Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 35)

Rockwell Automation Publication ENET-RM002C-EN-P - May 2013 35
Ethernet Infrastructure Features Chapter 3
Multicast Address Limit
In multicast communication, EtherNet/IP interfaces support a maximum of
32 devices that transmit multicast.
The multicast address limit is independent of the connection limit for a device.
Not all connections require a multicast address. In the case of produced and
consumed tags, one produced tag requires one multicast address, but it also
requires one connection for each consumer. If there are multiple consumers, the
one multicast address must use multiple connections.
Transmission Protocols The network layer (Layer 3) provides switching and routing that create logical
paths, known as virtual circuits, for transmitting data from node to node.
Routing and forwarding are functions of this layer, as well as addressing and
internetworking.
Address Resolution Protocol (ARP)
An ARP request is a broadcast message that asks ‘who has this IP address?’. The
device that has that IP address responds and the requestor adds the IP address
and hardware address pair to its ARP cache. The original device can now send the
message. This protocol enables the network to learn and adapt to changes.
EXAMPLE An Ethernet adapter that produces data uses a unique multicast address for
each I/O connection.
EXAMPLE A Logix controller that produces tags uses a unique multicast address for each
produced tag.
1756 Controller
1756 Controller
Device needs to send a
message to 130.151.3.4
Who has the IP address 130.151.3.4 ?
130.151.3.4
PowerFlex
I ha
ve
IP
addr
ess
13
0.15
1.3.4
1734 POINT I/O