TCP Syslog Input Module

Module Name: imtcp

Author: Rainer Gerhards <rgerhards@adiscon.com>

Multi-Ruleset Support: since 4.5.0 and 5.1.1

Description:

Provides the ability to receive syslog messages via TCP. Encryption is natively provided by selecting the approprioate network stream driver and can also be provided by using stunnel (an alternative is the use the imgssapi module).

Multiple receivers may be configured by specifying $InputTCPServerRun multiple times. This is available since version 4.3.1, earlier versions do NOT support it.

Configuration Directives:

$InputTCPServerAddtlFrameDelimiter <Delimiter>
This directive permits to specify an additional frame delimiter for plain tcp syslog. The industry-standard specifies using the LF character as frame delimiter. Some vendors, notable Juniper in their NetScreen products, use an invalid frame delimiter, in Juniper's case the NUL character. This directive permits to specify the ASCII value of the delimiter in question. Please note that this does not guarantee that all wrong implementations can be cured with this directive. It is not even a sure fix with all versions of NetScreen, as I suggest the NUL character is the effect of a (common) coding error and thus will probably go away at some time in the future. But for the time being, the value 0 can probably be used to make rsyslog handle NetScreen's invalid syslog/tcp framing. For additional information, see this forum thread.
If this doesn't work for you, please do not blame the rsyslog team. Instead file a bug report with Juniper!
Note that a similar, but worse, issue exists with Cisco's IOS implementation. They do not use any framing at all. This is confirmed from Cisco's side, but there seems to be very limited interest in fixing this issue. This directive can not fix the Cisco bug. That would require much more code changes, which I was unable to do so far. Full details can be found at the Cisco tcp syslog anomaly page.
$InputTCPServerDisableLFDelimiter <on/off> (available since 5.5.3)
Industry-strandard plain text tcp syslog uses the LF to delimit syslog frames. However, some users brought up the case that it may be useful to define a different delimiter and totally disable LF as a delimiter (the use case named were multi-line messages). This mode is non-standard and will probably come with a lot of problems. However, as there is need for it and it is relatively easy to support, we do so. Be sure to turn this setting to "on" only if you exactly know what you are doing. You may run into all sorts of troubles, so be prepared to wrangle with that!
$InputTCPServerNotifyOnConnectionClose [on/off] (available since 4.5.5)
instructs imtcp to emit a message if the remote peer closes a connection.
Important: This directive is global to all listeners and must be given right after loading imtcp, otherwise it may have no effect.
$InputTCPServerKeepAlive <on/off>
enable of disable keep-alive packets at the tcp socket layer. The default is to disable them.
$InputTCPServerRun <port>
Starts a TCP server on selected port
$InputTCPFlowControl <on/off>
This setting specifies whether some message flow control shall be exercised on the related TCP input. If set to on, messages are handled as "light delayable", which means the sender is throttled a bit when the queue becomes near-full. This is done in order to preserve some queue space for inputs that can not throttle (like UDP), but it may have some undesired effect in some configurations. Still, we consider this as a useful setting and thus it is the default. To turn the handling off, simply configure that explicitely.
$InputTCPMaxListeners <number>
Sets the maximum number of listeners (server ports) supported. Default is 20. This must be set before the first $InputTCPServerRun directive.
$InputTCPMaxSessions <number>
Sets the maximum number of sessions supported. Default is 200. This must be set before the first $InputTCPServerRun directive
$InputTCPServerStreamDriverMode <number>
Sets the driver mode for the currently selected network stream driver. <number> is driver specifc.
$InputTCPServerInputName <name>
Sets a name for the inputname property. If no name is set "imtcp" 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.
$InputTCPServerStreamDriverAuthMode <mode-string>
Sets the authentication mode for the currently selected network stream driver. <mode-string> is driver specifc.
$InputTCPServerStreamDriverPermittedPeer <id-string>
Sets permitted peer IDs. Only these peers are able to connect to the listener. <id-string> semantics depend on the currently selected AuthMode and network stream driver. PermittedPeers may not be set in anonymous modes.
$InputTCPServerBindRuleset <ruleset>
Binds the listener to a specific ruleset.

Caveats/Known Bugs:

module always binds to all interfaces
can not be loaded together with imgssapi (which includes the functionality of imtcp)

Example:

This sets up a TCP server on port 514 and permits it to accept up to 500 connections:

Note that the parameters (here: max sessions) need to be set before the listener is activated. Otherwise, the parameters will not apply.

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