IRTF Routing Research Avri Doria (co-editor)
Internet Draft Lulea University of Technology
Elwyn Davies (co-editor)
Nortel Networks
Informational Track
Document: draft-irtf-routing-history-00.txt February, 2002
Analysis of IDR requirements and History
Group B contribution
<draft-irtf-routing-history-00.txt>
Status of this Memo
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Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This draft is the product of Group B, which is one of, at least, two
subgroups in the IRTF-Routing Research Group working on requirements
for routing solutions for the future. This document analyses the
current state of IDR routing with respect to RFC1026 and other IDR
requirements and design efforts. It is the companion document to
draft-irtf-routing-reqs-groupb-00.txt, which is a discussion of
requirements for the future routing architecture and future routing
protocols.
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Acknowledgements
The draft is derived from draft-davies-fdr-reqs-01.txt, which was
produced by Babylon. Babylon is a loose association of individuals
from academia, service providers and vendors whose goal is to discuss
issues in Internet routing with the intention of finding solutions
for those problems.
The individual members who contributed text to this draft are:
Anders Bergsten, Howard Berkowitz, Malin Carlzon, Lenka Carr
Motyckova, Elwyn Davies, Avri Doria, Pierre Fransson, Yong Jiang,
Dmitri Krioukov, Tove Madsen, Olle Pers, and Olov Schelen.
Thanks also go to the members of Babylon who did substantial reviews
of this material. Specifically we would like to acknowledge the
helpful comments and suggestions of the following individuals: Loa
Andersson, Tomas Ahlstr÷m, Niklas Borg, Nigel Bragg, Thomas Chmara,
Krister Edlund, Owe Grafford, Torbj÷rn Lundberg, Jasminko Mulahusic,
Florian-Daniel Otel, Bernhard Stockman, Tom Worster, Roberto Zamparo.
In addition, the authors are indebted to the folks who wrote all the
references we have consulted in putting this paper together. This
includes not only the references explicitly listed below, but also
those who contributed to the mailing lists we have been participating
in for years.
Finally, it is the editors who are responsible for any lack of
clarity, all errors, any omissions or misunderstandings.
Changes from Draft-davies-fdr-reqs-01.txt
- The Future Domain Routing requirements have been separated into
another I-D. This ID is being presented as one of the contributions
to the IRTF for consideration as a RG document.
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CONTENTS
1. Introduction....................................................4
1.1 Background.................................................4
2. Historical Perspective..........................................5
2.1 The legacy of RFC1126......................................5
2.2 Nimrod Requirements.......................................15
2.3 PNNI......................................................17
2.4 Recent Research Work......................................17
3. Existing problems of BGP and the current EGP/IGP Architecture..19
3.1 BGP and Auto-aggregation..................................20
3.2 Convergence and Recovery Issues...........................20
3.3 Non-locality of Effects of Instability and Misconfiguration21
3.4 Multihoming Issues........................................21
3.5 AS-number exhaustion......................................22
3.6 Partitioned AS's..........................................22
3.7 Load Sharing..............................................22
3.8 Hold down issues..........................................22
3.9 Interaction between Inter domain routing and intra domain
routing................................................23
3.10 Policy Issues..........................................24
3.11 Security Issues........................................24
3.12 Support of MPLS and VPNS...............................25
3.13 IPv4 / IPv6 Ships in the Night.........................25
3.14 Existing Tools to Support Effective Deployment of Inter-
Domain Routing.........................................25
4. References.....................................................27
5. Author's Addresses.............................................30
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1. Introduction
It is generally accepted that there are major shortcomings in the
inter-domain routing of the Internet today and that these may result
in meltdown within an unspecified period of time. Remedying these
shortcomings will require extensive research to tie down the exact
failure modes that lead to these shortcomings and identify the best
techniques to remedy the situation.
Various developments in the nature and quality of the services that
users want from the Internet are difficult to provide within the
current framework as they impose requirements never foreseen by the
original architects of the Internet routing system.
The advent of IPv6 and the application of IP mechanisms to private
commercial networks offering specific service guarantees as an
improvement over the best efforts services of the Public Internet
epitomize the kind of radical changes which have to be accommodated:
Major changes to the inter-domain routing system are inevitable if it
is to provide an efficient underpinning for the radically changed and
increasingly, commercially-based networks which rely on the IP
protocol suite.
Current practice stresses the need to separate the concerns of the
control plane in a router and the forwarding plane: This document
will follow this practice, but we still use the term 'routing' as a
global portmanteau to cover all aspects of the system.
This draft makes a start on the analysis of domain routing in Section
2 by revisiting the requirements for a future routing system which
were last documented in RFC1126 - "Goals and Functional Requirements
for Inter-Autonomous System Routing" [4] as a precursor to the design
of BGP in 1989. This section also looks at some other work that has
been carried out since RFC1126 was published in order to flesh out
the historical perspective. Some of the requirements for new routing
architectures derive from the problems that are currently being
experienced in the Internet today. These will be discussed in
Section 3.
1.1 Background
Today's Internet uses an addressing and routing structure that has
developed in an ad hoc, more or less upwards-compatible fashion. It
has progressed from handling a single domain, non-commercial Internet
to a solution that is just about controlling today's multi-domain,
federated, combination commercial and not-for-profit Internet. The
result is not ideal, particularly as regards inter-domain routing
mechanisms that have to implement a host of domain specific routing
policies for competing, communicating domains, but it does a pretty
fair job at its primary goal of providing any-to-any connectivity to
many millions of computers.
Based on a large body of anecdotal evidence, but also on a growing
body of experimental evidence [11] and analytic work on the stability
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of BGP under certain policy specifications [12], the main Internet
inter-domain routing protocol, BGP4, appears to have a number of
problems that need to be resolved. Additionally, the hierarchical
nature of the inter-domain routing problem appears to be changing as
the connectivity between domains becomes increasingly meshed [13]
which alters some of the scaling and structuring assumptions on which
BGP4 is built. Patches and fix-ups may relieve some of these
problems but others may require a new architecture and new protocols.
2. Historical Perspective
2.1 The legacy of RFC1126
RFC1126 outlined a set of requirements that were to guide the
development of BGP. While the network is definitely different then it
was in 1989, many of the same requirements remain. As a first step
in setting requirements for the future, we need to understand the
requirements that were originally set for the current protocols. And
in charting a future architecture we must first be sure to do no
harm. This means a future domain routing has to support as its base
requirement, the level of function that is available today.
The following sections each relate to a requirement, or non-
requirement listed in RFC1126. In fact the section names are direct
quotes from the document. The discussion of these requirements
covers the following areas:
Optionally, interpretation for today's audience of the original
intent of the requirement
Relevance: Is the requirement of RFC1126 still relevant, and to
what degree? Should it be understood differently in today's
environment?
Current practice: How well is the requirement met by current
protocols and practice?
2.1.1 "General Requirements"
2.1.1.1 "Route to Destination"
Timely routing to all reachable destinations, including multihoming
and multicast.
