1 - 2 - 4 - 8 - A - B - C - D - E - F - G - H - I - L - M - N - O - P - Q - R - S - T - U - V - W - X
routing
Click on the red underlined text to get to the source
... network protocol (CLNP) [9] and supporting routing
protocols. Also required as part of this infrastructure are
guidelines for network service access point (NSAP ...
... addressed in this paper and Section 3 provides background information
on OSI routing and the implications for NSAP addresses.
...
... addresses the specific relationship between NSAP addresses
and routing, especially with regard to hierarchical routing and data
abstraction. This is followed in Section 5 with an application of
...
... NSAP addresses
and routing, especially with regard to hierarchical routing and data
abstraction. This is followed in Section 5 with an application of
these concepts to the Internet environment ...
... minor, and primarily editorial in nature. The descriptions of OSI
routing standards contained in Section 3 have been updated to reflect
the current status of the relevant standards, and a description of
the OSI ...
... the current status of the relevant standards, and a description of
the OSI Interdomain Routing Protocol (IDRP) has been added.
Recommendations specific to the European part of the Internet ...
... Recommendations specific to the European part of the Internet have
been added in Section 6, along with recommendations for Routing
Domain Identifiers and Routing ...
... NSAP addresses; the second
is the technical aspect of such assignments, having largely to do
with routing, both within a routing domain (intra-domain ...
... is the technical aspect of such assignments, having largely to do
with routing, both within a routing domain (intra-domain routing ...
... intra-domain routing) and
between routing domains (inter-domain routing). This paper focuses
...
... The technical issues in NSAP allocation are mainly related to
routing. This paper assumes that CLNP will be widely deployed in the
Internet ...
... CLNP will be widely deployed in the
Internet, and that the routing of CLNP traffic will normally be based
...
... traffic will normally be based
on the OSI end-system to intermediate system routing protocol (ES-IS)
[10 ...
... 16]. It is expected that in the future the OSI
routing architecture will be enhanced to include support for
multicast ...
... Internet, and have proven very valuable
both as an aid to scaling of CLNP routing, and to address
administration.
...
... Benefits of some topological information in NSAPs to reduce
routing protocol overhead, and specifically the overhead on
...
... addressing to support network growth and use of
the Routing Domain Confederation mechanism of IDRP to provide
...
... brief discussion of OSI routing is provided, followed by a review of
the intra-domain and inter-domain ...
... NSAP allocation. Finally, the
specific constraints that the routing protocols place on NSAPs are
listed.
...
... IS-IS advanced
to IS status within ISO in 1992. Inter-Domain Routing Protocol
(IDRP) advanced to IS status within ISO ...
... routing protocol, ISO/IEC 10589, provides
routing for OSI environments. In particular, IS-IS is designed to
...
... domain is a collection of ESs and ISs that operate common
routing protocols and are under the control of a single
administration (throughout this paper, "domain" and "routing ...
... routing protocols and are under the control of a single
administration (throughout this paper, "domain" and "routing domain"
are used interchangeably). Typically, a routing ...
... routing domain"
are used interchangeably). Typically, a routing domain may consist
of a corporate network ...
... backbone, or a similar contiguous network under control of
a single administrative organization. The boundaries of routing
domains are defined by network management ...
... IS-IS routing makes use of two-level hierarchical routing. A routing
domain is subdivided into areas (also known as level ...
... router. The set of all
level 2 routers in a routing domain are known as the level 2
subdomain, which can be thought of as a backbone ...
... routers can
exchange data packets or routing information directly with routers
located outside of their routing ...
... address
space; and (ii) How to assign addresses in a manner which makes
routing scale well in a worldwide Internet.
...
... NSAP selector
(SEL). The area address identifies both the routing domain and the
area within the routing ...
... The ID field may be from one to eight octets in length, but must have
a single known length in any particular routing domain. Each router
...
... regard to the internal structure of an area; or towards level 2
routers on the routing domain boundary that have advertised external
address prefixes ...
... link would be considered by both routers to be level 2
only, and only level 2 routing packets would flow on the link.
...
... backbone. In this case the level 2 router will indicate in
its level 1 routing packets that it is not "attached", thereby
allowing level 1 routers in the area to route ...
... destinations outside of their area only to level 2
routers which indicate in their level 1 routing packets that they are
"attached".
...
... IS-IS provides for optional Quality of Service (QOS) routing,
based on throughput (the default metric), delay, expense, or residual
...
