Impcap: network traffic capture¶

Module Name:	impcap
Author:	Theo Bertin <theo.bertin@advens.fr>

Purpose¶

Impcap is an input module based upon tcpdump’s libpcap library for network traffic capture.

Its goal is to capture network traffic with efficiency, parse network packets metadata AND data, and allow users/modules to make full use of it.

Configuration Parameters¶

Note

Parameter names are case-insensitive

Module Parameter¶

metadata_container¶

type	default	mandatory	`obsolete legacy` directive
word	!impcap	no	none

Defines the container to place all the parsed metadata of the network packet.

Warning

if overwritten, this parameter should always begin with ‘!’ to define the JSON object accompanying messages. No checks are done to ensure that and not complying with this rule will prevent impcap/rsyslog from running, or will result in unexpected behaviours.

data_container¶

type	default	mandatory	`obsolete legacy` directive
word	!data	no	none

Defines the container to place all the data of the network packet. ‘data’ here defines everything above transport layer in the OSI model, and is a string representation of the hexadecimal values of the stream.

Warning

snap_length¶

type	default	mandatory	`obsolete legacy` directive
number	65535	no	none

Defines the maximum size of captured packets. If captured packets are longer than the defined value, they will be capped. Default value allows any type of packet to be captured entirely but can be much shorter if only metadata capture is desired (500 to 2000 should still be safe, depending on network protocols). Be wary though, as impcap won’t be able to parse metadata correctly if the value is not high enough.

Input Parameters¶

interface¶

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

This parameter specifies the network interface to listen to. If ‘interface’ is not specified, ‘file’ must be in order for the module to run.

Note

The name must be a valid network interface on the system (such as ‘lo’). see Supported interface types for an exhaustive list of all supported interface link-layer types.

file¶

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

This parameter specifies a pcap file to read. The file must respect the pcap file format specification. If ‘file’ is not specified, ‘interface’ must be in order for the module to run.

Warning

This functionality is not intended for production environments, it is designed for development/tests.

promiscuous¶

type	default	mandatory	`obsolete legacy` directive
boolean	off	no	none

When a valid interface is provided, sets the capture to promiscuous for this interface.

Warning

Setting your network interface to promiscuous can come against your local laws and regulations, maintainers cannot be held responsible for improper use of the module.

filter¶

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

Set a filter for the capture. Filter semantics are defined on pcap manpages.

tag¶

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

Set a tag to messages coming from this input.

ruleset¶

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

Assign messages from this input to a specific Rsyslog ruleset.

no_buffer¶

type	default	mandatory	`obsolete legacy` directive
boolean	off	no	none

Disable buffering during capture. By default, impcap asks the system to bufferize packets (see parameters buffer_size, buffer_timeout and packet_count), this parameter disables buffering completely. This means packets will be handled as soon as they arrive, but impcap will make more system calls to get them and might miss some depending on the incoming rate and system performances.

buffer_size¶

type	default	mandatory	`obsolete legacy` directive
number (octets)	15740640	no	none

Set a buffer size in bytes to the capture handle. This parameter is only relevant when no_buffer is not active, and should be set depending on input packet rates, buffer_timeout and packet_count values.

buffer_timeout¶

type	default	mandatory	`obsolete legacy` directive
number (ms)	10	no	none

Set a timeout in milliseconds between two system calls to get bufferized packets. This parameter prevents low input rate interfaces to keep packets in buffers for too long, but does not guarantee fetch every X seconds (see pcap manpage for more details).

packet_count¶

type	default	mandatory	`obsolete legacy` directive
number	5	no	none

Set a maximum number of packets to process at a time. This parameter allows to limit batch calls to a maximum of X packets at a time.

Supported interface types¶

Impcap currently supports IEEE 802.3 Ethernet link-layer type interfaces. Please contact the maintainer if you need a different interface type !

Support: rsyslog Assistant | GitHub Discussions | GitHub Issues: rsyslog source project

Contributing: Source & docs: rsyslog source project