vo bng

routing table ca n.

7, Gi s mt host trong AS 3 gi mt gi tin n host trn mng

172.16.1.0/24. Host gi gi n router E v router E chuyn tip gi n router D sau

khi n kho st bng nh tuyn ca n.

8, Router D nhn gi v kim tra a ch ch a ra quyt nh chuyn

tip gi tin. Gi c chuyn ti router C.

9, Router C khng bit c tuyn 172.16.1.0/24 v tuyn khng c hc

qua OSPF hay BGP v th router C hy gi.

Mc nh cc router Cisco cho php ng b, cu lnhno synchronization chophp tt ch ny. Khi cc tuyn qung b bi router D s c chuyn n bng

IP routing table trn router C.

C#show ip bgp






Path

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*>i172.16.15.160/30 172.16.15.162 0 100

0 2 ?

*>i172.16.16.164/30 172.16.15.162 0 100

0 2 ?

*>i172.16.16.254/32 172.16.15.162 0 100

0 2 ?

C#show ip route | i B

B 172.16.16.164/30 [200/0] via 172.16.15.162,

00:02:28

B 172.16.16.254/32 [200/0] via 172.16.15.162,

00:02:28

Tip tc kho st vic qung b tuyn t router C n router B. qung b cc tuyn t router C n router B, 2 router cn thit lp mt tin

trnh BGP, mi quan h hng xm gia chng :

Router C

router bgp 1

no synchronization



no auto-summary

Router B

router bgp 1


Kho st thng tin u ra v mi quan h gia cc router v bng nh tuyn carouter B

B#show ip bgp neighbors 172.16.15.98 | include

Established


B#show ip bgp

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!no output

T cc thng tin u ra ta nhn thy router C khng qung b bt k tuyn BGP

no ti router B. c tnh ny minh ha s hot ng khc nhau gia IBGP v EBGP.

Tt c cc router chy IBGP khng c qung b cc tuyn hc c t mt IBGPhng xm n mt IBGP hng xm khc. S d IBGP hot ng nh vy l do c tnh

chng loop ca BGP. Do Thuc tnh AS_PATH c s dng chng loop nn n

khng qung b tuyn khi thy AS ca chnh n. V th cc tuyn IBGP khng c

qung b. Chnh iu ny khin cc IBGP routers cn mt cu hnh full mesh , tt c

cc routers chy IBGP u cn c kt ni n tt c cc router khc chy IBGP trong

cng mt AS.

Nh ni trn cc IBGP hng xm khng cn mt kt ni vt l thit lpmi quan h. Yu cu cn thit y ch l mt kt ni IP gia chng. Tuy nhin

chng ta s dng a ch cc giao din vt l thit lp mi quan h hng xm gia

cc router v th khi cc giao din vt l gp li cng s khin cho kt ni BGP li

theo. gii quyt vn ny BGP cng nh cc giao thc IGPs a ragii php v

a ch loopback

3.3.2 Giao din loopback trong IBGP

Vn t ra khi xy dng cu hnh cc router trong AS 1 l chuyn s g xuthin khi a ch vt l hoc tuyn gp s c.

Hnh 21 : IBGP khng yu cu kt ni vt l gia cc hng xm

Trong topo trn router D c ba tuyn n c router C tuy nhin nu kt ni

vt l gp s c nhng tuyn khc cng khng th c s dng nu nh mi quan h

hng xm c nh ngha trn cc giao din vt l gp s c.

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Thay cho vic s dng a ch trn cc giao din vt l ngi ta s dng a ch

loopback. Vi topo trn tuyn ng tt nht t router D ti C l kt ni trc tip

thng qua giao din loopback. Tng t nu kt ni trc tip ny li router D s la

chn cc tuyn qua A v n C hoc tuyn qua A, B v ti C. Vic khai bo v s

dng a ch loopback cng tng i d dng

Router A

router bgp 1

no synchronization


neighbor 172.16.15.252 update-source Loopback0





no auto-summary

Router B

router bgp 1

no synchronization







no auto-summary

Router C

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router bgp 1

no synchronization







no auto-summary

Router D

router bgp 1

no synchronization








no auto-summary

Mt vn na t ra khi s dng IBGP l vic thc hin mt cu hnh full mesh

gia cc router. Cu hnh full mesh s to ra mt s lng cc kt ni ln . S kt ni

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IBGP cn thit cho mt full mesh da vo s lng IBGP router v c cho bi cng

thc

S kt ni = [(n)(n-1)]/2.