... migration of passwords
without disrupting operation of the routing protocol. The
authentication functions are extensible so that a stronger,
...
... ISO/IEC 10747), developed in
ISO, provides routing for OSI environments. In particular, IDRP is
...
... participates in IDRP is called a Boundary Intermediate System (BIS).
Routing domains that participate in IDRP are not allowed to overlap -
...
...
IDRP governs the exchange of routing information between a pair of
neighbors, either external or internal. IDRP ...
... neighbors relies on
additional support provided by intra-domain routing (unless internal
neighbors share a common subnetwork ...
... IDRP
allows grouping of a set of connected domains into a Routing Domain
Confederation (RDC). A given domain ...
... Each domain participating in IDRP is assigned a unique Routing Domain
Identifier (RDI). Syntactically an RDI ...
... network layer address. Each RDC is assigned a unique Routing Domain
Confederation Identifier ...
... IDRP doesn't assume or require any particular internal structure for
the addresses. The protocol provides correct routing as long as the
following guidelines are met:
...
... NLRI) field for a route originated by a BIS in a
given routing domain should be associated with only that
routing ...
... routing domain should be associated with only that
routing domain; that is, no system identified by the prefix
...
... domain; that is, no system identified by the prefix
should reside in a different routing domain; ambiguous routing
...
... should reside in a different routing domain; ambiguous routing
may result if several routing domains ...
... domain; ambiguous routing
may result if several routing domains originate routes whose
NLRI field ...
... prefixes, since this
would imply that the same system(s) is simultaneously located
in several routing domains;
...
... NSAP prefixes may be associated with a single
routing domain which contains a mix of systems which use NSAP
addresses assigned by several different addressing ...
... group domains in RDCs provides a simple, yet powerful
mechanism for routing information aggregation and abstraction. It
allows reduction of topological information by replacing a sequence
...
... aggregation" mechanism of IDRP.
This mechanism is complementary to the Routing Domain Confederations
mechanism. Both mechanisms are intended to provide scalable routing ...
... Routing Domain Confederations
mechanism. Both mechanisms are intended to provide scalable routing
via information reduction/abstraction. However, the two mechanisms
are used for different purposes: route ...
... aggregation
and abstraction of routes (i.e., Network Layer Reachability
Information), Routing Domain Confederations for aggregation and
...
... Level 2 routing acts on address prefixes, using the longest address
prefix that matches the destination address ...
... Level 1 routing acts on the ID field. The ID field must be unique
within an area for ESs and level 1 ISs, and unique within the
...
... within an area for ESs and level 1 ISs, and unique within the
routing domain for level 2 ISs. The ID field is assumed to be
flat. The method ...
... addresses in any of the formats specified by
ISO 8348. However, within a routing domain that conforms to IS-IS,
...
... and SEL fields shown in Figure 1 to take full advantage of IS-IS
routing. End systems with addresses which do not conform may
require additional manual configuration ...
...
For purposes of efficient operation of the IS-IS routing protocol,
several observations may be made. First, although the IS-IS protocol
...
... routing domain,
the routing algorithm must efficiently route both: (i) Packets whose
final destination ...
... For those destinations which are in the domain, level 2 routing
treats the entire area address (i.e., all of the NSAP address ...
... NSAP address except
the ID and SEL fields) as if it were a flat field. Thus, the
efficiency of level 2 routing to destinations within the domain is
...
... destinations which are outside of the domain, level 2
routing routes according to address prefixes. In this case, there is
considerable potential advantage (in terms of reducing the amount of
...
... address prefixes. In this case, there is
considerable potential advantage (in terms of reducing the amount of
routing information that is required) if the number of address
prefixes required to describe any particular set of external
destinations ...
... address
prefixes required to describe any particular set of external
destinations can be minimized. Efficient routing with IDRP similarly
also requires minimization of the number of address prefixes ...
... Routing Data Abstraction ...
... NSAP assignment, it is
important to understand the technical consequences. The objective
behind the use of hierarchical routing is to achieve some level of
routing data abstraction, or summarization, to reduce the processing
...
... behind the use of hierarchical routing is to achieve some level of
routing data abstraction, or summarization, to reduce the processing
time, memory requirements, and transmission bandwidth ...
... memory requirements, and transmission bandwidth consumed in
support of routing. This implies that address assignment must serve
the needs of routing ...
