As per Relevance of the word provider, we have this rfc below:
Network Working Group G.
Request for Comments: 2036 Telstra
Category: Informational October 1996
Observations on the use of Components of the Class
Address Space within the
Status of this
This memo provides information for the Internet community. This
does not specify an Internet standard of any kind. Distribution
this memo is unlimited
This document is a commentary on the recommendation that
commence allocation of the presently unallocated components of
Class A address space to registries, for deployment within
Internet as class-less address blocks
The document examines the implications for service providers and
clients within this environment. The document notes the
conclusion that widespread adoption of class-less routing
is required, within a relatively rapid timeframe for
recommendation to be effective
The Address Lifetime Expectancy (ALE) Working Group of the IETF
recorded the allocation of Internet addresses from the
address pool. ALE has noted that the existing practice of
addresses from the Class C space (192/3 address prefix) will
in near to medium term exhaustion of this section of the
address pool. The largest remaining pool is in the Class A space
where some 25% of Internet addresses (the upper half of the Class
space) remain, to date, unallocated
This document is a commentary on the potential recommendation
the Internet Assigned Numbers Authority (IANA), through
registries, commence allocation of the presently
components of the Class A address space to registries,
deployment within the Internet through the mechanism of allocation
class-less address prefixes
The deployment of class-less address prefixes from the Class A
within the Internet will require some changes to the
structure within Internet component network domains. The
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RFC 2036 Components of the Class A Address Space October 1996
for, and nature of, such changes as they effect network domains
network service providers are outlined in this document
Current Practice with Address
To date the allocation of class-less network prefixed address
has followed a conservative practice of using address
which are compatible superblocks of Class C addresses, while
allocation of addresses within the space of Class A and Class
networks has continued to be aligned with the class-based
structure
Within this address allocation environment for non-transit
domains there is accordingly the option to continue to use
deployment strategies which involve fixed subnet address
within contiguous areas, and use Class-full interior
protocols. In the situation where variable length subnet masks
disconnected subnets are deployed within the network domain's
structure, interior routing protocols which use subnet-based
of Class-full networks can still be successfully deployed and the
network has the option of using an explicit or implicit sink
default route. Where such non-transit network domains are
to the Internet infrastructure the boundary exchange between
non-transit network and the network service provider (this term
used as a synonym for a transit network domain, which provides
traffic transit service to other non-transit and peer transit
domains) is either a class-full advertisement of routes, or
aggregated address advertisement where the aggregate is a
of the deployed component class-full networks. At the boundary
of the non-transit network it is a requirement that the non-
network's subnet default route (if used explicitly) not be
to the network service provider's domain, to avoid a routing loop
the domain boundary point
For network service providers the interior routing protocol can
either aggregated routing or explicit class-full routing within
environment. At the network service provider's boundary
points the strongly recommended practice is to advertise
routes to transit peers, which in turn may be further
across the Internet, within the parameters of permissible policies
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RFC 2036 Components of the Class A Address Space October 1996
Implications of Address Allocation from the Class A
Network Service Providers Must Use Class-less
For network service providers within the deployed Internet
implications from this recommendation to deploy prefixes from
Class A address space add more pressure to the requirement
uniformly deploy class-less routing protocols. While this is
a mandatory requirement for any domain which operates without
default route (ie. the provider carries full Internet routing
effectively calculates default), other providers currently can
an imported default route and operate within a class-full
configuration. This mode of operation is sub-optimal, in so far
the task of aggregating routes falls on peer network
providers performing proxy aggregation of contiguous class-
address blocks
In deploying components of the Class A the use of proxy
is no longer sufficient. Where a domain sees a default route and
subnet of a Class A route the routing structure, in a class-
configuration, may not necessarily follow the default route to
other parts of the Class A network not covered by the
Class A subnet route
Accordingly for Network Service Providers operating within
Internet domain the deployment of components of the Class A
entails a requirement to deploy class-less routing protocols, even
the presence of a default route. It is noted that this
requirement is not the case at present
Consideration of Non-Transit Network
For disconnected network environments, where the network domain
operated with no links to any peer networking domain, such
can continue to use class-full interior routing protocols with
support. Allocation of addresses using prefix blocks from the Class
space within such environments is possible without adding
