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@@ -592,80 +592,77 @@ SQLite version: 3.7.9sourceid version is 2011-11-01 00:52:41 c7c6050ef060877ebe7
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<section>
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<title>Purpose</title>
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<para>
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- There is a growing need to evaluate performance of DHCP servers in
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- different traffic conditions to understand their bottle necks.
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- This helps to elimante bugs in existing DHCP software as well
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- as make informed decisions regarding new DHCP software designs
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- to significantly improve its performance. The perfdhcp tool has
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- been created to fill the gap in performance measurement capabilities
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- mostly. However, the number of implemented features and parameters
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- exposed to the user make this tool useful for functional testing as
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- well.
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+ Evaluation of the performance of a DHCP server requires that it
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+ be tested under varying traffic loads. perfdhcp is a testing
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+ tool with the capability to create traffic loads
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+ and generate statistics from the results. Additional features,
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+ such as the ability to send customised DHCP packets, allow it to
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+ be used in a wide range of functional testing.
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</para>
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</section>
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<section id="perfdhcp-key-features">
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<title>Key features</title>
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<para>
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- The perfdhcp exposes the number of command line parameters to
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- control DHCP message exchanges. Currently they fall back to
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+ perfdhcp has a number of command line switches to
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+ control DHCP message exchanges. Currently they fall into
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the following categories:
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- <orderedlist>
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+ <itemizedlist>
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<listitem>
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<para>
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Rate control - control how many DHCP exchanges
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- are initiated within a period of time. Tool can also simulate
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- best effort conditions attempting to initiate as many DHCP
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- packet exchanges within a unit of time as possible.
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+ are initiated within a period of time. The tool can also simulate
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+ best effort conditions by attempting to initiate as many DHCP
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+ packet exchanges as possible within a unit of time.
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</para>
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</listitem>
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<listitem>
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<para>
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- Test exit specifiers - control the conditions when test
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- completes including number of initiated exchanges, test period or
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- maximum number of dropped packets.
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+ Test exit specifiers - control the conditions for test
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+ completion, including the number of initiated exchanges,
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+ the test period orthe maximum number of dropped packets.
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</para>
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</listitem>
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<listitem>
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<para>
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Packet templates - specify files containing packet templates that
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- are used by perfdhcp to create custom DHCP messages instead of
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- default. Tool also allows to specify number of values indicating
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- offsets of variable values within a packet that are modified in
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- flight by the tool.
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+ are used by perfdhcp to create custom DHCP messages. The tool
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+ allows the specification of a number of values indicating
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+ offsets of values within a packet that are set by the tool.
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</para>
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</listitem>
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<listitem>
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<para>
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- Reporting - for each test produce the set of performance data
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- including achieved packet exchange rate (server performance).
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- There is also a number of diagnostic selectors available that
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- enable periodic (intermediate) reporting, packet timestamps
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- printing and detailed information about perfdhcp internal
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+ Reporting - for each test produce a set of performance data
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+ including the achieved packet exchange rate (server performance).
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+ There are a number of diagnostic selectors available that
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+ enable periodic (intermediate) reporting, printing of packet timestamps,
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+ and the listing of detailed information about internal perfdhcp
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states (for debugging).
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</para>
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</listitem>
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<listitem>
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<para>
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- Different mode of operations - specify DHCP version used
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- (v4 or v6), 2-way or 4-way exchanges, use Rapid Commit option
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- for DHCPv6.
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+ Different mode of operations - specify the DHCP protocol used
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+ (v4 or v6), two-way or four-way exchanges, use of the
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+ Rapid Commit option for DHCPv6.
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</para>
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</listitem>
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<listitem>
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<para>
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- IP layer options - specify local/remote address, local interface
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+ IP layer options - specify the local/remote address, local interface
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and local port to be used for communication with DHCP server.
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</para>
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</listitem>
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- </orderedlist>
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+ </itemizedlist>
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</para>
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</section>
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<section id="perfdhcp-command-line">
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<title>Command line options</title>
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<para>
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- The following command line options may be used with perfdhcp tool.
