C bn v giao thc SNMP SNMP (Simple Network Management) SNMP l giao thc qun l mng n gin, dch t cm t Simple Network Management Protocol. L giao thc c s dng rt ph bin gim st v iu khin thit b mng nh switch, router, server ... Giao thc SNMP c thit k cung cp mt phng thc n gin qun l tp trung mng TCP/IP. Nu bn mun qun l cc thit b t 1 v tr tp trung, giao thc SNMP s vn chuyn d liu t client (thit b m bn ang gim st) n server ni m d liu c lu trong log file nhm phn tch d dng hn SNMP dng qun l tc l c th theo di, c th ly thng tin, c th c thng bo, v c th tc ng h thng hot ng nh mun. VD mt s kh nng ca phn mm SNMP : +Theo di tc ng truyn ca mt router, bit c tng s byte truyn/nhn. + Ly thng tin my ch ang c bao nhiu cng, mi cng cn trng bao nhiu. + T ng nhn cnh bo khi switch c mt port b down. + iu khin tt (shutdown) cc port trn switch. Hot ng ca SNMP C 2 nhn t chnh trong SNMP: Manager v Agent. Cc SNMP agent s gi mt s s d liu, c gi l Management Information Base (MIB), trong cha cc thng tin khc nhau v hot ng ca thit b m agent ang gim st. Phn mm qun tr SNMP Manager s thu thp thng tin ny qua giao thc SNMP.

u im khi thit k h thng qun tr vi SNMP s gip n gin ha cc qu trnh qun l cc thnh phn trong mng, gim chi ph trin khai.SNMP c thit k c th m rng cc chc nng qun l, gim st. SNMP c thit k c th hot ng c lp vi cc kin trc v c ch ca cc thit b h tr SNMP. Cc c ch bo mt cho SNMP

Mt SNMP management station c th qun l/gim st nhiu SNMP element, thng qua

hot ng gi request v nhn trap. Tuy nhin mt SNMP element c th c cu hnh ch cho php cc SNMP management station no c php qun l/gim st mnh. Cc c ch bo mt n gin ny gm c : community string, view v SNMP access control list. Community String Community string l mt chui k t c ci t ging nhau trn c SNMP manager v SNMP agent, ng vai tr nh mt khu gia 2 bn khi trao i d liu. Community string c 3 loi : Readcommunity, Write-Community v Trap-Community. View Mt view phi gn lin vi mt community string. Ty vo community string nhn c l g m agent x l trn view tng ng. SNMP access control list SNMP ACL l mt danh sch cc a ch IP c php qun l/gim st agent, n ch p dng ring cho giao thc SNMP v c ci trn agent. Nu mt manager c IP khng c php trong ACL gi request th agent s khng x l, d request c community string l ng. a s cc thit b tng thch SNMP u cho php thit lp SNMP ACL. Cc phin bn SNMP SNMP c 4 phin bn : SNMPv1, SNMPv2c, SNMPv2u v SNMPv3. Cc phin bn ny khc nhau mt cht nh dng bn tin v phng thc hot ng. Phin bn SNMPPhin bn SNMP 1 2 2c 3 M t Dng SMIv1 dng phng thc xc thc n gin vi community nhng ch dng MIB-I. ng SMIv2. Loi b vic s dng communities thm vo cc thng ip Getbulk v Inform nhng bt u vi phin bn MIB-II. Phin bn gi cho php SNMPv1 giao tip vi SNMPv2. Tng ng vi SNMPv2. Phn ln tng t nh SNMPv2 nhng thm vo cc tnh nng bo mt. H tr tng thch ngc. Dng MIB-II.

Cc phng thc SNMP Cc giao thc SNMPv1 v SNMPv2 nh ngha cch thc m mt phn mm manager v mt tc nhn agent c th giao tip vi nhau. V d, mt manager c th dng ba thng ip khc nhau ly cc thng tin MIB t cc tc nhn agents vi mt thng ip SNMP response c tr v t tc nhn agent. SNMP dng UDP truyn thng tin, dng thng tin SNMP response cung cp thng tin v cng nhn (ack) vic nhn cc thng ip khc.

Phng thc GetRequest GetNextReque st SetRequest GetResponse Trap

M t tc dng Manager gi GetRequest cho agent yu cu agent cung cp thng tinno da vo ObjectID (trong GetRequest c cha OID) Manager gi GetNextRequest c cha mt ObjectID cho agent yu cu cung cp thng tin nm k tip ObjectID trong MIB. Manager gi SetRequest cho agent t gi tr cho i tng ca agent da vo ObjectID. Agent gi GetResponse cho Manager tr li khi nhn c GetRequest/GetNextRequest Agent t ng gi Trap cho Manager khi c mt s kin xy ra i vi mt object no trong agent.

