How to set multiple static addresses for openthread

[tuopu]

In my project, I need to send data to a specific device, which has many sub-devices with different addresses. For ease of conversion, I need to set multiple static addresses in the OpenThread terminal, rather than using broadcast to search at the application layer. I would like to know if OpenThread can set multiple static addresses, and whether I can directly use UDP communication or set something else to enable direct communication using CoAP.

[jwhui]

The preferred approach is using DNS-SD (DNS Service Discovery) with SRP (Service Registration Protocol). If you choose to manually configure IPv6 addresses instead, it is important to use an on-mesh prefix to ensure those addresses are routable within the Thread network.

1. Preferred Approach: DNS-SD and SRP

Instead of assigning static IP addresses, each sub-device can register itself as a Service using SRP. This allows other nodes to discover them dynamically by name and service type (e.g., _ipps._tcp).

Key Advantages:

• Avoids Multicast: Unlike traditional mDNS, SRP uses unicast to register services with a server (usually the Border Router), and DNS-SD uses unicast for discovery. This avoids the high power and bandwidth overhead of multicast in a wireless mesh network.
• Dynamic: No need to hardcode or manually manage IP addresses across your fleet.
• Scalable: Multiple logical "sub-devices" can share the same IP address by using different ports.

Example: Registering a sub-device via CLI

# 1. Set the host name for the node
> srp client host name my-node

# 2. Register a "sub-device" as a service (name, type, port)
> srp client service add sub-device-1 _ipps._tcp 12345
Done

# 3. Enable autostart to find the SRP server and register via unicast
> srp client autostart enable

Other nodes can then discover these sub-devices using unicast DNS queries:

> dns browse _ipps._tcp.default.service.arpa.

---

2. Alternative: Manual IPv6 Configuration (using On-Mesh Prefixes)

If your specific integration requires unique IP addresses for each sub-device, you should use an on-mesh prefix already advertised in the network. Using an on-mesh prefix ensures the addresses are recognized as local and are routable within the Thread network.

How to find the On-Mesh Prefix:
Use the netdata show command to list available prefixes:

> netdata show
Prefixes:
fd00:1234:5678:abcd::/64 paos low 4000

In this example, fd00:1234:5678:abcd::/64 is an on-mesh prefix (indicated by the o flag).

Example: Adding a static address using the on-mesh prefix

# Use the prefix discovered above and add your own interface identifier (IID)
> ipaddr add fd00:1234:5678:abcd::1
Done
> ipaddr add fd00:1234:5678:abcd::2
Done

Key Considerations for Manual Addresses:

• Limit: The default limit for manually added addresses is 4 (configured by OPENTHREAD_CONFIG_IP6_MAX_EXT_UCAST_ADDRS).
• Persistence: These addresses are not persistent across reboots and must be re-added by your application during initialization.
• Routing: Always use a prefix advertised with the "on-mesh" (o) flag to ensure the address is reachable by other nodes.

Recommendation: Use DNS-SD/SRP to leverage efficient unicast discovery and avoid the power costs of multicast. Only use multiple static IPv6 addresses if your application layer specifically requires it, and always ensure they use an on-mesh prefix.

[tuopu]

Hello, thank you for the scheme you recommended. I also prefer to choose Scheme 1, which is more convenient for identification. The current problem is whether the recommended Scheme 1 can be implemented when there is no border router in the network. If so, whether it is necessary to designate an openthread node as a server, and use these addresses for discovery and communication between nodes. The specific operation involves the API in that file

[jwhui]

Any node in the network could serve as an SRP server, it does not have to be a Thread Border Router. In your overall system architecture, are there any nodes that could naturally host an SRP server?