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- This summary also presents its possible exit codes as well as
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- error counters printed along when test is complete:
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+ The following "help" output from the tool describes the
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+ command line switches. This summary also lists the tool's
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+ possible exit codes as well as describing the
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+ error counters printed when the test is complete:
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<screen>$ <userinput>./perfdhcp -h</userinput>
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<![CDATA[perfdhcp [-hv] [-4|-6] [-r<rate>] [-t<report>] [-R<range>] [-b<base>]
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[-n<num-request>] [-p<test-period>] [-d<drop-time>] [-D<max-drop>]
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@@ -794,46 +791,51 @@ The exit status is:
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<section id="starting-perfdhcp">
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<title>Starting perfdhcp</title>
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<para>
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- In order to run performance test at least two separate systems
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- have to be installed: client and server. The first one has to have
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- perfdhcp tool installed, the latter has to have DHCP server
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- running (v4 or v6). If only single system is available the client
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+ In order to run a performance test, at least two separate systems
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+ have to be installed: client and server. The first one must have
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+ perfdhcp installed, and the latter must be running the DHCP server
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+ (either v4 or v6). If only single system is available the client
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and server can be run on virtual machines (running on the same
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- phisical system) but in this case performance data may be heavily
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- impacted by the performance of VMs.
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+ physical system) but in this case performance data may be heavily
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+ impacted by the overhead involved in running such the virtual
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+ machines.
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+ </para>
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+ <para>
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+ Currently, perfdhcp is seen from the server perspective as relay agent.
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+ This simplifies its implementation: specifically there is no need to
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+ receive traffic sent to braodcast addresses. However, it does impose
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+ a requirement that the IPv4
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+ address has to be set manually on the interface that will be used to
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+ communicate with the server. For example, if the DHCPv4 server is listening
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+ on the interface connected to the 172.16.1.0 subnet, the interface on client
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+ machine has to have network address assigned from the same subnet, e.g.
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+ <screen><userinput>#ifconfig eth3 172.16.1.2. netmask 255.255.255.0 up</userinput></screen>
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</para>
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<para>
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- The DHCP operates on low port numbers (67 for DHCPv4 relays and
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- 547 for DHCPv6). Running perfdhcp with non-root priviliges will
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+ As DHCP uses low port numbers (67 for DHCPv4 relays and
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+ 547 for DHCPv6), running perfdhcp with non-root privileges will
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usually result in the error message similar to this:
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+
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<screen><userinput>$./perfdhcp -4 -l eth3 -r 100 all</userinput>
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Error running perfdhcp: Failed to bind socket 3 to 172.16.1.2/port=67
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</screen>
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- perfdhcp has the '-L' command line option that
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- imposes use of custom local port. Thus the following command
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- line will work:
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+
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+ The '-L' command line switch allows the use of a custom local port.
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+ However, although the following command line will work:
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+
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<screen><userinput>$./perfdhcp -4 -l eth3 -r 100 -L 10067 all</userinput></screen>
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- but in the standard configuration no responses will be received
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- from the ISC DHCP server because server responds to default relay
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- port 67.
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- Alternative way to overcome this issue is to run perfdhcp as root.
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- </para>
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- <para>
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- Currently, perfdhcp is seen from the server perspective as relay agent.
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- This simplifies its implementation (specifically there is no need to
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- receive traffic sent to braodcast addresses). This imposes that IPv4
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- address has to be set manually on the interface that will be used to
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- communicate with the server. For example, if DHCPv4 server is listening
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- on the interface connected to 172.16.1.0 subnet, interface on client
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- machine has to have network address assigned from the same subnet
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- on one of its interfaces connected to this subnet:
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- <screen><userinput>#ifconfig eth3 172.16.1.2. netmask 255.255.255.0 up</userinput></screen>
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+
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+ in the standard configuration no responses will be received
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+ from the DHCP server because the server responds to default relay
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+ port 67. A way to overcome this issue is to run
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+ perfdhcp as root.
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</para>
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+
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</section>
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<section id="perfdhcp-commandline-examples">
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<title>perfdhcp command line examples</title>
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<para>
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- In this section the perfdhcp command line examples
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+ In this section, a number of perfdhcp command line examples
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are presented as a quick start guide for new users. For the
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detailed list of command line options refer to
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<xref linkend="perfdhcp-command-line"/>.
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@@ -841,8 +843,8 @@ Error running perfdhcp: Failed to bind socket 3 to 172.16.1.2/port=67
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<section id="perfdhcp-basic-usage">
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<title>Example: basic usage</title>
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<para>
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- If server is listening on interface with IPv4 address 172.16.1.1
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- the simpliest perfdhcp command line will look like this:
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+ If server is listening on interface with IPv4 address 172.16.1.1,
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+ the simplest perfdhcp command line will look like:
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<screen><userinput>#./perfdhcp 172.16.1.1</userinput>
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***Rate statistics***
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Rate: 206.345
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@@ -871,15 +873,13 @@ max delay: 258.634 ms
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std deviation: 56.936 ms
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collected packets: 0
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</screen>
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- In this case perfdhcp will use remote address 172.16.1.1 as a
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- destination address and will use suitable local interface for
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- communication. Since, no rate control parameters have been specified
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- it will be initiating DHCP exchanges with the maximum possible
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- rate (it will try to initiate maximum number of exchanges per
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- second and count number of completed exchanged). Due to server's
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- performance constraints, many DHCP packets sent to server are likely
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- to be dropped. The performance test will be running until it is
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- not interrupted by the user (with ^C).