Li ni uTi liu ny trnh by gn nh hon chnh cc vn v giao thc SNMP (Simple Network Management Protocol), t nn tng hot ng ca giao thc, ng dng vo vic qun l cc thit b trong mng, tm hiu mt s cng c SNMP, n vic lp trnh phn mm gim st thit b v phn mm cho php c gim st bng SNMP. Ti liu c bin son di dng c th t hc, nn n cha rt nhiu ghi ch v v d. i tng c quyn ti liu ny bao gm : + Cc bn cha bit v SNMP, mun c mt kin thc nn tng bng vic bt u vi mt ti liu nhp mn tt nht. + Cc bn c kin thc c bn v SNMP, mun tm hiu cch thc hot ng ca cc cng c qun l mng da trn nn tng giao thc ny. + Cc bn mun vit phn mm qun l mng bng SNMP trn ngn ng a thch ca mnh nhng cha bit bt u t u, cn c mt ti liu hng dn v th tc thc hin v phn mm mu. V vy, b cc ca ti liu ny c th t nh sau :

Chng 1 : Giao thc SNMPChng ny trnh by ln lt cc khi nim, th tc hot ng ca giao thc SNMP. Tt c khi nim lin quan s c trnh by

km v d nu c th, tt c th tc lin quan s c m t km lu nu c th.

Chng 2 : Qun l mng vi SNMPChng ny trnh by ng dng gim st hiu sut thit b mng v gim st ti nguyn ca server thng quaSNMP. Ti liu s gii thiu mt s v d c th ngi c c th thc hnh trn my chy Windows v mt s thit b khc.

Chng 3 : Management Information Base (MIB)Chng ny trnh by cc vn lin quan n cu trc ca mib. Sau hng dn cch ly thng tin th cng bng cc tin ch SNMP trn Windows v Linux, nhm gip ngi c hiu su hn cc phn mm snmp hot ng nh th no.

Chng 4 : Cc phin bn SNMPChng ny trnh by chi tit cc phng thc hot ng v cu trc bn tin ca cc phin bn SNMP v1, v2c, v2u, v3.

Chng 5 : Lp trnh ng dng SNMP vi Delphi 2010Chng ny trnh by cch thc lp trnh 3 loi ng dng lin quan n SNMP l ng dng qun l SNMP (SNMP manager), ng dng h tr SNMP (SNMP agent) v ng dng SNMP Trap; vit theo cch s dng th vin Indy c sn trn Delphi 2010; tuy nhin ngi c c th chuyn i sang ngn ng a thch ca mnh. Phn cui chng trnh by Basic Encoding Rules ca ITU X.690 (cn gi l ASN.1 Abstract Syntax Notation One), l chun c SNMP dng nh dng bn tin. Ti liu ny c tc gi bin son khng da vo vic dch mt ti liu no ca nc ngoi, tuy nhin tc gi s ghi ch y thut ng ting Anh bn cnh thut ng ting Vit ngi c d tra cu. Do ti liu hng n ngi t hc nn tc gi c gng trnh by mt cch d hiu nht, tuy nhin khng nht thit phi qu ngn gn v s lm cho ngi c tn nhiu thi gian suy ngh. Ti liu khng cha nhng cu ch khng thc s cn thit vn thng thy nhng ti liu dch, n lm phn tn v lc li ngi c. Ti liu chc chn khng trnh khi nhng thiu st, tc gi mong nhn c nhng gp v khch l ca mi bn c hon thin ti liu nhng phin bn sau, v nng cao cht lng nhng ti liu khc s bin son. c gi c th gp , tho lun, download phin bn mi nht ca ti liu ny cng nh cc ti nguyn lin quan ti http://sites.google.com/site/snmptoantap TP.HCM, thng 04 nm 2010

Tc gi : V tc gi :

Dip Thanh Nguyn

Tc gi l mt ngi lm vic trong lnh vc vin thng v cng ngh thng tin. Ti thi im vit ti liu ny, tc gi c 6 nm lm vic chuyn mn cho Viettel Group Tp on Vin thng Qun i. Trong mi trng cng tc ti mt b phn c chc nng iu hnh k thut, tc gi c iu kin lm vic trc tip vi rt nhiu thit b mng ca nhiu hng khc nhau, tip xc v trao i kinh nghim vi cc k s hng u ca Viettel thuc cc lnh vc lin quan. l tin gip cho tc gi tch ly kin thc vit quyn ti liu ny.

Chng 1 - Giao thc SNMP Bi ton gim st cc thit b v ng dng trong mng Hai c ch gim st Poll v Alert Gii thiu giao thc SNMP Cc khi nim nn tng Cc loi phng thc trong SNMP Cc c ch bo mt cho SNMP

1. Gim st thit b mngM u, ti s cp n 3 bi ton thuc hng ph bin nht trong cc ng dng ca SNMP. cho cc bn ln u tm hiu SNMP cm thy c hng th, ti cng s cho cc bn thy ng dng SNMP gii bi ton trng nh th no. Bi ton th nht : Gim st ti nguyn my ch + Gi s bn c hng ngn my ch chy cc h iu hnh (HH) khc nhau. Lm th no c th gim st ti nguyn ca tt c my ch hng ngy, hng gi kp thi pht hin cc my ch sp b qu ti ? Gim st ti nguyn my ch ngha l theo di t l chim dng CPU, dung lng cn li ca cng, t l s dng b nh RAM, . + Bn khng th kt ni vo tng my xem v s lng my nhiu v v cc HH khc nhau c cch thc kim tra khc nhau. + gii quyt vn ny bn c th dng mt ng dng SNMP gim st c my ch, n s ly c thng tin t nhiu HH khc nhau. ng dng ny c th trng ging nh hnh di y :

