4 (5-7) (1-3) : ; , .
: FTP, HTTP, SMTP . IP- IP-, . IP- .
4 . (FTP SMTP) , . - , , . , .
4 ( ), . . 12-4. (5-7) 4 (.. " ") . OSPF, . 4 ( ), IP.
| .12-1 - |
(, DNS) UDP, - TCP. TCP , . UDP , . , , , .. UDP , TCP.
4, , 3 " " (. .12-4), . IP- . , , . ( ) - -, .
, (, HTTP, SMTP), - . .. FTP-, #21, Web- (HTTP), #80, e-mail (SMTP)- cp, #25 (. . 12-5). .. , .
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.12-5. IP-
: IP-, : . - IP- -, - IP- - , - . IP- .12-5.
TCP
TCP - TCP/IP, . , . RFC 793 (STD 0007) RFC 2018 (1072), 1146, 1323, 1623. TCP . (.12-6) , .
| 0 | 61 | 2 | |||||||||
| 7-4 | 3-0 | 7-6 | 5-0 | 7-4 | 3-0 | 7-4 | 3-0 | ||||
| Offset | Resrvd | Code-bits | Window | ||||||||
| Check sum | Urgent pointer | ||||||||||
| Options | Padding | ||||||||||
| TCP Data | |||||||||||
.12-6. TCP
TCP:
- 16- , ; ID , ;
- 16- , , , , FTP (20, 21), Telnet (23), TFTP (69), SNMP (161);
, TCP ( S ); 32 ;
Offset - ( 4-7 0) - , 32- - ;
Resrvd - ( 0-3 0 + 6-7 1) - ;
Code bits - 6 : U (URG - ), ( - ), (PSH - ), R (RST - ), S (SYN - ), F (FIN - ):
Window - ( ) ;
Check sum - , TCP IP ();
Urgent pointer - , , U;
Options - ( );
Padding - 1-3 4- ;
TCP Data - , .
TCP . , , . , . . TCP , , .
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UDP
UDP - , DG-, . , . , TFTP DNS. UDP, TCP, ( " " . 12-4) IP ( #17) . TCP, UDP " ", , . UDP - (4 ) , - (.12-7). " ", " " Check sum , TCP. Length - UDP.
| 0 | 1 | 2 | |||||
| 7-4 | 3-0 | 7-4 | 3-0 | 7-4 | 3-0 | 7-4 | 3-0 |
| Length | Check sum | ||||||
| UDP Data | |||||||
.12-7. UDP
ICMP
ICMP - (RFC 792) ( ) . IP DG DG . , DG .
ICMP. "" (0-16) "" (0-5) . , =3 =0 , ( ) . , ( .. ).
ICMP .. 4. .. #1, , IP 3. ICMP , , , .. , ( 3). ICMP .
ICMP :
- , , , , ;
- , Ping . Ping, ICMP ( IP) ; ICMP- . :
Ping→I→I→→ → IP- .
ICMP IPv4. IPv6, ICMPv6 (RFC 1885). IPv4, IGMP, IPv6 ( IGMP IP- #2).
