The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Version 6 (IPv6) / IP Next Generation (IPng)

IPv6 Datagram Size, Maximum Transmission Unit (MTU), Fragmentation and Reassembly 1 2 IP Network Address Translation (NAT) Protocol

Changes in Datagram Delivery and Routing in IPv6

Most of the changes in routing in IPv6 are directly related to changes that we have seen in other areas of the protocol. Some of the main issues of note related to routing and routers in IPv6 include the following:

• Hierarchical Routing and Aggregation: One of the goals of the structure used for organizing unicast addresses was to improve routing. The unicast addressing format is designed to provide a better match between addresses and Internet topology, and to facilitate route aggregation. Classless addressing using CIDR in IPv4 was an improvement, but lacked any formal mechanism for creating a scalable hierarchy.
  
  
• Scoped Local Addresses: Local-use addresses including site-local and link-local are defined in IPv6, and routers must be able to recognize them. They must route them or not route them when appropriate. Multicast addresses also have various levels of scope.
  
  
• Multicast and Anycast Routing: Multicast is standard in IPv6, not optional as in IPv4, so routers must support it. Anycast addressing is a new type of addressing in IPv6.
  
  
• More Support Functions: Capabilities must be added to routers to support new features in IPv6. For example, routers play a key role in implementing serverless autoconfiguration and path MTU discovery in the new IPv6 fragmentation scheme.
  
  
• New Routing Protocols: Routing protocols such as RIP must be updated to support IPv6.
  
  
• Transition Issues: Last but certainly not least, routers play a major role in supporting the transition from IPv4 to IPv6. They will be responsible for connecting together IPv6 “islands” and performing translation to allow IPv4 and IPv6 devices to communicate with each other during the multi-year migration to the new protocol.

IPv6 Datagram Size, Maximum Transmission Unit (MTU), Fragmentation and Reassembly 1 2 IP Network Address Translation (NAT) Protocol