Internet Protocol IP Basic Functions Connectionless Protocol Packet

Internet Protocol (IP) • Basic Functions • Connectionless Protocol • Packet Encapsulation

Basic Functions of IP • Provide for: – data transfer – packet addressing – packet routing – fragmentation – detection of packet errors

Packet encapsulation

IP Packet • • Version: This field contains the IP version number, IPv 4 or IPv 6 IP header length (IHL): The IP header has a minimum size of 20 bytes, but the size can vary depending on the size of the Options field. Type of service (TOS): This field indicates the precedence or priority given to the packet contents. It enables routing protocols to determine the type of path along which to send a packet. Length: The entire IP packet size, which can be up to 65, 535 bytes, is provided in this field

IP Packet • • • Identification : IP can convert packets from one size to another for dissimilar net works For example, an Ethernet packet may be 64 to 1518 bytes in length, while a Fiber Distributed Data Interface (FDDI) packet can be up to 4472 bytes, and a 16 Mbps token ring packet can be as long as 17, 800 bytes IP is able to transfer packets to different types of networks by fragmenting the packets – divide one FDDI packet into fragments to match the 1518 byte maximum on an Ethernet network When IP fragments a packet, it assigns a single group num ber for all of the fragments and places that number in the identification field to ensure that fragments are not reconstructed from the wrong pieces. Flags: Flags are used with fragmentation (1) to convey information and (2) to show when the last fragment in a sequence has been sent (when a packet is fragmented).

IP Packet • • Fragment offset: The fragment offset provides information about how to reconnect fragments within a single fragment group. Time to live (TTL): This field contains information that prevents a packet from continuously circulating around a network. – Each time an IP packet goes through a router, that router reduces the TTL value by a default amount determined by the router or set by a network administrator – It is checked by each router through which it passes, so that the packet is discarded when TTL equals 0. Protocol: This field is used to show which protocol TCP or UDP is encapsulated in IP Checksum: The checksum is a 16 bit cyclic redundancy check that is the sum of all values contained in every field in the IP header.

IP Packet • • Source address: This is the network address and the address of the device that sent the packet Destination address: This field contains the network address and the address of the receiving device Options: There are several options that can be used with IP For example, the time when the packet is created can be entered, and specialized security can be implemented for military and government implementations Padding: Padding fills the options area when there is not enough data to complete the allocated area, because the total size (in bits) of the IP header must be divisible by 32.