Control-Plane.md

+# Control Plane
+
+## Simple Switch CLI
+
+We can use the Simple Switch CLI to configure the switch and populate match-action tables.
+
+#### Running the CLI
+
+To get the switch CLI simply run:
+
+```bash
+simple_switch_CLI --thrift-port <port>
+```
+
+The CLI connect to the Thrift RPC server running in each switch process.
+9090 is the default value but of course if you are running several devices
+on your machine, you will need to provide a different port for each.
+One CLI instance can only connect to one switch device.
+
+#### Filling tables
+
+The most used commands to modify table contents are:
+
+  * table_set_default <table_name> <action_name> <action_parameters>
+  * table_add <table_name> <action_name> <match_fields> => <action_parameters>
+
+For example if we have the following table:
+
+```
+action drop(){
+     // drops packet
+     mark_to_drop(standard_metadata);
+}
+
+table table_name {
+
+   action action_name(bit<8> action_parameter){
+       ...
+   }
+
+   key = {
+       standard_metadata.ingress_port: exact;
+   }
+
+   actions = {
+       drop;
+       action_name;
+   }
+```
+
+
+```
+table_set_default table_name drop
+table_add table_name action_name 1 => 5
+```
+
+The first command would set the default action, and action parameters (none in this case) for table `table_name`. Thus, when
+using the `table_name` table if there is no match, the drop action will be called.
+
+In the second example command adds an entry that matches if the `standard_metadata.ingress_port` is equal to 1 and executes the
+action `action_name` with `action_parameter` set to 5.
+
+#### Writing the CLI input in a file
+
+You can also populate the table writing the commands directly in a text file and then feeding the CLI:
+
+```bash
+simple_switch_CLI --thrift-port <port> < command_file.txt
+```
+
+#### Using P4 utils configuration file
+
+Alternatively, you can use the p4-utils configuration file (i.e `p4app.json`) to set a `cli` configuration
+file for each switch. When creating the topology, or rebooting switches, p4-utils will automatically use
+the file to populate and configure switches.
+
+To set default `cli` configuration files you need to define your switches like:
+
+```json
+    "switches": {
+      "s1": {
+        "cli_input": "<path_to_cli_commands_file>"
+      }
+    }
+```
+
+You can find all the documentation about `p4app.json` in the `p4-utils` [documentation](https://github.com/nsg-ethz/p4-utils#topology-description).
+
+
+### P4 Utils Control Plane API
+
+You can find a wrapper of the Control Plane CLI as one of the features of p4-utils. It basically allows you to do the same but instead of using text sent to
+the CLI you can use the power of a scripting language such as python. You can read more about this API [here](https://github.com/nsg-ethz/p4-utils#control-plane-api).
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