IP packets are send by the help of TCP, UDP, ICMP etc. The IP packets are connection less and unreliable. if any problem occurs in network( like router is not responding ) it simply sends ICMP packet to the source. The reliability is provided by upper layers i.e TCP.
The IP header:
The most significant is at 0 and least significant bit at 31. Hence it is called big-endian byte order.
Data is transmitted from left to right i.e from 0 to 31.
Vers: It tells what version of IP packet it may be 4 or 6 according to the requirement.
IHL: The no of 32 bit words used in the header including any options. Normal value for this field is 5.
TOS: This tells the type of service of the packet. It tells minimum delay, maximum throughput, maximum reliability, minimize monetary cost. XXXUUUU0.
Total Length: This is the total length of IP Datagram in bytes. It is possible to send 65535 size packets, but the link layer divides in into small packets using fragmentation.
Indentification: This value is increased while sending packets continuously. This is mainly used in fragmentation. Reassembly program at the other end is used to combine the fragmented packets.
Time to live:A no which tells the no of routers through which this IP datagram is passed. When ii reaches to zero. The send is informed with an ICMP message indicating destination is not reachable.
Protocol: Which protocol gave the data to IP to send.
Option Field: This field is defined for
Security and handling restrictions.
Record route: Each router record its IP Address.
Time stamp: ( how long the router will keep the recorded IP Address).
loose Source routing : Specifies list of IP Address that must be traversed by datagram.
strict source routing : Specifies the list of fixed ip Address to be traversed. ( It is rarely used, All router may or may not use this feature).
Subnetting: The process of dividing hostid into small subnets is called subnetting.
IP Address: 192.168.40.33, subnet Mask: 255.255.255.224 this means each subnet network is in the gap of 32 Addresses.
therefore subnet ID is : 192.168.40.32 and host ID is: 1