Manage Slack connection issues

This article is for IT or network administrators in charge of managing an organization’s network. If you ever need a hand with troubleshooting connection issues, we're here to help.

If you’re not a network admin, check out our guide for troubleshooting Slack’s most common connection issues.


Desktop app

Older versions of the Slack desktop app can result in connection issues and even broken features. 


Network settings

Slack must have a persistent connection between our messaging server and members’ apps or browsers. To do so, Slack uses WebSockets over port 443.

Proxies and firewalls can sometimes interrupt this connection. If someone using Slack can’t connect from a specific location, or if there’s a WebSocket failure in our Slack connection test, you’ll need to adjust your proxy or firewall to keep the connection to Slack open. Here’s how:

  • Whitelist the following domains: * * * * * * *
  • Check if your proxy is running SSL decryption. If it is, the proxy must either support WebSockets, or you’ll need to exempt the following domains: *

Network administrators can restrict access to specific Slack workspaces using proxy header injection on their network. The header injection solution has the same network requirements as above. 

Additionally, network administrators can restrict access to a specific Slack workspace using exact URL whitelisting. To view a list of all URLs, visit and whitelist any URLs you'd like. 

Both of these solutions ensure full product functionality alongside controlled workspace access.  

Network environment

Certain software, security settings, and firewalls can interfere with Slack connections:


  • Avira Browser Safety
  • Browser Guard
  • Pokki
  • Smart Panel
  • Spyware and adware
  • Visual Discovery by Superfish

Antivirus or ad-blocking software

  • Avast
  • McAfee
  • Norton
  • AVG
  • AdBlock Plus


Temporarily turning off your antivirus or ad-blocking software will let you troubleshoot your connection issue. If this fixes your issue, add * to your software’s exemption list before re-enabling.

Still having trouble? If you’re unable to resolve your connection issue, get in touch and include a Net Log if possible. 

Check connections

  1. Sign in to your Slack workspace.
  2. Visit to check your network's connection to Slack.
  3. Under the WebSockets section, note the results for WebSocket (Flannel [Primary]) and WebSocket (Flannel [Backup]).

    • A successful test will show the  checked circle icon.
    • A failed test will show the   warning icon.
Who can use this feature?
  • Workspace Owners and Admins
  • FreeStandardPlus, and Enterprise Grid plans

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