Bi ton th hai : Gim st lu lng trn cc port ca switch, router + Bn c hng ngn thit b mng (network devices) ca nhiu hng khc nhau, mi thit b c nhiu port. Lm th no gim st lu lng ang truyn qua tt c cc port ca cc thit b sut 24/24, kp thi pht hin cc port sp qu ti ? + Bn cng khng th kt ni vo tng thit b g lnh ly thng tin v thit b ca cc hng khc nhau c lnh khc nhau. + gii quyt vn ny bn c th dng mt ng dng SNMP gim st lu lng, n s ly c thng tin lu lng ang truyn qua cc thit b ca nhiu hng khc nhau. ng dng ny c th trng ging nh hnh di y :

Bi ton th ba : H thng t ng cnh bo s c tc thi + Bn c hng ngn thit b mng v chng c th gp nhiu vn trong qu trnh hot ng nh : mt port no b mt tn hiu (port down), c ai c kt ni (login) vo thit b nhng nhp sai username v password, thit b va mi b khi ng li (restart), . Lm th no ngi qun tr bit c s kin khi n va mi xy ra ? + Vn ny khc vi hai vn trn. trn l lm th no cp nht lin tc mt s thng tin no (bit trc s ly ci g), cn y l lm th no bit c ci g xy ra (cha bit ci g s n). + gii quyt bi ton ny bn c th dng ng dng thu thp s kin (event) v cnh bo (warning) bng SNMP, n s nhn cnh bo t tt c cc thit b v hin n ln mn hnh hoc gi email cho ngi qun tr. ng dng ny c th trng ging nh hnh di y :

2. Hai phng thc gim st Poll v AlertTrc khi tm hiu SNMP, ti mun trnh by hai phng thc gim st Poll v Alert (C ti liu gi l Poll v Trap, hoc Get v Trap) . y l 2 phng thc c bn ca cc k thut gim st h thng, nhiu phn mm v giao thc c xy dng da trn 2 phng thc ny, trong c SNMP. Vic hiu r hot ng ca Poll & Alert v u nhc im ca chng s gip bn d dng tm hiu nguyn tc hot ng ca cc giao thc hay phn mm gim st khc. Hoc nu bn mun t pht trin mt c ch gim st ca ring bn th n cng l c s bn xy dng mt nguyn tc hot ng ng n. Phng thc Poll

Nguyn tc hot ng : Trung tm gim st (manager) s thng xuyn hi thng tin ca thit b cn gim st (device). Nu Manager khng hi th Device khng tr li, nu Manager hi th Device phi tr li. Bng cch hi thng xuyn, Manager s lun cp nht c thng tin mi nht t Device.

V d : Ngi qun l cn theo di khi no th lm xong vic. Anh ta c thng xuyn hi ngi th Anh lm xong cha ?, v ngi th s tr li Xong hoc Cha. Phng thc Alert

Nguyn tc hot ng : Mi khi trong Device xy ra mt s kin (event) no th Device s t ng gi thng bo cho Manager, gi l Alert. Manager khng hi thng tin nh k t Device. V d : Ngi qun l cn theo di tnh hnh lm vic ca th, anh ta yu cu ngi th thng bo cho mnh khi c vn g xy ra. Ngi th s thng bo cc s kin i loi nh Tin hon thnh 50%, Mt in lc 10h, C in li lc 11h, Mi c tai nn xy ra. Device ch gi nhng thng bo mang tnh s kin ch khng gi nhng thng tin thng xuyn thay i, n cng s khng gi Alert nu chng c s kin g xy ra. Chng hn khi mt port down/up th Device s gi cnh bo, cn tng s byte truyn qua port s khng c Device gi i v l thng tin thng xuyn thay i. Mun ly nhng thng tin thng xuyn thay i th Manager phi ch ng i hi Device, tc l phi thc hin phng thc Poll. So snh phng thc Poll v Alert Hai phng thc Poll v Alert l hon ton khc nhau v c ch. Mt ng dng gim st c th s dng Poll hoc Alert, hoc c hai, ty vo yu cu c th trong thc t.

Poll hay Alert ?

Hai phng thc Poll v Alert c im thun li v bt li ngc nhau, do nhiu trng hp ta nn s dng kt hp c Poll ln Alert t c hiu qu kt hp ca c hai. Cc v d ng dng c ch Poll & Alert : + Giao thc Syslog : mi khi c s kin xy ra th thit b s gi bn tin syslog n Syslog Server. + Phn mm NetworkView, gim st tnh trng cc server bng cch ping lin tc. + Giao thc STP, pht hin loop trong mng bng cch gi nhn cc gi BPDU v gi bn tin Topology change mi khi pht hin thay i. + Trong qun l ngi ta lun thc hin song song ch kim tra v bo co, thng xuyn kim tra pht hin vn v bo co ngay khi xy ra vn .

3. Gii thiu giao thc SNMPSNMP l giao thc qun l mng n gin SNMP l giao thc qun l mng n gin, dch t cm t Simple Network Management Protocol. Th no l giao thc qun l mng n gin ? Giao thc l mt tp hp cc th tc m cc bn tham gia cn tun theo c th giao tip c vi nhau. Trong lnh vc thng tin, mt giao thc quy nh cu trc, nh dng (format) ca dng d liu trao i vi nhau v quy nh trnh t, th tc trao i dng d liu . Nu mt bn tham gia gi d liu khng ng nh dng hoc khng theo trnh t th cc bn khc s khng hiu hoc t chi trao i thng tin. SNMP l mt giao thc, do n c nhng quy nh ring m cc thnh phn trong mng phi tun theo. Mt thit b hiu c v hot ng tun theo giao thc SNMP c gi l c h tr SNMP (SNMP supported) hoc tng thch SNMP (SNMP compartible). SNMP dng qun l, ngha l c th theo di, c th ly thng tin, c th c thng bo, v c th tc ng h thng hot ng nh mun. VD mt s kh nng ca phn mm SNMP : + Theo di tc ng truyn ca mt router, bit c tng s byte truyn/nhn.

