6.1 VLAN Issues
6.1.3 Isolated broadcast domains
You learned that VLANs are designed to control the size of broadcast domains and to keep local traffic local. Because a VLAN isolates traffic on one broadcast domain, typically that broadcast domain is given a single layer 3 subnet so network devices in different VLANs cannot communicate with one another without some intervening Layer 3 device.

In switched networks, Route Processors are used to provide communications between VLANs. Route processors provide VLAN access to shared resources and connect to other parts of the network that are either logically segmented with the more traditional subnet approach or require access to remote sites across wide-area links.

Before you can configure routing between VLANs, you must have defined the VLANs on the switches in your network. Issues related to network design and VLAN definition should be addressed during your network design phase. The issues that you need to consider include the following:

  • Sharing resources between VLANs
  • Load balancing
  • Redundant links
  • Logical addressing
  • How to segment the network using VLANs