IP address
An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
An IP address serves two principal functions: host or network interface identification and location addressing.
RTP-MIDI
IP stacks need to correlate Ethernet addresses (MAC address) and IP addresses, using a specific protocol named ARP. When a RTP-MIDI application wants to send a packet to a remote device, it must locate it first on the network, since Ethernet does not understand IP-related concepts, in order to create the transmission path between the routers/switches. This is done automatically by the IP stack by sending first an ARP (Address Recognition Protocol) request. When the destination device recognizes its own IP address in the ARP packet, it sends back an ARP reply with its MAC address. The IP stack can then send the RTP-MIDI packet. The next RTP-MIDI packets do not need the ARP sequence anymore, unless the link becomes inactive for a few minutes, which clears the ARP entry in the sender's routing table.