Relevance: Valid, but requirements for multihoming need further
discussion and elucidation. The requirement should include
multiple source multicast routing.
Current practice: Multihoming is not efficient and the proposed
inter-domain multicast protocol BGMP is an add-on to BGP
following many of the same strategies but not integrated
into the BGP framework [23].
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2.1.1.2 "Routing is Assured"
This requires that a user be notified within a reasonable time period
of attempts, about inability to provide a service.
Relevance: Valid
Current practice: There are ICMP messages for this, but in many cases
they are not used, either because of fears about creating
message storms or uncertainty about whether the end system
can do anything useful with the resulting information.
2.1.1.3 "Large System"
The architecture was designed to accommodate the growth of the
Internet.
Relevance: Valid. Properties of Internet topology might be an issue
for future scalability (topology varies from very sparse
to quite dense at present). Instead of setting growth in a
time-scale, indefinite growth should be accommodated. On
the other hand, such growth has to be accommodated without
making the protocols too expensive - trade-offs may be
necessary.
Current practice: Scalability of the current protocols will not be
sufficient under the current rate of growth. There are
problems with BGP convergence for large dense topologies,
problems with routing information propagation between
routers in transit domain, limited support for hierarchy,
etc.
2.1.1.4 "Autonomous Operation"
Relevance: Valid. There may need to be additional requirements for
adjusting policy decisions to the global functionality and
for avoiding contradictory policies. This would decrease
the possibility of unstable routing behavior.
There is a need for handling various degrees of trust in
autonomous operations, ranging from no trust (e.g.,
between separate ISPs) to very high trust where the
domains have a common goal of optimizing their mutual
policies.
Policies for intra domain operations should in some cases
be revealed, using suitable abstractions.
Current practice: Policy management is in the control of network
managers, as required, but there is little support for
handling policies at an abstract level for a domain.
Cooperating administrative entities decide about the
extent of cooperation independently. Lack of coordination
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combined with global range of effects results in
occasional melt-down of Internet routing.
2.1.1.5 "Distributed System"
The routing environment is a distributed system. The distributed
routing environment supports redundancy and diversity of nodes and
links. Both data and operations are distributed.
Relevance: Valid. RFC1126 is very clear that we should not be using
centralized solutions, but maybe we need a discussion on
trade-offs between common knowledge and distribution
(i.e., to allow for uniform policy routing, e.g., GSM
systems are in a sense centralized, but with hierarchies)
Current practice: Routing is very distributed, but lacking abilities
to consider optimization over several hops or domains.
2.1.1.6 "Provide A Credible Environment"
Routing mechanism information must be integral and secure (credible
data, reliable operation). Security from unwanted
modification and influence is required.
Relevance: Valid.
Current practice: BGP provides a mechanism for authentication and
security. There are however security problems with
current practice.
2.1.1.7 "Be A Managed Entity"
Requires that a manager should get enough information on a state of
network so that s/he could make informed decisions.
Relevance: The requirement is reasonable, but we might need to be
more specific on what information should be available,
e.g. to prevent routing oscillations.
Current practice: All policies are determined locally, where they may
appear reasonable but there is limited global coordination
through the routing policy databases operated by the
Internet registries (ARIN, RIPE, APNIC etc). Operators
are not required to register their policies; even when
policies are registered, it is difficult to check that the
actual policies in use match the declared policies and
therefore a manager cannot guarantee to make a globally
consistent decision.
2.1.1.8 "Minimize Required Resources"
Relevance: Valid, however, the paragraph states that assumptions on
significant upgrades shouldn't be made. Although this is
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reasonable, a new architecture should perhaps be prepared
to use upgrades when they occur.
Current practice: Most bandwidth is consumed by the exchange of the
NLRI. Usage of CPU depends on the stability of the
Internet. Both phenomena have a local nature, so there are
not scaling problems with bandwidth and CPU usage.
Instability of routing increases the consumption of
resources in any case. The number of networks in the
Internet dominates memory requirements - this is a scaling
problem.
2.1.2 "Functional Requirements"
2.1.2.1 "Route Synthesis Requirements"
2.1.2.1.1 "Route around failures dynamically"
Relevance: Valid. Should perhaps be stronger. Only providing a best-
effort attempt may not be enough if real-time services are
to be provided for. Detections may need to be faster than
100ms to avoid being noticed by end-users.
Current practice: latency of fail-over is too high; sometimes minutes
or longer.
2.1.2.1.2 "Provide loop free paths"
Relevance: Valid. Loops should occur only with negligible probability
and duration.
Current practice: both link-state intra domain routing and BGP inter-
domain routing (if correctly configured) are forwarding-
loop free after having converged. However, convergence
time for BGP can be very long and poorly designed routing
policies may result in a number of BGP speakers engaging
in a cyclic pattern of advertisements and withdrawals
which never converges to a stable result [20]. Perhaps
this is one context in which the need for global
convergence needs to be reviewed.
2.1.2.1.3 "Know when a path or destination is unavailable"
Relevance: Valid to some extent, but there is a trade-off between
aggregation and immediate knowledge of reachability. It
requires that routing tables contain enough information to
determine that the destination is unknown or a path cannot
be constructed to reach it.
Current practice: Knowledge about lost reachability propagates slowly
through the networks due to slow convergence for route
withdrawals.
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2.1.2.1.4 "Provide paths sensitive to administrative policies"
Relevance: Valid. Policy control of routing is of increasingly
importance as the Internet has turned into business.
Current practice: Supported to some extent. Policies are only
possible to apply locally in an AS and not globally. At
least there is a very small probability of affecting
policies in other AS's. Furthermore, only static policies
are supported; between static policies and `policies
dependent upon volatile events of great celerity` there
should exist events that routing should be aware of.
Lastly, there is no support for policies other than route-
properties (such as AS-origin, AS-path, destination
prefix, MED-values etc).
2.1.2.1.5 "Provide paths sensitive to user policies"
Relevance: Valid to some extent, as they may conflict with the
policies of the network administrator. It is likely that
this requirement will be met by means of different bit
transport services offered by an operator, but at the cost
of adequate provisioning, authentication and policing when
utilizing the service.
Current practice: not supported in normal routing. Can be
accomplished to some extent with loose source routing,
resulting in inefficient forwarding in the routers. The
various attempts to introduce QoS (Integrated Services and
DiffServ) can also be seen as means to support this
requirement but they have met with limited success.
2.1.2.1.6 "Provide paths which characterize user quality-of-service
requirements"
Relevance: Valid to some extent, as they may conflict with the
policies of the operator. It is likely that this
requirement will be met by means of different bit
transport services offered by an operator, but at the cost
of adequate provisioning, authentication and policing when
utilizing the service. It has become clear that offering
to provide a particular QoS to any arbitrary destination
from a particular source is generally impossible: QoS
except in very 'soft' forms such as overall long term
average packet delay, is generally associated with
connection oriented routing.
Current practice: Creating routes with specified QoS is not generally
possible at present.
