Cc cu 4 im v bn cht ging ht nhau nn ch cn hc k 1 cu l ok ht! quan trng nht l phi cp n l cp Object, Value.***Trnh by cu trc bn tin SNMPv2 v phn tch cch thc truyn bn tin ny trong mng IP.cu trc hay khun dng bn tin SNMPv2: phi v cu trc bn tin sau gii ngha tng trng (nh l khng c b st trng no c). Cu trc bn tin SNMPv2, phn tch cc trng trong

(ci ny 1 v vo my tnh )+ version : phin bn SNMP (v1 = 0, v2c = 1, v2u = 2, v3 = 3).+ community string : chui community. y l password xc nhn + data : phn data l cc bn tin ng vi cc phng thc ca SNMP.Trong SNMPv2c, bn tin PDU c 2 loi cu trc l PDU v BulkPDU. Cc bn tin GetRequest, GetNextRequest, SetRequest, Response, Trap, InformRequest v Report c cng cu trc l PDU; cn GetBulkRequest c cu trc l BulkPDU ring (ci ny c bit vn cha thng nht nhng s da vo mib lm)

Cu lnhGi tr trong trng PDU

GetRequest 0

GetNextRequest 1

Response 2

SetRequest 3

GetBulkRequest 4

InformRequest5

SNMPv2-Trap 6

Report7

Trng hp 1: Cu trc PDU

Trng PDU type th ly bng trn request-id : m s ca request. ID ny l s ngu nhin do manager to ra, agent khi gi bn tin Response cho request no th n phi gi requestID ging nh lc nhn. Gia manager v agent c th c nhiu request & reponse, mt request v mt response l cng mt phin trao i khi chng c requestID ging nhau. error-status : nu = 0 l thc hin thnh cng khng c li, nu 0 l c li xy ra v gi tr ca n m t m li. Trong cc bn tin request th error-status lun = 0. error-index : s th t ca objectid lin quan n li nu c. Trong variable-bindings c nhiu objectid,c nh s t 1 n n. variable-bindings : danh sch cc cp [ObjectID Value] cn ly thng tin, trong objectId l nhdanh ca object cn ly, cn value l gi tr ca object . Khi agent gi bn tin request th value l khng xc nh, khi gi tr li th n s in vo value bng gi tr ca object.

Trng hp 2: Cu trc Bulk PDU

Cc trng kia th ging trn nha, lu 2 trng sau: + non-repeaters : s lng item u tin trong variable-bindingsca GetBulk m agent phi tr li bng item nm ktip trong mib, mi item trong request th s c mt item trongresponse.+ max-repetitions : cc item cn li trong variable-bindingss c agent tr li bng max-repetitions item nm k tipchng trong mib, mi item cn li trong request ny s cmax-repetitions item tng ng trong response.Ngoi l: cho dy s nguyn 1 2 3 4 5 6 7 8 9 Nu chn 1,3,5 th s item l 3Nu t gi tr non=2, max =2 th kt qu tr v s l2,4,6,7***cch thc truyn bn tin ny trong mng IP.Cu trc chung ca bn tin SNMPv2c nh sau

ti lp ng dng: cc cp object v value c tp hp li thnh trng variable, sau c thm phn PDU header to thnh trng PDU SNMPv2. Sau PDU SNMPv2 c gn thm trng version v community to thnh bn tin SNMPv2 hon chnh v chuyn xung lp vn chuyn ti lp vn chuyn: gi tin SNMP c gn thm UDP header ng vo gi UDP, trng UDP header bao gm Port ch v Port ngunAgent lng nghe request cng UDP 161 cn manager nhn trap & inform cng UDP 162.Ni dung header bao gm cc thng tin c bn:-phng thc truyn udp-source port: (random)-destination port: 161-checksum( kim tra li)-total length: tong chiu di lp lin mng gi udp c ng gi ip bng cch gn thm ip header, trong phn ip header gm cc trng-version:-headerlength-precedence-tos-total length-datagram id-fragmentaion -ttl-protocol-checksum-source address-destination addressOptions

sau gi ny c chuyn xung lp truy cp mng ti lp truy cp mng, gi ip c ng gi vo khung Ethernet, c gn thm cc trng saupreamble, sfd, destination address, source address type/length v fcs ri chuyn xung lp vt l, lp vt l thc hin nt nhim v cn lici ny tham kho lm phn sau:SetRequest: Thc hin t Manager ti Agent. SetRequest tm kim cc thng tin m rng trong bng MIB v yu cu Agent t gi tr cho cc i tng qun l hoc cc i tng cha trong cu lnh. SetRequest lin quan ti s tn ti ca cc i tng b qun l v cc phng thc truy nhp.GetResponse: Thc hin t Agent ti Manager. Cu lnh ny cung cp c ch p ng cho cc cu lnh GetRequest, GetNextRequest v SetRequest. Cc thng tin trong cu lnh GetResponse gm mt s trng chc nng cho php p ng cc cu lnh nhn trc .Trap: Cu lnh c lp.Trap a ra cc thng tin lin quan ti cc iu kin c nh ngha trc v c gi t cc Agent ti Manager.GetBulkRequest: Chc nng ca cu lnh GetBulkRequest tng t nh cu lnh GetNextRequest ngoi tr vn lin quan ti s lng d liu c ly ra. GetBulkRequest cho php Agent gi li Manager d liu lin quan ti nhiu i tng thay v tng i tng b qun l. Nh vy, GetBulkRequest c th gim bt lu lng truyn dn v cc bn tin p ng thng bo v cc iu kin vi phm. InformRequest: Cu lnh InformRequest cung cp kh nng h tr cc Manager b tr theo cu hnh phn cp.Cho php mt Manager trao i thng tin vi cc Manager khc. Cc cnh bo v s kin c gi i trong cu lnh InformRequest pht hin v khi to li cc tuyn truyn bn tin. Phn cn li cc bn nn tham kho ca qu ptit! Bi cc bn y lm kh ok