Routing Traffic between Networks

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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Protecting Internet-based Attacks

If you’re planning on taking the Network+ exam, you should have a basic understanding of protecting internet-based attacks. For example, can you answer this question?

Q. Which of the following devices uses an ACL to prevent unauthorized access into a network?

A. Firewall

B. Proxy server

C. Load balancer

D. VPN concentrator

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.

Network Firewalls

A firewall provides protection for networks and individual computers. Most networks have a firewall at the border, directly between the private network and the public Internet. These network firewalls help protect networks from Internet-based attacks. Additionally, computers commonly have software-based firewalls that provide an added layer of protection for the computer. They protect against potential threats within a network.

IT-based firewalls are similar to firewalls in cars. The firewall in a car is between the engine compartment and the passenger compartment. If the engine catches fire, the firewall helps block the fire from getting into the passenger compartment.

The firewall in a car isn’t foolproof. A collision can damage the firewall, significantly reducing the protection it provides. Similarly, a firewall in a network isn’t foolproof. Attackers might be able to bypass the firewall, or find holes that they can exploit. However, the IT-based firewalls do provide a good front line defense.

A very basic firewall is a packet-filtering router with an access control list (ACL). The ACL is a group of rules that define network access. These rules define traffic based on IP addresses, protocols, logical port numbers, and other information included within data packets. The router then examines each packet and filters traffic based on the rules.


Learn more about several common network components.

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Advanced firewalls have a lot of sophistication and can be much more selective about what traffic they block and allow. Instead of looking at individual packets, they can look at a full conversation of traffic between systems and block malicious traffic.

Firewalls are very useful for protecting private networks from attackers. Many attackers try to attack a network through the Internet so the most common place you’ll see a firewall is at the border of a network, between a private internal network and the public Internet as shown in the figure. This also clearly shows the order of connectivity for devices to the Internet: from a network client such as a desktop PC to a switch, to a router, to a firewall, to an ISP and then to the Internet.

The following figure shows a typical network with a switch, router, and firewall. The switch connects devices together into a network. The router connects networks together – in this figure, it is connecting the private network with the Internet via the modem and ISP. The firewall provides a layer of protection to the router and the internal network.

Internet-based Attacks

Network connectivity with a firewall

Remember This

Routers and firewalls use a group of rules in an ACL to define network access and prevent unauthorized access. Most organizations have network-based firewalls at their network border, providing a barrier between a private network and the public Internet. Device connectivity to the Internet in a typical network takes this path:

Network device –> Switch –> Router –> Firewall –> ISP –> Internet.


 

Q. Which of the following devices uses an ACL to prevent unauthorized access into a network?

A. Firewall

B. Proxy server

C. Load balancer

D. VPN concentrator

Answer: A is correct. A firewall uses rules within an access control list (ACL) to prevent unauthorized access into a network.

A proxy server reduces bandwidth by storing copies of web site pages in cache and then serving these cached pages to other users. It does not use an ACL.

A load balancer can balance traffic among multiple servers. It does not use an ACL.

A virtual private network (VPN) concentrator supports multiple VPN connections but it doesn’t use an ACL.

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

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Connecting Network Devices

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

For example can you answer this question?

Q.  You need to network six PCs together for a basic network. The business owner does not want these devices to access the Internet. Which of the following items do you need? (Select TWO.)

A. Switch

B. Router

C. Firewall

D. CAT6 cables

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.

Connecting Devices with a Switch

Switches connect devices in a network similar to how hubs connect devices. The primary difference is that switches have more intelligence and make decisions on what traffic to send to each port. Switches make these decisions based on the media access control (MAC) address assigned to each connected device.

A MAC address is a 48-bit address assigned to a client’s NIC and it is typically displayed as six pairs of hexadecimal characters like this 1A-2B-3C-4D-5E-6F or this1A:2B:3C:4D:5E:6F. Valid hexadecimal characters are the numbers 0-9 and the letters A-F. Four bits represent each character. For example, 0001 represents 1 in hexadecimal and 1110 represents E in hexadecimal. If you need to review decimal, hexadecimal, and binary topics, check out this blog post.

You might hear that MAC addresses are unique and are permanently assigned to a NIC. This isn’t exactly correct.

