# WHATPORT(1718)

## NAME

port 1718 — H.323 gatekeeper discovery — H.323 endpoints shouting for a gatekeeper — multicast discovery, the step before RAS registration on 1719.

Protocol: UDP  
IANA registry

## DESCRIPTION

An H.323 endpoint that has not been told where its gatekeeper is sends a GRQ (Gatekeeper Request) to the multicast group 224.0.1.41 on UDP 1718; a gatekeeper that wants the endpoint answers with a GCF, after which all RAS traffic — registration, admission, bandwidth — moves to unicast UDP 1719 and call signalling to TCP 1720. IANA registers 1718 to ITU-T for both TCP and UDP, but the discovery exchange is UDP only. It appears on VoIP networks running legacy H.323 gear: video conferencing MCUs, gateways, and older IP phones.

## EXPOSURE

**Do not expose.** Gatekeeper discovery is unauthenticated by design and is a link-local mechanism — an endpoint that accepts a GCF from a stranger has just been told where to send its calls, so keep it inside the voice VLAN.

## CHECK

```sh
nmap -sU -p 1718 TARGET
```

## SEE ALSO

- spec — [ITU-T Recommendation H.323 — Packet-based multimedia communications systems](https://www.itu.int/rec/T-REC-H.323) (itu.int)
- iana — [IANA port registry — 1718](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=1718) (iana.org)

---

HTML: <https://whatport.net/1718/> · JSON: <https://whatport.net/1718.json> · full dataset: <https://whatport.net/ports.json>