+ Ly thng tin my ch ang c bao nhiu cng, mi cng cn trng bao nhiu. + T ng nhn cnh bo khi switch c mt port b down. + iu khin tt (shutdown) cc port trn switch. SNMP dng qun l mng, ngha l n c thit k chy trn nn TCP/IP v qun l cc thit b c ni mng TCP/IP. Cc thit b mng khng nht thit phi l my tnh m c th l switch, router, firewall, adsl gateway, v c mt s phn mm cho php qun tr bng SNMP. Gi s bn c mt ci my git c th ni mng IP v n h tr SNMP th bn c th qun l n t xa bng SNMP. SNMP l giao thc n gin, do n c thit k n gin trong cu trc bn tin v th tc hot ng, v cn n gin trong bo mt (ngoi tr SNMP version 3). S dng phn mm SNMP, ngi qun tr mng c th qun l, gim st tp trung t xa ton mng ca mnh. u im trong thit k ca SNMP SNMP c thit k n gin ha qu trnh qun l cc thnh phn trong mng. Nh cc phn mm SNMP c th c pht trin nhanh v tn t chi ph (trong chng 5 tc gi s trnh by cch xy dng phn mm gim st SNMP, bn s thy tnh n gin ca n). SNMP c thit k c th m rng cc chc nng qun l, gim st. Khng c gii hn rng SNMP c th qun l c ci g. Khi c mt thit b mi vi cc thuc tnh, tnh nng mi th ngi ta c th thit k custom SNMP phc v cho ring mnh (trong chng 3 tc gi s trnh by file cu trc d liu ca SNMP). SNMP c thit k c th hot ng c lp vi cc kin trc v c ch ca cc thit b h tr SNMP. Cc thit b khc nhau c hot ng khc nhau nhng p ng SNMP l ging nhau. VD bn c th dng 1 phn mm theo di dung lng cng cn trng ca cc my ch chy HH Windows v Linux; trong khi nu khng dng SNMP m lm trc tip trn cc HH ny th bn phi thc hin theo cc cch khc nhau. Cc phin bn ca SNMP SNMP c 4 phin bn : SNMPv1, SNMPv2c, SNMPv2u v SNMPv3. Cc phin bn ny khc nhau mt cht nh dng bn tin v phng thc hot ng. Hin ti SNMPv1 l ph bin nht do c nhiu thit b tng thch nht v c nhiu phn mm h tr nht. Trong khi ch c mt s thit b v phn mm h tr SNMPv3. Do trong 3 chng u ca ti

liu ny tc gi s trnh by cc vn theo chun SNMPv1. Cc phin bn khc s c trnh by trong chng 4.

4. Cc khi nim nn tng ca SNMPCc thnh phn trong SNMP Theo RFC1157 , kin trc ca SNMP bao gm 2 thnh phn : cc trm qun l mng (network management station) v cc thnh t mng (network element). Network management station thng l mt my tnh chy phn mm qun l SNMP (SNMP management application), dng gim st v iu khin tp trung cc network element.

Network element l cc thit b, my tnh, hoc phn mm tng thch SNMP v c qun l bi network management station. Nh vy element bao gm device, host v application. Mt management station c th qun l nhiu element, mt element cng c th c qun l bi nhiu management station. Vy nu mt element c qun l bi 2 station th iu g s xy ra ? Nu station ly thng tin t element th c 2 station s c thng tin ging nhau. Nu 2 station tc ng n cng mt element th element s p ng c 2 tc ng theo th t ci no n trc. Ngoi ra cn c khi nim SNMP agent. SNMP agent l mt tin trnh (process) chy trn network element, c nhim v cung cp thng tin ca element cho station, nh station c th qun l c element. Chnh xc hn l application chy trn station v agent chy trn element mi l 2 tin trnh SNMP trc tip lin h vi nhau. Cc v d minh ha sau y s lm r hn cc khi nim ny : + dng mt my ch (= station) qun l cc my con (= element) chy HH Windows thng qua SNMP th bn phi : ci t mt phn mm

qun l SNMP (=application) trn my ch, bt SNMP service (= agent) trn my con. + dng mt my ch (= station) gim st lu lng ca mt router (= element) th bn phi : ci phn mm qun l SNMP (= application) trn my ch, bt tnh nng SNMP (=agent) trn router.

