Provided by: flent_1.3.2-2_all 
NAME
flent - Flent: The FLExible Network Tester
INTRODUCTION
Flent is a wrapper around netperf and similar tools to run predefined tests and aggregate and plot the
results. It defines several tests that can be run against one or more hosts, primarily targeted at
testing for the presence of bufferbloat under various conditions.
The aggregated data is saved in (gzipped) JSON format for later processing and/or import into other
tools. The JSON format is documented below.
Apart from the JSON format, the data can be output as csv values, emacs org mode tables or plots. Each
test can specify several different plots, including time-series plots of the values against each other,
as well as CDF plots of (e.g.) ping times.
Plots can be output to the formats supported by matplotlib by specifying the output filename with -o
output.{png,ps,pdf,svg}. If no output file is specified, the plot is displayed using matplotlib’s
interactive plot browser, which also allows saving of the output (in .png format).
Requirements
Flent runs on Python, versions 2.7+ and 3.3+. Plotting requires a functional matplotlib installation (but
everything else can run without matplotlib). For the interactive plot viewer, a graphical display (and
suitably configured matplotlib) is required.
Most tests employ the netperf benchmarking tool to run the tests. Version 2.6 or higher is required, and
netperf must be compiled with the --enable-demo option passed to ./configure. Some tests use iperf in
addition to, or instead of netperf. Both tools must be available in the PATH.
For ICMP ping measurements, the version of ping employed must support output timestamping (the -D
parameter to GNU ping). This is not supported by the BSD and OSX versions of ping. As an alternative to
the regular ping command, the fping utility (see http://fping.org) can be employed. In that case fping
must be version 3.5 or greater. Flent will attempt to detect the presence of fping in the PATH and check
for support for the -D parameter. If this check is successful, fping will be employed for ping data,
otherwise the system ping will be used.
The irtt tool is highly recommended for UDP measurements. See https://github.com/peteheist/irtt. Flent
will automatically detect if irtt is available in the PATH and use it if it is detected. Note that the
server component of irtt needs to be running on the target host(s) as well.
RUNNING FLENT
When run, flent must be supplied either (a) a test name and one or more host names to connect to, or (b)
one or more input files containing data from previous runs to post-process.
Test names, hostnames and input file names can all be specified as unqualified arguments, and flent will
do its best to guess which is which. For each argument, if it is an existing file, it is assumed to be an
input file, if it is the name of an existing test configuration it’s assumed to be a test name, and if
neither of those are true, it is assumed to be a host name. The -i and -H switches can be used to
explicitly specify the interpretation of an argument.
Invocation
flent [options] <host|test|input file ...>
General options
-o OUTPUT, --output=OUTPUT
File to write processed output to (default standard out).
-D DATA_DIR, --data-dir=DATA_DIR
Directory to store data files in. Defaults to the current directory.
-i INPUT, --input=INPUT
File to read input from (instead of running tests). Input files can also be specified as
unqualified arguments without using the -i switch.
-f FORMAT, --format=FORMAT
Select output format (plot, csv, org_table, stats). Default is no processed output (just writes
the JSON data file).
-p PLOT, --plot=PLOT
Select which plot to output for the given test (implies -f plot). Use the --list-plots option to
see available plots.
-t TITLE, --title-extra=TITLE
Text to add to plot title and data file name.
-n NOTE, --note=NOTE
Add arbitrary text as a note to be stored in the JSON data file (under the NOTE key in the
metadata object).
-r RCFILE, --rcfile=RCFILE
Load configuration data from RCFILE (default ~/.flentrc). See section below for information on the
rc file format.
-x, --extended-metadata
Collect extended metadata and store it with the data file. May include details of your machine you
don’t want to distribute; see the section on the data format below.
--remote-metadata=HOSTNAME
Collect extended metadata from a remote host. HOSTNAME is passed verbatim to ssh, so can include
hosts specified in ~/.ssh/config. Note that gathering the data can take some time, since it
involves executing several remote commands. This option can be specified multiple times and
implies --extended-metadata.
--gui Run the flent GUI. All other options are used as defaults in the GUI, but can be changed once it
is running. The GUI can also be started by running the flent-gui binary. For more information on
the GUI, see the gui section.