  • MAC addresses are theoretically unique. You are not likely to see any two identical MAC addresses assigned to different NICs, but it is possible.
  • MAC addresses can be changed. MACs are typically burned into the NIC making them semi-permanent. However, you can change the MAC address for the NIC through the operating system or a software tool.

When devices transmit data from one device to another, they include their MAC address as the source MAC address and the other device’s MAC address as the destination MAC address. A switch typically doesn’t know which MAC addresses are associated with each physical port when it is first powered up. However, over time, it tracks the traffic and eventually learns the MAC addresses associated with each of its ports.


Learn more about  the other common network devices.

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As an example, consider the following figure. It shows four computers connected to a basic switch with four ports, and a Port-MAC table created within the switch’s memory. When the switch first turns on, the Port-MAC table is empty. However, when computer A transmits data, the switch captures the MAC address, associates it with port 1, and enters it into the Port-MAC table. At this point, it doesn’t know the MAC addresses for other computers. Over time, the other computers transmit data with their MAC address and the switch populates the Port-MAC table with the captured data.

Network Devices

Basic switch

A switch sends broadcast transmissions to all other ports. However, it evaluates unicast and multicast transmissions and sends them to the destination computers based on the MAC address. For example, if Computer A sends a unicast message to Computer B, the switch sends the data to port 2 of the switch. Computers C and D do not see the data transmission at all.

Remember This

You connect devices together in a network with a hub or a switch. Switches pass all broadcast traffic. They evaluate traffic and forward unicast and multicast traffic based on the destination MAC address.


 

Q.  You need to network six PCs together for a basic network. The business owner does not want these devices to access the Internet. Which of the following items do you need? (Select TWO.)

A. Switch

B. Router

C. Firewall

D. CAT6 cables

Answer are A and D are correct. You would connect the devices with cables (such as CAT6 or CAT5e cables) and a switch.

The business owner doesn’t want the devices to access the Internet so a router or a firewall isn’t needed.

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

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Basic Wireless Network

The Network+ exam expects you to be able to plan and implement a basic network, sometimes referred to as a small office home office (SOHO) network. If you’re planning on taking the Network+ exam, you should have a basic understanding of the device list for a basic wireless network.

For example, can you answer this question?

Q. You are helping a business owner set up a small office network. Employees have ten laptops, each with Wi-Fi capabilities. The office has a DSL line. What equipment needs to be purchased? (Choose TWO.)

A. ISP

B. Wireless router

C. Modem

D. DSL balancer

E. Ten cables for the ten computers

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.

Wireless Network

A wireless network is less expensive than a wired network because you don’t need to purchase and run cables to all the devices. A basic access point functions like a switch eliminating the need for a switch in many networks. An access point with routing capabilities (a wireless router) includes the capabilities of a switch, a router, and a firewall eliminating the need for additional hardware. In other words, you can purchase a wireless router and the only other device you’ll need is an Internet access device such as a modem.

For a basic wireless network, your device list might look like this:

  • Wireless router. Most wireless routers include RJ-45 ports so you can plug in wired devices, if necessary.
  • Wireless NICs. Most devices include wireless NICs, but you can purchase wireless adapters for any PCs that don’t have wireless capabilities. Wireless USB adapters are widely available and they provide any PC with wireless capabilities through an available USB port.
  • Internet access device. This device is dependent on the ISP and might be a DSL modem or a cable modem.
  • Cables. You’ll still need a cable to connect the wireless router to the Internet access device and any wired devices that need to plug into the wireless router.

Wireless Network

Remember This

A wireless network typically uses a wireless router instead of a switch and a router and only requires cables for devices that cannot connect wirelessly. You also need a cable to connect the router to the Internet, using the device specified by the ISP such as a DSL or cable modem.

If your network requires cables, you’ll need to ensure the cable length is within the required standards. While there are many different types of cables, most basic networks use twisted pair cable and the maximum length of most twisted pair cables is 100 meters (about 328 feet). The signal degrades as it passes through the cable and if the cable is too long, the signal is unusable. While you can use repeaters to amplify the signal, the best bet is to ensure the cables are within the required length.


Q. You are helping a business owner set up a small office network. Employees have ten laptops, each with Wi-Fi capabilities. The office has a DSL line. What equipment needs to be purchased? (Choose TWO.)

