Nhom 17 - De Tai 04 - DHCP

ti 4: NTH, Ci t V Cu Hnh Dch V DHCP

I HC NNG TRNG I HC KINH T KHOA THNG K - TIN HC BI TP LN MNG V TRUYN THNG ti: NGUYN TC HOT NG, CI T V CU HNH DCH V DHCP

Gio vin hng dn: ng Trung Thnh Cc thnh vin :1. Phm Th Cm T 2. Hunh Th Thu Tin 3. Ng Thy Nhi 4. Mai Th nh Phng 5. Phng Th Bch Ngc Lp: 37H11K14.1

Nng, Thng 09 nm 2011

GVHD: ng Trung Thnh

Nhm 17


Trang 2

LI M U Ngy nay, cng ngh thng tin tr nn ph bin v m bo tnh hiu qu cho hot ng sn xut, kinh doanh ca cc doanh nghip. i lin vi n l s i hi v kh nng p ng v cng ngh thng tin ni chung v s thng sut ca h tng mng ni ring. S pht trin ca Internet cng ng ngha vi vic tng trng v quy m v cng ngh nhiu mng LAN, WAN, Chnh iu lm cho vn s dng vi tnh cng tng v vi quy m ln. Do , vn qun l v cu hnh tr nn quan trng hn bao gi ht. Vic thit k mng v cp pht a ch IP t ng sao cho nhanh chng, tit kim thi gian v cng sc, ti nguyn ca t chc l vn ng quan tm. Internet pht trin cng mnh, lng ngi truy cp cng tng, nhu cu s dng vi tnh cng nhiu th ngi qun tr mng cng phi tn nhiu cng sc bo tr, qun l, m rng kh khn hn. Dynamic host configuration protocol l giao thc cu hnh a ch IP ng, l dch v trn nn giao thc TCP/IP nhm n gin ha vai tr qun tr ca vic cu hnh a ch IP ca mng Client. trin khai dch v ny ta xy dng DHCP Server trn Windows cu hnh v cp pht cc thng s cu hnh TCP/IP n cc my Client trong h thng mng nhm gim bt cng vic cp pht a ch IP 1 cch th cng. V vy, chng em quyt nh chn ti Nguyn tc hot ng, cu hnh, ci t dch v DHCP tm hiu. Trong thi gian qua, chng em xin chn thnh cm n thy ng Trung Thnh hng dn v gip chng em trong sut qu trnh hon thin bi bo co ny. Chng em xin chn thnh cm n!

GVHD: ng Trung Thnh

Nhm 17


Trang 3

Bng phn cng cng vic Tn Cng Vic Nguyn tc hot ng Ci t v cu hnh dch v DHCP Slide bo co Bo co ti Thi gian bt u 12-09-2011 19-09-2011 26-09-2011 03-10-2011 Ngi thc hin Hunh Th Thy Tin Phm Th Cm T Ng Thy Nhi Mai Th nh Phng Phng Th Bch Ngc Tt c thnh vin trong nhm

MC LC

GVHD: ng Trung Thnh

Nhm 17


Trang 4

LI M U....................................................................................................................................................2 I. GII THIU V DHCP ...............................................................................................................................4

I. GII THIU V DHCP I.1-

DHCP l g? DHCP l vit tt ca Dynamic Host Configuration Protocol

l giao thc cu hnh a ch IP ng, l phn m rng ca BootProtocol, DHCP c nhim v l cp pht a ch IP ng cho cc Client.-

My tnh c cu hnh mt cch t ng v th vic s dng

DHCP s gim vic can thip vo h thng mng. N cung cp mt database trung tm theo di tt c cc my tnh trong h thng mng. Mc ch quan trng nht l trnh trng hp hai my tnh khc nhau li c cng a ch IP.-

DHCP bn cht l mt dch v c s h tng c trn bt k mt

h thng mng no nhm cung cp a ch IP v thng tin DNS server ti cc "PC client" hay mt s thit b khc. I.2-

ngha ca vic s dng DHCP. DHCP c s dng gip bn khng phi n nh a ch

IP tnh cho tt c cc thit b c trong h thng mng ca mnh v gip bn qun l mi vn m a ch IP tnh c th to ra.GVHD: ng Trung Thnh Nhm 17


