Splunk Stream

Installation and Configuration Manual

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Configure Stream forwarder

There are two types of configuration that apply to Stream forwarder:

  • Configure Streams: The Configure Streams UI lets you create and configure the specific network data "streams" that you want to capture. These stream configurations are sent at regular intervals to the streamfwd binary in Splunk_TA_stream where data capture actually occurs. You can access the Configure Streams UI in the Splunk App for Stream main menu in Splunk Web. For more information, see "Configure Streams" in the Splunk App for Stream User Manual.
  • streamfwd.xml: The streamfwd.xml configuration file lets you specify system-level data capture parameters for the streamfwd binary. You can access streamfwd.xml from the command line at $SPLUNK_HOME/etc/apps/Splunk_TA_stream/default. For more information, see Configure streamfwd.xml.

Verify streamfwd can communicate with splunk_app_stream

Before you configure stream data capture in the Configure Streams UI, make sure that the streamfwd binary can communicate with splunk_app_stream. To do so, confirm that the local inputs.conf file for Splunk_TA_stream contains the correct location of your splunk_app_stream installation.

1. Open $SPLUNK_HOME/etc/apps/Splunk_TA_stream/local/inputs.conf.

2. Confirm that the [streamfwd://streamfwd] stanza contains the correct location (URI) of your splunk_app_stream installation.

For example:

splunk_stream_app_location = https://localhost:8000/en-us/custom/splunk_app_stream/
disabled = 0

Specify the location of splunk_app_stream

You specify the location (URI) of your splunk_app_stream installation when you create a Wire Data modular input for your Stream data in Splunk Enterprise. The streamfwd binary uses this location to communicate with the splunk_app_stream over HTTP port 8000. splunk_app_stream stores the location that you specify in the local inputs.conf file of Splunk_TA_stream. See How streamfwd communicates with splunk_app_stream.

1. Go to Settings > Data Inputs > Wire Data.

2. Click New.

3. Enter a Name for your Wire Data modular input. For example "streamfwd."

4. Enter the URI (including the full path) to your splunk_app_stream installation. The URI must specify protocol, server, and port variables in the following syntax:


For example:


Note: The splunk_app_stream location URI only supports http and https protocols.

Note: If you enable SSL for the Stream forwarder, you must change the URI path to specify https. If you change the http port, you must change the URI path to specify the new port.

Configure Stream forwarder identifier

If using a deployment server, be aware that when you set or modify the stream_forwarder_id of a specific Stream forwarder while a streamfwd process is running, you must restart the universal forwarder for the changes to the stream_forwarder_id to apply. Further, note that multiple Stream forwarder deployments can share the same stream_forwarder_id.

Configure streamfwd.xml

The streamfwd.xml configuration file lets you specify system-level parameters for the streamfwd binary. You can configure streamfwd.xml to listen on specific IP addresses and ports, enable SSL, redirect log files, collect network events, and specify network interfaces. streamfwd.xml is included with Splunk_TA_stream and is located in:


Caution: Do not edit the streamfwd.xml file in the $SPLUNK_HOME/etc/apps/Splunk_TA_stream/default directory. To edit streamfwd.xml, copy the streamfwd.xml to $SPLUNK_HOME/etc/apps/Splunk_TA_stream/local and make your edits there .

Basic configuration

streamfwd.xml is configured by default to listen for traffic on all available network interfaces.

<?xml version="1.0" encoding="UTF-8"?>
<CmConfig xmlns="http://purl.org/cloudmeter/config" version="6.0.0">

streamfwd.xmlaccepts these basic configuration parameters:

Tag Description
<DataDirectory> Location of failover and other data files
<DefaultVocabularyPath> Location of default vocabulary files (do not change)
<Group> Name of group the streamfwd process runs as
<IPAddr> IP address that the Stream Forwarder listens on
<LocalVocabularyPath> Location of custom vocabulary files (do not change)
<LogConfig> Configuration file to use for logging
<Port> TCP port that the Stream Forwarder listens on (use "0" to disable)
<UIDirectory> Location of user interface files (do not change)
<User> Name of user the streamfwd process runs as

Advanced configuration

The streamfwd.xmlfile accepts these advanced configuration options.

Caution: Do not modify these options unless your Splunk Support representative advises you to do so.

Tag Description Value type Default value
<ClientIpSslHashBytes> Defines number of client IP octets to use for SSL processor thread hash algorithm. (min value = 0; max value = 4) Applies only if you have _disabled_ <UseGlobalSSLSessionKeyCache> client IP octets 2
<DuplicatePacketWindow> Defines number of packets cached in memory (using a rolling window) to detect duplicate packets. Set this to a value greater than zero to enable automatic deduplication of network packets. packets cached in-memory 0
<HideCreditCardNumbers> Masks credit card numbers. Set to false to show all credit card numbers. boolean true
<MapSslServers> Set to false to disable automatic caching of encrypted versus unencrypted services. boolean true
<MaxEventQueueSize> Defines maximum number of events queued for delivery to Splunk. events 10000
<MaxFieldSize> Defines maximum size of content field. bytes 10240
<MaxPacketQueueSize> Defines maximum size for each processing threads' packet queue. packets 250000
<MaxTcpReassemblyPacketCount> Defines maximum number of TCP packets in reassembly queue per processing thread. TCP packets 500000
<MaxTcpSessionCount> Defines maximum number of concurrent TCP/UDP flows per processing thread. TCP/UDP flows 50000
<PcapBufferSize> Defines buffer size for each network device. Increase the number of bytes if you see dropped packets. bytes 33554432
<PingInterval> Modifies the ping server interval. seconds 5
<ProcessingThreads> Defines number of threads to use for processing network traffic. threads 1
<QueueEventDelivery> Determines thread use for processing captured events. Set to true to use a separate thread for processing. boolean false
<SessionKeyTimeout> Indicates idle time before SSL session keys expire. seconds 3600
<TcpConnectionTimeout> Indicates idle time before TCP/UDP flows expire. seconds 180
<UseGlobalSSLSessionKeyCache> Enables sharing of SSL cache across processing threads. Set to true to share. boolean false
<UsePacketMemoryPool> When set to true, Stream Forwarder uses a pool allocator to allot memory for storing network packets. Because the pool allocator does not release unused memory back to the operating system, setting this parameter to true may result in high memory usage. Set to true only when Splunk App for Stream is running on a dedicated capture server that processes large traffic volumes. boolean false

