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.
The example below shows ports that are listed as
closed responded to the scan with a
TCP RST. This indicates 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
IPv6 Port Scan
It is very important when port scanning targets to test both IPv4 and IPv6 addresses. A system administrator needs only to make a small mistake that can have big consequences. A well configured firewall may protect a system from connections on the IPv4 interface but without a matching IPv6 firewall the host may be vulnerable.
:~$ dig +short -t aaaa scanme.nmap.org 2600:3c01::f03c:91ff:fe18:bb2f Starting Nmap 7.70 ( https://nmap.org ) at 2021-03-12 00:48 UTC Nmap scan report for scanme.nmap.org (2600:3c01::f03c:91ff:fe18:bb2f) Host is up (0.070s latency). PORT STATE SERVICE 21/tcp closed ftp 22/tcp open ssh 23/tcp closed telnet 80/tcp open http 110/tcp closed pop3 143/tcp closed imap 443/tcp closed https 3389/tcp closed ms-wbt-server Nmap done: 1 IP address (1 host up) scanned in 0.32 seconds
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.
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