Trang 5

-

Thng thng trong 1 m hnh mng, ngi qun tr c th cu

hnh IP cho cc my client theo 2 cch l th cng (static) v cp pht ng (dynamic). Vi cc h thng mng nh static c th p ng c nhu cu y, nhng vi cc mng ln th vic cp pht IP mt cch t ng l thit yu hn c v DHCP ra i p ng nhu cu y.-

DHCP cho php cc nh qun tr mng c th t 1 trung tm

qun l v t ng m ho qu trnh gn IP cc thng s cho 1 mng my tnh trong 1 khong thi gian nht nh.-

Tt c vic trao i thng tin gia mt DHCP server v DHCP Ngoi vic cung cp a ch IP, DHCP cn cung cp thng tin

client s s dng User Datagram Protocol (UDP) port l 67 v 68.-

cu hnh khc, c th nh DNS. Hin nay DHCP c 2 version: cho IPv4 v IPv6.

I.3-

Mt s thut ng c dng trong DHCP DHCP client - My trm DHCP: l mt thit b ni vo mng

v s dng giao thc DHCP ly cc thng tin cu hnh nh l a ch mng, a ch my ch DNS.-

DHCP server - My ch DHCP: l mt thit b ni vo mng BOOTP relay agents - Thit b chuyn tip BOOTP: l mt

c chc nng tr v cc thng tin cn thit cho my trm DHCP khi c yu cu.-

my trm hoc mt router c kh nng chuyn cc thng ip DHCP gia DHCP server v DHCP client.-

Binding - Ni kt: l mt tp hp cc thng tin cu hnh trong

c t nht mt a ch IP, c s dng bi mt DHCP client. Cc ni kt c qun l bi my ch DHCP. I.4 Server Giao thc DHCP lm vic theo m hnh client /server, do quy trnh cp pht IP cho client c thc hin qua 4 bc sau: 1 IP lease requestGVHD: ng Trung Thnh Nhm 17

C ch xin v cp pht IP Address cho DHCP Client ca DHCP


Trang 6

2 IP lease offer 3 IP lease selection 4 IP lease acknowledgement a. IP Lease Request-

u tin t DHCP client s broadcast mt message tn l

DHCP discover. V lc ny client cha c a ch IP nn n s c source l 0.0.0.0 v cng ko bit c ch n l server no nn n s gi 1 tin broadcast vi a ch 255.255.255.255. Lc ny gi tin DHCP discover s c broadcast ln ton mng. Gi tin ny bao gm c a ch MAC DHCP server c th bit c client no gi yu cu n.

b. IP Lease Offer-

Nu

c

mt

DHCP

server

nhn

c

gi

tin

DHCPDISCOVER ca client th n s tr li li bng mt gi tin DHCPOFFER, gi tin ny i km theo nhng thng tin sau: MAC address ca client -

IP address cp cho (offer IP address) Mt subnet mask

Thi gian thu (mc nh l 8 ngy) a ch IP ca DHCP cp IP cho client ny Lc ny DHCP server s c gi li mt IP offer (cp) cho DHCP client ch mt vi giy cho mt offer, nu n khng

client n khng cp cho DHCP client no khc. nhn mt offer n s rebroadcast (broadcast gi DHCPDISCOVER) trong khong thi gian l 2, 4, 8 v 16 giy.-

Nu DHCP client khng nhn mt offer sau 4 ln yu cu, n

s dng mt a ch IP trong khong [169.254.0.1 n 169.254.255.254] vi subnet mask l [255.255.0.0]. N s s dng trong mt s trong khong IP v vic s

GVHD: ng Trung Thnh

Nhm 17


Trang 7

gip cc DHCP client trong mt mng khng c DHCP server thy nhau. DHCP client tip tc c gng tm kim mt DHCP server sau mi 5 pht. c. IP lease selection-