--new-gui-instance
Start a new GUI instance. Otherwise, flent will try to connect to an already running GUI instance
and have that load any new data files specified as arguments. Implies --gui when passed on the
command line, but not when set in the rc file. Note that when multiple GUI instances are running,
there is no guarantee as to which instance will get a subsequent open request (if run again
without --new-gui-instance).
--gui-no-defer
Normally, the GUI defers redrawing plots until they are needed to avoid redrawing all open plots
every time an option changes. This switch turns off that optimisation in favour of always
redrawing everything straight away. This is useful when loading a bunch of plots from the command
line and then wanting to flip through them without drawing delay.
-b BATCH_NAME, --batch-name=BATCH_NAME
Run test batch BATCH_NAME (must be specified in a batch file loaded by the --batch-file option).
Can be supplied multiple times.
-B BATCH_FILE, --batch-file=BATCH_FILE
Load batch file BATCH_FILE. Can be specified multiple times, in which case the files will be
combined (with identically-named sections being overridden by later files). See appropriate
section below for an explanation of the batch file format.
--batch-override=key=value
Override parameter ’key’ in the batch config and set it to ’value’. The key name will be case
folded to lower case. Can be specified multiple times.
--batch-dry-run
Dry batch run. Prints what would be done, but doesn’t actually run any tests.
--batch-verbose
Be verbose during batch run: Print all commands executed.
--batch-no-shuffle
Do not randomise the order of test runs within each batch.
--batch-repetitions=REPETITIONS
Shorthand for --batch-override 'repetitions=REPETITIONS’.
--batch-title=TITLE
Shorthand for --batch-override 'batch_title=TITLE’.
--batch-resume=DIR
Try to resume a previously interrupted batch run. The argument is the top-level output directory
from the previous run.
This will attempt to find a data file in the resume directory and load the BATCH_TIME from the
previous run from that and continue. The assumption is that the output directory and filenames are
generated from the batch time, so that they will match with the previous run when the same time is
used. Then, tests for which data files already exist will be skipped on this run. If the rest of
the batch invocation is different from the one being resumed, results may not be what you want.
There's a check to ensure that the generated output path is a subdirectory of the resume
directory, and the whole run will be aborted if it isn't.
Test configuration options
These options affect the behaviour of the test being run and have no effect when parsing input files.
-H HOST, --host=HOST
Host to connect to for tests. For tests that support it, multiple hosts can be specified by
supplying this option multiple times. Hosts can also be specified as unqualified arguments; this
parameter guarantees that the argument be interpreted as a host name (rather than being subject to
auto-detection between input files, hostnames and test names).
--local-bind=IP
Local hostname or IP address to bind to (for test tools that support this). Can be specified
multiple times for tests that connect to more than one host; if it is, it must be specified as
many times as there are hosts.
--remote-host=idx=HOSTNAME
A remote hostname to connect to when starting a test. The idx is the runner index, which is
assigned sequentially to each runner (and so it is not the same as the sequence of hostnames).
Look for the 'IDX' key in SERIES_META for a test get the idx used here, but note that the idx
assignment depends on the exact arguments to the test.
This works by simply prepending 'ssh HOSTNAME' to the runner command, so it relies on the same
binaries being in the same places on both machines, and won't work for all runners.
This option can be specified multiple times to have multiple runners run on remote hosts.
-l LENGTH, --length=LENGTH
Base test length (some tests may add some time to this).
-s STEP_SIZE, --step-size=STEP_SIZE
Measurement data point step size.
-d DELAY, --delay=DELAY
Number of seconds to delay parts of test (such as bandwidth loaders).
-4, --ipv4
Use IPv4 for tests (some tests may ignore this).
-6, --ipv6
Use IPv6 for tests (some tests may ignore this).
--socket-timeout=SOCKET_TIMEOUT
Socket timeout (in seconds) used for UDP delay measurement, to prevent stalls on packet loss. Only
enabled if the installed netperf version is detected to support this (requires SVN version of
netperf).
For the default value, see the output of flent -h. The value of this parameter is an implicit
upper bound on how long a round-trip time that can be measured. As such you may need to adjust it
if you are experiencing latency above the default value. Set to 0 to disable.
--test-parameter=key=value
Arbitrary test parameter in key=value format. Key will be case folded to lower case. The values
are stored with the results metadata, and so can be used for storing arbitrary information
relevant for a particular test run.
