Debugging WebRTC ICE Candidate Gathering Failures in Genesys Cloud Agent Desktop for Edge Deployments behind NAT

How-To-Articles
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Debugging WebRTC ICE Candidate Gathering Failures in Genesys Cloud Agent Desktop for Edge Deployments behind NAT

What This Guide Covers

This guide details the systematic diagnosis and resolution of WebRTC ICE candidate gathering failures when Genesys Cloud Agent Desktop operates behind a NAT boundary using an Edge deployment. You will configure STUN/TURN relay policies, validate SDP exchange patterns, and deploy diagnostic logging to isolate network topology breaks. The end result is a deterministic troubleshooting workflow that eliminates media path blackholes and restores stable WebRTC signaling and media routing.

Prerequisites, Roles & Licensing

  • Licensing Tier: CX 1, CX 2, or CX 3 with Genesys Cloud Edge deployment. WebRTC media routing and advanced agent desktop features require CX 2 or higher. Edge node licensing must cover the target geographic region.
  • Administrative Permissions: Telephony > Edge > Manage, Admin > User > Edit, Telephony > Trunk > View, Telephony > Media > Edit, Reporting > System > View
  • OAuth Scopes: edge:read, telephony:media:read, user:read, admin:read, diagnostics:read
  • External Dependencies: RFC 8489 compliant STUN server, RFC 5766 compliant TURN relay, RFC 8445 WebRTC stack, NAT device supporting UDP hole punching or symmetric NAT traversal policies, enterprise firewall permitting outbound UDP 3478-50000 and TCP 443/WSS traffic.

The Implementation Deep-Dive

1. Validate Edge STUN/TURN Configuration and Candidate Allocation

Genesys Cloud Edge acts as a signaling proxy and media relay for WebRTC sessions. The Edge node does not generate ICE candidates locally. Instead, it advertises STUN and TURN server endpoints to the browser during the initial WebSocket handshake. The browser then performs candidate gathering using those advertised servers. Misalignment between the Edge configuration and the actual network path causes immediate gathering failures.

Navigate to Admin > Telephony > Edge > [Your Edge Instance]. Locate the WebRTC Media Settings section. Verify the following configuration keys:

  • stunServer: Must resolve to a publicly accessible STUN endpoint.
  • turnServer: Must resolve to a TURN relay capable of UDP allocation.
  • turnServerRelayMode: Set to allowUdp for standard NAT environments. Set to relayOnly only when strict firewall policies block all UDP traffic.
  • turnServerAuthentication: Must use longTerm credentials for Genesys Edge deployments. Short-term credentials introduce rotation latency that breaks active sessions.

Validate the configuration programmatically using the Edge Management API. This approach eliminates UI caching delays and returns the exact configuration payload pushed to the Edge node.

GET /api/v2/telephony/edges/{edgeId}
Authorization: Bearer <ACCESS_TOKEN>
Accept: application/json

Response payload verification focuses on the webRtcConfiguration object:

{
  "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "name": "US-East-Production",
  "webRtcConfiguration": {
    "stunServer": "stun.edge-us-east.genesiscloud.com:3478",
    "turnServer": "turn.edge-us-east.genesiscloud.com:3478",
    "turnServerRelayMode": "allowUdp",
    "turnServerAuthentication": "longTerm",
    "iceTransportPolicy": "all"
  }
}

The Trap: Configuring turnServerRelayMode to relayOnly when the corporate NAT supports UDP hole punching. This forces all media through the TURN relay, increasing latency by 40-60 milliseconds and saturating Edge node CPU resources during peak hours. When the TURN allocation fails due to firewall restrictions on dynamic UDP port ranges, the browser enters an iceConnectionState: failed state without generating useful diagnostic logs. The downstream effect is a complete media path blackhole that manifests as silent agent desktops.

Architectural Reasoning: WebRTC prioritizes candidates following the ICE hierarchy: host > srflx > relay. Forcing relayOnly bypasses this hierarchy and violates RFC 8445 optimization rules. We configure allowUdp to permit STUN-assisted direct paths before falling back to TURN. This reduces Edge node load, complies with standard NAT traversal expectations, and ensures that candidate gathering failures originate from network policy blocks rather than artificial relay constraints.

2. Intercept and Decode SDP Exchange for Candidate Type Mismatches

The Session Description Protocol (SDP) exchange carries the ICE candidate list. Genesys Cloud modifies the standard WebRTC SDP flow by injecting Edge-specific relay candidates into the answer message. You must decode the SDP payload to verify candidate type allocation and STUN binding responses.

Open the browser developer tools. Navigate to the Network tab and filter for WebSocket or WSS traffic. Locate the signaling handshake between the Agent Desktop and the Edge WebSocket endpoint. The SDP offer originates from the browser, and the SDP answer originates from the Edge node. Copy the raw message body and parse the a=candidate: lines.

