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When FileZilla cannot connect, check the connection details first, then switch to passive mode and open the server’s passive port range. After that, investigate FTPS certificate or mode mismatches, timeouts, local firewalls, NAT, and IP bans. The sequence below separates login failures from data-channel and directory-listing failures so you can fix the fault without changing unrelated settings.
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Use this diagnostic order first
Make one change at a time and reconnect after each change. This prevents a successful fix from being hidden by several simultaneous edits.
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- Confirm the hostname, protocol, port, encryption requirement, username, and password supplied by the server administrator.
- In FileZilla, select passive transfer mode.
- If you administer the server or router, configure and forward a passive port range.
- Match the FTPS mode and port to the server, and validate its certificate.
- Investigate the exact timeout message, especially whether it appears during login, after login, or while listing a directory.
- Check your computer’s firewall or antivirus, then ask the host whether your public IP has been blocked.
- Update FileZilla and retest with a deliberately simple connection before restoring stricter settings.
Verify the host, protocol, port, and credentials
A wrong protocol or port can look like a network outage. Ask the server owner for the connection type and whether encryption is mandatory; do not infer these values from a web address.
| Connection type | FileZilla host and port | What it means |
|---|---|---|
| Plain FTP | Hostname; port 21 | Control traffic and, unless separately protected, file data are unencrypted. |
| Explicit FTPS (AUTH TLS) | Enter the host with the FTPES:// prefix; port 21 |
The session starts as FTP and upgrades the control connection to TLS. |
| Implicit FTPS | Enter the host with the FTPS:// prefix; normally port 990 |
TLS is required immediately when the connection opens. |
These protocol, prefix, and port distinctions are described in the FileZilla FTP over TLS documentation. A server configured for explicit FTPS will generally reject an implicit-FTPS attempt on port 990, while an implicit server will not complete an explicit handshake on port 21.
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Enter the details in Site Manager
- Open File > Site Manager and select the saved site, or create a new entry.
- On the connection details page, enter the exact hostname. Do not add a path such as
/public_htmluntil a basic connection works. - Choose the protocol and encryption setting that the administrator specified. If you use a URL-style host prefix, ensure it agrees with the selected protocol rather than overriding it accidentally.
- Enter the supplied port. Leave it blank only when the server documentation explicitly says to use the protocol default.
- Select the appropriate logon type and enter the username and password exactly, including capitalization. Anonymous access is not interchangeable with a named account.
- Connect and read the message log. A failure before a welcome banner points to DNS, routing, port, or firewall problems; a rejection after the banner usually indicates credentials or account policy.
FileZilla menu labels can change between releases, so use the current wording in your installed version while keeping the same settings sequence.
Switch FileZilla to passive transfer mode
Passive mode is the best first response when FileZilla connects but cannot retrieve a directory listing or transfer a file. In passive mode, the client opens both the control connection and the data connection, which usually works better through home and office routers.
- Open Edit > Settings > Connection > FTP.
- Set Transfer Mode to Passive.
- If your release offers Allow fall back to other transfer mode on failure, enable it only as a diagnostic fallback. A fallback can make an intermittent setup appear to work while leaving the underlying firewall rule unresolved.
- Save the setting, disconnect, reconnect, and request a directory listing.
Passive mode does not by itself open the server’s data ports. The server must advertise a reachable passive port, and its firewall and any intervening NAT device must permit that connection.
Configure the server’s passive port range and NAT
If the login succeeds but the listing hangs, the control channel is working and the data channel is the likely failure point. On a server you control, define a fixed passive range instead of allowing an unrestricted set of ephemeral ports.
- The FileZilla network-configuration guidance says a range of 50 ports should be sufficient in most cases.
- That guidance recommends choosing ports at or above 50000 for passive FTP.
- Permit the complete range in the server’s operating-system firewall and in any cloud or hosting firewall.
- If the server is behind NAT, forward every port in the range from the public address to the machine running the FTP service.
- Configure the server to advertise its public address when it is behind NAT; advertising a private address such as 192.168.x.x sends the client to an unreachable destination.
