Port 219 is officially assigned to uarps (Unisys ARPs), a proprietary protocol from Unisys Corporation. It lives in the well-known ports range (0-1023), which means it was assigned in the early days of the Internet when IANA was handing out low port numbers to protocols that seemed important at the time.
Most of those protocols are still running. Port 219 is not one of them.
What Is Unisys ARPs?
Unisys ARPs (the "u" distinguishes it from standard ARP—Address Resolution Protocol) is a proprietary networking protocol used by Unisys ClearPath MCP systems.1 It was part of Unisys's own networking stack, built for their mainframe computers.
Standard ARP operates at Layer 2 of the OSI model and doesn't use port numbers at all—it works below the transport layer. Unisys ARPs is different. It operates at the transport layer and uses port 219 for both TCP and UDP.2
This is a protocol from an era when computer manufacturers wrote their own networking rules. IBM had theirs. DEC had theirs. Unisys had theirs. The Internet standards eventually won, but the port assignments remain.
The Port Assignment
Port 219 is registered with IANA under the contact name Ashok Marwaha.3 The assignment covers both TCP and UDP protocols. It sits in the well-known ports range—the first 1024 ports that were reserved for system services and protocols deemed important enough to warrant permanent, privileged assignments.
Getting a well-known port number was once a significant achievement. It meant your protocol was recognized as infrastructure-level important. Port 219 was assigned when people believed proprietary mainframe protocols would be part of the Internet's permanent architecture.
They were wrong.
The IMAP3 Confusion
Some older references incorrectly associate port 219 with IMAP3 (Interactive Mail Access Protocol Version 3).4 This is a misunderstanding. IMAP3 was specified in RFC 1203 in 1991 and used port 220, not 219.5
IMAP3 itself is a dead protocol. It was never accepted by the marketplace and was reclassified as "Historic" by the IESG in 1993.6 The IMAP Working Group bypassed it entirely and continued development from IMAP2, eventually creating IMAP4—the protocol that actually runs the world's email today on port 143.
So if you see references to IMAP3 on port 219, they're conflating two separate pieces of abandoned Internet history.
Security Considerations
Port 219 has been flagged in security databases as having been used by malware in the past.7 This doesn't mean the port itself is dangerous—it means that trojans and viruses have exploited it for command and control traffic.
This is common with obscure, rarely-used ports. Attackers like them because they're less likely to be monitored. A connection on port 80 or 443 is normal. A connection on port 219 is unusual enough that it might slip past casual observation.
If you see traffic on port 219 and you're not running Unisys mainframe systems, investigate it.
Checking What's Listening
To see if anything is listening on port 219 on your system:
Linux/Mac:
Windows:
On modern systems, you'll almost certainly find nothing. This port belongs to a different era of computing.
Why This Port Matters
Port 219 doesn't matter because of what it carries—almost nothing uses it anymore. It matters because of what it represents.
The well-known ports range is a record of what people thought would be important. Some of those bets paid off: SSH on 22, HTTP on 80, HTTPS on 443. Others didn't. Port 219 is one of the ones that didn't.
Unisys still exists. ClearPath systems still run in some enterprises. But the proprietary networking protocols that required their own port assignments have been replaced by Internet standards. Port 219 is a tombstone in the registry—a reminder that the protocols that won weren't necessarily the ones that got there first.
The Internet is built on layers of abandoned ideas. Port 219 is one of them.
Related Ports
- Port 220: IMAP3, another dead protocol from the same era
- Port 143: IMAP4, the email protocol that actually survived
- Port 22: SSH, an example of a well-known port that became essential infrastructure
Frequently Asked Questions
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