DHCP client nhn c DHCP offer. N s phn hi broadcast

li mt gi tin DHCP request chp nhn ci offer . DHCP request bao gm cc thng tin v DHCP cp a ch cho n. Ni 1 cch d hiu y DHCP client gi DHCP request nh 1 thng bo tm thy v chp nhn thu 1 a ch IP t con DHCP server v thi khng cho cc DCHP server khc gi cc DHCP offer trong trng hp h thng mng c nhiu hn 1 DHCP server. d. IP lease acknowledgement-

Khi DHCP server nhn c DHCP request s tr li DHCP

client 1 DHCP ACK or NACK. cho bit l chp nhn cho DHCP client thu a ch IP. Gi tin ny s bao gm a ch IP v cc thng tin cu hnh khc (DNS server, WINS server, default getway ). Khi DHCP client nhn c DHCP ACK or NACK th chnh thc kt thc qu trnh xin, tm kim a ch IP ca DHCP client. Lu : Quy trnh xin, cp pht IP gia DHCP Client v DHCP Server tn hiu truyn i l tn hiu Broadcast. I.4 C ch t ng refresh li thi gian ng k (lease time).-

Theo mc nh ca DHCP server th mi IP lease ch c c 8

ngy. Nu theo nh mc nh (8 ngy) th mt DHCP client sau mt khong thi gian l 50% (tc l 4 ngy) n s t ng xin li IP address vi DHCP m n xin ban u. DHCP client lc ny s gi mt DHCPREQUEST trc tip (unicast) n DHCP server m n xin ban u.-

Nu m DHCP server "cn sng", n s gi li gi tin

DHCPACK renew ti DHCP client, gi ny bao gm thng s cu hnh mi cp nht nht trn DHCP server.-

Nu DHCP server " cht" th DHCP client s tip tc s

dng cu hnh hin thi ca n. V nu sau 87.5% (7 ngy) ca thi gian thu hin thi ca n, n s broadcast mt DHCPDISCOVER update a ch IP ca n.

GVHD: ng Trung Thnh

Nhm 17


Trang 8

Vo lc ny, n khng tm ti DHCP server ban u cho n thu na m n l s chp nhn bt c mt DHCP server no khc. Nu thi gian lease ht, th client s ngay lp tc dng li vic s dng IP address lease . V DHCP client sau s bt u tin trnh thu mt a ch nh ban u. Lu : Khi bn khi ng (restart) li DHCP client th n s t ng renew li IP address m trc khi n shut down.

Bn vn gi tin ca MS v CISCO-

y l c ch ca MS

-

y l c ch ca CISCO

GVHD: ng Trung Thnh

Nhm 17


Trang 9

S khc nhau y l c ch gi gi tin ca MS l broadcast 4 gi tin cn CISCO th s dng unicast vi offer v ACK.

II. CI T V CU HNH DHCP II.1-

Qu trnh tng tc gia Client v Server. Khi my Client khi ng n s t ng gi mt gi tin yu My Server trn mng nhn c yu cu lin cp mt a

cu n my Server trong gi tin c km theo a chi MAC ca my Client. ch IP ng cho my Client trong khong thi gian nht nh ng thi cng km theo mt SubnetMask v a ch IP ca Server.-

Sau Client s gi thng ip chp nhn IP li cho Server v Cch kim tra my Client nhn c IP ng. G IPCONFIG /RELEASE sau l IPCONFIG /RENEW Kim tra a ch IP ca my Client t DHCP Server trong Nh vy l chng ta bit c DHCP server c cu hnh

my Server s lc ra nhng IP no cha cp v cp cho cc Client tip theo. II.2-

v kim tra nhn c mt a ch IP t DHCP server mi cha.-

Address Releases.-

ng v hot ng tt trong mng.GVHD: ng Trung Thnh Nhm 17


Trang 10

II.3

Ci t dch v DHCP

a. Ci t dch v DHCP trn my 1B1. Vo Start Settings Control panel Add/Remove Windowns Components . B2. Ko thanh trt xung chn Networking Services Dynamic Host Configuration Protocol (DHCP) OK Finish .

