LET'S TALK ABOUT – NETWORKING FUNDAMENTALS

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LET'S TALK ABOUT – NETWORKING FUNDAMENTALS
PART 1 – BASIC CONCEPTS

This topic will divide in 4 parts: Computer Networks, IP address, DNS and DHCP

1-   COMPUTER NETWORK
Or can be called Data Network is a digital telecommunications network which allows nodes (hosts, computers, servers, printers, etc.) to share resources and connected.

In computer networks, networked computing devices exchange data with each other using a data link. The connections between nodes are established using either cable media or wireless media.

Network computer devices that originate, route and terminate the data are called network nodes. Nodes can include hosts such as personal computers, phones, servers as well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, whether or not they have a direct connection to each other.

Computer networks support an enormous number of applications and services such as access to the World Wide Web (all webpages that we access), digital video (Yourtube), digital audio (Deezer), shared use of application and storage servers (dropbox), printers, and fax machines, and use of email (Gmail / Hotmail) and instant messaging applications (Skype, Whatsapp) as well as many others.

Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the network's size, topology and organizational intent. The best-known computer network is the Internet.

2-   WHAT ARE IP ADDRESSES
Each device on your internal home/office network is assigned a private IP address, of the form 192.168.x.x or 10.0.x.x (Why these particular numbers? It was just decided that these were the numbers that would be reserved for private networks.

When your computer asks to browse a website, it’s the router’s job to send requests out to that website, then direct the replies back to the appropriate device on your network. Your router will have also have a public IP address, through which Internet services and websites will know where to send their data back to your house, at which point the router examines the data packet and says, “Oh, this was meant for that PC in the bedroom, I’ll send it there.”


At this moment, your home/office network operates on IPv4, with the router handling the address translation between the Internet and locally. You may also have heard that the world is running out of IP addresses, and everything needs to be fixed by upgrading to IPv6. When your ISP upgrades to IPv6, they will replace your router to one that’s compatible with IPv6 capable.

IPv6 vs. IPv4 :
More recently, there's been a lot of talk about switching to IPv6 and how it will bring a lot of benefits to the Internet. But, this "news" keeps repeating itself, as there's always an occasional...

Most of the time you can forget all about IP addresses: computers and devices will appear automatically on the Windows or OS X network browser. But sometimes it’s useful to know the IP address if something needs to be configured manually, and there are couple of ways to go about doing this.



3-   DOMAIN NAME SYSTEM (DNS)
The Domain Name System or simple as “DNS” is a hierarchical decentralized naming system for computers, services, or other resources connected to the Internet or a private network.

It translates more readily memorized domain names to the numerical IP addresses needed for locating and identifying computer services and devices with the underlying network protocols.

By providing a worldwide, distributed directory service, the Domain Name System is an essential component of the functionality on the Internet that has been in use since 1985.

The Domain Name System delegates the responsibility of assigning domain names and mapping those names to Internet resources by designating authoritative name servers for each domain. Network administrators may delegate authority over sub-domains of their allocated name space to other name servers. This mechanism provides distributed and fault tolerant service and was designed to avoid a single large central database.

The Internet maintains two principal namespaces, the domain name hierarchy and the Internet Protocol (IP) address spaces. The Domain Name System maintains the domain name hierarchy and provides translation services between it and the address spaces. Internet name servers and a communication protocol implement the Domain Name System. A DNS name server is a server that stores the DNS records for a domain; a DNS name server responds with answers to queries against its database.

The most common types of records stored in the DNS database are for Start of Authority (SOA), IP addresses (A and AAAA), SMTP mail exchangers (MX), name servers (NS), pointers for reverse DNS lookups (PTR), and domain name aliases (CNAME). Although not intended to be a general purpose database, DNS can store records for other types of data for either automatic lookups, such as DNSSEC records, or for human queries such as responsible person (RP) records. As a general purpose database, the DNS has also been used in combating unsolicited email (spam) by storing a real-time blackhole list. The DNS database is traditionally stored in a structured zone file.

4- DHCP (DYNAMIC HOST CONFIGURATION PROTOCOL)
Is a standardized network protocol used on Internet Protocol (IP) networks. The DHCP is controlled by a DHCP server that dynamically distributes network configuration parameters, such as IP addresses, for interfaces and services.

A router or a residential gateway can be enabled to act as a DHCP server. A DHCP server enables computers to request IP addresses and networking parameters automatically, reducing the need for a network administrator or a user to configure these settings manually. In the absence of a DHCP server, each computer or other device (e.g., a printer) on the network needs to be statically (i.e., manually) assigned to an IP address.

General and Technical Aspects
TCP/IP defines how devices on one network communicate with devices on another network. A DHCP server can manage TCP/IP settings for devices on a network, by automatically or dynamically assigning Internet Protocol (IP) addresses to the devices. As of 2011, networks ranging in size from home networks to large campus networks and regional Internet service provider networks commonly use DHCP. Most residential network routers receive a globally unique IP address within the provider network. Within a local network, a DHCP server assigns a local IP address to each device connected to the network.

The DHCP operates based on the client–server model. When a computer or other device connects to a network, the DHCP client software sends a broadcast query requesting the necessary information.

Any DHCP server on the network may service the request. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as default gateway, domain name, the name servers, and time servers. On receiving a request, the server may respond with specific information for each client, as previously configured by an administrator, or with a specific address and any other information valid for the entire network and for the time period for which the allocation (lease) is valid.

A client typically queries for this information immediately after booting, and periodically thereafter before the expiration of the information. When a DHCP client refreshes an assignment, it initially requests the same parameter values, but the DHCP server may assign a new address based on the assignment policies set by administrators.

On large networks that consist of multiple links, a single DHCP server may service the entire network when aided by DHCP relay agents located on the interconnecting routers. Such agents relay messages between DHCP clients and DHCP servers located on different subnets.

Depending on implementation, the DHCP server may have three methods of allocating IP addresses:

DYNAMIC ALLOCATION: A network administrator reserves a range of IP addresses for DHCP, and each DHCP client on the LAN is configured to request an IP address from the DHCP server during network initialization. The request-and-grant process uses a lease concept with a controllable time period, allowing the DHCP server to reclaim (and then reallocate) IP addresses that are not renewed.

AUTOMATIC ALLOCATION:
The DHCP server temporarily assigns an IP address to a requesting client from the range defined by the administrator. This is like dynamic allocation, but the DHCP server keeps a table of past IP address assignments, so that it can preferentially assign to a client the same IP address that the client previously had.

MANUAL ALLOCATION (CALLED STATIC ALLOCATION)
The DHCP server issues a private IP address dependent upon each client's MAC address, based on a predefined mapping by the administrator. This feature is variously called static DHCP assignment by DD-WRT, fixed-address by the dhcpd documentation, address reservation by Netgear, DHCP reservation or static DHCP by Cisco and Linksys, and IP address reservation or MAC/IP address binding by various other router manufacturers. If no match for the client's MAC address is found, the server may or may not optionally fall back to either Dynamic or Automatic allocation.

DHCP is used for Internet Protocol version 4 (IPv4), as well as for IPv6. While both versions serve the same purpose, the details of the protocol for IPv4 and IPv6 differ sufficiently that they may be considered separate protocols. For the IPv6 operation, devices may alternatively use stateless address autoconfiguration. IPv6 hosts may also use link-local addressing to achieve operations restricted to the local network link.

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