Routing Traffic between Networks

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If you’re planning on taking the Network+ exam, you should have a basic understanding of network devices that connect networks together by routing traffic between the networks.

For example, can you answer this question?

Q. You are helping a business owner set up a basic network and you have the following equipment:

  • 2 laptops with wired and wireless NICs
  • 2 desktop PCs with wired and wireless NICs
  • 2 Ethernet cables
  • 1 wireless router with three physical ports
  • 1 cable modem

The owner wants to connect as many systems as possible to the network and the Internet using wired connections. The owner does not have a budget for any more equipment. How should you configure the network?

A. Connect the wireless router to the modem with a cable. Connect two computers to the router with a cable. Connect the two other computers to the wireless router wirelessly.

B. Connect the modem to the wireless router with a cable. Connect two computers to the modem with a cable. Connect the two other computers to the modem wirelessly.

C. Connect the modem to the wireless router with a cable. Connect one computer to the modem with a cable. Connect the three other computers to the modem wirelessly.

D. Connect the wireless router to the modem with a cable. Connect one computer to the router with a cable. Connect the three other computers to the wireless router wirelessly.

More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.

Using a Router

Routers connect networks together into a single “network of networks” by routing traffic between the networks. They provide a path or gateway out of a network and once traffic reaches the router, the router determines the best path for the traffic to reach its destination.

Routers use Internet Protocol (IP) addresses to identify the best path. In comparison, switches use 48-bit MAC addresses. Data transmissions include both source and destination MAC addresses. They also include both source and destination IP addresses. While the MAC addresses are semi-permanent and burnt into the NIC, the IP address is much more dynamic. You assign the IP address dynamically with something like Dynamic Host Configuration Protocol (DHCP), or manually when you first configure the computer.

IPv4 addresses use 32-bits and are typically expressed in a dotted decimal format, such as 192.168.1.5. Each decimal represents an octet of eight bits. For example, 192 is 1100 0000, 168 is 1010 1010, 1 is 0000 0001, and 5 is 0000 0101. It’s much more difficult to read a 32-bit binary address such as 11000000101010100000000100000101 than it is to read a dotted decimal address like this 192.168.1.5 so you’ll see IPv4 addresses in a dotted decimal format much more often.


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The following figure shows Switch 1 connecting several computers together in one network and Switch 2 connecting several computers together in another network. Each of the computers in Network 1 has an assigned IP address that is compatible with Network 1. Similarly, each of the computers in Network 2 has an assigned IP address that is compatible with Network 2.

Routing Traffic

Router connecting networks

When Computer A sends unicast traffic to Computer B, it goes through Switch 1. When Computer A sends unicast traffic to Computer D, Computer A sends the traffic to the Network 1 gateway, which is the near side of the router. The router looks at the destination IP address, realizes it needs to go to Network 2, and sends the traffic to Computer D through Switch 2. When any computer needs to access the network, it sends the traffic to the router, and the router then sends it to the Internet connection.

Notice that this router has three connections. Each connection works similar to the network interface card on a computer. It has an assigned MAC address and an assigned IP address. In the figure, you can see that the router has three interfaces, but it could just as easily have four, five, or more. Each interface would connect the router to another network and the router would be able to route any traffic it receives to the correct network based on the destination IP address.


 

Q. You are helping a business owner set up a basic network and you have the following equipment:

  • 2 laptops with wired and wireless NICs
  • 2 desktop PCs with wired and wireless NICs
  • 2 Ethernet cables
  • 1 wireless router with three physical ports
  • 1 cable modem

The owner wants to connect as many systems as possible to the network and the Internet using wired connections. The owner does not have a budget for any more equipment. How should you configure the network?

A. Connect the wireless router to the modem with a cable. Connect two computers to the router with a cable. Connect the two other computers to the wireless router wirelessly.

B. Connect the modem to the wireless router with a cable. Connect two computers to the modem with a cable. Connect the two other computers to the modem wirelessly.

C. Connect the modem to the wireless router with a cable. Connect one computer to the modem with a cable. Connect the three other computers to the modem wirelessly.

D. Connect the wireless router to the modem with a cable. Connect one computer to the router with a cable. Connect the three other computers to the wireless router wirelessly.

Answer is D. You would connect the wireless router to the modem with a cable. Internet access is through the modem to an Internet service provider (ISP) in a basic network. You would then connect one of the computers to the wireless router with the second cable and connect the remaining computers to the wireless router using wireless connections.

If you have only one computer, you could connect it directly to the modem but in order to share the connection, you would need to connect the computers to the wireless router.

You only have two cables, so you only have one more cable to connect a computer to the router with a wired connection.

You may want to view a blog post about Basic Wireless Network.

Practice Test Questions To Help You Pass the Network+ Exam (N10-006) The First Time You Take It.

 

 

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