Monthly Archives: June 2010

OSI, Network Layer Header

Kompai, Kompiuterių tinklai, Paskaitos, , , , , , , , , , ,

Sveiki, OSI lygyje mes turime lygi Network (Tinklo).
OSI model from blessedhands3333.com
Sis lygis (kaip ir dauguma ju) ant siunciamo / perduodamo paketo uzdeda savo raktini vokeli, kad kitame kompiuteryje, tas pats lygmuo suprastu, ka daryti su siame voke esancia informacija. Sio vokelio turini galime perziureti pasitelkdami programele wireshark:

aptitude install wireshark

Taigi is ko susideda si antraste?

Network Layer Header – Tinklo lygio antraste
b it a i: 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Version IHL Type of service Total Length
Identification Flags Fragment Offset
Time To Live Protocol Header checksum
Source address
Destination address
Options (Optional)

Lenteles reiksmes

Version:
4 - IP versija 4
Internet header length
32bitu zodziu kiekis IP antrasteje,
minimali reiksme: 5 (20 Baitu) ir
maksimali reiksme: 15 (60 Baitu)

Type of service (PreDTRCx) Differentiated Services
Precedence(000-111) 000
D (1 minimize delay) 0
T (1 maximize throughout) 0
R (1 maximize reliability) 0
C (1 minimize cost) 1 = ECN capable
x (reserved and set to 0) 1 = congestion experienced

Total Length
Kiekis Baitu pakete. Maximalus dydis: 65535.
Flags (xDM)
x - rezervuotas ir yra 0
D = 1 - Nefragmentuoti
M = 1 - Daugiau fragmentu
Fragment Offset
Sio fragmento vieta originalioje deitagramoje (nepatinka man sis zodis) po 8 Baitus...
Protocol
1) ICMP
2) IGMP
6) TCP
9) IGRP
17) UDP
47) GRE
50) ESP
51) AH
57) SKIP
88) EIGRP
89) OSPF
115) L2TP
Header checksum
Tik IP antrastes kontroline suma
Adresai
Siuntejo (source) ir gavejo (destination) IP adresai
Options (0-40 Baitu; padded to 4-byte boundary)
0 - end of options list
1 - No operation (pad)
7 - Record route
68 - Timestamp
131 - Loose source route
137 - Strict source route

External Links

sans.org/security-resources/tcpip.pdf