Lecture 13 IP V4 & IP V6

Figure Protocols at network layer

IP IP Datagram Fragmentation

Internet Protocol Version 4 (IPv4) is the fourth version of the IP and a widely used protocol in data communication over different kinds of networks. IPv4 is a connectionless protocol used in packet- switched layer networks, such as Ethernet. It provides the logical connection between network devices by providing identification for each device. There are many ways to configure IPv4 with all kinds of devices - including manual and automatic configurations - depending on the network type. IPv4 is based on the best-effort model. This model guarantees neither delivery nor avoidance of duplicate delivery; these aspects are handled by the upper layer transport.

IPv4 uses 32-bit addresses for Ethernet communication in five classes, named A, B, C, D and E. Classes A, B and C have a different bit length for addressing the network host. Class D addresses are reserved for multicasting, while class E addresses are reserved for future use.

Figure IP datagram

Details of fields IP Datagram Version Number – The 4-bit version number (VER) field defines the version of the IPv4 protocol, which, obviously, has the value of 4. Header Length – The 4-bit header length (HLEN) field defines the total length of the datagram header in 4-byte words. Service Type – In the original design of the IP header, this field was referred to as type of service (TOS), which defined how the datagram should be handled. Total Length – This 16-bit field defines the total length (header plus data) of the IP datagram in bytes. Identification, Flags and Fragmentation Offset – These three fields are related to the fragmentation of the IP datagram when the size of the datagram is larger than the underlying network can carry. Protocol – In TCP/IP, the data section of a packet, called the payload, carries the whole packet from another protocol.

Header checksum – IP is not a reliable protocol; it does not check whether the payload carried by a datagram is corrupted during the transmission. IP puts the burden of error checking of the payload on the protocol that owns the payload, such as UDP or TCP. Source and Destination Addresses – These 32-bit source and destination address fields define the IP address of the source and destination respectively. The source host should know its IP address. The destination IP address is either known by the protocol that uses the service of IP or is provided by the DNS. Options – A datagram header can have up to 40 bytes of options. Options can be used for network testing and debugging. Payload – Payload, or data, is the main reason for creating a datagram. Payload is the packet coming from other protocols that use the service of IP.

Fragmentation The Internet Protocol (IP)implements datagram fragmentation by breaking it into smaller pieces, so that packets may be formed that can pass through a link with a smaller maximum transmission unit (MTU) than the original datagram size.

Figure Maximum Transfer Unit MTU

Figure Fragmentation example

IPv6 IPv6 Addresses Categories of Addresses IPv6 Packet Format Fragmentation

IP V6 Methods to handle limitations of IP v4 addressing were classless addressing, DHCP & NAT were not sufficient, so new method was to be discovered. Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet.Internet Protocolcommunications protocolInternet IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the long-anticipated problem of IPv4 address exhaustion.Internet Engineering Task ForceIPv4 address exhaustion IPv6 is intended to replace IPv4.IPv4 IP V6 consist of 16 bytes, i.e. It is 128 bits long

Advantages of IP V6 : Larger address space Better header format New options Possibility of extension More security Support to resource allocation Plug & play Clear specifications & optimization

Figure IPv6 address Hexa Decimal Colon Notation : IP V6 works on hexa decimal colon notation. 128 bits are divided into 8 sections. Each 2 bytes in length which further require 4 Hexadecimal digits. Thus 32 hexadecimal notations are used.

Figure Abbreviated address Even 32 Hexa decimal digits are too long, there are many zeros in address so we abbreviate them. The leading zeros of a section can be omitted. The trailing zeros remain as such.

Figure : Abbreviated address with consecutive zeros

Example

Figure CIDR address

Figure Format of an IPv6 datagram

Base Header : Figure shows the base header. It has eight fields. These fields are as follows : 1.Version (VER) : It is a 4 bit field which defines the version of IP such as IPv4 or IPv6. For IPv6 the value of this field is 6. 2.Priority : It is a 4 bit field which defines the priority of the packet which is important in connection with the traffic congestion. 3.Flow label : It is a 24 bit (3 byte) field which is designed for providing special handling for a particular flow of data. 4.Payload Length : This is a 2 byte length field which is used to define the total length of the IP datagram excluding the base header. 5.Next header : It is an 8 bit field which defines the header which follows the base header in the datagram. 6.Hop limit : This is an 8 bit field which has the same purpose as TTL (time to live) in IPv4. 7.Source address : It is a 16 byte (128 bit) Internet address which identifies the original source of datagram. 8.Destination address : This is a 16 byte (128 bit) internet address which identifies the final destination of datagram. But this field will contain the address of the next router if source routing is being used.

Figure Comparison of network layers in version 4 and version 6

Comparison between IPv4 and IPv6 : IPv4IPv6 In IPv4 there are only 2 32 possible ways how to represent the address (about a billion possible addresses) In IPv6 there are possible way (about 3.4x10 38 possible addresses) The IPv4 address is written by dotted- decimal notation, e.g IPv6 is written in hexadecimal and consists of 8 groups, containing 4 hexadecimal digits or 8 groups of 16 bits each, e.g. FABC:AC77:7834: 2222:FACB:AB98: 5432:4567. The basic length of the IPv4 header comprises a minimum of 20 bytes (without option fields). The maximum total length of the IPv4 header is 60 bytes (with option fields), and it uses 13 fields to identify various control settings. The IPv6 header is a static header of 40 bytes in length, and has only 8 fields. Option information is carried by the extension header, which is placed after the IPv6 header.

IPv4IPv6 IPv4 header has a checksum, which must be computed by each router. IPv6 has no header checksum because checksums are, for example, above the TCP/IP protocol suite, and above the Token Ring, Ethernet, etc. IPv4 contains an 8-bit field called Service Type. The Service Type field is composed of a TOS (Type of Service) field and a procedure field. The IPv6 header contains an 8-bit field called the Traffic Class Field. This field allows the traffic source to identify the desired delivery priority of its packets. The IPv4 node has only Stateful auto- configuration. The IPv6 node has both a stateful and a stateless address autoconfiguration mechanism. Security in IPv4 networks is limited to tunneling between two networks IPv6 has been designed to satisfy the growing and expanded need for network security. Source and destination addresses are 32 bits (4 bytes) in length. Source and destination addresses are 128 bits (16 bytes) in length. IPsec support is optional.IPsec support is required.

IPv4IPv6 No identification of packet flow for QoS handling by routers is present within the IPv4 header. Packet flow identification for QoS handling by routers is included in the IPv6 header using the Flow Label field. Address Resolution Protocol (ARP) uses broadcast ARP Request frames to resolve an IPv4 address to a link layer address. ARP Request frames are replaced with multicast Neighbour Solicitation messages. Must be configured either manually or through DHCP. Does not require manual configuration of DHCP. ICMP Router Discovery is used to determine the IPv4 address of the best default gateway and is optional. ICMP Router Discovery is replaced with ICMPv6 Router Solicitation and Router Advertisement messages and is required. Header includes optionsAll optional data is moved to IPv6 extension headers.