Port 42NameServer (ARPA Hostname)
Port 42 was historically assigned to the Host Name Server Protocol (NameServer), a part of the ARPA Network designed to manage and resolve hostnames in early networking environments, predating more modern DNS protocols. Though largely obsolete today, understanding this port helps contextualize the evolution of network naming solutions..
- transport
- tcp · udp
- in transit
- cleartext
- assignment
- official
- risk
- 4/10
- lookups
- 17,157
2 transports registered
payload readable on path
registered with iana
caution
rank 167 of 993 · top 17%
1 other service is registered on port 42. compare all 2 →
Technical Details
what runs on :42-
The NameServer protocol defined for port 42 originally served in the early ARPANET/Internet environment to resolve hostnames before the adoption of DNS.
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It allowed network nodes to query centralized or distributed hosts tables, fetching hostname or address information as needed to facilitate communication on the nascent Internet.
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Over time, the protocol became obsolete with the introduction of the Domain Name System (DNS) standard in the 1980s, which provided a scalable, hierarchical method for name resolution and replaced many of the functions formerly provided by NameServer.
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Technically, NameServer supported both TCP and UDP transport layers, enabling hostname lookup operations via connection-oriented or connectionless communication.
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Today, port 42 is still officially designated for NameServer, but its practical use is virtually nonexistent; modern systems rely on port 53 (DNS) for hostname resolution.
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However, old legacy systems, historical emulations, or academic studies of protocol evolution might still reference or implement aspects of the NameServer protocol.
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Given its age and replacement by DNS, software support and documentation for NameServer are limited; most contemporary network stacks do not implement the protocol.
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In network scanning, port 42 might still be reported open on certain historical or custom devices but should typically be considered unused in modern infrastructures.
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Understanding the legacy of port 42 provides insight into how Internet naming strategies evolved from flat hosts files to the global distributed DNS framework.
Security Information
exposure of :42risk score
4/ 10caution
worth attention. how exposed you are depends on configuration — don't leave it reachable from the internet without a reason.
network services averages 3.9 across 604 ports — this one sits 0.1 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
Common Vulnerabilities:
- Since NameServer is practically obsolete, active exploitation is rare, but if in use, vulnerabilities could include:
- Unauthorized hostname queries that could leak network topology information.
- Spoofed server responses leading to incorrect hostname resolution.
- Lack of authentication, making it susceptible to man-in-the-middle attacks.
- Attackers might also use open port 42 responses as reconnaissance data during scans.
Common Mitigations:
- Disable port 42 services unless required for legacy reasons.
- Block inbound and outbound traffic on port 42 at firewalls to prevent misuse or reconnaissance.
- Rely exclusively on secure, modern DNS implementations that support security extensions (DNSSEC).
- Regularly audit network ports and services to identify and retire legacy or unused protocols.
- Maintain updated network documentation to ensure legacy ports are not inadvertently exposed.
Related Ports
the 8 most looked-up other ports in network services — 604 ports carry that label.
| port | service | risk | |||
|---|---|---|---|---|---|
| :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