Terminology

IPv6/IPv4 Coexistence terminology

• Address: An IPv6 layer identifier for an interface or a set of interfaces.
• Datagram: A synonym for packet.
• Host: Any node that is not a router; these are typically end-user systems.
• Interface: A node's attachment to a link.
• Link: A communication facility or medium over which nodes can communicate at the Data Link layer—that is, at layer 2 of the ISO/OSI reference model. Examples of links are Ethernet, PPP, X.25, Frame Relay, and ATM, or tunnels over other protocols such as IPv4 or IPv6 itself.
• Link MTU: The Maximum Transmission Unit, that is, the maximum packet size in octets (bytes) that can be conveyed unfragmented over a link.
• Neighbors: Nodes attached to the same link.
• Node: A device that implements IPv6.
• Packet: An IPv6 protocol data unit (PDU), comprising a header and the associated payload. In IPv4, this would have been termed packet or datagram.
• Path MTU: The minimum link MTU of all the links in a path between a source node and a destination node.
• Router: An IPv6 node that forwards packets, based on the IP address, not explicitly addressed to itself. In former TCP/IP terminology, this device was often referred to as a gateway.
• Upper layer: A protocol layer immediately above IPv6, for example, transport protocols such as TCP and UDP, control protocols such as ICMP, routing protocols such as OSPF, or lower layer protocols being tunneled over IPv6 such as IPX and AppleTalk.

• Access Router: The closest router to the mobile node in the visited domain that the mobile node uses to access the network.
• Crossover Router: When a mobile node is performing a regional registration, the Crossover Router is the router where the old path leading to a mobile node and the new path cross, i.e. the regional router in the hierarchy where a connection state change is needed to maintain an up-to-date communication path to the mobile node.
• Gateway Mobility Agent: The software module implementing regional registrations in the gateway router.
• Gateway Router: A router controlling the regional care-of-address of a mobile node; This is the gateway through which traffic for the mobile node enters the visited domain.
• Highest Router: Router used in a visited domain as the root of a physical hierarchy; The gateway mobility agent can exist anywhere in the physical hierarchy. The visible hierarchy for a mobile node is thus rooted at the gateway router possibly below the highest router.
• Home Binding: The binding cache entry in a home agent used for storing home registration state.
• Home Registration: Sending of a binding update to the home agent to create a home binding.
• Regional-aware Router: Router that supports regional registrations.
• Regional Binding Cache: A conceptual data structure in regional-aware routers; it is keyed on the home address of a mobile node and contains the care-of-address, lifetime, flags, security association, and network interface as data elements. All regional routing state is contained in this entry.
• Regional Care-of-address: A care-of-address, as seen from outside the visited domain, used to locate a mobile node. Remains the same while the mobile node does regional binding updates within a visited domain.
• Regional Mobility Agent: The software module implementing regional registrations in a regional-aware router.
• Visited Domain: A domain that is visited by the mobile node; A set of subnets usually administered by one entity. In this document, all routers in a visited domain are assumed to have a security association with one another.