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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

IP functions such as addressing, datagram encapsulation and if necessary, fragmentation and reassembly, all lead up to the ultimate objective of the protocol: the actual delivery of datagrams from a source device to one or more destination devices.

Most of the concepts related to how datagram delivery is accomplished in IPv6 are the same as in IPv4:

• Datagrams are delivered directly when the source and destination nodes are on the same network. When they are on different networks, delivery is indirect using routing to the destination's network, and then direct to the destination.
  
  
• Routing is performed by looking at IP addresses and determining which portion is the network ID and which the host ID. IPv6 does this in the same basic way as in classless IPv4, despite the fact that IPv6 unicast addresses are assigned using a special hierarchical format.
  
  
• Routing is still done on a next-hop basis, with sources generally not knowing how datagrams get from Point A to Point B.
  
  
• Routing is performed by devices called routers that maintain tables of routes that tell them where to forward datagrams to reach different destination networks.
  
  
• Routing protocols are used to allow routers to exchange information about routes and networks.

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