Port 9900ISDN Q.921 User Adaptation (IUA)

Carries ISDN Q.921 signaling over IP, typically between signaling gateways and call-control systems.

transport: tcp · udp · sctp
in transit: cleartext
assignment: official
risk: 5/10
lookups: 0

also known as iua, ISDN User Adaptation, RFC 4233

Technical Details

what runs on :9900

IUA adapts ISDN Q.921 signaling for transport over IP, as specified by RFC 4233. It is normally carried over SCTP, whose association setup provides the transport handshake; IUA then uses management and Application Server Process state messages such as ASP Up and ASP Active before exchanging encapsulated Q.921 signaling. IUA itself does not provide encryption, authentication, or confidentiality; deployments generally restrict peers at the network layer or protect the signaling network separately.

Security Information

exposure of :9900

risk score

5/ 10caution

worth attention. how exposed you are depends on configuration — don't leave it reachable from the internet without a reason.

network services averages 3.2 across 862 ports — this one sits 1.8 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 · sctp

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

security overview

An exposed IUA endpoint could be targeted for SCTP or application-layer denial of service, spoofed signaling, or unauthorized manipulation of ISDN call-control traffic. It should normally be reachable only by explicitly authorized signaling peers, not exposed to the public internet; IUA traffic is cleartext unless protected by an external mechanism such as IPsec.

Record

iana registry entry

port: :9900
service: ISDN Q.921 User Adaptation (IUA)
transport: TCPUDPSCTP
encryption: cleartext
assignment: iana registered
risk: 5/10caution
category: Network Services Voice and Chat
usage: IUA transports ISDN Q.921 user signaling across an IP-based SIGTRAN network, commonly between a signaling gateway and a media gateway controller or other call-control system. Real deployments normally use SCTP on port 9900, although the registry lists TCP, UDP, and SCTP.
lookups: 0rank 994
added: 2026-08-30
updated: 2026-08-30
references: IANA service name registry — port 9900

Something wrong?

This record is maintained by the engineers who use port 9900. 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 2026-08-30.

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

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risk mix of the 8 listed

caution100%

0 of 8 encrypted

Port :9900ISDN Q.921 User Adaptation (IUA)

Technical Details

Security Information

Related Ports

Port 9900ISDN Q.921 User Adaptation (IUA)