In addition to serving as simple metadata, the test parameters can also affect the behaviour of
some test configurations. See the tests section for information on these.
This option can be specified multiple times to set multiple test parameters.
--swap-up-down
Switch upstream and downstream directions for data transfer. This means that ’upload’ will become
’download’ and vice versa. Works by exchanging netperf TCP_MAERTS and TCP_STREAM parameters, so
only works for tests that employ these as their data transfer, and only for the TCP streams.
--socket-stats
Parse socket stats during test. This will capture and parse socket statistics for all TCP upload
flows during a test, adding TCP cwnd and RTT values to the test data. Requires the 'ss' utility to
be present on the system, and can fail if there are too many simultaneous upload flows; which is
why this option is not enabled by default.
Plot configuration options
These options are used to configure the appearance of plot output and only make sense combined with -f
plot.
--label-x=LABEL
--label-y=LABEL
Override the figure axis labels. Can be specified twice, corresponding to figures with multiple
axes.
-I, --invert-latency-y
Invert latency data series axis (typically the Y-axis), making plots show ’better' values upwards.
-z, --zero-y
Always start Y axis of plot at zero, instead of autoscaling the axis. Autoscaling is still
enabled for the upper bound. This also disables log scale if enabled.
--log-scale={log2,log10}
Use the specified logarithmic scale on plots.
--norm-factor=FACTOR
Data normalisation factor. Divide all data points by this value. Can be specified multiple times,
in which case each value corresponds to a data series.
--bounds-x=BOUNDS
--bounds-y=BOUNDS
Specify bounds of the plot axes. If specifying one number, that will become the upper bound.
Specify two numbers separated by a comma to specify both upper and lower bounds. To specify just
the lower bound, add a comma afterwards. Can be specified twice, corresponding to figures with
multiple axes.
-S, --scale-mode
Treat file names (except for the first one) passed as unqualified arguments as if passed as
--scale-data (default as if passed as --input).
--concatenate
Concatenate multiple result sets into one data series. This means that each data file will have
its time axis shifted by the preceding series duration and appended to the first data set
specified. Only works for data sets from the same test, obviously.
--absolute-time
Plot data points with absolute UNIX time on the x-axis. This requires the absolute starting time
for the test run to be stored in the data file, and so it won’t work with data files that predates
this feature.
--subplot-combine
When plotting multiple data series, plot each one on a separate subplot instead of combining them
into one plot. This mode is not supported for all plot types, and only works when --scale-mode is
disabled.
--skip-missing-series
Skip missing series entirely from bar plots, instead of leaving an empty space for it.
--no-print-n
Do not print the number of data points on combined plots. When using plot types that combines
results from several test runs, the number of data series in each combined data point is normally
added after the series name, (n=X) for X data series. This option turns that off.
--no-annotation
Exclude annotation with hostnames, time and test length from plots.
--figure-note=NOTE, --fig-note=NOTE
Add a note (arbitrary text) to the bottom-left of the figure.
--no-title
Exclude title from plots.
--override-title=TITLE
Override plot title with this string. Completely discards the configured title (from the test
configuration), as well as the title stored in the data set, and replaces it with the value
supplied here. This is useful to override the plot title at the time of plotting, for instance to
add a title to an aggregate plot from several data series. When this parameter is specified,
--no-title has no effect.
--no-labels
Hides tick labels from box and bar plots.
--no-markers
Don’t use line markers to differentiate data series on plots.
--no-legend
Exclude legend from plots.
--horizontal-legend
Place a horizontal legend below the plot instead of a vertical one next to it. Doesn't always work
well if there are too many items in the legend.
--legend-title=LEGEND_TITLE
Override legend title on plot.
--legend-placement=LEGEND_PLACEMENT
Control legend placement. Enabling this option will place the legend inside the plot at the
specified location. Can be one of 'best', 'upper right', 'upper left', 'lower left', 'lower
right', 'right', 'center left', 'center right', 'lower center', 'upper center' or 'center'.
--legend-columns=LEGEND_COLUMNS
Set the number of columns in the legend.
--reverse-legend
Reverse the order of items in the legend. This can be useful to make the legend order match the
data series in some cases.
