Port 1990Cisco STUN Priority 1

Cisco's STUN Priority 1 service uses port 1990 over TCP and UDP.

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 6/10
lookups: 0

also known as stun-p1

Technical Details

what runs on :1990

Port 1990 is the Cisco STUN Priority 1 service, used by Cisco IOS Serial Tunnel deployments to carry encapsulated serial or legacy WAN protocol traffic between configured peers. The service can use TCP or UDP, with the port identifying the highest STUN priority class; related STUN priority classes may use additional ports. This is not the modern WebRTC STUN protocol, and traffic is not encrypted by default.

Security Information

exposure of :1990

risk score

6/ 10risk

treat as sensitive. widely scanned and regularly exploited when reachable — restrict it to known sources.

network services averages 2.6 across 1,638 ports — this one sits 3.4 above.

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 · udp

udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite

security overview

Cisco STUN should normally be restricted to explicitly configured router peers and never exposed broadly to the Internet. Because it is a legacy tunneling mechanism and provides no default confidentiality, an exposed listener could disclose or relay encapsulated serial traffic and may permit unwanted peer connections depending on the IOS configuration; allowlisting and network-level protection are appropriate.

Record

iana registry entry

port: :1990
service: Cisco STUN Priority 1
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 6/10risk
category: Network Services
usage: Cisco STUN is a legacy Cisco IOS feature that tunnels serial traffic, such as SDLC, between routers over IP. Engineers may encounter TCP or UDP traffic on port 1990 on routers providing serial-to-IP connectivity; it is uncommon on modern Internet-facing systems.
lookups: 0rank 993
added: 2026-08-28
updated: 2026-09-22
references: IANA service name registry — port 1990

Something wrong?

This record is maintained by the engineers who use port 1990. Every field on it is editable — change what's wrong, say how you know, and a reviewer publishes it, usually within a minute. Last touched 2026-09-22.

01edit any field on a page of its own
02a model checks it for accuracy and spam
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edit this record →back to the registry

Related Ports

all 1,638 in network services →

the 8 most looked-up other ports in network services — 1,638 ports carry that label.

port	service	proto	category	risk	views
:9080	Groove RPC	TCPUDP	Web Services	caution	70.8k
:6543	Jetnet	UDP	Network Services	caution	65.3k
:5938	TeamViewer	TCPUDP	Remote Access	caution	65.0k
:8291	Winbox MikroTik Admin	TCP	Security	caution	62.9k
:3233	WhiskerControl Protocol	TCPUDP	Network Services	caution	61.9k
:3268	Microsoft Global Catalog (GC)	TCPUDP	Security	caution	54.6k
:135	Microsoft EPMAP	TCPUDP	Security	caution	51.9k
:3128	Tatsoft Default HTTP Proxy	TCP	Web Services	caution	46.8k

risk mix of the 8 listed

caution100%

0 of 8 encrypted

Port :1990Cisco STUN Priority 1

Technical Details

Security Information

Related Ports

Port 1990Cisco STUN Priority 1