Nodes with more than four ports
The Art-Net protocol sets a limit of 4 DMX input or output ports. This is because the ArtPollReply packet has a fixed array size.
To overcome this limitation, the concept of a BindingIp was introduced. Any Art-Net node that wishes to support more than 4 DMX ports sends multiple ArtPollReplies on receipt of an ArtPoll. However each ArtPollReply must be sent from a different IP address.
In the ArtPollReply, the BindIp field is set to the IP address of the root IP address of the node. A field called BindIndex is used to order the data.
For example, consider a node with 12 DMX output ports. Let’s say its root IP address is 22.214.171.124. The following table shows how the 3 ArtPollReplies will be structured:
An Art-Net controller will parse these packets to discover which ports are at which IP address. It will then unicast to those discovered IP addresses. The following is the discovery table:
Equally, for a node with 4 or less ports, the following table shows the structure: