Network Working Group A. Doria
Internet-Draft ETRI
Expires: January 17, 2005 E. Davies
Nortel Networks
July 19, 2004
Analysis of IDR requirements and History
draft-irtf-routing-history-01.txt
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Abstract
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 version 03 of the inter-domain routing
requirements draft [41], which is a discussion of requirements for
the future routing architecture and future routing protocols.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Historical Perspective . . . . . . . . . . . . . . . . . . . 4
2.1 The legacy of RFC1126 . . . . . . . . . . . . . . . . . . 4
2.1.1 "General Requirements" . . . . . . . . . . . . . . . . 5
2.1.2 "Functional Requirements" . . . . . . . . . . . . . . 7
2.1.3 "Non-Goals" . . . . . . . . . . . . . . . . . . . . . 14
2.2 Nimrod Requirements . . . . . . . . . . . . . . . . . . . 16
2.3 PNNI . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4 ISO . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.5 Recent Research Work . . . . . . . . . . . . . . . . . . . 18
2.5.1 Developments in Internet Connectivity . . . . . . . . 18
2.5.2 Defending the End To End Principle . . . . . . . . . . 19
3. Existing problems of BGP and the current EGP/IGP
Architecture . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1 BGP and Auto-aggregation . . . . . . . . . . . . . . . . . 21
3.2 Convergence and Recovery Issues . . . . . . . . . . . . . 21
3.3 Non-locality of Effects of Instability and
Misconfiguration . . . . . . . . . . . . . . . . . . . . . 22
3.4 Multihoming Issues . . . . . . . . . . . . . . . . . . . . 22
3.5 AS-number exhaustion . . . . . . . . . . . . . . . . . . . 23
3.6 Partitioned AS's . . . . . . . . . . . . . . . . . . . . . 24
3.7 Load Sharing . . . . . . . . . . . . . . . . . . . . . . . 24
3.8 Hold down issues . . . . . . . . . . . . . . . . . . . . . 24
3.9 Interaction between Inter domain routing and intra
domain routing . . . . . . . . . . . . . . . . . . . . . . 25
3.10 Policy Issues . . . . . . . . . . . . . . . . . . . . . 26
3.11 Security Issues . . . . . . . . . . . . . . . . . . . . 26
3.12 Support of MPLS and VPNS . . . . . . . . . . . . . . . . 26
3.13 IPv4 / IPv6 Ships in the Night . . . . . . . . . . . . . 27
3.14 Existing Tools to Support Effective Deployment of
Inter-Domain Routing . . . . . . . . . . . . . . . . . . 27
3.14.1 Routing Policy Specification Language RPSL (RFC
2622, 2650) and RIPE NCC Database (RIPE 157) . . . . 28
4. Security Considerations . . . . . . . . . . . . . . . . . . 28
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 29
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 32
Intellectual Property and Copyright Statements . . . . . . . 33
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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
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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
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.
Since the original version of this draft was published a number of
the initiatives mentioned (such as the DARPA NewArch project
described in Section 2.5.2) have continued researching the way
forwards for the Internet. There have also been continuing efforts
in the IETF multi6 working group to resolve the problems of
multihoming especially in IPv6. Some of the explosive growth of the
routing tables has been quenched by the economic downturn since the
end of 2000, but this has not resolved the problems that existed with
inter-domain routing. The contents of this draft remain relevant to
the Internet today and the intention is to provide further updates to
document the research efforts that have been going on over the last
couple of years.
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:
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Explanation: Optional 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].
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.
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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 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.
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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 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"
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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.
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
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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"
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.
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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
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locations to minimise the cost of routing if
bandwidth is cheaper than processing.
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.
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Current practice: BGP-4 allows for arbitrary interconnections.
2.1.2.5 "General Objectives"
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"
Relevance: 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.
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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?
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.
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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.
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
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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
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.
- 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
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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
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?
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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 long time ago now 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 still pending a year later.
Any volunteers to write this section?]
2.5 Recent Research Work
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.
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- 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. When this draft was originally published, work was only just
getting under way and little in the way of results had been
published. Since then significant work has been done both on
addressing architectures and a novel routing paradigm.
The main conclusion of the the initial work was 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
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 included:
- 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
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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.
