Adding starter code and solution for p4runtime exercise (#81)
Summary of changes: - Adding the p4runtime starter code and solution. - Adding NO_P4, BMV2_SWITCH_EXE and P4C_ARGS to utils/Makefile - Updated p4runtime/Makefile to use variables - Adding conversion functions for match and action param values - Separating P4Info and P4Runtime libraries - Updating global README and adding p4runtime/README.md - Disabling screen saver on VM GUI - Adding desktop icons for Terminal, Wireshare and Sublime Text - Updating topo.pdf -> png for Markdown viewing in basic_tunnel and p4runtime READMEs
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Brian O'Connor
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Robert Soule
Robert Soule
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P4D2_2017_Fall/exercises/p4runtime/README.md
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P4D2_2017_Fall/exercises/p4runtime/README.md
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# Implementing a Control Plane using P4 Runtime
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## Introduction
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In this exercise, we will be using P4 Runtime to send flow entries to the
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switch, instead of using the switch's CLI. We will be using the same P4
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program that you used in the previous in the basic_tunnel exercise. The
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P4 program has be renamed to `advanced_tunnel.py` and has been augmented
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with a counter, `tunnelCount`, and two new actions, `myTunnel_ingress`
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and `myTunnel_egress`.
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You will use the starter program, `mycontroller.py`, and a few helper
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libraries in the `p4runtime_lib` directory to create the table entries
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necessary to tunnel traffic between host 1 and 2.
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> **Spoiler alert:** There is a reference solution in the `solution`
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> sub-directory. Feel free to compare your implementation to the
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> reference.
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## Step 1: Run the (incomplete) starter code
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The starter code for this assignment is in a file called `mycontroller.py`
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and it will install only some of the rules that you need tunnel traffic between
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two hosts.
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Let's first compile the new P4 program, start the network, use `mycontroller.py`
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to install a few rules, and look at the tunnel ingress counter to see that things
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are working as expected.
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1. In your shell, run:
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```bash
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make
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```
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This will:
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* compile `advanced_tunnel.p4`, and
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* start a Mininet instance with three switches (`s1`, `s2`, `s3`)
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configured in a triangle, each connected to one host (`h1`, `h2`,
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and `h3`).
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* The hosts are assigned IPs of `10.0.1.1`, `10.0.2.2`, etc.
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2. You should now see a Mininet command prompt. Start a ping between h1 and h2:
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```bash
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mininet> h1 ping h2
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```
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Because there are no rules on the switches, you should **not** receive any
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replies yet.
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3. Open another shell and run the starter code:
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```bash
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cd ~/tutorials/P4D2_2017_Fall/exercises/p4runtime
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./mycontroller.py
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```
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This will install the `advanced_tunnel.p4` program on the switches and push the
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tunnel ingress rules.
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The program prints the tunnel ingress and egress counters every 2 seconds.
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You should see the ingress tunnel counter for s1 increasing:
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```
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s1 ingressTunnelCounter 100: 2 packets
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```
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The other counters should remain at zero.
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4. Press `Ctrl-C` to the second shell to stop `mycontroller.py`
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Each switch is currently mapping traffic into tunnels based on the destination IP
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address. Your job is to write the rules that forward the traffic between the switches
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based on the tunnel ID.
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### A note about the control plane
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A P4 program defines a packet-processing pipeline, but the rules
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within each table are inserted by the control plane. In this case,
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`mycontroller.py` implements our control plane, instead of installing static
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table entries like we have in the previous exercises.
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**Important:** A P4 program also defines the interface between the
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switch pipeline and control plane. This interface is defined in the
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`advanced_tunnel.p4info` file. The table entries that you build in `mycontroller.py`
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refer to specific tables, keys, and actions by name, and we use a P4Info helper
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to convert the names into the IDs that are required for P4 Runtime. Any changes
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in the P4 program that add or rename tables, keys, or actions will need to be
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reflected in your table entries.
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## Step 2: Implement Tunnel Forwarding
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The `mycontroller.py` file is a basic controller plane that does the following:
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1. Establishes a gRPC connection to the switches for the P4 Runtime service.
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2. Pushes the P4 program to each switch.
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3. Writes tunnel ingress and tunnel egress rules for two tunnels between h1 and h2.
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4. Reads tunnel ingress and egress counters every 2 seconds.
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It also contains comments marked with `TODO` which indicate the functionality
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that you need to implement.
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Your job will be to write the tunnel transit rule in the `writeTunnelRules` function
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that will match on tunnel ID and forward packets to the next hop.
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## Step 3: Run your solution
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Follow the instructions from Step 1. If your Mininet network is still running,
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you will just need to run the following in your second shell:
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```bash
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./my_controller.py
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```
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You should start to see ICMP replies in your Mininet prompt, and you should start to
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see the values for all counters start to increment.
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### Extra Credit and Food for Thought
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You might notice that the rules that are printed by `mycontroller.py` contain the entity
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IDs rather than the table names. You can use the P4Info helper to translate these IDs
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into entry names.
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Also, you may want to think about the following:
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- What assumptions about the topology are baked into your implementation? How would you
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need to change it for a more realistic network?
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- Why are the byte counters different between the ingress and egress counters?
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- What is the TTL in the ICMP replies? Why is it the value that it is?
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Hint: The default TTL is 64 for packets sent by the hosts.
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#### Cleaning up Mininet
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If the Mininet shell crashes, it may leave a Mininet instance
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running in the background. Use the following command to clean up:
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```bash
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make clean
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```
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#### Running the reference solution
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To run the reference solution, you should run the following command from the
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`~/tutorials/P4D2_2017_Fall/exercises/p4runtime` directory:
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```bash
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solution/my_controller.py
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```
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## Next Steps
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Congratulations, your implementation works! Move onto the next assignment
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[ecn](../ecn)!
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