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Internet Ports Blocked or Restricted by Cox


Reasons For Filtering Ports

  • Protecting customers - Certain ports are filtered to protect our customers. They can protect against certain common worms and from dangerous services on our customers' computers that could allow intruders access.
  • Protecting upstream bandwidth - Upstream bandwidth to a cable plant is limited. If customers overuse their upstream bandwidth by running high-traffic servers, or becoming infected with a worm or virus, it can affect the service of other customers in their area.
  • Protecting the rest of the Internet - Some filters prevent against attacks on other computers by way of the Internet. In addition to being in our best interests for protecting our bandwidth, Cox considers preventing the abuse of our network as its responsibility.
Port Transport Protocol Direction Reason for Filtering
25 TCP SMTP Both
Note: SMTP is only permitted outbound to Cox-provided SMTP servers.
SMTP Relays
80 TCP HTTP Inbound Web servers, worms
135 UDP NetBios Both Net Send Spam / Pop-ups, Worms
136-139 UDP, TCP NetBios Both Worms, Network Neighborhood
143 TCP IMAP Inbound Without Transport Layer Security (TLS) enabled, customers are more susceptible to having their passwords compromised
445 TCP MS-DS/ NetBios Both Worms, Network Neighborhood
1433 TCP MS-SQL Inbound Worms, Trojans
1434 UDP MS-SQL Inbound Worms, SQLslammer
1900 UDP MS-DS / NetBios Both Worms, Network Neighborhood

Explanations of Filtered Ports

Port Explanation
25 / TCP - SMTP Mail servers use Simple Mail Transport Protocol (SMTP) to exchange email. We block this to protect upstream bandwidth and prevent customers from running open relays could potentially be used by others to send spam via our network.
80 / TCP - HTTP Web browsers use Hypertext Transport Protocol (HTTP) to communicate with web servers. In addition to protecting bandwidth by preventing customers from running high-traffic web servers, we can stop many destructive worms that spread through security holes in web server software.
135, 137 / UDP, 135, 139 / TCP, 445 MS-DC – NetBIOS NetBIOS, also known as Server Message Block, LanManager, and Common Internet File System, are networked file sharing protocols. The Microsoft Windows Network Neighborhood runs over NetBIOS. Cox filters these ports to protect customers from exposing files on their computers, and to block worms which spread through open file shares. The latest addition to this series, a consolidated service port, such as TCP445, has also opened new similar security risks in Win2K and WinXP.
143 - IMAP The Internet Message Access Protocal (IMAP) is a mail protocol used for receiving email. We block this port because without TLS enabled, it is not encrypted and leaves customers vulnerable to having their user information and passwords compromised.
1433 / TCP, 1434 / UDP –
Microsoft SQL Server is a database application with a long history of security exploits, and is noted for the propagation of the SQLslammer worm. These ports are filtered to prevent exploitation and propagation of such MS-SQL exploits.
1900 / UDP - UPnP Discovery / SSDP is a service that runs by default on WinXP. It creates an immediately exploitable security vulnerability for any network. Filtering this port proactively prevents XP systems from being remotely compromised by malicious worms or intruders.

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