bwctl (1)

bwctl [options] -c recvhost -s sendhost

bwctl [options] -c recvhost

bwctl [options] -s sendhost

bwctl is a command line client application that is used to initiate throughput tests.

This version of bwctl is capable of initiating Iperf, Nuttcp, and Thrulay tests.

bwctl works by contacting a bwctld daemon on both the receiving host and the sending host. bwctld manages and schedules the resources of the host it runs on. In the case where only one of the receiving host or sending host is specified, bwctl assumes the local host is the other endpoint. bwctl will attempt to contact a local bwctld if it can. If there is no local bwctld running, bwctl assumes the local host does not require policy controls and will execute the bwctld functionality required to run the test directly.

If cases where bwctl is directly running the throughput test on the host, there are several configuration options that are shared with bwctld. Those configuration options can be set using the bwctlrc(5) configuration file in a way very similar to the way they are specified in the bwctld.conf(5) file.

The bwctl client is used to request the desired type of throughput test. Furthermore, it requests when the test is wanted. bwctld on each endpoint either responds with a tentative reservation or a test denied message. Once bwctl is able to get a matching reservation from both bwctld processes (one for each host involved in the test), it confirms the reservation. Then, the bwctld processes run the test and return the results. The results are returned to the client from both sides of the test from the respective bwctld processes. Additionally, the bwctld processes share the results from their respective side of the test with each other.

BWCTL (bwctl and bwctld) is used to enable non-specific throughput tests to hosts without having to give full user accounts on the given systems. Users want the ability to run throughput tests to determine the achievable or available bandwidth between a pair of hosts. It is often useful to test to multiple points along a network path to determine the network characteristics along that path. Typically, users who want to do this path decomposition have to directly contact the network/system administrators who control the hosts along the path. The administrator needs to either run half of the test for the user or give them a user account on the host. Also, network paths of interest are typically controlled by multiple administrators. These hurdles have made this kind of testing difficult in practice.

BWCTL was designed to help with this problem. It allows an administrator to configure a given host as an Iperf, Thrulay, or Nuttcp endpoint. The endpoint can be a packet sender (e.g. Iperf client) or a packet receiver (e.g. Iperf server). It can be shared by multiple users without concern that those users will interfere with each other. Specific policy limits can be applied to specific users, and individual tests are scheduled so they will not interfere with each other. Additionally, full user accounts are not required for the users running the tests.

BWCTL allows the administrator to classify incoming connections based upon a user name and AES key combination or, alternatively, based upon an IP/netmask. Once the connection is classified, the bwctld can determine the exact type and intensities of througput tests that will be allowed. More information on the policy controls can be found in the bwctld(8) man page.

BWCTL makes use of a distributed scheduling algorithm. Each host maintains a schedule independently. As a client requests a test, the two endpoints are contacted and each bwctld server responds with the first available open schedule slot. This enables on-demand tests to co-exist with regularly scheduled tests since regularly scheduled tests are implemented by having the client request tests on regular intervals. Different priorities can be implemented using the event_horizon configuration directive to bwctld. (By allowing clients that implement regularly scheduled tests to reserve their time slots further into the future.)

Connection/Authentication Arguments:

-4

Forces bwctl to use IPv4 addresses only.

Default:

Unspecified (IPv6 is preferred).

-6

Forces bwctl to use IPv6 addresses only.

Default:

Unspecified (IPv6 is preferred).

-A authmethod

authmethod is used to specify the authentication method the bwctl client is willing to use for communication with the bwctld on the sendhost and recvhost. The authentication options of bwctl are intended to be extensible. The communication from the bwctl client to each bwctld server may take different options for different types of authentication. If the authmethod option is specified for either the -s, or the -c argument, it overrides the authmethod specified with the -A option for communication with that particular host. (Therefore, the -A argument is really only useful if the same authentication can be used with both hosts.)

Allowing different authentication methods for each connection should allow a client to use different authentication methods with different servers which should in turn allow cross-domain tests to occur more easily.

The format for authmethod is:

authmode [authscheme schemeopts]

authmode

Specifies the authentication mode the client is willing to speak with a server. It must be set as a character string with any or all of the characters "AEO". The modes are:

A

[A]uthenticated. This mode encrypts the control connection.

E

[E]ncrypted. This mode encrypts the control connection. If the test supports encryption, this mode will additionally encrypt the test stream. (Encryption of the test stream is not currently supported, so this mode is currently identical to authenticated.)

O

[O]pen. No encryption of any kind is done.

The client can specify all the modes with which it is willing to communicate. The most strict mode that both the server and the client are willing to use will be selected.