B3. Vo Start Administrative Tools DHCP

B4. Right click ln tn my win2k39b5cd08f Authorize ( ng k vi AD)

GVHD: ng Trung Thnh

Nhm 17


Trang 11

b. To Scope trn DHCP ServerB1. Right click ln Server1 New Scope . B2. Ti hp thoi Welcome Next .

B3. Ti hp thoi Scope Name t tn cho Scope (vd: Nhom 17) Next .

B4. Ti y ta nhp a ch IP bt u v IP kt thc cho Scope nh hnh bn di Next

GVHD: ng Trung Thnh

Nhm 17


Trang 12

B5. Ti y ta nhp dy IP s loi tr s khng c cp trong DHCP, ta dng cc IP ny t IP tnh cho cc Server Next .

B6. Ti hp thoi ny l quy nh thi gian cho thu a ch IP mc nh l 8 ngy, chng ta c th thay i c Next .

B7. Ti y ta chn Yes, I want to configure these option now Next .

B8. Ti hp thoi ny ta nhp a ch IP Default Gateway (vd: 192.168.1.1) Next .

GVHD: ng Trung Thnh

Nhm 17


Trang 13

B9. Ti hp thoi DNS nhp a ch DNS vo (vd: 192.168.1.1) Next

B10. Ti hp thoi WINS ta c th nhp a ch WINS vo (vd: 192.168.1.1) Next .

B11. Ti hp thoi ny chn Yes, I want to activate this scope now Next .

B12. Chn Finish hon thnh .

GVHD: ng Trung Thnh

Nhm 17


Trang 14

II.4

Cu hnh DHCP

a. Cu hnh DHCP Client nhn IP ng t DHCP ServerB1. Vo Network Connections Right click ln Card LAN Properties . B2. Ti hp thoi LAN Properties chn Internet Protocol (TCP/IP) Properties .

B3. Chn ch nhn IP ng l Obtain an IP address automatically OK .

B4. xem IP va cp cho DHCP Client th vo Start Run g cmd OK .

GVHD: ng Trung Thnh

Nhm 17


Trang 15

B5. Ta s g lnh ipconfig /all Enter xem IP nh hnh bn di .

b. Cu hnh DHCP Reservations.

GVHD: ng Trung Thnh

Nhm 17


Trang 16

B1. Ti my 2 ta dng lnh ipconfig /all xem MAC Address ca card LAN l : 00-0C29-AA-EB-85

B2. Ti my 1 m DHCP Right click Reservations New Reservations .

B3. Tip tc ta s t c nh IP v nhp MAC Address ca My 2 vo Add .

B4. Ta chn Reservations th s thy c IP va t cho My 2 .

B5. Kim tra: Ti my 2 c nhn IP c nh c khng vo Run cmd g lnh ipconfig /release xa IP c v g ipconfig /renew nhn IP mi t DHCP

GVHD: ng Trung Thnh

Nhm 17


Trang 17

Server cp .

c. Server Options Thc hin trn my 1B1. Trong Scope Nhom 17 Scope Option Right click vo 2 gi tr 003 v 006 Delete . - Kim tra li thy 2 Option 003 v 006 c xa

GVHD: ng Trung Thnh

Nhm 17


Trang 18

B2. Right click ln Server Option Configure Option.

B3. Tip tc chn Option 003 Router Add a ch IP Gateway vo l 192.168.1.1 Add .

B4. Tip tc chn Option 006 DNS Server Add a ch DNS vo l 192.168.1.1 Add Apply

B5. Kim tra: Ta vo li Scope Option ta s thy 2 Option 003 v 006 c li sau khi vo Server Option cu hnh li.