--filter-legend
Filter legend labels by removing the longest common substring from all entries. This is not
particularly smart, so use with care.
--replace-legend=src=dest
Replace 'src' with 'dst' in legends. Can be specified multiple times.
--filter-regexp=REGEXP
Filter the plot legend by the supplied regular expression. Note that for combining several plot
results, the regular expression is also applied before the grouping logic, meaning that a too wide
filter can mess up the grouping.
--override-label=LABEL
Override dataset label. Can be specified multiple times when multiple datasets are being plotted,
in which case the order of labels corresponds to the order of datasets.
Like --override-title, this is applied at the time of plotting.
--filter-series=SERIES
Filter out specified series from plot. Can be specified multiple times.
--split-group=LABEL
Split data sets into groups when creating box plots. Specify this option multiple times to define
the new groups; the value of each option is the group name.
Say you're plotting nine datasets which are really testing two variables with three values each.
In this case, it can be useful to have the box plot of the results be split into three parts
(corresponding to the values of one variable) with each three boxes in each of them (corresponding
to the values of the second variable). This option makes this possible; simply specify it three
times with the labels to be used for the three groups.
A constraint on this option is that the number of datasets being plotted must be divisible by the
number of groups.
--colours=COLOURS
Comma-separated list of colours to be used for the plot colour cycle. Can be specified in any
format understood by matplotlib (including HTML hex values prefixed with a #).
Yes, this option uses British spelling. No, American spelling is not supported.
--override-colour-mode=MODE
Override colour_mode attribute. This changes the way colours are assigned to bar plots. The
default is 'groups' which assigns a separate colour to each group of data series. The alternative
is 'series' which assigns a separate colour to each series, repeating them for each data group.
--override-group-by=GROUP
Override the group_by setting for combination plots. This is useful to, for instance, switch to
splitting up combined data sets by batch run instead of by file name.
--combine-save-dir=DIRNAME
When doing a combination plot save the intermediate data to DIRNAME. This can then be used for
subsequent plotting to avoid having to load all the source data files again on each plot.
--figure-width=FIG_WIDTH
Figure width in inches. Used when saving plots to file and for default size of the interactive
plot window.
--figure-height=FIG_HEIGHT
Figure height in inches. Used when saving plots to file and for default size of the interactive
plot window.
--figure-dpi=FIG_DPI
Figure DPI. Used when saving plots to raster format files.
--fallback-layout
Use the fallback layout engine (tight_layout built in to matplotlib). Use this if text is cut off
on saved figures. The downside to the fallback engine is that the size of the figure (as specified
by --figure-width and --figure-height) is no longer kept constant.)
--no-matplotlibrc
Don’t load included matplotlibrc values. Use this if autodetection of custom matplotlibrc fails
and flent is inadvertently overriding rc values.
--no-hover-highlight
Don't highlight data series on hover in interactive plot views. Use this if redrawing is too slow,
or the highlighting is undesired for other reasons.
--scale-data=SCALE_DATA
Additional data files to consider when scaling the plot axes (for plotting several plots with
identical axes). Note, this displays only the first data set, but with axis scaling taking into
account the additional data sets. Can be supplied multiple times; see also --scale-mode.
Test tool-related options
--control-host=HOST
Hostname for the test control connection (for test tools that support this). Default: First
hostname of test target.
When running tests that uses D-ITG as a test tool (such as the voip-* tests), this switch controls
where flent will look for the D-ITG control server (see section below on running tests with
D-ITG). For Netperf-based tests, this option is passed to Netperf to control where to point the
control connection. This is useful to, for instance, to run the control server communication over
a separate control network so as to not interfere with test traffic.
There is also a per-flow setting for this for tests that connect to multiple hosts; see the
control_hosts test parameter in tests. If both are set, the per-flow setting takes precedence for
those tests that use it.
--control-local-bind=IP
Local hostname or IP to bind control connection to (for test tools that support it; currently
netperf). If not supplied, the value for --local-bind will be used. Note that if this value is
passed but --local-bind is not, netperf will use the value specified here to bind the data
connections to as well.
--netperf-control-port=PORT
Port for Netperf control server. Default: 12865.
--ditg-control-port=PORT
Port for D-ITG control server. Default: 8000.
--ditg-control-secret=SECRET
Secret for D-ITG control server authentication. Default: ’’.