Standard candidate format follows RFC 8445:
a=candidate:<foundation> <component> <protocol> <priority> <connection-address> <port> typ <type> [raddr <raddr>] [rport <rport>]

Candidate types indicate traversal method:

  • typ host: Direct local interface IP
  • typ srflx: STUN-reflexive IP (NAT-mapped)
  • typ relay: TURN-relayed IP

Use chrome://webrtc-internals to view the live ICE state machine. Filter by PeerConnection and expand the iceCandidate events. You will observe the candidate type, priority, and network interface used.

{
  "candidate": {
    "candidate": "candidate:0 1 UDP 2130706431 192.168.1.15 52341 typ host generation 0",
    "sdpMid": "0",
    "sdpMLineIndex": 0,
    "usernameFragment": "a1b2c3d4",
    "password": "e5f67890abcd"
  },
  "type": "srflx",
  "protocol": "udp",
  "networkType": "wifi"
}

The Trap: Allowing the browser to generate host candidates before the Edge signaling handshake completes. This results in STALE candidates being injected into the SDP answer. The ICE agent immediately attempts connectivity checks against invalid IP addresses, transitions to failed state, and aborts further candidate gathering. The downstream effect is a cascading signaling timeout that triggers Genesys Cloud to terminate the WebSocket session and drop the agent from the queue.

Architectural Reasoning: Genesys Cloud uses a modified SDP exchange where the Edge node injects relay candidates dynamically based on load balancing algorithms. We must validate that the a=ice-ufrag and a=ice-pwd match between the offer and answer. Mismatches indicate a signaling cache inconsistency on the Edge node. We enforce candidate generation sequencing by delaying browser ICE gathering until the WebSocket handshake completes. This ensures the Edge node has allocated the correct TURN credentials and injected valid relay candidates before the browser initiates connectivity checks.

3. Configure Browser and Agent Desktop Network Policy Overrides

Enterprise environments enforce strict network policies to prevent IP address leakage. Corporate proxies, PAC files, and endpoint security agents frequently block UDP traffic or restrict interface selection. These policies directly conflict with WebRTC ICE candidate gathering requirements.

Configure the Agent Desktop network behavior using browser command-line flags or Group Policy Object (GPO) enforcement. The critical flag controls IP handling policy:
--force-webrtc-ip-handling-policy=default_public_interface_only

Alternative policies include:

  • default: Exposes all local interfaces (high leakage risk)
  • default_public_and_private_interfaces: Exposes public and private interfaces
  • disable_non_proxied_udp: Blocks UDP unless routed through proxy

Apply the policy via registry key for Windows deployments:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome\WebRtcIPHandlingPolicy
Value: default_public_interface_only

Validate the policy by executing a STUN binding request from the restricted interface. Use a command-line STUN client or browser console:

const pc = new RTCPeerConnection({ iceServers: [{ urls: 'stun:stun.l.google.com:19302' }] });
pc.createDataChannel('test');
pc.onicecandidate = (event) => {
  if (event.candidate) {
    console.log('Gathered Candidate:', event.candidate.candidate);
  }
};
pc.createOffer().then(offer => pc.setLocalDescription(offer));

The Trap: Applying default_public_interface_only without verifying that the public IP matches the Edge advertised STUN server. The browser drops all host candidates and relies exclusively on srflx candidates. If the STUN server cannot allocate a reflexive address that matches the expected routing table, ICE connectivity checks fail. The downstream effect is a deterministic gathering timeout that occurs consistently across all agents on the restricted network segment.

Architectural Reasoning: We restrict IP handling to prevent IP leakage compliance requirements, but we must align the policy with the Edge node advertised STUN server. The STUN server must be reachable from the restricted interface. We validate connectivity using RFC 8489 binding requests before deploying the policy organization-wide. This approach ensures that srflx candidate generation succeeds while maintaining compliance boundaries. We cross-reference the gathered srflx IP with the Edge node routing table to confirm that the NAT mapping aligns with the expected media path.

4. Deploy Telemetry and Packet Capture at the Edge Boundary

When candidate gathering fails consistently, you must correlate browser-side ICE state transitions with Edge node telemetry. Genesys Cloud provides diagnostic endpoints that expose ICE state machines, candidate allocation logs, and TURN credential rotation events.

Enable diagnostic logging for the specific Edge instance. Scope the telemetry to the failing agent session to avoid log volume saturation.