BGP cng a ra cc phng n gii quyt vn ny

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3.3.3 Route-Reflector (RR)

Mt route reflector l mt router c cu hnh chuyn nhng cp nht nh

tuyn n cc router hng xm hoc cc router chy BGP bn trong mt AS. Cc

router IBGP cn phi c ch ra nh l client trong khi cu hnh. Khi mt client gimt cp nht nh tuyn n route-reflector, n s chuyn update n cc router

client khc. c bit, route-reflector nh ngha lut split horizon. Lt ny qui nh

rng mt IBGP router s khng truyn mt tuyn c hc t mt router hng xm

trong cng mt AS. Route Reflector v client s i hi mt quan h hng xm y

bi v route reflector s gi cc cp nht t cc client khc nhng vic thit lp hng

xm gia cc client l khng cn thit.

Mt route-reflector s kt ni n cc hng xm m n khng y tuyn n. Tquan im ca route-reflector, cc hng xm ny c gi l non-clients. Cc router

non clients phi c kt ni full mesh vi cc route-reflector v vi cc non-client

khc. Khi mt router cu hnh nh mt route-reflector, n s y nhng ng i

c hc t cc IBGP khc ch n cc route-reflector clients v ti cc IBGP/EBGP

hng xm. iu ny c ngha l mt thit k hub-and-spoke c th c trin khai

trong mt AS gia cc IBGP hng xm, nh vy gim thiu s phin gia cc router.

C route-reflector v cc client ca n hnh thnh nn mt n v chia s thng tin.

n v ny gi l cluster.

Mt Autonomous System c th c chia ra thnh cc cluster, trong cc cluster

s c cc route-reflector c ch nh v cu hnh. Phi c t nht mt route-reflector

trong mi cluster. Nu mt route-reflector kt ni n cc route reflector khc, route-

reflector phi c full mesh. iu ny nhm m bo cc bng IBGP routing l y

. Khi mt route-reflector chuyn i mt cp nht nh tuyn, thuc tnh

Originator_ID s c thit lp. y l BGP routerID ca router to ra ng i.

Nu router ny nhn li bn cp nht nh tuyn , router s thy ID ca chnh n vs b qua thng tin ny. iu ny nhm ngn nga v tng kh nng loop. Nu c

nhiu route-reflector trong cluster, cc router s phn bit vi nhau bng clusterID.

Thng s ny phc v cng mt mc ch nh thuc tnh Originator_ID ngn nga

loop.

Vi cch dng route-reflector, router ng vai tr route-reflector s tn nhiu ti

nguyn hn. Nu cu hnh route-reflector khng chnh xc, n c th gy ra loop. C

nhiu mc route-reflector c th c cu hnh bng cch to ra cc thit k theo th

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bc. Cc router khng l thnh phn ca route-reflector s khng b nh hng trong

nhng thay i v thit k v nhng thay i v qu trnh truyn cc cp nht. Thay

vo , cc router ny s khng nhn bit c bt c thay i no v n vn nhn

c cc cp nht m n cn. Bn thn cc cp nht nh tuyn cng khng b thay i

bi v khng c s thay i no trong gi tr cc thuc tnh c mang trong cc cp

nht nh tuyn.

Chnh v cc c im trn, qu trnh chuyn i thit k mt h thng mng no

sang dng dng route-reflector th rt d dng. Mt thit k quan trng l bn thn

cc route-reflector trong mt AS cng phi full mesh. Ngoi ra, mt route-reflector

ny c th l client cho mt route-reflector khc. Thit k nh vy kh phc tp v yu

cu xem xt cn thn bi v khi cc route-reflector c cu hnh v split horizon b

hy b, khng cn mt c ch no bo v v chng loop.

Hnh 22: Thit k Route-reflector

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Cc li ch ca route-reflector bao gm

- Kh nng m rng mng

- Thit k mang tnh cu trc cao

- Gim lu lng mng.

- Gim b nh v CPU cn thit duy tr cc phin TCP trn cc IBGP hng

xm.

