Aggregatable Global Unicast Address

Aggregatable global unicast addresses are identified by the prefix 001, as shown earlier, in Table 3-2. The initial address specification defined provider-based addresses; the name has been changed to aggregatable global unicast address. The name change reflects the addition of an ISP-independent means of aggregation called exchange-based aggregation .

The prefix is followed by five components, as shown in Figure 3-3.

Format of the aggregatable global unicast address

Figure 3-3. Format of the aggregatable global unicast address

The format prefix 001 is assigned to the aggregatable global unicast address range. The top-level aggregation identifier contains the highest level of routing information about the address. Its size of 13 bits limits the number of top-level routes to 8192. In the earlier specification, the TLA was the provider-based identifier. It was assigned to the American Registry for Internet Numbers (ARIN) in North America, Réseau IP Européens (RIPE) Network Coordination Center in Europe, and Asia Pacific Network Information Center (APNIC). With this change in the specification, the commercial touch of the TLA has been removed and the focus is now on routing optimization; the TLA does not need to be a provider. At the core of the Internet, the routing tables need just one route entry per TLA, so the 13-bit TLA is large enough.

Providers and exchange points use the next-level ...

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