Internet Protocol being a layer-3 protocol (OSI) takes data Segments from layer-4
(Transport) and divides it into packets. IP packet encapsulates data unit received from
above layer and add to its own header information.
The encapsulated data is referred to as IP Payload. IP header contains all the necessary
information to deliver the packet at the other end.
IP header includes many relevant information including Version Number, which, in this
context, is 4. Other details are as follows:
Version: Version no. of Internet Protocol used (e.g. IPv4).
IHL: Internet Header Length; Length of entire IP header.
DSCP: Differentiated Services Code Point; this is Type of Service.
ECN: Explicit Congestion Notification; It carries information about the congestion
seen in the route.
Total Length: Length of entire IP Packet (including IP header and IP Payload).
Identification: If IP packet is fragmented during the transmission, all the
fragments contain same identification number to identify original IP packet they
belong to.
Flags: As required by the network resources, if IP Packet is too large to handle,
these ‘flags’ tell if they can be fragmented or not. In this 3-bit flag, the MSB is
always set to ‘0’.
Fragment Offset: This offset tells the exact position of the fragment in the
original IP Packet.
Time to Live: To avoid looping in the network, every packet is sent with some
TTL value set, which tells the network how many routers (hops) this packet can
cross. At each hop, its value is decremented by one and when the value reaches
zero, the packet is discarded.
Protocol: Tells the Network layer at the destination host, to which Protocol this
packet belongs to, i.e. the next level Protocol. For example protocol number of
ICMP is 1, TCP is 6 and UDP is 17.
Header Checksum: This field is used to keep checksum value of entire header
which is then used to check if the packet is received error-free.
Source Address: 32-bit address of the Sender (or source) of the packet.
Destination Address: 32-bit address of the Receiver (or destination) of the
packet.
Options: This is optional field, which is used if the value of IHL is greater than 5.
These options may contain values for options such as Security, Record Route,
Time Stamp, etc.
(Transport) and divides it into packets. IP packet encapsulates data unit received from
above layer and add to its own header information.
information to deliver the packet at the other end.
context, is 4. Other details are as follows:
Version: Version no. of Internet Protocol used (e.g. IPv4).
IHL: Internet Header Length; Length of entire IP header.
DSCP: Differentiated Services Code Point; this is Type of Service.
ECN: Explicit Congestion Notification; It carries information about the congestion
seen in the route.
Total Length: Length of entire IP Packet (including IP header and IP Payload).
Identification: If IP packet is fragmented during the transmission, all the
fragments contain same identification number to identify original IP packet they
belong to.
Flags: As required by the network resources, if IP Packet is too large to handle,
these ‘flags’ tell if they can be fragmented or not. In this 3-bit flag, the MSB is
always set to ‘0’.
Fragment Offset: This offset tells the exact position of the fragment in the
original IP Packet.
Time to Live: To avoid looping in the network, every packet is sent with some
TTL value set, which tells the network how many routers (hops) this packet can
cross. At each hop, its value is decremented by one and when the value reaches
zero, the packet is discarded.
Protocol: Tells the Network layer at the destination host, to which Protocol this
packet belongs to, i.e. the next level Protocol. For example protocol number of
ICMP is 1, TCP is 6 and UDP is 17.
Header Checksum: This field is used to keep checksum value of entire header
which is then used to check if the packet is received error-free.
Source Address: 32-bit address of the Sender (or source) of the packet.
Destination Address: 32-bit address of the Receiver (or destination) of the
packet.
Options: This is optional field, which is used if the value of IHL is greater than 5.
These options may contain values for options such as Security, Record Route,
Time Stamp, etc.
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