For example, a 50-port range beginning at 50000 must have all 50 ports allowed and forwarded, not only the first port. The exact configuration screen depends on the FTP server, so apply the principle to that product’s current documentation. After changing it, restart or reload the FTP service if required, then test from a network outside the server’s LAN.
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Fix FTPS and TLS negotiation errors
TLS failures occur before a usable encrypted session is established, or when the server cannot protect the data channel after login. Common causes are an expired certificate, a self-signed certificate that the client does not trust, a certificate whose hostname does not match the address you entered, and selecting explicit FTPS for an implicit server (or the reverse).
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Recheck the protocol table above against the provider’s instructions. Explicit FTPS normally uses port 21 and starts with an FTP connection that sends AUTH TLS. Implicit FTPS normally uses port 990 and expects TLS immediately. Changing only the port while leaving the wrong encryption mode selected will still fail.
Decide how to handle the certificate
When FileZilla displays a certificate prompt, inspect the subject, issuer, validity dates, and hostname. A self-signed certificate can be legitimate on a private server, but accept it only after confirming its fingerprint or identity with the administrator. Do not bypass a hostname mismatch merely to make the connection work; instead, connect using the hostname covered by the certificate or have the administrator issue a corrected certificate.
Check data-channel protection
FTP over TLS can protect only the control channel (PROT C) or both control and data channels (PROT P). The FileZilla TLS documentation explains this distinction. If the server requires encrypted data, a control-only setting can allow login but fail at listing or transfer. Select the server’s required protection level in its current FileZilla site settings.
Interpret “421 cleartext sessions not accepted”
This response means the server is refusing an unencrypted session. Community reports commonly interpret it as a requirement for explicit FTP over TLS, but that interpretation is not confirmed by a primary FileZilla reference. Treat it as a prompt to obtain the server’s exact FTPS mode and port, then configure those values rather than guessing.
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FileZilla’s issue tracker records failures caused by servers that are not correctly configured for FTP over TLS; see ticket #9995 for an example. If the certificate and client settings are correct, the server administrator may need to repair its TLS configuration.
Resolve “Connection timed out after 20 seconds of inactivity”
The message indicates that FileZilla received no qualifying response during the timeout interval. The location in the log matters:
- Before the welcome banner: suspect DNS, routing, a blocked control port, or a server that is offline.
- During TLS negotiation: suspect the wrong FTPS mode or port, certificate validation, or a server-side TLS failure.
- After login while listing or transferring: suspect passive ports, NAT, a firewall, or an idle connection being discarded.
A hosting knowledge-base article documents this exact 20-second message and troubleshooting context at this FileZilla timeout article. The default value and message are not an official FileZilla specification and may differ by release or environment.
Increase the client timeout only after fixing connectivity
In FileZilla’s settings, locate the connection timeout value and raise it cautiously if a slow server needs more time to answer. A third-party guide reports that changing 20 seconds to 60 seconds resolves the problem for many users, but that is anecdotal rather than a measured statistic. A longer timeout cannot open a blocked port; it only makes FileZilla wait longer.
Account for idle-connection drops
Routers and firewalls may silently close an idle control or data connection. This explains the pattern in which small files succeed but a large transfer eventually times out: the connection sits without traffic long enough for an intermediary to discard it. Enable a keep-alive option if your FileZilla release provides one, or adjust the router, firewall, or server idle policy. Do not confuse an idle drop with a throughput problem; the remedy is to keep the session active or extend the intermediary’s idle limit.
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When login works but directory listing hangs
A successful username/password exchange proves only that the control channel reached the server. FileZilla then opens a separate data connection for the directory listing. A FileZilla forum report documents this login-then-timeout symptom; forum reports are useful for recognizing the pattern but are not authoritative fixes.
- Confirm that the transfer mode is passive.
- Check the server’s advertised passive address and port range.
- Allow and forward the entire range through host and network firewalls.
- Retry from a different network, such as a mobile hotspot, to distinguish a local firewall from a server-side block.