In line with a number of other research and discussion streams, the
NewArch project appears to be embracing the necessity of separating
the locator and identifier functions of today's IP addresses with the
resultant consequences for the inter-domain routing system. A number
of interesting papers have now been published covering possible
modifications to the addressing architecture (FARA) and an
alternative inter-domain routing scheme (NIRA). Pointers to these
papers can be found on the NewArch website.
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],
particularly with respect to its stability and the problems produced
by explosions in the size of the Internet.
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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.
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Auto-aggregation as previously discussed would tend to mask such
instability and prevent it being propagated across the whole network.
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
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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 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].
Since the original publication of this draft the IETF multi6 working
group has been struggling to determine how to provide a mechanism to
allow multihoming with IPv6 while maintaining the beneficial effects
that strict provider addressing brings to the size of the core
routing tables. The process has been long and difficult and a full
resolution is not yet in sight. The main conclusion has been, as
with the NewArch group, that the locator and identifier functions of
the IP address will need to be decoupled which was one of the major
proposals of the Nimrod project Section 2.2. One major difficulty is
that it is not clear how to solve the problem in such a way that the
basic structure of IP in general and IPv6 in particular is not
compromised. Many of the proposals considered effectively provide an
overlay on IP which may not be the most desirable solution but the
alternatives might mean designing yet another new version of IP
before IPv6 has been fully deployed.
3.5 AS-number exhaustion
The domain identifier or AS-number is a 16-bit number. Allocation of
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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
'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
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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.
- 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.
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3.10 Policy 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.
3.11 Security 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
in the current architecture or in the protocols that serves to
protect the forwarders from these attacks.
3.12 Support 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.
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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.
3.13 IPv4 / 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.
3.14 Existing 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.
- 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).
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- 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.
4. Security Considerations
As this is an informational draft on the history of requirements in
IDR and on the problems facing the current Internet IDR architecture,
it does not as such create any security problems. On the other hand,
some of the problems with today's Internet routing architecture do
create security problems and these have been discussed in the text
above.
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5. Acknowledgments
The draft is derived from work originally produced by Babylon.
Babylon was a loose association of individuals from academia, service
providers and vendors whose goal was to discuss issues in Internet
routing with the intention of finding solutions for those problems.
The individual members who contributed materially 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 and others 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 Ahlstrom, Erik Aman, Thomas
Eriksson, Niklas Borg, Nigel Bragg, Thomas Chmara, Krister Edlund,
Owe Grafford, Torbjorn 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, any errors, glaring omissions or misunderstandings.
6 References
[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, Nov 1989.
[3] Steenstrup, M., "An Architecture for Inter-Domain Policy
Routing", RFC 1478, Jun 1993.
[4] Little, M., "Goals and Functional Requirements for
Inter-Autonomous System Routing", RFC 1126, Jul 1989.
[5] Perlman, R., "Interconnections Second Edition", Addison Wesley
Longman Inc., 1999.
[6] Perlman, R., "Network Layer Protocols with Byzantine
Robust-ness", Ph.D Thesis, Department of Electrical Engineering
and Computer Science, MIT, Aug 1988.
[7] Castineyra, I., Chiappa, N. and M. Steenstrup, "the Nimrod
Routing Architecture", RFC 1992, Aug 1996.
Doria & Davies Expires January 17, 2005 [Page 29]
Internet-Draft IDR History July 2004
[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"",
, 2002.
[10] Wroclowski, J., "The Metanet White Paper - Workshop on Research
Directions for the Next Generation Internet", , 1995.
[11] Labovitz, C., Ahuja, A., Farnam, J. and A. Bose, "Experimental
Measurement of Delayed Convergence", NANOG , 2002.
[12] Griffin, T. and G. Wilfong, "An Analysis of BGP Convergence
Properties", , 1999.
[13] Huston, G., "Commentary on Inter-Domain Routing in the
Internet,RFC 3221", , Dec 2001.
[14] Alaettinoglu, C., Jacobson, V. and H. Yu, "",
draft-alaettinoglu-isis-convergence-00 (work in progress), Nov
2000.
[15] Sandick, H., Squire, M., Cain, B., Duncan, I. and B. Haberman,
"Fast LIveness Protocol (FLIP)", draft-sandick-flip-00 (work in
progress), Feb 2000.
