Internet DRAFT - draft-ietf-grow-rift
draft-ietf-grow-rift
INTERNET-DRAFT D. Meyer (Editor)
draft-ietf-grow-rift-01.txt
Category Informational
Expires: August 2004 February 2004
Operational Concerns and Considerations for Routing Protocol
Design -- Risk, Interference, and Fit (RIFT)
<draft-ietf-grow-rift-01.txt>
Status of this Document
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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The key words "MUST"", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC 2119].
This document is a product of the RIFT Design Team. Comments should
be addressed to the authors, or the mailing list at
grow@lists.uoregon.edu.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
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Abstract
The Risk, Interference, and Fit (RIFT) design team was formed to
document the concerns and considerations surrounding the use of
Internet routing protocols for functions not directly related to
routing of IP packets within the Internet and IP networks. This
document is the output of that activity.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Scope of this Work . . . . . . . . . . . . . . . . . . . . . . 5
3. Problem Statement. . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Risk, Interference, and Application Fit (RIFT) . . . . . . 6
3.1.1. Risk: Software Engineering . . . . . . . . . . . . . . . 7
3.1.2. Interference: Protocol Specification/Dynamic Behavior . 7
3.1.3. Application Fit: Distribution Topology . . . . . . . . . 7
4. Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Reachability Information. . . . . . . . . . . . . . . . . . 8
4.2. Layer 3 Routing Information . . . . . . . . . . . . . . . . 8
4.2.1. Standard Routing Information . . . . . . . . . . . . . . 9
4.3. Auxiliary (non-routing) Information . . . . . . . . . . . . 9
4.4. Address Family Identifier (AFI) . . . . . . . . . . . . . . 9
4.5. Subsequent Address Family Identifier (SAFI) . . . . . . . . 10
4.6. Network Layer Reachability. . . . . . . . . . . . . . . . . 10
4.7. Application . . . . . . . . . . . . . . . . . . . . . . . . 10
4.8. Routing Protocol. . . . . . . . . . . . . . . . . . . . . . 10
4.9. Fate Sharing. . . . . . . . . . . . . . . . . . . . . . . . 11
5. Architectural Models . . . . . . . . . . . . . . . . . . . . . 11
5.1. General Purpose Transport Infrastructure (GPT) Model. . . . 12
5.2. Special Purpose Transport Infrastructure (SPT) Model. . . . 12
6. Analyzing Risk and Interference. . . . . . . . . . . . . . . . 13
6.1. Risk: Code Impact, and Resource Sharing . . . . . . . . . . 13
6.1.1. Code Impact. . . . . . . . . . . . . . . . . . . . . . . 13
6.1.2. Resource Sharing . . . . . . . . . . . . . . . . . . . . 14
6.1.2.1. Resource Sharing and Operating System Level Issues . 14
6.2. Interference. . . . . . . . . . . . . . . . . . . . . . . . 15
7. GTP and SPT Models: Risk and Interference. . . . . . . . . . . 15
7.1. Risk. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1.1. Code Impact. . . . . . . . . . . . . . . . . . . . . . . 16
7.1.2. Resource Sharing . . . . . . . . . . . . . . . . . . . . 17
7.1.3. Multisession BGP . . . . . . . . . . . . . . . . . . . . 17
7.2. Interference. . . . . . . . . . . . . . . . . . . . . . . . 19
7.2.1. Multisession BGP . . . . . . . . . . . . . . . . . . . . 19
8. Application Fit. . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. RFC 2547 Style VPNs . . . . . . . . . . . . . . . . . . . . 20
8.1.1. RFC 2547 and Label Distribution. . . . . . . . . . . . . 21
8.2. VPWS. . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.2.1. Assertion #1 . . . . . . . . . . . . . . . . . . . . . . 22
8.2.2. Counter-Assertion #1 . . . . . . . . . . . . . . . . . . 22
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8.2.3. Assertion #2 . . . . . . . . . . . . . . . . . . . . . . 23
8.2.4. Counter-Assertion #2 . . . . . . . . . . . . . . . . . . 23
8.2.4.1. Assertion #2a . . . . . . . . . . . . . . . . . . . . 23
8.2.4.2. Counter-Assertion #2a . . . . . . . . . . . . . . . . 23
8.2.5. Assertion #3 . . . . . . . . . . . . . . . . . . . . . . 24
8.2.6. Counter-Assertion #3 . . . . . . . . . . . . . . . . . . 25
8.3. VPWS and Per-Wire Attributes. . . . . . . . . . . . . . . . 27
8.3.1. Assertion #4 . . . . . . . . . . . . . . . . . . . . . . 27
8.3.2. Counter-Assertion #4:. . . . . . . . . . . . . . . . . . 27
8.3.3. Assertion #5 . . . . . . . . . . . . . . . . . . . . . . 27
8.3.4. Counter-Assertion #5 . . . . . . . . . . . . . . . . . . 27
8.3.5. Assertion #6 . . . . . . . . . . . . . . . . . . . . . . 28
8.3.6. Counter-Assertion #6 . . . . . . . . . . . . . . . . . . 28