- Review the FileZilla log for the server’s
227or229passive-response line and compare the advertised address and port with the rule you opened.
If the server advertises a private address to an Internet client, or a port outside the permitted range, the administrator must correct the server configuration; changing the client timeout will not solve it.
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Test local security software safely
Desktop firewalls and antivirus network filters can block FileZilla or its data connections. Temporarily pause the relevant network inspection feature only long enough to perform a controlled test, then turn it back on. If the test succeeds, create a narrow allow rule for the FileZilla application and the required network profile instead of leaving protection disabled. On a managed work computer, ask the administrator to make the rule.
Consider a server-side IP ban
If the same site worked previously and now rejects every attempt from one connection, the server may have blocked your public IP after repeated failed logins. Automated tools such as fail2ban are one possible cause. Ask the hosting or server administrator to check its authentication and ban logs and to remove an erroneous block. Changing your FileZilla password repeatedly can extend a ban if the saved credentials are wrong.
Update the client
Install the current FileZilla release from its official distribution channel before deeper troubleshooting. Updates can correct TLS-library, certificate, and protocol-compatibility issues, but they do not replace correct server settings.
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Read the FileZilla log by symptom
| Log symptom | Most likely location of the fault | Next check |
|---|---|---|
| “Could not resolve host” or no address returned | Hostname or DNS | Verify spelling and ask whether the DNS record is active; test the supplied hostname rather than an assumed IP. |
| “Connection refused” immediately | Wrong port, stopped service, or server firewall | Confirm port 21 versus 990 (or the custom port supplied by the administrator). |
| “Connection timed out” before login | Routing, firewall, NAT, or unavailable service | Test from another network and have the administrator inspect the control-port rule. |
| TLS handshake or certificate error | Certificate or explicit/implicit mismatch | Validate hostname and dates; match the server’s FTPS mode and port. |
| Login rejected | Username, password, account policy, or IP ban | Re-enter credentials and ask the administrator to check account and ban logs. |
| Login succeeds, then listing times out | Passive data channel, NAT, or data-port firewall | Use passive mode and repair the advertised passive range and forwarding. |
| Small transfers work; large transfers stop | Idle timeout or intermediary closing a long-lived connection | Use keep-alives and review router, firewall, and server idle limits. |
A practical decision path for common situations
Nothing connects from any network
Reconfirm the hostname and port with the server owner, then verify that the FTP service is running and reachable. If the server is behind NAT, the control port must be forwarded to the correct internal host. A client-side change cannot repair a stopped service or a missing provider firewall rule.
It connects at home but not at work
The office firewall or proxy is the differentiator. Ask the network administrator whether outbound FTP, FTPS, or passive data ports are restricted. Do not switch to active mode blindly: active mode can require inbound connections to your workstation and is often harder to permit on managed networks.
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Compare the two paths for router NAT, DNS filtering, and outbound firewall rules. Ensure the server’s passive range is reachable from the public Internet and that the home router is not rewriting or blocking the FTP data connection.
Plain FTP works but FTPS does not
Check the certificate and the explicit-versus-implicit selection first. If the server requires encrypted data, ensure the data channel uses PROT P. A successful unencrypted test does not prove that the server’s TLS configuration is valid.
Prevent the next failed connection
- Keep a written record of the server hostname, protocol, port, encryption requirement, username, and passive range.
- Save the site in Site Manager so every connection uses the same verified settings.
- Prefer passive mode for clients behind NAT, and document the server’s fixed passive range.
- Use a certificate whose hostname matches the address users enter, and renew it before expiry.
- Allow only the required control and passive data ports in host and network firewalls.
- Monitor failed-login bans so a mistyped password does not lock out a legitimate address.
- Retest after FileZilla, server, router, or firewall updates because menu labels and security defaults can change.
The fastest reliable fix is therefore a matched pair of configurations: FileZilla must use the server’s exact protocol and port, while the server and network must expose a correctly advertised passive data path. Once those agree, certificate validation, timeout tuning, and security rules can be adjusted without masking the original fault.
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