This program illustrates as simply as possible how to use meters in P4 with bmv2. bmv2 uses two-rate three-color meters as described [here] (https://tools.ietf.org/html/rfc2698).

For each incoming packet the m_table table is applied and the appropriate meter (based on the packet's source MAC address) is executed. Based on the observed traffic rate for this sender and the meter's configuration, executing the meter will yield one of 3 values: 0 (GREEN), 1 (YELLOW) or 2 (RED). This value will be copied to metadata field meta.meter_tag. Note that if no meter was associated to the sender's MAC address, the table will be a no-op. This table also redirects all packets - with a known source MAC address- to port 2 of the switch.

After that, the packet will go through a second table, m_filter, which can either be a no-op or drop the packet based on how the packet was tagged by the meter. If you take a look at the [runtime commands] (commands.txt) we wrote for this example, you will see that we configure the table to drop all the packets for which the color is not GREEN (i.e. all packets for which meta.meter_tag is not 0).

The [commands.txt] (commands.txt) file also gives you the meter configuration. In this case, the first rate is 0.5 packets per second, with a burst size of 1, and the second rate is 10 packets per second, with a burst size of 1 also. Feel free to play with the numbers, but these play nicely with the demonstration below.

Note that we use an indirect meter array, because direct ones are not supported yet by bmv2.

Running the demo

We provide a small demo to let you test the program. It consists of the following scripts:

[run_switch.sh] (run_switch.sh): compile the P4 program and starts the switch, also configures the data plane by running the CLI [commands] (commands.txt).
[send_and_receive.py] (send_and_receive.py): send packets periodically on port 0 and listen for packets on port 2.

To run the demo:

start the switch and configure the tables and the meters: sudo ./run_switch.sh.
run the Python script: sudo python send_and_receive.py 1. As you can see, the script takes one argument, which is the time interval (in seconds) between two consecutive packets.

If you run the script with an interval of one second, you should observe the following output:

Received one
Sent one
Sent one
Received one
Sent one
Sent one
Received one
Sent one
...

This is because we send one packet every second, while the first rate of the meter is 0.5 packets per second. The P4 program therefore drops on average one packet out of two.