8.3.7. Assertion #7:. . . . . . . . . . . . . . . . . . . . . . 28
8.3.8. Counter-Assertion #7:. . . . . . . . . . . . . . . . . . 29
8.4. VPLS. . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8.4.1. Assertion #8 . . . . . . . . . . . . . . . . . . . . . . 29
8.4.2. Counter-Assertion #8 . . . . . . . . . . . . . . . . . . 29
8.4.3. Assertion #9 . . . . . . . . . . . . . . . . . . . . . . 30
8.4.4. Counter-Assertion #9 . . . . . . . . . . . . . . . . . . 30
9. Operational Implications . . . . . . . . . . . . . . . . . . . 30
9.1. OAM Functionality . . . . . . . . . . . . . . . . . . . . . 30
9.1.1. Assertion #10: . . . . . . . . . . . . . . . . . . . . . 30
9.1.2. Counter-Assertion #10: . . . . . . . . . . . . . . . . . 31
9.2. Full-Mesh Issues. . . . . . . . . . . . . . . . . . . . . . 31
10. Conclusions and Recommendations . . . . . . . . . . . . . . . 31
11. Intellectual Property . . . . . . . . . . . . . . . . . . . . 31
12. Design Team . . . . . . . . . . . . . . . . . . . . . . . . . 31
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32
14. Security Considerations . . . . . . . . . . . . . . . . . . . 33
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
16. References. . . . . . . . . . . . . . . . . . . . . . . . . . 34
16.1. Normative References . . . . . . . . . . . . . . . . . . . 34
16.2. Informative References . . . . . . . . . . . . . . . . . . 37
17. Editor's Address. . . . . . . . . . . . . . . . . . . . . . . 38
18. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 38
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1. Introduction
The stability of the global Internet routing system has been the
subject of much research (see e.g., [RVBIB]) and discussion on
various IETF mailing lists [IETFOL]. Much of the research into the
routing system has centered around the analysis of the dynamics and
stability of the Border Gateway Protocol Version 4 [BGP] (hereafter
referred to as BGP).
However, while the theoretical properties of BGP remains a topic of
great interest, a more recent discussion has focused on effects of
the addition of new types of Network Layer Reachability Information,
or NLRI to BGP. In particular, the advent of two BGP attributes,
Multiprotocol Reachable NLRI (MP_REACH_NLRI), and Multiprotocol
Unreachable NLRI (MP_UNREACH_NLRI) [RFC2858], have made it possible
to encode and transport a wide variety of features and their
associated signaling using the BGP transport infrastructure. Examples
include include IPv6 [RFC2460], flow specification rules [FLOW], IP
VPNs [RFC2547BIS], Virtual Private LAN services [VPLS], Virtual
Private Wire Service [VPWS], and auto-discovery mechanisms for VPNs
in general [BGPVPN],
This document outlines the concerns and issues surrounding using the
BGP infrastructure as a generic feature and signaling transport.
However, the similar concerns apply to the Interior Gateway Protocols
(IGPs) in common use (e.g., ISIS [RFC1142] or OSPF [RFC2328]).
The rest of this document is organized as follows: Section 2 outlines
the scope of this work. Section 3 introduces the problem statement
which is the focus of this document, section 4 provides definitions,
and section 5 outlines the main architectural models that are
discussed. The remaining sections discuss the the implications of
those models.
2. Scope of this Work
It is the intention of the RIFT design team that this document serve
as a guide for both protocol designers and network operators. The
goal is to outline the implications associated with employing
existing routing protocols to enable additional feature sets and
functionality, as contrasted with designing new mechanisms to carry
those feature sets and functionalities.
The issues, concerns and considerations discussed in this document
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focus on the implications for BGP [BGP,RFC1771]. It is important to
note that similar issues will arise when considering generalizations
to the information that the IGPs carry.
3. Problem Statement
The advent of the MP_REACH_NLRI and MP_UNREACH_NLRI attributes,
combined with the resulting generalization to the BGP infrastructure,
have created the opportunity to use BGP to transport a wide variety
of data types and their associated signaling. The combination of a
BGP data type and its associated signaling is frequently called an
"application"; example applications include the IPv4 and IPv6
[RFC2460] routing systems, flow specification rules [FLOW], auto-
discovery mechanisms for Layer 3 VPNs [BGPVPN], virtual private LAN
services [VPLS], and virtual private Wire Service [VPWS].