... routing. This implies that address assignment must serve
the needs of routing, in order for routing to scale to very large
networks ...
... address assignment must serve
the needs of routing, in order for routing to scale to very large
networks.
...
...
While the notion of routing data abstraction may be applied to
various types of routing information, this and the following sections
...
... While the notion of routing data abstraction may be applied to
various types of routing information, this and the following sections
primarily emphasize one particular type, namely reachability
...
... reachability information dictates that NSAPs be
assigned according to topological routing structures. However,
administrative assignment falls along organizational or political
boundaries. These may not be congruent to topological boundaries,
...
...
Routing data abstraction occurs at the boundary between
hierarchically arranged topological routing structures. An element ...
... Routing data abstraction occurs at the boundary between
hierarchically arranged topological routing structures. An element
lower in the hierarchy reports summary routing information ...
... routing structures. An element
lower in the hierarchy reports summary routing information to its
parent(s). Within the current OSI routing ...
... routing information to its
parent(s). Within the current OSI routing framework [13] and routing
protocols ...
... routing framework [13] and routing
protocols, the lowest boundary at which this can occur is the
boundary between an area and the level 2 subdomain within a IS-IS
...
... boundary between an area and the level 2 subdomain within a IS-IS
routing domain. Data abstraction is designed into IS-IS at this
...
... compute next-hop forwarding information to all advertised address
prefixes. Level 2 routing is determined by the longest advertised
address prefix that matches the destination address ...
... domain boundaries, address prefix information is exchanged
with other routing domains via IDRP. If area addresses ...
... address prefix and
assign area addresses based upon it, boundary routing information can
be summarized into the single prefix. This can allow substantial
...
...
If routing domains are interconnected in a more-or-less random (non-
hierarchical) scheme, it is quite likely that no further abstraction
...
... domains are interconnected in a more-or-less random (non-
hierarchical) scheme, it is quite likely that no further abstraction
of routing data can occur. Since routing domains would have no
...
... hierarchical) scheme, it is quite likely that no further abstraction
of routing data can occur. Since routing domains would have no
defined hierarchical relationship, administrators ...
... addresses out of some common prefix for the purpose of
data abstraction. The result would be flat inter-domain routing; all
routing domains ...
... data abstraction. The result would be flat inter-domain routing; all
routing domains would need explicit knowledge of all other routing
...
... example, we expect growth in the future to an international Internet
which has tens or hundreds of thousands of routing domains in the
U.S. alone. Even larger numbers of routing ...
... routing domains in the
U.S. alone. Even larger numbers of routing domains are possible when
each home, or each small company ...
... domains are possible when
each home, or each small company, becomes its own routing domain.
This requires a greater degree of data abstraction beyond that which
...
... domain.
This requires a greater degree of data abstraction beyond that which
can be achieved at the "routing domain" level.
...
... In the Internet, however, it should be possible to exploit the
existing hierarchical routing structure interconnections, as
discussed in Section 5. Thus, there is the opportunity for a group
...
... The most straightforward case of this occurs when there is a set of
subscribers whose routing domains are all attached only to a single
service provider ...
... reach, to abbreviate the reachability information for a large number
of routing domains as a single prefix. This approach therefore can
...
... domains as a single prefix. This approach therefore can
allow a great deal of hierarchical abbreviation of routing
information, and thereby can greatly improve the scalability of
inter-domain routing ...
... routing
information, and thereby can greatly improve the scalability of
inter-domain routing.
...
...
Clearly, this approach is recursive and can be carried through
several iterations. Routing domains at any "level" in the hierarchy
may use their prefix ...
... NSAP addresses facilitates
this form of hierarchical address assignment and routing. As one
example of how NSAPs may be used, the GOSIP Version 2 ...
... ceases to produce significant benefits. Determination of the point
at which data abstraction ceases to be of benefit requires a careful
consideration of the number of routing domains that are expected to
occur at each level of the hierarchy (over a given period of time),
...
... domains that are expected to
occur at each level of the hierarchy (over a given period of time),
compared to the number of routing domains and address prefixes that
...
... domains and address prefixes that
can conveniently and efficiently be handled via dynamic inter-domain
routing protocols. As the Internet grows, further levels of
hierarchy may become necessary. Again, this requires considerable
...
... requirements on
NSAPs for efficient routing and the need for decentralized NSAP
administration. The NSAP ...
... reserved field is left to accommodate future growth and to provide
additional flexibility for inter-domain routing). Routing domains
...