III. GIM ST V QUN L DHCPGVHD: ng Trung Thnh Nhm 17


Trang 19

III.1 Gim st hot ng ca DHCP. Ci t cu hnh dch v DHCP l mt phn ca gii php mng. V mi trng lm vic ca dch v DHCP l ng, thay i lin tc. Vy nn vic theo di hot ng ny l cn thit trnh nhng s c c th xy ra trong h thng mng. Cu hnh mc nh ca Windows Server 2003 c s d liu ca DHCP c lu theo ng dn : %SystemRoot% \ System32 \ DHCP Sao lu phc hi d liu i vi dch v DHCP cng quan trng khng km, tng kh nng chu li ca DHCP Server khi gp s c v phn cng hoc phc hi trong trng hp c bit. Mc nh dch v DHCP t ng sao lu trong mi 60 pht theo ng dn %SystemRoot% \ System32 \ DHCP \ Backup. Trong cc trng hp dch v DHCP khng th np d liu th n t ng khi phc li theo ng dn mc nh trn. Lu : Khi bn thay i ng dn sao lu th qu trnh sao lu v phc hi bn phi thao tc bng tay(Manual) ng b d liu: thng thng khi c mt s thay i v thng tin trong h thng mng hoc sau khi phc hi d liu ca DHCP th s ng b din ra cha kp thi nn gy ra nhng sai st. khc phc ta tin hnh ng b trn h thng. Khi i tin hnh ng b d liu dch v DHCP s tng hp 2 thng tin t Registry v trong c s d liu tng hp chnh xc cc thng s cu hnh hin ti. Ta c th thy trong Console qun l. a ra cc nh mc hot ng cho DHCP Server thng qua tt c nhng g lin quan n Server bao gm: cc services, memory, processor Theo di thng qua cc gi tin Discovers,Offer,Requests,Acks... Right Click ln DHCP Server chn Display Statistics. Dng cc file log theo di s hot ng hng ngy. Cc File + Khi DHCP Server va khi ng hoc qua ngy mi (sau 12h m) DHCP Server s ghi nhn s kin mi ln File Log. C 2 trng hp c th xy ra : Nu File Log ang c c hn 24h th DHCP Server s ghi ln d liu ny. + Nu File Log ghi nhn s kin cha qu 24h th DHCP Server s ghi ni tip. Log ghi nhn mi 24 gi :

GVHD: ng Trung Thnh

Nhm 17


Trang 20

+ Sau khi cc d liu bt u ghi nhn th ta nn kim tra xem s hot ng cc File Log c kch hot cha, dung lng cc file log c tng t bin hay khng, kim tra chnh xc ngy gi h thng, dung lng a cng c lu File Log hay khng. * trng thi mc nh th cc File Log ch lu 50 s kin. * Nu dung lng cng khng nhu cu ti thiu l 20 megabytes th cc File Log dng li khng ghi tip. * Trong Registry cng quy nh khng cho cc File Log ghi qu 1/7 dung lng trng trn Server (khng qu 10MB nu dung lng trng trn Server l 70MB).Trong trng hp ny DHCP Server s ng cc File Log ang c v t chi ghi nhn s kin tip theo. III.2 Sao lu v phc hi DHCP. a. Sao lu DHCP Ton b Database ca DHCP Server nm trong ng dn %systemroot %\system32\dhcp. Ni thc hin: Domain Admin, DHCP Admin, Local Admin, Backup Operator. Vo Start Run g lnh dhcpmgmt.msc Chut phi vo DHCP Server --> Chn Backup

-

Ch ng dn lu tr Database ca DHCP Server

GVHD: ng Trung Thnh

Nhm 17


Trang 21

-

Nhn OK hon tt backup

b. Phc hi DHCP Ni thc hin : Domain Admin, DHCP Admin, Local Admin, Backup Operator. Vo Start --> Run g lnh dhcpmgmt.msc Chut phi vo DHCP Server --> chn Restore

-

Ch ng dn n th mc backup dhcp trc --> OK

GVHD: ng Trung Thnh

Nhm 17


Trang 22

--> OK

H thng s yu cu stop v sau s restart li dch v DHCP

-

Refesh li DHCP, tip n chut phi vo DHCP Server chn

Reconcile All Scopes ng b ha gia Database v Registry.