A. ISP

B. Wireless router

C. Modem

D. DSL balancer

E. Ten cables for the ten computers

Answer are B and C. You would need to have a modem (more specifically, a digital subscriber line (DSL) modem) to connect to the DSL line. Additionally, you would need to have a wireless router to connect the ten laptops to the wireless router using wireless capabilities. You would then connect the wireless router to the DSL modem.

A small business owner does not need to purchase an Internet service provider (ISP), but would subscribe to Internet access through an ISP.

There is no such thing as a DSL balancer.

The ten wireless laptops connect wirelessly, so cables are not needed.

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

 

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Network Safety Precautions

When working on computers and networks, it’s important to pay attention to safety. If you’re planning on taking the Network+ exam, you should have a basic understanding of network safety precautions.

For example, can you answer this question?

Q. A technician has had prolonged contact with a cleaning agent and is getting a rash. Which of the following will provide the best information in this scenario?

A. SLA
B. MOU
C. SOW
D. MSDS

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.

Successful technicians remember that computing devices are just things that can be replaced, but people cannot be replaced. In other words, it’s always important to value people over things when working on computers and networks.

The following are some of the common safety precautions mentioned in the Network+ objectives.

ESD

Electrostatic discharge (ESD) refers to the discharge of static electricity. It can damage electronic components so technicians take steps to prevent ESD damage. You’ve probably experienced a static discharge at some point in your life. The most common way is after walking across a carpeted floor and touching a door knob. The static builds up on you, and when you touch the doorknob, it discharges.

The shock you felt might have been unpleasant, but it wasn’t harmful. If you felt it, at least 3,000 volts were discharged from your hand to the door knob. If you actually saw the spark when it discharged, it was at least 8,000 volts. The good news is these voltages won’t kill or hurt people, mostly because static discharge has very little current.

Network Safety

In contrast, as little as 250 volts can damage electronic components inside computing and networking devices. You won’t see it. You won’t feel it. However, the damage is real.

A primary method of preventing ESD is by controlling humidity. If humidity is too low, it allows static to build up quickly. If you live in a colder area, you’ll notice that static is more common in the colder months because heating systems remove humidity from the air. In contrast, when the humidity is higher, the static charges dissipate naturally. Ideally, humidity should be around 50 percent. Static can build up on carpets easier than other floor surfaces so computing devices should not be placed on carpets.

Technicians prevent ESD damage with ESD wrist straps, antistatic bags, and ESD mats. These help prevent the buildup of static by ensuring the technician and the equipment are at the same ground potential. Even without these ESD tools, if you touch the computer case before working on any components, it will harmlessly discharge built-up static onto the case. If you remove any circuit cards, don’t touch the components or the pins. Instead, hold the outside edges or the plastic handles.

Installation Safety

Installation safety refers to some miscellaneous topics beyond electrical safety or ESD.

  • Lifting equipment. When lifting equipment, it’s best to lift with your legs, not your back. In other words, instead of bending down to pick up heavy equipment, you should squat by bending your knees to pick it up. There aren’t any firm guidelines on safe weight limitations. However, many standards recommend that individuals do not try to lift equipment more than 70 pounds without help.
  • Rack installation. Servers and networking devices are commonly mounted in racks about the size of refrigerator. When mounting the equipment, it’s often best to do so with two people. One person can hold the equipment, while the other person screws the device into rack.
  • Placement. When mounting devices within racks, another concern is ensuring there is enough room for airflow between the devices. In some situations, instead of mounting devices directly on top of each other, it’s necessary to mount them so that there are gaps between them. This helps prevent equipment damage from overheating.
  • Tool safety. It’s also important to follow general safety practices when working with tools. The practices vary from one tool to another, but are outlined in the tools documentation.

MSDS

Material Safety Data Sheets (MSDSs) are available for most products that have a potential to cause harm to people or equipment. This includes materials such as cleaning solutions, paints, and chemicals. The MSDS identifies important safety facts about the material such as its contents and characteristics.

A primary element of the MSDS is first aid steps to take if the product causes an adverse reaction to either people or equipment. For example, you may use cleaning products that clean computer screens or keyboards. If any of these products is causing an adverse reaction to either people or the equipment, you can refer to the MSDS sheet for information on the product and additional steps to take after the exposure.

