# WHATPORT(42)

## NAME

port 42 — Host Name Server / WINS replication — Registered as the ARPANET Host Name Server; in practice this is Microsoft WINS replication traffic.

Protocol: TCP/UDP  
IANA registry

## DESCRIPTION

IANA registers 42 under the service names 'name' and 'nameserver' for the Host Name Server, a pre-DNS lookup service that no longer exists in the wild. What actually uses the port today is Windows Internet Name Service replication: WINS servers push and pull NetBIOS name-to-address mappings between each other over TCP 42, and Microsoft's network-port requirements documentation lists the port under WINS. Seeing it open means a Windows Server with the WINS role, which is a deprecated feature kept alive for legacy NetBIOS applications.

## EXPOSURE

**Do not expose.** Internal Windows name-infrastructure replication with no place on a public interface; keep it inside the network boundary between WINS partners only.

## CHECK

```sh
nmap -Pn -sV -p 42 TARGET
```

## SEE ALSO

- docs — [Service overview and network port requirements for Windows](https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/service-overview-and-network-port-requirements) (learn.microsoft.com)
- iana — [IANA Service Name and Transport Protocol Port Number Registry](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml) (iana.org)

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HTML: <https://whatport.net/42/> · JSON: <https://whatport.net/42.json> · full dataset: <https://whatport.net/ports.json>