Port 2728: SQDR — The Database Replication Nudge

What This Port Does

Port 2728 is registered with IANA for SQDR — the StarQuest Data Replicator, an enterprise tool that keeps databases in sync across IBM Db2, SQL Server, Oracle, Informix, and MySQL.¹

The port's job is narrow: UDP notifications. When new change data is captured at the source database and ready for replication, SQDR fires a UDP message to port 2728 telling subscribers to come get it. It's optional — subscriptions can be configured to poll instead — but with notifications enabled, replication latency drops to near-zero. The source commits a transaction; within moments, the target knows about it.²

This is change data capture (CDC) in action. Rather than copying entire tables on a schedule, SQDR watches the database transaction log for changes and ships only what's new. Port 2728 is the signal that a new batch is waiting.

The Registered Port Range

Port 2728 sits in the registered port range (1024–49151). This range is managed by IANA, and software vendors or protocol authors can apply to claim a port number for their application. Unlike the well-known ports (0–1023), registered ports don't require elevated privileges to open, and their services tend to be commercial middleware, enterprise tools, or niche protocols rather than foundational Internet infrastructure.

A port being "registered" doesn't mean it's universally used or even widely known. SQDR is a legitimate IANA registrant,¹ but it's enterprise database middleware — the kind of software that runs quietly in server rooms and rarely makes it into general port reference databases. Most sources that list port 2728 get it wrong, marking it unassigned.

Checking What's Listening

If you see traffic on port 2728 on a machine you manage, the tools are straightforward:

On Linux/macOS:

# Show what process is listening on port 2728
ss -tlnp | grep 2728
lsof -i :2728

On Windows:

netstat -ano | findstr :2728
# Then look up the PID in Task Manager, or:
Get-Process -Id (Get-NetTCPConnection -LocalPort 2728).OwningProcess

If you're running SQDR Plus and see this port active, it's the notification service doing its job. If you're not running any database replication software, it's worth investigating — the registered port range is also territory where malware has been known to squat on obscure, low-profile ports.

Why Unassigned (and Obscure) Ports Matter

The IANA registry exists so that port numbers mean something. When a vendor registers a port, it signals intent: this number belongs to this application, and network administrators can make informed decisions about whether to allow it.

But the registry is only as useful as its coverage. Thousands of registered ports belong to products that most administrators have never heard of. SQDR serves a real purpose — near-real-time database replication is critical infrastructure in many enterprises — but it's invisible to the wider Internet. The result is a port that's technically claimed but effectively unknown, sitting quietly in the registry until someone's firewall team needs to know whether to allow UDP 2728.

Most ports in the registered range are like this. Known to the teams that use them. Invisible to everyone else.