Port 556RFS Server
Remote File Sharing (RFS) is a protocol designed to provide transparent access to files and directories across a network. Operating over TCP port 556, RFS enables users and applications to interact with remote resources as if they reside locally, making distributed file management more efficient. Although largely obsolete now, RFS was historically significant in Unix environments for enabling seamless file sharing between systems..
- transport
- tcp
- in transit
- cleartext
- assignment
- official
- risk
- 4/10
- lookups
- 8,955
single transport
payload readable on path
registered with iana
caution
rank 551 of 993 · top 55%
Technical Details
what runs on :556Remote File Sharing (RFS) is a distributed file system protocol that facilitates sharing directories and files between UNIX systems over a network. Originating from AT&T UNIX System V, RFS was designed in the 1980s as a solution to allow seamless remote resource access, integrating deeply into the host's file system namespace.
Using port 556 over TCP, the rfs_server process listens for and manages RFS requests, handling file directory sharing, mounting, and permission management. Unlike more modern equivalents such as NFS or SMB, RFS aimed for tight kernel integration for transparent namespace management but suffered from lack of scalability and protocol extensibility.
Today, port 556 and RFS are rarely used, replaced by more robust networked file systems. However, understanding legacy protocols like RFS can still be important for maintaining compatibility in legacy environments or performing security reviews on older network infrastructure.
Security Information
exposure of :556risk score
4/ 10caution
worth attention. how exposed you are depends on configuration — don't leave it reachable from the internet without a reason.
file transfer averages 4.1 across 114 ports — this one sits 0.1 below.
in transit
cleartext
credentials and payloads are readable by anyone on path
assignment
official
registered with iana for this service — scanners fingerprint it by number
reachable over
tcp
every listening transport is another surface to filter at the edge
security overview
Common vulnerabilities associated with RFS implementations include:
- Lack of strong authentication or encryption, making transmitted data susceptible to interception or unauthorized access.
- Weak access controls that could allow unauthorized resource mounts or directory listings.
- Susceptibility to man-in-the-middle attacks, given its cleartext communication.
Mitigation strategies include:
- Segmentation of networks running RFS systems, restricting access via firewalls.
- Disabling unused or legacy services like RFS where possible.
- Replacing RFS with more secure, maintained protocols such as NFSv4 with Kerberos.
- Employing logging and intrusion detection systems to monitor for anomalous network activity on port 556.
Related Ports
the 8 most looked-up other ports in file transfer — 114 ports carry that label.
| port | service | risk | |||
|---|---|---|---|---|---|
| :9080 | Groove RPC | TCPUDP | Web Services | caution | 70.8k |
| :17500 | Dropbox LAN Sync | TCPUDP | File Transfer | caution | 43.7k |
| :548 | Apple Filing Protocol | TCP | File Transfer | caution | 36.8k |
| :7000 | Vuze HTTPS Tracker | TCPtls | Security | caution | 28.9k |
| :1337 | PowerFolder P2P | TCP | Security | caution | 27.1k |
| :9001 | SharePoint Authoring | Web Services | caution | 26.3k | |
| :8080 | FilePhile Relay | UDP | File Transfer | caution | 25.6k |
| :1337 | WASTE Encrypted Sharing | TCP | Security | caution | 22.9k |
risk mix of the 8 listed
- caution100%
1 of 8 encrypted