Port 1624: UDP Service Resolver — The officially assigned port nobody talks about

What Lives Here

Port 1624 is officially registered with IANA for udp-sr-port (UDP Service Resolver) on both TCP and UDP protocols.¹ That's about where the story ends for most people.

If you're expecting detailed protocol specifications, widespread adoption, or even a Wikipedia article—you won't find them. Port 1624 exists in that peculiar space of registered ports that are technically assigned but rarely seen in the wild.

The Registered Ports Range

Port 1624 sits in the registered ports range (1024-49151). This middle territory of the port space is where protocols can claim a number by registering with IANA, but don't need the same level of standardization or adoption as well-known ports (0-1023).²

Think of it like reserved parking. The space is claimed. The name is on record. Whether anyone actually parks there is another question entirely.

What We Know (And Don't Know)

What we know:

• Official service name: udp-sr-port
• Likely purpose: UDP Service Resolver
• Protocol support: Both TCP and UDP
• Registration status: Officially assigned by IANA

What we don't know:

• Which applications actually use it
• What "service resolution" it performs
• Whether it's still actively deployed anywhere
• If there's an RFC or technical specification

This is the reality of the registered ports range. Thousands of assignments exist. Many are documented only by their registry entry and nothing more.

Why This Matters

Even obscure registered ports serve a purpose—they prevent collisions. When someone registered port 1624 for UDP Service Resolver, they ensured no other protocol would claim that number and create conflicts.

It's the difference between assigned and occupied. Port 1624 is assigned. Whether it's occupied on your network is something you can check.

How to Check What's Using Port 1624

On Linux or macOS:

# See what's listening on port 1624
sudo lsof -i :1624

# Or using netstat
sudo netstat -tulpn | grep 1624

On Windows:

# Check port 1624 usage
netstat -ano | findstr :1624

If nothing returns, the port is unused on your system. That's probably the case for port 1624 on most networks.

The Honest Truth

Port 1624 represents a common pattern in networking: official registration doesn't guarantee adoption. Someone, somewhere, at some point needed a port number for UDP service resolution. They registered it properly. The protocol may or may not have succeeded.

The port number remains, officially claimed, quietly waiting in the registry alongside thousands of other registered ports that serve more as placeholders than active infrastructure.

This is what most of the port range actually looks like.