Object ID Mt thit b h tr SNMP c th cung cp nhiu thng tin khc nhau, mi thng tin gi l mt object. V d : + My tnh c th cung cp cc thng tin : tng s cng, tng s port ni mng, tng s byte truyn/nhn, tn my tnh, tn cc process ang chy, . + Router c th cung cp cc thng tin : tng s card, tng s port, tng s byte truyn/nhn, tn router, tnh trng cc port ca router, . Mi object c mt tn gi v mt m s nhn dng object , m s gi l Object ID (OID). VD : + Tn thit b c gi l sysName, OID l 1.3.6.1.2.1.1.5 . + Tng s port giao tip (interface) c gi l ifNumber, OID l 1.3.6.1.2.1.2.1. + a ch Mac Address ca mt port c gi l ifPhysAddress, OID l 1.3.6.1.2.1.2.2.1.6. + S byte nhn trn mt port c gi l ifInOctets, OID l 1.3.6.1.2.1.2.2.1.10. Bn hy khoan thc mc ngha ca tng ch s trong OID, chng s c gii thch trong phn sau. Mt object ch c mt OID, chng hn tn ca thit b l mt object. Tuy nhin nu mt thit b li c nhiu tn th lm th no phn bit ? Lc ny ngi ta dng thm 1 ch s gi l scalar instance index (cng c th gi l sub-id) t ngay sau OID. V d :

+ Tn thit b c gi l sysName, OID l 1.3.6.1.2.1.1.5; nu thit b c 2 tn th chng s c gi l sysName.0 & sysName.1 v c OID ln lt l 1.3.6.1.2.1.1.5.0 & 1.3.6.1.2.1.1.5.1. + a ch Mac address c gi l ifPhysAddress, OID l 1.3.6.1.2.1.2.2.1.6; nu thit b c 2 mac address th chng s c gi l ifPhysAddress.0 & ifPhysAddress.1 v c OID ln lt l 1.3.6.1.2.1.2.2.1.6.0 & 1.3.6.1.2.1.2.2.1.6.1. + Tng s port c gi l ifNumber, gi tr ny ch c 1 (duy nht) nn OID ca n khng c phn cp con v vn l 1.3.6.1.2.1.2.1. hu ht cc thit b, cc object c th c nhiu gi tr th thng c vit di dng c sub-id. VD mt thit b d ch c 1 tn th n vn phi c OID l sysName.0 hay 1.3.6.1.2.1.1.5.0. Bn cn nh quy tc ny ng dng trong lp trnh phn mm SNMP manager. Sub-id khng nht thit phi lin tc hay bt u t 0. VD mt thit b c 2 mac address th c th chng c gi l ifPhysAddress.23 v ifPhysAddress.125645. OID ca cc object ph bin c th c chun ha, OID ca cc object do bn to ra th bn phi t m t chng. ly mt thng tin c OID chun ha th SNMP application phi gi mt bn tin SNMP c cha OID ca object cho SNMP agent, SNMP agent khi nhn c th n phi tr li bng thng tin ng vi OID . VD : Mun ly tn ca mt PC chy Windows, tn ca mt PC chy Linux hoc tn ca mt router th SNMP application ch cn gi bn tin c cha OID l 1.3.6.1.2.1.1.5.0. Khi SNMP agent chy trn PC Windows, PC Linux hay router nhn c bn tin c cha OID 1.3.6.1.2.1.1.5.0, agent lp tc hiu rng y l bn tin hi sysName.0, v agent s tr li bng tn ca h thng. Nu SNMP agent nhn c mt OID m n khng hiu (khng h tr) th n s khng tr li.

Mt trong cc u im ca SNMP l n c thit k chy c lp vi cc thit b khc nhau. Chnh nh vic chun ha OID m ta c th dng mt SNMP application ly thng tin cc loi device ca cc hng khc nhau. Object access Mi object c quyn truy cp l READ_ONLY hoc READ_WRITE. Mi object u c th c c nhng ch nhng object c quyn READ_WRITE mi c th thay i c gi tr. VD : Tn ca mt thit b (sysName) l READ_WRITE, ta c th thay i tn ca thit b thng qua giao thc SNMP. Tng s port ca thit b (ifNumber) l READ_ONLY, d nhin ta khng th thay i s port ca n. Management Information Base MIB (c s thng tin qun l) l mt cu trc d liu gm cc i tng c qun l (managed object), c dng cho vic qun l cc thit b chy trn nn TCP/IP. MIB l kin trc chung m cc giao thc qun l trn TCP/IP nn tun theo, trong c SNMP. MIB c th hin thnh 1 file (MIB file), v c th biu din thnh 1 cy (MIB tree). MIB c th c chun ha hoc t to. Hnh sau minh ha MIB tree :

Mt node trong cy l mt object, c th c gi bng tn hoc id. V d : + Node iso.org.dod.internet.mgmt.mib-2.system c OID l 1.3.6.1.2.1.1, cha tt c cc object lin quan n thng tin ca mt h thng nh tn ca thit b (iso.org.dod.internet.mgmt.mib-2.system.sysName hay 1.3.6.1.2.1.1.5). + Cc OID ca cc hng t thit k nm di iso.org.dod.internet.private.enterprise. V d : Cisco nm di iso.org.dod.internet.private.enterprise.cisco hay 1.3.6.1.4.1.9, Microsoft nm di iso.org.dod.internet.private.enterprise.microsoft hay 1.3.6.1.4.1.311. S 9 (Cisco) hay 311 (Microsoft) l s dnh ring cho cc cng ty do IANA cp. Nu Cisco hay Microsoft ch to ra mt thit b no , th thit b ny c th h tr cc MIB chun c nh ngha sn

(nh mib-2) hay h tr MIB c thit k ring. Cc MIB c cng ty no thit k ring th phi nm bn di OID ca cng ty . Cc objectID trong MIB c sp xp th t nhng khng phi l lin tc, khi bit mt OID th khng chc chn c th xc nh c OID tip theo trong MIB. VD trong chun mib-2 th object ifSpecific v object atIfIndex nm k nhau nhng OID ln lt l 1.3.6.1.2.1.2.2.1.22 v 1.3.6.1.2.1.3.1.1.1. Mun hiu c mt OID no th bn cn c file MIB m t OID . Mt MIB file khng nht thit phi cha ton b cy trn m c th ch cha m t cho mt nhnh con. Bt c nhnh con no v tt c l ca n u c th gi l mt mib. Mt manager c th qun l c mt device ch khi ng dng SNMP manager v ng dng SNMP agent cng h tr mt MIB. Cc ng dng ny cng c th h tr cng lc nhiu MIB. Trong chng ny chng ta ch cp n khi nim MIB ngn gn nh trn. Chng 3 s m t chi tit cu trc ca file MIB.

