Address Allocation from the Reserved Class A Address Space

An Internet Draft,  Observations on the Use of Components of the Class

A Address Space within the Internet,  explores the allocation of the

upper half of the currently reserved Class A address space through dele 

gated registries. As the demand for IP addresses continues to grow, it

may be necessary to allocate the 64.0.0.0/2 address space. The 64.0.0.0/2

address block is huge and represents 25 percent of the IPv4 unicast

address space. 

Implications of Address Allocation Policies

An Internet Draft,  Implications of Various Address Allocation Policies

for Internet Routing,  discusses the fundamental issues that must be

considered as the Internet develops new unicast address allocation and

management policies. The draft compares the benefits and limitations of

an  address ownership  policy with an  address lending  policy. 

Address ownership means that when an address block is assigned to an

organization, it remains allocated to that organization for as long as the

organization wants to keep it. This means that the address block is

portable and that the organization could use it to gain access to the

Internet no matter where the organization connects to the Internet. 

Address lending means that an organization obtains its address block on

a loan basis. If the loan ends, the organization can no longer use the

borrowed address block. It must obtain new addresses and must renum 

ber those addresses before using them. 

Hierarchical routing requires that addresses reflect the network topol 

ogy in order to permit route aggregation. The draft argues that two fun 

damental problems break the hierarchical addressing and routing model

supported by CIDR:

  The continued existence of routes prior to CIDR that cannot be aggre 

gated.

  Organizations that switch ISPs and continue to use addresses from

their previous ISP's address block. 

The new ISP cannot aggregate the old address block as part of its aggre 

gation, so it must inject an exception route into the Internet. If the

number of exception routes continues to increase, it will erode the ben 

efits of CIDR and prevent the scalability of the Internet's routing sys 

tem. 

The draft recommends that large providers, which can express their

destinations with a single prefix, be assigned address blocks following

the address ownership model. However, all allocations from these

providers to a downstream client should follow the address lending

model. This means that if an organization changes its provider, the loan

is canceled and the client is required to renumber addresses.

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