But in some cases like the above result of the UDP Scan image, the host does not send an ACK packet like in TCP Scan so due to the lack of response means the port may be open. Open | Filtered: No answer is given by the host so the port may be filtered by a firewall. Like in the above image of the UDP Scan Result when the host sends a response like ICMP Unreachable then the port is considered as filtered.Ĥ. Nmap (Zenmap is the official Nmap GUI) is a free, open-source(license) utility for network exploration and security auditing. If the host sends an Unusual response then also the port is filtered. Filtered: Port is filtered by a security system like Firewall and whether the port is open or closed is not determined. Closed: This means the service is not listening at that port.ģ. Open: A port is Open means that a service is listening to the port, for example, a MySQL service running at port 3306 as you can see in the TCP Scan result image.Ģ. In this scenario two things can occur : The target responds with an RST packet that signifies that the port is closed. TCP Connect Scans ( -sT) In this type of scan, Nmap sends a TCP packet to a port with the SYN flag set. There are mainly 4 types of State in the port scan results.ġ. Nmap supports a lot of different scan types. you can also use it to check for a single IP to check that the host is up or not.ĭifferent States of the Port Scan Results and their Meaning: The above command does not tell anything about the ports of the system. Only print the available host that responds to the host Discovery probes within the network. Here: -sn and -sP both are used for Ping Scan. It generally sends the empty UDP packets and it takes more time than TCP Scan. Here: -sU is used to activate the UDP Scan. This scan is done by the privileged users only i.e for Linux system the Root user and for Windows system Admin. The host keeps any record of the system by which this scan is done. The host Does not keep any record of the system by which this scan is done. Because of the interruption Destination or host does not keep a record of the Source system.ĭifference between SYN Scan and TCP Scan: SYN SCAN In this scan, Source sends the SYN packet and the destination responds with SYN/ACK packets but the source interrupts the 3-way handshake by sending the RST packet. SYN Scan is the same as TCP Scan but it does not complete the 3-way handshake process. SYN Scan/Stealth Scan/Half Open Scan: nmap -sS 192.168.1.12 -top-ports 50 Take Control of Nmap with the Zenmap GUI: Run Zenmap.
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