... reserved field is left to accommodate future growth and to provide
additional flexibility for inter-domain routing). Routing domains
allocate Area identifiers ...
... This provides for summarization of all area addresses within a
routing domain into one prefix. If the AA ...
... subscribers. A natural mapping from these components to OSI routing
components is that each provider and subscriber ...
... provider domain; that is, as an area within the provider's routing
domain. However, in such a case the discussion ...
...
We assume that most subscribers will prefer to operate a routing
domain separate from their provider ...
... provider's. Such subscribers can exchange
routing information with their provider via interior routing protocol
...
... routing information with their provider via interior routing protocol
route leaking or via IDRP ...
... end-user sites, where the
primary purpose is to provide intra-domain routing services. Provider
...
...
The greatest burden in transmitting and operating on routing
information is at the top of the routing hierarchy, where routing
information tends to accumulate. In the Internet ...
... The greatest burden in transmitting and operating on routing
information is at the top of the routing hierarchy, where routing
information tends to accumulate. In the Internet, for example, each
...
... transmitting and operating on routing
information is at the top of the routing hierarchy, where routing
information tends to accumulate. In the Internet, for example, each
provider ...
... provider will route
based on inter-domain routing information obtained from other
providers or, in some cases, to a default provider.
...
...
In general, higher levels of the routing hierarchy will benefit the
most from the abstraction of routing information at a lower level of
...
... In general, higher levels of the routing hierarchy will benefit the
most from the abstraction of routing information at a lower level of
the routing hierarchy. There is relatively little direct benefit to
...
... most from the abstraction of routing information at a lower level of
the routing hierarchy. There is relatively little direct benefit to
the administration that performs the abstraction, since it must
maintain routing information ...
... routing hierarchy. There is relatively little direct benefit to
the administration that performs the abstraction, since it must
maintain routing information individually on each attached
topological routing structure.
...
... maintain routing information individually on each attached
topological routing structure.
...
... prefix or another; the source of the prefix has little effect on
routing efficiency within the subscriber's routing domain ...
... However, there is a difference when the local provider distributes
routing information to other providers. In the first case, the
provider cannot aggregate the subscriber ...
... prefix; the address must be explicitly listed in routing exchanges,
resulting in an additional burden to other providers which must
exchange and maintain this information.
...
... provider which encompasses the new subscriber. This
avoids the exchange of additional routing information to identify the
new subscriber's address prefix ...
... subscriber's address prefix. Thus, the advantages primarily
benefit other providers which maintain routing information about this
provider (and its subscribers ...
... interest of all providers, enabling them to more efficiently support
CLNP routing to their customers. The guidelines discussed below
describe reasonable ways of managing the OSI ...
... beyond what is built into IS-IS. For example, assume that within a
routing domain three areas take their area addresses, respectively,
...
...
As described in Section 3.3, from the point of view of any particular
routing domain, there is no harm in having the different areas in the
routing ...
... routing domain, there is no harm in having the different areas in the
routing domain use addresses obtained from a wide variety of
...
... domain use addresses obtained from a wide variety of
administrations. For routing within the domain, the area addresses
...
...
However, this does have a negative effect on inter-domain routing,
particularly on those other domains which need to maintain routes to
...
... these NSAPs and therefore no summarization can take place at the
routing domain boundary. When addresses are advertised by this
...
... domain boundary. When addresses are advertised by this
routing domain to other routing domains ...
... routing domain to other routing domains, an enumerated list must be
used consisting of the three area addresses ...
...
This situation is roughly analogous to the dissemination of routing
information in the TCP/IP Internet prior to the introduction of CIDR ...
... addresses to network
numbers. The result of allowing areas within a routing domain to
take their NSAPs ...
... take their NSAPs from unrelated authorities is flat routing at the
area address level. The number of address prefixes ...
... address prefixes that subscriber
routing domains would advertise is on the order of the number of
attached areas; the number of prefixes ...
... attached areas; the number of prefixes a provider routing domain
would advertise is approximately the number of areas attached to all
...
... would advertise is approximately the number of areas attached to all
its subscriber routing domains. For "default-less" providers (i.e.,
those that don't use default routes ...
... domains. For "default-less" providers (i.e.,
those that don't use default routes) the size of the routing tables
would be on the order of the number of area addresses globally. As
...
... comes at the lowest levels of the hierarchy. Providing each
subscriber routing domain (that is, site) with a unique prefix
...
