246

Port 246 is registered with IANA (dual-registered on both tcp and udp, identical entries) as dsp3270, described as "Display Systems Protocol," with assignee and contact both listed as Weldon J. Showalter. The IANA registry leaves the reference (RFC) column, registration date, and modification date all blank for this entry, so none of those are invented here. Independent web research on the protocol itself (euclideanspace.com's protocol documentation) describes DSP3270 as a legacy protocol from roughly 1980-81, developed jointly by GTE Telenet, TransCanada Telephone System (TCTS), Tymnet, and Comtan, designed to let bisynchronous (BSC) IBM 3270 display terminals communicate over X.25 packet-switched networks. It works by establishing PAD-to-PAD sessions and runs as a layer-4-like protocol above X.25's level 3, rather than being OSI-Transport-compatible, with an explicit design goal of avoiding the need to carry BSC polling traffic across the network. This places dsp3270 squarely in the category of a niche, historical telecom/mainframe-terminal protocol tied to X.25 packet networks and IBM 3270 terminal emulation — technology that predates the modern Internet stack and has essentially no contemporary deployment footprint. No current scanning-prevalence data, honeypot reports, named malware family, or CVE tied specifically to port 246 was found in this pass; a generic port-lookup site carries a boilerplate "used by a Trojan or Virus in the past" disclaimer that appears on many ports and names no specific threat, so it is not treated as a substantive finding.

IANA assignment

dsp3270 — "Display Systems Protocol"; assignee/contact Weldon J. Showalter; reference field blank in registry; dual-registered 246/tcp + 246/udp [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry (lines 561-562); cross-checked at https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=246

Range class

well-known (0-1023) [Confirmed]

IANA RFC/reference

none listed — left blank per registry, not fabricated [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry

Registration/modification date

Unknown — IANA registry does not publish a date for this entry; not invented [Unknown] — the IANA Service Name and Transport Protocol Port Number Registry

Prevalence / security implications

no current scanning-prevalence, honeypot, or threat-intel data specific to port 246 found; a generic port-lookup site's boilerplate "used by a Trojan or Virus in the past" disclaimer names no specific malware and is common across many unrelated ports, so it is not treated as evidence of an actual threat

[Unknown] — https://www.auditmypc.com/tcp-port-246.asp

Related ports

no directly related modern port cluster identified for this legacy X.25/3270 protocol family

Primary use

legacy protocol (circa 1980-81) letting bisynchronous IBM 3270 display terminals communicate over X.25 packet-switched networks via PAD-to-PAD sessions, developed by GTE Telenet, TCTS, Tymnet, and Comtan [Likely] — https://www.euclideanspace.com/coms/protocol/bi_sync/systems/dsp/index.htm (single independent source; not corroborated by a second angle)

Other/unofficial uses

no confirmed modern software or product implementing dsp3270 found

Typically seen on

legacy X.25 networks bridging BSC IBM 3270 terminal traffic; essentially absent from modern IP networks

Port 246/udp is registered with IANA as dsp3270, described as "Display Systems Protocol," with both assignee and contact listed as Weldon J. Showalter. The registry leaves the reference (RFC) column, registration date, and modification date all blank for this entry, so none of those are invented here. Port 246 carries a dual registration: the identical service name, description, and assignee also appear on 246/tcp, one row above this one in the IANA CSV. The name "dsp3270" ties this assignment to IBM 3270-family display-terminal connectivity — a mainframe-era terminal protocol lineage — though no primary specification document or currently maintained implementation could be sourced in this pass, so the "still in active use" question is left Unknown rather than asserted. No named vendor or open-source project implementing dsp3270 today was found. On the security side, SANS Internet Storm Center's per-port dashboard shows only routine background internet-wide scan traffic reaching port 246 as of the date checked, with a "green" threat level and no CVEs listed against the port; this reads as generic full-range scanner noise rather than protocol-specific targeting, and — because ISC's per-port numbers are a live rolling snapshot — it is recorded here as a point-in-time observation, not a fixed historical fact.

IANA assignment

dsp3270 — "Display Systems Protocol"; assignee/contact [Weldon_J_Showalter]; registration date, modification date, reference, service code, unauthorized-use-reported, and assignment-notes columns all blank in the registry [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry; cross-checked at https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml

Dual registration

246/tcp carries an identical entry (same service name, description, assignee/contact, same blank fields) [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry

Range class

well-known (0–1023) [Confirmed]

IANA RFC/reference

none listed — left blank per registry, not fabricated [Confirmed] — the IANA Service Name and Transport Protocol Port Number Registry

Prevalence / exposure

SANS ISC per-port dashboard shows only background, internet-wide scan traffic hitting port 246 as of the date checked (2026-07-17 PDT), threat level green, no CVEs listed — read as routine full-range scanner noise, not targeted activity, and as a live rolling snapshot rather than a fixed historical fact

[Confirmed, time-bound] — https://isc.sans.edu/port.html?port=246

Related ports

no directly related modern port cluster identified for this legacy protocol family [Unknown]

Primary use

name suggests IBM 3270-family display-terminal connectivity (legacy mainframe terminal emulation networking); no primary spec/RFC or actively-maintained implementation could be sourced, so current/active use is Unknown rather than asserted [Likely] — https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml, https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers

Common software

Unknown — no current, verifiable vendor or open-source implementation found; presumed IBM 3270 terminal-software lineage is not confirmed

Typically seen on

no confirmed contemporary deployment identified; if legacy 3270-terminal infrastructure persists it would be the presumed context, but this is not independently confirmed for the UDP registration [Unknown]

Vulnerabilities/CVEs

none found specific to dsp3270 or port 246 in sources checked [Likely] — https://isc.sans.edu/port.html?port=246