Configuring a Cisco Router for Multiple VLANs on Two Fast Ethernet Interfaces

Efficiently Connect Multiple VLANs on a Cisco Router with Two Fast Ethernet Interfaces

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A router has two Fast Ethernet interfaces and needs to connect to four VLANs in the local network. How can you accomplish this task, using the fewest physical interfaces and without decreasing network performance?



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A. B. C. D.


A router on a stick allows you to use sub-interfaces to create multiple logical networks on a single physical interface.

The correct answer to the question is D. Implement a router-on-a-stick configuration.


When a router needs to connect to multiple VLANs, a common approach is to use a technique called router-on-a-stick. This approach allows a router to route traffic between VLANs using a single physical interface, which helps to reduce the number of physical interfaces required and simplify the network design.

To implement a router-on-a-stick configuration, the following steps are typically taken:

  1. Configure the router interface that will connect to the switch as a trunk port. This will allow the router to receive traffic from all VLANs on the switch.

  2. Create subinterfaces on the router interface, one for each VLAN. Each subinterface will be associated with a specific VLAN and will be configured with an IP address in the appropriate subnet.

  3. Configure the router to perform inter-VLAN routing by enabling a routing protocol or configuring static routes between the subinterfaces.

By using a single physical interface to connect to multiple VLANs, a router-on-a-stick configuration can help to reduce the number of physical interfaces required on the router, which can lower costs and simplify network management. Additionally, by using a trunk port to connect the router to the switch, the configuration can be more flexible and can support additional VLANs in the future if needed.

Option A, using a hub, is not a recommended solution as hubs are outdated and can significantly decrease network performance. Using a hub will also not be able to segregate the VLAN traffic, which is the main purpose of VLANs.

Option B, adding a second router, would add unnecessary complexity to the network design and is not the most efficient solution.

Option C, adding two more Fast Ethernet interfaces, would increase the number of physical interfaces on the router, but it is not the most efficient solution as it would require more hardware and increase the complexity of the network.

Therefore, the best solution for connecting a router to multiple VLANs is to use a router-on-a-stick configuration.