... AA
value of zzz under ICD=0005. The agency then assigns a routing
domain identifier to a routing ...
...
There is a close relationship between areas and routing domains
implicit in the fact that they operate a common routing protocol ...
... routing domains
implicit in the fact that they operate a common routing protocol and
are under the control of a single administration. The routing domain ...
... implicit in the fact that they operate a common routing protocol and
are under the control of a single administration. The routing domain
administration subdivides the domain ...
... level 2 subdomain (i.e., a level 2 backbone) which provides
connectivity among the areas. The routing domain represents the only
path between an area and the rest of the internetwork. It is
...
...
Two kinds of provider routing domains are considered, direct
providers and indirect providers. Most of the subscribers ...
... It is interesting to consider whether direct service providers'
routing domains should be the common authority for assigning NSAPs ...
... from a unique prefix to the subscriber routing domains that they
serve. In the long term the number of routing ...
... routing domains that they
serve. In the long term the number of routing domains in the
Internet ...
... Internet will grow to the point that it will be infeasible to route
on the basis of a flat field of routing domains. It will therefore
be essential to provide a greater degree of information abstraction.
...
... AA value
may be assigned to each direct provider, and routing domain values
may be assigned by the provider ...
... may be assigned by the provider to each attached subscriber routing
domain. A similar hierarchical address assignment ...
... prefixes of the subscriber routing domains. This represents a
significant savings given the expected scale of global
...
... its costs of operation. This includes the "price" of obtaining
service from one or more indirect providers and exchanging routing
information with other direct providers. In general, providers will
want to handle as few address prefixes as possible to keep costs low.
...
... In the Internet environment, subscriber routing domains must be
sensitive to the resource constraints ...
... sensitive to the resource constraints of the providers (both direct
and indirect). The efficiencies gained in routing clearly warrant
the adoption of NSAP administration by the direct providers.
...
... provider is assigned a unique prefix, from which it allocates
slightly longer routing domain prefixes for its attached subscriber ...
... prefixes for its attached subscriber
routing domains. For GOSIP NSAPs, this means that a direct provider ...
... prefix. For example, assume that NIST is a subscriber routing
domain whose sole inter-domain ...
... provider (e.g. backbone in today's terms). The benefit in
routing data abstraction is relatively small. The number of direct
providers today is in the tens and an order of magnitude increase
would not cause an undue burden on the indirect providers. Also, it
...
... inter-connection of the direct providers, subscriber routing domains
directly attached to the "indirect" providers, and international
...
... NSAP
addresses based on service provider connectivity. This allows a
great deal of information reduction to be achieved for those routing
domains which are attached to a single provider ...
... domains which are attached to a single provider. In particular, such
routing domains may select their NSAP addresses from a space
...
... address prefix to describe a large number
of NSAP addresses corresponding to multiple routing domains.
...
...
However, there are additional considerations for routing domains
which are attached to multiple providers. Such "multi-homed" routing ...
... routing domains
which are attached to multiple providers. Such "multi-homed" routing
domains may, for example, consist of single-site campuses and
...
... locations in the same country, or multi-national organizations which
are attached to providers in a variety of countries worldwide. There
are a number of possible ways to deal with these multi-homed routing
domains.
...
... prefix for this organization to
other providers. Other providers (potentially worldwide) will need
to maintain an explicit entry for that organization in their routing
tables. If other providers do not maintain a separate route for this
organization, then packets destined to this organization will be
...
... Version 2 address space. It is likely that outside of the
U.S., a single entry may be maintained in routing tables for all U.S.
GOSIP addresses. However, within the U.S., every "default-less"
...
... separate entry for MBII (including providers to which MBII is not
attached). Clearly this may be acceptable if there are a small
number of such multihomed routing domains, but would place an
unacceptable load on routers ...
... provider,
and to assign a single address prefix to each area within its routing
domain(s) based on the closest interconnection point. For example,
...
... destination inside of MBII, this approach works similarly to treating
MBII as six separate organizations. For purposes of internal
routing, or for routing traffic from inside of MBII to a destination ...
... destination inside of MBII, this approach works similarly to treating
MBII as six separate organizations. For purposes of internal
routing, or for routing traffic from inside of MBII to a destination
...
... address is taken from its own address space.
This implies that no additional routing information needs to be
exchanged between providers, resulting in a smaller load on the
inter-domain routing ...
