In a publish/subscribe protocol such as MQTT, Internet-of-Things (IoT) devices communicate as follows. A device with a message pertaining to a certain topic publishes the message to a cloud-based server. A device that subscribes to the topic receives messages pertaining to the topic from the cloud-based server. The traditional publish/subscribe protocol fails if the internet is unavailable. This disclosure describes techniques for publish/subscribe messaging without the need for a central coordinating server. A subscriber translates the topic of interest to a multicast IP address. To publish a message, the publisher simply sends a UDP packet with the message content to that address, and it is delivered to all listening subscribers. Inter-device communication is thereby made robust to internet connectivity failures
