RTCIceCandidate.address

A string providing the IP address from which the candidate comes.

It's important to note here that although WebRTC does not require the two peers on an RTCPeerConnection to know one another's true IP addresses, the address property on RTCIceCandidate can expose more information about the source of the remote peer than the user expects. The IP address can be used to derive information about the remote device's location, network topology, and so forth. It can also be used for fingerprinting purposes.

The candidate IP addresses are always exposed to the application through address, and unsavory applications can in turn potentially reveal the address to the user. This can occur without the remote peer's consent.

Applications being built with user privacy and security in mind can choose to limit the permitted candidates to relay candidates only. Doing so prevents the remote user's address from being exposed, but reduces the pool of available candidates to choose from. To do this, configure the ICE agent's ICE transport policy with an object confirming to the configuration property described in RTCPeerConnection.setConfiguration, like this:

const rtcConfig = {
  iceServers: [
    {
      urls: "turn:myturn.server.ip",
      username: "username",
      credential: "password"
    }
  ],
  iceTransportPolicy: "relay"
}

By setting iceTransportPolicy to "relay", any host candidates (candidates where the IP address is the peer's own IP address) are left out of the pool of candidates, as are any other candidates which aren't relay candidates.

Consider this SDP attribute line (a-line) which describes an ICE candidate:

a=candidate:4234997325 1 udp 2043278322 192.168.0.56 44323 typ host

The fifth field, "192.168.0.56" is the IP address in this candidate's a-line string.

This code snippet uses the value of address to implement an IP address based ban feature.

if (ipBanList.includes(candidate.address)) {
  rejectCandidate(candidate);
} else {
  acceptCandidate(candidate);
}