Installation guide

Network Infrastructure for EtherNet/IP™
Designing the Infrastructure
4-52
4.10 Virtual Local Area Networks
As networks have grown in size and complexity, many companies have turned to Virtual Local Area
Networks (VLANs)
to provide a means for structuring this growth logically. Basically, a VLAN is a
network that is created logically, using software, as opposed to physical cabling. Therefore, only devices
predefined according to a specific criterion for the same broadcast domain will receive a transmission
generated by a station on a VLAN.
A
broadcast domain is a network (or portion of a network) that will receive a broadcast packet from
any node located within that network. Since routers do not pass along broadcast messages, in a typical
network everything on the same side of the router is part of the same broadcast domain.
Switches Implemented with VLANs
A switch implemented with VLANs has multiple broadcast domains similar to a router. The
switching device used to construct a VLAN can be an advanced managed Layer 2 switch that
operates at the MAC sub-layer of the OSI Model, or a Layer 3 switch that operates at the network
layer.
Here are some common reasons why a company might want to install VLANs:
•
Security. Separating systems with sensitive data from the rest of the network decreases
the chance that someone will gain access to information they are not authorized to see.
•
Projects/special applications. Managing a project or working with a specialized
application can be simplified by using a VLAN to bring all the required nodes together.
•
Performance/bandwidth. Monitoring of network use allows the network administrator
to create VLANs that reduce the number of router hops and increase the apparent
bandwidth for network users.
•
Broadcasts/traffic flow. Since a principle element of a VLAN is that it does not pass
broadcast traffic to nodes that are not part of the VLAN, it automatically reduces
broadcasts. Access lists provide the network administrator with a way to control who sees
what network traffic.
•
Departments/specific job types. Companies may want to set up VLANs for
departments that are heavy network users (such as Multimedia or Engineering). A VLAN
dedicated to specific types of employees from different departments (such as managers or
sales people) might also be set up across departments.
While more than one VLAN can exist on a single switch, these VLANs cannot communicate directly with
each other. If they could, it would defeat the purpose of having a VLAN, which is to isolate a part of the
network. Communication between VLANs requires the use of a router.