--http-getter-urllist=FILENAME
When running HTTP tests, the http-getter tool is used to fetch URLs (see
https://github.com/tohojo/http-getter). This option specifies the filename containing the list of
HTTP URLs to get. Can also be a URL, which will then be downloaded as part of each test iteration.
If not specified, this is set to http://<hostname>/filelist.txt where <hostname> is the first test
hostname.
--http-getter-dns-servers=DNS_SERVERS
DNS servers to use for http-getter lookups. Format is host[:port][,host[:port]]... This option
will only work if libcurl supports it (needs to be built with the ares resolver). Default is none
(use the system resolver).
--http-getter-timeout=MILLISECONDS
Timeout for HTTP connections. Default is to use the test length.
--http-getter-workers=NUMBER
Number of workers to use for getting HTTP urls. Default is 4.
Misc and debugging options:
-L LOG_FILE, --log-file=LOG_FILE
Write debug log (test program output) to log file.
--list-tests
List available tests and exit.
--list-plots
List available plots for selected test and exit.
-V, --version
Show Flent version information and exit.
-v, --verbose
Enable verbose logging to console.
-q, --quiet
Disable normal logging to console (and only log warnings and errors).
--debug-error
Print full exception backtraces to console.
-h, --help
Show usage help message and exit.
Signals
Flent will abort what it is currently doing on receiving a SIGINT -- this includes killing all runners,
cleaning up temporary files and shutting down as gracefully as possible. Runners are killed with SIGTERM
in this mode, and their output is discarded. If a batch run is in progress, the current test will be
interrupted in this way, and the rest of the batch run is aborted. Previously completed tests and their
results are not aborted. Post-commands marked as ’essential’ will be run after the test is interrupted.
Additionally, flent converts SIGTERM into SIGINT internally and reacts accordingly.
Upon receiving a SIGUSR1, flent will try to gracefully abort the test it is currently running, and parse
the output of the runners to the extent that any such output exists. That is, each runner will be killed
by a SIGINT, which will cause a graceful shutdown for at least ping and netperf (although netperf running
in TCP_MAERTS mode will bug out when interrupted like this, so end-of-tests statistics will be missing).
Flent will only react once to a SIGUSR1, sending exactly one SIGINT to the active runners, then wait for
them to exit. This may take several seconds in the case of netperf. If the runners for some reason fail
to exit, flent will be stuck and will need to be killed with SIGINT. If running in batch mode, SIGUSR1
will only affect the currently running test; subsequent tests will still be run.
SUPPLIED TESTS
Test are supplied as Python files and can specify commands to run etc. For a full list of the tests
supported by flent, see the --list-tests option.
The Realtime Response Under Load (RRUL) test
This test exists in a couple of variants and is a partial implementation of the RRUL specification as
written by Dave Taht (see https://github.com/dtaht/deBloat/blob/master/spec/rrule.doc?raw=true). It works
by running RTT measurement using ICMP ping and UDP roundtrip time measurement, while loading up the link
with eight TCP streams (four downloads, four uploads). This quite reliably saturates the measured link
(wherever the bottleneck might be), and thus exposes bufferbloat when it is present.
Simple TCP flow tests
These tests combine a TCP flow (either in one direction, or both) with an ICMP ping measurement. It’s a
simpler test than RRUL, but in some cases the single TCP flow can be sufficient to saturate the link.
UDP flood test
This test runs iperf configured to emit 100Mbps of UDP packets targeted at the test host, while measuring
RTT using ICMP ping. It is useful for observing latency in the face of a completely unresponsive packet
stream.
Test parameters
Some test parameters (set with --test-parameter) affect the way tests behave. These are:
upload_streams
download_streams
These set the number of upload or download streams for the tcp_nup, tcp_ndown and rrul_be_nflows
tests. If set to the special value num_cpus the number of streams will be set to the number of
CPUs on the system (if this information is available).
tcp_cong_control
Set the congestion control used for TCP flows, for platforms that supports setting it. This can be
specified as a simple string to set the same value for upstream and downstream, or two
comma-separated values to set it separately for the upstream and downstream directions. On Linux,
any value in the sysctl net.ipv4.tcp_allowed_congestion_control can be used.
