Referensi Flag TCP
Panduan referensi flag TCP dan status koneksi.
Initiates a connection. Used in the three-way handshake to synchronize sequence numbers.
Use cases: Connection establishment, port scanning
Acknowledges receipt of data. Almost all packets after the initial SYN have ACK set.
Use cases: All established connection packets, connection teardown
Indicates no more data from the sender. Initiates the four-way connection teardown.
Use cases: Graceful connection termination
Abruptly terminates a connection. Sent when an error occurs or connection is refused.
Use cases: Error handling, refusing connections, terminating half-open connections
Tells receiver to pass data to the application immediately without buffering.
Use cases: Interactive applications, real-time data, small payloads
Indicates the urgent pointer field is significant — data should be processed out-of-order.
Use cases: Telnet, SSH interrupt signals, rarely used in modern protocols
Used in Explicit Congestion Notification (ECN). Indicates ECN-capable transport during SYN.
Use cases: Congestion control negotiation and signaling
Sent by host to indicate it received a TCP segment with ECE flag and has reduced its congestion window.
Use cases: Congestion control feedback
Tentang alat ini
Flag TCP adalah sinyal kontrol yang mengelola aliran data dan mengontrol pembentukan atau pemutusan koneksi dalam komunikasi jaringan. Enam flag (SYN, ACK, FIN, RST, PSH, dan URG) masing-masing melayani tujuan khusus dalam protokol TCP. Memahami flag-flag ini sangat penting bagi insinyur jaringan, profesional keamanan, dan siapa pun yang melakukan debugging masalah koneksi, karena mereka mengontrol proses handshake, menentukan kapan data harus disampaikan segera, dan mengatur penutupan koneksi yang anggun versus mendadak.
Panduan referensi ini menyediakan pencarian visual dan dapat dicari untuk semua flag TCP dan artinya. Anda dapat dengan cepat memahami apa yang dilakukan setiap flag, bagaimana penggunaannya dalam three-way handshake, dan perannya dalam pemutusan koneksi dan penanganan kesalahan. Panduan juga mencakup status koneksi TCP seperti ESTABLISHED, TIME_WAIT, dan SYN_RECV, memberi Anda pemahaman lengkap tentang bagaimana TCP mengelola seluruh siklus hidup koneksi dari inisiasi hingga penghentian.
Pertanyaan yang Sering Diajukan
Implementasi Kode
import socket
import struct
# TCP flags constants
TCP_FIN = 0x01
TCP_SYN = 0x02
TCP_RST = 0x04
TCP_PSH = 0x08
TCP_ACK = 0x10
TCP_URG = 0x20
TCP_ECE = 0x40
TCP_CWR = 0x80
def decode_tcp_flags(flags_byte):
"""Decode TCP flags from a byte"""
flags = []
if flags_byte & TCP_FIN: flags.append('FIN')
if flags_byte & TCP_SYN: flags.append('SYN')
if flags_byte & TCP_RST: flags.append('RST')
if flags_byte & TCP_PSH: flags.append('PSH')
if flags_byte & TCP_ACK: flags.append('ACK')
if flags_byte & TCP_URG: flags.append('URG')
if flags_byte & TCP_ECE: flags.append('ECE')
if flags_byte & TCP_CWR: flags.append('CWR')
return flags
def check_tcp_connection(host, port, timeout=3):
"""Check if TCP port is open (SYN-ACK received)"""
try:
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(timeout)
result = sock.connect_ex((host, port))
sock.close()
return result == 0 # 0 = connected (SYN-ACK received)
except Exception:
return False
# Common flag patterns
print("SYN packet flags:", decode_tcp_flags(TCP_SYN)) # ['SYN']
print("SYN-ACK flags:", decode_tcp_flags(TCP_SYN | TCP_ACK)) # ['SYN', 'ACK']
print("FIN-ACK flags:", decode_tcp_flags(TCP_FIN | TCP_ACK)) # ['FIN', 'ACK']
print("PSH-ACK flags:", decode_tcp_flags(TCP_PSH | TCP_ACK)) # ['PSH', 'ACK']
# Check if port is open
is_open = check_tcp_connection('example.com', 80)
print(f"Port 80 open: {is_open}")
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