Port 477 is assigned to ss7ns (Signaling System 7 Name Server), a service that provides name resolution for the telecommunications protocol that connected the world before IP telephony existed—and still does.
What SS7 Is
Signaling System 7 is a set of telephony signaling protocols developed in the 1970s.1 It's the nervous system of the Public Switched Telephone Network (PSTN)—the global telephone infrastructure that predates the Internet.
SS7 does everything a phone call needs:
- Sets up the connection between caller and recipient
- Tears down the call when someone hangs up
- Handles number translation and routing
- Enables caller ID, call forwarding, conference calls
- Powers SMS text messaging
- Manages local number portability (keeping your number when you switch carriers)
- Processes prepaid billing
The protocol was introduced by Bell System in the United States in the 1970s and standardized internationally by ITU-T in 1980.2
What Port 477 Does
Port 477 hosts ss7ns—the SS7 Name Server.3 This service provides name resolution within SS7 networks, mapping network addresses and identifiers so that signaling messages can find their destinations across the global telephone network.
Think of it as DNS for the phone network, but older and more obscure.
The service was registered with IANA by Jean-Michel Ursch and operates on both TCP and UDP.4
Why This Matters
The phone network didn't die when VoIP arrived. SS7 still routes billions of calls:
- Every 911 emergency call
- Landline-to-landline connections
- Mobile calls that fall back to circuit-switched networks
- SMS messages on traditional cellular networks
- International calls crossing different network types
SS7 is the bridge between the telephone era and the Internet era. Port 477's naming service keeps that bridge functional.
The Security Problem
SS7 has a critical flaw: it was designed in the 1970s, before anyone thought about security.
The protocol lacks authentication and encryption.5 If you can access the SS7 network (and surprisingly many people can through various telecommunications backdoors), you can:
- Intercept calls and text messages
- Track someone's location by querying the network
- Reroute calls and SMS
- Bypass two-factor authentication that uses SMS
This isn't theoretical. SS7 vulnerabilities have been exploited in the wild to compromise bank accounts, spy on journalists, and track individuals.
The protocol was built for a world where only trusted telephone companies had access to the signaling network. That world no longer exists.
Related Ports
Other telephony-related ports in the well-known range:
- Port 5060-5061: SIP (Session Initiation Protocol) — the modern VoIP alternative to SS7
- Port 1720: H.323 — another VoIP signaling protocol
- Port 2427: MGCP (Media Gateway Control Protocol) — coordinates gateways between VoIP and PSTN
How to Check What's Using Port 477
On Linux or macOS:
On Windows:
Unless you're operating telecommunications infrastructure or SS7 gateway equipment, you shouldn't see anything listening on this port.
The Bigger Picture
Port 477 represents the hidden infrastructure that still runs beneath modern communications. The PSTN was supposed to be obsolete by now—replaced entirely by Voice over IP and Internet-based messaging.
But legacy systems are harder to kill than anyone expects. The phone network still exists because:
- Emergency services depend on it
- Billions of devices still use it
- International regulations require it
- It works when Internet connectivity fails
Port 477's SS7 name server sits in that gap between past and future—maintaining address resolution for a protocol from the 1970s that still routes calls in 2026.
The Internet didn't replace the phone network. It just became another thing connected to it.
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