- Hi t nhanh hn v mng tr nn n gin hn bi v c n hai giao thc

nh tuyn c dng: IBGP cho cc thng tin nh tuyn bn ngoi i qua AS; IGP

cho cc router bn trong mt AS.

Hnh 23: Cu hnh cc route-reflector

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Hot ng ca Route Reflector:

Mt Route Reflector n gin ging nh mt tm gng phn hi cc bn cp

nht nh tuyn t cc client n cc client khc m khng yu cu mt mng phi full

mesh. Khi mt RR nhn c mt cp nht:

- Client s chuyn cp nht tuyn cho router hng xm ca n, trong trng

hp ny l RR

- Mt cp nht tuyn t client c nhn t RR v cp nht s c chuyn n

cc RR clients cng nh nonclients. Thng s originatorID ban u s b loi tr ra

khi cp nht.

- Nu c nhiu ng i nhn c t RR, ng i tt nht s c chn thng

qua RR.

- Mt nonclient router s chuyn cc cp nht ti cc lng ging ca n, c th l

mt RR.

- Mt RR nhn mt cp nht tuyn t mt router nonclient v cp nht tuyn ch

c chuyn n clients

- Khi cp nht tuyn n t EBGP c client v non-clients u nhn c thng

tin nh tuyn t RR

Hnh 24: Phn x tuyn RR

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Router C hot ng nh mt router reflector vi cc router A,B,D l cc client.

Cu hnh ca cc router c cho di y

Router A

router bgp 1

no synchronization



no auto-summary

Router B

router bgp 1

no synchronization



no auto-summary

Router D

router bgp 1

no synchronization




no auto-summary

Router C

router bgp 1

no synchronization


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neighbor 172.16.15.251 route-reflector-client







no auto-summary

3.3.4 Phn cp nh tuyn trong cc AS (Confederations)

Confederations cng l mt cng ngh nhm gim s kt ni IBGP. Hot ng

ca phng php ny da trn vic phn chia AS thnh cc AS con c nh s AS

theo qui tc AS ring ( 64512 n 65534).

Hnh 25 : Phn chia AS trong confederations

Trong topo v d hnh 25 AS 1 c phn chia ra lm hai AS khc v c nh

s theo qui nh m bo lm mt AS ring ( private AS ). Hai router B v C c

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nhm vo cng mt AS l 64555 , Hai router cn li trong AS 1 l A v D c nhm

vo AS 64556. Cu hnh cc router c cho di y :

Router A

router bgp 64556

no synchronization

bgp confederation peers 64555




no auto-summary

Router B

router bgp 64555

no synchronization



no auto-summary

Router C

router bgp 64555

no synchronization

bgp confederation peers 64556




no auto-summary

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Router D

router bgp 64556

no synchronization

bgp confederation identifier 1




no auto-summary

Trn y l hai phng php gim s kt ni trong IBGP. Hai phng php trn

c th s dng ring r hoc c th kt hp vi nhau. Tuy nhin s kt hp gia hai

phng php trn s ko theo mt cu hnh phc tp gy kh khn cho qun tr vin.

Hnh 26: S kt hp ca 2 phng php RR v Confederations

3.4 Gii thut nh tuyn trong BGP

nh tuyn trong BGP nh ni trn da vo cc thuc tnh. Da vo u

tin gia cc thuc tnh m BGP a ra quyt nh nh tuyn. Gii thut nh

tuyn c th hin qua s di y :

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Qu trnh chn tuyn c m t theo th t u tin gia cc thuc tnh nh sau :

Khi cc tuyn c nhn bi cc BGP router vic u tin n lm l kim tra thuc

tnh NEXT_HOP. Nu NEXT_HOP khng th t c (khng nm trong bng IP

routing ) tuyn s b t chi. Vi cc tuyn c nhn t cc IBGP hng xm,

ngoi vic kim tra thuc tnh NEXT_HOP router s kim tra lut ng b trn router.

