COMPUTER NETWORKS-II IPv6 CHANGES FROM IPv4 TO IPv6 1) Longer address fields: Length of address field is extended from 32 bits to 128 bits. The address space can support up to 3.4*1038 hosts. 2) Simplified header format: Some of the header fields in IPv4 such as identification, flags and fragment offset do not appear in the IPv6 header. 3) Flexible support for options: The options in IPv6 appear in optional extension headers that are encoded in a more efficient and flexible fashion than they are in IPv4. 4) Flow label capability: IPv6 adds a "flow label" to identify a certain packet "flow" that requires a certain QoS. 5) Security: IPv6 supports build-in authentication and confidentiality. 6) Large packets: IPv6 supports payloads that are longer than 65 Kbytes called jumbo payloads. 7) Fragmentation at source only: Routers do not perform packet fragmentation. If a packet needs to be fragmented, the source should check the minimum MTU along the path and perform the necessary fragmentation. 8) No checksum fields: The checksum field has been removed to reduce packet processing time in a router. Packets carried by the physical network(such as Ethernet, token shop) are typically already checked. Furthermore, higher-layer protocols( such as TCP and UDP) also perform their own verification. HEADER FORMAT 1) Version: This specifies version number of protocol. For IPv6,version=6. 2) Traffic class: This specifies priority of packet. This is used to support differential service (Figure 8.16). 3) Flow label: This is used to identify QoS requested by packet. A flow is defined as "a sequence of packets sent from a particular source to a particular destination for which the source desires special handling by the interventing routers. 4) Payload length: This indicates length of data (excluding header). Maximum length=65535 bytes. 5) Next header: This identifies type of extension header that follows the basic header. 6) Hop limit: This specifies number of hops the packet can travel before being dropped by a router. 7) Source address & destination address: These identify source host and destination host respectively.
Figure 8.16:IPv6 basic header
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