POST /api/v2/telephony/edges/{edgeId}/diagnostics
Authorization: Bearer <ACCESS_TOKEN>
Content-Type: application/json

Request payload:

{
  "diagnosticType": "webrtc_ice",
  "sessionId": "sess_a1b2c3d4-e5f6-7890",
  "edgeId": "edge_us_east_prod_01",
  "durationSeconds": 300,
  "includeCandidateDetails": true,
  "includeTurnCredentials": false
}

Retrieve the diagnostic export:

GET /api/v2/telephony/edges/{edgeId}/diagnostics/{diagnosticId}

Response payload structure:

{
  "diagnosticId": "diag_98765432",
  "status": "completed",
  "iceStateTransitions": [
    {"timestamp": "2023-10-25T14:30:00Z", "state": "checking"},
    {"timestamp": "2023-10-25T14:30:02Z", "state": "checking"},
    {"timestamp": "2023-10-25T14:30:05Z", "state": "failed"}
  ],
  "failedCandidates": [
    {
      "type": "srflx",
      "address": "203.0.113.45:52341",
      "failureReason": "stun_binding_timeout",
      "rttMilliseconds": 0
    }
  ],
  "turnAllocationStatus": "success"
}

The Trap: Enabling debug logging without configuring log rotation retention. This causes the Edge node disk to fill rapidly during peak hours. The operating system triggers a graceful shutdown of the WebRTC signaling service to preserve core telephony processes. The failure manifests as candidate gathering timeouts rather than a clear disk space error. The downstream effect is a complete Edge node outage that impacts all agents in the region.

Architectural Reasoning: We scope telemetry to the specific sessionId and edgeId to maintain log volume control. We parse the iceState transitions in the diagnostic payload. The sequence checking > connected > completed indicates success. The sequence checking > failed indicates a NAT or firewall block. We correlate timestamps with the browser chrome://webrtc-internals log to pinpoint the exact candidate that failed the STUN binding request. This correlation isolates whether the failure originates from the client network policy, the corporate firewall, or the Edge node STUN allocation service.

Validation, Edge Cases & Troubleshooting

Edge Case 1: Symmetric NAT UDP Port Mismatch

  • The failure condition: The browser gathers host and srflx candidates successfully. ICE connectivity checks fail with stun_binding_error. The Edge diagnostic log shows iceState: failed with failureReason: udp_port_mismatch.
  • The root cause: Symmetric NAT devices assign a different external UDP port for each unique destination IP. WebRTC ICE relies on port consistency for STUN binding requests. When the browser sends a STUN binding request to the Edge STUN server, the NAT maps it to port 52341. When the browser sends the next STUN request to the TURN server, the NAT maps it to port 52342. The ICE agent cannot correlate the responses because the port mapping changed between requests.
  • The solution: Configure the corporate firewall to create a static UDP port forwarding rule for the WebRTC port range (3478-50000). Alternatively, set iceTransportPolicy: relay in the Edge configuration to force TURN usage, which bypasses symmetric NAT port inconsistency. Validate by forcing a single UDP destination using a network policy that pins STUN and TURN to the same IP address.

Edge Case 2: Corporate Proxy Intercepting WebSocket Signaling

  • The failure condition: Agent Desktop loads successfully. Initial WebSocket handshake completes. Candidate gathering times out after 15 seconds. Browser console shows WebSocket error: 1006 Abnormal Closure. Edge diagnostics show no ICE state transitions.
  • The root cause: Enterprise reverse proxies intercept WSS traffic on port 443 and downgrade the connection to HTTP/1.1. WebRTC signaling requires HTTP/2 or WebSocket upgrade persistence. The proxy terminates the connection before the SDP exchange completes. Candidate gathering never initiates because the signaling channel drops prematurely.
  • The solution: Configure the corporate proxy to whitelist the Genesys Cloud WebSocket endpoint (*.mypurecloud.com/api/v2/telephony/edges/*/webrtc). Set proxy-bypass-list in the browser or GPO to exclude signaling domains. Validate using curl -v --http2 -k https://<edge-endpoint>/webrtc to confirm HTTP/2 upgrade persistence. Cross-reference with the WFM scheduling module to ensure agents are not routed through restricted network segments during peak hours.

Edge Case 3: TURN Credential Rotation Latency

  • The failure condition: Candidate gathering succeeds initially. Media streams establish. The session drops exactly 300 seconds after initiation. Edge diagnostics show turnCredentialExpired followed by iceRestartRequired. Browser console shows IceConnectionState: disconnected then failed.
  • The root cause: Genesys Edge uses long-term TURN credentials with a 300-second refresh cycle. If the Edge node experiences high CPU load during credential rotation, the new credentials do not propagate to the browser in time. The TURN server rejects the relay allocation request. The ICE agent cannot restart because the browser policy blocks dynamic credential updates.
  • The solution: Increase the Edge node CPU allocation or enable horizontal scaling for the Edge cluster. Configure turnServerCredentialRefreshInterval to 600 seconds in the Edge advanced settings. Implement a fallback TURN server with independent credential rotation to eliminate single-point-of-failure during refresh cycles. Validate by monitoring turnAllocationLatency metrics in the Edge health dashboard and correlating with credential rotation timestamps.

Official References