Internet Ports Blocked or Restricted by OzarksGo

Reasons For Filtering Ports

OzarksGo blocks certain ports on residential service to protect our customers, the bandwidth of our network and the security of other internet users.

Blocking certain ports helps protect our customers against common worms and blocks some services that intruders could use to gain access to customers’ computers. Preventing worms also protects our bandwidth — if subscribers devices get infected with a worm or virus, it can affect the service of other subscribers in their area.

Some of the filters prevent attacks against other computers. OzarksGo considers preventing the abuse of our network as our responsibility.


25 TCP SMTP Both 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, subscribers 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


25 / TCP - SMTP

Simple Mail Transport Protocol (SMTP) is used by mail servers to exchange email. This port is blocked protect bandwidth and prevent subscribers from running open relays that could potentially be used by others to send spam via our network.

80 / TCP - HTTP

Web browsers communicate with web servers using HyperText Transfer Protocol (HTPP). Blocking this port protects bandwidth by preventing subscribers from running high-traffic web servers and stops destructive worms that spread through security holes in web server software.

110 - POP and 143 - IMAP

The Post Office Protocol (POP) and Internet Message Access Protocol are used by email clients to retrieve email. Without the property security protocols, traffic over these port is not encrypted, leaving subscribers vulnerable to having passwords and other information compromised.

135, 137 / UDP, 135, 139 / TCP, 445 MS-DC – NetBIOS

NetBIOS, Server Message Block, LanManager, and Common Internet File System, are networked file-sharing protocols. Filtering these ports prevents subscribers from accidentally exposing their files and blocks worms that 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.

1900 / UDP - UPnP

Discovery / SSDP is a service that runs by default on Windows XP, creating an immediately exploitable security vulnerability for any network. Filtering this port prevents Windows XP systems from being compromised by malicious worms or intruders.