TNG QUAN GIAO THC NH TUYN BGP TRN ROUTER CISCOSinh vin thc hin : L V Thng Gio vin hng dn: Th.s Trn Quang t

1. Tng quan v giao thc BGP

BGP(Border Gateway Protocol) l giao thc nh tuyn nng ct trn Internet. BGP hot ng da trn vic cp nht mt bng cha cc a ch mng v cho bit mi lin kt gia cc h t tr BGP l giao thc path vector qu trnh nh tuyn ca BGP da trn cc thuc tnh (Atribute)

2. AS v cc thuc tnh ca BGP2.1 H t tr (Autonomous System) L mt tp hp cc mng c cng chnh sch nh tuyn v thng thuc quyn qun l, khai thc ca mt ch th. 2.2 Cc thuc tnh ca BGP Cc thuc tnh ca BGP c chia lm 4 nhm:

Nhm well-known mandatory: Nhm ny l cc thuc tnh cn c bit bi tt c cc router v qung b ti tt c cc router Nhm well-known discretionary: Nhm ny l cc thuc tnh khng bt buc cc router cn bit tuy nhin nu bit cc router s c x l thch hp

Nhm optional transitive : Cc thuc tnh ca router nu thuc nhm ny s c chuyn tip nu router khng hiu n Nhm optional nontransitive: Cc thuc tnh ny s khng c chuyn tip nu router khng hiu n

2.2.1 Thuc tnh WEIGHT - y l trng s s dng nh tuyn. N c tc dng cc b trn mi router. Router c trng s weight ln s c u tin hn trong vic la trn ng i - Thuc tnh ny do cisco nh ngha. Trn cc router gi tr ny mc nh l 32768

2.2.2 Thuc tnh Local Preference (LOCAL_PREF) - Thuc tnh ny thuc nhm well-known discretionary. - LOCAL_PREF l mt s 32 bit, c s dng trong mt AS v c gi tr mc nh trn cc router l 100 - Cc gi tr ln ca LOCAL_PREF c u tin s dng nh tuyn

2.2.3 Thuc tnh AS_PATH - Thuc tnh ny thuc nhm well-known mandatory v c s dng cho vic chn tuyn v tng t nh vic m s hop trong rip - AS_PATH l mt s 16 bit chia lm 2 loi: AS public v AS private - AS_PATH cn c s dng chng loop trong BGP

2.2.4 Thuc tnh MED (Metric)- Thuc tnh ny thuc nhm optional nontransitive v c s dng chn tuyn gia cc AS khc nhau - Khc vi cc thuc tnh trn MED u tin cc gi tr nh hn khi n c s dng nh tuyn - u tin nh tuyn ca thuc tnh ny ng sau cc thuc tnh Weight, Local_Pref, AS_Path.

2.2.5 Thuc tnh ORIGIN - Nm trong nhm well-known mandatory : Thuc tnh ny cho php xc nh cc tuyn c hc nh th no: + IGP: T cu lnh network + EGP: T mt EBGP hng xm + Incomplete : Tuyn c hc thng qua redistribution

2.2.6 Thuc tnh NEXT_HOP L tiu ch u tin kim tra iu kin nh tuyn. Nu NEXT_HOP khng t c trn mt router. Qa trnh nh tuyn s chm dt

3. Thit lp mi quan h gia cc router trong BGP

Khi s dng BGP cho vic nh tuyn cn ch r hng xm cho n. Qu trnh thit lp mi quan h vi hng xm v trao i thng tin nh tuyn c thc hin qua 6 giai on:

Idle State Connect State Active State OpenSent State OpenConfirm State Entablished

Cu trc cc thng bo trong BGP

Thng bo OPEN

Thng bo UPDATE

Thng bo Notification

4. Qa trnh nh tuyn trong BGP

Qu trnh nh tuyn c thc hin theo th t cc bc sau: - 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 (Thuc 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 tuyn c IGP metric thp nht n BGP NEXT_HOP - u tin nhng tuyn t BGP router c RouterID nh nht