Chapter 1 Mininet Walkthrough¶
Part 1 Everyday Mininet Usage¶
$preceeds Linux commands that should be typed at the shell promptmininet>preceeds Mininet commands that should be typed at Mininet’s CLI,#preceeds Linux commands that are typed at a root shell prompt
Display Startup Options¶
display a help message describing Mininet’s startup options
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Start Wireshark¶
To view control traffic using the OpenFlow Wireshark dissector(解析器), first open wireshark in the background:
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And then it will show that:
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Interact with Hosts and Switches¶
Start a minimal topology and enter the CLI:
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The default topology is the minimal topology, which includes
- one OpenFlow kernel switch connected to two hosts,
- and the OpenFlow reference controller.
This topology could also be specified on the command line with --topo=minimal. Other topologies are also available out of the box; see the --topo section in the output of mn -h.
All four entities (2 host processes, 1 switch process, 1 basic controller) are now running in the Virtual Machine. The controller can be outside the VM, and instructions for that are at the bottom.
If no specific test is passed as a parameter, the Mininet CLI comes up:
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Basic Orders¶
- Display Mininet CLI commands:
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- Display nodes:
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- Display links:
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- Dump information about all nodes:
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and You should see the switch and two hosts listed.
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Orders concerning Individuals¶
You should be careful with "namespace" here! It's a bit confusing.
If the first string typed into the Mininet CLI is a host, switch or controller name, the command is executed on that node. Run a command on a host process:
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You should see the host’s h1-eth0 and loopback (lo) interfaces.
Note that this interface (h1-eth0) is not seen by the primary Linux system when ifconfig is run, because it is specific to the network namespace of the host process.
In contrast, the switch by default runs in the root network namespace, so running a command on the “switch” is the same as running it from a regular terminal:
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This will show the switch interfaces, plus the VM’s connection out (eth0).
For other examples highlighting that the hosts have isolated network state, run arp and route on both s1 and h1.
It would be possible to place every host, switch and controller in its own isolated network namespace, but there’s no real advantage to doing so, unless you want to replicate a complex multiple-controller network. Mininet does support this; see the --innamespace option.
Note that only the network is virtualized; each host process sees the same set of processes and directories. For example, print the process list from a host process:
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This should be the exact same as that seen by the root network namespace:
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It would be possible to use separate process spaces with Linux containers, but currently Mininet doesn’t do that. \
Having everything run in the “root” process namespace is convenient for debugging, because it allows you to see all of the processes from the console using ps, kill, etc.
Test connectivity between hosts¶
Now, verify that you can ping from host 0 to host 1:
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If a string appears later in the command with a node name, that node name is replaced by its IP address; this happened for h2.
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You should see OpenFlow control traffic:
- The first host ARPs for the MAC address of the second, which causes a
packet_inmessage to go to the controller. - The controller then sends a
packet_outmessage to flood the broadcast packet to other ports on the switch (in this example, the only other data port). - The second host sees the ARP request and sends a reply.
- This reply goes to the controller, which sends it to the first host and pushes down a flow entry.
- Now the first host knows the MAC address of the second, and can send its ping via an ICMP Echo Request.
- This request, along with its corresponding reply from the second host, both go the controller and result in a flow entry pushed down (along with the actual packets getting sent out).
If we try to repeat this ping again:
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At the first time, it costs us 6.37ms while costs only 0.854ms now!
- We can see a much lower
pingtime for the second try (< 100us). - A flow entry covering ICMP
pingtraffic was previously installed in the switch, so no control traffic was generated, and the packets immediately pass through the switch.
An easier way to run this test is to use the Mininet CLI built-in pingall command, which does an all-pairs ping:
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Run a simple web server and client¶
Remember that ping isn’t the only command you can run on a host! Mininet hosts can run any command or application that is available to the underlying Linux system (or VM) and its file system.
You can also enter any bash command, including job control (&, jobs, kill, etc..)
