Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 36)

36 Rockwell Automation Publication ENET-RM002C-EN-P - May 2013
Chapter 3 Ethernet Infrastructure Features
If you replace a Rockwell Automation EtherNet/IP communication module with
a new module, the new module has a different MAC ID. The ARP cache entries
in other devices are now invalid because the MAC ID corresponding to the
module's IP address has changed. This can cause a delay in reestablishing
communication with the replacement module. The delay varies depending on the
module and the network configuration in use.
When a Rockwell Automation EtherNet/IP device starts up, it issues a gratuitous
ARP that causes other devices to update their ARP caches. This generally results
in a quick recovery of communication with the replacement module (less than a
minute). However, some switches do not forward the gratuitous ARP message
onto the network, such as if the Spanning Tree Protocol is enabled on that port.
We recommend that you disable the Spanning Tree Protocol on ports to which
EtherNet/IP communication modules are directly connected, but not on ports
that are linked to other switches. In the worst case, if the gratuitous ARP is not
seen, an originating device can wait as long as 10 minutes for the ARP cache entry
to age out and be deleted.
Domain Name System (DNS)
DNS is a name resolution protocol that enables you to identify devices by names
rather than IP addresses. For DNS to work, a DNS server is configured to hold a
table of names and the associated IP addresses. When a device attempts to send a
message to a device with an unknown name, it requests the IP address of the
named device from the DNS server.
DNS Server
What is the IP address
for the PowerFlex drive?
1756 Controller
The controller needs to
send a message to the
PowerFlex drive.
1734 POINT I/O
PowerFlex Drive
130.151.3.4