CTI Products NCB/FL with Fiber Interface - Manual (Page 37)

CTI Products, Inc. NCB-EL/FL User Guide
Appendix F. IP Addresses 34
IP Addressing modes
Unicast/Replicated
Unicast/Replicated addressing mode allows point-to-point or point-to-multipoint communications in any IP
network. A table of Target IP Addresses is configured into each of the NCB-Etherlon™ Routers, the table in
each containing the IP addresses of the other modules in the group. The maximum number of NCBs that can be
configured into one Unicast/Replicated group is 96.
Each NCB is programmed with a Host IP Address, a list of Target IP Addresses, and optionally, a Default
Gateway IP Address. The Default Gateway IP Address is the address of the IP router to which the respective
NCB-Etherlon is attached and allows for IP routers or gateways that may exist between NCB-Etherlon units.
Using Unicast/Replicated mode, a single L ON T ALK packet entering any of the NCB modules of the group will
be sent out the Ethernet port of that module as multiple Unicast IP messages, one to each of the other NCB
modules in the group.
Multicast
Multicast addressing mode allows efficient point-to-multipoint communications in a network. Each NCB is
assigned a Host IP Address, a multicast Target IP Address, and optionally, a Default Gateway IP Address. A
single multicast Target IP Address is assigned to all NCB in the network within the range 224.0.1.0 through
239.255.255.255.
A single L ON T ALK packet entering any one of the NCB modules results in a single multicast IP packet being
sent out the Ethernet port of that module to be received by all other NCB members configured to the same
Multicast IP address.
Multicast addressing mode can be used with a very large number of NCB-Etherlon modules, allowing
combinations of very large number of L
ON W ORKS network. Because only one IP packet is generated for every
L ON T ALK packet, multicast addressing mode uses far less network bandwidth that Unicast/Replicated.
Before choosing multicast addressing mode, it is important to determine the following capabilites of the IP
network to which the NCB units will be connected:
• IP routers must be capable of handling IP multicast traffic.
• IP routers must have IP multicast enabled
• IP routers must forward the NCB multicast port numbers of 1100 (destination port) and 1283 (source
port).
MAC Addresses
Whereas IP uses Logical Addresses to identify a host (node), other protocols use Hardware Addresses called
Media Access Control addresses, or MAC addresses. MAC addresses are set at the factory at time of
manufacture and cannot be changed. (IP addresses can be changed at any time.) A MAC address consists of
six octets, in hexadecimal notation, separated by colons. An example would be:
00:10:EE:00:02:34.
The first three octets in a MAC address identify the manufacturer. In the above example, 00:10:EE identifies
CTI Products as the manufacturer of this device. The last three octets are sequentially assigned by the
manufacturer to form a type of serial number. In this way, no two devices have the same MAC address.
Multicast addressing is also possible using MAC addresses, just as in IP addressing. MAC addresses reserved
for broadcast messages start at: 00:01:5E:00:00:00.
Address Resolution Protocol (ARP)
Since IP uses Logical Addresses at the OSI Network Layer (Layer 3) and Ethernet uses MAC addresses at the
OSI Data Link Layer (Layer 2), Address Resolution Protocol is used whenever IP is used over the Ethernet.
ARP is needed to convert an IP address to a MAC address. The client then stores this resolved address for a
period of time in its ARP cache. An ARP cache is a lookup table, typically in a router, that will store a quantity
of resolved addresses for devices that it must communicate with.