Nu lut ng b c cho php hot ng trn router th cc tuyn khng ng b s

b t chi cp nht vo bng nh tuyn. Sau khi kim tra v tt c cc iu kin

trn u tha mn qu trnh chn tuyn trong BGP s c thc hin da trn mc

u tin gia cc thuc tnh v theo th t ln lt di y :

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- u tin tuyn c thuc tnh WEIGHT cao nht (Ch c tc dng trn router)

- u tin tuyn c thuc tnh LOCAL_PREF cao nht (Thuct tnh ny c tc

dng trong mt AS). Nhng tuyn khng c thuc tnh LOCAL_PREF s c gi tr

mc nh l 100.- u tin cc tuyn gc (c NEXT_HOP l 0.0.0.0)

- u tin tuyn c thuc tnh AS_PATH thp nht

- u tin cc tuyn c ngun gc thp nht theo th t u tin IGP, EGP v

INCOMPLETE

- u tin tuyn c thuc tnh MED (metric) thp nht (thuc tnh ny c gi tr

gia cc AS khc nhau ).

- u tin cc tuyn EBGP hn so vi IBGP

- u tin nhng ng i c IGP metric thp nht n BGP NEXT_HOP

- u tin nhng ng i n t BGP router c routerID nh nht

3.5 S tm tt tuyn trong BGP

kho st qu trnh tm tt tuyn trong BGP ta xt topo mng di y :

Hnh 27 : Tm tt tuyn trong BGP

Router A qung b 4 tuyn n cc router B v Router C thng qua EBGP.

Thuc tnh AS_PATH cho tuyn 156.26.0.0 trn Router B bng 1 v trn Router C

bng 2 1.

Kho st thng tin v tuyn trn 2 router B v C ta thu c nh sau:

B#show ip bgp




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Path

*> 156.26.32.0/24 172.16.15.1 0

0 1 i

*> 156.26.33.0/24 172.16.15.1 0

0 1 i

*> 156.26.34.0/24 172.16.15.1 0

0 1 i

*> 156.26.35.0/24 172.16.15.1 0

0 1 I

C#show ip bgp






Path

*> 156.26.32.0/24 172.16.15.97 0

2 1 i

*> 156.26.33.0/24 172.16.15.97 0

2 1 i

*> 156.26.34.0/24 172.16.15.970 2 1 i

*> 156.26.35.0/24 172.16.15.97

0 2 1 i

Trn cc thit b ca Cisco qu trnh tm tt tuyn c thc hin bi cu lnh

aggregate-address. BGP ch tm tt tuyn trong bng BGP routing table.

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Hnh 28 : Tm tt tuyn trong BGP

Xt qu trnh tm tt bn tuyn ca router A trn router B. Qa trnh tm tt

c thc hin nh sau :

Router B

router bgp 2

aggregate-address 156.26.32.0 255.255.252.0



Kho st bng BGP routing trn router B ta thy xut hin tuyn tm tt.

B#show ip bgp






Path

*> 156.26.32.0/24 172.16.15.1 0

0 1 i

*> 156.26.32.0/22 0.0.0.0

32768 i

*> 156.26.33.0/24 172.16.15.1 0

0 1 i

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*> 156.26.34.0/24 172.16.15.1 0

0 1 i

*> 156.26.35.0/24 172.16.15.1 0

0 1 i

Tuyn tm tt ny c NEXT_HOP l 0.0.0.0 v n xut pht t chnh router B.

Cng v th m thuc tnh AS_PATH khng c t y.

Tip tc kho st bng BGP routing trn 2 router A v C :

A#show ip bgp



best, i - internal



Path

*> 156.26.32.0/24 0.0.0.0 0

32768 i

*> 156.26.32.0/22 172.16.15.2

0 2 i

*> 156.26.33.0/24 0.0.0.0 0

32768 i

*> 156.26.34.0/24 0.0.0.0 0

32768 i

*> 156.26.35.0/24 0.0.0.0 032768 I

C#show ip bgp





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Weight Path

*> 156.26.32.0/24 172.16.15.97

0 2 1 i

*> 156.26.32.0/22 172.16.15.97

0 2 i

*> 156.26.33.0/24 172.16.15.97

0 2 1 i

*> 156.26.34.0/24 172.16.15.97

0 2 1 i

*> 156.26.35.0/24 172.16.15.970 2 1 i

Tuyn tm tt c qung b ti hai router A v C ng thi cc tuyn nm

trong tuyn tm tt cng c qung b. y l im khc ca BGP so vi cc

giao thc IGPs v cc giao thc IGPs ch qung b cc tuyn tm tt m khng qung

b cc tuyn con nm trong tuyn tm tt y.