Default:

"AEO"

authscheme schemeopts

authscheme indicates the authentication scheme that should be used to achieve the authenticated or encrypted modes. schemeopts are a list of arguments specific to each particular authentication scheme. Supported authscheme values follow (listed with the schemeopts each scheme requires):

AESKEY userid [keyfile]

This is the initial "simple" shared secret (AES key) model. userid is required to identify which shared secret the server and client should use. keyfile optionally specifies a file to retrieve the AES key from. If keyfile is not specified, the user will be prompted for a passphrase. keyfile can be generated using the aespasswd(1) application.

Default:

Unauthenticated

authscheme and schemeopts are only needed if authenticated communication (A or E modes of authmode) is wanted with sendhost and recvhost.

-B srcaddr

Bind the local address of the client socket to srcaddr. srcaddr can be specified using a DNS name or using standard textual notations for the IP addresses.

Default:

Unspecified (wild-card address selection).

-c recvhost[:port] [authmethod]

Specifies the host that will run the Iperf, Thrulay or Nuttcp server. The :port suffix is optional and is only needed if bwctld is being run on a non-default port number. If an IPv6 address is being specified, note that the accepted format contains the recvhost portion of the specification in square brackets as: [fe80::fe9f:62d8]:4823. This ensures the port number is distinct from the address specification, and is not needed if the :port suffix is not being used.

At least one of the -c or -s options must be specified. If one of them is not specified, it is assumed to be the local host.

authmethod is a specifically ordered list of keywords that is only needed if authenticated communication is wanted with recvhost. These keywords are used to describe the type of communication and authentication that should be used to contact the recvhost. If recvhost and sendhost share the same authentication methods and identities, it is possible to specify the authmethod for both recvhost and sendhost using the -A argument. An authmethod specified with the -c option will override an authmethod specified with the -A argument for communication with the recvhost.

The format for authmethod and a description of the currently available authentication methods are described with the -A argument.

-k

This option has been deprecated. Originally, it was used to specify the keyfile for authentication. All authentication options can now be specified using the -A argument. For the next several versions this option will report an error. Eventually, it may be reclaimed for another purpose.

-s sendhost[:port] [authmethod]

Specifies the host that will run the Iperf, Thrulay or Nuttcp client. The :port suffix is optional and is only needed if bwctld is being run on a non-default port number. If an IPv6 address is being specified, note that the accepted format contains the sendhost portion of the specification in square brackets as: [fe80::fe9f:62d8]:4823. This ensures the port number is distinct from the address specification, and is not needed if the :port suffix is not being used.

At least one of the -c or -s options must be specified. If one of them is not specified, it is assumed to be the local.

authmethod is a specifically ordered list of keywords that is only needed if authenticated communication is wanted with sendhost. These keywords are used to describe the type of communication and authentication that should be used to contact the sendhost. If recvhost and sendhost share the same authentication methods and identities, it is possible to specify the authmethod for both recvhost and sendhost using the -A argument. An authmethod specified with the -s option will override an authmethod specified with the -A argument for communication with the sendhost.

The format for authmethod and a description of the currently available authentication methods are described with the -A argument.

-U

This option has been deprecated. Originally, it was used to specify the username to identify the AES key for authentication. All authentication options can now be specified using the -A argument. For the next several versions this option will report an error. Eventually, it may be reclaimed for another purpose.

Throughput Test Arguments:

The arguments were named to match their counterparts in Iperf as closely as possible.

Some of the options are not available for some of the throughput testers. BWCTL does not support UDP tests, changing the output format or changing the output units for either Nuttcp or Thrulay.

-T

Specify which throughput tester to use:

iperf

thrulay

nuttcp

Default:

None. Selects a tool that the client and server have in common

-S TOS

Set the TOS byte in the sending packets.

Default:

None.

-D DSCP

Set an RFC 2474 style DSCP value for the TOS byte in the sending packets. This can be set using a 6-bit numeric value in decimal, hex, or octal. Additionally, the following set of symbolic DSCP name constants are understood. (Example applications are taken from RFC 4594.)

Default:

Unset.

-b bandwidth

Limit UDP send rate to bandwidth (bits/sec).

Default:

1 Mb

-i interval

Report interval (seconds).

Default:

unset (no intervals reported)

-l len

length of read/write buffers (bytes).

Default:

8 KB TCP, 1470 bytes UDP

-P nStreams

Number of concurrent streams for the test. See the -P option of Iperf for details.

-S TOS

Set the TOS (See RFC 1349) byte in packets.

Default:

0 (not set)

-t time

Duration of test (seconds).

Default:

10

-u

UDP test.

Default:

TCP test

-W window

Same as the -w option, except that the value is advisory. bwctl will attempt to dynamically determine the appropriate TCP window, based upon RTT information gathered from the control socket. If bwctl is unable to dynamically determine a window, the value window will be used.