5. Cc phng thc ca SNMPGiao thc SNMPv1 c 5 phng thc hot ng, tng ng vi 5 loi bn tin nh sau :

Mi bn tin u c cha OID cho bit object mang trong n l g. OID trong GetRequest cho bit n mun ly thng tin ca object no. OID trong GetResponse cho bit n mang gi tr ca object no. OID trong SetRequest ch ra n mun thit lp gi tr cho object no. OID trong Trap ch ra n thng bo s kin xy ra i vi object no.

GetRequest Bn tin GetRequest c manager gi n agent ly mt thng tin no . Trong GetRequest c cha OID ca object mun ly. VD : Mun ly thng tin tn ca Device1 th manager gi bn tin GetRequest OID=1.3.6.1.2.1.1.5 n Device1, tin trnh SNMP agent trn Device1 s nhn c bn tin v to bn tin tr li. Trong mt bn tin GetRequest c th cha nhiu OID, ngha l dng mt GetRequest c th ly v cng lc nhiu thng tin. GetNextRequest Bn tin GetNextRequest cng dng ly thng tin v cng c cha OID, tuy nhin n dng ly thng tin ca object nm k tip object c ch ra trong bn tin. Ti sao phi c phng thc GetNextRequest ? Nh bn bit khi c qua nhng phn trn : mt MIB bao gm nhiu OID c sp xp th t nhng khng lin tc, nu bit mt OID th khng xc nh c OID k tip. Do ta cn GetNextRequest ly v gi tr ca OID k tip. Nu thc hin GetNextRequest lin tc th ta s ly c ton b thng tin ca agent. SetRequest Bn tin SetRequest c manager gi cho agent thit lp gi tr cho mt object no . V d : + C th t li tn ca mt my tnh hay router bng phn mm SNMP manager, bng cch gi bn tin SetRequest c OID l 1.3.6.1.2.1.1.5.0 (sysName.0) v c gi tr l tn mi cn t. + C th shutdown mt port trn switch bng phn mm SNMP manager, bng cch gi bn tin c OID l 1.3.6.1.2.1.2.2.1.7 (ifAdminStatus) v c gi tr l 2 * ifAdminStatus c th mang 3 gi tr l UP (1), DOWN (2) v TESTING (3). Ch nhng object c quyn READ_WRITE mi c th thay i c gi tr. GetResponse Mi khi SNMP agent nhn c cc bn tin GetRequest, GetNextRequest hay SetRequest th n s gi li bn tin GetResponse tr li. Trong bn tin GetResponse c cha OID ca object c request v gi tr ca object .

Trap Bn tin Trap c agent t ng gi cho manager mi khi c s kin xy ra bn trong agent, cc s kin ny khng phi l cc hot ng thng xuyn ca agent m l cc s kin mang tnh bin c. V d : Khi c mt port down, khi c mt ngi dng login khng thnh cng, hoc khi thit b khi ng li, agent s gi trap cho manager. Tuy nhin khng phi mi bin c u c agent gi trap, cng khng phi mi agent u gi trap khi xy ra cng mt bin c. Vic agent gi hay khng gi trap cho bin c no l do hng sn xut device/agent quy nh. Phng thc trap l c lp vi cc phng thc request/response. SNMP request/response dng qun l cn SNMP trap dng cnh bo. Ngun gi trap gi l Trap Sender v ni nhn trap gi l Trap Receiver. Mt trap sender c th c cu hnh gi trap n nhiu trap receiver cng lc. C 2 loi trap : trap ph bin (generic trap) v trap c th (specific trap). Generic trap c quy nh trong cc chun SNMP, cn specific trap do ngi dng t nh ngha (ngi dng y l hng sn xut SNMP device). Loi trap l mt s nguyn cha trong bn tin trap, da vo m pha nhn trap bit bn tin trap c ngha g. Theo SNMPv1, generic trap c 7 loi sau : coldStart(0), warmStart(1), linkDown(2), linkUp(3), authenticationFailure(4), egpNeighborloss(5), enterpriseSpecific(6). Gi tr trong ngoc l m s ca cc loi trap. ngha ca cc bn tin generic-trap nh sau : + coldStart : thng bo rng thit b gi bn tin ny ang khi ng li (reinitialize) v cu hnh ca n c th b thay i sau khi khi ng. + warmStart : thng bo rng thit b gi bn tin ny ang khi ng li v gi nguyn cu hnh c. + linkDown : thng bo rng thit b gi bn tin ny pht hin c mt trong nhng kt ni truyn thng (communication link) ca n gp li. Trong bn tin trap c tham s ch ra ifIndex ca kt ni b li. + linkUp : thng bo rng thit b gi bn tin ny pht hin c mt trong nhng kt ni truyn thng ca n khi phc tr li. Trong bn tin trap c tham s ch ra ifIndex ca kt ni c khi phc. + authenticationFailure : thng bo rng thit b gi bn tin ny nhn c mt bn tin khng c chng thc thnh cng (bn tin b chng

