As data travels down the protocol stack it is encapsulated. At the Internet layer it is encapsulated intoa PDU (commonly called a packet). The header for this packet has several fields.
• Source Address: Specifies the sending node’s IP address.
• Destination Address: Specifies the receiving node’s IP address.
IP Address Format: Dotted Decimal Notation
In any given [[IP address]], some portion of the 32-bit number represents the network and the remaining bits represent the host. While many computers may share the same network address, combining the network address with a host address uniquely identifies any device connected to the network.
As shown in the figure, the IP binary number is 10101 100000100001000000000010001.
For usability, these 32-bit numbers are broken up into 4 groups of numbers called octets (1 octet = 8 bits). Each octet is then represented as a decimal number between 0 and 255 and separated by a period, or dot. This scheme is known as “dotted decimal notation.” The IP address shown above can be written as 172.16.128.17 and spoken as “172 dot 16 dot 128 dot 17.”