IP ADDRESS AND ROUTING

INTERNET PROTOCOL

• The IP is a N/W layer protocol that contains addressing information and some control information that enable packets to be routed.
• The IP consist of a suite of communication protocols, of which the two best known are the Transmission Control Protocol and Internet Protocol (TCP/IP).
• IP has two primary responsibilities: 
  
  
  

        •Providing connectionless, best-effort delivery of datagram's through an internetwork 

       •Providing fragmentation and reassembly of datagram’s to support data links with different                            Maximum Transmission Units(MTU). 

IPv4 DATAGRAM

•VER(4 bits) : Version of the IP protocol. 

•HLEN(4 bits): Length of the Header, Expressed as the number of 32 bit words. Min Size is 5 and Max Size is 15.

•TOTAL LENGTH (16 bits): Length in bytes of datagram, including headers. Max Datagram Size is (2 16) 65536 bytes. 

•SERVICE TYPE (8 bits): Allows packet to be assigned a priority. Router can use this field to route packets. 

•Fragment Offset: Tells where in the current packet this fragment belongs. All fragments except the last one in a datagram must be multiple of 8 bytes, there is a maximum of 8192 fragments per datagram. 

•TIME TO LIVE (8 bits): Prevents a packet from travelling forever in a loop. Sender sets a value, that is decremented at each loop. 

•PROTOCOL: Defines the higher level protocol that uses the service of the IP layer. 

•SOURCE IP ADDRESS: Address of Source station. 

•DESTINATION IP ADDRESS: Address of Destination station. 

•IDENTIFICATION, FLAGS & FRAGMENTATION: Used for handling Fragmentation. •OPTIONS(variable width): Can be used to provide more functionality to the IP datagram. 

•Header Check Sum: 

Precedence/Priority Filed Explanations (Lowest-Highest): 

Routine: (R) “…is used for all messages that justify transmission by electrical means unless the message delivery is of sufficient urgency to require higher precedence.” 

Priority: (P) “…is used for all messages that require expeditious action by the addressee(s) and/or furnish essential information for the conduct of ongoing operations.” 

Immediate (O) “…is reserved for messages relating to situations that gravely affect the security of National/Allied forces or populace.” 

Flash (Z) “…is reserved for initial enemy contact messages or operational combat messages of extreme urgency.” 

Flash Override (X) “… is reserved for messages relating to the outbreak of hostilities and/or detonation of nuclear devices.”

CRITIC/ECP “…stands for “Critical and Emergency Call Processing” and should only be used for authorized emergency communications, for example in the United States Government Emergency Telecommunications Service (GETS), the United Kingdom Government Telephone Preference Scheme (GTPS) and similar government emergency preparedness or reactionary implementations elsewhere.” 

IPv4 REPRESENTAION

• IPv4 is represented in the form of 32 bits. 
• IPv4 contains 4 octets.
• It contains two parts: Network and Host

SUBNETMASK

• Each IP address is made up of two different pieces: Network Portion- Define the Network Address Host Portion – Defines Host on that specific network
• A Subnet mask is also a 32 bit number that tells the router which bits of the IP address are for the network portion and which bits are for the host portion.
• Subnet mask is binary number but is also usually communicated in dotted decimal format or CIDR format. Example: Subnet Mask: 11111111.11111111.11111111.00000000 In dotted Decimal: 255 . 255 . 255 . 0

SUBNETTING

A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting. 

Computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. 

Dividing the network into a number of subnets provides the following benefits: 

•Reduces the network traffic by reducing the volume of broadcasts •Helps to surpass the constraints in a local area network (LAN), for example, the maximum number of permitted hosts. 

•Enables users to access a work network from their homes; there is no need to open the complete network.

CLASS C Subnetting

Given N/W is 192.168.1.0 class full 

 Subnet mask: 255.255.255.0