CompTIA N10–007 Key Points
1. Open System Interconnection model
The OSI (Open Systems Interconnection) Model is a standardized model which we use to demonstrate the theory behind computer networking. In practice, it’s actually the more compact TCP/IP model that real-world networking is based on; however, the OSI model, in many ways, is easier to get an initial understanding from.
The main functions of each of the layers are as follows −
- Physical Layer − Its function is to transmit individual bits from one node to another over a physical medium.
- Data Link Layer − It is responsible for the reliable transfer of data frames from one node to another connected by the physical layer.
- Network Layer − It manages the delivery of individual data packets from source to destination through appropriate addressing and routing.
- Transport Layer −It is responsible for the delivery of the entire message from the source host to the destination host.
- Session Layer − It establishes sessions between users and offers services like dialog control and synchronization.
- Presentation Layer − It monitors the syntax and semantics of transmitted information through translation, compression, and encryption.
- Application Layer − It provides high-level APIs (application program interface) to the users.
2. DNS — Domain Name System
The key functionality of DNS is to translate between human-friendly identifiers (URLs) and a computer-friendly registry (IP and port #) of where to best access a variety of resources.
- DNS affects URLs (Uniform Resource Locator), E-mail addresses, IP addresses, and more.
- DNS can often be related to a phone book, wherein you look up something easy to remember to gain more specific information.
The chief difference in functionality between a phone book and DNS is that DNS will output the location of specific data based on proximal servers.
In other words, if I, in America, and someone in China both type in a URL, we may be given a different IP from which to pull the data we’re requesting, based on whichever server is closer to each of us that houses that data.
- Another key function of DNS is that, rather than creating one centralized database which can be difficult to change, DNS typically assigns a domain range to each ‘user.’
For instance, www.example.com gives us information about three zones.
The highest level domain is “com”.
The first subdomain is “example”
And the second subdomain is “www”
The ‘.’ indicates the distinction between multiple labels.
- Each top-level domain (‘com’ in the example) requires two servers to contain master lists of its NS data. This is to provide redundancy in case one server should fail or become inaccessible.
- ICANN delegates the management of all top-level domains.
- FQDN — Fully Qualified Domain Name comprises two parts: hostname and domain name
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