... routing information needs to be
exchanged between providers, resulting in a smaller load on the
inter-domain routing tables maintained by providers when compared to
the first solution. This solution therefore scales better to
extremely large internets containing very large numbers of multi-
...
... provider would become unreachable via inter-
domain routing. The impact of this problem can be reduced somewhat
by maintenance of additional information within routing tables, but
...
... domain routing. The impact of this problem can be reduced somewhat
by maintenance of additional information within routing tables, but
this reduces the scaling advantage of the second approach.
...
... address may be assigned to those NSAPs which are within
country X, thereby allowing routing policies to be followed.
Similarly, suppose that "Little Small Company" (LSC ...
... connections to a provider. Other providers to which
the multi-homed organization are attached maintain a routing table
entry for the organization, but are extremely selective in terms of
which indirect providers are told of this route ...
... which indirect providers are told of this route. This approach will
produce a single "default" routing entry which all providers will
know how to reach the organization (since presumably all providers
will maintain routes to each other), while providing more direct
...
... know how to reach the organization (since presumably all providers
will maintain routes to each other), while providing more direct
routing in those cases where providers agree to maintain additional
routing information.
...
... routing in those cases where providers agree to maintain additional
routing information.
...
... group will run their internal
networks as separate routing domains, and most of them will also be
attached to other providers (since most of the organizations involved
...
... number of organizations involved in the widget group is small enough
that it is reasonable to maintain a routing table containing one
entry per organization, but that they are distributed throughout a
larger internet ...
... group). The widget backbone would need to maintain routes to
the routing domains associated with the various member organizations.
Similarly, all members of the widget group ...
... backbone is not intended for use by other outside organizations), the
relatively large set of routing prefixes needs to be maintained only
in a limited number of places. The addresses assigned to the various
...
... A fourth solution involves assignment of a particular address prefix
for routing domains which are attached to two or more specific
cooperative public service providers ...
... have a very large number of customers in common (i.e., there are a
large number of routing domains which are attached to both). Rather
than getting two address prefixes ...
... address space) these organizations could obtain three
prefixes. Those routing domains which are attached to NorthSouthNet
but not attached to SouthNorthNet obtain an address assignment ...
... address assignment based
on one of the prefixes. Those routing domains which are attached to
SouthNorthNet but not to NorthSouthNet would obtain an address ...
... address based
on the second prefix. Finally, those routing domains which are
multi-homed to both of these networks ...
... networks becomes more common. In particular, it is likely that at
some point in the future a substantial percentage of all routing
domains will be attached to public data networks ...
... There are therefore a number of possible solutions to the problem of
assigning NSAP addresses to multi-homed routing domains. Each of
these solutions has very different advantages and disadvantages.
...
... non-local prefixes and
agree to exchange them in routing information with a defined set of
other providers (this set could be an a priori group of providers
...
... discussion up to this point concentrates on the relationship
between NSAP addresses and routing between various routing domains
...
... over transit routing domains, where each transit routing domain
interconnects a large number of routing ...
... routing domain
interconnects a large number of routing domains and offers a more-
or-less public service ...
... However, there may also exist a large number of private point-to-
point links which interconnect two private routing domains. In many
cases such private point-to-point links ...
... cases such private point-to-point links may be limited to forwarding
packets directly between the two private routing domains.
...
... may be ignored for the purpose of NSAP allocation, and do not pose a
problem for routing. This is because the routing information
associated with private links ...
... NSAP allocation, and do not pose a
problem for routing. This is because the routing information
associated with private links is not propagated throughout the
...
... point-to-point links may be permitted to
forward traffic for a small number of other routing domains, such as
closely affiliated organizations. This will increase the
...
... addressing
described in other sections of this paper is concerned with problems
in scaling caused by large, essentially public transit routing
domains which interconnect a large number of routing ...
... routing
domains which interconnect a large number of routing domains.
However, for the purpose of NSAP ...
... However, for the purpose of NSAP allocation, private point-to-point
links which interconnect only a small number of private routing
domains do not pose a problem, and may be ignored. For example, this
...
... domains do not pose a problem, and may be ignored. For example, this
implies that a single subscriber routing domain which has a single
connection to a "public" provider ...
... to-point links to other subscriber routing domains, can be treated as
if it were single-homed ...
... point-to-point links that they use for communications with other
organizations. Such organizations do not participate in global
routing, but are satisfied with reachability to those organizations
with which they have established private links ...
