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2. Information Technology #cyber-security #networking Information Security
Module 1
Network Types
The internet is not owned by any individual or group. The internet is a worldwide collection of interconnected networks (internetwork or internet for short), cooperating with each other to exchange information using common standards. Through telephone wires, fiber-optic cables, wireless transmissions, and satellite links, internet users can exchange information in a variety of forms.
Small home networks connect a few computers to each other and to the internet. The SOHO network allows computers in a home office or a remote office to connect to a corporate network, or access centralized, shared resources. Medium to large networks, such as those used by corporations and schools, can have many locations with hundreds or thousands of interconnected hosts. The internet is a network of networks that connects hundreds of millions of computers world-wide.
There are devices all around that you may interact with on a daily basis that are also connected to the internet. These include mobile devices such as smartphones, tablets, smartwatches, and smart glasses. Things in your home can be connected to the internet such as a security system, appliances, your smart TV, and your gaming console. Outside your home there are smart cars, RFID tags, sensors and actuators, and even medical devices which can be connected.
Data Transmission The following categories are used to classify types of personal data:
- Volunteered data - This is created and explicitly shared by individuals, such as social network profiles. This type of data might include video files, pictures, text, or audio files.
- Observed data - This is captured by recording the actions of individuals, such as location data when using cell phones.
- Inferred data - This is data such as a credit score, which is based on analysis of volunteered or observed data.
The term bit is an abbreviation of “binary digit” and represents the smallest piece of data. Each bit can only have one of two possible values, 0 or 1.
There are three common methods of signal transmission used in networks:
- Electrical signals - Transmission is achieved by representing data as electrical pulses on copper wire.
- Optical signals - Transmission is achieved by converting the electrical signals into light pulses.
- Wireless signals - Transmission is achieved by using infrared, microwave, or radio waves through the air.
Bandwidth and Throughput
Bandwidth is the capacity of a medium to carry data. Digital bandwidth measures the amount of data that can flow from one place to another in a given amount of time. Bandwidth is typically measured in the number of bits that (theoretically) can be sent across the media in a second. Common bandwidth measurements are as follows:
- Thousands of bits per second (Kbps)
- Millions of bits per second (Mbps)
- Billions of bits per second (Gbps)
Throughput does not usually match the specified bandwidth. Many factors influence throughput including:
- The amount of data being sent and received over the connection
- The latency created by the number of network devices encountered between source and destination
Latency refers to the amount of time, including delays, for data to travel from one given point to another.
What Did I Learn in This Module? )3.0.0
How a Host Routes
A host can send a packet to itself, another local host, and a remote host. In IPv4, the source device uses its own subnet mask along with its own IPv4 address and the destination IPv4 address to determine whether the destination host is on the same network. In IPv6, the local router advertises the local network address (prefix) to all devices on the network, to make this determination. The default gateway is the network device (i.e. router) that can route traffic to other networks. On a network, a default gateway is usually a router that has a local IP address in the same address range as other hosts on the local network, can accept data into the local network and forward data out of the local network, and route traffic to other networks. A host routing table will typically include a default gateway. In IPv4, the host receives the IPv4 address of the default gateway either dynamically via DHCP or it is configured manually. In IPv6, the router advertises the default gateway address, or the host can be configured manually. On a Windows host, the route print or netstat -r command can be used to display the host routing table.
Routing Tables
When a host sends a packet to another host, it consults its routing table to determine where to send the packet. If the destination host is on a remote network, the packet is forwarded to the default gateway which is usually the local router. What happens when a packet arrives on a router interface? The router examines the packet’s destination IP address and searches its routing table to determine where to forward the packet. The routing table contains a list of all known network addresses (prefixes) and where to forward the packet. These entries are known as route entries or routes. The router will forward the packet using the best (longest) matching route entry.
The routing table of a router stores three types of route entries: directly connected networks, remote networks, and a default route. Routers learn about remote networks manually, or dynamically using a dynamic routing protocol. Static routes are route entries that are manually configured. Static routes include the remote network address and the IP address of the next hop router. OSPF and EIGRP are two dynamic routing protocols. The show ip route privileged EXEC mode command is used to view the IPv4 routing table on a Cisco IOS router. At the beginning of an IPv4 routing table is a code that is used to identify the type of route or how the route was learned. Common route sources (codes) include:
L - Directly connected local interface IP address
C - Directly connected network
S - Static route was manually configured by an administrator
O - Open Shortest Path First (OSPF)
D - Enhanced Interior Gateway Routing Protocol (EIGRP)