Assume SLA I is assigned 3FFE:2900:D:E::/63. Starting at the bottom

aggregators, SLA I must announce its block 3FFE:2900:1:10::/63 to NLA

I. Because this is a subset of NLA I's space,  NLA I is not required to

announce this SLA (from SLA I) to TLA I. A similar situation exists with

NLA II. TLA I only needs to hear the NLA aggregations that it dele 

gated to the two NLAs, regardless of how the NLAs have subdelegated

their space. 

At this point, TLA I has to carry only three announcements for non 

backbone space. Note that the first two of these announcements are

simply subsets of the block assigned to TLA I. Therefore, in the bilat 

eral peering between TLA I and TLA II, only one route needs to be

exchanged between these peers. Although this is a limited example, it

shows the routing simplicity that has come to pass as a result of this

aggregation. 

The IPv6 routing will greatly increase the long term efficiency of the

Internet backbone routing tables for two main reasons. The current

IPv4 addresses are portable and can be taken with an individual who

leaves a certain service provider's jurisdiction and goes to another

provider. This leads to many extraneous announcements in the core of

the Internet backbone as Network Service Providers lose the ability to

aggregate announcements properly. 

The second reason is that only TLAs will be assigned address space

from the Numbering Authorities. Today, IANA is the responsible party

for numbering, which in turn delegates numbers to regional registries

such as ARIN, RIPE, and APNIC. These regional numbers authorities in

turn assign IPv4 address space to Internet providers, businesses, and

organizations that can demonstrate sufficient need for their own IP

blocks. Notice how this process leads to more small blocks being carried

in the core Internet table. If renumbering were simple, then getting IP

space directly from upstream providers of connectivity would not be

such an issue. Users who are dissatisfied with service could simply get

another provider and then renumber. By ensuring that only TLAs get

address space, only big blocks of space are delegated, which ensures

that aggregation can always occur. 

U N D E R S TA N D I N G   I P   A D D R E S S I N G

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