If a congestion control is specified that is not available on the system running the test, setting
it will simply fail. In addition, some tests override the congestion control for one or more
flows. The actual congestion control used is stored in the CONG_CONTROL per-test metadata field.
udp_bandwidth
This sets the bandwidth of each UDP stream in the udp_* tests. The option is passed to iperf so
can be in any syntax the iperf understands (e.g. 20M for 20 Mbps).
burst_length
burst_ports
burst_psize
burst_tos
These set the length, number of ports to use, packet size and TOS value for the packet bursts
generated in the burst* tests.
cpu_stats_hosts
netstat_hosts
qdisc_stats_hosts
wifi_stats_hosts
These set hostnames to gather statistics from from during the test. The hostnames are passed to
SSH, so can be anything understood by SSH (including using username@host syntax, or using hosts
defined in ~/.ssh/config). This will attempt to run remote commands on these hosts to gather the
required statistics, so passwordless login has to be enabled for. Multiple hostnames can be
specified, separated by commas.
CPU stats and netstat output is global to the machine being connected to. The qdisc and WiFi stats
need extra parameters to work. These are qdisc_stats_interfaces, wifi_stats_interfaces and
wifi_stats_stations. The two former specify which interfaces to gather statistics from. These are
paired with the hostnames, and so must contain the same number of elements (also comma-separated)
as the _hosts variables. To specify multiple interfaces on the same host, duplicate the hostname.
The wifi_stats_stations parameter specifies MAC addresses of stations to gather statistics for.
This list is the same for all hosts, but only stations present in debugfs on each host are
actually captured.
The qdisc stats gather statistics output from tc -s, while the WiFi stats gather statistics from
debugfs. These are gathered by looping in a shell script; however, for better performance, the
tc_iterate and wifistats_iterate programmes available in the misc/ directory of the source code
tarball can be installed. On low-powered systems this can be critical to get correct statistics.
The helper programmes are packaged for LEDE/OpenWrt in the flent-tools package.
ping_hosts
ping_local_binds
These are used to define one or more extra host names that will receive a ping flow while a test
is run. The ping_hosts variable simply specifies hostnames to ping (several can be specified by
separating them with commas). The ping_local_binds variable sets local IP address(es) to bind to
for the extra ping flows. If specified, it must contain the same number of local addresses as the
number of ping hosts. The same local address can be specified multiple times, however.
voip_host
voip_local_bind
voip_control_host
voip_marking
Similar to the ping variants above, these parameters specify a hostname that will receive a VoIP
test. However, unlike the ping parameters, only one hostname can be specified for VoIP tests, and
that end-host needs to have either D-ITG (and the control server) or the IRTT server running. The
marking setting controls which DiffServ marking is applied to the VoIP flow and defaults to no
marking being set.
control_hosts
Hostnames to use for the control connections for the rtt_fair* tests. Comma-separated. If
specified, it must contain as many hostnames as the number of target hostnames specified for the
test.
markings
Flow markings to use for each of the flows in the rtt_fair* tests. Comma-separated values of
markings understood by Netperf (such as "CS0"). Only supports setting the same marking on both
the upstream and downstream packets of each flow (so no "CS0,CS0" setting as can be used for
Netperf). If not set, defaults to CS0 (best effort). If set, each value corresponds to a flow, and
any extra flows will be set to CS0.
THE FLENT GUI
Flent comes equipped with a GUI to browse and plot previously captured datasets. The GUI requires PyQt4;
if this is installed, it can be launched with the --gui parameter, or by launching the flent-gui binary.
Additionally, if Flent is launched without parameters and without a controlling terminal, the GUI will be
launched automatically.
The GUI can be used for interactively plotting previously captured datasets, and makes it easy to compare
results from several test runs. It presents a tabbed interface to graphs of data files, allows dynamic
configuration of plots, and includes a metadata browser. For each loaded data file, additional data files
can be loaded and added to the plot, similar to what happens when specifying multiple input files for
plotting on the command line. A checkbox controls whether the added data files are added as separate
entries to the plot, or whether they are used for scaling the output (mirroring the --scale-mode) command
line switch.
The GUI also incorporates matplotlib’s interactive browsing toolbar, enabling panning and zooming of the
plot area, dynamic configuration of plot and axis parameters and labels and saving the plots to file. The
exact dynamic features supported depends on the installed version of matplotlib.