GVHD: ng Trung Thnh

Nhm 17


Trang 23

Ok, n y cng vic khi phc Database trn DHCP hon thnh III.3 Di chuyn DHCP Server qua mt Server khc Trong thc t, i lc chng ta cn phi di chuyn mt DHCP Server t server ny qua mt server khc p ng nhu cu cng vic ca cng ty. hin thc vic di chuyn mt DHCP Server chy trn Windows Server 2003, bn cn phi tin hnh cc bc sau : ra mt file text. mi. Server mi. Cc bc thc hin nh sau: 1 Log on vo DHCP Server c vi account thuc nhm Administrators2

Xut c s d liu ca DHCP Server ang s dng trn my c Ci t mt DHCP Server trn my tnh Windows Server 2003 Nhp c s d liu ca DHCP Server c t file text vo DHCP

Vo Start --> Run g lnh cmd --> OK c c s d liu ca DHCP Server c ra file text export_dhcp.txt

3 Nhp vo dng lnh netsh dhcp server export C:\export_dhcp.txt all xut tt 4 Ci t DHCP Server trn my tnh mi. Ch ci t dch v, khng cn phi cu hnh bt k mt scope no. 5 Trn my DHCP Server mi, copy file export t Server c vo my tnh (copy vo C:\).6

Trn my DHCP Server mi, vo Start --> Run g lnh cmd --> OK s d liu t Server c vo Server mi.

7 Nhp vo dng lnh netsh dhcp server import C:\export_dhcp.txt nhp file c 8 Khi ng li DHCP Server hon thnh vic di chuyn ny.

GVHD: ng Trung Thnh

Nhm 17


Trang 24

IV. VN BO MT TRONG DHCP IV.1 Cc kiu tn cng c th xy ra i vi DHCP-

Nh bit, hu ht dch v DNS v DHCP mc nh khng

c bo mt. Li dng iu ny, cc attacker c th tin hnh tn cng cc my ch chy dch v DNS v DHCP. i vi dch v DHCP th cc kiu tn cng m attacker c th thc hin l : a. Tn cng t chi dch v bng cch vt cn tt c cc gi tr m DHCP c th cp cho client

GVHD: ng Trung Thnh

Nhm 17


Trang 25

-

Khi DHCP Server nhn c mt DHCP request t client,

DHCP Server s cung cp cho client mt a ch IP nm trong dy IP m n c php cp. V khng c c ch chng thc trong qu trnh ny, cc attacker c th d dng tn cng lm ngng dch v ny trn DHCP Server. Attacker c th thc hin c vic ny bng cch gi mt lng ln DHCP request vi cc gi tr MAC address thay i lin tc n DHCP Server. Khi DHCP Server nhn c cc request vi cc MAC address khc nhau, DHCP s cp mt gi tr IP ng vi mi request . V s lng a ch IP c gii hn nn ch cn mt lng request tng i l attacker c th ng k ht s lng IP ny trn DHCP. Kt qu l cc request hp l ca client s khng c DHCP Server cung cp IP v lc ny dch v DHCP s khng cn phc v cho ngi n sau. y l kiu tn cng t chi dch v DHCP d dng nht m attacker c th thc hin. iu ng ni y l k tn cng ch cn rt t thi gian v bandwidth l c th thc hin c vic tn cng ny. Tuy nhin, kiu tn cng ny c th khc phc c bng cch s dng cc switch c tnh nng bo mt ca Cisco. Cc switch ny s gii hn s lng MAC address c th s dng trn mt port. Mc ch l ngn chn vic trong mt khon thi gian gii hn, mt port ca n c qu nhiu MAC address c php s dng. Nu vt qua quy nh ny, port s shutdown ngay lp tc. Thi gian port ny c th hot ng li ty thuc vo gi tr mc nh hoc do ngi qun tr mng thit lp. Bng cch ny, thit b ny c th ngng kiu tn cng vt cn i vi dch v DHCP.

