Adapter behavior when the -FIREWALL command Is present
A firewall is used in order to isolate and restrict some computers from reaching other computers.
If a firewall comes into discussion, only a small part of the FTP adapter is aware of the presence of the firewall.
Without a firewall, the start of a file transfer begins with:
- Establish a Socket connection to the remote host.
- Issue the USER command over the connection.
- Issue the PASS command over the connection.
When a firewall is used, more steps are performed in the beginning of the file transfer.
These steps are dependent on the method specified in the last part of the -FIREWALL command.
OPEN
- Establish a Socket connection to the firewall host
- Issue the following command over the connection in this
order:
OPEN ftp_host USER ftp_user PASS ftp_pass
SITE
- Establish a Socket connection to the firewall host
- Issue the following command over the connection in this
order:
USER fw_user PASS fw_pass SITE ftp_host USER ftp_user PASS ftp_pass
TRANSPARENT
- Establish a Socket connection to the remote host
- Issue the following command over the connection in this
order:
USER fw_user PASS fw_pass USER ftp_user PASS ftp_pass
USERFW
- Establish a Socket connection to the firewall host
- Issue the following command over the connection in this
order:
USER ftp_user@ftp_host fw_user PASS ftp_pass USER ftp_user PASS ftp_pass
USERFWPASS
- Establish a Socket connection to the firewall host
- Issue the following command over the connection in this
order:
USER ftp_user@fw_user@ftp_host PASS ftp_pass@fw_pass
USERLOGON or USER
- Establish a Socket connection to the firewall host
- Issue the following command over the connection in this
order:
USER fw_user PASS fw_pass USER ftp_user@ftp_host PASS ftp_pass USER
USERLOGONFW or USERFW
- Establish a Socket connection to the firewall host
- Issue the following command over the connection in this
order:
USER fw_user@ftp_host PASS fw_pass USER ftp_user PASS ftp_pass