451
Summary
- // typical exposure
- Internal-only — sfs-smp-net is Cray's legacy internal cluster/semaphore-coordination service for Cray supercomputer nodes - a vendor-specific management-plane protocol that was never meant to be reachable from the public internet.
- // analyst note
- an open 451/tcp is statistically rare (nmap-services frequency ≈0.0013%) and traces to an obsolete Cray-specific service — treat it as worth investigating rather than routine traffic, and don't confuse the port number with the unrelated HTTP 451 status code.
- // if you see it open
- No CVE or named malware family is documented specifically for 451/tcp as of an August 2026 search. General web searches for the port number mostly surface unrelated results for the HTTP 451 'Unavailable For Legal Reasons' status code, a distinct concept from this transport-layer port. As an obsolete, single-vendor internal cluster-coordination service, it has no legitimate reason to be exposed to the public internet, and its rarity makes an unexpected open 451/tcp worth investigating.
About port 451/tcp.
Port 451/tcp carries sfs-smp-net, IANA's registered name for Cray Research's Network Semaphore server; it is a legacy, vendor-specific cluster-coordination service that has no legitimate reason to be reachable from the public internet.
IANA registers 451 for both TCP and UDP under the service name sfs-smp-net, described only as "Cray Network Semaphore server." The registry row carries no assignee, no reference RFC, and no registration date. That gap is typical of an early vendor-specific system-port assignment, one that predates IANA's later contact-and-citation requirements.
The name suggests an internal service for synchronizing processes across a Cray supercomputer cluster, but that reading is inferred from the service name and Cray's history — IANA's registry gives no protocol detail, and no independent specification was found to confirm it. The adjacent port 452/tcp+udp (sfs-config, "Cray SFS config server") is a companion service in the same IANA-registered family. No RFC documents a wire protocol, and no current, actively maintained software was found using 451/tcp — it reads as an obsolete, single-vendor system assignment rather than a protocol in active deployment.
No CVE or malware family is documented against 451/tcp specifically as of an August 2026 search, and general web searches for the port number mostly surface unrelated results for the HTTP 451 status code ("Unavailable For Legal Reasons") — a distinct concept from this transport-layer port assignment and not evidence of any usage here.
- IANA assignment
sfs-smp-net— "Cray Network Semaphore server"; reference (blank — no RFC cited in IANA registry); assignee Unknown; dual-registered 451/tcp + 451/udp [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry sfs-smp-net 451/tcp; sfs-smp-net 451/udp- Range class
- well-known (0–1023) [Confirmed]
- Prevalence
- nmap-services open-frequency 451/tcp ≈ 0.000013 (~0.0013%, essentially never observed open); 451/udp ≈ 0.000774 [Confirmed] — this site's own tooling (built from nmap-services)
- Related ports
- 452/tcp + 452/udp (
sfs-config, "Cray SFS config server") — companion service in the same Cray SFS family, assigned to Walter Poxon [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry sfs-config 452/tcp; sfs-config 452/udp
Primary use
legacy Cray Research proprietary Network Semaphore server (registry description only); plausibly an internal process/semaphore-coordination service between nodes in a Cray supercomputer cluster, but that reading is inferred from the service name and Cray's history — no independent protocol specification confirms it; a vendor-specific IANA system-port registration, not a general-purpose internet protocol [Unknown for protocol detail] — https://www.grc.com/port_451.htm, https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=451
Other/unofficial uses
none confirmed; no current, actively maintained software was found using this port as of an August 2026 search
Security implications
no CVE or named malware family documented for 451/tcp as of an August 2026 search; port 451 does not appear on vulners.com's TROJAN_HORSES.NASL trojan-port listing; general web results for the port number are mostly noise from the unrelated HTTP 451 "Unavailable For Legal Reasons" status code
Typically seen on
legacy Cray supercomputer cluster deployments, largely obsolete today; otherwise rare enough to be anomalous
- Analyst note
- an open 451/tcp is statistically rare (nmap-services frequency ≈0.0013%) and traces to an obsolete Cray-specific service — treat it as worth investigating rather than routine traffic, and don't confuse the port number with the unrelated HTTP 451 status code.
About port 451/udp.
Port 451/udp carries sfs-smp-net, IANA's registration for the "Cray Network Semaphore server"; it should stay off the public internet, since this is a legacy supercomputer coordination protocol with no evidence of any active modern deployment.
IANA registers 451 as sfs-smp-net on both TCP and UDP, with a blank Reference column (no RFC is cited) and no assignee or contact listed in the registry. The description gives only the four-word phrase "Cray Network Semaphore server" — no protocol specification is published anywhere in the IANA record.
Cray Research built vector and parallel supercomputers from the 1970s through the 1990s (later Cray Inc., now part of Hewlett Packard Enterprise). The name suggests an internal service for synchronizing processes across a Cray system, but that reading is inferred from the service name and Cray's history — IANA's registry gives no protocol detail, and no independent specification was found to confirm it.
An August 2026 search for software, forum posts, or vendor documentation naming a live user of sfs-smp-net traffic turned up nothing beyond mirrors of the same bare IANA registry entry; no CVE, malware list, or scanning-telemetry writeup ties port 451 (either transport) to any documented incident.
- IANA assignment
sfs-smp-net— "Cray Network Semaphore server"; dual-registered 451/tcp + 451/udp; Assignee, Contact, Registration Date, and Reference fields all blank [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry sfs-smp-net 451/udp- Range class
- well-known (0–1023)
- Prevalence
- nmap-services open-frequency 451/udp = 0.000774 (~0.077%); 451/tcp = 0.000013 (~0.0013%) [Confirmed] — this site's own tooling
- Related ports
- 451/tcp (dual IANA registration of the same service name) [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry sfs-smp-net 451/tcp
Primary use
Cray Network Semaphore server (registry description only); plausibly an internal process-coordination service on Cray Research supercomputer systems, but no independent protocol specification confirms this
Other/unofficial uses
none identified
Security implications
no CVE, malware association, or scanning-telemetry writeup found for port 451 (either transport) as of an August 2026 search; absent from standard trojan-port reference tables
Typically seen on
no confirmed modern deployments; historically, Cray Research supercomputer systems [Unknown]
- Analyst note
- sfs-smp-net has no known legitimate modern purpose; treat an open 451/udp as an anomaly worth investigating rather than assume it is benign legacy traffic.
Service assignments.
| Name | Protocol | Description | Open frequency |
|---|---|---|---|
| sfs-smp-net | UDP | Cray Network Semaphore server | 0.08% |
| sfs-smp-net | TCP | Cray Network Semaphore server | 0.00% |
Service assignments from the IANA Service Name and Transport Protocol Port Number Registry, with open-frequency data from nmap-services.