More recently, the discussion in the IETF community has focused on
the use of the BGP as a generalized feature transport infrastructure
[IETFOL]. The debate has recently intensified due to the emergence of
a new class of application that uses the BGP infrastructure to
distribute information that is not directly related to inter-domain
routing. Examples of such applications include the use of the BGP
transport infrastructure to provide auto-discovery for IP VPNs
[RFC2547BIS], the virtual private LAN services mentioned above [VPLS]
and VPNs in general [BGPVPN].
3.1. Risk, Interference, and Application Fit (RIFT)
As mentioned above, much of the debate surrounding these new uses of
the BGP transport infrastructure has focused on the potential
tradeoffs between the stability of the Internet routing system, as
effected by the deployment of new applications, and the desire on the
part of service providers to rapidly deploy these new applications,
and to reduce the operational cost by re-using existing protocols.
These tradeoffs have at times been described in terms of risk,
interference, and application fit. Risk models the software
engineering impact of new applications on a generic implementation,
while interference models the impact of new applications on protocol
definition and behavior. Finally, application fit models the
similarity between an application's data and signaling requirements
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and a specific distribution algorithm. Each is described below.
3.1.1. Risk: Software Engineering
Risk attempts to assess the robustness tradeoffs inherent in the
addition of new applications to a given implementation. That is, risk
models the impact of generic software engineering issues on a given
implementation. These issues include the impact of new applications
on existing implementations and on the fate sharing properties of
those implementations.
A second aspect of risk lies in the trade-off of extending an
existing protocol versus designing, implementing, and deploying a new
protocol.
3.1.2. Interference: Protocol Specification/Dynamic Behavior
Interference models the potential for a new application to adversely
effect the operation of an existing implementation at the protocol
level, by inadvertently introducing a detrimental dependency of some
kind. That is, an application is said to "interfere" with an existing
application if, by virtue of the application's protocol extension(s),
one or more fundamental properties of the protocol's operation are
detrimentally altered. For example, could we create a new state which
introduces an unanticipated deadlock situation to occur? Or could we
destabilize the distributed behavior of the protocol? Or might we
simply run out of the attributes or bits available (as happened, for
example, with RADIUS [RFC2138])?
3.1.3. Application Fit: Distribution Topology
Application fit refers to how closely the requirements of the data to
be distributed match the underlying capabilities of a distribution
mechanism. For example, it is clearly inefficient to broadcast data
to all peers that is only required between two peers, just as it is
inefficient to unicast (replicate) data that is required by all peers
when a single broadcast would do.
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4. Definitions
4.1. Reachability Information
Reachability information refers to information describing some part
of a network, along with how one can reach it, and perhaps also
containing attributes of the implied path to the network locale.
Typically, this information pertains to IP routing information; an
example of non-IP reachability is VPLS information [VPLS].
4.2. Layer 3 Routing Information
Layer 3 routing information represents either link state information
or network reachability information. Link state information
represents Layer 3 adjacencies and topology. Link state routing
protocols, such as OSPF [RFC2328] and ISIS [RFC1142], flood link
state information throughout an IGP domain, so that each
participating router maintains an identical copy of a database that
is computed to reflect the complete Layer 3 topology.
Layer 3 reachability information expressed as an IP address prefix
represents the set of destinations (systems) whose IP addresses are
contained in the IP address prefix. Distance/path vector routing
protocols, such as BGP, distribute Layer 3 reachability information
among routing domains.
Routers use both types of Layer 3 routing information (link state and
reachability) to produce IP forwarding tables. That, is, for purposes
of this discussion, "routing information" relates to the Layer 3
inter-domain routing data traditionally carried by BGP.
Finally, if one defines routing information as "information used to
forward packets", combined with the above definition of reachability
information, then we can consider information such as described in
[FLOW] (for example) to be routing information (since it is
attempting to add a level of granularity to how an 'aggregate' is
defined). That is, [FLOW] intends to complement to the existing
routing information, and the flow information is dependent on IP4
unicast reachability advertised by the same neighbor.
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4.2.1. Standard Routing Information
In the most general terms, then, a routing protocol distributes data
to accomplish the following three functionalities:
(i). To govern the routing decision process (e.g., the
standard BGP decision process)
(ii). To constrain the flow of information (for example, with
BGP communities)
(iii). To tell the recipient how to get packets to the next hop
We will refer to information that falls into this class as "standard
routing information".
4.3. Auxiliary (non-routing) Information
Auxiliary Information is any information that is exchanged by routers
which is neither Layer 3 routing information, nor reachability
information. IS-IS hostname TLVs are an example of auxiliary
information [RFC1142].