additional routing or address deployment restrictions on the
domain
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RFC 2036 Components of the Class A Address Space October 1996
For non-transit network domains which are connected to one or
peer network domains the situation does involve consideration
additional factors. The observation which is made in the context
this consideration is that there are at present relatively few non
transit networks operating a fully class-less interior
protocol, as there has been no absolute requirement for
functionality when using single class-full network addresses, or
using block prefixed address allocations which are clusters of class
full network addresses
For non-transit network domains which support external
connections to a network service provider, deployment of a
of the Class A space would be supportable using a fully class-
interior routing protocol
In this case there is an additional constraint placed on the
connection such that the non-transit domain either agrees that
network service will undertake proxy aggregation of the
class-less address components, or the network domain is configured
advertise to the provider an aggregate route. In both cases
aggregate route must be either the allocated address block, or
fully contained sub-block. Advertising aggregatable address
without proxy aggregation permission, or advertising multiple sub
blocks of the registry allocated address block is considered
deleterious to the provider's internetworking environment due
considerations of consequent growth in routing table size
If the externally connected non-transit network domain uses class
full interior routing protocols then deployment of Class A
space prefixes implies that the domain must configure the Class
subnet default route along the same path as the default route to
network service provider (which is noted to be the exact opposite
the necessary routing configuration for those address prefixes
are either aligned to class-full address boundaries or are
blocks of such class-full address blocks). The network
provider may also receive leaked explicit subnet
information in such a routing configuration, potentially placing
responsibility for advertising the correct aggregate address
with the network service provider as a case of proxied aggregation
Within this configuration model, even when explicit subnet
routing is deployed, there is the risk of unintentional
leakage and routing loops. If the network service provider
undertaking proxy aggregation using the registry allocated
block then traffic originating within the non-transit domain which
(mis)directed to non-deployed components of the address block
loop at the interface between the network domain and the provider.
the network service provider is configured to explicitly route
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RFC 2036 Components of the Class A Address Space October 1996
those address components which are also explicitly routed within
non-transit domain, such (mis)directed traffic will be passed
the internetworking environment along the default route until
default-less routing point is encountered, where it can then
discarded. The outcome of this consideration is that the non-
network domain should explicitly configure sink subnet routes for
non-deployed components of the allocated address block,
conservative operational practice would be to configure the
aggregation undertaken by the network service provider to
according to the registry allocated address block
There is an additional constraint placed on the non-transit
domain using class-full interior routing protocols, such that
domain has no other exterior peer connections to other
domains which deploy class-full routing interior routing protocols
There is the further constraint placed on the of use of
class-full routing protocols within a non-transit network domain.
the case where the non-transit network domain has multiple
connections to Network Service Providers (ie the network domain
multiply homed within a number of network providers) there is
possibility that each provider may wish to announce components of
same Class A parent. Accordingly the network domain must use a class
less interior routing protocol in the case where the network
is multiply homed within network service providers
There are also additional constraints placed on the non-
network domain where the network has exterior connections to
peer networks. Even in the case where the network domain uses
class-less interior routing protocol, there is the
consideration that this requirement for use of a class-less
domain is transitive to other connected network domains. An
network domain, externally connected to the class-less domain
part of the Class A space, will interpret the boundary
advertisement as a complete Class A network advertisement, if
class-full routing. Even if both network domains are connected to
same network provider the provider's default routing
default to the class-full domain will be overridden by the
class A advertisement through the domain-to-domain connection
leading to unintended traffic diversion. The diversion occurs in
case as the traffic directed to parts of the Class A network
are not deployed within the first domain will transit the
domain before entering the network service provider's domain
It is also possible to have configurations with unintended
holes. An example of such a configuration is two stub clients
different network service providers, both using class-less
routing (X and Y), both directly connected to a third network
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RFC 2036 Components of the Class A Address Space October 1996
(Z), which uses class-full interior routing, which is configured as
transit between X and Y. X's advertisement of a component of a
A to Z will be assumed by Z to be a complete Class A network, and