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+ Here, perfdhcp uses remote address 172.16.1.1 as a
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+ destination address and will use a suitable local interface for
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+ communication. Since, no rate control parameters have been specified,
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+ it will initiate DHCP exchanges at the maximum possible rate. Due to the server's
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+ performance limitation, it is likely that many of the packets will be dropped.
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+ The performance test will continue running until it is
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+ interrupted by the user (with ^C).
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</para>
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<para>
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The default performance statistics reported by perfdhcp have the
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@@ -893,52 +893,56 @@ collected packets: 0
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<listitem><para>received packets - total number of DHCP packets
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of specific type received from the server.</para></listitem>
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<listitem><para>drops - number of dropped packets for the
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- particular exchange. Number of dropped packets is calculated as
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- a difference between number of sent packets and number of
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- response packets received from the server. It is likely that
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- server sent the reponse but perfdhcp execution had ended before
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- reponse arrived. In such case this packet will be assumed
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- dropped.</para></listitem>
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+ particular exchange. The number of dropped packets is calculated as
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+ the difference between the number of sent packets and number of
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+ response packets received from the server. In some cases, the
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+ server will have sent a reponse but perfdhcp execution ended before
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+ the reponse arrived. In such case this packet will be counted
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+ as dropped.</para></listitem>
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<listitem><para>orphans - number of packets that have been
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received from the server and did not match any packet sent by
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perfdhcp. This may occur if received packet has been sent
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- to some other host or if exchange time out has occured and
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- has been been garbage collected.</para></listitem>
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+ to some other host or if then exchange timed out and
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+ the sent packet was removed from perfdhcp's list of packets
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+ awaiting a response.</para></listitem>
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<listitem><para>min delay - minimum delay that occured between
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- sending the packet to the server and receiving reponse from
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+ sending the packet to the server and receiving a reponse from
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it.</para></listitem>
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<listitem><para>avg delay - average delay between sending the
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- packet of the specific type the server and receiving response
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+ packet of the specific type the server and receiving a response
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from it.</para></listitem>
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- <listitem><para>max delay - maximum delat that occured between
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- sedning the packet to the server and receiveing response from
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+ <listitem><para>max delay - maximum delay that occured between
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+ sending the packet to the server and receiving a response from
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it.</para></listitem>
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- <listitem><para>std deviation - standard deviation of delay
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+ <listitem><para>std deviation - standard deviation of the delay
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between sending the packet of a specific type to the server and
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receiving response from it.</para></listitem>
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- <listitem><para>collected packets - number of garbage collected
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- sent packets. Packets may get garbage collected when waiting time
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- for server response exceeds value set with
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+ <listitem><para>collected packets - number of sent packets that
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+ were garbage collected. Packets may get garbage collected when
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+ the waiting time for server a response exceeds value set with the
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+ '-d' (drop time) switch.