2.1.2.1.7 "Provide autonomy between inter- and intra-autonomous system
route synthesis"
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Relevance: Inter and intra domain routing should stay independent,
but one should notice that this to some extent contradicts
the previous three requirements. There is a trade-off
between abstraction and optimality.
Current practice: inter-domain routing is performed independently of
intra-domain routing. Intra-domain routing is, especially
in transit domains, very interrelated to inter-domain
routing.
2.1.2.2 "Forwarding Requirements"
2.1.2.2.1 "Decouple inter- and intra-autonomous system forwarding
decisions"
Relevance: Valid.
Current practice: As explained in 2.1.2.1.7, intra-domain forwarding
in transit domains is codependent with inter-domain
forwarding decisions.
2.1.2.2.2 "Do not forward datagrams deemed administratively
inappropriate"
Relevance: Valid, and increasingly important in the context of
enforcing policies correctly expressed through routing
advertisements but flouted by rogue peers which send
traffic for which a route has not been advertised. On the
other hand, packets that have been misrouted due to
transient routing problems perhaps should be forwarded to
reach the destination, although along an unexpected path.
Current practice: at stub domains there is packet filtering, e.g., to
catch source address spoofing on outgoing traffic or to
filter out unwanted incoming traffic. Filtering can in
particular reject traffic (such as unauthorized transit
traffic) that has been sent to a domain even when it has
not advertised a route for such traffic on a given
interface. The growing class of 'mid boxes' (e.g. NATs)
is quite likely to apply administrative rules that will
prevent forwarding of packets. Note that security
policies may deliberately hide administrative denials. In
the backbone, intentional packet dropping based on
policies is not common.
2.1.2.2.3 "Do not forward datagrams to failed resources"
Relevance: Unclear, although it is clearly desirable to minimise
waste of forwarding resources by discarding datagrams
which cannot be delivered at the earliest opportunity.
There is a trade-off between scalability and keeping track
of unreachable resources. Equipment closest to a failed
node has the highest motivation to keep track of failures
so that waste can be minimised.
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Current practice: routing protocols use both internal adjacency
management sub-protocols (e.g. Hello protocols) and
information from equipment and lower layer link watchdogs
to keep track of failures in routers and connecting links.
Failures will eventually result in the routing protocol
reconfiguring the routing to avoid (if possible) a failed
resource, but this is generally very slow (30s or more).
In the meantime datagrams may well be forwarded to failed
resources. In general terms, end hosts and some non-
router midboxes do not participate in these notifications
and failures of such boxes will not affect the routing
system.
2.1.2.2.4 "Forward datagram according to its characteristics"
Relevance: Valid. This is necessary in enabling differentiation in
the network, based on QoS, precedence, policy or security.
Current practice: ingress and egress filtering can be done based on
policy.
2.1.2.3 "Information Requirements"
2.1.2.3.1 "Provide a distributed and descriptive information base"
Relevance: Valid, however hierarchical information bases might
provide more possibilities.
Current practice: the information base is distributed, it is unclear
whether they support all necessary routing functionality.
2.1.2.3.2 "Determine resource availability"
Relevance: Valid. It should be possible for resource availability
and levels of resource availability to be determined.
This prevents needing to discover unavailability through
failure. Resource location and discovery is arguably a
separate concern that could be addressed outside the core
routing requirements.
Current practice: Resource availability is predominantly handled
outside of the routing system.
2.1.2.3.3 "Restrain transmission utilization"
Relevance: Valid. However certain requirements in the control plane,
such as fast detection of faults may be worth consumption
of more resources. Similarly, simplicity of
implementation may make it cheaper to 'back haul' traffic
to central locations to minimise the cost of routing if
bandwidth is cheaper than processing.
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Current practice: BGP messages probably do not ordinarily consume
excessive resources, but might during erroneous
conditions. In the data plane, the near universal
adoption of shortest path protocols could be considered to
result in minimization of transmission utilization.
2.1.2.3.4 "Allow limited information exchange"
Relevance: Valid. But perhaps routing could be improved if certain
information could be available either globally or at least
for a wider defined locality.
Current practice: Policies are used to determine which reachability
information that is exported.
2.1.2.4 "Environmental Requirements"
2.1.2.4.1 "Support a packet-switching environment"
Relevance: Valid but routing system should not be limited to this
exclusively.
Current practice: supported.
2.1.2.4.2 "Accommodate a connection-less oriented user transport service"
Relevance: Valid, but routing system should not be limited to this
exclusively.
Current practice: accommodated.
2.1.2.4.3 "Accommodate 10K autonomous systems and 100K networks"
Relevance: No longer valid. Needs to be increased potentially
indefinitely. It is extremely difficult to foresee the
future size expansion of the Internet so that the utopian
solution would be to achieve an Internet whose
architecture is scale invariant. Regrettably, this may
not be achievable without introducing undesirable
complexity and a suitable trade off between complexity and
scalability is likely to be necessary.
Current Practice: Supported but perhaps reaching its limit.
2.1.2.4.4 "Allow for arbitrary interconnection of autonomous systems"
Relevance: Valid. However perhaps not all interconnections should be
accessible globally.
Current practice: BGP-4 allows for arbitrary interconnections.
2.1.2.5 "General Objectives"
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2.1.2.5.1 "Provide routing services in a timely manner"
Relevance: Valid, as stated before. The more complex a service is the
longer it should be allowed to take, but the
implementation of services requiring (say) NP-complete
calculation should be avoided.
Current practice: More or less, with the exception of convergence and
fault robustness.
2.1.2.5.2 "Minimize constraints on systems with limited resources"
Relevance: Valid
Current practice: Systems with limited resources are typically stub
domains that advertise very little information.
2.1.2.5.3 "Minimize impact of dissimilarities between autonomous systems"
Relevance: Important. This requirement is critical to a future
architecture. In a domain routing environment where the
internal properties of domains may differ radically, it
will be important to be sure that these dissimilarities
are minimized at the borders.
Current: practice: For the most part this capability isn't required
in today's networks since the intra-domain attribute are
nearly identical to start with.
2.1.2.5.4 "Accommodate the addressing schemes and protocol mechanisms
of the autonomous systems"
Relevance: Important, probably more so than when RFC1126 was
originally developed because of the potential deployment
of IPv6, wider usage of MPLS and the increasing usage of
VPNs.
Current practice: Largely only one global addressing scheme is
supported in most autonomous systems.
2.1.2.5.5 "Must be implementable by network vendors"³
Requirement: Valid, but note that what can be implemented today is
different from what was possible when RFC1126 was written:
a future domain routing architecture should not be
unreasonably constrained by past limitations.
Current practice: BGP was implemented.
2.1.3 "Non-Goals"
RFC1126 also included a section discussing non-goals. To what extent
are these still non-goals? Does the fact that they were non-goals
adversely affect today's IDR system?
