Installation guide

Network Infrastructure for EtherNet/IP™
Planning the Infrastructure
3-16
Managed Switches
Managed switches provide the basic switching capabilities of unmanaged switches, plus they offer
additional diagnostic or traffic-management functions.
In essence, a managed switch is configured or tailored for a particular part of the overall application. The
different switches in an application can each have different configurations that the user must maintain. If
a managed switch is replaced, the particular configuration settings must be downloaded or entered into the
new switch. Unmanaged switches, however, perform only the basic switch functions and do not need to
be reconfigured if they are replaced. Since managed switches perform the basic switching functions “out
of the box,” they can be used as “plug-and-go” replacements for unmanaged switches. For more specific
details on the requirements for switches in EtherNet/IP networks, see Appendix A Recommendations for
Ethernet Switches in EtherNet/IP Systems.
3.2.5 Media Converters
Hubs and switches that allow connection of fiber and twisted-pair wire to the same device may be
purchased. In cases where the mix of ports does not match the requirements, twisted-pair to fiber-media
converters are available for converting a single cable of one type to another.
3.2.6 Routers
Routers provide added functionality not usually found in switches. A hub or a switch will pass along any
broadcast or multicast packets they receive to all the other segments, but a router will not. A four-way
traffic intersection is a good example. With a hub or unmanaged switch, all of the traffic passes through
the intersection no matter where it is going. If, however, this intersection is at an international border, the
rules are different. To pass through the intersection, the driver must provide the border guard with a
specific destination address. If the driver doesn’t have a specific destination address, the guard will not let
the vehicle pass.
Routers work the same way. Without a specific address of a destination device, the router will not let the
data packet through. This is good for keeping networks separate from each other, but is less desirable
when different parts of the same network need to communicate. Switches allow different devices on the
same network to talk to each other.
Routers are typically used when traffic from two different networks needs to be interconnected. Routers
direct traffic based on the network address (OSI Layer 3) information of the packet. Routers can help the
performance of factory-floor Ethernet networks by blocking Ethernet multicast and broadcast data traffic.
Routers can isolate the traffic of other connected but unrelated Ethernet networks, which could otherwise
reduce the performance of factory-floor systems. Routers also can determine the optimal path along
which network traffic should be forwarded and can be used to help implement network security.
Routers normally do not have as many interfaces (ports) as switches, but like managed switches, they
require setup and configuration. Most switches add very little latency (or delay) to the messages that pass
through them. However, based on the added functions a router performs and the specific vendor’s
hardware implementation, added latency may be introduced. Engineers need to check the latency
specifications of a router if real-time control information will pass through it.