Last Updated on August 1, 2021 by Admin
When TCP packet is sent to an open port with the SYN flag set, what response would be expected from the open port?
- a packet with the SYN and ACK flags set
- a packet with an RST flag
- no response
- a packet with the ACK flag set
Transmission Control Protocol (TCP) is a session-oriented or connection-based protocol. It uses a three-way handshake to ensure that every packet sent is successfully received and acknowledged by the destination. The handshake is performed at the start of each session by TCP, and contains a set of three segments (TCP “packets”).
– The sender sends the first segment to the receiver with the Synchronization (SYN) flag enabled.
– Step two: The receiver sends the second segment back to the sender with both the Acknowledgement flag (ACK) and the Synchronization (SYN) flag enabled.
– Step three: The sender sends the third segment back to the receiver with just the Acknowledgement (ACK) flag enabled (in response to the server’s Synchronization request).
A packet with the RST flag would be received if the port were closed. An open port responds with a SYN/ACK segment, while a closed port responds with a RST (reset) flagged segment.
A packet with the ACK flag set would only follow a packet with the SYN and ACK flags set. The first step is to send a SYN packet. When the port is open, the receiver will send back a packet the YSN and ACK flags set.
No response would occur only if the port were blocked on the firewall. Firewalls do not send diagnostic or error messages when blocking a transmission.
Objective: Network Concepts
Sub-Objective: Describe the operation of the following: IP, TCP, UDP, ICMP