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2.1.3.1 "Ubiquity"
In a sense this 'non-goal' has effectively been achieved by the
Internet and IP protocols. This requirement reflects a different
worldview where there was serious competition for network protocols,
which is really no longer the case. Ubiquitous deployment of inter-
domain routing in particular has been achieved and must not be undone
by any proposed future domain routing architecture. On the other
hand:
- ubiquitous connectivity cannot be reached in a policy sensitive
environment and should not be an aim,
- it must not be required that the same routing mechanisms are
used throughout provided that they can interoperate
appropriately
- the information needed to control routing in a part of the
network should not necessarily be ubiquitously available and it
must be possible for an operator to hide commercially sensitive
information that is not needed outside a domain.
Relevance: De facto essential for a future domain routing
architecture, but what is required is ubiquity of the
routing system rather than ubiquity of connectivity.
Current practice: de facto ubiquity achieved.
2.1.3.2 "Congestion control"
Relevance: It is not clear if this non-goal was to be applied to
routing or forwarding. It is definitely a non-goal to
adapt the choice of route at transient congestion.
However, to add support for congestion avoidance (e.g.,
ECN and ICMP messages) in the forwarding process would be
a useful addition. There is also extensive work going on
in traffic engineering which should result in congestion
avoidance through routing as well as in forwarding.
Current practice: Some ICMP messages (e.g. source quench) exist to
deal with congestion control but these are not generally
used as they either make the problem worse or there is no
mechanism to reflect the message into the application
which is providing the source.
2.1.3.3 "Load splitting"
Relevance: This should neither be a non-goal, nor an explicit goal.
It might be desirable in some cases and should be
considered as an optional architectural feature.
Current practice: Can be implemented by exporting different prefixes
on different links, but this requires manual configuration
and does not consider actual load.
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2.1.3.4 "Maximizing the utilization of resources"
Relevance: Valid. Cost-efficiency should be strived for; maximizing
resource utilization does not always lead to greatest
cost-efficiency.
Current practice: Not currently part of the system, though often a
'hacked in' feature done with manual configuration.
2.1.3.5 "Schedule to deadline service"
This non-goal was put in place to ensure that the IDR did not have to
meet real time deadline goals such as might apply to CBR services in
ATM.
Relevance: The hard form of deadline services is still a non-goal for
the future domain routing architecture but overall delay
bounds are much more of the essence than was the case when
RFC1126 was written.
Current Practice: Service providers are now offering overall
probabilistic delay bounds on traffic contracts. To
implement these contracts there is a requirement for a
rather looser form of delay sensitive routing.
2.1.3.6 "Non-interference policies of resource utilization"
The requirement in RFC1126 is somewhat opaque, but appears to imply
that what we would today call QoS routing is a non-goal and that
routing would not seek to control the elastic characteristics of
Internet traffic whereby a TCP connection can seek to utilize all the
spare bandwidth on a route, possibly to the detriment of other
connections sharing the route or crossing it.
Relevance: Open Issue. It is not clear whether dynamic QoS routing
can or should be implemented. Such a system would seek to
control the admission and routing of traffic depending on
current or recent resource utilization. This would be
particularly problematic where traffic crosses an
ownership boundary because of the need for potentially
commercially sensitive information to be made available
outside the ownership boundary.
Current practice: Routing does not consider dynamic resource
availability. Forwarding can support service
differentiation.
2.2 Nimrod Requirements
Nimrod as expressed by Noel Chiappa in his early document, "A New IP
Routing and Addressing Architecture" (1991) and later in the NIMROD
Working Group documents RFC 1753 and RFC1992 established a number of
requirements that need to be considered by any new routing
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architecture. The Nimrod requirements took RFC1126 as a starting
point and went further.
The goals of Nimrod, quoted from RFC1992, were as follows:
1. To support a dynamic internetwork of *arbitrary size* (our
emphasis) by providing mechanisms to control the amount of
routing information that must be known throughout an
internetwork.
2. To provide service-specific routing in the presence of multiple
constraints imposed by service providers and users.
3. To admit incremental deployment throughout an internetwork.
It is certain that these goals should be considered requirements for
any new domain routing architecture.
- As discussed in other sections of this document the amount of
information needed to maintain the routing system is growing at
a rate that does not scale. And yet, as the services and
constraints upon those services grow there is a need for more
information to be maintained by the routing system.
One of the key terms in the first requirements is 'control'.
While increasing amounts of information need to be known and
maintained in the Internet, the amounts and kinds of information
that are distributed can be controlled.
This goal should be reflected in the requirements for the future
domain architecture.
- If anything, the demand for specific services in the Internet
has grown since 1996 when the Nimrod architecture was published.
Additionally the kinds of constraints that service providers
need to impose upon their networks and that services need to
impose upon the routing have also increased. Any changes made
to the network in the last half-decade have not significantly
improved this situation.
- The ability to incrementally deploy any new routing architecture
within the Internet is still a absolute necessity. It is
impossible to imagine that a new routing architecture could
supplant the current architecture on a flag day
At one point in time Nimrod, with its addressing and routing
architectures was seen as a candidate for IPng. History shows that
it was not accepted as the IPng, having been ruled out of the
selection process by the IESG in 1994 on the grounds that it was 'too
much of a research effort' [35], although input for the requirements
of IPng was explicitly solicited from Chiappa [8]. Instead IPv6 has
been put forth as the IPng. Without entering a discussion of the
relative merits of IPv6 versus Nimrod, it is apparent that IPv6,
while it may solve many problems, does not solve the critical routing
problems in the Internet today. In fact in some sense it exacerbates
them by adding a requirements for support of two internet protocols
and their respective addressing methods. In many ways the addition
of IPv6 to the mix of methods in today's Internet only points to the
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fact that the goals, as set forth by the Nimrod team, remain as
necessary goals.
There is another sense in which study of Nimrod and its architecture
may be important to deriving a future domain routing architecture.
Nimrod can be said to have two derivatives:
- MPLS in that it took the notion of forwarding along well known
paths
- PNNI in that it took the notion of abstracting topological
information and using that information to create connections for
traffic.
It is important to note, that whilst MPLS and PNNI borrowed ideas
from Nimrod, neither of them can be said to be an implementation of
this architecture.
2.3 PNNI
PNNI was developed under the ATM Forum's auspices as a hierarchical
route determination protocol for ATM, a connection oriented
architecture. It is reputed to have developed several of it methods
from a study of the Nimrod architecture. What can be gained from an
analysis of what did and did not succeed in PNNI?
The PNNI protocol includes the assumption that all peer groups are
willing to cooperate, and that the entire network is under the same
top administration. Are there limitations that stem from this 'world
node' presupposition? As discussed in [13], the Internet is no
longer a clean hierarchy and there is a lot of resistance to having
any sort of 'ultimate authority' controlling or even brokering
communication.
PNNI is the first deployed example of a routing protocol that uses
abstract map exchange (as opposed to distance vector or link state
mechanisms) for inter-domain routing information exchange. One
consequence of this is that domains need not all use the same
mechanism for map creation. What were the results of this
abstraction and source based route calculation mechanism?
