What is an IPP package

IP, IP protocol, IP address

The Internet Protocol IP (standard in RFC 791) is a connectionless and unreliable datagram service for the protocols of the transport layer, i.e. TCP and UDP. IP does not guarantee the delivery or the integrity of the data packets sent. It adds its own header to the data packets from the transport layer, including a 32-bit IP address for addressing the source and destination computer.

Figure: Structure of an IP packet

Version:
Indicates which IP version it is.

Header length:
Because the option field has a variable length, it has to be determined somehow where the header ends and the user data begins.

Quality of service:
The quality of service field is hardly used today, but it is assumed that it will gain importance in connection with new routing protocols in the future.

Total length of the datagram:
This field specifies the length of the entire packet, i.e. the IP header and the data. Since it is a 16-bit field, an IP packet can be no more than 65535 bytes (64 KB) in size.

Datagram identification:
The identification is a type of serial number that is primarily used to identify fragments that belong to the same IP packet.

DF:
(Don't Fragment) Indicates whether fragmentation is prohibited.

MF:
(More Fragments) Indicates whether further fragments of the original datagram follow.


Fragment offset: The fragment offset is used to defragment individual IP fragments. If an IP packet is larger than the maximum amount of data that the hardware can transport in one go, then the packet has to be divided or fragmented.

Lifespan:
The Time To Live (TTL) indicates how long a data packet can survive in the network. It is reduced by each system that processes the package by the time it took to process it. If the TTL has reached the value 0 and the data packet has not reached the destination, it is discarded.

Protocol:
The protocol field specifies what protocol is being transported in the data field of the IP packet. TCP, UDP and ICMP are the most common protocols.

Header checksum:
The header checksum is used to detect errors in the IP header. Every router has to recalculate the checksum because it has to change the TTL field.

Source IP address:
The source address specifies the source of the IP packet as a 32-bit IP address. If this address is not entered correctly, it is called spoofing.

Destination IP address:
The destination address specifies the destination of the IP packet. This does not necessarily have to be set correctly in all cases, because as long as the network layers under IP (e.g. Ethernet) have the target address in their own format, the target IP address is not absolutely necessary.

Options:
Some special functions such as source routing and time stamping are implemented via the option field. The option field does not have a fixed length, so that the IP header as a whole does not have a fixed length either.

Usage data:
The actual "user data" that the IP packet transports.