DNS Resolution Failing — Upstream Resolver Unreachable

Firewall rule block detected — legitimate traffic is being denied by a firewall ACL or security policy. This may be caused by an overly restrictive rule, a recent policy change, or an implicit deny catching traffic that should be permitted. Blocked traffic can prevent application connectivity, break integrations, and disrupt business operations.

1. Identify the specific firewall rule or ACL entry causing the block from the firewall logs (note rule ID, source, destination, port). 2. Verify whether the traffic should be permitted — confirm with the application owner or network documentation. 3. If the block is a false positive, create or modify a firewall rule to allow the traffic with the principle of least privilege. 4. Check for recent firewall policy changes that may have inadvertently blocked the traffic. 5. Test the fix by re-initiating the blocked connection and verifying it passes through the firewall.