CONFIGURATION FILES
The RC file
Some of the command line options can be specified in an rc file. By default, flent looks for this in
~/.flentrc, but an alternative location can be specified with the --rcfile command line option.
The rc file allows options to be specified globally, an optionally overridden for specific tests. For an
explanation of the options, refer to the annotated example rc file, by default installed to
/usr/share/doc/flent/flentrc.example.
Batch Files
Flent supports reading batch files to automate running several tests and do setup/teardown of test
environment etc. This greatly aids reproducibility of tests.
The batch file is parsed as an ini file, and can have three types of sections: batches, commands and
args. Each section also has a name; type and name are separated with two colons. 'Batches' are named
tests that can be selected from the command line, 'commands' are system commands to be run before or
after each test run, and 'args' are used in the looping mechanism (which allows repeating tests multiple
times with different parameters).
Variables in sections control the operation of Flent and can be modified in several ways: Sections of the
same type can inherit from each other and the variables in an 'arg' section will be interpolated into the
batch definition on each iteration of a loop. In addition, variable contents can be substituted into
other variables by using the ${varname} syntax. These three operations are resolved in this order
(inheritance, arg interpolation and variable substitution).
An annotated example batchfile is distributed with the source code, and is by default installed to
/usr/share/doc/flent/batchfile.example.
THE DATA FILE FORMAT
The aggregated test data is saved in a file called <test_name>-<date>.<title>.flent.gz (the title part is
omitted if no title is specified by the -t parameter). This file contains the data points generated
during the test, as well as some metadata.
The top-level object keys
version
The file format version as an integer.
x_values
An array of the x values for the test data (typically the time values for timeseries data).
results
A JSON object containing the result data series. The keys are the data series names; the value for
each key is an array of y values for that data series. The data array has the same length as the
x_values array, but there may be missing data points (signified by null values).
metadata
An object containing various data points about the test run. The metadata values are read in as
configuration parameters when the data set is loaded in for further processing. Not all tests use
all the parameters, but they are saved anyway.
raw_values
An array of objects for each data series. Each element of the array contains the raw values as
parsed from the test tool corresponding to that data series.
Metadata keys
NAME The test name.
TITLE Any extra title specified by the --title-extra parameter when the test was run.
HOSTS List of the server hostnames connected to during the test.
LOCAL_HOST
The hostname of the machine that ran the test.
LENGTH Test length in seconds, as specified by the --length parameter.
TOTAL_LENGTH
Actual data series length, after the test has added time to the LENGTH.
STEP_SIZE
Time step size granularity.
TIME ISO timestamp of the time the test was initiated.
NOTE Arbitrary text as entered with the --note switch when the test was run.
FLENT_VERSION
Version of Flent that generated the data file.
IP_VERSION
IP version used to run test (as specified by command line parameters, or auto-detected from
getaddrinfo() if unspecified).
KERNEL_NAME
The kernel name as reported by uname -s.
KERNEL_RELEASE
The kernel release as reported by uname -r.
MODULE_VERSIONS
The sha1sum of certain interesting Linux kernel modules, if available. Can be used to match test
data to specific code versions, if the kernel build is instrumented to, e.g., set the build ID to
a git revision.
SYSCTLS
The values of several networking-related sysctls on the host (if available; Linux only).
EGRESS_INFO
Interface name, qdisc, offload, driver and BQL configuration of the interface used to reach the
test target. This requires that the ip binary is present on Linux, but can be extracted from route
on BSD. Qdisc information requires the tc binary to be present, and offload information requires
ethtool.
If the --remote-metadata is used, the extended metadata info is gathered for each of the hostnames
specified. This is gathered under the REMOTE_METADATA key in the metadata object, keyed by the
hostname values passed to --remote-metadata. Additionally, the REMOTE_METADATA object will contain
an object called INGRESS_INFO which is a duplicate of EGRESS_INFO, but with the destination IP
exchanged for the source address of the host running flent. The assumption here is that
--remote-metadata is used to capture metadata of a router known to be in the test path, in which
case INGRESS_INFO will contain information about the reverse path from the router (which is
ingress from the point of view of the host running flent). If the host being queried for remote
metadata is off the path, the contents of INGRESS_INFO will probably be the same as that of
EGRESS_INFO .
