A simple TCP Port Scan to quickly determine the status of an Internet facing service or firewall. Uses the powerful Nmap port scanner. Note that this scan will test for common services only (21) FTP, (22) SSH, (23) Telnet, (80) HTTP, (110) POP3, (143) IMAP, (443) HTTPS and (3389) RDP. Nmap version detection ( -sV ) is not enabled.
Common TCP Ports
|21||FTP||File Transfer Protocol is a very common service from the early days of the Internet. Allowing transfer of files. A key point on today's modern Internet is that
|22||SSH||Secure Shell is a protocol from remote access to systems usually in a "Terminal Shell". It is an encrypted protocol that performs a similar function to the clear text
| 23 ||Telnet||Legacy remote management service. Access to text shell on remote system. No encryption.|
| 80 ||HTTP||Hyper Text Transport Protocol is the service that delivers web pages to a browser.|
|443||HTTPS||The Secure version of
|3389||RDP||Remote Desktop Protocol is a way to remotely access Windows based systems, giving the user a full desktop environment of the remote computer.|
What is this TCP Port Scan?
The TCP Port Scan will test an IP Address for common open ports. This technique of testing for listening services is known as a port scan. Try our advanced online port scanner that is able to scan any IP Address or IP range and all 65535 ports.
Test Firewall through Port Status
By reviewing the results of a TCP Port Scan it is usually possible to determine whether a Firewall is present and blocking all traffic to ports that are not available. If some ports are in a closed state and some filtered this indicates a firewall or router may be blocking traffic but is not necessarily configured correctly as
closed ports in most cases should be
filtered by the firewall.
In the following example, the ports that are listed as
closed responded to the scan with a
TCP RST indicating there is no service listening on that port. The filtered services did not respond and the open port responded with a full three way handshake. Check out the Nmap Tutorial for a more in depth explanation.
Nmap scan report for falcon (172.16.2.100) Host is up (0.00042s latency). PORT STATE SERVICE 21/tcp filtered ftp 22/tcp closed ssh 23/tcp filtered telnet 80/tcp open http 443/tcp closed https Nmap done: 1 IP address (1 host up) scanned in 0.19 seconds
More Nmap Resources
Additional resources are available on:
- Online Nmap Port Scanner
- Port Scanner Introduction
- Nmap Tutorial
- Nmap Cheatsheet: a quick reference guide
API for the TCP Port Scan (BETA)
In addition to the web form on this page there is another way to quickly check the port status of the four ports. With this simple API,
curl or any other HTTP based tool or software can be used to get the status of ports and often the presence of a firewall. Output is of content type text.
The API is simple to use and aims to be a quick reference tool; like all our IP Tools there is a limit of 100 queries per day or you can increase the daily quota with a Membership. For those who need to send more packets HackerTarget has Enterprise Plans.
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