Blocked Internal Port List

Find out which ports are automatically blocked on our network and why.

Ports on the internet are like virtual passageways where data can travel. All information on the internet passes through ports to get to and from computers and servers. When a certain port is known to cause vulnerability to the security and privacy of your information, MCF blocks it to protect you.

Port
Transport
Protocol
Direction
Reasons For Blocking
IP Version
1080
UDP
SSDP
Both
Port 1900 is vulnerable to DoS attacks.
IPv4/IPv6
1900
TCP
SOCKS
Downstream
Port 1080 is vulnerable to, among others, viruses, worms and DoS attacks.
IPv4/IPv6
547
UDP
DHCPv6
Downstream
UDP Port 547, which is used to obtain dynamic Internet Protocol (IP) address information from our dynamic host configuration protocol (DHCP) server, is vulnerable to malicious hacks.
IPv6
520
UDP
RIP
Both
Port 520 is vulnerable to malicious route updates, which provides several attack possibilities.
IPv4
445
TCP
MS-DS, SMB
Both
Port 445 is vulnerable to attacks, exploits and malware such as the Sasser and Nimda worms.
IPv4/IPv6
161
UDP
SNMP
Both
SNMP is vulnerable to reflected amplification distributed denial of service (DDoS) attacks.
IPv4/IPv6
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.
IPv4/IPv6
67
UDP
BOOTP, DHCP
Downstream
UDP Port 67, which is used to obtain dynamic Internet Protocol (IP) address information from our dynamic host configuration protocol (DHCP) server, is vulnerable to malicious hacks.
IPv4
25
TCP
SMTP
Both
Port 25 is unsecured, and Botnet spammers can use it to send spam. This does not affect MCF Connect usage. We recommend learning more about configuring your email settings to Comcast email to use port 587.
IPv4/IPv6
0
TCP
N/A
Downstream
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.
IPv4/IPv6