What Runs on Port 3565
Port 3565 is assigned to M2PA (MTP2 User Peer-to-Peer Adaptation Layer), a protocol defined in RFC 4165.1 M2PA runs over SCTP (Stream Control Transmission Protocol), not TCP or UDP — a third transport protocol designed specifically for telecom signaling traffic that needs reliability and low latency.
You won't encounter this port on a typical server or home network. M2PA belongs to carrier infrastructure — the backbone of the global telephone system.
The Problem M2PA Solves
The telephone network runs on SS7 (Signaling System No. 7), a protocol designed in the 1970s for dedicated circuit-switched networks.2 SS7 handles everything behind the scenes when you make a call: finding the destination number, setting up the connection, managing billing, enabling SMS delivery. It assumes a world of dedicated copper wires and purpose-built signaling links.
When carriers began migrating their backbones to IP, they faced a problem: how do you carry SS7 signaling over a packet-switched network? The answer was SIGTRAN — a suite of IETF protocols that adapt SS7 for transport over IP using SCTP.3
M2PA is one piece of that suite. It replaces MTP2 (the data link layer of SS7) with an IP equivalent, while keeping MTP3 (the network layer above it) completely unchanged. To MTP3, M2PA looks exactly like MTP2. The upper layers of the phone network don't need to know the wires changed underneath.
How It Works
M2PA sits between MTP3 and SCTP:
It preserves all the MTP2 primitives — the exact signals MTP3 expects to exchange with its lower layer — while routing them over SCTP associations instead of dedicated circuits. M2PA is primarily used for Signaling Gateway to Signaling Gateway (SG-to-SG) connections, where two carrier nodes need to exchange SS7 traffic across an IP network.1
SCTP was chosen over TCP for good reason. TCP's head-of-line blocking is dangerous for real-time signaling. SCTP supports multi-streaming (so one delayed message doesn't block others) and multi-homing (automatic failover across network paths) — both critical for carrier-grade reliability.4
Who Uses This Port
This is a telecom carrier port. If you work in enterprise IT, cloud infrastructure, or web development, you will almost certainly never see traffic on port 3565.
You'd encounter it in:
- Carrier-grade Signaling Gateways
- Telecom core network equipment
- VoIP interconnect infrastructure where SS7 networks meet IP networks
- Network monitoring for telecommunications providers
Checking What's on This Port
If you see unexpected activity on port 3565 on a server you manage, something is wrong. No ordinary application uses this port.
On Linux:
On macOS:
On Windows:
Unexpected traffic here could indicate a misconfigured application that picked this port arbitrarily, or — rarely — malware attempting to blend into legitimate telecom traffic patterns.
The Registered Port Range
Port 3565 sits in the registered ports range (1024–49151). IANA maintains this range for services that have applied for an official assignment — distinct from the well-known ports (0–1023, requiring root/admin to bind) and the ephemeral ports (49152–65535, used for temporary outbound connections).5
Registered ports don't require special privileges to bind, which makes them practical for application-layer protocols like M2PA that run as services rather than system daemons.
Frequently Asked Questions
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