What Runs Here
Port 400 carries Oracle Secure Backup (OSB) traffic on both TCP and UDP. This is the primary communication port for Oracle's enterprise backup system - the daemons that coordinate backups of Oracle databases across tape libraries, disk storage, and cloud targets.1
When an Oracle backup job starts, when a tape library robot receives a mount command, when backup clients authenticate to the administrative server - that's port 400 working.
How It Works
Oracle Secure Backup uses a client-server architecture built around several specialized daemons that communicate over port 400:2
The Service Daemon (observiced) runs on the administrative server and coordinates everything. It processes job requests from the scheduler, manages configuration data, and acts as the Certificate Authority for the entire backup domain. When a new host joins the domain, it sends a certificate signing request to port 400 and receives a signed X.509 certificate back.3
The Scheduler Daemon (obscheduled) sends backup job requests to observiced over port 400. When it's 2am and your scheduled database backup kicks off, this daemon is making that happen.
The NDMP Daemon (obndmpd) implements the Network Data Management Protocol, which defines how file servers get backed up over a network. It handles data movement between media servers and clients, passing control connections to subprocesses while staying free to respond to control messages.4
The Robot Daemon (obrobotd) controls tape libraries. Mount tape 47 in drive 3? That command flows through port 400 to obrobotd, which manipulates the physical tapes.
All of this communication is encrypted using SSL/TLS. Oracle Secure Backup uses X.509 certificates to identify and authenticate every host in the administrative domain. The security happens at the SSL layer, wrapped around the protocol running on port 400.5
The Architecture
Oracle Secure Backup divides the world into administrative domains. Each domain has one administrative server running the full daemon stack on port 400. Media servers (the machines connected to tape libraries or disk arrays) and backup clients all communicate with the administrative server over this port.
When a backup job runs:
- obscheduled sends a job request to observiced (port 400)
- observiced coordinates with obrobotd to mount the required volumes (port 400)
- The backup engine (obtar) moves data while daemons exchange control messages (port 400)
- Status updates flow back to the administrative server (port 400)
Port 400 is the nervous system of this entire operation.
The History You Can Still See
The IANA registry notes that port 400 was "Formerly Workstation Solutions."6 The details are lost - there's no public record of what Workstation Solutions built or when Oracle acquired the port assignment. But you can see the transition in the registry metadata. Port reassignments in the well-known range (0-1023) are uncommon. When they happen, it's usually because a service died or a company got acquired.
Oracle took over port 400 and assigned it to their backup system. The port carries that history in its registration notes.
Security Considerations
Port 400 should never be exposed to the public Internet. This is internal infrastructure - backup servers talking to backup clients within a trusted network.
Firewall it. If you run Oracle Secure Backup, configure your firewall to allow port 400 only between known backup infrastructure hosts. Block it at the perimeter.7
Monitor it. Unusual traffic on port 400 might indicate unauthorized backup operations or an attacker trying to access backup data. Backups contain everything. If someone compromises your backup system, they have your entire database.
SSL is mandatory. Oracle Secure Backup enforces SSL for all daemon communication. Don't try to disable it. The certificate-based authentication is what prevents rogue hosts from joining your backup domain.
Related Ports
- Port 10000/TCP - Oracle Secure Backup uses this for NDMP communication with NAS hosts by default8
- Port 1521/TCP - Oracle Database listener, the database that OSB backs up
- Port 443/TCP - HTTPS, used by Oracle Secure Backup's web administration interface (obhttpd)
Checking Port 400
On Linux or macOS:
On Windows:
If Oracle Secure Backup is installed and running, you'll see observiced or other OSB daemons listening on port 400.
Frequently Asked Questions
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