such will be advertised to Y, overriding Y's default route
from the network service provider. Y will pass all Class A
traffic to Z, who will in turn pass it to X. As X is configured as
non-transit stub network X must discard all non-locally
traffic
Thus reasonable operational practice would be to ensure that if
network domain deploys a component of the Class A address space,
network domain is configured to use class-less interior
protocols, and the network has a single exterior connection to
class-less network provider domain, with the boundary configured as
class-less routing exchange. Multiply homed network domains do
a common requirement of class-less routing exchanges and
class-less routing protocols across all peer connected
domains
It is possible to propose that multi homed network domains
probably not get subnets of a class A for these reasons,
with an increasing diversity of network service providers
of multi-homed network domains may become more prevalent, and
requirement to transition to an interior class-less routing
as a consequence of moving to a multi-homed configuration may not
explicitly apparent to all network domains
Potential Guidelines for Allocation of an Address Prefix from the
A Address
To summarise the possible guidelines for allocation from the Class
space, such addresses should only be assigned to network
which
- have no exterior connection (in which case the domain can
either class-full or class-less interior routing protocols
further implication),
- are a component of a private internet domain which uses class-
routing exchanges and no other part of the same Class A
assigned into the domain (this is probably an unlikely
given a probable direction to use the Class A space as the
resource for the unallocated pool of addresses for allocation),
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RFC 2036 Components of the Class A Address Space October 1996
- have a single default exterior connection to a class-less
domain, use class-full routing protocols and explicitly direct
subnet default route to the exterior connection
- use class-less interior routing protocols and connect only
other network domains which also use class-less interior
protocols
It is a reasonable objective to nominate a transition objective
the final configuration (uniform use of class-less routing
within the Internet) which would enable deployment of components
the Class A space uniformly across the Internet
Related Potential
Given the pressures on the remaining Class C address space in
unallocated address pool, it is noted that there would be
deployment of components of the remaining Class A space in class-
allocation guidelines. There is a consequent requirement
widespread deployment of class-less interior routing protocols
order to ensure continued correct operation of the routed Internet
This is a more significant transition than that deployed to date
the network service providers' deployment of Class-less Inter-
Routing (CIDR) protocols, in that there is a necessary transition
deploy Class-less Interior Routing Protocols (CIRP) within a
number of network domains which are currently configured with class
full routing
However this would appear to be a necessary task if we wish
continue to utilise a pool of globally unique Internet addresses
allocate to new systems and networks, but one requiring
effort considering the space of the routing transition required
make this work
There are a number of directed activities which can assist in
transition
- The network registries commence initial class-less allocation
the unallocated Class A space to those entities who either
o operate a CIRP environment, and either have no
connectivity, or are singly homed to a network service
using a CIDR environment, with no other exterior connections
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RFC 2036 Components of the Class A Address Space October 1996
o operate a class-full routing protocol, and either have
external connectivity, or are singly homed to a network
provider using a CIDR environment, with no other
connections, and are willing to point the subnet default
towards the network service provider
- In deploying the Class A space there is a requirement within
vendors' product sets to allow explicit configuration of
the router operates in a class-less or class-full mode,
correct behaviour of the default route in each case. Class-
mode of operation must also allow explicit configuration
subnet default behaviour as to whether to follow the
route, or to operate a subnet default sink
- There is a similar, but longer term, activity within the
configuration environment to support a mode of
configuration which uses a local network prefix and host address
possibly in addition to the current configuration mode of class
full network, subnet and host
- Internet Service Providers also must support full class-
configurations in both interior routing configurations
interdomain peering routing exchanges, and provide support
client network domains operating a class-less boundary
exchange configuration and be able to undertake proxy
as permitted
Security
Correct configuration of the routing environment of the Internet
essential to the secure operation of the Internet
The potential use of the Class A space raises no
considerations in this area
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RFC 2036 Components of the Class A Address Space October 1996
[CIDR
Fuller, V., T. Li, J. Yu, and K. Varadhan, "Classless Inter
Domain Routing (CIDR): an Address Assignment and
Strategy", RFC 1519, BARRnet, cisco, MERIT, OARnet,
1993.
Author's
Geoff
Telstra
Locked Bag 5744
Canberra ACT 2601
phone: +61 6 208 1908
email: gih@telstra.
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if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
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