Knowing the device's IP address does not always tell you which port the service it offers is located on. DNS-SD records can present service information in a more structured format.
Basic approach
DNS-SD uses a combination of DNS records such as PTR, SRV, and TXT for service instances. SRV specifies the destination name and port, while TXT can carry additional attributes. This approach can be used in both local discovery scenarios and managed DNS infrastructures.
Application steps
- Keep the found service type, instance name, and source protocol in separate fields.
- Verify the address resolution of the SRV destination and the reported port.
- Store TXT fields as device assertion; Do not interpret it as a credential or password.
Practical example
A print service may report a non-standard port. A check that only tries common printer ports would miss this, while the service announcement might point to the correct target. However, actual print access should be tested separately.
Interpret the result correctly
Receiving an announcement does not guarantee that the service is working properly. Sleeping devices, stale caches, and access rules can affect connectivity. Separating the announced and connection confirmed statuses in the inventory gives more understandable results.
Source and follow-up reading
Protocol or command details: RFC 6763. The steps and example scenario are IPScans editorial narrative.