GVHD: ng Trung Thnh

Nhm 17


Trang 26

b. Tn cng theo kiu Man-in-the-middle bng vic s dng DHCP Server gi mo

-

Nh chng ta bit, DHCP khng yu cu chng thc trong

qu trnh cp pht IP cho client v DHCP client khng bit a ch IP ca DHCP Server trong qu trnh xin cp IP. Li dng vic ny, attacker c th xy dng mt DHCP Server gi mo (Rogue DHCP Server), mc ch l cung cp a ch Default Gateway gi mo (a ch IP ny l ca attacker hoc mt my tnh no c t di s kim sot ca attacker) cho DHCP client. Vic ny cho php attacker c th xem trm ni dung gi tin. Cc bc tin hnh nh sau : 1 u tin, attacker xy dng mt DHCP gi mo vi y cc thng s cp cho client. 2 Khi mt DHCP client broadcast mt gi tin DHCPDISCOVERY, c hai DHCP hp l v DHCP gi mo cng gi gi tin DHCPOFFER n client. 3 Client s tip nhn gi tin no n trc, nu gi tin ca DHCP Server hp l n trc th qu trnh tn cng theo dng ny s tht bi. Do chc chn

GVHD: ng Trung Thnh

Nhm 17


Trang 27

rng client s nhn c gi tin do DHCP Server gi mo cp, attacker thng tin hnh tn cng t chi dch v theo kiu vt cn i vi DHCP Server tht. 4 Trong gi tin response n client, a ch Default Gateway li ch v my tnh cho attacker kim sot. 5 Sau , khi no client gi gi tin cho mng bn ngoi (thng l internet). Gi tin ny s c chuyn tip n cho my tnh c a ch Default Gateway gi mo v ni dung bn trong b xem trm. Sau khi xem trm ni dung, gi tin s c forward n Default Gateway tht. Nhng khuyt im ca kiu tn cng ny l, attacker ch c th xem trm gi tin theo chiu t client gi i m thi, chiu ngc li t bn ngoi gi n client th attacker hon ton khng bit. khc phc kiu tn cng ny, cc thit b switch ca Cisco cung cp tnh nng bo mt dnh cho DHCP. Tnh nng ny c gi l DHCP snooping, bng cch ch cho kt ni n DHCP trn mt hoc mt s port nht nh m thi. Cc port ny c gi l trusted port, ch c nhng port ny mi cho php gi tin DHCP response hot ng. Port ny c ngi qun tr mng kt ni n DHCP Server tht trong mng. Mc ch l ngn chn khng cho DHCP gi mo hot ng trn nhng port cn li. c. Tn cng theo kiu DNS redirect bng cch s dng DHCP Server gi mo

GVHD: ng Trung Thnh

Nhm 17


Trang 28

-

y l kiu tn cng rt thng dng ca phng php man-in-

the-middle. Thay v gi mo a ch Default Gateway, DHCP Server gi mo s cung cp a ch IP ca DNS Server gi. Trn DNS Server ny cha cc thng tin phn gii tn b nhim bn (DNS Server nm trong s kim sot ca attacker). Khi ngi dng mun phn gii tn a ch First Place - Your First Place on the Internet. DNS Server gi mo s dn client n a ch 99.99.99.99 l website gi c dng ln bi attacker. Bng cch gi mo trang ch ging y website tht l First Place - Your First Place on the Internet. Attacker c th capture cc thng tin nhy cm nh user id v mt khu. Sau khi nhn c thng tin ny, website gi mo s thng bo ng nhp sai, sau s redirect n website First Place - Your First Place on the Internet tht.