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<![CDATA[-d<drop-time>]]>.</para></listitem>
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</itemizedlist>
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</para>
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<para>
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- perfdhcp allows to run the test using specified interface:
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+ Note: should multiple interfaces on the system running perfdhcp be
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+ connected to the same subnet, the interface to be used for the test
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+ can be specified using either the interface name:
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<screen><userinput>#./perfdhcp -l eth3</userinput></screen>
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- or local address assigned to it:
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+ or a local address assigned to it:
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<screen><userinput>#./perfdhcp -l 172.16.1.2</userinput></screen>
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</para>
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</section>
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<section id="perfdhcp-rate-control">
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<title>Example: rate control</title>
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<para>
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- In the examples above perfdhcp initiates new exchanges with best
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- effort rate. In this case many packets is expected to be dropped by the
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- server due to performance limitations. Many times it is desired to set
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- the expected (reasonable) rate and verify if generated traffic is
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- handled without packet dropes by DHCP server. The following command will
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- make perfdhcp to initiate 300 4-way exchanges per second and test will
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- last for 60 seconds:
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+ In the examples above perfdhcp initiates new exchanges with a best
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+ effort rate. With this setting, many packets are expected to be dropped
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+ by the server due to performance limitations. In many cases though, it is
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+ desired to verify that the server can handle an expected (reasonable) rate
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+ without dropping any packets. The following command is an example of such
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+ a test: it causes perfdhcp to initiate 300 four-way exchanges
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+ per second, and runs the test for 60 seconds:
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<screen><userinput>#./perfdhcp -l eth3 -p 60 -r 300</userinput>
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***Rate statistics***
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Rate: 256.683 exchanges/second, expected rate: 300 exchanges/second
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@@ -967,12 +971,13 @@ max delay: 576.749 ms
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std deviation: 58.189 ms
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collected packets: 0
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</screen>
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- Note that in this example the packet drops have been significantly
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- reduced thanks to setting reasonable rate. The non-zero number of
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- packet drops and achived rate (256/s) below expected rate (300/s)
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- indicate that server's measured performance is lower than 300 leases
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- per second. Further rate decrease should eliminate most of the packet
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- drops and bring achived rate close to expected rate:
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+ Note that here, the packet drops for the DISCOVER-OFFER
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+ exchange have been significantly reduced (when compared with the
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+ output from the previous example) thanks to the setting of a
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+ reasonable rate. The non-zero number of packet drops and achieved
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+ rate (256/s) indicate that server's measured performance is lower than 300 leases
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+ per second. A further rate decrease should eliminate most of the packet
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+ drops and bring the achieved rate close to expected rate:
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<screen><userinput>#./perfdhcp -l eth3 -p 60 -r 100 -R 30</userinput>
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***Rate statistics***
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Rate: 99.8164 exchanges/second, expected rate: 100 exchanges/second
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@@ -1001,25 +1006,29 @@ max delay: 189.658 ms
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std deviation: 5.876 ms
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collected packets: 0
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</screen>
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+ There are now no packet drops, confirming that the server is able to
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+ handle a load of 100 leases/second.
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Note that the last parameter (-R 30) configures perfdhcp to simulate
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- traffic from distinct 30 clients.
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+ traffic from 30 distinct clients.
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</para>
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</section>
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<section id="perfdhcp-templates">
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<title>Example: templates</title>
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<para>
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- By default the DHCP messages are formed in-flight with default options.
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- If desired, there is a way to define custom packet format with template
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- files. Content in template files is encoded in hexadecimal format. The
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+ By default the DHCP messages are formed with default options. With
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+ template files, it is possible to define a custom packet format.
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+ </para>
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+ <para>
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+ The content in template files is encoded in hexadecimal format.
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perfdhcp forms the packet by replacing parts of the binary stream read
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- from the file with variable data such as elapsed time, HW address, DUID
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+ from the file with variable data such as elapsed time, hardware address, DUID
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etc. The offsets where such variable data is placed is specific to the
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template file and have to be specified from the command line. Refer to
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<xref linkend="perfdhcp-command-line"/> to find out how to
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specify offsets for particular options and fields. With the following
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command line the DHCPv6 SOLICIT and REQUEST packets will be formed from
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- solicit-example.hex and request6-example.hex packets:
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- <screen><userinput>#./perfdhcp -6 -l eth3 -r 100 -R 20 -T templates/solicit-example.hex -T templates/request6-example.hex -O 21 -E 84 -S 22 -I 40 servers</userinput>
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+ solicit.hex and request6.hex packets:
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+ <screen><userinput>#./perfdhcp -6 -l eth3 -r 100 -R 20 -T solicit.hex -T request6.hex -O 21 -E 84 -S 22 -I 40 servers</userinput>
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***Rate statistics***
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Rate: 99.5398 exchanges/second, expected rate: 100 exchanges/second
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@@ -1047,15 +1056,15 @@ max delay: 6.490 ms
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std deviation: 0.518 ms
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collected packets: 0
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</screen>
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- where:
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+ where the switches have the following meaning:
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<itemizedlist>
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<listitem><para>two occurences of -O 21 - DUID's last octet
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positions in SOLICIT and REQUEST respectively.</para></listitem>
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- <listitem><para>-E 84 - elapsed time option position in
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+ <listitem><para>-E 84 - elapsed time option position in the
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REQUEST template</para></listitem>
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- <listitem><para>-S 22 - server id position in REQUEST
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+ <listitem><para>-S 22 - server id position in the REQUEST
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template</para></listitem>
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- <listitem><para>-I 40 - IA_NA option position in REQUEST
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+ <listitem><para>-I 40 - IA_NA option position in the REQUEST
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template</para></listitem>
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</itemizedlist>
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</para>
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Stephen Morris