Tuy nhin cc thit b ca Cisco cng cho php ch qung b tuyn tm tt m

khng qung b cc tuyn con bng cch thm t kha summary-onlytrong cu lnhaggregate-address.

Cu hnh c th c cho di y :

Router B

router bgp 2

aggregate-address 156.26.32.0 255.255.252.0 summary-only



Kt qu thng tin thu c u raB#show ip bgp


172.16.15.252

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best, i - internal



Weight Path

s> 156.26.32.0/24 172.16.15.1 0

0 1 i

*> 156.26.32.0/22 0.0.0.0

32768 i

s> 156.26.33.0/24 172.16.15.1 00 1 i

s> 156.26.34.0/24 172.16.15.1 0

0 1 i

s> 156.26.35.0/24 172.16.15.1 0

0 1 i

Cc tuyn con u trong trng thi treo v khng c qung b. Vic khng

qung b c th hin trong bng BGP routing ca router C

C#show ip bgp


172.16.15.253


best, i - internal



Weight Path

*> 156.26.32.0/22 172.16.15.97

0 2 i

3.6 Qun l lu lng trong BGP

Cc cp nht tuyn BGP c th c kim sot. Nhn chung, trong cc giao thc

nh tuyn, kim sot cc cp nht tuyn l vic phi lm. Vic kim sot cc cp nht

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gip cho n gin ho h thng mng v d dng bo tr. Vic thit k cc thng tin

nh tuyn c chuyn i nh th no cng c xem l mt tc v c bn ca bo

mt mng v iu ny gip cho gim nguy c b routing-loop.

C ba cch p t PBR (Policy Based Routing) trong BGP:- Ra quyt nh da trn thuc tnh AS_PATH, thuc tnh community hoc

prefix

- T chi hay chp nhn cc tuyn c chn

- Thit lp cc thuc tnh nh hng n qu trnh chn la ng i.

Qu trnh t chi hay chp nhn cc routes yu cu mt vi dng ca tc v lc

tuyn thng qua cc ACL. Tc v lc tuyn khng ch c dng trong PBR m cn

kim sot lu lng trong mng. C ba dng lc tuyn trong Cisco router:

- Access-list cho AS_PATH

c dng lc cc AS. Mt ACL c dng trong BGP s lc cc cp nht tuyn

gi t mt router hng xm da trn AS path.

- Prefix list

c dng lc cc tuyn, c bit trong qu trnh redistribution. T Cisco

IOS v.11.2, cc ISP s dng cc prefix-list l mt dng kh hiu qu ca lc tuyn. C

ch dng prefix-list da trn a ch ca mt tuyn.

- Distribute lists

+ Distribute-list c dng lc cc cp nht. Mc d distribute-list thng

c dng trong redistribution, cng c ny khng ch dnh ring cho qu trnh

redistribution. N c th p dng cho cc lu lng theo chiu vo v chiu ra t bt

c cc hng xm no. C prefix-list v distribute-list u lc da trn a ch mng

ch khng dng AS_PATH.

+ Route maps: Route map c dng nh ngha chnh sch nh tuyn. Mt

route-map l mt access-list phc tp qua router hot ng khi mt match c

nhn dng. Route map c dng trong BGP xc lp cc thuc tnh ca BGP

chn ra ng i tt nht.

Hot ng ca Prefix-list:

Prefix-list ch tm kim trn phn network ca mt a ch nn qu trnh tm kim

l rt nhanh. iu ny c bit quan trng trong khi tm kim nhng bng nh tuyn

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kch thc ln trong BGP. Mt thun li khc ca prefix-list l kh nng son tho.

Mc d trong ACL truyn thng vn cho php son tho ng (dng named ACL),

prefix-list c th to v s dng d dng. iu ny khng ch ng vi tnh nng son

tho m cn vi giao din ci tin.

Trc khi p dng mt prefix-list vo mt qu trnh hay mt cng giao tip,

ngi qun tr phi nh ngha cc tiu ch cho access-list. Mi dng trong prefix-list

c kt hp vi mt ch s, tng t nh cc dng trong mt chng trnh my tnh.

