Web/API/RTCIceCandidate/relatedPort

The RTCIceCandidate interface's read-only relatedPort property indicates the port number of reflexive or relay candidates. If the candidate is a host candidate (that is, its ip is in fact the real IP address of the remote peer), relatedPort is null.

The relatedPort field's value is set when the RTCIceCandidate() constructor is used. You can't specify the value of relatedPort in the options object, but the address is automatically extracted from the candidate a-line, if it's formatted properly, being taken from its rel-port field.

The related address (relatedAddress) and port are not used at all by ICE itself; they are provided for analysis and diagnostic purposes only, and their inclusion may be blocked by security systems, so do not rely on them having non-null values.

Syntax

var relPort = RTCIceCandidate.relatedPort;

Value

An unsigned 16-bit value containing the candidate's related port number, if any. For both peer and server reflexive candidates, the related address and port describe the base for that candidate. For relay candidates, the related address and port provide the mapped address selected by the TURN server.

For host candidates, relatedPort is null, meaning the field is not included in the candidate's a-line.

Usage notes

The related address and port are not used by ICE itself, and are only present for diagnostic and Quality-of-Service purposes. They may in fact be omitted for security reasons, but if present can be a useful tool during debugging. See the example, which shows a bit of this.

Here's an SDP attribute line (a-line) describing an ICE candidate discovered by the STUN server:

a=candidate:4234997325 1 udp 2043278322 192.168.0.56 6502 typ srflx raddr 192.168.2.77 rport 32768 generation 0

The remote port, relatedPort, is the number immediately following the "rport" label on the a-line, or 32768.

Example

In this example, the candidate's type is checked, and then debugging output is presented, based on the candidate type, including the candidate's type, address (ip and port), and related address (relatedAddress and relatedPort).

var ip = candidate.ip;
var port = candidate.port;
var relIP = candidate.relatedAddress;
var relPort = candidate.relatedPort;

if (relIP && relPort) {
  console.log("Candidate type '" + type + "' -- contact address: " + ip + " " + port + ", related address: " + relIP + " " + relPort);
} else {
  console.log("Host candidate address is " + ip + " " + port);
}

Specifications

Specification	Status	Comment
WebRTC 1.0: Real-time Communication Between BrowsersThe definition of 'RTCIceCandidate.relatedPort' in that specification.	Candidate Recommendation	Initial definition.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`relatedPort`	Chrome Full support 74	Edge Full support ≤18	Firefox No support No	IE No support No	Opera No support No	Safari ?	WebView Android Full support 74	Chrome Android Full support 74	Firefox Android No support No	Opera Android No support No	Safari iOS ?	Samsung Internet Android Full support 11.0

Legend

Full support: Full support
No support: No support
Compatibility unknown: Compatibility unknown