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Stunnel Configuration

Default Stunnel configuration:

Stunnel default config.png

Stunnel configuration field explanation table:

Field Name Value Description
Enabled yes | no; Default: no Enables the Stunnel configuration.
Operating Mode Client | Server; Default: "" Specifies whether this configuration will be used for Stunnel client or server.
Listen IP ip | host; Default: "" OPTIONAL Specifies which IP address or host should Stunnel listen to. If left empty, defaults to localhost.
Listen Port port (integer [0..65535]); Default: "" Specifies TCP port which Stunnel should listen to. Port cannot be taken by another service!
Connect IP's [host:]port; Default: "" Uses the standard host:port convetion (e.g.; localhost:6001). Host part can be emmited - empty host part defaults to localhost. Must contain at least one item. If multiple options are specified, remote address is chosen using a round-robin algorithm.
TLS Cipher None | Secure | Custom Select permitted TLS ciphers (TLSv1.2 and below). If custom is selected, a new field appears to enter custom ciphers.
Allowed TLS Ciphers Cipher[:Cipher]..; Default: "" Only appears if a Custom TLS Cipher is selected
A colon-delimited TLS cipher list (e.g. DES-CBC3-SHA:IDEA-CBC-MD5)
Application Protocol Not specified | Connect | SMTP; Default: Not specified CLIENT SIDE ONLY

This option enables initial, protocol-specific negotiation of the TLS encryption. The protocol option should not be used with TLS encryption on a separate port.

If Connect or SMTP is selected, more customization fields appear.
Protocol Authentication Connect: Basic | NTLM; Default: Basic SMTP: Plain | Login; Default: Plain CLIENT SIDE ONLY

Options depend on the selected protocol

Authentication type for the protocol negotiations.
Protocol Domain domain (text); Default: "" CLIENT SIDE ONLY

Only appears if a Connect protocol is selected

Domain for the protocol negotiations.
Protocol Host host:port; Default: "" CLIENT SIDE ONLY

Only appears if a Connect protocol is selected

Destination address for the protocol negotiations.

Specifies the final TLS server to be connected to by the proxy, and not the proxy server directly connected by Stunnel. The proxy server should be specified with the connect option.
Protocol Username username (text); Default: "" CLIENT SIDE ONLY

Only appears if a protocol is selected

Username for the protocol negotiations.
Protocol Password password (text); Default: "" CLIENT SIDE ONLY

Only appears if a protocol is selected

Password for the protocol negotiations.
Verification None | Verify Chain | Verify Peer; Default: None Verification type. Verify Chain verifies connections against a Certificate Authority (CA) file, while Verify Peer verifies connections against a list of approved certificates.
Verification file file; Default: "" Only appears if a verification type is selected

File which is used to verify peer(s) or a peer chain. A different type of file is expected depending on the verification type selected:

Verify Chain: Expects a CA (Certificate Authority) file.

Verify Peer: Expects a file with one (or more, concatenated) peer certificate(s).
Certificate File file; Default: "" Mandatory for a server configuration. Optional for a client configuration

The parameter specifies the file containing certificates used by stunnel to authenticate itself against the remote client or server.

The file should contain the whole certificate chain starting from the actual server/client certificate, and ending with the self-signed root CA certificate.

Can be a certificate only, or both certificate and private key concatenated into a single file.
Private Key file; Default: Certificate File Can be skipped if the Certificate File is appended with the private key

Must be uploaded if the Certificate File does not contain the private key

A private key, required to authenticate the certificate owner.

After setting the parameters, click the Save button; otherwise, changes will not be saved. Some parameters will be shown in the configuration list table.

Stunnel Global Configuration

Default Stunnel global configuration:

Stunnel default global config.png

Stunnel global configuration field explanation table:

Field Name Value Description
Enabled yes | no; Default: no Enables/activates all the enabled Stunnel configurations.
Debug Level integer [0..7]; Default: 5 Debugging level. Level is one of the syslog level names or numbers emerg (0), alert (1), crit (2), err (3), warning (4), notice (5), info (6), or debug (7). All logs for the specified level and all levels numerically less than it will be shown. Use 7 for greatest debugging output.
Use alternative config yes | no; Default: no Enable alternative configuration option (Config upload). Be aware that when using alternative configuration, all configurations in Stunnel Configuration section will be skipped.
Upload alternative config file; Default: "" Only appears if the "Use alternative config" is enabled
Upload the alternative Stunnel configuration file.


The router can have multiple configurations set up and enabled at the same time. Note that if at least one configuration is not set correctly, none of them will be enabled, despite the "Enabled" flag being marked.

Also, you must mark the global "Enabled" flag to actually enable all the individually marked configurations.

See also