Port Scanning Protocols

Port Scanning Protocols

There are many different types of scanning, each one having its own
advantages and disadvantages. All methods of scanning discussed here
are subsets of TCP, UDP or ICMP scanning.
Transmission Control Protocol (TCP)
Transmission Control Protocol (TCP) is defined in RFC 793. The
objective of TCP is to provide a reliable connection-oriented delivery
service; it views data as a stream of bytes, not frames. The unit of
transfer is referred to as a segment. The attributes that TCP uses to
ensure a reliable connection-oriented service over IP are:
• Flow control.
• Connection maintenance.
TCP is able to recover from data that is:
• Damaged.
• Lost.

• Duplicated.
• Delivered out of sequence.
To do this TCP assigns a sequence number to each byte transmitted.
The receiving host's TCP stack must return an ACK for bytes received
within a specified period; if it does not, the data is retransmitted.
Damaged data is recognized by adding a checksum to each segment. If
a segment is detected as damaged by the receiving host's TCP, it will be
discarded. The sender will resend the segment if it does not receive its
corresponding ACK.