IV.2 Bo mt c bn cho DHCP Server

GVHD: ng Trung Thnh

Nhm 17


Trang 29

secure)-

Bo mt v mt vt l cho cc my ch DHCP (physically Nn s dng h thng file NTFS lu tr d liu h thng. Trin khai v ng dng cc gii php anti-virus mnh cho h Thng xuyn cp nht cc bn v li cho cc phn mm v Cc dch v hay cc phn mm khng s dng th nn xa Thc hin vic qun l DHCP vi user c quyn hn ti thiu DHCP Server phi c t pha sau firewall. ng tt c cc port khng s dng n. tng thm tnh bo mt cho DHCP Server, bn c th s S dng filter MAC Address. Gim st hot ng ca DHCP bng cch xem qua cc file log

thng. Windows. hoc uninstall i. nht. -

dng VPN tunnel bo mt traffic DHCP.

v xem thng tin thng k ca h thng trn DHCP Server. IV.3 S dng Event Viewer gim st hot ng ca DHCP Bn c th s dng cng c Event Viewer nm trong th mc Administrative Tools gim st hot ng ca DHCP. Event Viewer lu tr cc s kin ca system, application v security. Tt c cc s kin gim st hot ng ca DHCP c ghi nhn trong security log. Cc thng tin ny ghi nhn c hot ng ca dch v DHCP v DHCP Server, v d nh DHCP Server c start v stop vo lc no, dy IP cp cho client gn cn kit vo lc no, database ca DHCP b li vo lc no. Mi mt s kin trong log c nh mt m s (ID number) ring bit vi nhau. Sau y l mt vi ID s kin thng gp trong system log ca DHCP : sch c s d liu. Event ID 1037 (Information): cho bit DHCP Server xa

GVHD: ng Trung Thnh

Nhm 17


Trang 30

-

Event ID 1044 (Information): cho bit DHCP Server c y Event ID 1042 (Warning): cho bit dch v DHCP ang chy

quyn (authorized) c th cung cp a ch IP cho client. trn h thng th pht hin c dch v DHCP khc cng c chy trn mng (tc l c 2 my tnh chy dch v DHCP trong h thng). ng. Event ID 1046 (Error): cho bit dch v DHCP chy trn Server ny cha c y quyn (authorized) c th cung cp IP ng cho client. IV.4 Cc vn cn lu ca dch v DHCP C cc trng hp Client t ci dch v DHCP trong h thng mng(DHCP Server gi mo) iu ny gy nh hng n cc Client mun c cp IP nhng nm xa v tr DHCP Server tht s. Do tnh hiu xin v cp a ch IP l Broadcast nn s c trng hp Client nhn khng ng thng s IP do DHCP Server gi mo cp. Bn cn r sot k trong h thng mng ca mnh. Cc thit b phn cng nh Router ADSL,Wireless.. cng c kh nng cp a ch IP, do cn tt chc nng cp IP ng trn cc thit b trc khi a vo s dng. Ch c thnh vin ca nhm DHCP Administrators mi cu hnh v s ung cc tnh nng trong dch v DHCP. Ch cn cung cp quyn cho cc i tng lin quan n qun l duy tr hot ng ca dch v ny Event ID 1056 (Warning): cho bit dch v DHCP c chy trn my ch Domain Controller nhng n khng c cu hnh cp nht DNS

GVHD: ng Trung Thnh

Nhm 17


Trang 31

V. KT LUN Vic tm hiu v dch v DHCP phn no hiu c tm quan trng ca n trong qun tr mng hin nay, cng nh nhng u v nhc im ca dch v DHCP. T , gip ch cho cc nh qun tr trong vic qun l v cu hnh ph hp vi yu cu, mc ch ca t chc. Tuy nhin, do thi gian c hn v vi nhng kin thc cn hn ch nn nhm chng em cha th tm hiu su, v trnh by k lng, xc ng cc vn lin quan n ti. y ch l mt phn kin thc m chng em tng hp c, bi bo co vn cn s si, nhiu im hn ch.

GVHD: ng Trung Thnh

Nhm 17


Trang 32

DANH MC TI LIU THAM KHO Sch Qun Tr Mng My Tnh trng i Hc Cn Th Gio trnh H Thng Thng Tin Mng V Truyn Thng, i Hc S Phm Thnh Ph H Chnh Minh

Gio trnh CCNA, trung tm o to Nht Ngh. http://www.nhatnghe.com

V cc ti liu tham kho khc trn Internet.

GVHD: ng Trung Thnh

Nhm 17

Documents

Nhom 17 - De Tai 04 - DHCP