Firstly, check the version of your python:
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Next, try starting a simple HTTP server on h1, making a request from h2, then shutting down the web server:
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Exit and Cleanup¶
Exit the mininet CLI and back to your terminal
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If the mininet crashes for some reason, you should clean it up
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Part 2: Advanced Startup Options¶
Changing Topology Size and Type¶
The default topology is a single switch connected to two hosts listed in Part1.
You could change this to a different topo with --topo, and pass parameters for that topology’s creation.
For example, to verify all-pairs ping connectivity with one switch and three hosts: Run a regression test:
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Another example, with a linear topology (where each switch has one host, and all switches connect in a line):
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Parametrized topologies are one of Mininet’s most useful and powerful features.
Link variations¶
Mininet 2.0 allows you to set link parameters, and these can even be set automatially from the command line:
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- tc: 表示使用 Linux 中的 Traffic Control（流量控制）工具来模拟链路
- bw: bandwidth of this link
- delay: the delay for each link is 10 ms
From the message listed above, we can know that:
the round trip time (RTT) should be about 40 ms (10x4), since the ICMP request traverses two links (one to the switch, one to the destination) and the ICMP reply traverses two links coming back.
You can customize each link using Mininet’s Python API, but for now you will probably want to continue with the walkthrough.
Adjustable Verbosity¶
"Adjustable Verbosity(冗长)" 意味着能够根据需要调整程序或系统输出的详细程度：
- 在软件开发或系统管理中，通常会有不同级别的详细程度来描述输出信息，从简洁的摘要到详细的调试信息。
- 通过可调节的详细程度，用户可以根据自己的需求来控制输出的丰富程度，这对于诊断问题、调试代码或监控系统状态非常有用。
- 等价于ns-3中的日志组件 Log ( )
The default verbosity level is info, which prints what Mininet is doing during startup and teardown. Compare this with the full debug output with the -v param:
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Lots of extra detail will print out. Now try output, a setting that prints CLI output and little else:
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Outside the CLI, other verbosity levels can be used, such as warning, which is used with the regression tests to hide unneeded function output.
Custom Topologies¶
In fact, there are 2 main methods to customize your own topology
You can learn more details in my personal study note concerning different ways to design topology
Custom topologies can be easily defined as well, using a simple Python API, and an example is provided in custom/topo-2sw-2host.py. This example connects two switches directly, with a single host off each switch:
When a custom mininet file is provided, it can add new topologies, switch types, and tests to the command-line. For example:
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ID = MAC¶
- By default, hosts start with randomly assigned MAC addresses.
- This can make debugging tough, because every time the Mininet is created, the MACs change, so correlating control traffic with specific hosts is tough.
The --mac option is super-useful, and sets the host MAC and IP addrs to small, unique, easy-to-read IDs.
Before:
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After:
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- In contrast, the MACs for switch data ports reported by Linux will remain random.
- This is because you can ‘assign’ a MAC to a data port using OpenFlow.
- This is a somewhat subtle point which you can probably ignore for now.
XTerm Display¶
For more complex debugging, you can start Mininet so that it spawns one or more xterms.
To start an xterm for every host and switch, pass the -x option:
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After a second, the xterms will pop up, with automatically set window names.
Alternately, you can bring up additional xterms as shown below.
- By default, only the hosts are put in a separate namespace
- the window for each switch is unnecessary (that is, equivalent to a regular terminal), but can be a convenient place to run and leave up switch debug commands, such as flow counter dumps.
Xterms are also useful for running interactive commands that you may need to cancel, for which you’d like to see the output.
For example:
In the xterm labeled “switch: s1 (root)”, run:
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Nothing will print out; the switch has no flows added. To use ovs-ofctl with other switches, start up mininet in verbose mode (详细模式) and look at the passive listening ports for the switches when they’re created.
Now, in the xterm labeled “host: h1”, run:
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Go back to s1 and dump the flows: # ovs-ofctl dump-flows tcp:127.0.0.1:6654
You should see multiple flow entries now.
Alternately (and generally more convenient), you could use the dpctl command built into the Mininet CLI without needing any xterms or manually specifying the IP and port of the switch.