thc khng thnh cng c th thuc nhiu giao thc khc nhau nh telnet, ssh, snmp, ftp, ). Thng thng trap loi ny xy ra l do user ng nhp khng thnh cng vo thit b. + egpNeighborloss : thng bo rng mt trong s nhng EGP neighbor ca thit b gi trap b coi l down v quan h i tc (peer relationship) gia 2 bn khng cn c duy tr. + enterpriseSpecific : thng bo rng bn tin trap ny khng thuc cc kiu generic nh trn m n l mt loi bn tin do ngi dng t nh ngha. Ngi dng c th t nh ngha thm cc loi trap lm phong ph thm kh nng cnh bo ca thit b nh : boardFailed, configChanged, powerLoss, cpuTooHigh, v.v. Ngi dng t quy nh ngha v gi tr ca cc specific trap ny, v d nhin ch nhng trap receiver v trap sender h tr cng mt MIB mi c th hiu ngha ca specific trap. Do nu bn dng mt phn mm trap receiver bt k nhn trap ca cc trap sender bt k, bn c th c v hiu cc generic trap khi chng xy ra; nhng bn s khng hiu ngha cc specific trap khi chng hin ln mn hnh v bn tin trap ch cha nhng con s.

i vi cc phng thc Get/Set/Response th SNMP Agent lng nghe port UDP 161, cn phng thc trap th SNMP Trap Receiver lng nghe port UDP 162.

6. Cc c ch bo mt cho SNMPMt SNMP management station c th qun l/gim st nhiu SNMP element, thng qua hot ng gi request v nhn trap. Tuy nhin

mt SNMP element c th c cu hnh ch cho php cc SNMP management station no c php qun l/gim st mnh. Cc c ch bo mt n gin ny gm c : community string, view v SNMP access control list. Community string Community string l mt chui k t c ci t ging nhau trn c SNMP manager v SNMP agent, ng vai tr nh mt khu gia 2 bn khi trao i d liu. Community string c 3 loi : Read-community, WriteCommunity v Trap-Community. Khi manager gi GetRequest, GetNextRequest n agent th trong bn tin gi i c cha Read- Community. Khi agent nhn c bn tin request th n s so snh Read-community do manager gi v Readcommunity m n c ci t. Nu 2 chui ny ging nhau, agent s tr li; nu 2 chui ny khc nhau, agent s khng tr li. Write-Community c dng trong bn tin SetRequest. Agent ch chp nhn thay i d liu khi write- community 2 bn ging nhau. Trap-community nm trong bn tin trap ca trap sender gi cho trap receiver. Trap receiver ch nhn v lu tr bn tin trap ch khi trapcommunity 2 bn ging nhau, tuy nhin cng c nhiu trap receiver c cu hnh nhn tt c bn tin trap m khng quan tm n trapcommunity. Community string c 3 loi nh trn nhng cng mt loi c th c nhiu string khc nhau. Ngha l mt agent c th khai bo nhiu readcommunity, nhiu write-community. Trn hu ht h thng, read-community mc nh l public, writecommunity mc nh l private v trap-community mc nh l public. Community string ch l chui k t dng cleartext, do hon ton c th b nghe ln khi truyn trn mng. Hn na, cc community mc nh thng l public v private nn nu ngi qun tr khng thay i th chng c th d dng b d ra. Khi community string trong mng b l, mt ngi dng bnh thng ti mt my tnh no trong mng c th qun l/gim st ton b cc device c cng community m khng c s cho php ca ngi qun tr. View Khi manager c read-community th n c th c ton b OID ca agent. Tuy nhin agent c th quy nh ch cho php c mt s OID c lin quan

nhau, tc l ch c c mt phn ca MIB. Tp con ca MIB ny gi l view, trn agent c th nh ngha nhiu view. V d : agent c th nh ngha view interfaceView bao gm cc OID lin quan n interface, storageView bao gm cc OID lin quan n lu tr, hay AllView bao gm tt c cc OID. Mt view phi gn lin vi mt community string. Ty vo community string nhn c l g m agent x l trn view tng ng. V d : agent nh ngha read-community inf trn view interfaceView, v sto trn storageView; khi manager gi request ly OID ifNumber vi community l inf th s c p ng do ifNumber nm trong interfaceView; nu manager request OID hrStorageSize vi community inf th agent s khng tr li do hrStorageSize khng nm trong interfaceView; nhng nu manager request hrStorageSize vi community sto th s c tr li do hrStorageSize nm trong storageView. Vic nh ngha cc view nh th no ty thuc vo tng SNMP agent khc nhau. C nhiu h thng khng h tr tnh nng view. SNMP access control list Khi manager gi khng ng community hoc khi OID cn ly li khng nm trong view cho php th agent s khng tr li. Tuy nhin khi community b l th mt manager no vn request c thng tin. ngn chn hon ton cc SNMP manager khng c php, ngi qun tr c th dng n SNMP access control list (ACL). SNMP ACL l mt danh sch cc a ch IP c php qun l/gim st agent, n ch p dng ring cho giao thc SNMP v c ci trn agent. Nu mt manager c IP khng c php trong ACL gi request th agent s khng x l, d request c community string l ng. a s cc thit b tng thch SNMP u cho php thit lp SNMP ACL.

