Some network and security administrators view port blocking as a critical tool for securing systems and information, and see it as part of the ISP’s mission to manage the security risk to its users from theft and destruction of personal information, business records, and other critical electronic forms of information.

One of the original and enduring motivations for blocking ports is to prevent network attacks and abuse associated with particular application protocols. The practical reality is that blocking of Internet port numbers, either in the short or long term, is a technique that has been used by both wireline and wireless network providers for various reasons for over a decade. Additionally, Internet standards assume all hosts on the global Internet can connect directly to each other, on any specified port number.

The Internet was built around the premise of an open and shared environment.

Port blocks can be deployed in a range of network locations, from where the ISP connects with other networks to datacenters and customer locations. The practice can potentially prevent the use of particular applications altogether by blocking the ports those applications use. Port blocking thus affects the traffic associated with a particular combination of port number and transport protocol on that ISP, regardless of source or destination IP address. The term “port blocking” refers to the practice of an Internet Service Provider (ISP) identifying Internet traffic by the combination of port number and transport protocol, and blocking it entirely. * Suggested Citation: Broadband Internet Technical Advisory Group (BITAG), Port Blocking (2013),

Port blocker