If you see Zoom Error Code 104120 while starting or joining a meeting, the app is typically failing to complete a network connection to Zoom services. The fix is rarely a single button. You get the best results by checking connectivity, then confirming firewall and proxy rules, and only then rebuilding the client if needed.
Helpful signal If Zoom Error Code 104120 happens only on one Wi-Fi network (but works on mobile hotspot), you are looking at a network policy issue: firewall, proxy, DNS filtering, or a security gateway.
Table of Contents
Understanding Zoom Error Code 104120
Error Code 104120 is best approached as a connection-to-service failure. Zoom documents a group of 1041xx meeting error codes as connection problems with Zoom servers, often tied to firewall or proxy environments. That guidance maps cleanly to 104120 troubleshooting: verify your path to Zoom services first, then remove network blockers, then refresh the client. [✅Source-1]
Common Symptoms
- The app stays on Connecting for an unusual time.
- Joining a meeting fails, even with a valid link or ID.
- Switching networks changes the result immediately.
What It Usually Means
- A proxy or security gateway is interrupting traffic.
- A firewall blocks key UDP or meeting ports.
- DNS resolution is slow, stale, or filtered.
Fast Checks Before Deep Troubleshooting
These checks take minutes and often clear Zoom Error Code 104120 without touching advanced settings. Keep your goal simple: confirm whether the problem is your device or the network you are on.
- Test a different network: try a mobile hotspot or another Wi-Fi.
- Disable VPN and proxy temporarily, then retry the meeting.
- Open a browser and confirm you can reach zoom.us without warnings.
- Restart the device and the router/modem if you control it.
Step-by-Step Fixes That Work Most Often
Update Zoom Workplace
Start here. A mandatory update or a partially updated build can show up as a connection failure, especially on managed networks. In the Zoom desktop app, sign in, open your profile menu, and use Check for Updates. If your organization uses MSI packaging, that button may be removed and updates may be handled by IT. [✅Source-2]
Restart Network and Remove Interference
Now remove the common blockers that trigger Error Code 104120: turn off any VPN, pause “secure web” features in antivirus suites for a short test, and stop any “network optimizer” apps. Then try joining again. If the error vanishes on a hotspot, skip ahead to Network Rules because the problem is almost certainly policy-based.
Reset Windows Networking (If You Are on Windows)
If you are on Windows and the same network works fine for other devices, clean up local DNS and adapter state. This is safe, quick, and frequently restores Zoom connectivity after a router change or a DNS hiccup.
ipconfig /flushdns
ipconfig /renewRun the commands in an elevated Command Prompt, then restart Zoom and retry the meeting. Microsoft documents ipconfig options like /flushdns and /renew for DNS and DHCP troubleshooting. [✅Source-3]
Network and Firewall Settings That Commonly Block Zoom
If Zoom Error Code 104120 appears on office Wi-Fi, a school network, or any managed environment, focus on outbound rules. Zoom’s guidance is to allow outbound traffic and ensure the firewall permits the return connections established by the client.
| Use Case | Protocol | Ports | Why It Matters for 104120 |
|---|---|---|---|
| Web Sign-In and Core Access | TCP / UDP | TCP 80, 443 and UDP 443 | Basic service reachability. If blocked, the app may never complete the initial handshake. |
| Meetings and Webinars | TCP | 443, 8801, 8802 | Meeting control and media fallback paths. Blocking these can trigger repeated connect attempts. |
| Media Transport (Preferred) | UDP | 3478, 3479, 8801–8810 | Audio/video path reliability. If UDP is restricted, the client may fail or degrade before joining. |
The port values above come directly from Zoom’s published firewall and proxy server settings guidance. If you cannot change the network, share this port list with your network administrator and ask for outbound allowances for Zoom traffic. [✅Source-4]
Proxy and Security Gateway Notes
When a proxy is required, confirm Zoom is set to use the correct proxy mode and that the proxy allows TLS traffic to Zoom domains. If a web security gateway performs SSL inspection, ask your administrator whether Zoom traffic is excluded from interception, as meeting media paths can behave differently than standard web browsing.
Diagnose With Zoom’s Built-In Network Connectivity Tool
When the fix is not obvious, use Zoom’s own diagnostics to learn whether your device can reach Zoom services and where the path breaks. This is especially useful for Error Code 104120 because it separates local issues from network issues fast.
How to Open It
- Open the Zoom desktop app.
- Use the shortcut Ctrl + Alt + Shift + D (Windows) or Cmd + Option + Shift + D (macOS).
- Run a Network Test, then review the results for detected proxy and route information.
Zoom documents the tool, the shortcuts, and the tests it runs (including network information and route tracing). If the tool shows stable connectivity on one network and failures on another, you have a clean, shareable signal for IT. [✅Source-5]
Clean Reinstall When the Client Is Corrupted
If your network is confirmed healthy, updates are current, and Zoom Error Code 104120 persists on every network, treat it as a local client issue. A reinstall replaces damaged components and resets many client-level settings that can interfere with service negotiation.
Reinstall Checklist
- Uninstall Zoom Workplace from your device using the standard OS method.
- Restart the device to clear locked files and services.
- Install the latest version again, then sign in and re-test the meeting.
Zoom provides step-by-step uninstall and reinstall instructions across Windows, macOS, Linux, Android, and iOS. If you are in an organization with special encryption features, follow the standard uninstall path unless your admin recommends a deeper cleanup. [✅Source-6]
FAQ
Does Error Code 104120 Mean My Account Is Blocked?
Error Code 104120 usually behaves like a connectivity problem, not an account status message. If you can sign in on another network or device, your account is likely fine and the issue is the connection path on the affected device or network.
Why Does It Work on Mobile Hotspot but Not on Wi-Fi?
This pattern points to network rules: firewall policies, proxy requirements, DNS filtering, or a security gateway on the Wi-Fi network. Focus on outbound ports and proxy behavior, then re-test.
Which Network Details Should I Share With My IT Team?
Share the time of the failure, your device type, whether it works on a hotspot, and the ports and protocols from the network rules section. If you ran Zoom’s diagnostics, include the results summary (latency, packet loss, proxy detection, and route notes).
Can a VPN or Proxy Trigger Error Code 104120?
Yes. A VPN can change routing and DNS resolution, and a proxy can block or inspect TLS traffic. For a clean test, disable VPN and confirm the Zoom client is set to the right proxy mode for your environment.
Should I Reinstall Zoom Immediately?
Reinstall is most useful after you confirm the network is healthy and Zoom is up to date. If the issue appears only on one network, reinstalling rarely helps because the root cause is network policy.
What If the Error Appears Only When Joining a Specific Meeting?
First, confirm you can join other meetings. If only one meeting fails, test by joining from another network or device. If it succeeds elsewhere, the issue is still likely local connectivity on the failing setup rather than the meeting itself.