Nu ta khng nhp vo ch s th t (sequence-number), ch s ny s c t ng

to ra, vi mi ln tng l 5. Cc s khng c dng, chng hn nh t 1 n 4 cho

php cc dng thm vo v sau. Ta c th son tho prefix-list bng cch ch ra ch s

dng hoc sequence-number. Kh nng ny l khng c trong ACL.

Prefix-list hot ng bng cch tm cc prefix trong danh sch ph hp vi cc

prefix ang kim tra. Nu mt iu kin kim tra ph hp xy ra, tuyn s c dng

hay b loi b. C th, khi c mt prefix b t chi hoc c cho php, cc lut sau s

c dng:

- Nu mt tuyn c cho php, tuyn s c dng

- Nu mt tuyn b t chi, tuyn s khng c dng

- Kt thc ca mi prefix-list l mt pht biu ngm nh t chi tt c cctuyn. Nh vy, nu cho trc mt tuyn m tuyn ny khng ph hp vi mt u

vo trong prefix-list, prefix s b t chi theo lut mc nh.

- Nu c nhiu u vo trong mt prefix list ph hp vi mt tuyn, u vo c

ch s sequence number nh nht s c dng.

- Router bt u tm kim nh ca prefix-list, vi ch s sequence-number

bng 1. Khi mt thng tin lc tuyn ph hp c tm thy, qu trnh tm kim kt

thc. Thi gian x l s c gim nu cc iu kin match/deny c t u ca

danh sch. iu ny ngn nga vic phi x l cc iu kin him khi gp mi khi mttuyn c kim tra.

- Cc ch s sequence number t ng gia tng theo mc nh. cu hnh

sequence-number, dng thng s seq seq-value trong lnh ip prefix-list.

- Ch s sequence number khng cn thit ch ra khi xa mt dng trong cu

hnh.

Cu hnh BGP prefix-list

Dng lnh sau cu hnh prefix-list:

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Router(config-router)#ip prefix-list prefix-list-name [seq seq-value] {deny|

permit} network/len [ge ge-value] [le le-value]

Thng s (Parameter) M t (Description)Prefix-list-name Tn ca prefix-list

[ seq seq-value ] S th t c gn n tiu chun angnh ngha

{deny | permit} Hnh ng l t chi hoc cho php ivi kt qu

Network/len chiu di ca prefix phi ph hp[ge ge] [le le_value] Ch ra chiu di ca prefix cn phi ph

hp cu hnh mt router dng prefix-list nh l tc v lc trong distribute-list,

dng lnh sau:

Router(config-router)#neighbor {ip address|peer-group} prefix-list prefix-list-

name {in|out}

KT LUN

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Vi s pht trin ngy cng mnh m ca mng Internet, ti nghin cu Tng

quan giao thc nh tuyn BGP trn router Cisco l ti thc t gip ngi c tip

cn v c hiu bit c bn v cch thc nh tuyn gia cc vng t tr, mt thnh

phn quan trng trn Internet . ti gp phn gip cho tc gi v nhng ngi thamkho:

- Hiu v nm c cc thuc tnh, gii thut c s dng trong BGP nh

tuyn.

- Hiu r vai tr, hot ng v cu trc cc thng bo ca EBGP v IBGP trong

h thng mng ngy nay.

- Cc phng php gii quyt vn full mesh trong BGP.

- Mt s phng php c s dng kim sot lu lng trong BGP.

Mc d t c mt s kt qu nu trn nhng do iu kin thi gian v thit b thc

nghim cn hn ch nn vic nghin cu giao thc BGP trn nn Ipv6 cha th c

thc hin.

ti c th c m rng nghin cu v trin khai giao thc BGP cng cc

giao thc IGP da trn phn mm m phng GNS3. Vic nghin cu hot ng ca

BGP trn h thng Ipv6 cng l mt vn cn c quan tm khi h thng Ipv4 ang

ngy cng cn kit.

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TI LIU THAM KHO

[1] CCNP Self-Study, CCNP BSCI Exam Certification Guide, Third

Edition. Cisco Press. 2004

[2] CCIE 350-001 Routing and Switching Prep Kit. BareWolf, Inc. 2000

[3] Routing FirstStep By Bill Parkhurst. Cisco Press. 2004

[4] http://www.cisco.com

[5] http://www.vnpro.org

Documents

TaiLieuTongHop.com---Giao Thuc Dinh Tuyen Bgp (Border Gateway Protocol)