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.


var relPort = RTCIceCandidate.relatedPort;


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 6502 typ srflx raddr rport 32768 generation 0

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


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);


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

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
relatedPortChrome Full support 74Edge Full support ≤18Firefox No support NoIE No support NoOpera No support NoSafari ? WebView Android Full support 74Chrome Android Full support 74Firefox Android No support NoOpera Android No support NoSafari iOS ? Samsung Internet Android Full support 11.0


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See also