Internet Protocol

Internet Protocol

• IP addresses 32 bit addresses (divided into 4 octets) used by the Internet Protocol  for delivering packet to a device located in same or remote network. 
• MAC addres is a globally unique address which represents the network card and cannot be changed. 
• IP address refers to a logical address, which is a configurable address used to identify which network this host belongs to and also a network specific host number. 
• In other words, an IP V4 address consists of two parts, a network part and a host part.
• This can be compared to your home address. 
• A letter addressed to your home address will be delivered to your house because of this logical address. 
• If you move to another house, your address will change, and letters addressed to you will be sent to your new address.
• IP addresses are stored internally as binary numbers but they are represented in decimal numbers because of simplicity.
• An example of IP address is 192.168.10.100, which is actually 11000000.10101000.00001010.01100100.
• For Each network, one address is used to represent the network and one address is used for broadcast. Network address is an IP address with all host bits are "0". Broadcast address is an IP address with all host bits are "1".
• That means, for a network, the first IP address is the network address and the last IP address is the broadcast address. 
• All the usable IP addresses in any IP network are between network address and broadcast address.
• We can use the following equation for find the number of usable IP addresses in a network
• Number of usable IP addresses = (2ⁿ)-2. Where "n" is the number of bits in host part.
• Many IP addresses are reserved and we cannot use those IP address. 
• There are five IP address Classes and certain special addresses.

Default Network

• The IP address of 0.0.0.0 is used for the default network. When a program sends a packet to an address that is not added in the on the computer's routing table, the packet is forwarded to the gateway for 0.0.0.0, which may able to route it to the correct address.

Class A IP addresses

• "Class A" IP addresses are for very large networks. The left most bit of the left most octet of a "Class A" network is reserved as "0". 
• The first octet of a "Class A" IP address is used to identify the Network and the three remaining octets are used to identify the host in that particular network.
• The 32 bits of a "Class A" IP address can be represented as 0xxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.
• The minimum possible value for the leftmost octet in binaries is 00000000 (decimal equivalent is 0) and the maximum possible value for the leftmost octet is 01111111 (decimal equivalent is 127). Therefore for a "Class A" IP address, leftmost octet must have a value between 0-127 (0.X.X.X to 127.X.X.X).
• The network 127.0.0.0 is known as loopback network. The IP address 127.0.0.1 is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing.
• Computers not connected directly to the Internet need not have globally-unique IP addresses. 
• They need an IP addresses unique to that network only. 10.0.0.0 network belongs to "Class A" is reserved for private use and can be used inside any organization.

Class B IP addresses

• "Class B" IP addresses are used for medium-sized networks. 
• Two left most bits of the left most octet of a "Class B" network is reserved as "10". 
• The first two octets of a "Class B" IP address is used to identify the Network and the remaining two octets are used to identify the host in that particular network.
• The 32 bits of a "Class B" IP address can be represented as 10xxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.
• The minimum possible value for the leftmost octet in binaries is 10000000 (decimal equivalent is 128) and the maximum possible value for the leftmost octet is 10111111
• Therefore for a "Class B" IP address, leftmost octet must have a value between 128-191 (128.X.X.X to 191.X.X.X).
• Network 169.254.0.0 is known as APIPA (Automatic Private IP Addresses). 
• APIPA range of IP addresses are used when a client is configured to automatically obtain an IP address from the DHCP server was unable to contact the DHCP server for dynamic IP address.
• Networks starting from 172.16.0.0 to 172.31.0.0 are reserved for private use.

Class C IP addresses

• "Class C" IP addresses are commonly used for small to mid-size businesses. 
• Three left most bits of the left most octet of a "Class C" network is reserved as "110". 
• The first three octets of a "Class C" IP address is used to identify the Network and the remaining one octet is used to identify the host in that particular network.
• The 32 bits of a "Class C" IP address can be represented as 110xxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.

Class D IP addresses

• Class D IP addresses are known as multicast IP addresses. Multicasting is a technique developed to send packets from one device to many other devices, without any unnecessary packet duplication. 
• In multicasting, one packet is sent from a source and is replicated as needed in the network to reach as many end-users as necessary. You cannot assign these IP addresses to your devices.
• Four left most bits of the left most octet of a "Class D" network is reserved as "1110". 
• The other 28 bits are used to identify the group of computers the multicast message is intended for.

Class E IP addresses

• Class E is used for experimental purposes only and you cannot assign these IP addresses to your devices.
• Four left most bits of the left most octet of a "Class E" network is reserved as "1111".

Limited Broadcast

• 255.255.255.255 is used to send messages to all devices in the LAN and this IP addrress is known as limited broadcast IP address.