... with which they have established private links. These are referred
to as zero-homed routing domains.
...
... routing domains can be considered as the degenerate case
of routing domains with private links, as discussed in the previous
...
... domains with private links, as discussed in the previous
section, and do not pose a problem for inter-domain routing. As
above, the routing information exchanged across the private links ...
... section, and do not pose a problem for inter-domain routing. As
above, the routing information exchanged across the private links
sees very limited distribution, usually only to the RD ...
... valid
globally unique NSAP addresses. Suppose that the zero-homed routing
domain is connected through a private link ...
... ISO 8348). This RD must be able to
distinguish between the zero-homed routing domain's NSAPs and any
...
... NSAPs that it may need to route to. The only way this can be
guaranteed is if the zero-homed routing domain uses globally unique
NSAPs ...
... Allocation of NSAP addresses based on connectivity to providers is
important to allow scaling of inter-domain routing to an internet
containing millions of routing ...
... inter-domain routing to an internet
containing millions of routing domains. However, such address
...
... addresses is a natural, inevitable
consequence of any method for routing data abstraction. The basic
notion of routing data abstraction is that there is some
...
... method for routing data abstraction. The basic
notion of routing data abstraction is that there is some
correspondence between the address and where a system (i.e., a
...
... correspondence between the address and where a system (i.e., a
routing domain, area, or end system) is located. Thus if the system
moves, in some cases the address ...
... moves, in some cases the address will have to change. If it were
possible to change the connectivity between routing domains without
changing the addresses ...
... changing the addresses, then it would clearly be necessary to keep
track of the location of that routing domain on an individual basis.
...
... topology changes before finalizing a plan for address
allocation. For example, in the case of a routing domain which is
initially single-homed ...
... In general, it will not be practical to transition the NSAP addresses
assigned to a routing domain in an instantaneous "change the address
...
... limited period of time. During the transition period, both the old
and new addresses are accepted by the end systems in the routing
domain, and both old and new addresses ...
... domain, and both old and new addresses must result in correct routing
of packets to the destination.
...
... address be forwarded correctly, even when the topology has
changed. This is facilitated by the use of "best match" inter-domain
routing.
...
... provider. The XYZ Corporation
therefore went off to the NorthSouthNet administration and got a
routing domain assignment based on the AA value obtained by the
...
... traffic to XYZ using the old address allocation
would be forwarded via NewCommercialNet. However, other routing
domains would not need to be aware of the new location for XYZ
...
... provider and the new provider are separated by a
non-cooperative routing domain, or by a long path of routing domains ...
... non-cooperative routing domain, or by a long path of routing domains.
In this case, the old provider ...
...
Also, those locations which do a significant amount of business with
XYZ Corporation could have a specific entry in their routing tables
added to ensure optimal routing of packets to XYZ. For example,
...
... XYZ Corporation could have a specific entry in their routing tables
added to ensure optimal routing of packets to XYZ. For example,
suppose that another commercial backbone "OldCommercialNet" has a
...
... provider is directly connected to
both NorthSouthNet and NewCommercialNet. In this case
OldCommercialNet will continue to have a single entry in its routing
tables for other traffic destined for NorthSouthNet, but may choose
to add one additional (more specific) entry to ensure that packets
...
... internationalization of the
Internet. The ability of routing to scale is dependent upon the use
of data abstraction based on hierarchical NSAP addresses. As CLNP ...
... cost of operations be kept to a minimum where possible. In the case
of NSAP allocation, this again means that routing data abstraction
must be encouraged.
...
... The intra-domain IS-IS routing protocol allows for information
abstraction to be maintained at two levels: systems are grouped into
areas, and areas are interconnected to form a routing ...
... routing protocol allows for information
abstraction to be maintained at two levels: systems are grouped into
areas, and areas are interconnected to form a routing domain. The
inter-domain ...
... inter-domain IDRP routing protocol allows for information abstraction
to be maintained at multiple levels by grouping routing domains ...
... IDRP routing protocol allows for information abstraction
to be maintained at multiple levels by grouping routing domains into
Routing ...
...
For zero-homed and single-homed routing domains (which are expected
to remain zero-homed or single-homed ...
... single-homed), we recommend that the NSAP
addresses assigned for OSI use within a single routing domain use a
single address prefix ...
... connectivity to a public service provider. We recommend that zero-
homed routing domains use globally unique addresses.
...
