Port 3551apcupsd Network Information Server

The apcupsd Network Information Server port used by UPS monitoring clients to retrieve status and operational data.

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 6/10
lookups: 0

also known as apcupsd NIS, Apcupsd Information Port

Technical Details

what runs on :3551

The apcupsd Network Information Server uses a simple, cleartext, line-oriented application protocol over TCP, normally on port 3551. Clients connect and request UPS status or related information, which the daemon returns as key-value records and other text responses. The service is configured through apcupsd settings such as NISPORT and NISIP; it has no standard encryption layer and is commonly bound to localhost or a trusted management network.

Security Information

exposure of :3551

risk score

6/ 10risk

treat as sensitive. widely scanned and regularly exploited when reachable — restrict it to known sources.

network services averages 3.2 across 848 ports — this one sits 2.8 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

Traffic is normally unauthenticated and unencrypted, so exposed status data can reveal UPS, host, load, and power-event information. The port should not be exposed to the public internet; restrict it with firewall rules and bind it to trusted monitoring networks, because vulnerable or permissive configurations may provide more than a harmless status view.

Record

iana registry entry

port: :3551
service: apcupsd Network Information Server
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 6/10risk
category: Network Services System
usage: apcupsd, the APC UPS daemon, normally listens on TCP port 3551 for clients such as `apcaccess` and network-connected monitoring systems. It provides UPS status, event, and measurement information; the IANA registry also lists UDP, although normal apcupsd NIS deployments use TCP.
lookups: 0rank 994
added: 2026-08-30
updated: 2026-08-30
references: IANA service name registry — port 3551

Something wrong?

This record is maintained by the engineers who use port 3551. Every field on it is editable — change what's wrong, say how you know, and a reviewer publishes it, usually within a minute. Last touched 2026-08-30.

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edit this record →back to the registry

Related Ports

all 848 in network services →

the 8 most looked-up other ports in network services — 848 ports carry that label.

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:3268	Microsoft Global Catalog (GC)	TCPUDP	Security	caution	54.6k
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:3128	Tatsoft Default HTTP Proxy	TCP	Web Services	caution	46.8k

risk mix of the 8 listed

caution100%

0 of 8 encrypted

Port :3551apcupsd Network Information Server

Technical Details

Security Information

Related Ports

Port 3551apcupsd Network Information Server