Welcome to today’s CCENT and CCNA in-depth exam question. Our goal with our Cisco certification exam questions is not to have you memorize answers but to really learn why the answers are right and more importantly why if you picked the wrong answer why it is wrong so you do not do the same thing on your Cisco test. Today we will look at the exam topic of Inter-VLAN routing.
Inter-VLAN routing is where you break up a switch into multiple VLANs(virtual LANs). So you can have two VLANs on a switch, one could be VLAN 200 and the other VLAN 300. A host in VLAN 200 may have a IP Address of 192.168.1.10 and a host in VLAN 300 may have a an IP Address of 192.168.1.20 which usually if they were on the same switch they would be able to ping each other. But when the switch is VLANed they may not be able to do such without some extra configuration and devices in our CCNA lab topology. So now that we provided you with a quick overview, let’s take a look at our Cisco exam question before I explain the answer fully before you even have a change to give it a shot.
CCNA Inter-VLAN Routing
A network administrator is troubleshooting a connectivity problem in the office. Users on VLAN 45 are complaining that they cannot access users on VLAN 55. What is needed to allow communication between the VLANs?
A. a router with an IP address on the physical interface connected to the switch
B. a switch with an access link that is configured between the switches
C. a switch with a trunk link that is configured between the switches
D. a router with subinterfaces configured on the physical interface that is connected to the switch
So let’s talk a little bit more about the theory of Inter-VLAN routing. Inter-VLAN routing is used to permit devices on separate VLANs to communicate. “Router-on-a-stick” is a type of router configuration in which a single physical interface routes traffic between multiple VLANs on a network.
The router interface is configured to operate as a trunk link and is connected to a switch port configured in trunk mode. The router performs the inter-VLAN routing by accepting VLAN tagged traffic on the trunk interface coming from the adjacent switch and internally routing between the VLANs using subinterfaces. The router then forwards the routed traffic-VLAN tagged for the destination VLAN-out the same physical interface.
In this scenario, answer A would not work since the router would require 2 physical interfaces or subinterfaces.
B and C are wrong since adding another switch still would not allow communication on layer 3.
So that leaves us with the correct answer D which is we would configure the router with subinterfaces on the actual physical interface that is on the router that is connected to the switch via a patch cable. The switch will send the data to the router and it will bounce off the router’s interface and go back to the switch where the tagging will be stripped off and then directed to the appropriate VLAN to complete the transmission of data.
This was a sample of one of the CCENT and CCNA lab topologies that is pretty easy to setup and replicate with even the most basic of CCNA lab equipment available to you.
You can replicate a lab scenario like this with as little as two hosts (it can be two computers, a computer and a printer or any other device you can assign an IP address), one Cisco switch such as a 2950, 2960, 3550 or 3560; and a router with a 100mb fastethernet interface such as a 1760, 1841, 2801, 2811 router. So it is a pretty easy lab to configure and we have quite a few of these labs in our 450 page, 60 lab exercise lab workbook. If you need help on designing your own CCENT or CCNA lab you may want to check out our lab suggestions article http://www.certificationkits.com/cisco-lab-suggestions/ or video http://www.certificationkits.com/ccna-videos/ and if you are still confused, shoot us an email via the Contact Us link in the upper right and we will help you create the most cost-efficient, best bang for the buck CCNA lab!
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