Disable stream forwarder admin interface

By default, the Stream Forwarder admin interface is enabled, listening on TCP port 8889. To disable the interface:

1. Go to $SPLUNK_HOME/etc/apps/Splunk_TA_stream/local.

2. Open the streamfwd.xml configuration file and change <Port>8889</Port> to <Port>0</Port>.

Use TcpServer parameter to specify TCP servers

Stream forwarder automatically detects the client and server endpoints when it captures the beginnings of TCP connections. If it starts capturing traffic after establishing a TCP connection, Stream forwarder normally assumes that the sender of the first packet it sees is the client.

You can modify this behavior by inserting <TcpServer> clauses that define the endpoints of specific TCP servers. If the sender of a packet matches the endpoint, Stream forwarder correctly categorizes it as a server response packet.

TCP Server element examples

Example 1: Single HTTP server endpoint


Example 2: Wildcard endpoint


Use SSLServer element to specify SSL servers

Stream forwarder detects endpoint encryption, and attempts to decrypt SSL sessions using the available private keys. Optionally, you can explicitly define the traffic as encrypted or decrypted by inserting <SSLServer> clauses.


Use Capture element to specify network interfaces

By default streamfwd.xml listens for traffic on all available network interfaces. To restrict data capture to specific network interfaces, you must insert a separate XML <Capture></Capture> clause into the streamfwd.xml file for each network interface on which you want to capture data.

You can specify multiple Capture elements in a single streamfwd.xml file, and each Capture element can have its own <Filter> that applies to the specified network interface only.

For example, to specify a network interface on *nix:

    <Filter>tcp port 80</Filter>

The <Capture> element supports the following options:

Tag Description
<Interface> Should be set to the path of your pcap file
<Offline> True means use pcap, false means <Interface> is a network device name
<Filter> Lets you set a BPF (Berkeley Packet Filter) for kernel-level packet filtering. The value of this tag must comply with BPF syntax. Only one <Filter> tag per <Capture> element is supported.
<Repeat> True means to play back the pcap file repeatedly for continuous load
<SysTime> True means to use the system time for packet timestamps
<BitsPerSecond> Rate limiter, defaults to 10 Mbps if undefined and <Repeat> is true

Specify a network interface on Windows

The following Capture clause specifies a Windows network interface:

    <Filter>tcp port 80</Filter>

On Windows, you can substitute the <Interface> or <InterfaceRegex> name (such as <Interface>\Device\NPF_{D6995D00-B75C-48DB-99AA-69F0150126BC}</Interface>) with the <Alias> or <Description> value returned by the --iflist command line option.

For example, <Interface>Local Area Connection 2</Interface> or <InterfaceRegex>Local Area.*</IntefaceRegex>.

For more information, see "List network interfaces on Windows and Linux" in this manual.

Capture element examples

Example 1: Configure streamfwd.xml to include local loopback capture

Stream Forwarder by default does not capture traffic that originates and terminates on the same machine. You can enable capture of this "local loopback" traffic using a Capture element in the configuration file:


The <InterfaceRegex> element instructs streamfwd.xml to expand and enumerate the interfaces that are actually available on the host machine, and dynamically generates internal configurations for each network interface that matches the regular expression.

Example 2: Configure streamfwd.xml for use across multiple systems

You might want to maintain a master copy of streamfwd.xml that you can reuse across multiple systems that have different network device names. The following streamfwd.xml configuration listens on all matching interfaces found.


Note that this configuration may generate startup warnings for any devices that do not support passive data capture.

Example 3: Capture data on specific network interfaces

In this example, on a system with 8 network interfaces, streamfwd.xml would listen only for tcp port 80 traffic on only two of those interfaces (4 and 5):

    <Filter>tcp port 80</Filter>

Example 4: Use pcap file instead of network interface

You can also use a previously generated pcap file instead of an actual network interface, using this variation of the <Capture> element.

    <Filter>tcp port 80</Filter>

Example 5: Add <Capture> element to streamfwd.xml configuration file

When you add your <Capture> element to your streamfwd.xml configuration, place it inside the <CmConfig> element.

<?xml version="1.0" encoding="UTF-8"?>
<CmConfig xmlns="http://purl.org/cloudmeter/config" version="6.4.0">
    <Filter>tcp port 80</Filter>
Last modified on 12 April, 2016
Configure universal forwarder for use with Stream
Add SSL keys for decryption

This documentation applies to the following versions of Splunk Stream: 6.4.0, 6.4.1, 6.4.2

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