Port 51IMP Logical Address Maintenance
Port 51, designated for IMP Logical Address Maintenance, historically supported communication within ARPANET Infrastructure by facilitating management and maintenance of IMP (Interface Message Processor) logical addressing. Though now largely obsolete, it played a crucial role in early network routing and device management tasks..
- transport
- tcp · udp
- in transit
- cleartext
- assignment
- official
- risk
- 4/10
- lookups
- 15,019
2 transports registered
payload readable on path
registered with iana
caution
rank 220 of 993 · top 22%
Technical Details
what runs on :51Port 51 was initially assigned for IMP Logical Address Maintenance, a protocol foundational during the ARPANET era. IMPs were specialized packet-switching nodes enabling host-to-host communication by managing logical addressing and routing within the burgeoning Internet. This maintenance protocol allowed operators and processes to configure, verify, and update IMP routing tables and logical addresses dynamically.
Technically, communications over port 51 served to send maintenance commands, status queries, and to synchronize logical address mappings across IMP devices. It allowed for seamless integration and updating without disrupting data flows, essential in maintaining network resilience and adaptability during early Internet expansion.
Today, port 51 has no standardized contemporary application, as the protocols it supported have been deprecated or replaced by more advanced networking mechanisms such as IP-based routing protocols (like OSPF or BGP). Systems rarely, if ever, utilize this port in production, and it is often unassigned or filtered out in modern deployments.
Security Information
exposure of :51risk 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 for port 51 stem primarily from its obsolete nature. If inadvertently left open or accessible, it may become a vector for network reconnaissance or unauthorized access attempts, especially in legacy environments where outdated IMP maintenance processes might still exist. Attackers could attempt to exploit unpatched or misconfigured legacy systems exposed through this port.
Mitigation involves ensuring port 51 is blocked or filtered at network perimeters and internal firewalls unless explicitly required for legacy reasons. Organizations should audit and disable unused and obsolete ports on all network devices, apply updated access control lists (ACLs), and implement network segmentation to limit potential exposure. Additionally, vulnerability scanning and intrusion detection systems can help flag any unexpected traffic involving this port.
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