[16] Rosen, E. and Y. Rekhter, "BGP/MPLS VPNs", RFC 2547, Mar 1999.
[17] Clark, D., Chapin, L., Cerf, V., Braden, R. and R. Hobby,
"towards the Future Internet Architecture", RFC 1287, Dec 1991.
[18] Jacobson, V., Nichols, K. and K. Poduri, "The 'Virtual Wire'
Behavior Aggregate", draft-ietf-diffserv-pdb-vw-00 (work in
progress), Jul 2000.
[19] Seddigh, N., Nandy, B. and J. Heinanen, "An Assured Rate
Per-Domain Behaviour for Differentiated Services",
draft-ietf-diffserv-pdb-ar-00 (work in progress), Feb 2001.
[20] McPherson, D., Gill, V., Walton, D. and A. Retana, "BGP
Persistent Route Oscillation Condition", RFC 3345, Aug 2002.
[21] Hain, T., "Architectural Implications of NAT", RFC 2993, Nov
2000.
[22] McPherson, D. and T. Przygienda, "OSPF Transient Blackhole
Avoidance", draft-mcpherson-ospf-transient-00 (work in
progress), Jul 2000.
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[23] Thaler, D., Estrin, D. and D. Meyer, "Border Gateway Multicast
Protocol (BGMP): Protocol Specification",
draft-ietf-bgmp-spec-06 (work in progress), Nov 2000.
[24] Rosen, E., "Multiprotocol Label Switching Architecture", RFC
3031, 2004.
[25] Ashwood-Smith, P., "Generalized MPLS - Signaling Functional
Description", draft-ietf-mpls-generalized-signaling-09 (work in
progress), 2002.
[26] "IETF Resource Allocation Protocol working group", , 2002,
<http://www.ietf.org/html.charters/rap-charter.html>.
[27] "IETF Configuration management with SNMP working group", ,
2002,
<http://www.ietf.org/html.charters/snmpconf-charter.html>.
[28] "IETF Policy working group", , 2002,
<http://www.ietf.org/html.charters/policy-charter.html>.
[29] Yu, J., "Scalable Routing Design Principles", RFC 2791, 2002.
[30] "Telcordia Technologies Netsizer web site
http://www.netsizer.com/", , 2002.
[31] "Inference of Shared Risk Link Groups",
draft-many-inference-srlg-02 (work in progress), 2001.
[32] Blumenthal, M. and D. Clark, "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, "Link Management Protocol", draft-lang-mpls-lmp-02 (work
in progress), 2000.
[34] Xu, Z., Dai, S. and J. Garcia-Luna-Aceves, "A More Efficient
Distance Vector Routing Algorithm", Proc IEEE MILCOM 97,
Monterey, California, Nov 1997,
<http://www.cse.ucsc.edu/research/ccrg/publications/zhengyu.milcom97.pdf>
.
[35] Bradner, S. and A. Mankin, "The Recommendation for the IP Next
Generation Protocol", RFC 1752, Jan 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 , 1993.
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[37] Bates, T., Rekhter, Y., Chandra, R. and D. Katz, "Multiprotocol
Extensions to BGP-4", RFC 2858, Jun 2000.
[38] Berkowitz, H. and D. Krioukov, "To Be Multihomed: Requirements
and Definitions", draft-berkowitz-multirqmt-02 (work in
progress), 2002.
[39] Ferguson, P. and H. Berkowitz, "Network Renumbering Overview:
Why would I want it and what is it anyway?", RFC 2071, Jan
1997.
[40] Berkowitz, H., "Router Renumbering Guide", RFC 2072, Jan 1997.
[41] Doria, "Requirements for Inter-Domain Routing",
draft-irtf-routing-reqs-03 (work in progress), 2004.
Authors' Addresses
Avri Doria
ETRI
161 Gajeong-dong
Yuseong-gu
Daejeon 305-350
Korea
Phone: +1 401 663 5024
EMail: avri@acm.org
Elwyn B. Davies
Nortel Networks
Harlow Laboratories
London Road
Harlow, Essex CM17 9NA
UK
Phone: +44 1279 405 498
Fax: +44 1279 405 514
EMail: elwynd@nortelnetworks.com
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Internet-Draft IDR History July 2004
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