4.4. Address Family Identifier (AFI)
An Address Family contains addresses that share common structure and
semantics. An Address Family Identifier (AFI) uniquely identifies
each address family. Several routing protocol messages contain a
field that represents the AFI. The AFI identifies the address type
used by another data item contained in that message. The Routing
Information Protocol (RIP) [RFC2453], Distance Vector Multicast
Routing Protocol (DVMRP) [RFC1075], and BGP all employ the AFI field.
For example, the BGP MP_REACH_NLRI and MP_UNREACH_NLRI attributes
contain an AFI field. These BGP attributes also contain a NLRI field
that enumerates reachable or unreachable subnetworks corresponding to
the associated address family. The AFI field indicates the address
type by which reachable subnetworks are identified. When BGP is used
to distribute Layer 3 routing information, AFIs can indicate the
following address types: IPv4, IPv6, VPNv4 [RFC2547BIS]. When BGP is
used to distribute auxiliary information, AFIs can indicate other
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address families.
4.5. Subsequent Address Family Identifier (SAFI)
A Subsequent Address Family Identifier (SAFI) is part of the BGP
MP_REACH_NLRI and MP_UNREACH_NLRI attributes. These BGP attributes
also contain a NLRI field that enumerates reachable or unreachable
subnetworks. The SAFI augments the AFI, carrying additional
information regarding networks enumerated in the NLRI field.
4.6. Network Layer Reachability
Network Layer Reachability Information, or NLRI is the data described
by the AFI/SAFI fields [AFI,SAFI]. While these concepts were
originally described for protocols such as DVMRP [RFC1075], the bulk
of the generalization of the NLRI described in this document derives
from the introduction of the MP_REACH_NLRI and MP_UNREACH_NLRI
attributes to BGP [RFC2858].
4.7. Application
The term application is used in this document to refer to the
combination of a BGP data type and any signaling data that is carried
by BGP in support of the service the data type carries. The data type
is typically described in an AFI/SAFI, while the actual data is
frequently contained in both NLRI and BGP community attributes
[RFC1997].
4.8. Routing Protocol
A routing protocol is composed of two basic components: a data
distribution algorithm and a decision algorithm. A router typically
obtains Layer 3 routing information via its data distribution
algorithm, and it uses this information to produce an IP forwarding
table (by applying the protocol's decision algorithm to the received
routing data). Note that it is the use of BGP's data distribution
algorithm that is the focus of this document. However, when judging
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application fit, one may also consider whether the decision
algorithms suit the application.
4.9. Fate Sharing
The fate sharing principle for end to end network protocols was first
enunciated by Dave Clark [CLARK]. As applied to software systems,
fate sharing refers to the sharing of common resources among a group
of applications. In our case, the particular "fate" of most interest
is the ability of one application, call it application A, to cause an
application with which it is fate sharing, call it application B, to
experience one or more faults due to faults in application A. Fate-
sharing can exist at many levels, including between modules on a
system, between routing protocols, between sessions of a routing
protocols such as BGP, or between applications within a routing
protocol.
5. Architectural Models
In this section, we consider the two architectural models which are
motivated by salient questions considered in this document, namely:
(i). Does the BGP distribution protocol suit a particular
application (i.e., does an application fit the BGP
distribution protocol)?
(ii). What are the effects on the global routing system (if
any) of carrying that application using the BGP distribution
protocol?
These questions must be analyzed in terms of the cost of protocol and
code development, as well as in terms of the operational expense that
may be incurred by utilizing (or not utilizing) the mechanisms
already present in BGP.
Two models, describing alternate viewpoints, are examined in the
following sections.
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5.1. General Purpose Transport Infrastructure (GPT) Model
The GPT model models BGP data distribution infrastructure as a
generic application transport mechanism. As such, it focuses on
application fit, and assumes that the tradeoffs, both in terms of
risk and interference can be managed in an efficient manner. As a
result, the GTP models these issues not in terms of whether the
application and signaling data that need to be distributed are part
of some particular class (routing, in this case), but rather whether
the requirements for the distribution these attributes are similar
enough to the distribution mechanisms of BGP. In those cases when
distribution requirements are sufficiently similar, BGP can be a
logical candidate for a transport infrastructure. Note that this is
not because of the nature of information distributed, but rather due
to the similarity in the transport requirements. There are of course
other operational considerations that make BGP a logical candidate,
including its close to ubiquitous deployment in the Internet (as well
as in intra-nets), its policy capabilities, and operator comfort
levels with the technology.
5.2. Special Purpose Transport Infrastructure (SPT) Model
The SPT model, on the other hand, models the BGP infrastructure as a
special purpose transport designed specifically to transport inter-
domain routing information. As such, it is more sensitive to risk and
interference than to application fit.
