# omdtls: Output Module for DTLS Protocol over UDP

Module Name: | omdtls
Author: | Andre Lorbach <alorbach@adiscon.com>
Available since: | v8.2402.0

## Purpose

The omdtls module for rsyslog is designed to securely transmit syslog data over a network using the Datagram Transport Layer Security (DTLS) protocol. This module leverages the robustness and security features of OpenSSL to provide an encrypted transport mechanism for syslog messages via UDP.

DTLS, being an adaptation of TLS for datagram-based protocols, offers integrity, authenticity, and confidentiality for messages in transit. The omdtls module is particularly useful in environments where secure transmission of log data is crucial, such as in compliance-driven industries or when transmitting across untrusted networks.

By operating over UDP, omdtls offers the benefits of lower latency and reduced protocol overhead compared to TCP-based transport, making it well-suited for high-throughput logging scenarios or in networks where connection-oriented protocols may face challenges.

## Requirements

To send messages by DTLS you will need to fulfill the following requirements:

- OpenSSL 1.0.2 or Higher

## Configuration Parameters

Note

Parameter names are case-insensitive.

### Module Parameters

#### Template

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
word | RSYSLOG_TraditionalForwardFormat | no | `$ActionForwardDefaultTemplateName`

Sets a non-standard default template for this module.

### Action Parameters

#### target

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
word | none | no | none

Specifies the target hostname or IP address to send log messages to.

#### port

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
word | 4433 | yes | none

Defines the port number on the target host where log messages will be sent. The default port number for DTLS is 4433.

#### tls.AuthMode

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
string | none | no | none

Sets the mode of authentication to be used. Supported values are either “fingerprint“, “name” or “certvalid“.

Fingerprint: Authentication based on certificate fingerprint. Name: Authentication based on the subjectAltName and, as a fallback, the subject common name. Certvalid: Requires a valid certificate for authentication. Certanon: Anything else will allow anonymous authentication (no client certificate).

#### tls.cacert

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
string | none | no | none

The CA certificate that is being used to verify the client certificates. Has to be configured if tls.authmode is set to “fingerprint“, “name” or “certvalid“.

#### tls.mycert

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
string | none | no | none

Specifies the certificate file used by omdtls. This certificate is presented to peers during the DTLS handshake.

#### tls.myprivkey

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
string | none | no | none

The private key file corresponding to tls.mycert. This key is used for the cryptographic operations in the DTLS handshake.

#### tls.tlscfgcmd

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
string | none | no | none

Used to pass additional OpenSSL configuration commands. This can be used to fine-tune the OpenSSL settings by passing configuration commands to the openssl libray. OpenSSL Version 1.0.2 or higher is required for this feature. A list of possible commands and their valid values can be found in the documentation: https://docs.openssl.org/1.0.2/man3/SSL_CONF_cmd/

The setting can be single or multiline, each configuration command is separated by linefeed (n). Command and value are separated by equal sign (=). Here are a few samples:

### Example 1

This will allow all protocols except for SSLv2 and SSLv3:

    tls.tlscfgcmd="Protocol=ALL,-SSLv2,-SSLv3"

### Example 2

This will allow all protocols except for SSLv2, SSLv3 and TLSv1. It will also set the minimum protocol to TLSv1.2

    tls.tlscfgcmd="Protocol=ALL,-SSLv2,-SSLv3,-TLSv1
    MinProtocol=TLSv1.2"

#### Template

type | default | mandatory | `obsolete legacy` directive
--- | --- | --- | ---
word | RSYSLOG_TraditionalForwardFormat | no |

Sets a non-standard default template for this action instance.

## Statistic Counter

This plugin maintains global statistics for omdtls that accumulate all action instances. The statistic origin is named “omdtls” with following counters:

- submitted - This counter tracks the number of log messages that have been successfully send by the current output instance.

- failures - This counter tracks the number of log messages that have been failed to send to the target server.

These statistics counters are updated in real-time by the rsyslog output module as log data is processed, and they provide valuable information about the performance and operation of the input module.

For multiple actions using statistics callback, there will be one record for each action.

## Examples

### Example 1: Basic

The following sample does the following: - loads the omdtls module - Sends all syslog messages to 192.168.2.1 by DTLS on port 4433.

    module(load="omdtls")
    action(type="omdtls" name="omdtls" target="192.168.2.1" port="4433")

### Example 2: Message throttling

The following sample does the following:

- loads the omdtls module

- Sends all syslog messages to 192.168.2.1 by DTLS on port 4433.

- Slows down sending to avoid package loss due the nature of UDP. In this sample, using dequeueSlowDown 1000 will limit the messages per second to 1000.

    module(load="omdtls")
    action(type="omdtls"
        name="omdtls"
        target="192.168.2.1"
        port="4433"
        queue.type="FixedArray"
        queue.size="100000"
        queue.dequeueBatchSize="1"
        queue.minDequeueBatchSize.timeout="1000"
        queue.timeoutWorkerthreadShutdown="1000"
        queue.timeoutshutdown="1000"
        queue.dequeueSlowDown="1000"
    )

See also

Help with configuring/using `Rsyslog`:

- Mailing list - best route for general questions

- GitHub: rsyslog source project - detailed questions, reporting issues that are believed to be bugs with `Rsyslog`

See also

Contributing to `Rsyslog`:

- Source project: rsyslog project README.

- Documentation: rsyslog-doc project README

Copyright 2008-2023 Rainer Gerhards (Großrinderfeld), and Others.