66 lines
2.6 KiB
Markdown
66 lines
2.6 KiB
Markdown
# Meter
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## Description
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This program illustrates as simply as possible how to use meters in P4 with
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bmv2. bmv2 uses two-rate three-color meters as described [here]
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(https://tools.ietf.org/html/rfc2698).
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For each incoming packet the `m_table` table is applied and the appropriate
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meter (based on the packet's source MAC address) is executed. Based on the
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observed traffic rate for this sender and the meter's configuration, executing
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the meter will yield one of 3 values: `0` (*GREEN*), `1` (*YELLOW*) or `2`
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(*RED*). This value will be copied to metadata field `meta.meter_tag`. Note that
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if no meter was associated to the sender's MAC address, the table will be a
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no-op. This table also redirects all packets - with a known source MAC address-
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to port 2 of the switch.
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After that, the packet will go through a second table, `m_filter`, which can
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either be a no-op or drop the packet based on how the packet was tagged by the
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meter. If you take a look at the [runtime commands] (commands.txt) we wrote for
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this example, you will see that we configure the table to drop all the packets
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for which the color is not *GREEN* (i.e. all packets for which `meta.meter_tag`
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is not `0`).
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The [commands.txt] (commands.txt) file also gives you the meter
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configuration. In this case, the first rate is 0.5 packets per second, with a
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burst size of 1, and the second rate is 10 packets per second, with a burst size
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of 1 also. Feel free to play with the numbers, but these play nicely with the
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demonstration below.
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Note that we use an `indirect` meter array, because `direct` ones are not
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supported yet by bmv2.
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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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- [send_and_receive.py] (send_and_receive.py): send packets periodically on port
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0 and listen for packets on port 2.
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To run the demo:
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- start the switch and configure the tables and the meters: `sudo
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./run_switch.sh`.
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- run the Python script: `sudo python send_and_receive.py 1`. As you can see,
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the script takes one argument, which is the time interval (in seconds) between
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two consecutive packets.
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If you run the script with an interval of one second, you should observe the
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following output:
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Received one
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Sent one
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Sent one
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Received one
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Sent one
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Sent one
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Received one
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Sent one
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...
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This is because we send one packet every second, while the first rate of the
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meter is 0.5 packets per second. The P4 program therefore drops on average one
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packet out of two.
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