Network+ N10-008 ExamNotes for sub-objective 1.2 – Explain the characteristics of network topologies and network types.

This is the second installment of our free study guide for the CompTIA Network+ N10-008 exam.

We’ll start by examining the types of network topologies, how they operate logically and physically. Then we will look at some of the technologies these networks use to utilize the topologies.

Wired topologies

Logical vs. physical

The physical topology refers to the hardware used to create the network. Hubs, switches, and routers along with the cables and connectors used to define the physical aspect of networks.

The logical topology refers to the non-hardware aspects of the network. This includes the operating systems and protocols used to communicate on a network. The logical topology covers how the nodes on a network use applications and share data.

Star topology

In a star topology, all network devices are connected to a central device like a hub or switch. Consider the spokes of a wheel connecting to a hub. In networking, a hub acts at Layer 1 of the OSI model and the switch at Layer 2. In a star topology, switches are preferred because hubs generate frequent collisions.

Ring topology

Considered a legacy topology the ring topology is a continuous ring of connections where each node is connected to the nodes directly adjacent to it.

Data is passed from each node to the next, in a circular pattern. A node can only transmit to the next node on the ring. Token ring is the method using a token that is passed from one node to the next. While a node has the token it can pass it to the next node. It can also receive and replace the data if it is the destination of the token. While actually resembling a star topology the central point is a MAU (Multistation Access Unit) that receives a token and forwards it to the next node in the ring. A failure in any node will isolate the other nodes and the failed node must then be removed or disabled by the MAU.

Mesh

In today’s wired environment mesh networks are rare. The concept of redundant connections remains applicable to the wireless environment as you will see later.

The wired mesh is configured so that each node will have a direct connection to every other node. For example, if you have a network with four PCs, each would have three connection points with each connection linking to another network node, as the network grows the wiring itself becomes more challenging. Mesh networking reduces the “single point of failure” that a hub or switch would represent.

Bus

The bus topology uses a single cable to connect all network nodes. This cable has only two endpoints and must remain intact. Signals can travel in either direction on the bus.

So, a signal can be transmitted in both directions from a node. The signal will travel the length of the bus until the destination node is reached. If a signal is allowed to continue to the end of the cable it will bounce back, creating interference and unwanted noise on the line. This signal bounce is mitigated by using terminators at both ends of the cable. This topology is economical to implement but hard to manage since the bus itself represents a (large) single point of failure. You may find the bus topology as a backbone for routers and switches. A good example would be a network that covers five floors of a building. Here each floor would be a star topology with a router serving each floor. The routers would use a simple bus cable to connect to each other.

Wireless topologies

Mesh

Wireless mesh networks can be connected with or without wireless routers and gateways. This configuration is best deployed in a static environment. Network devices can be used to support more connections. The movement of nodes triggers routing updates to all which create network congestion.

Ad hoc

Special purpose ad-hoc wireless mesh networks can be configured to enable communication between nodes without routers and gateways. The nodes must be in close proximity to each other. This configuration is best used where there are few connections to static devices.

Infrastructure 

The wireless infrastructure uses connectivity devices to distribute the signal over the intended coverage area. Wireless Access Points (WAPs) can be used to create or extend the coverage area. WAPs should be centrally placed to provide even coverage to the nodes. Multiple APs can be used to extend the coverage area.

Types

LAN

A Local Area Network (LAN) typically consists of several network nodes or devices where each node can connect to other nodes directly through a switch. LANs can be a small as an office or cover an entire building using multiple switches and routers.

WLAN

A Wireless LAN (WLAN) describes the wireless topology of a small office or home office.

MAN

A group of LANs in the same geographic area is considered a MAN (Metropolitan Area Network). This network type can support local government, schools, Police, and Fire departments. A CAN (Campus Area Network) also covers a geographical area much the same as a MAN. These are not widely used terms but are testable on the Network+.