There are two basic arguments supporting the SPT model: The first is
based on the perceived risk profile involved in adding new
applications to the BGP transport infrastructure or new features to
existing BGP applications. The concern here is that changes to BGP
implementations will cause software quality to degrade, and hence
destabilize the global routing system. This position is based upon
well understood software engineering principles, and is strengthened
by long-standing experience that there is a direct correlation
between software features and software stability [MULLER1999]. This
concern is augmented by the fact that in many cases, the existence of
the code for these features, even if unused, can also cause
destabilization in the routing system, since in many cases software
faults cannot be isolated.
A second concern is based on interference arguments, notably that the
increase in complexity of BGP due to the number of data types that it
carries can also potentially destabilize the global routing system.
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This concern is based on a wide range of concerns, including the fact
that the interaction of BGP dynamics and current deployment practices
are poorly understood, and that the addition of non-routing data
types may adversely effect convergence and other scaling properties
of the global routing system.
6. Analyzing Risk and Interference
One way to frame the tradeoffs involved in a model's risk profile is
in terms of the software engineering issues surrounding where an
implementation might demultiplex among applications. The important
point here is that an implementation's choice of demultiplexing point
directly affects the implementation's risk profile due to its effects
on existing code, and on the system resources it requires to be
shared among those applications.
6.1. Risk: Code Impact, and Resource Sharing
For purposes of this discussion, then, we consider the risk profile
of the SPT and GPT models with respect to their application
demultiplexing point. The GPT model typically provides a single point
for demultiplexing all applications (i.e., the AFI/SAFI). On the
other hand, the SPT model, provides an application demultiplexing
point above BGP (typically at the TCP port level). That is, in the
GPT model, applications typically share a common transport session,
while the SPT model generally envisions one or more applications per
transport session (see section 7.1.3 for a discussion of the impact
of multisession BGP [MULTISESSION,SOFTNOTIFY] on this taxonomy).
Finally, note that these models can have very different risk profiles
with respect to code impact and resource sharing. Some of the
questions relating to risk assessment are considered below.
6.1.1. Code Impact
In this section, we outline the high-level questions one might ask in
assessing the difference in risk between GPT model and the SPT model
based on their effect on an existing code base.
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o Does the code below the demultiplexing point need to be
changed when a new application is added?
o Does the code in existing applications have to be changed when
a new application is added (that is, to what extent are the
applications decoupled)?
o Can the code in separate applications be developed, tested,
released, debugged and packaged independently from other
applications?
o Is there significant code below the demultiplexing point that
can be shared among all applications?
6.1.2. Resource Sharing
In this section, we outline the high-level questions one might ask in
assessing the difference in risk between GPT model and the SPT model
with respect to the requirements and properties of the system
resource sharing they require. In particular:
o Do applications have to compete for socket buffers, and hence
have the potential to block or starve each other (at the TCP
port level)?
o Do applications have to compete for possible protocol-level
transport-related buffers and queues, and hence have the
potential to starve or block each other at the protocol
send/receive level?
o Do applications have to compete for a possible per-connection
processing time budget, hence have the potential to starve
each other at the intra-process scheduling level?
6.1.2.1. Resource Sharing and Operating System Level Issues
In this section, we outline the high-level questions one might ask in
assessing the difference in risk between GPT model and the SPT model
based on the affect on resource sharing at the operating system
level. In particular:
o Do applications share a common scheduling context? That is,
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do applications have to compete for per-process scheduling
budgets?
o What is the degree of fate sharing between applications?
6.2. Interference
Interference models the potential for an application to affect the
behavior of an existing application or applications. For example, in
the case of the Internet routing system, one might ask if a certain
application "interferes" with IPv4 Unicast routing by affecting some
aspect of its protocol operation (e.g., convergence time).
Interference in the Internet routing system has its roots in the
observation that the routing system itself can be described as highly
self-dissimilar, with extremely different scales and levels of
abstraction. Complex systems with this property are susceptible to
"coupling", which RFC 3439 [RFC3439] defines as follows:
The Coupling Principle states that as things get larger, they
often exhibit increased interdependence between components.
COROLLARY: The more events that simultaneously occur, the larger
the likelihood that two or more will interact. This phenomenon
has also been termed "unforeseen feature interaction"
[WILLINGER2002].
That is, interference, if and where it occurs, has its roots in
complexity and is frequently the result of application coupling.
7. GTP and SPT Models: Risk and Interference
In this section, we analyze the risk and interference profiles of the
SPT and GPT models.
7.1. Risk
As mentioned above, risk models the robustness tradeoffs around
generic software architecture and engineering associated with
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protocol implementations, including the impact on existing protocol
implementations, and on the fate sharing properties of those
implementations. In the following sections we consider these
components of risk for both the GPT and SPT models.
