Control-Plane.md

+## *Simple Switch* Client
+
+We can use the `simple_switch_CLI` to configure the switch and populate match-action tables.
+
+### Running the client
+
+To get the switch client simply run:
+
+```bash
+simple_switch_CLI --thrift-port <port>
+```
+
+The client connect to the *Thrift* server running in each switch process. `9090` is the default port number but of course if you are running several devices on your machine, you will need to provide a different port for each. One client instance can only connect to one switch device.
+
+### Filling tables
+
+The most used commands to modify table contents are the following.
+
+- `table_set_default <table_name> <action_name> <action_parameters>` is used to set the default action (i.e. the action executed when no match is found) of a table.
+- `table_add <table_name> <action_name> <match_fields> => <action_parameters>` is used to set the action related to a specific match in a table.
+
+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 client input in a file
+
+You can also populate the table writing the commands directly in a text file and then feeding the client:
+
+```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 client 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 APIs
+
+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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