TCP (Transmission Control Protocol) is a standard protocol used in Internet connections on networking. Sometimes, when diagnifying network issues, performing network scanning becomes crucial, and here is where TCP connect and TCP SYN scans come in.
TCP Connect and TCP SYN scan are both techniques used in port scanning. Port scanning is a method used to detect vulnerable points or open ports in a network, which can be exploited for malicious activities.
Let’s start with TCP Connect. TCP Connect is essentially a three-way handshake method used to create a connection between the client and the server. It’s a full open connection which requires more processes and time. It goes through the steps SYN, SYN-ACK, and ACK. The client sends a synchronize packet (SYN), waits for a synchronization acknowledgment packet (SYN-ACK) from the server, sends an acknowledgment packet (ACK), and initiates the connection. It’s called connect scan since nmap uses the function connect() to establish this connection (nmap.org).
On the other hand, TCP SYN scan, commonly referred to as “half-open” scanning, is more efficient and flexible. It uses the SYN packet, similarly to TCP Connect scan, but it doesn’t complete the andshake process. It also starts with the client sending a SYN packet, and when it gets SYN-ACK from the server, instead of sending ACK, it sends a RST (reset) segment. This process helps to identify whether a port is open without fully connecting, thus reducing the chances of detection by intrusion detection systems (IDSs) or firewalls. Like TCP Connect, the source of this is also Nmap, an open source tool for network exploration and security auditing (nmap.org).
In terms of difference, the main distinction between them lies in their level of stealth and the way they deal with firewalls and IDSs. TCP SYN scan is generally considered to be stealthier than TCP Connect. Firewalls and log files will document TCP Connect scans as legitimate connections, drawing attention and potentially triggering alerts. TCP SYN scan, due to its half-open technique, does not log into the connection history and is therefore considered more obscure to detect.
In conclusion, both TCP Connect and TCP SYN scans are important methods for port scanning and diagnosing network issues, but they use different methods and have different impacts on system detection and the scanning process. It’s crucial to use each one appropriately depending on the network system’s environment and the specific scenario one is dealing with.
Sources:
1. “Port Scanning Techniques”. (n.d.). Nmap.org – Free Security Scanner For Network Exploration & Security Audits. https://nmap.org/book/man-port-scanning-techniques.html
2. “Understanding TCP/IP and OSI Models”. (2020). Cisco.com – A multinational technology conglomerate. https://www.cisco.com/c/en/us/support/docs/getting-started-with-lan-switching/200748-Understanding-the-TCP-IP-Transport-Layer.html
3. “TCP SYN scan”. (2019). Networklessons.com – IT and Networking Lessons. https://networklessons.com/cisco/ccie-routing-switching/introduction-to-tcp-ip-networking