Since the authors of this document do not have experience running a
PNNI network, the comments above are from a theoretical perspective.
Information on these issues, and any other relevant issues, is
solicited from those who do have such operational experience. Any
volunteers?
2.4 ISO
Note: [At IETF52, a presentation on this draft was made to the IETF
routing group was made. I was reminded that ISO had already tackled
this problem as well, and that their efforts should be reviewed as
well. That work is pending. Any volunteers to write this section?]
2.5 Recent Research Work
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2.5.1 Developments in Internet Connectivity
The recent work commissioned from Geoff Huston by the Internet
Architecture Board [13] draws a number of conclusions from analysis
of BGP routing tables and routing registry databases:
- The connectivity between provider ASs is becoming more like a
dense mesh than the tree structure that was commonly assumed to be
commonplace a couple of years ago. This has been driven by the
increasing amounts charged for peering and transit traffic by
global service providers. Local direct peering and internet
exchanges are becoming steadily more common as the cost of local
fibre connections drops.
- End user sites are increasingly resorting to multi-homing onto two
or more service providers as a way of improving resiliency. This
has a knock-on effect of spectacularly fast depletion of the
available pool of AS numbers as end user sites require public AS
numbers to become multi-homed and corresponding increase in the
number of prefixes advertised in BGP.
- Multi-homed sites are using advertisement of longer prefixes in
BGP as a means of traffic engineering to load spread across their
multiple external connections with further impact on the size of
the BGP tables.
- Operational practices are not uniform, and in some cases lack of
knowledge or training is leading to instability and/or excessive
advertisement of routes by incorrectly configured BGP speakers.
- All these factors are quickly negating the advantages in limiting
the expansion of BGP routing tables that were gained by the
introduction of CIDR and consequent prefix aggregation in BGP. It
is also now impossible for IPv6 to realize the world view in which
the default free zone would be limited to perhaps 10,000 prefixes.
- The typical 'width' of the Internet in AS hops is now around five,
and much less in many cases.
These conclusions have a considerable impact on the requirements for
the future domain routing architecture:
- Topological hierarchy (e.g. mandating a tree structured
connectivity) cannot be relied upon to deliver scalability of a
large Internet routing system
- Aggregation cannot be relied upon to constrain the size of routing
tables for an all-informed routing system
2.5.2 Defending the End To End Principle
DARPA is funding a project to think about a new architecture for
future generation Internet, called NewArch
(http://www.isi.edu/newarch/). Work started in the first half of
2000 but the published results are limited.
The main development so far is to conclude that as the Internet
becomes mainstream infrastructure, fewer and fewer of the
requirements are truly global but may apply with different force or
not at all in certain parts of the network. This (it is claimed)
makes the compilation of a single, ordered list of requirements
deeply problematic. Instead we may have to produce multiple
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requirement sets with support for differing requirement importance at
different times and in different places. This 'meta-requirement'
significantly impacts architectural design.
Potential new technical requirements identified so far include:
- Commercial environment concerns such as richer inter-provider
policy controls and support for a variety of payment models
- Trustworthiness
- Ubiquitous mobility
- Policy driven self-organisation ('deep auto configuration')
- Extreme short-time-scale resource variability
- Capacity allocation mechanisms
- Speed, propagation delay and Delay/BandWidth Product issues
Non-technical or political 'requirements' include:
- Legal and Policy drivers such as
o Privacy and free/anonymous speech
o Intellectual property concerns
o Encryption export controls
o Law enforcement surveillance regulations
o Charging and taxation issues
- Reconciling national variations and consistent operation in a
world wide infrastructure
One of the participants in this work (Dave Clark) with one of his
associates has also published a very interesting paper analyzing the
impact of some of these new requirements on the end-to-end principle
that has guided the development of the Internet to date [32]. Their
primary conclusion is that the loss of trust between the users at the
ends of end to end has the most fundamental effect on the Internet.
This is clear in the context of the routing system, where operators
are unwilling to reveal the inner workings of their networks for
commercial reasons. Similarly, trusted third parties and their
avatars (mainly mid-boxes of one sort or another) have a major impact
on the end-to-end principles and the routing mechanisms that went
with them. Overall, the end to end principles should be defended so
far as is possible - some changes are already too deeply embedded to
make it possible to go back to full trust and openness - at least
partly as a means of staving off the day when the network will ossify
into an unchangeable form and function (much as the telephone network
has done). The hope is that by that time a new Internet will appear
to offer a context for unfettered innovation.
3. Existing problems of BGP and the current EGP/IGP Architecture
Although most of the people who have to work with BGP today believe
it to be a useful, working protocol, discussions have brought to
light a number of areas where BGP or the relationship between BGP and
the IGPs in use today could be improved. This section is, to a large
extent, a wish list for the future domain routing architecture based
on those areas where BGP is seen to be lacking, rather than simply a
list of problems with BGP. The shortcomings of today's inter-domain
routing system have also been extensively surveyed in 'Architectural
Requirements for Inter-Domain Routing in the Internet' [13],
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particularly with respect to its stability and the problems produced
by explosions in the size of the Internet.
3.1 BGP and Auto-aggregation
The stability and later linear growth rates of the number of routing
objects (prefixes) that was achieved by the introduction of CIDR
around 1994, has now been once again been replaced by near-
exponential growth of number of routing objects. The granularity of
many of the objects advertised in the default free zone is very small
(prefix length of 22 or longer): This granularity appears to be a
by-product of attempts to perform precision traffic engineering
related to increasing levels of multi-homing. At present there is no
mechanism in BGP that would allow an AS to aggregate such prefixes
without advance knowledge of their existence, even if it was possible
to deduce automatically that they could be aggregated. Achieving
satisfactory auto-aggregation would also significantly reduce the
non-locality problems associated with instability in peripheral ASs.
On the other hand, it may be that alterations to the connectivity of
the net as described in [13] and Section 2.5.1 may limit the
usefulness of auto-aggregation
3.2 Convergence and Recovery Issues
BGP today is a stable protocol under most circumstances but this has
been achieved at the expense of making the convergence time of the
inter-domain routing system very slow under some conditions. This
has a detrimental effect on the recovery of the network from
failures.
The timers that control the behavior of BGP are typically set to
values in the region of several tens of seconds to a few minutes,
which constrains the responsiveness of BGP to failure conditions.
In the early days of deployment of BGP, poor network stability and
router software problems lead to storms of withdrawals closely
followed by re-advertisements of many prefices. To control the load
on routing software imposed by these 'route flaps', route flap
damping was introduced into BGP. Most operators have now implemented
a degree of route flap damping in their deployments of BGP. This
restricts the number of times that the routing tables will be rebuilt
even if a route is going up and down very frequently. Unfortunately,
the effect of route flap damping is exponential in its behavior that
can result in some parts of the Internet being inaccessible for hours
at a time.
