To ensure the security, stability, and reputation of our network, Chicagoservers LLC blocks a small number of network ports by default. Some ports are blocked permanently to prevent DDoS amplification attacks, while others can be unblocked upon request.
Permanently Blocked Ports (DDoS Prevention)
The following ports are blocked permanently across our network. These ports correspond to protocols that are commonly exploited by malicious actors for Distributed Denial of Service (DDoS) amplification attacks. These blocks are strictly enforced and cannot be removed.
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TCP/UDP Port 17 (QOTD) - Legacy Quote of the Day protocol.
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TCP/UDP Port 19 (Chargen) - Legacy Character Generator protocol.
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TCP/UDP Port 1900 (SSDP) - Used for UPnP discovery; frequently abused for reflection attacks.
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UDP Port 11211 (Memcached) - When exposed to the public internet, this caching service is highly vulnerable to massive amplification attacks.
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UDP Port 53413 - Associated with known router backdoors and amplification vulnerabilities.
Ports Blocked for Abuse Prevention (Unblockable)
To prevent network abuse such as outbound spam, the following port is blocked by default but can be unblocked by submitting a request to our team.
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TCP/UDP Port 25 (SMTP - Email Routing) Blocked to protect our IP space from blacklisting due to unauthorized spam or compromised servers.
How to Request a Port 25 Unblock:
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open the product in the control panel.
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Open the server details, under the "SMTP/PORT 25 on the left side. Click to request port 25 open.
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If you are new customer(less then 30 days) this will open a ticket. Please let us know why port 25 needs to be opened on your server. It will be reviewed before the port is opened.
If you are an existing customer(more then 30 days) the process is automated. Just provide the reason for port 25 being open on your server then the port is automatically opened on your server.
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If spam is detected coming from a server port 25 is automatically blocked.
