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Support XFINITY Internet List of Blocked Ports

Introduction

Find out which ports are blocked by XFINITY and Comcast services, and why.

Find the Reasons for Blocking Listed Below

Port Transport Protocol Inbound/ Outbound Reason for block
0 TCP N/A Both Port 0 is a reserved port, which means it should not be used by applications. Network abuse has prompted the need to block this port.
25 TCP SMTP Both Port 25 is unsecured, and Botnet spammers can use it to send spam. This does not affect XFINITY Connect usage. We recommend viewing Using Email Client Programs with Comcast Email to use port 587.
68 UDP BOOTP, DHCP Inbound UDP Port 68, which is used to obtain dynamic Internet Protocol (IP) address information from our dynamic host configuration protocol (DHCP) server, is vulnerable to malicious hacks.
135-139 TCP/UDP NetBios Both NetBios services allow file sharing over networks. When improperly configured, ports 135-139 can expose critical system files or give full file system access (run, delete, copy) to any malicious intruder connected to the network.
161-162 TCP/UDP SNMP Both SNMP is vulnerable to reflected amplification distributed denial of service (DDoS) attacks.
445 TCP MS-DS, SMB Both Port 445 is vulnerable to attacks, exploits and malware such as the Sasser and Nimda worms.
520 TCP/UDP RIP Both Port 520 is vulnerable to malicious route updates, which provides several attack possibilities.
1080 TCP SOCKS Inbound Port 1080 is vulnerable to, among others, viruses, worms and DoS attacks.

Find this article at:

http://customer.comcast.com/help-and-support/internet/list-of-blocked-ports/