You can tell whether an xterm is in the root namespace by checking ifconfig; if all interfaces are shown (including eth0), it’s in the root namespace. Additionally, its title should contain “(root)”.
Close the setup, from the Mininet CLI:
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and the xterms should automatically close.
Other Switch Types¶
Other switch types can be used. For example, to run the user-space switch:
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Note the much lower TCP iperf-reported bandwidth compared to that seen earlier with the kernel switch.
Traits:
- If you do the ping test shown earlier, you should notice a much higher delay, since now packets must endure additional kernel-to-user-space transitions.
- The ping time will be more variable, as the user-space process representing the host may be scheduled in and out by the OS.
- On the other hand, the user-space switch can be a great starting point for implementing new functionality, especially where software performance is not critical.
Another example switch type is Open vSwitch (OVS), which comes preinstalled on the Mininet VM. The iperf-reported TCP bandwidth should be similar to the OpenFlow kernel module, and possibly faster:
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Mininet Benchmark¶
To record the time to set up and tear down a topology, use test ‘none’:
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Add some supplementary materials:
Benchmark（基准测试）是通过 在已知条件下运行一系列测试 来评估系统、设备或软件性能的过程。基准测试 旨在量化系统在特定负载或条件下的性能水平，通常涉及测量各种指标，如处理速度、内存利用率、响应时间、吞吐量等。这些测试可以用于比较不同系统之间的性能差异，或者评估系统在不同条件下的性能表现。
在计算机领域，基准测试可用于评估 CPU、内存、存储设备、网络设备等硬件的性能，也可用于评估软件、数据库系统、操作系统和网络性能。Benchmark 结果可以帮助用户选择最佳的硬件或软件配置，或者优化系统以提高性能。
对 Mininet 进行基准测试可以帮助评估其在不同条件下的性能表现，例如，创建大型网络拓扑时的性能、数据包转发速率、延迟和吞吐量等。Benchmark 测试还可以用于比较不同版本的 Mininet 或不同硬件配置下的性能差异。
Part 3: Mininet Command-Line Interface (CLI) Commands¶
Display Options¶
To see the list of Command-Line Interface (CLI) options, start up a minimal topology and leave it running. Build the Mininet:
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Display the options:
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Python Interpreter¶
- If the first phrase on the Mininiet command line is
py, then that command is executed with Python. - This might be useful for extending Mininet, as well as probing its inner workings.
- Each host, switch, and controller has an associated Node object.
At the Mininet CLI, run:
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Print the accessible local variables:
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Next, see the methods and properties available for a node, using the dir() function:
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You can read the on-line documentation for methods available on a node by using the help() function:
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You can also evaluate methods of variables:
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Here are some results below:
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Link Up/Down¶
For fault tolerance testing, it can be helpful to bring links up and down.
To disable both halves of a virtual ethernet pair:
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You should see an OpenFlow Port Status Change notification get generated. To bring the link back up:
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XTerm Display¶
To display an xterm for h1 and h2:
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Part 4: Python API Examples¶
The examples directory in the Mininet source tree includes examples of how to use Mininet’s Python API, as well as potentially useful code that has not been integrated into the main code base.
SSH daemon per host¶
One example that may be particularly useful runs an SSH daemon on every host:
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From another terminal, you can ssh into any host and run interactive commands:
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Exit SSH example mininet:
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You will wish to revisit the examples after you’ve read the Introduction to Mininet, which introduces the Python API.
Other Uses¶
It's highly recommended to refer to Intro2Mininet
Part 5: Next Steps to master Mininet¶
Congrats! You’ve completed the Mininet Walkthrough. Feel free to try out new topologies and controllers or check out the source code.
- If you haven’t done so yet, you should definitely go through the OpenFlow tutorial
- Although you can get reasonably far using Mininet’s CLI, Mininet becomes much more useful and powerful when you master its Python API. The Introduction to Mininet provides an introduction to Mininet and its Python API.