There is evidence ([13] and our own measurements - results yet to be
published) that in today's network route flap is disproportionately
associated with the fine grain prefices (length 22 or longer)
associated with traffic engineering at the periphery of the network.
Auto-aggregation as previously discussed would tend to mask such
instability and prevent it being propagated across the whole network.
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Another question that needs to be studied is the continuing need for
an architecture that requires global convergence. Some of our
studies (yet to be published) show that, in some localities at least,
the network never actually reaches stability; i.e. never really
globally converges. Can a global, and beyond, network be designed
with the requirement of global convergence?
3.3 Non-locality of Effects of Instability and Misconfiguration
There have been a number of instances, some of which are well
documented of a mistake in BGP configuration in a single peripheral
AS propagating across the whole Internet and resulting in misrouting
of most of the traffic in the Internet.
Similarly, route flap in a single peripheral AS can require route
table recalculation across the entire Internet.
This non-locality of effects is highly undesirable, and it would be a
considerable improvement if such effects were naturally limited to a
small area of the network around the problem. This is another
argument for an architecture that does not require global
convergence.
3.4 Multihoming Issues
As discussed previously, the increasing use of multi-homing as a
robustness technique by peripheral ASs requires that multiple routes
have to be advertised for such domains. These routes must not be
aggregated close in to the multi-homed domain as this would defeat
the traffic engineering implied by multi-homing and currently cannot
be aggregated further away from the multi-homed domain due to the
lack of auto-aggregation capabilities. Consequentially the default
free zone routing table is growing exponentially, as it was before
CIDR.
The longest prefix match routing technique introduced by CIDR, and
implemented in BGP4, when combined with provider address allocation
is an obstacle to effective multi-homing if load sharing across the
multiple links is required: If an AS has been allocated its
addresses from an upstream provider, the upstream provider can
aggregate those addresses with those of other customers and need only
advertise a single prefix for a range of customers. But, if the
customer AS is also connected to another provider, the second
provider is not able to aggregate the customer addresses because they
are not taken from his allocation, and will therefore have to
announce a more specific route to the customer AS. The longest match
rule will then direct all traffic through the second provider, which
is not as required.
Example:
AS3 has received its addresses from AS1, which means AS1 can
aggregate. But if AS3 want its traffic to be seen equally both
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ways, AS1 is forced to announce both the aggregate and the more
specific route to AS3.
\ /
AS1 AS2
\ /
AS3
This problem has induced many ASs to apply for their own address
allocation even though they could have been allocated from an
upstream provider further exacerbating the default free zone route
table size explosion. This problem also interferes with the desire of
many providers in the default free zone to route only prefixes that
are equal to or shorter than 20 or 19 bits.
Note that some problems which are referred to as multihoming issues
are not and should not solvable through the routing system (e.g.
where a TCP load distributor is needed), and multihoming is not a
panacea for the general problem of robustness in a routing
system [38].
3.5 AS-number exhaustion
The domain identifier or AS-number is a 16-bit number. Allocation of
AS-numbers is currently increasing 51% a year [13] with the result
that exhaustion is likely around 2005. The IETF is currently studying
proposals to increase the available range of AS-numbers to 32 bits,
but this will present a deployment challenge during transition.
3.6 Partitioned AS's
Tricks with discontinuous ASs are used by operators, for example, to
implement anycast. Discontinuous ASs may also come into being by
chance if a multi-homed domain becomes partitioned as a result of a
fault and part of the domain can access the Internet through each
connection. It may be desirable to make support for this kind of
situation more transparent than it is at present.
3.7 Load Sharing
Load splitting or sharing was not a goal of the original designers of
BGP and it is now a problem for today's network designers and
managers. Trying to fool BGP into load sharing between several links
is a constantly recurring exercise for most operators today. Traffic
engineering extensions to the future domain routing architecture that
will facilitate load sharing should be considered.
3.8 Hold down issues
As with the interval between 'hello' messages in OSPF, the typical
size and defined granularity (seconds to tens of seconds) of the
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'keep-alive' time negotiated at start-up for each BGP connection
constrains the responsiveness of BGP to link failures.
The recommended values and the available lower limit for this timer
were set to limit the overhead caused by keep-alive messages when
link bandwidths were typically much lower than today. Analysis and
experiment ([14], [15] & [33]) indicate that faster links could
sustain a much higher rate of keep-alive messages without
significantly impacting normal data traffic. This would improve
responsiveness to link and node failures but with a corresponding
increase in the risk of instability, if the error characteristics of
the link are not taken properly into account when setting the
keep-alive interval.
An additional problem with the hold-down mechanism in BGP is the
amount of information that has to be exchanged to re-establish the
database of route advertisements on each side of the link when it is
re-established after a failure. Currently any failure, however brief
forces a full exchange which could perhaps be constrained by
retaining some state across limited time failures and using revision
control, transaction and replication techniques to re-synchonise the
databases. Various techniques have been implemented to try to reduce
this problem but they have not yet been standardised.
3.9 Interaction between Inter domain routing and intra domain routing
Today, many operators' backbone routers run both I-BGP and an IGP
maintain the routes that reach between the borders of the domain.
Exporting routes from BGP into IGP and bringing them back up to BGP
is not recommended [29], but it is still necessary for all backbone
routers to run both protocols. BGP is used to find the egress point
and IGP to find the path (next hop router) to the egress point across
the domain. This is not only a management problem but may also create
other problems:
- BGP is a distance vector protocol, as compared with most IGPs,
which are link state protocols, and as such it is not optimised
for convergence speed although they generally require less
processing power. Incidentally, more efficient distance vector
algorithms are available such as [34].
- The metrics used in BGP and the IGP are rarely comparable or
combinable. Whilst there are arguments that the optimizations
inside a domain may be different from those for end-to-end paths,
there are occasions, such as calculating the 'topologically
nearest' server when computable or combinable metrics would be of
assistance.
- The policies that can be implemented using BGP are designed for
control of traffic exchange between operators, not for controlling
paths within a domain. Policies for BGP are most conveniently
expressed in RPSL and this could be extended if thought desirable
to include additional policy information.
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- If the NEXT HOP destination for a set of BGP routes becomes
inaccessible because of IGP problems, the routes using the
vanished next hop have to be invalidated at the next available
UPDATE. Subsequently, if the next hop route reappears, this would
normally lead to the BGP speaker requesting a full table from its
neighbour(s). Current implementations may attempt to circumvent
the effects of IGP route flap by caching the invalid routes for a
period in case the next hop is restored.
- Synchronization between IGP and EGP is a problem as long as we use
different protocols for IGP and EGP, which will most probably be
the case even in the future because of the differing requirements
in the two situations. Some sort of synchronization between those
two protocols would be useful. In the draft 'OSPF Transient
Blackhole Avoidance' [22], the IGP side of the story is covered.
- Synchronizing in BGP means waiting for the IGP to know about the
same networks as the EGP, which can take a significant period of
time and slows down the convergence of BGP by adding the IGP
convergence time into each cycle.