7.1.1. Code Impact
In this section, we outline the answers to the questions posed above.
o Does the code below the demultiplexing point need to be
changed when a new application is added?
In theory, such code changes are unlikely to be required in
the SPT model, as the SPT model envisions that a new
application will have a new demultiplexing point (port).
The GPT model does not by definition require new code below
the demultiplexing point either. Specifically, it should in
theory be possible to isolate code below the demultiplexing
point with suitable abstraction and constructs such as
AFI/SAFI API registries.
o Does the code in existing applications have to be changed when
a new application is added (that is, to what extent are the
applications decoupled)?
The SPT model envisions application independence with respect to
demultiplexing point. As such, it is unlikely to require such
changes. However, it is important to note that good software
engineering practices encourage code reuse and construction of
general purpose libraries. As a result, if applications share
libraries and/or other code, the practical independence
decreases, and consequently risk increases. The same analysis
can be made for the GPT model, since in this case we are already
demultiplexing on the AFI/SAFI fields.
o Can the code in separate applications be developed, tested,
released, debugged and packaged independently from other
applications?
While this is theoretically possible in the SPT model (and
possibly more difficult in the GPT model) practice and
experience has shown that achieving this type of independence is
difficult in either model.
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7.1.2. Resource Sharing
In this section, we address the questions raised above to assess the
difference in risk between GPT model and the SPT model based on the
effect on resource sharing considerations.
o Do applications have to compete for socket buffers, and hence
have the potential the to block or starve each other (at the GPT
level)?
The SPT model does not require applications to compete for
socket level resources. It should also be possible to achieve
this type of application independence in the GPT model with
multisession BGP.
o Do applications have to compete for possible protocol-level
transport-related buffers and queues, and hence have the
potential to starve or block each other at the protocol
send/receive level?
Again, while the SPT model does not require competition for
transport-level resources, it should be possible to achieve
similar behavior with multisession BGP.
o Do applications have to compete for a possible per-connection
processing time budget, hence have the potential to starve
each other at the intra-process scheduling level?
Applications written to the the SPT model should not require
this type of resource competition. It should also be possible to
reduce this type of resource competition with multisession BGP.
o Do applications have to compete for resources within the
network (e.g., bandwidth), when the protocol session spans
multiple hops ?
Neither the SPT model nor the GPT model (again, with
multisession BGP) should require competition for network
resources in this case.
7.1.3. Multisession BGP
Suppose that one makes the simplifying assumption that a GPT
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implementation's risk profile is dominated by the probability that an
error in one AFI/SAFI stream will cause some subset of the other
AFI/SAFI streams to malfunction (e.g., reset). In this case, risk
might be characterized as a function of the model and the number of
AFI/SAFI carried. Given this simplification, the risk profile looks
loosely like
Risk = f(Model, |{AFI,SAFI}|)
where
f:{GPT, SPT} X |{AFI, SAFI}| -> N
Note that we assume that
f(SPT,n) = O(f(GPT,n))
where
O(f) = {g:N->R | there exists c > 0 and n such that g(n) < c*f(n)}
That is, that the SPT risk profile is bounded by the GPT risk
profile. Clearly, the existence of such an upper bound is an integral
aspect of any argument favoring the SPT model.
Note that for the SPT model, we can think of the number of AFI/SAFI
that a single session carries as a small constant, call it k. k will
typically be small (close to 1), since by definition the SPT model
envisions a small number of AFI/SAFI per session (e.g., for AFI/SAFI
IPv4/unicast and IPv6/unicast, k = 2).
When formulated in this way, one can see that one objective of
multisession BGP is to find a value, call it g, such that
f(GPT, g) ~ f(SPT,k), for small values of k (i.e., k close to 1)
where
A(n) ~ B(k) ==> A(n) = B(k) + h(n), h(n) >= 0
That is, A(n) is approximately equal to B(k)
In this case, g is the size of the multisession AFI/SAFI grouping,
and for small values of g, multisession BGP can have a risk profile
that looks very much like the SPT risk profile. In particular, for g
= 1, both models would have similar risk profiles. Of course, there
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are many other components of risk that that are not considered by
this analysis, such as collateral issues resulting from the existence
of faulty shared code, operating system process and memory structure,
etc.
7.2. Interference
Interference concerns stem from the possibility that application
coupling can lead to the destabilization of the Internet routing
system in unanticipated and unexpected ways. In this section we
consider interference properties of the GPT and SPT models.