7. Cu trc bn tin SNMPSNMP chy trn nn UDP. Cu trc ca mt bn tin SNMP bao gm : version, community v data.

+ Version : v1 = 0, v2c = 1, v2u = 2, v3 = 3. + Phn Data trong bn tin SNMP gi l PDU (Protocol Data Unit). SNMPv1 c 5 phng thc hot ng tng ng 5 loi PDU. Tuy nhin ch c 2 loi nh dng bn tin l PDU v Trap-PDU; trong cc bn tin Get, GetNext, Set, GetResponse c cng nh dng l PDU, cn bn tin Trap c nh dng l Trap-PDU. Chng 4 s trnh by cu trc ca tng loi PDU.

T m tt+ C 2 phng php gim st l Hi/Tr li (Poll) v t ng thng bo khi xy ra s kin (Alert). gim st tt ta cn kt hp c 2 k thut ny. + SNMP l giao thc qun l mng TCP/IP, c thit k c th m rng thm cc chc nng v c lp kin trc ca cc thit b. + 2 thnh phn trong SNMP gi l Network Management Station v Network Element, cn c th c gi l SNMP manager v SNMP agent. + ObjectID l nh danh ca mt i tng c th gim st c, cc thao tc get/set thng tin ca i tng u thng qua nh danh ca n. + MIB l mt cu trc d liu m t tp hp cc i tng c lin quan nhau. SNMP manager c th gim st c SNMP agent th c hai phi h tr cng mt MIB. + SNMPv1 c 5 phng thc : GetRequest, GetNextRequest, SetRequest, GetResponse v Trap. + SNMP c mt s c ch bo mt n gin nh : community string, view v SNMP Access Control List.

V i s pht trin mnh m ca my trm, my ch v mng LAN lm thay i mng my tnh lin tc. Mt khc do s mua bn cc h thng v thit b, phn mm ca cc nh sn xut khc nhau. Do vy cc nh sn xut thit b hoc phn mm phi cung cp phn mm giao tip vi thit b c th cu hnh v qun l chng. V nh vy, mi mt nh sn xut t nht l phi c mt phn mm qun l ring vi nguyn tc hot ng ring cho sn phm ca mnh. iu ny gy ra nhiu bt tin. Do vy, ngi ta xy dng cc giao thc qun l thit b chung cho tt c cc nh sn xut. Trong cc giao thc , th giao thc c bit n nhiu nht l giao thc SNMP (Simple Network Management Protocol). Cc thit b d n gin hay phc tp u cha phn mm SNMP dng tham gia vo vic qun l mng. Hin nay, cc n v nghin cu pht trin trong lnh vc vin thng trong nc ni chung v CDiT ni ring c nhiu sn phm c s dng trn mng li. Tuy nhin vic qun l cc sn phm ny vn cha c thc hin theo tiu chun quc t nh cc sn phm nhp hay chuyn giao t nc ngoi. Trn th gii vic nghin cu v ng dng th tc SNMP trong vic qun l cc h thng v thit b vin thng lm t lu, v vic ng dng SNMP vo qun l l mc nh. ng trc c hi hi nhp quc t, th vic p dng mt giao thc tiu chun quc t vo qun l sn phm l cn thit v n thng nht c giao din qun l trn mng, to iu kin thun li cho vic cung cp giao din qun l chun khi pht trin cc h thng v thit b vin thng trong nc. Trong phm vi ca bi bo, tc gi trnh by v cc phn c bn ca giao thc SNMP v mt s k thut pht trin ng dng. 2. Giao thc SNMP 2.1. Gii thiu v giao thc SNMP Cc thit b mng cha thng tin v bn thn chng, cc thng tin ny c th l cc tham s la chn cu hnh thit b, trng thi hot ng hin ti ca thit b, cc thng tin v thng k nh lu lng vo ra ca cc gi thng tin hoc cc thng tin v li ca thit b. c th qun l c h thng hoc mng th cn phi c nhng thit b c kh nng bit c cc thng tin ca cc thit b khc tn ti xung quanh n. Nh vy, thc cht ca vic qun l cc thit b chnh l vic qun l cc thng tin m cc thit b b qun l lu tr. Tt c cc thng tin ny l trung tm ca giao thc SNMP. Ta cn qun l nhng thng tin g? Cc chuyn gia thit k ra mt tp hp cc thng tin chung m tt c cc thit b thuc cc hng khc nhau u c, v chng c tiu chun ho v cc nh sn xut khc nhau u cung cp cc thng tin ny qun l thit b ca h. Cn nu nh sn xut mun qun l nhng c im c th ca sn phm ca h th cc chuyn gia ginh cho cc nh sn xut mt nhnh thng tin ring, trong mi nh sn xut li c mt nhnh ring pht trin. qun l thng tin th mi thng tin phi c mt tn ring bit v duy nht. Cch t tn nh th no? Khi c tn cho mi thng tin, th lm th no c th ly thng tin hoc thay i thng tin ? SNMP l mt giao thc ch ra cch t tn bin v cch ly thng tin, cch thay i thng tin ca thit b b qun l