Hosts cannot communicate with hosts on a separate VLAN unless there is a configured router in place. Inter VLAN routing is the process of forwarding one VLANs traffic to another.
The two main options for inter VLAN routing are;
1. Router on a stick for small - medium businesses
2. Layer 3 switches that use SVI's - large enterprises
A router on a stick
The router on a stick method only requires one physical ethernet interface to route traffic between multiple VLANS. This sub interface on a Cisco router is configured as a trunk connecting to a layer 2 switch using the 802.1Q protocol. the configured sub interfaces are software based and each is configured with an independent IP address and VLAN assignment. When VLAN- tagged traffic enters the router interface it is forwarded to the VLAN sub interface, then a routing decision can be made based on the destination IP address. This method does not scale beyond 50 VLANS. See below video for a simple practical scenario for configuring the router on a stick method and an image showing which interface the configurations need to take place;
Layer 3 Switching or Multilayer Switching
The router on a stick method is limited in scalability so larger organisations would be recommended to use a multi layer switch. A multi layer switch can;
-Route between VLANs using switch virtual interfaces (SVIs)
-Be configured with different methods of routing ie OSPF (This will be discussed in a later lesson)
In packet tracer the multi layer switch looks like the below. We will configure these when we discuss routing
From this post and the last lesson you should now be ready to excel in this Quiz
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