Extended metadata
If the --extended-metadata switch is turned on, the following additional values are collected and stored
(to the extent they are available from the platform):
IP_ADDRS
IP addresses assigned to the machine running flent.
GATEWAYS
IP addresses of all detected default gateways on the system, and the interfaces they are reachable
through. Only available if the netstat binary is present on the system.
EGRESS_INFO
In the EGRESS_INFO key, the IP address of the next-hop router and the interface MAC address are
added if extended metadata is enabled.
OUTPUT FORMATS
The following output formats are currently supported by Flent:
Plot output (-f plot)
Output test data as one of a series of graphical plots of timeseries data or summarised as a CDF plot.
Each test supplies a number of different plots; the list of plots for a given test is output by the
--list-plots switch (which must be supplied along with a test name).
The plots are drawn by matplotlib, and can be displayed on the screen interactively (requires a graphical
display), or output to a file in svg, pdf, ps and png formats. Using the -o switch turns out file output
(the file format is inferred from the file name), while not supplying the switch turns on the interactive
plot viewer.
Tabulated output (-f csv and -f org_table)
These formats output the numeric data in a tabulated format to be consumed by other applications. The csv
output format is a comma-separated output that can be imported into e.g. spreadsheets, while org_table
outputs a tabulated output in the table format supported by Emacs org mode. The data is output in text
format to standard output, or written to a file if invoked with the -o parameter.
Statistics output (-f stats)
This output format outputs various statistics about the test data, such as total bandwidth consumed, and
various statistical measures (min/max/mean/median/std dev/variance) for each data source specified in the
relevant test (this can include some data sources not includes on plots). The data is output in text
format to standard output, or written to a file if invoked with the -o parameter.
Metadata output (-f metadata)
This output format outputs the test metadata as pretty-printed JSON (also suitable for human
consumption). It is output as a list of objects, where each object corresponds to the metadata of one
test. Mostly useful for inspecting metadata of stored data files.
MISC INFO
Running Tests With The D-ITG Tool
This version of flent has experimental support for running and parsing the output of the D-ITG test tool
(see http://traffic.comics.unina.it/software/ITG/). Flent supports parsing the one-way delay as measured
by D-ITG. However, in order to do so, the data needs to be collected at the receiver end, statistics
extracted, and the result passed back to flent on the sending side.
To perform this function, flent supports a control server which will listen to XML-RPC requests, spawn an
appropriate ITGRecv instance and, after the test is done, parse its output and make it available for
flent to retrieve. This control server is available as a Python file that by default is installed in
/usr/share/doc/flent/misc. It currently requires a patched version of D-ITG v2.8.1. The patch is also
included in the same directory.
Note that the D-ITG server is finicky and not designed with security in mind. For this reason, the
control server includes HMAC authentication to only allow authenticated clients to run a test against the
server; however there is currently no support for enforcement of this in e.g. firewall rules. Please bear
this in mind when running a publicly reachable ITGRecv instance (with or without the control server).
Another security issue with the control server is that the Python XML-RPC library by default is
vulnerable to XML entity expansion attacks. For this reason, it is highly recommended to install the
defusedxml library (available at https://pypi.python.org/pypi/defusedxml/) on the host running the
control server. The server will try to find the library on startup and refuse to run if it is not
available, unless explicitly told otherwise.
Due to the hassle of using D-ITG, it is recommended to install irtt instead and use that for VoIP tests.
Bugs
Under some conditions (such as severe bufferbloat), the UDP RTT measurements done by netperf can
experience packet loss to the extent that the test aborts completely, which can cause missing data points
for some measurement series. The --socket-timeout feature can alleviate this, but requires a recent SVN
version of netperf to work. Flent tries to detect if netperf supports this option and enables it for the
UDP measurements if it does. Using irtt for UDP measurements is a way to alleviate this; Flent will
automatically detect the availability of irtt and use it if available.
Probably many other bugs. Please report any found to https://github.com/tohojo/flent/issues and include
the output of flent --version in the report. A debug log (as obtained with flent --log-file) is also
often useful.
AUTHOR
Toke Høiland-Jørgensen
COPYRIGHT
2012-2017, Toke Høiland-Jørgensen and contributors. Source code is GPLv3. Documentation is CC-BY-SA