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Internet Ports Blocked or Restricted by Cox

Last Updated: Tue, 17 Mar 2015 > Related Articles

232 rated this


Learn why certain ports are blocked or restricted by Cox High Speed Internet.


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.
PortTransportProtocolDirectionReason for Filtering
Note: SMTP is only permitted outbound to Cox-provided SMTP servers.
SMTP Relays
80TCPHTTPInboundWeb servers, worms
135UDPNetBiosBothNet Send Spam / Pop-ups, Worms
136-139UDP, TCPNetBiosBothWorms, Network Neighborhood
445TCPMS-DS/ NetBiosBothWorms, Network Neighborhood
1433TCPMS-SQLInboundWorms, Trojans
1434UDPMS-SQLInboundWorms, SQLslammer
1900UDPMS-DS / NetBiosBothWorms, Network Neighborhood

Explanations Of Filtered Ports

25 / TCP - SMTPMail 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 - HTTPWeb 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 – NetBIOSNetBIOS, 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.
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 - UPnPDiscovery / 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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