Computer Network
Modem
A modem (modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information.

MAC Address
In computer networking, a Media Access Control address (MAC address) is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification, and used in the Media Access Control protocol sub-layer. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number. It may also be known as an Ethernet Hardware Address (EHA), hardware address, adapter address, or physical address..

Domain Name System (DNS) / Domain Name Servers
The Domain Name System (DNS) servers distribute the job of mapping domain names to IP addresses among servers allocated to each domain.

IP Address

Network
Type
Address Range
Normal
Netmask
Comments
Class A
001.x.x.x to 126.x.x.x
255.0.0.0
For very large networks
Class B
128.1.x.x to 191.254.x.x
255.255.0.0
For medium size networks
Class C
192.0.1.x to 223.255.254.x
255.255.255.0
For small networks
Class D
224.x.x.x to 239.255.255.255
 
Used to support multicasting
Class E
240.x.x.x to 247.255.255.255
 
 

There are some network addresses reserved for private use by the Internet Assigned Numbers Authority (IANA) which can be hidden behind a computer which uses IP masquerading to connect the private network to the internet. There are three sets of addresses reserved. These address are shown below:
10.x.x.x
172.16.x.x - 172.31.x.x
192.168.x.x
Other reserved or commonly used addresses:

127.0.0.1 - The loopback interface address. All 127.x.x.x addresses are used by the loopback interface which copies data from the transmit buffer to the receive buffer of the NIC when used.

0.0.0.0 - This is reserved for hosts that don't know their address and use BOOTP or DHCP protocols to determine their addresses.

255 - The value of 255 is never used as an address for any part of the IP address. It is reserved for broadcast addressing. Please remember, this is exclusive of CIDR. When using CIDR, all bits of the address can never be all ones.

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