66

Port 66/tcp is registered with IANA as sql-net with the description "Oracle SQL*NET," assignee Jack Haverty, and a blank reference field (no RFC cited). The well-formed service name sql-net was introduced by IANA as a replacement for the historic alias sql*net, which contains a character that is not usable with many common service discovery mechanisms; IANA flags that older alias as deprecated. The port is dual-registered on TCP and UDP under the same service name and the same assignee. SQL*NET was Oracle's legacy client-to-server networking layer, letting database clients reach a database server across a network before Oracle standardized on port 1521/tcp (the TNS, or Transparent Network Substrate, listener). In practice port 66 is effectively abandoned for its original purpose: well-known ports (0–1023) require root or administrator privileges to bind on Unix-like systems, which is an unnecessary operational risk for a long-running database listener, so Oracle moved its listener to the registered/ephemeral range and 1521/tcp became the de-facto standard. No currently active mainstream software is known to use port 66 legitimately. For an analyst, a host listening on port 66 today is statistically unusual: the assignment is historical, and any observed listener warrants investigation rather than being assumed to be Oracle. AuditMyPC notes that a trojan or virus has used this port in the past to communicate, but lists no current active malware association and no specific named trojan; the port does not appear in the Gary Kessler "bad ports" list.

IANA assignment

sql-net — "Oracle SQL*NET"; reference (blank — no RFC cited in IANA registry); assignee Jack Haverty; dual-registered 66/tcp + 66/udp [Confirmed] — IANA Service Name and Transport Protocol Port Number Registry (https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv)

Range class

well-known (0–1023)

Related ports

1521/tcp (Oracle TNS listener — the modern successor in practice)

Primary use

Oracle SQL*NET, the legacy Oracle client-to-server database networking protocol (pre-TNS era)

Common software

early Oracle SQL*NET client/server stacks (pre-TNS, likely late 1980s–early 1990s); no modern software known to use this port legitimately

Security implications

abandoned well-known port; AuditMyPC reports past (unspecified) trojan/virus use with no current active malware association and no specific trojan name; not in the Gary Kessler bad-ports list; a listener on port 66 on a modern host warrants investigation as no legitimate current software is expected [Confirmed] — AuditMyPC (https://www.auditmypc.com/tcp-port-66.asp), Gary Kessler bad ports (https://www.garykessler.net/library/bad_ports.html)

Typically seen on

historical/legacy Oracle environments; otherwise an anomaly worth investigating

Historic alias

sql*net — listed by IANA but marked not usable with many common service discovery mechanisms; sql-net is the well-formed replacement [Confirmed] — IANA registry (CSV)

Modern reality

effectively abandoned for its original purpose; Oracle standardized on 1521/tcp (TNS listener), partly because well-known ports require root/admin to bind on Unix [Likely] — SpeedGuide; IANA registry

Analyst note

The IANA registration is intact (sql-net, assignee Jack Haverty, no RFC) but the port is historical. Treat a live port 66 as statistically rare and investigate rather than assuming legitimate Oracle use.

Port 66/udp is registered with IANA under the canonical service name sql-net for Oracle SQL*NET, with both assignee and contact listed as Jack Haverty and a blank reference field (no RFC or other document is cited). The name sql-net was assigned as a well-formed replacement for the original sql*net, whose asterisk is an illegal character in a modern service name; the historic sql*net alias still appears for the same port and protocol but IANA explicitly notes it is not usable with many common service-discovery mechanisms. The assignment is dual-registered: port 66/tcp carries an identical sql-net registration with the same assignee and the same sql*net alias. SQL*NET was Oracle's legacy proprietary network layer for database client-to-server communication, predating the Transparent Network Substrate (TNS) introduced around the Oracle 7 era (~1992). With that transition, real Oracle connectivity moved to the Oracle Net Services listener on 1521/tcp, and no current Oracle product documentation references port 66 for active use — it is a pre-TNS registration that survives in the registry rather than in live deployments. For an analyst, port 66/udp is essentially a legacy stub: open instances are extremely rare, no CVEs or malware families are known to specifically target it, and no meaningful internet-scanning or exploitation activity against this specific port has been documented in publicly available sources as of June 2026. General hardening guidance is simply to block unused legacy database ports.

IANA assignment

sql-net — "Oracle SQL*NET"; reference (blank — no RFC cited in IANA registry); assignee/contact Jack Haverty [Confirmed] — IANA Service Name and Transport Protocol Port Number Registry (https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv)

Dual registration

66/tcp also registered as sql-net (Oracle SQL*NET) with the same assignee and the same sql*net alias [Confirmed] — IANA registry (https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv)

Range class

well-known (0–1023)

Status

legacy / historic. IANA primary service name sql-net; sql*net alias explicitly historic [Confirmed] — IANA registry

Related ports

66/tcp (same dual registration); 1521/tcp (modern Oracle Net Services / TNS listener)

Primary use

legacy Oracle SQL*NET v1 client-to-database connectivity (pre-TNS); actual Oracle connectivity moved to Oracle Net Services / TNS on 1521/tcp with the Oracle 7 era (~1992) [Confirmed] — Oracle docs (https://docs.oracle.com/cd/E11882_01/install.112/e41962/ports.htm), SpeedGuide (https://www.speedguide.net/port.php?port=66)

Common software

Oracle SQL*NET v1; no current Oracle product documentation references port 66 for active use (TNS uses 1521/tcp by default)

Security implications

no significant internet scanning or exploitation activity specifically targeting 66/udp documented in public sources as of June 2026; no known CVEs or malware families specifically exploit it; open instances extremely rare due to Oracle's migration to 1521/tcp [Likely — no dedicated Shodan/scan data retrievable] — AuditMyPC (https://www.auditmypc.com/tcp-port-66.asp)

Historic alias

sql*net — present for 66/udp but flagged by IANA as not usable with many common service-discovery mechanisms; sql-net is the canonical well-formed replacement [Confirmed] — IANA registry (https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml)

Analyst note

an open port 66/udp is statistically rare and a legacy stub; treat as anomalous and investigate rather than assume legitimate Oracle SQL*NET use.