48 lines
2.1 KiB
Markdown
48 lines
2.1 KiB
Markdown
# Copy to CPU
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## Description
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This program illustrates as simply as possible how to *send packets to CPU*
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(e.g. to a controller).
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The P4 program does the following:
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- incoming packets are mirrored to the CPU port using the
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`clone_ingress_pkt_to_egress` action primitive
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- packets mirrored to CPU are encapsulated with a custom `cpu_header` which
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includes 2 fields: `device` (1 byte, set to `0`) and `reason` (one byte, set
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to `0xab`)
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- the original packet is dropped in the egress pipeline
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Take a look at the [P4 code](p4src/copy_to_cpu.p4). The program is very short
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and should be easy to understand. You will notice that we use a mirror session
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id of `250` in the program. This number is not relevant in itself, but needs to
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be consistent between the P4 program and the runtime application.
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### Running the demo
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We provide a small demo to let you test the program. It consists of the
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following scripts:
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- [run_switch.sh](run_switch.sh): compile the P4 program and starts the switch,
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also configures the data plane by running the CLI [commands](commands.txt)
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- [receive.py](receive.py): sniff packets on port 3 (veth7) and print a hexdump
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of them
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- [send_one.py](send_one.py): send one simple IPv4 packet on port 0 (veth1)
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If you take a look at [commands.txt](commands.txt), you'll notice the following
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command: `mirroring_add 250 3`. This means that all the cloned packets with
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mirror id `250` will be sent to port `3`, which is our de facto *CPU port*. This
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is the reason why [receive.py](receive.py) listens for incoming packets on port
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`3`.
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To run the demo:
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- start the switch and configure the tables and the mirroring session: `sudo
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./run_switch.sh`
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- start the CPU port listener: `sudo python receive.py`
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- send packets with `sudo python send_one.py`. Every time you send one packet,
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it should be displayed by the listener, encapsulated with our CPU header.
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This is a very simple example obviously. Feel free to build upon it. For
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example, instead of dropping the original packet, you could try to broadcast it
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out of every non-ingress port to have a working L2 switch. You could also build
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a L2 controller which receives CPU packets and modifies tables appropriately.
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