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IP Addressing step by step

in blog, IP Addressing on July 2, 2014

IPv4 addresses

  • Consist of 32 bits.
  • Are broken into four octets (8 bits each).
  • Use dotted-decimal format; an example is
  • Minimum value (per octet) is 0, and the maximum value is 255.
  • is a network ID.
  • is a broadcast IP.

IPv4 Address Classes

TABLE FF.13 IPv4 Address Classes
First Octet Second Octet Third Octet Fourth Octet
Class A Network Host Host Host
Class B Network Network Host Host
Class C Network Network Network Host

TCP/IP defines two additional address classes:

  • Class D: Used for multicast addresses.
  • Class E: Used for research purposes.

ip address

TABLE FF.14 Address Class Ranges

Class                                    First Octet Decimal Range

A                                              1 to 126

B                                             128 to 191

C                                             192 to 223

D                                             224 to 239

E                                              240 to 255

The 127.x.x.x address range is reserved for loopback addresses.

Default subnet masks:

  •  Class A:
  • Class B:
  • Class C:

Classless Addressing

Classless Interdomain Routing (CIDR) notation might also be used to identify the subnet mask. The CIDR notation for each network class can be determined by counting the 1s in binary or the number of bits that make up the network portion of the address.

The mask is written in slash notation as follows:

  • Class A: /8
  • Class B: /16
  • Class C: /24

Private Ranges

IANA private address space allocations:

  • Class A: to
  • Class B: to
  • Class C: to


TABLE FF.15 Decimal to Binary Conversions

Class First Octet Decimal Range
0128 0000000010000000
192 11000000
224 11100000
240 11110000
248 11111000
252 11111100
254 11111110
255 11111111

To calculate the hosts in a subnet, we can use the formula 2H – 2. The exponent H represents the number of host bits in a network.

To calculate the networks in a subnet, we can use the formula 2N – 2. The exponent N repre­sents the number of subnet bits in a network.

The range of valid IP addresses in a subnet is the first IP address after the Network ID and the last IP address before the broadcast IP address.

The following represents IP subnetting: IP address =

Subnet mask =

Network ID =

Broadcast IP =

Valid IP range = to


IPv6 is a workable IP version that was created in the event that the IP space from IPv4 is exhausted.

IPv6 address format summary:

  • Defined by RFC 2373 and RFC 237.
  • Consists of 128 bits, with a 64-bit network prefix and a 64-bit local identifier.
  • Represented by 32 hexadecimal digits broken into eight smaller groups of four.
  • Utilizes CIDR notation (slash notation) to discern a subnet range, so you might see the same IP address subnetted and written out as

2001 :0BD2:0200:08F1 :0000:0000:0000: 16AB/16.

The same IPv6 IP address can be written out in all of the following ways: 2001 :0BD2 :0200:08F1 :0000:0000:0000: 16AB

200 1:BD2 :200:8F1 :0:0:0:16AB

200 1:BD2 :200:8F1 ::16AB


Types of IPv6 Addresses

1. Link-local addresses: Addresses that have the shortest reach of the IP address types. They can only go as far as the Layer 2 domain. These addresses are autogenerated with or without the use of a DHCP server. So, when an IPv6 node goes online, this address is assigned automatically.

2. Unique/site-local addresses: Addresses that have a broader scope than link-local addresses. They can expand to the size of an organization and are used to describe the boundary of the organizational network. These are the private addresses for IPv6.

3. Global addresses: Addresses that have the broadest scope of all. As the name indi­cates, these addresses are for global use—that is, for Internet communications.

4. Multicast: Addresses that are extremely important because of their use in group com­munications and broadcast messaging.

Integrating IPv4 and IPv6

There are several ways to integrate IPv4 and IPv6 addressing. You can implement dual-stack,tunneling, or translation techniques to help IPv4 and IPv6 addresses exist together on the net-work simultaneously.

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