Default:

Unset (system defaults)

-w window

Socket buffer sizes (bytes). For TCP, this sets the TCP window size. For UDP, this sets the socket receive buffer size.

Default:

Unset (system defaults)

Scheduling Arguments:

-a syncfuzz

Allow bwctl to run without a synchronized system clock. Use this to specify how far off the local clock is from UTC. bwctl prefers to have an NTP synchronized system clock to ensure the two endpoints of the test are actually agreeing to the same scheduled time window for test execution.

If two systems do NOT have a close enough notion of time, then the throughput test will eventually fail because one endpoint of the test will attempt to run at a different time than the other.

If the operating system supports the NTP system calls, and the system clock is determined to be unsynchronized, error messages will still be reported depending upon the value of the -e flag.

When calculating the time errors, this value will be aded in to account for the difference. The maximum time offset can be bounded on the server side, using the max_time_error directive, to prevent a denial of service attack. If set, the server will reject any requests to test with a peer that has too high a timestamp error.

Default:

Unset (Defaults to Set for systems without the NTP system calls)

-I interval

Specifies that bwctl should attempt to run a throughput test every interval seconds.

Default:

Unset. If it is unset, bwctl only runs the test once.

-L longest

Specifies the longest amount of time the client is willing to wait for a reservation window. When bwctl requests a test from the bwctld server, it specifies the earliest time and the latest time it is willing to accept. The latest time is determined by adding this longest option to the earliest time. The earliest time is essentially 'now'. The longest time is specified as a number of seconds.

Default:

If interval is set, the default is 50% of interval. Otherwise, the default is twice the test duration time but no smaller than 5 minutes. (See -t.)

-n nIntervals

Number of tests to perform if the -I option is set.

Default:

Continuous

-R alpha

Randomize the start time of the test within this alpha percent of the interval. Valid values for alpha are from 0-50. bwctl will attempt to run the test every interval +/- alpha percent. For example, if the interval is 300 seconds and alpha is set to 10 percent, then bwctl will attempt to run a test every 270-330 seconds. This option is only useful with the -I option.

Default:

0 (no randomness)

Output Arguments:

-d dir

Specifies directory for results files if the -p option is set.

-e facility

Syslog facility to log messages to.

Default:

LOG_USER

-f units

Specify the units for the tool to use when displaying the results. The accepted values for units are tool specific.

Iperf:

k

Kilobits per second

K

Kilobytes per second

m

Megabits per second

M

Megabytes per second

-h

Print a help message.

-p

Place test results in files. Print the filenames to stdout when results are complete.

-q

Quiet output. Output as little as possible.

-r

Send syslog messages to stderr. This is the default unless the -q option is specified so this option is only useful with the -q option.

-V

Print version information and exit.

-v

Verbose output. Specifying additional -v's increases the verbosity.

-x

Output sender (client) results as well as receiver results. By default, sender results are not output. If the -p option is specified, the sender results are placed in an additional file.

-y format

Specify the output format of the tool. The accepted values for format are tool specific.

Iperf:

c

[c]omma-separated output

Only tested with versions 1.7.0 and 2.0.b of Iperf.

bwctl -c somehost.example.com

• Run a default 10 second TCP test as soon as possible with local as the sender and somehost.example.com as the receiver, using whichever tools they have in common. Return the results from the receive side of the test.

bwctl -x -c somehost.example.com

• Like the previous test, but also return the results from the sender side of the test.

bwctl -x -c somehost.example.com -s otherhost.example.com

• Like the previous test, but with otherhost.example.com as the sender instead of local.

bwctl -t 30 -T iperf -s somehost.example.com

• Run a 30 second TCP Iperf test with somehost.example.com as the sender and local as the receiver.

bwctl -I 3600 -R 10 -t 10 -u -b 10m -s somehost.example.com

• Run a 10 second UDP test about every hour (3600 +/- 360 seconds) with the sender rate limited to 10 Mbits per second from somehost.example.com to local.

bwctl -s somehost.example.com AE AESKEY someuser

• Run the default 10 second TCP test. Authenticate using the identity someuser. bwctl will prompt for a passphrase that will be used to create an AES key.

bwctld(8) and the http://e2epi.internet2.edu/bwctl/ web site.

For details on Iperf, see the http://sourceforge.net/projects/iperf web site.

For details on Nuttcp, see the http://www.wcisd.hpc.mil/nuttcp/Nuttcp-HOWTO.html web site.

For details on Thrulay, see the http://e2epi.internet2.edu/thrulay/ web site.

This material is based in part on work supported by the National Science Foundation (NSF) under Grant No. ANI-0314723. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.