7.2.1. Multisession BGP
Multisession BGP also seeks to reduce the interference profile of the
GPT model by eliminating one potential source of interference,
namely, the potential interference due to presence of multiple
AFI/SAFIs in a single BGP session. Following the analysis presented
in section 7.1.3, we can see that for small groupings (described as
small values of g in section 7.1.3), the interference profiles of
both models converge.
8. Application Fit
In the following sub-sections, application fit is examined from the
perspective of analyzing the signaling and data distribution needs of
three representative applications, namely:
RFC 2547 Style VPNs
VPWS
VPLS
However, before investigating how the BGP data distribution mechanism
(and its extensions) fit the requirements of these applications, it
is useful to briefly review the gross characteristics of the BGP data
distribution infrastructure. In particular, we examine which
distribution topologies can be naturally built using internal BGP (or
iBGP).
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iBGP has been described loosely as a broadcast mechanism since an
iBGP speaker sends information to all its peers. This is typically
achieved by means of one or more route reflectors (or RRs); a more
direct but less scalable means is for each iBGP speaker to have a BGP
session with each iBGP peer. It may, however, be more accurate to
characterize iBGP as a constrained broadcast mechanism. This is
because the use of communities in conjunction with import and export
policies allows an iBGP speaker to effectively limit its
communication to a subset of the full set of iBGP peers; the
efficiency of constrained broadcast can be improved by techniques
such as described in [ORF] and [RTCONST].
8.1. RFC 2547 Style VPNs
There are five classes of information that need to be distributed for
RFC 2547 style VPNs:
(a). Membership (auto-discovery)
(b). Prefixes
(c). Labels
(d). BGP nexthop, and
(e). Path selection attributes
The first of these, membership or auto-discovery, must be sent to all
peers, as a BGP speaker does not know a priori which of its peers are
members of a given VPN. Membership of a given VPN is recognized by
the use of extended communities called Route Targets. BGP is well-
suited for this mode of distribution.
The next three of these constitute the reachability information.
They say what part of a given VPN (b) is reachable, and how it is to
be reached (c and d). The final piece of information is used for
selection if there are multiple paths to a given prefix of a VPN, as
in the case of multi-homing. All of these pieces of information need
only be distributed to members of the VPN, i.e., they require a
constrained broadcast mechanism. BGP is reasonably well-suited for
this mode of distribution using import and export NLRI filtering.
The addition of the mechanism in [RTCONST] makes BGP even better
suited to this.
The encoding of this information as defined in [RFC2547BIS] puts all
of this information in a single NLRI. This seems to imply that a
broadcast mechanism has to be used for the distribution of RFC 2547
VPN information. However, the combination of [RTCONST] and [RFC2918]
allow BGP to distribute this information correctly yet efficiently.
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In summary, there seems to be little argument that the RFC 2547
application is a routing application. This is because the information
that gets sent via BGP in RFC 2547 is generally considered to be
"routing information". That is, the protocol distributes address
prefixes, along with their next hops (and of course, some additional
attributes). Finally (and perhaps most importantly), there seems to
be little argument that the information distributed by the RFC 2547
application is standard routing information.
8.1.1. RFC 2547 and Label Distribution
One issue that is frequently raised with respect to whether or not
the RFC 2547 VPN application is a routing application surrounds the
fact that, in the 2547 application, BGP distributes MPLS labels along
with the routes. The contention then, is that the RFC 2547
application represents more than just a routing application. However,
in this case the MPLS label is just a shorthand way of representing
one or more address prefixes. That is, the assertion is that in this
case, the label represents "standard routing information".
8.2. VPWS
The question of whether VPWS is a "good fit" for the BGP transport
infrastructure is the source of much discussion (and controversy). In
this section, we will review both positions and their supporting
arguments as a series of assertions and counter-assertions (we will
use this format throughout the rest of this section).
The key debate with respect to VPWS centers around what set of
services are being defined, and how they are to be signaled. One way
to analyze the VPWS application, then is in terms of two of its more
contentious functionalities, namely:
(a). Auto-discovery
Auto-discovery refers to discovery of the set of nodes
that belong in a common L2VPN, and
(b). Signaling
Signaling refers to the setup and maintenance of the
point-to-point pseudo-wires that carry the traffic of
the L2VPN.
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The next sections examine the various assertions and counter-
assertions around auto-discovery and signaling for VPLS.
8.2.1. Assertion #1
Assertion #1 states VPWS is not a routing application. Those
supporting this assertion argue that in the case of VPWS, we are not
distributing address prefixes, and (importantly) unlike the case of
RFC 2547 style VPNs, the BGP decision process is not used (or at
least it is not used in the same way). Further, proponents argue that
what we are distributing is state information that corresponds to
point-to-point entities, i.e., pseudo-wires, and thus argues that
that the VPWS application is completely different.
