Address Space
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... hosts of different
enterprises. The cost of using private internet address space is the
potentially costly effort to renumber hosts and networks ...
... exponential growth continues to introduce new challenges. One
challenge is a concern within the community that globally unique
address space will be exhausted. A separate and far more pressing
concern is that the amount of routing overhead ...
... Internet Provider obtains a
block of address space from an address registry, and then assigns to
...
... registries are requiring more justification than ever
before, making it harder for organizations to acquire additional
address space [RFC1466].
...
... Private Address Space ...
...
An enterprise that decides to use IP addresses out of the address
space defined in this document can do so without any coordination
with IANA or an Internet registry ...
... with IANA or an Internet registry. The address space can thus be used
by many enterprises. Addresses within this private address space ...
... address space can thus be used
by many enterprises. Addresses within this private address space will
only be unique within the enterprise, or the set of enterprises which
choose to cooperate over this space so they may communicate with each
...
...
As before, any enterprise that needs globally unique address space is
required to obtain such addresses from an Internet registry ...
...
In order to use private address space, an enterprise needs to
determine which hosts do not need to have network ...
... outside the enterprise in the foreseeable future and thus could be
classified as private. Such hosts will use the private address space
defined above. Private hosts can communicate with all other hosts ...
...
All other hosts will be public and will use globally unique address
space assigned by an Internet Registry. Public hosts can communicate
...
... Routers in networks not
using private address space, especially those of Internet service
providers, are expected to be configured to reject (filter out)
...
... Advantages and Disadvantages of Using Private Address Space ...
...
The obvious advantage of using private address space for the Internet
at large is to conserve the globally unique address space ...
... address space for the Internet
at large is to conserve the globally unique address space by not
using it where global uniqueness is not required.
...
...
Enterprises themselves also enjoy a number of benefits from their
usage of private address space: They gain a lot of flexibility in
network design by having more address space ...
... address space: They gain a lot of flexibility in
network design by having more address space at their disposal than
they could obtain from the globally unique pool. This enables
operationally and administratively convenient addressing ...
... hosts without getting this
space assigned from the IANA. In some cases this address space had
been already assigned to other enterprises. If such an enterprise
would later connects to the Internet ...
... route filters, this does not always happen in practice.
Using private address space provides a safe choice for such
enterprises, avoiding clashes once outside connectivity is needed.
...
...
A major drawback to the use of private address space is that it may
actually reduce an enterprise's flexibility to access the Internet.
...
...
Another drawback to the use of private address space is that it may
require renumbering when merging several private internets into a
single private internet ...
... companies prior to
the merge maintained their uncoordinated internets using private
address space, then if after the merge these private internets would
be combined into a single private internet, some addresses ...
... One possible strategy is to design the private part of the network
first and use private address space for all internal links. Then plan
public subnets ...
... (class A network) of private address space and make an addressing
plan with a good growth path. If subnetting is a problem, the 16-bit ...
... itself from ambiguous routing situations which can occur if routes to
the private address space point outside the enterprise.
...
...
It is possible for two sites, who both coordinate their private
address space, to communicate with each other over a public network.
To do so they must use some method ...
...
If an enterprise uses the private address space, or a mix of private
and public address spaces, then DNS ...
... If an enterprise uses the private address space, or a mix of private
and public address spaces, then DNS clients outside of the enterprise
...
... clients outside of the enterprise
should not see addresses in the private address space used by the
enterprise, since these addresses would be ambiguous. One way to
...
... containing both publically and privately addressed hosts. One server
would be visible from the public address space and would contain only
the subset of the enterprise's addresses which were reachable using
...
... IP
address space. The Internet at large benefits through conservation of
globally unique address space which will effectively lengthen the
lifetime of the IP address ...
... lifetime of the IP address space. The enterprises benefit from the
increased flexibility provided by a relatively large private address
space. However, use of private addressing requires that an
organization renumber part or all of its enterprise network ...