3.10Policy Issues
There are several classes of issue with current BGP policy:
- Policy is installed in an ad-hoc manner in each autonomous
system. There isn't a method for ensuring that the policy
installed in one router is coherent with policies installed in
other routers.
- As described in Griffin [12] and in McPherson [20] it is
possible to create policies for ASs, and instantiate them in
routers, that will cause BGP to fail to converge in certain
types of topology
- There is no available network model for describing policy in a
coherent manner.
Policy management is extremely complex and mostly done without the
aid of any automated procedures. The extreme complexity means that a
highly qualified specialist is required for policy management of
border routers. The training of these specialists is quite lengthy
and needs to involve long periods of hands-on experience. There is,
therefore, a shortage of qualified staff for installing and
maintaining the routing policies. Also many training courses cover
only the basic configuration aspects and do not cover policy issues.
3.11Security Issues
While many of the issues with BPG security have been traced either to
implementation issues or to operational issues, BGP is vulnerable to
DDOS attacks. Additionally routers can be used as unwitting
forwarders in DDOS attacks on other systems.
Though DDOS attacks can be fought in a variety of ways, most
filtering methods, it is takes constant vigilance. There is nothing
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in the current architecture or in the protocols that serves to
protect the forwarders from these attacks.
3.12Support of MPLS and VPNS
Recently BGP has been modified to function as a signaling protocol
for MPLS and for VPNs [16]. Some people see this over-loading of
the BGP protocol as a boon whilst others see it as a problem. While
it was certainly convenient as a vehicle for vendors to deliver extra
functionality for to their products, it has exacerbated some of the
performance and complexity issues of BGP. Two important problems are,
the additional state that must be retained and refreshed to support
VPN tunnels and that BGP does not provide end-to-end notification
making it difficult to confirm that all necessary state has been
installed or updated.
In creating the future domain routing architecture, serious
consideration must be given to the argument that VPN signaling
protocols should remain separate from the route determination
protocols.
3.13IPv4 / IPv6 Ships in the Night
The fact that service providers would need to maintain two completely
separate networks; one for IPv4 and one for IPv6 has been a real
hindrance to the introduction of IPv6. When IPv6 does get widely
deployed it will do so without causing the disappearance of IPv4.
This means that unless something is done, service providers would
need to maintain the two networks in, relative, perpetuity.
It is possible to use a single set of BGP speakers with multiprotocol
extensions [37] to exchange information about both IPv4 and IPv6
routes between domains, but the use of TCP as the transport protocol
for the information exchange results in an asymmetry when choosing to
use one of TCP over IPv4 or TCP over IPv6. Successful information
exchange confirms one of IPv4 or IPv6 reachability between the
speakers but not the other, making it possible that reachability is
being advertised for a protocol for which it is not present.
Also, current implementations do not allow a route to be advertised
for both IPv4 and IPv6 in the same UPDATE message, because it is not
possible to explicitly link the reachability information for an
address family to the corresponding next hop information. This could
be improved, but currently results in independent UPDATEs being
exchanged for each address family.
3.14Existing Tools to Support Effective Deployment of Inter-Domain
Routing
The tools available to network operators to assist in configuring and
maintaining effective inter-domain routing in line with their defined
policies are limited, and almost entirely passive.
For example:
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- There are no tools to facilitate the planning of the routing of a
domain (either intra- or inter-domain); there are a limited number
of display tools that will visualize the routing once it has been
configured
- There are no tools to assist in converting business policy
specifications into the RPSL language; there are limited tools to
convert the RPSL into BGP commands and to check, post-facto, that
the proposed policies are consistent with the policies in adjacent
domains (always provided that these have been revealed and
accurately documented).
- There are no tools to monitor BGP route changes in real time and
warn the operator about policy inconsistencies and/or
instabilities.
The following section summarises the tools that are available to
assist with the use of RPSL. Note they are all batch mode tools used
off-line from a real network. These tools will provide checks for
skilled inter-domain routing configurers but limited assistance for
the novice.
3.14.1 Routing Policy Specification Language RPSL (RFC 2622, 2650) and
RIPE NCC Database (RIPE 157)
Routing Policy Specification Language RPSL enables a network operator
to describe routes, routers and autonomous systems ASs that are
connected to the local AS.
Using the RPSL language a distributed database is created to describe
routing policies in the Internet as described by each AS
independently. The database can be used to check the consistency of
routing policies stored in the database.
Tools exist (RIPE 81, 181, 103) that can be applied on the database
to answer requests of the form, e.g.
- Flag when two neighboring network operators specify conflicting or
inconsistent routing information exchanges with each other and
also detect global inconsistencies where possible;
- Extract all AS-paths between two networks that are allowed by
routing policy from the routing policy database; display the
connectivity a given network has according to current policies.
The database queries enable a partial static solution to the
convergence problem. They analyze routing policies of very limited
part of Internet and verify that they do not contain conflicts that
could lead to protocol divergence. The static analysis of convergence
of the entire system has exponential time complexity, so
approximation algorithms would have to be used.
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4. References
The following were consulted in the writing of this document. Not
all are specifically referred to in the document, but all helped in
forming this work. These references are not intended as normative.
[1] Clark, D., "Policy Routing in Internet
Protocols", RFC 1102, May 1989.
[2] Estrin, D., "Requirements for Policy Based
Routing in the Research Internet", RFC 1125,
November 1989.
[3] Steenstrup, M,. "An Architecture for Inter-Domain
Policy Routing", RFC 1478, June 1993
[4] Little, M., "Goals and Functional Requirements
for Inter-Autonomous System Routing", RFC 1126,
July 1989.
[5] Perlman, R., "Interconnections Second Edition",
1999, Addison Wesley Longman, Inc.
[6] Perlman, R., "Network Layer Protocols with
Byzantine Robust-ness", Ph.D. Thesis, Department
of Electrical Engineering and Computer Science,
MIT, August 1988.
