ex-6.md

Exercise 6 - Access Control

By configuration the Zenoh router can deny some topics to be published via a specified interface (e.g. WiFi).

Configuration

Partner with another attendee and decide who will connect their container (A) to the other's container (B). The attendee using container A will configure its router to connect to the container B's router, and to deny the publication of a topic via the WiFi interface:

Both attendees shall reset the zenoh_confs/ROUTER_CONFIG.json5 file, copying again the zenoh_confs/DEFAULT_RMW_ZENOH_ROUTER_CONFIG.json5 as zenoh_confs/ROUTER_CONFIG.json5

Then in container A:

1. Edit zenoh_confs/ROUTER_CONFIG.json5 and set the connect.endpoints configuration as follows (Replace <host_B_IP> with the IP address of the host running container B):

   connect: {
     endpoints: [
       "tcp/<host_B_IP>:7447"
     ],
   },

2. Run ip a command to list your network interfaces and find the name of the WiFi interface.

3. Add this access_control configuration at the end of your zenoh_confs/ROUTER_CONFIG.json5 file (just before the last }):

   access_control: {
     enabled: true,
     default_permission: "allow",   // allow all by default
     /// List of rules
     rules: [
       {
         // Rule identifier
         id: "my_rule",
         // Deny publications ("put" Zenoh operation) in egress on WiFi interface for a Zenoh key expression
         permission: "deny",
         messages: [ "put" ],
         flows:["egress"],
         key_exprs: [
           // The Zenoh key expression used for the "/chatter" topic
           //"0/chatter/std_msgs::msg::dds_::String_/RIHS01_df668c740482bbd48fb39d76a70dfd4bd59db1288021743503259e948f6b1a18"
           "*/chatter/**"
         ],
       },
     ],
     /// list of subjects:
     subjects: [
       {
         // Interface identifier
         id: "my_interface",
         interfaces: ["<YOUR_WIFI_INTERFACE>"],
       },
     ],
     /// apply rule to subject in the policies list
     policies: [
       {
         rules: ["my_rule"],
         subjects: ["my_interface"],
       },
     ],
   },

   Don't forget to replace "<YOUR_WIFI_INTERFACE>" with your WiFi interface name !

Running the Test

Now, run the following commands in each container:

• In container A:
  • Start the router (with the custom configuration): ZENOH_ROUTER_CONFIG_URI=/ros_ws/zenoh_confs/ROUTER_CONFIG.json5 ros2 run rmw_zenoh_cpp rmw_zenohd You can also add this environment variable to see the router applying the access control: RUST_LOG=info,zenoh::net::routing::interceptor=debug
  • Start the publisher on the denied topic: ros2 topic pub /chatter std_msgs/msg/String "data: Hello just me!"
  • Start another publisher on an allowed topic: ros2 topic pub /chatter_public std_msgs/msg/String "data: Hello World!"
• In container B:
  • Start the router (with the default configuration): ros2 run rmw_zenoh_cpp rmw_zenohd
  • Start the listener on the denied topic: ros2 topic echo /chatter
  • Start the listener on an allowed topic: ros2 topic echo /chatter_public

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Note

What's the pattern of the Zenoh key expression ?

In a similar way than with DDS RMWs, rmw_zenoh has to make sure that a publisher and a subscriber can communicate only if they use:

• the same Domain ID
• the same ROS Namespace
• the same Topic name
• the same Topic type name
• the same Topic type definition (using a hash)

Therefore the Zenoh key expression for a ROS Topic is organized as such: "<DominID>/[<Namespace/>]<TopicName>/<TopicType>/<TopicHash>"

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Note

Isn't it a simpler way to specify the key expression ?

In rmw_zenoh based on Zenoh 1.0.0 wildcard characters are allowed. The key expression could then be simplified to */chatter/**. Where * matches 1 chunk (between /) and ** matches multiple chunks

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Note

How can I find the key expression for my topic ?

In rmw_zenoh based on Zenoh 1.0.0 the wildcard characters are allowed. The key expression could then be simplified to */chatter/**. Where * matches 1 chunk (between /) and ** matches multiple chunks

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