... OSI Internet to be great enough that additional levels of
hierarchical data abstraction beyond the routing domain level will be
necessary. To provide the needed data abstraction we recommend to
...
... domain level will be
necessary. To provide the needed data abstraction we recommend to
use Routing Domain Confederations and route aggregation ...
...
We anticipate that, in the U.S., public interconnectivity between
private routing domains will be provided by a diverse set of
providers, including (but not necessarily limited to) regional
...
... set of providers via a flat address space. These providers will be
used to interconnect a wide variety of routing domains, each of which
may comprise a single corporation, part of a corporation, a
...
...
We anticipate that the great majority of routing domains will be
attached to only one of the providers. This will permit hierarchical
...
... other major government backbones). For those subscriber routing
domains which are connected to a single provider ...
... domains which are connected to a single provider, they should be
assigned a Routing Domain (RD) value from the space assigned to that
...
... subscriber domains form a
Routing Domain Confederation. That, combined with hierarchical
address assignment ...
... address assignment, would provide significant reduction in the volume
of routing information that needs to be handled by IDRP. Note that
the presence of multihomed subscriber ...
... address
abbreviation exists. We do not, therefore, make any additional
recommendations for such "isolated" routing domains, except to note
that there is no technical reason to preclude assignment of GOSIP AA ...
... to-point links, and where such links are used solely for routing
between the two domains that they interconnect, no additional
...
... octet syntax selected by the AFI value 38 or 39) satisfying both the
routing requirements (IS-IS) and the logical requirements ...
... prefixes as possible, we further recommend
that NSAPs allocated to routing domains should be assigned based on
each routing ...
... routing domains should be assigned based on
each routing domain's connectivity to a national Internet backbone ...
...
Some routing domains will be attached to multiple providers within
the same country, or to providers within multiple countries. We
...
... domains will be attached to multiple providers within
the same country, or to providers within multiple countries. We
refer to these as "multi-homed" routing domains. Clearly the strict
hierarchical model discussed above does not neatly handle such
...
... domains. Clearly the strict
hierarchical model discussed above does not neatly handle such
routing domains.
...
...
There are several possible ways that these multi-homed routing
domains may be handled. Each of these methods ...
... domains may be handled. Each of these methods vary with respect to
the amount of information that must be maintained for inter-domain
routing and also with respect to the inter-domain routes. In
addition, the organization that will bear the brunt of this cost
...
... difficulty of configuration of policy-based inter-domain
routing information within subscriber routing domains ...
... all situations. Rather, economic considerations will require a
variety of solutions for different subscriber routing domains and
providers.
...
... its RDI. If a service provider forms a Routing Domain Confederation
with some of its subscribers ...
... ISO/IEC, "End System to Intermediate System Routing Exchange Protocol for use in Conjunction with the Protocol for the Provision of the Connectionless-mode Network Service", International Standard 9542, ISO/IEC ...
... Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter- Domain Routing (CIDR): an Address Assignment and Aggregation Strategy ...
... an Administrative Authority identifier, two octets for Routing
Domain, two octets for Area, six octets for the System Identifier ...
... NSAP selector. Note that two octets have been
reserved to accommodate future growth and to provide additional
flexibility for inter-domain routing. The last seven octets of the
GOSIP NSAP format are structured in accordance with IS-IS ...
... The administrative authority may delegate the responsibilityfor
registering areas to the routing domains, and the routing domains ...
... registering areas to the routing domains, and the routing domains may
delegate the authority ...
...
A routing domain is a set of end systems and intermediate systems
which operate according to the same routing ...
... routing domain is a set of end systems and intermediate systems
which operate according to the same routing procedures and is wholly
contained within a single administrative domain. An area uniquely
...
... contained within a single administrative domain. An area uniquely
identifies a subdomain of the routing domain. The system identifier
...
... authority should ensure that procedures exist for
disseminating NSAPs to routing domains and to areas within
each routing ...
... network address itself contains information that may be
used to aid routing, but does not contain a source route [12].
...
... NSAPs
is gathered and maintained by each intermediate system through
routing protocol exchanges.
...
... GOSIP end systems and intermediate systems in federal agencies
must be capable of routing information correctly to and from any
subdomain defined by ISO 8348.
...
... registration authority itself. In turn, it may delegate registration
authority to routing domains, and these may make further delegations,
...
... domains, and these may make further delegations,
for instance, from routing domains to areas. Again, the
responsibilities of each Registration Authority ...