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Port Mirroring

Introduction

The objective of this exercise is to write a P4 program that mirrors all the incoming packets to a specific port where a collector is located at.

Upon receiving a packet, your program should make a copy of the corresponding packet and send it to the collector host. Your switch will have a single table, which we have populated with static rules. You will only need to implement the logic for cloning packets.

We will use a simple topology for this exercise. It is a single switch connected to three hosts, h1, h2 and h3 where h3 acts as the collector connected to the mirroring port (port 3) as follow:

                h1       h3 (Collector)
                 \      /
                  \    /
                    s1  
                  /    
                 /      
               h2

Spoiler alert: There is a reference solution in the solution sub-directory. Feel free to compare your implementation to the reference.

Step 1: Run the (incomplete) starter code

The directory with this README also contains a skeleton P4 program, mirroring.p4, which forwards packets between h1 and h2. Your job will be to extend this skeleton program to mirror all the packets to the collector host, h3.

Before that, let's compile the incomplete mirroring.p4 and bring up a switch in Mininet to test its behavior.

  1. In your shell, run:

    make run

    This will:

    • compile mirroring.p4, and
    • start the topology in Mininet and configure all switches with the appropriate P4 program + table entries, and
    • configure all hosts with the commands listed in topology.json

  2. You should now see a Mininet command prompt. Bring up the terminal for h3.

    mininet> Xterm h3

    Since this is the collector host, run tcpdump to observe incoming mirrored packets.

    root@p4:~/tutorials/exercise/mirroring# tcpdump -i eth0

  3. You should now see a Mininet command prompt. Try to ping between hosts in the topology:

    mininet> h1 ping h2
mininet> pingall

    If the packets are mirrored properly, you should observe the corresponding packets on tcpdump.

  4. Type exit to leave each xterm and the Mininet command line. Then, to stop mininet:

    make stop

    And to delete all pcaps, build files, and logs:

    make clean

No packets should be received by h3, since the mirror action is not implemented yet. Your job is to extend this file so it mirrors packets to the collector host.

Step 2: Implement Port Mirroring

  1. TODO: An action (called mirror) that:
    1. Invokes the clone extern of the V1Model.
    2. Passes the appropriate CloneType and session ID as the parameter to the clone method.
  2. TODO: Call the mirror action in your program so that it mirrors all arriving packets.
  3. TODO: Add port 3 to your specified session.
    1. In a new terminal, start the simple_switch_CLI
    2. Execute the command mirroring_add followed the session ID the port number.

Step 3: Run your solution

Follow the instructions from Step 1. This time, you should be able to observe packets being mirrored to h3. And, you're done!

Useful Resources

Check out the resources below that contains further details/explanations on clone/clone3.

Food for thought

Questions to consider:

  • What is the difference between clone and clone3?

Troubleshooting

There are several problems that might manifest as you develop your program:

  1. mirroring.p4 might fail to compile. In this case, make run will report the error emitted from the compiler and halt.

  2. mirroring.p4 might compile, but the switch might not process packets in the desired way. The logs/s1.log file contain detailed logs describing how each switch processes each packet. The output is detailed and can help pinpoint logic errors in your implementation.

Cleaning up Mininet

In the latter two cases above, make run may leave a Mininet instance running in the background. Use the following command to clean up these instances:

make stop