TCP connection timeout (firewall issue)
Why FTP/SFTP connections time out and how to diagnose firewall, routing, or allowlist blocking.
Diagnose this automatically
Test whether the network port is reachable before investigating authentication problems.
Shareable output
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A TCP timeout means your request didn’t get a response at all.
This is usually a firewall/security-group block, routing issue, or the service is only reachable from a private network/VPN.
Common causes
- Inbound firewall/security group blocks the port
- Server is private/internal-only (not reachable from the public internet)
- IP allowlist missing your source IP
- Network routing/VPN required
- Upstream device silently drops packets
Fix checklist
- Confirm protocol + port with the vendor/admin.
- Ask the server owner to verify firewall/security-group rules on the server side.
- Check IP allowlist requirements and add your source IP.
- If the host is internal, run checks from inside the network/VPN.
Quick commands
nc -vz <host> <port>
telnet <host> <port>Related
- TCP connection failed — General TCP failure causes when connecting to FTP, FTPS, or SFTP services.
- DNS resolution failed — Why FTP/SFTP DNS lookups fail and how to fix hostname resolution issues quickly.
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