What ports are blocked by Comcast High Speed Internet?
Comcast is committed to providing a secure internet experience for all of our customers. For the protection of the network and our customers, certain ports are blocked by Comcast High Speed Internet. The blocking of these ports protects against common viruses and worms, malicious intruders, and other security exploits.
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Port
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Transport
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Protocol
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Inbound/ Outbound
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Reason for block
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Blocked by Default?
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25
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TCP
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SMTP
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Both
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Port 25 is an unsecured port on a computer that those sending spam can take control of to send spam - often without the user ever knowing his/her computer has been compromised. When spam from a compromised computer is detected, Comcast’s anti-spam systems automatically apply a sending block and send an email notification to the affected subscriber’s comcast.net email address. This block does not interrupt mail service for Webmail (e.g. Comcast, Yahoo, Gmail, or Hotmail); however, this block does prevent email programs or clients (e.g. Outlook Express) from sending email. Client e-mail programs will still receive email. The instructions at our mail client help page explain how to configure common email client programs to use Port 587, which includes authentication, instead of Port 25.
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No
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68
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UDP
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BOOTP, DHCP
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Inbound
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UDP Port 68 is used by customer computers to obtain dynamic Internet Protocol (IP) address information from the Comcast’s dynamic host configuration protocol (DHCP) server that assigns IP addresses to customer computers. DHCP ports can be used for malicious attacks such as, for example, obtaining access to a customer’s home computer or home network and its devices
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Yes
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135-139
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TCP/UDP
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NetBios
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Both
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NetBios services allow file sharing over networks. When improperly configured, they can expose critical system files or give full file system access (run, delete, copy) to any malicious intruder connected to the network.
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Yes
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445
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TCP
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MS-DS, SMB
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Both
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Security risks; vulnerable to attacks/exploits/worms such as the Sasser and Nimda worms..
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Yes
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520
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TCP/UDP
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RIP
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Both
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Vulnerable to malicious route updates which provides several attack possibilities.
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Yes
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1080
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TCP
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SOCKS
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Inbound
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Multiple vulnerabilities (Viruses, Worms, DoS attacks).
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Yes
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