FTP passive mode firewall issues
Why FTP PASV fails behind firewalls/NAT and how to configure passive ports correctly.
Diagnose this automatically
Test whether the server allows directory listing with valid credentials.
Shareable output
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FTP uses separate control + data channels. Passive mode requires a range of server ports to be open.
Many “can login but cannot list” failures are passive-mode port issues.
Symptoms
- Auth succeeds but LIST hangs or times out
- Data connection errors after PASV response
- Works on LAN but fails from outside network
Fix checklist
- Configure a fixed passive port range on the server.
- Open that passive range in the firewall/security group.
- Ensure the server advertises the correct public IP in PASV responses (NAT).
- If possible, prefer SFTP to avoid FTP data-channel complexity.
Quick tests
lftp -e 'set ftp:passive-mode true; ls; quit' -u user,pass <host>FTPMonitor Help
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Related
- FTP data connection failed — Why FTP data connections fail and how to troubleshoot passive and active data channel issues.
- FTP directory listing timeout — Why FTP directory listings hang or timeout and how to resolve passive mode firewall problems.
- FTP passive mode not working — Why FTP passive mode fails and how to configure passive ports and NAT correctly.
- FTP EPSV error — Understanding FTP EPSV errors and how to resolve extended passive mode problems.
- FTP timeout during transfer — Why FTP transfers timeout and how to fix idle timeout or firewall issues.
- FTP transfer stalls — Why FTP transfers stall mid-transfer and how to troubleshoot data channel issues.
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