Remember This

An MSDS includes important safety information about potentially hazardous products. If a product causes an adverse reaction, the MSDS will include first aid information to minimize the effects.


 

Q. A technician has had prolonged contact with a cleaning agent and is getting a rash. Which of the following will provide the best information in this scenario?

A. SLA
B. MOU
C. SOW
D. MSDS

Answer: D is correct. The Material Safety Data Sheet (MSDS) for the cleaning agent will provide the best information, such as first aid treatment.

A service level agreement (SLA) stipulates performance expectations, such as minimum uptime and maximum downtime levels.

A memorandum of understanding (MOU) expresses an understanding between two or more parties indicating their intention to work together toward a common goal.

A statement of work (SOW) identifies the scope of work for a contractor.


Learn more about the other common safety precautions.

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Using a Logical Token

If you’re planning on taking the Network+ exam, you should have a basic understanding of several common network topologies such as a topology that uses a logical token.

For example, can you answer this question?

Q. Computers within a network are only able to transfer data when they have access to a logical token. What type of topology does this describe?

A. Star

B. Ring

C. Bus

D. MPLS

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.

Token Ring Topologies

A ring topology has devices logically connected in a circle or ring. Data travels around the ring in a single direction through each device. Ring topologies use a logical token and are often referred to as token ring topologies. A token is special three-byte data unit passed around the ring. Devices only transmit data when they have the token.

You may have heard of talking sticks used by some Native American cultures. A group of people sits in a circle and they pass a stick around the circle to each other. Members of the group can only talk when they have the stick, and they listen when they don’t have the stick. As long as the group doesn’t get too large, this is an effective method of ensuring that everyone’s voice is heard. The three-byte token is similar to an electronic file, but it works just like the talking stick.

Ring topologies have two significant weaknesses: scalability and fault tolerance. Traditional token ring topologies have been replaced with newer technologies that don’t have these weakness, but that doesn’t stop CompTIA from listing them on the objectives.

First, ring topologies do not scale well. Performance degrades with each computer added to the ring. With five computers on the network, each computer has the token about 20 percent of the time (1/5). If you increase the number of computers on the network to 100, each computer only has the token about 1 percent of the time (1/100).

Second, a single break in the circle takes down the entire network. The break can be in the ring itself or a failure from any single device in the ring. Ring topologies commonly add a multistation access unit (MAU) to compensate for this. The devices are still connected in a logical circle and data travels one way around the circle. However, each device connects to the MAU instead of adjoining devices. Devices then transmit and receive data to and from the MAU. If one of the devices in the ring fails, the MAU senses the failure logically removes it from the ring.


Learn more about  several common network topologies.

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The following figure shows the logical layout of a token ring network topology. On the right, you can see how devices connect to each other via central MAU. The ring with the MAU looks similar to a star topology but the difference is that data travels in a circle around the ring. In a star network, data can travel to and from any device without regard to any direction.

Token

Ring topology

Some fiber optic networks use Fiber Distributed Data Interface (FDDI). These are similar to token ring networks with one significant difference. Instead of the network using a single closed circle network for data transmissions, the FDDI network has two rings. Each ring transmits data in the opposite direction providing redundancy for the network.

Synchronous Optical Networking (SONET) is a group of protocols using fiber optic cables, and some SONET implementations use ring topologies.

Remember This

A ring network connects devices in a circle and transmits a token one way around the circle. Devices in the ring only transmit data when they have the token. FDDI networks use two rings and each ring transmits data in the opposite direction providing redundancy for the network.


 

Q. Computers within a network are only able to transfer data when they have access to a logical token. What type of topology does this describe?

A. Star

B. Ring

C. Bus

D. MPLS

Answer: B is correct. Ring topologies (often called token ring) use a logical token and devices can only communicate when they have access to the token. A ring topology is configured in a circle or ring.

Star topologies use a central device such as an Ethernet switch or a hub, which do not use tokens.

Bus topologies do not use tokens. They are rarely used on networks because a failure in one connection results in a failure for all devices on the bus.

Multiprotocol Label Switching (MPLS) does not use tokens. MPLS is a wide area network (WAN) protocol that uses labels to identify addressing paths.

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

 

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