WAN

When a group of LANs covers a large geographical area it is called a WAN (Wide Area Network). Consider the Internet as the largest WAN.

SDWAN

A WAN that is primarily controlled with a software-defined virtual architecture is called an SDWAN.

CAN

See MAN

SAN

A Storage Area Network (SAN) describes a network made up of block-level storage devices providing high throughput connections for storage devices, disk arrays, and tape storage. The servers consider all devices as one object, enhancing the access speed of data. The SAN uses controllers connected to Fibre Channel (FC) or Fibre Channel over Ethernet (FCoE) switches. Later in the objectives, you will see how these switches provide redundancy.

PAN

Bluetooth users will be familiar with the PAN (Personal Area Network). A pan can be considered the smallest network topology a piconet) because it is centered by a personal object’s workspace. A PAN can consist of a pair of devices like your smartphone and PC as well as the smartphone connecting to your vehicle. Since the connection is based on a master/slave hierarchy the smartphone, as a master, can support up to seven slave devices.

Multiprotocol label switching (MPLS)

MLPS uses a dedicated leased line for connection and applies Layer 2 or Layer 3 labels to each packet to define the path to its destination. This is highly reliable and fast supporting real-time communication like VoIP and video calls.

Multipoint Generic Routing Encapsulation (mGRE)

mGRE provides enhanced tunneling capabilities over normal point-to-point GRE tunnels by supporting multiple endpoints and dynamic configuration. This obviously reduces the administrative overhead with no impact on performance.

Termination

Demarcation point

It is important to know where the provider’s responsibilities end and the customer’s begins. This point is called the demarc (demarcation point). Today’s demarks will be a NID (Network Interface Device) or NIU (Network Interface Unit) placed on the outside of your building or directly inside the premise. The provider is responsible for the delivery of the signal to the demarc and its operation while the customer is responsible for the signal distribution from that point. This is a good place to start troubleshooting network issues.

Smart jack

Often you will find that the demarc device is a smart jack capable of monitoring the connection for data errors and reporting them to the carrier. The smart jack can also be checked by the technician by monitoring the status and activity LEDs.

CSU/DSU

The CSU (channel service unit) is usually a stand-alone device that is placed between the NID and the first internal router. It serves as a digital signal termination point and uses error correction and line monitoring to ensure data integrity. The DSU (data service unit), built-in with the CSU, converts the incoming frames from the T-carrier into Ethernet frames for the network. The process is reversed for transmissions. The evolution of these devices has made the CSU/DSU available as an add-on card in a router lowering cost and maintenance concerns.

Virtual network concepts

Virtual switch

In virtual networking, a virtual switch (vSwitch) is created to allow your virtual devices to communicate with each other as well as the physical LAN. It operates at Layer 2 (Data Link) Layer and you may see it called a bridge.

Virtual NIC

The Virtual NIC (VNIC) is the network connection for each virtual node. VNICs connect to the vSwitch which connects them to the VLAN, vRouter, or physical LAN.

Virtual router

A virtual router (vRouter) is a fully functional software version of a router. As the highest level virtual device you will probably connect to the physical LAN through it.

Virtual firewall

A virtual firewall can be placed at strategic locations within your virtual environment enabling a greater level of control.

Hypervisor

The Hypervisor or Virtual Machine Manager (VMM) is the software component that contains and controls all the virtual machines and devices on a host. When installing a hypervisor be sure that your processor supports hardware virtualization. Intel-based processors use VT-x and AMD uses AMD-V. Be sure these are available and running in UEFI/BIOS. Remember that all storage and memory allocated to your devices will impact the host machine performance.

Here’s a look at a Windows 10 PC Resource Monitor with a VMM running. The first screen shows the CPU usage before launching a virtual machine. In the left pane, the application usage on the CPU cores is displayed as the barely visible green line in the graphs represents the usage by VMM.

Now, here is a look at the CPU usage with a Windows 10 VM running. Both the CPU and Memory (not shown) are significantly impacted.