[7] Castineyra, I., Chiappa, N., Steenstrup, M., "the
Nimrod Routing Architecture", RFC1992, Aug 1996
[8] Chiappa, N., "IPng Technical Requirements of the
Nimrod Routing and Addressing Architecture", RFC
1753, Dec 1994
[9] Chiappa, N., "A New IP Routing and Addressing
Architecture"
[10] Wroclowski, J., The Metanet White Paper -
Workshop on Research Directions for the Next
Generation Internet, 1995
[11] Labovitz, C., Ahuja, A., Farnam J., Bose, A.,
Experimental Measurement of Delayed Convergence,
NANOG
[12] Griffin, T.G., Wilfong, G., An Analysis of BGP
Convergence Properties, SIGCOMM 1999
[13] Huston, G., Commentary on Inter-Domain Routing in
the Internet,RFC 3221, Dec 2001
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[14] Alaettinoglu, C., Jacobson, V. and Yu, H, ,
Towards Milli-Second IGP Convergence, Internet
Draft - draft-alaettinoglu-isis-convergence-00,
Nov 2000 Work in Progress
[15] Sandick, H., Squire, M., Cain, B., Duncan, I.,
Haberman, B., Fast LIveness Protocol (FLIP),
Internet Draft - draft-sandiick-flip-00,
Feb 2000, Work in Progress
[16] Rosen, E. and Rekhter, Y., BGP/MPLS VPNs,
RFC2547, March 1999
[17] Clark, D., Chapin, L., Cerf, V., Braden, R.,
Hobby, R., "towards the Future Internet
Architecture", RFC1287, December 1991
[18] Jacobson, V., Nichols, K. and Poduri, K., The
'Virtual Wire' Behavior Aggregate, Internet Draft
- draft-ietf-diffserv-pdb-vw-00, July 2000, Work
in Progress
[19] Seddigh, N., Nandy, B., and Heinanen, J.,
An Assured Rate Per-Domain Behaviour for
Differentiated Services, Internet Draft -
draft-ietf-diffserv-pdb-ar-00, Feb 2001, Work in
Progress
[20] McPherson, D., Gill, V., Walton, D. and Retana,
A., "BGP Persistent Route Oscillation Condition",
Internet Draft - draft-mcpherson-bgp-route-
oscillation-00, Dec 2000, Work in Progress
[21] Hain, T, "Architectural Implications of NAT", RFC
2993, November 2000
[22] McPherson, D. and Przygienda, T., OSPF Transient
Blackhole Avoidance, Internet Draft - draft-
mcpherson-ospf-transient-00, July 2000 Work In
Progress
[23] Thaler, D., Estrin, D. and Meyer, D. (editors),
Border Gateway Multicast Protocol (BGMP):
Protocol Specification, Internet Draft - draft-
ietf-bgmp-spec-02, Nov 2000 Work in progress
[24] Rosen, E. Et al., Multiprotocol Label Switching
Architecture, RFC 3031
[25] Ashwood-Smith, P. Et al., Generalized MPLS -
Signaling Functional Description, Internet Draft
- draft-ietf-mpls-generalized-signaling-01.txt,
Work in progress
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[26] IETF Resource Allocation Protocol working group,
http://www.ietf.org/html.charters/rap-
charter.html
[27] IETF Configuration management with SNMP working
group,
http://www.ietf.org/html.charters/snmpconf-
charter.html
[28] IETF Policy working group,
http://www.ietf.org/html.charters/policy-
charter.html
[29] Yu J., "Scalable Routing Design Principles", RFC
2791
[30] Telcordia Technologies Netsizer web site
http://www.netsizer.com/
[31] Inference of Shared Risk Link Groups,
draft-many-inference-srlg-00.txt,
Work in progress
[32] Blumenthal, Marjory S. and Clark, David D.,
Rethinking the design of the Internet:
The end to end arguments vs. the brave new world,
May 2001,
http://ana-www.lcs.mit.edu/anaweb/papers.html
[33] Lang et al, Link Management Protocol,
draft-lang-mpls-lmp-02.txt,
Work in progress
[34] Xu, Z., Dai, S. and Garcia-Luna-Aceves, J.J.,
A More Efficient Distance Vector Routing
Algorithm, Proc. IEEE MILCOM 97, Monterey,
California, November 2-5, 1997,
http://www.cse.ucsc.edu/research/ccrg/
publications/zhengyu.milcom97.pdf
[35] Bradner, S. and Mankin, A., "The Recommendation
for the IP Next Generation Protocol", RFC 1752,
January 1995.
[36] ISO/IEC, "Protocol for Exchange of Inter-Domain
Routeing Information among Intermediate
Systems to support Forwarding of ISO 8473 PDUs",
International Standard 10747,
ISO/IEC JTC 1,Switzerland 1993
[37] Bates, T., Rekhter, Y., Chandra, R. and Katz, D,
"Multiprotocol Extensions to BGP-4",
RFC2858, June 2000
Group B Expires: September 2002 29
INTERNET DRAFT IDR History February, 2002
[38] Berkowitz, H. and Krioukov, D, "To Be Multihomed:
Requirements and Definitions",
draft-berkowitz-multirqmt-02.txt,
Work in progress.
[39] Ferguson, P. and Berkowitz, H. "Network
Renumbering Overview: Why would I want it and
what is it anyway?", RFC2071, January 1997
[40] Berkowitz, H., "Router Renumbering Guide",
RFC2072, January 1997
[41] [FDR-REQS] Doria (ed), draft-groupb-irtf-rr-reqs-
00.txt, work in progress
5. Author's Addresses
Elwyn Davies
Nortel Networks
London Road
Harlow, Essex CM17 9NA
UK
Phone: +44-1279-405498
Email: elwynd@nortelnetworks.com
Avri Doria
Div. of Computer Communications
Lulea University of Technology
S-971 87 Lulea
Sweden
Phone: (+46) 920 46 3030
Email: avri@sm.luth.se
Howard Berkowitz
Gett Communications
5012 25th Street South
Arlington, VA 22206
USA
Phone +1 703 998 5819
Email: hcb@gettcomm.com
Dmitri Krioukov
Nortel Networks
2325 Dulles Corner Boulevard
11th Floor
Herndon
VA 20171, USA
Phone: +1 571 331 1104
Email: dima@krioukov.net
Group B Expires: September 2002 30
INTERNET DRAFT IDR History February, 2002
Malin Carlzon
Royal Institute of Technology
Network Operating Centre
KTHNOC
SE-100 44 Stockholm
Sweden
Phone: +46 70 269 6519
Email: malin@sunet.se
Anders Bergsten
Telia Research AB
Aurorum 6
S-977 75 Lulea
Sweden
Phone: +46 920 754 50
Email: anders.p.bergsten@telia.se
Olle Pers
Telia Research AB
S- 123 86 Farsta
Sweden
Phone: +46 8 713 8182
Email: olle.k.pers@telia.se
Yong Jiang
Telia Research AB
S- 123 86 Farsta
Sweden
Phone: +46 8 713 8125
Email: yong.b.jiang@telia.se
Lenka Carr Motyckova
Div. of Computer Communications
Lulea University of Technology
S-971 87 Lulea
Sweden
Phone: +46 920 91769
Email: lenka@sm.luth.se
Pierre Fransson
Div. of Computer Communications
Lulea University of Technology
S-971 87 Lulea
Sweden
Phone: +46 70 646 0384
Email: pierre@cdt.luth.se
Olov Schelen
Div. of Computer Communications
Lulea University of Technology
S-971 87 Lulea
Sweden
Phone: +46 70 536 2030
Email: Olov.Schelen@cdt.luth.se
Group B Expires: September 2002 31
INTERNET DRAFT IDR History February, 2002
Tove Madsen
Utfors Bredband AB
R
sundavgen 12
P.O. Box 525
SE-169 29 Solna
Sweden
Phone: +46 8 5270 5040
Email: tove.madsen@utfors.se
Group B Expires: September 2002 32
Datatracker
draft-irtf-routing-history-00
Internet-Draft
