09dba5c63d
* Added Makefile and topology.jsons for all examples. * use branch * Updated MRI exercise (#73) * Updated MRI exercise * Updated basic_tunnel.p4 for changes to p4 lang * updated other examples
113 lines
3.7 KiB
Markdown
113 lines
3.7 KiB
Markdown
# Implementing a P4 Calculator
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## Introduction
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The objective of this tutorial is to implement a basic calculator
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using a custom protocol header written in P4. The header will contain
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an operation to perform and two operands. When a switch receives a
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calculator packet header, it will execute the operation on the
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operands, and return the result to the sender.
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## Step 1: Run the (incomplete) starter code
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The directory with this README also contains a skeleton P4 program,
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`calc.p4`, which initially drops all packets. Your job will be to
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extend it to properly implement the calculator logic.
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As a first step, compile the incomplete `calc.p4` and bring up a
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switch in Mininet to test its behavior.
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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 `calc.p4`, and
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* start a Mininet instance with one switches (`s1`) connected to
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two hosts (`h1`, `h2`).
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* The hosts are assigned IPs of `10.0.1.1` and `10.0.2.2`.
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2. We've written a small Python-based driver program that will allow
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you to test your calculator. You can run the driver program directly
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from the Mininet command prompt:
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```
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mininet> h1 python calc.py
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>
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```
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3. The driver program will provide a new prompt, at which you can type
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basic expressions. The test harness will parse your expression, and
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prepare a packet with the corresponding operator and operands. It will
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then send a packet to the switch for evaluation. When the switch
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returns the result of the computation, the test program will print the
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result. However, because the calculator program is not implemented,
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you should see an error message.
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```
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> 1+1
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Didn't receive response
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>
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```
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## Step 2: Implement Calculator
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To implement the calculator, you will need to define a custom
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calculator header, and implement the switch logic to parse header,
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perform the requested operation, write the result in the header, and
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return the packet to the sender.
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We will use the following header format:
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0 1 2 3
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+----------------+----------------+----------------+---------------+
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| P | 4 | Version | Op |
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+----------------+----------------+----------------+---------------+
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| Operand A |
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+----------------+----------------+----------------+---------------+
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| Operand B |
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+----------------+----------------+----------------+---------------+
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| Result |
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+----------------+----------------+----------------+---------------+
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- P is an ASCII Letter 'P' (0x50)
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- 4 is an ASCII Letter '4' (0x34)
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- Version is currently 0.1 (0x01)
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- Op is an operation to Perform:
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- '+' (0x2b) Result = OperandA + OperandB
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- '-' (0x2d) Result = OperandA - OperandB
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- '&' (0x26) Result = OperandA & OperandB
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- '|' (0x7c) Result = OperandA | OperandB
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- '^' (0x5e) Result = OperandA ^ OperandB
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We will assume that the calculator header is carried over Ethernet,
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and we will use the Ethernet type 0x1234 to indicate the presence of
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the header.
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Given what you have learned so far, your task is to implement the P4
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calculator program. There is no control plane logic, so you need only
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worry about the data plane implementation.
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A working calculator implementation will parse the custom headers,
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execute the mathematical operation, write the result in the result
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field, and return the packet to the sender.
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## Step 3: Run your solution
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Follow the instructions from Step 1. This time, you should see the
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correct result:
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```
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> 1+1
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2
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>
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```
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## Next Steps
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Congratulations, your implementation works! Move on to
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[Load Balancer](../load_balance).
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