Tuan_5_2_Minh Hoa Phan Tich Goi Tin - DHCP

BM MMT&VT Khoa CNTT Trng H KHTN TPHCM Trang 1

Minh ho phn tch gi tin giao thc DHCP

Mc Tiu:

Bi hng dn ny gip sinh vin c th:

Nhc li c ch hot ng ca giao thc DHCP

S dng cng c wireshark bt gi tin v phn tch hot ng ca mt

giao thc

I. Nhc li dch v DHCP l g

I.1.DHCP l g?

Dynamic Host Configuration Protocol (DHCP) l mt giao thc hot ng

tng ng dng, cho php cu hnh a ch IP ca cc my trm mt cch t ng. T

c th qun l tp trung a ch IP ca cc my trong mt mng ni b hn ch c

xung t c th xy ra cng nh d dng cp nht cc thay i c th c v a ch IP

ca cng ty.

DHCP hot ng nh mt phn m rng ca giao thc BOOTP. Ngoi vic cung cp

kh nng cu hnh IP cho cc my con, DHCP cn cho php ngi qun tr thit lp cc

trng khc nh DNS server hay WINS server.


I.2.C ch hot ng

Qu trnh hot ng ca giao thc DHCP c m t gm 4 bc sau y :

II. Phn tch qu trnh hot ng ca DHCP

II.1.Chun b :

Chng trnh Vmware tt dch v DHCP

Hai my o : client v server (c hai my o u dng card mng host-only; my server

ci h iu hnh Windows server 2003) kt ni vi nhau theo s bn di

Ci t dch v DHCP trn my server v cu hnh cp pht a ch cho mt lp mng

192.168.1.0/24, khong cp pht nm trong khong t 192.168.1.10/24 -

192.168.1.100/24 theo m hnh sau vi xx = 01:

DHCP server

192.168.xx.254/24

192.168.xx.0/24

DHCP client

Host-only Host-only

1. Ci t Wireshark trn my client.

2. Cu hnh cho my client nhn IP ng.


II.2.Tin hnh bt gi tin trn my client theo cc bc sau :

1. M ca s Windows Command Prompt ( Start Run cmd ) v g lnh

ipconfig /release.

2. Khi ng qu trnh bt gi tin ca Wireshark.

3. Quay li ca s Windows Command Prompt g lnh ipconfig /renew.

4. i n khi lnh ipconfig /renew kt thc, g lnh ipconfig /renew mt ln

na.

5. i n khi lnh ipconfig /renew th hai kt thc, g lnh ipconfig /release

mt ln na.

6. Cui cng, thc hin li lnh ipconfig /renew ln th ba.

7. Kt thc qu trnh bt gi tin ca Wireshark.

II.3.Bt cc gi tin vi Wireshark :

S dng Wireshark bt cc gi tin theo cc bc trn, ta s thu c rt nhiu

cc gi tin thuc cc giao thc khc nhau, khng ch l cc gi tin ca DHCP. V mi

khi my nhn c mt a ch IP mi, n thng pht sinh km theo cc gi tin

thng bo cho cc my khc s tn ti ca mnh trong mng.

Ta ch quan tm n giao thc DHCP v vy cn phi tin hnh lc cc gi tin

dng ny. DHCP s dng da trn giao thc BOOTP nn ta nhp tn giao thc ny vo

ca s Filter.


Cu hi 1 : DHCP s dng giao thc no cho tng vn chuyn ?

V mt lch s DHCP xy dng da trn giao thc BOOTP s dng giao thc

UDP cho tng vn chuyn. Ta c th thy r iu ny khi khng thy cc bt tay ba

bc ca giao thc TCP trn cc gi tin bt c.

Kim tra vi cc gi tin bt c bng Wireshark, ta thy mc Internet Protocal

s dng UDP.


Cu hi 2 : V th thi gian th hin th t ca 4 gi tin DHCP :

Client Server -192.168.1.254/24

DHCP DISCOVER

DHCP OFFER

DHCP REQUEST

DHCP ACK

Port 67 Port 68

Cu hi 3 : ia ch tng Datalink ca my Client l g :

Ta s coi a ch Mac ca my client phn Ethernet II thu c a ch sau:

MAC = 00:0c:29:5b:ef:6a


Cu hi 4 : a ch ngun v ch ca cc gi tin :

DHCP DISCOVER

Source IP : 0.0.0.0

Destination IP : 255.255.255.255

DHCP OFFER

Source IP : 192.168.1.254


DHCP REQUEST

Source IP : 0.0.0.0


DHCP ACK

Source IP : 192.168.1.254


Cu hi 5 : Gi tin no ch a ch IP m Server mun cp cho my client :

Ta c th thy gi DHCP OFFER m my DHCP server gi cho client cha cc

thng tin v a ch IP ca client cng nh cc phn ph thm nh Subnet mask, DNS IP


I.

Gi tin trn cha cc thng tin c bn sau :

a ch IP Client 192.168.1.10

Subnet Mask 255.255.255.0

DHCP Server 192.168.1.254

DNS Server 8.8.8.8

Lease Time 8 days

Cu hi 6 : a ch IP m Client mun DHCP cp trong gi DHCP REQUEST :


Sau khi nhn c thng tin v a ch IP DHCP Server mong mun cp ti gi

DHCP OFFER. Client s xc nhn n mun nhn a ch IP no gi tin DHCP

REQUEST.

y a ch l: 192.168.1.10.

Cu hi 7 : Gi tin no ch a ch IP m Server s cp cho Client :

y l gi cui cng, xc ch cc thng tin tha thun gia Server v Client

trong sut qu trnh trao i cng nh l gi tin cui cng trong qu trnh giao tip

DHCP c tn gi DHCP ACK.


Ti liu tham kho

http://www.wikipedia.org/

http://technet.microsoft.com/

http://www.nhatnghe.com/

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Tuan_5_2_Minh Hoa Phan Tich Goi Tin - DHCP