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Key Terms

anycast@An identifier for a set of interfaces that typically belong to different nodes. A packet sent to an anycast address is delivered to the nearest, or first, interface in the anycast group.

CIDR (classless interdomain routing)@An IP addressing scheme that replaces the older system based on Classes A, B, and C. With CIDR, a single IP address can be used to designate many unique IP addresses.

Format Prefix (FP) field@The 3-bit FP identifies the type of address—unicast, multicast, and so on. The bits 001 identify aggregatable global unicasts.

interface identifier@The level specific to a node's individual interface.

Interface ID field@The 64-bit Interface ID field identifies individual interfaces on a link. This field is analogous to the host portion of an IPv4 address, but it is derived using the IEEE EUI-64 format. When this field is on LAN interfaces, the Interface ID adds a 16-bit field to the interface MAC address.

multicast@An identifier for a set of interfaces that typically belong to different nodes. A packet sent to a multicast address is delivered to all interfaces in the multicast group.

Next-Level Aggregation Identifier (NLA ID) field@The 24-bit NLA ID field is used to identify ISPs. The field itself can be organized to reflect a hierarchy or a multitiered relationship among providers.

public topology@The collection of providers that offer Internet connectivity.

Reserved (Res) field@The IPv6 architecture defines the 8-bit Res field so that the TLA or NLA IDs can be expanded as future growth warrants. Currently, this field must be set to 0.

RIP (Routing Information Protocol)@An Interior Gateway Protocol (IGP) supplied with the FreeBSD version of UNIX. The most common IGP in the Internet. RIP uses hop count as a routing metric.

RIPv2 (Routing Information Protocol version 2)@Defined in RFC 1723 and supported in Cisco IOS software versions 11.1 and later. RIPv2 is not a new protocol; it is just RIPv1 with some extensions to bring it up-to-date with modern routing environments. RIPv2 has been updated to support VLSM, authentication, and multicast updates.

route summarization@The consolidation of advertised addresses in OSPF and IS-IS. In OSPF, this causes a single summary route to be advertised to other areas by an area border router.

Site-Level Aggregation Identifier (SLA ID) field@The 16-bit SLA ID is used by an individual organization to create its own local addressing hierarchy and to identify subnets.

site topology@The level local to an organization that does not provide connectivity to nodes outside itself.

Top-Level Aggregation Identifier (TLA ID) field@The 13-bit TLA ID field is used to identify the authority responsible for the address at the highest level of the routing hierarchy. Internet routers necessarily maintain routes to all TLA IDs. With 13 bits set aside, this field can represent up to 8192 TLAs.

unicast@An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address.

VLSM (variable-length subnet masking)@The ability to specify a different subnet mask for the same network number on different subnets. VLSM can help optimize available address space.

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