Vlans why

I understand that smaller VLANs or subnets are good for separating broadcast domains, but what happens when devices in different VLANs need to communicate? A device called a router handles requests for devices to communicate when not belonging to the same VLAN.

This function is called interVLAN routing. This IP address will typically be the default gateway IP address for each device on the network. A best practice is to have your subnet, broadcast domain, and VLAN relationship to all be the same. They are not required to be the same, but industry standards over time have made it this way.

Access to all devices is possible unlike when using physical segmentation like a CIP bride with two Ethernet cards using ControlLogix see an example to the right. Modern network design with small VLANs and routing allow fewer network interface cards while maintaining segmentation. Segmentation is logically controlled because VLANs cannot communicate inherently without assistance from layer 3 devices allowing rules to be created for what devices and VLANs can communicate. We also covered CPwE in a past blog post.

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Add a comment. Active Oldest Votes. Improve this answer. Everton Everton 1, 11 11 silver badges 23 23 bronze badges. There can be many reasons to split a network into VLANs. Security seggregation. You may want to filter or forbid communication between some systems on your networks. Limiting of broadcast and effectively broadcast traffic. The larger your L2 domain gets the more bandwidth and CPU time this eats up.

Limiting MAC address counts. Most switches can handle a limited number of MAC addresses before they start to have problems with the amount varying by device. Toplogy, trees get inefficient as networks get larger and more robust. Splitting into VLANs and using an appropriate variant of spanning tree protocol can allow different trees to be used for each VLAN better utilising links.

On the flip-side though having multiple VLANs can force local traffic to take circuitous routes via a router.

Handling overlapping IP addresses. In an ideal world you wouldn't have these but if you must then VLANs give you a way to isolate them. Devices that are connected to this port will belong to the same broadcast domain that is because all other ports are configured with a similar VLAN number.

The challenge of this type of network is to know which ports are appropriate to each VLAN. You can determine it by checking the configuration information. This type of VLAN processes traffic based on a protocol that can be used to define filtering criteria for tags, which are untagged packets. It works in multi-protocol environments.

This method is not practical in a predominately IP based network. The configurations of tables are shared among all device ports. Skip to content. What is VLAN? How to Increase Upload Speed. Report a Bug. Previous Prev.