Provided by: flent_2.1.1-2_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 The Flent 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.
--send-size=SEND_SIZE
Send size (in bytes) used for TCP tests. Netperf uses the socket buffer size by
default, which if too large can cause spikes in the throughput results. Lowering
this value will increase CPU usage but also improves the fidelity of the throughput
results without having to decrease the socket buffer size.
Can be specified multiple times, with each value corresponding to a stream of a
test. If only specified once, the same value will be applied to all flows.
--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 Supplied 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.
--marking-name
Define a new symbolic name that can be used when specifying flow markings using the
'markings' test parameter. This can be used to make it easier to specify custom
diffserv markings on flows by using symbolic names for each marking value instead
of the hex codes. Values specified here will be used in addition to the common
values (listed below), and cannot override the built-in names. Names will be
case-folded when matching.
The list of symbolic markings natively supported, along with their hex expansions,
are:
AF11: 0x28 CS0: 0x00
AF12: 0x30 CS1: 0x20
AF13: 0x38 CS2: 0x40
AF21: 0x48 CS3: 0x60
AF22: 0x50 CS4: 0x80
AF23: 0x58 CS5: 0xa0
AF31: 0x68 CS6: 0xc0
AF32: 0x70 CS7: 0xe0
AF33: 0x78 EF: 0xb8
AF41: 0x88
AF42: 0x90
AF43: 0x98
Note that the hexadecimal values denote the value of the full ToS byte (including
the two ECN bits), so they need to be right-shifted by two bits to get the
corresponding diffserv code points.
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 (removing any text from
the legend that matches the expression). Can be specified multiple times, in which
case the filters will be applied in the order specified. 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 Supplied 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.
--irtt-sampling-interval=MILLISECONDS
Override the sampling interval passed to irtt, in milliseconds. Can be used to run
irtt with a higher sampling frequency than the rest of the test. If set, this will
override the sampling interval for all instances of irtt used in the test.
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://www.bufferbloat.net/projects/bloat/wiki/RRUL_Spec/). 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
bidir_streams
These set the number of streams for the tests that are configurable. The tcp_nup,
tcp_ndown and rrul_be_nflows tests understand upload_streams and download_streams,
while the rrul_var test understands bidir_streams. If any of these parameter is 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
udp_bandwidths
udp_pktsize
udp_pktsizes
This sets the bandwidth and packet size 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).
When running multiple UDP streams use the plural versions of the options
(udp_bandwidths and udp_pktsizes) to specify individual per-stream values
(comma-separated per stream), or the singular versions to specify the same value
for all streams.
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
ping_labels
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. The
ping_labels variable is used to label each of the ping flows; if not specified,
Flent will create a default label based on the target hostname for each flow.
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
labels 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. By default each flow will be labelled according to its marking; to override
these labels, use the labels parameter.
stream_delays
Specify a per-stream delay (in seconds) for the different streams started up by a
test. Use commas to separate values for the different streams. This can be used to
create tests with staggered start times, for example to test TCP flow startup
convergence times. What exactly constitutes a stream depends on the test. For
example, the rtt_fair* tests considers each hostname a stream, whether or not there
is one or two flows going to that host.
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
2012-2022, Toke Høiland-Jørgensen and contributors. Source code is GPLv3. Documentation is
CC-BY-SA. Neither license affects any output produced by Flent