# WHATPORT(3551)

## NAME

port 3551 — apcupsd NIS — apcupsd's Network Information Server — UPS status for apcaccess and dashboards, unauthenticated.

Protocol: TCP  
IANA registry

## DESCRIPTION

apcupsd monitors an APC UPS and shuts the machine down cleanly on a power failure; its Network Information Server listens on TCP 3551 and hands out the status block you see from apcaccess — line voltage, battery charge, time on battery, load percentage. Home servers, NAS boxes, Home Assistant installs, and monitoring agents poll it. The NIS is read-only status by design, and it has no authentication: access control is the NISIP bind address and your firewall.

## EXPOSURE

**Do not expose.** Unauthenticated and cleartext, and it advertises exactly when a host is running on battery — bind NISIP to 127.0.0.1 or a LAN address and keep it off any public interface.

## CHECK

```sh
apcaccess status TARGET:3551
```

## SEE ALSO

- docs — [apcupsd project page](https://sourceforge.net/projects/apcupsd/) (sourceforge.net)
- iana — [IANA port registry — 3551 (apcupsd)](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=3551) (iana.org)

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HTML: <https://whatport.net/3551/> · JSON: <https://whatport.net/3551.json> · full dataset: <https://whatport.net/ports.json>