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The numbers in this headline cannot be read as port numbers for rsync, NFS or SMB. In the IANA port registry, TCP 106 is assigned to 3COM-TSMUX and TCP/UDP 110 is assigned to POP3. Neither is an rsync or NFS port. The figure 1771 is not tied to any file transfer protocol in the sources this article relies on, and we have not found a published dataset that explains where the three numbers came from. What the headline does point to is a real gap: file transfer services are often missing from asset inventories, because they run on ports that are not the ones people expect, use helper services, or can be started by a user rather than an administrator.
What the headline numbers do and do not establish
A reader who sees “106 rsync” or “110 NFS” will reasonably assume a port-to-protocol mapping. That mapping is wrong for these examples. The numbers also read like result counts, but no owner, date, dataset or counting method is attached to them, so they cannot be cited as statistics about deployed services or exposed hosts. Treat the headline as a prompt to check, not as a finding.
Three distinctions make the rest of this article easier to follow:
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minute- Protocol is the set of rules two programs use to exchange files. rsync and NFS are protocols, and an SMB file share is served under the SMB protocol family.
- Application is the software that implements a protocol, such as the rsync program, an NFS server in the Linux kernel, or a Samba server.
- Port assignment is a number a transport layer uses to direct traffic to a service. IANA’s registry records which service names and port numbers are assigned or in use, but a listed number does not prove that the listed service is running on a given host.
What the port registry says
The table below uses the IANA Service Name and Transport Protocol Port Number Registry (last updated 2026-09-30), the rsync(1) manual page for the current rsync 3.5.1 release, and the Linux nfs(5) manual page. Where a source does not state a value, the cell says so.
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| Number | What the cited source says | Relation to the named protocol |
|---|---|---|
| TCP 106 | IANA lists 3COM-TSMUX and notes known unauthorized use of this port. | Not an rsync port. Not an NFS or SMB port. |
| TCP and UDP 110 | IANA lists POP3 (mail retrieval). | Not an NFS port. Not an rsync port. |
| TCP 873 | The rsync manual states that connections to an rsync daemon typically use this port. | The usual daemon port for rsync. Remote-shell transfers do not use it. |
| TCP 2049 | The Linux nfs(5) manual states that NFS often uses this standard port. | The usual NFS port, but not guaranteed on every server. |
| TCP and UDP 111 | The nfs(5) manual describes rpcbind on this well-known port, which helps clients find RPC services. | Endpoint discovery for NFS and other RPC services, not the file data path itself. |
| 1771 | Not established by the sources cited here. | Not stated. Do not assign it to SMB or any other protocol without a source. |
| SMB | Not covered by the sources cited here. | This article makes no claim about SMB port numbers, protocol versions or security settings. |
The practical lesson is that a number in a log, a firewall rule or a scan result is a claim that needs confirmation. A registered number says what a service is supposed to be. It does not say what is listening.
rsync: a daemon, a remote shell, or both
rsync is usually described as a file-copy tool, but it has two transport paths that inventories often conflate:
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- Remote shell. rsync starts over SSH or another remote shell. No rsync daemon is involved, and the transfer appears as an SSH session. A scan of TCP 873 will not show it.
- rsync daemon. A server runs rsync in daemon mode and clients connect directly. The rsync manual says these connections typically use TCP 873. The daemon’s modules, which are the named directories it shares, are defined in its configuration file.
To check the daemon path, a administrator can ask a host to list its modules. The command rsync rsync://host.example.net:873/ is the documented way to request a module listing from a daemon. A host that answers this way has a daemon on that port. A host that does not answer has no daemon there, which says nothing about whether rsync runs over SSH on the same machine.
NFS: a standard port plus helper services
NFS is a useful example of why one-port checklists miss things. The nfs(5) manual notes that NFS often uses the standard port 2049, but auxiliary services can use other ports. The manual gives the NLM lock service as an example, which can select any unused port number. Clients locate RPC services through rpcbind on port 111. Firewall rules that allow only 2049 may therefore break some NFS behavior, and a scan that checks only 2049 can miss the rest of the NFS footprint.
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On a Linux NFS server, the usual checks are:
- Run
rpcinfo -pon the server, orrpcinfo -p server.example.netfrom a client, to list the RPC programs and ports registered with rpcbind, including NFS and its helpers. - Run
showmount -e server.example.netto list exported directories. This depends on the server and client supporting the mount protocol queries involved, and an empty or refused answer does not prove NFS is absent. - Run
ss -tlnpon the server to see which processes are listening on which TCP ports. Compare the result with the rpcinfo output rather than assuming 2049 is the only port in use.
SMB: what this article does not claim
SMB is part of the headline, but the sources behind this article do not establish its ports, protocol versions or security settings, and we do not state them here. If your inventory depends on SMB details, take them from the documentation for the specific server you run, such as the Samba or Windows server documentation for your version, and record the version you confirmed.
Why file transfer layers get missed
File transfer services are missed for reasons that have little to do with how well a team tracks applications. They can be started by a user or a script, they may be bundled with a backup or sync job, they may use a remote shell so no separate listener appears, and they often answer on helper ports that were never added to the asset list. Inventory work also tends to start from the perimeter, which catches externally reachable services and misses internal segments, containers and managed storage.
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Different inventory methods answer different questions. The table below compares them using criteria, not measured results. No test was run to rank them.
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| Approach | What it can show | Main limitation |
|---|---|---|
| Static port list | Which default or assigned ports an administrator expects to see. | A registered number does not confirm a running service. It misses remote-shell transfers and helper ports. |
| Active observation (listening sockets and scans) | Which ports are open right now, and which process owns them when run on the host. | A scan from outside the network sees only what the firewall allows. Scan results have a timestamp and go stale. |
| Endpoint and service configuration review | Exports, modules, shares and RPC registrations defined on each system. | Requires access to each system and its configuration, and can drift from what is running. |
| Confirmed process or negotiated protocol | The actual service and protocol a host is serving. | Needs host-level access or a protocol handshake, and is the most work per host. |
A practical way to build the file transfer inventory
Use the following sequence to create a record that can be trusted. Each entry should carry a scan or check timestamp, the system that produced it, the owner, and the date the service was last confirmed.
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- List every host that can run file transfer software: servers, NAS devices, backup hosts, build systems and container hosts.
- On each host, check listening sockets with
ss -tlnp(Linux) and record the process names, not just the port numbers. - For rsync, record whether a daemon answers a module listing on its configured port and whether rsync runs over SSH from cron jobs or scripts.
- For NFS, record
rpcinfo -poutput, the exports from the server configuration, and any firewall rules that affect helper ports. - For SMB, record the server software and version from its own documentation and the shares it publishes.
- Compare each record against the port registry only to explain a number. Do not treat a registry match as proof that the service exists.
- Repeat the checks on a schedule, and remove or re-own any entry whose service cannot be confirmed.
A figure in a headline is a poor substitute for this kind of record. When a number like 106, 110 or 1771 appears in a report, the first question should be where it came from, and the second should be whether the host behind it was actually checked.
Sources used
- IANA, Service Name and Transport Protocol Port Number Registry, last updated 2026-09-30.
- rsync project, rsync(1) manual page, current for rsync 3.5.1.
- rsync project, release announcement for rsync 3.5.1, 2026-09-21.
- Linux man-pages project, nfs(5) manual page.
The 2026-09-21 rsync release notes fix regressions reported after rsync 3.5.0 and add protocol 33 for logical-block statistics. They do not change the port behavior described above.
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