Installation guide

Network Infrastructure for EtherNet/IP™
Planning the Infrastructure
3-22
• DHCP - Dynamic Host Configuration Protocol
This is a protocol to allow a device, acting as a DHCP server, to assign 4-byte IP addresses to
devices connected to the network.
• DNS - Domain Name Services
This protocol searches for resources on a TCP/IP network using a database connected to the
TCP/IP network. It makes correlations between computer names, their 4-byte IP addresses,
and the resources and information available in the network. There are many other tools and
protocols available. See 5 Deploying the Network for more information.
3.5 Diagnostics via Infrastructure Components
Industrial Ethernet infrastructure components, like their device-level network counterparts, can provide a
full range of diagnostics over displays such as built-in LEDs or seven-segment readouts. Typical
diagnostics include transmit/receive status by port, port active/cable connected status, and 10-Mbps
versus 100-Mbps operation. Most intelligent infrastructure components perform periodic self-tests and
provide LED indication of failure. Some units also provide a hardware contact that can be wired to an
alarm or nearby industrial controller to signal a device failure.
3.5.1 Simple Network Management Protocol
Simple Network Management Protocol (SNMP) is an industry standard protocol supported by virtually all
infrastructure component manufacturers. Through the SNMP protocol, engineers can set configuration
parameters (e.g., assign IP addresses) and receive diagnostics (i.e., remote monitoring data). This
information, however, only relates to infrastructure components, not to Ethernet embedded controllers,
devices, or I/O. EtherNet/IP is used to access Ethernet control device data.
SNMP drivers are available as standard in virtually all infrastructure-related (network management)
software packages. SNMP allows a software package from vendor X to display and set parameters in
vendor A, B, and C’s infrastructure components.
Managed infrastructure components provide added
diagnostics, such as port status (cable connected/unconnected, communications active/inactive), packet
size, and statistics on the packet type transmitted (unicast, multicast, broadcast), power supply status, etc.
These devices contain a data table called a
Management Information Base (MIB) that contains
diagnostic and other information.
The SNMP defines the format and standard types of
remote monitoring (RMON) information. This
standard allows multiple vendor diagnostics to be accessed by vendor-independent software. The standard
also allows vendor-specific information to be added. Within a point-to-point tree structure containing
hundreds of connected devices, the ability to quickly locate cabling or other faults in the Ethernet
infrastructure can be key to expediting start-ups. For more information, see 5 Deploying the Network.
3.5.2 Traps
Managed infrastructure devices allow a network engineer to set up SNMP traps. If it is important that
multiple devices receive diagnostic information, all the extra network traffic could significantly affect the
response time of the control network. Traps concentrate, or “trap,” the diagnostics from a quantity of
infrastructure devices. Without traps, PCs, etc. would have to constantly poll the MIB data from all the
infrastructure devices to determine if errors occurred. Infrastructure components can be configured with
the IP addresses of one or more networked PCs and devices.
When an alarm or error condition happens (some infrastructure diagnostics can determine if a parameter
exceeds a high or low limit), the infrastructure component sends an error message to the trap. This