A LonTalk/IP device may have multiple Layer 3 addresses. There are two types of LonTalk/IP Layer 3 addresses. They are unicast and multicast addresses. Unicast addresses are used to uniquely identify an individual LonTalk/IP device. Multicast addresses are used to identify a group of LonTalk/IP devices. The LonTalk/IP network address is an IP address. The format of the IP address is channel-type dependent. For IP-70 LAN channels, a standard IPv4 network address format is used. For LON channels, a standard ISO/IEC 14908-1 network address format is used. The LonTalk/IP protocol specifies the conversion between the different address formats using a stateless algorithm. LonTalk/IP LAN to LON routers such as an IzoT router use this algorithm to route packets between LAN and LON channels, automatically converting the addresses as required. Since the algorithm is stateless, IzoT routers do not require special provisioning or configuration to perform the network address format conversion. This topic describes the formats and requirements for unicast and multicast LonTalk/IP network addresses.

Unicast Network Addresses

Network address conversion for unicast addresses is dependent on the LonTalk/IP domain length and value. The LonTalk/IP domand length can be 0, 1, or 3 bytes. LonTalk/IP does not support 6-byte domains. The following table summarizes the conversion between a LAN channel and a LON channel for a LonTalk IP address with a domain of up to 3 bytes (D1, D2, and 00), a one-byte subnet ID (S), and a one-byte node ID (N).

The LonTalk/IP domain, subnet, and node IDs must meet the following requirements:

• The domain ID length must be 0, 1, or 3 bytes. A 6-byte LonTalk/IP domain ID is not valid.
• The first byte of a 3-byte domain ID must not be 10 (0x0A), or a value between 224 (0xE0) and 239 (0xEF).
• The first two bytes of 3 byte domain ID must not be 192, 168 (0xC0, 0xA8).
• The third byte of a 3-byte domain ID must 0.
• The subnet ID must be a value between 1 and 254, inclusive. The subnet ID cannot be 0 or 255.
• The node ID must be a value between 1 and 127, inclusive. The node ID cannot be 0 or a value greater than 127.

Other domain IDs may not be valid in a particular IP infrastructure as they may conflict with existing IP addresses.

Multicast Network Addresses

There are three types of LonTalk/IP multicast addresses. They are domain broadcast, subnet broadcast, and group addresses. Network address conversion for multicast addresses is dependent on the type of multicast, as shown in the table below: