dc08948a34
* Repository reorganization for 2018 Spring P4 Developer Day. * Port tutorial exercises to P4Runtime with static controller (#156) * Switch VM to a minimal Ubuntu 16.04 desktop image * Add commands to install Protobuf Python bindings to user_bootstrap.sh * Implement P4Runtime static controller for use in exercises From the exercise perspective, the main difference is that control plane rules are now specified using JSON files instead of CLI commands. Such JSON files define rules that use the same name for tables, keys, etc. as in the P4Info file. All P4Runtime requests generated as part of the make run process are logged in the exercise's “logs” directory, making it easier for students to see the actual P4Runtime messages sent to the switch. Only the "basic" exercise has been ported to use P4Runtime. The "p4runtime" exercise has been updated to work with P4Runtime protocol changes. Known issues: - make run hangs in case of errors when running the P4Runtime controller (probably due to gRPC stream channel threads not terminated properly) - missing support for inserting table entries with default action (can specify in P4 program as a workaround) * Force install protobuf python module * Fixing Ctrl-C hang by shutdown switches * Moving gRPC error print to function for readability Unforuntately, if this gets moved out of the file, the process hangs. We'll need to figure out how why later. * Renaming ShutdownAllSwitches -> ShutdownAllSwitchConnections * Reverting counter index change * Porting the ECN exercise to use P4 Runtime Static Controller * updating the README in the ecn exercise to reflect the change in rule files * Allow set table default action in P4Runtime static controller * Fixed undefined match string when printing P4Runtime table entry * Updated basic_tunnel exercise to use P4Runtime controller. * Changed default action in the basic exercise's ipv4_lpm table to drop * Porting the MRI exercise to use P4runtime with static controller * Updating readme to reflect the change of controller for mri * Update calc exercise for P4Runtime static controller * Port source_routing to P4 Runtime static controller (#157) * Port Load Balance to P4 Runtime Static Controller (#158)
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 `10.0.1.2`.
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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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