# imrelp: RELP Input Module

Module Name: imrelp

Author: Rainer Gerhards

Provides the ability to receive syslog messages via the reliable RELP protocol. This module requires librelp to be present on the system. From the user’s point of view, imrelp works much like imtcp or imgssapi, except that no message loss can occur. Please note that with the currently supported relp protocol version, a minor message duplication may occur if a network connection between the relp client and relp server breaks after the client could successfully send some messages but the server could not acknowledge them. The window of opportunity is very slim, but in theory this is possible. Future versions of RELP will prevent this. Please also note that rsyslogd may lose a few messages if rsyslog is shutdown while a network connection to the server is broken and could not yet be recovered. Future version of RELP support in rsyslog will prevent that. Please note that both scenarios also exists with plain tcp syslog. RELP, even with the small nits outlined above, is a much more reliable solution than plain tcp syslog and so it is highly suggested to use RELP instead of plain tcp. Clients send messages to the RELP server via omrelp.

## Module Parameters

`Ruleset <name>`
`(requires v7.5.0+)`

  Binds the specified ruleset to all RELP listeners. This can be overridden at the instance level.

## Input Parameters

`Port <port>`

  Starts a RELP server on selected port

`Name <name>`

  Sets a name for the inputname property of this listener. If no name is set, “imrelp” is used by default. Setting a name is not strictly necessary, but can be useful to apply filtering based on which input the message was received from.

`Ruleset <name>`

  Binds specified ruleset to this listener. This overrides the module-level Ruleset parameter.

`tls on/off`

  Default is off

  If set to “on”, the RELP connection will be encrypted by TLS, so that the data is protected against observers. Please note that both the client and the server must have set TLS to either “on” or “off”. Other combinations lead to unpredictable results.

  Attention when using GnuTLS 2.10.x or older

  Versions older than GnuTLS 2.10.x may cause a crash (Segfault) under certain circumstances. Most likely when an imrelp inputs and an omrelp output is configured. The crash may happen when you are receiving/sending messages at the same time. Upgrade to a newer version like GnuTLS 2.12.21 to solve the problem.

`tls.compression on/off`

  Default is off

  The controls if the TLS stream should be compressed (zipped). While this increases CPU use, the network bandwidth should be reduced. Note that typical text-based log records usually compress rather well.

`tls.dhbits <integer>`

  This setting controls how many bits are used for Diffie-Hellman key generation. If not set, the librelp default is used. For secrity reasons, at least 1024 bits should be used. Please note that the number of bits must be supported by GnuTLS. If an invalid number is given, rsyslog will report an error when the listener is started. We do this to be transparent to changes/upgrades in GnuTLS (to check at config processing time, we would need to hardcode the supported bits and keep them in sync with GnuTLS - this is even impossible when custom GnuTLS changes are made...).

`tls.``permittedPeer`()

  Peer Places access restrictions on this listener. Only peers which have been listed in this parameter may connect. The validation bases on the certificate the remote peer presents.

  The peer parameter lists permitted certificate fingerprints. Note that it is an array parameter, so either a single or multiple fingerprints can be listed. When a non-permitted peer connects, the refusal is logged together with it’s fingerprint. So if the administrator knows this was a valid request, he can simple add the fingerprint by copy and paste from the logfile to rsyslog.conf.

  To specify multiple fingerprints, just enclose them in braces like this:

      tls.permittedPeer=["SHA1:...1", "SHA1:....2"]

  To specify just a single peer, you can either specify the string directly or enclose it in braces.

`tls.authMode <mode>`

  Sets the mode used for mutual authentication.

  Supported values are either “fingerprint” or “name”.

  Fingerprint mode basically is what SSH does. It does not require a full PKI to be present, instead self-signed certs can be used on all peers. Even if a CA certificate is given, the validity of the peer cert is NOT verified against it. Only the certificate fingerprint counts.

  In “name” mode, certificate validation happens. Here, the matching is done against the certificate’s subjectAltName and, as a fallback, the subject common name. If the certificate contains multiple names, a match on any one of these names is considered good and permits the peer to talk to rsyslog.

`tls.prioritystring <string>`

  This parameter permits to specify the so-called “priority string” to GnuTLS. This string gives complete control over all crypto parameters, including compression setting. For this reason, when the prioritystring is specified, the “tls.compression” parameter has no effect and is ignored.

  Full information about how to construct a priority string can be found in the GnuTLS manual. At the time of this writing, this information was contained in section 6.10 of the GnuTLS manual.

  Note: this is an expert parameter. Do not use if you do not exactly know what you are doing.

`KeepAlive on/off`

  enable of disable keep-alive packets at the tcp socket layer. The default is to disable them.

`KeepAlive.Probes <number>`

  Default is 0

  The number of unacknowledged probes to send before considering the connection dead and notifying the application layer. The default, 0, means that the operating system defaults are used. This has only effect if keep-alive is enabled. The functionality may not be available on all platforms.

`KeepAlive.Interval <number>`

  Default is 0

  The interval between subsequent keepalive probes, regardless of what the connection has exchanged in the meantime. The default, 0, means that the operating system defaults are used. This has only effect if keep-alive is enabled. The functionality may not be available on all platforms.

`KeepAlive.Time <number>`

  Default is 0

  The interval between the last data packet sent (simple ACKs are not considered data) and the first keepalive probe; after the connection is marked to need keepalive, this counter is not used any further. The default, 0, means that the operating system defaults are used. This has only effect if keep-alive is enabled. The functionality may not be available on all platforms.

### Caveats/Known Bugs

- see description
- To obtain the remote system’s IP address, you need to have at least librelp 1.0.0 installed. Versions below it return the hostname instead of the IP address.

### Sample

This sets up a RELP server on port 20514.

    module(load="imrelp") # needs to be done just once
    input(type="imrelp" port="20514")

### Legacy Configuration Directives

- InputRELPServerBindRuleset <name> (available in 6.3.6+) equivalent to: RuleSet
- InputRELPServerRun <port> equivalent to: Port

### Caveats/Known Bugs

- To obtain the remote system’s IP address, you need to have at least librelp 1.0.0 installed. Versions below it return the hostname instead of the IP address.
- Contrary to other inputs, the ruleset can only be bound to all listeners, not specific ones. This issue is resolved in the non-Legacy configuration format.

Sample:

### Legacy Sample

This sets up a RELP server on port 20514.

    $ModLoad imrelp # needs to be done just once
    $InputRELPServerRun 20514

This documentation is part of the rsyslog project. Copyright © 2008-2014 by Rainer Gerhards and Adiscon. Released under the GNU GPL version 3 or higher.