8.2.2. Counter-Assertion #1
Counter-Assertion #1 states that VPWS is a routing application. More
specifically, this position is outlined in [VPLS] (section 3.4),
namely:
"It is often desired to multi-home a VPLS site, i.e., to connect
it to multiple PEs, perhaps even in different ASes. In such a
case, the PEs connected to the same site can either be
configured with the same VE ID or with different VE IDs. In the
latter case, it is mandatory to run STP on the CE device, and
possibly on the PEs, to construct a loop-free VPLS topology.
In the case where the PEs connected to the same site are
assigned the same VE ID, a loop-free topology is constructed by
routing mechanisms, in particular, by BGP path selection. When a
BGP speaker receives two equivalent NLRIs (see below for the
definition), it applies standard path selection criteria such as
Local Preference and AS Path Length to determine which NLRI to
choose; it MUST pick only one.
If the chosen NLRI is subsequently withdrawn, the BGP speaker
applies path selection to the remaining equivalent VPLS NLRIs to
pick another; if none remain, the forwarding information
associated with that NLRI is removed."
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8.2.3. Assertion #2
Assertion #2 states that auto-discovery for VPWS requires some form
of constrained broadcast. There doesn't seem to be much controversy
that auto-discovery does require some sort of constrained broadcast
mechanism (which we don't want to be limited to a single AS), and we
may want to be able to optimize it by using a RP (rendezvous point)
like mechanism. BGP route reflectors (RR) provide a convenient and
ubiquitously deployed candidate RP. In this case (RR as RP), the fit
is good since auto-discovery, like routing, requires an n-party
protocol where each party has no a priori knowledge of the existence
or identity of the other n-1 parties.
8.2.4. Counter-Assertion #2
There is no real counter-position to Assertion #2, as it simply
states that VPWS auto-discovery requires some form of constrained
broadcast (about which there is some controversy; see Assertion #2a
below).
8.2.4.1. Assertion #2a
Assertion #2a states that auto-discovery is not needed for VPWS.
Further, the Assertion #2a states that there is not a validated need
for VPWS auto-discovery, since auto-discovery is useful only when
creating full mesh layer 2 topologies, which are undesirable due to
their (well-understood) poor scaling properties; hence auto-discovery
for VPWS is not useful.
8.2.4.2. Counter-Assertion #2a
<what is the counter-assertion here? auto-discovery is useful for
partial mesh? cite?>
In summary, with the exception of Assertion #2a, the major
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controversy surrounding VPWS is in signaling piece of the
application. The "VPWS is not a routing application" camp argues that
the VPWS signaling requirements do not fit the BGP distribution
infrastructure, while the "VPWS is a routing application" camp
believes that BGP is a good fit. The next sections examine these
assertions.
8.2.5. Assertion #3
Assertion #3 states that VPWS applications are not a good fit for
BGP. This argument is based on the assertion that BGP is poorly
suited to the VPWS signaling requirements because pseudo-wires are
inherently point-to-point (see, for example [L2VPNSIG]). Further, the
assertion is that VPWS signaling is qualitatively different than in
routing or auto-discovery, in which each piece of information must be
distributed to the n participants. The conclusion here is that BGP's
distribution mechanisms are a poor match for VPWS signaling. Another
way to think about this is that BGP generally works from a single
database, and then applies some filtering on a per-connection basis;
this only makes sense if most of the information is going to go to a
lot of places.
For example, suppose that a RR is used for VPWS signaling, and there
is the need to set up n pseudo-wires. In this case, instead of
sending n setup messages, one sends one large "meta-setup" message
with all the info that would have been in the n setup messages. That
is, let
n = number of pseudo-wires
l = the size of the per-wire label information
k = the size of the per-wire information
In this case, the meta-setup message will be of size O((l + k) * n).
After receiving the setup message, the RR then must send the n
messages that could have been sent by the endpoint (note that this is
almost true; the endpoint would have to send n messages of size (l +
k), but the RR will have to send n copies of the larger setup
message).
Meyer, et. al. Section 8.2.5. [Page 24]
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8.2.6. Counter-Assertion #3
Counter-Assertion #3 states that the VPWS application is a good fit
for BGP (see, for example [L2VPNT]). In particular, this camp
suggests that a RR really only needs to distribute the label-range
[LABELRANGE], so the setup message isn't really n times as large, but
rather is analyzed as follows:
Let n = number of pseudo-wires
m = the size of the label-range data
k = the size of the per-wire information
Then the messages will be of size O(m + (k * n)), and most
importantly for the label-range argument:
O(m + (k * n)) < O((l + k) * n)
That is, the label-range concept reduces the size of the
messages that need to be sent to and by the RR.
However, some will argue that the label-range concept is efficient if
and only if:
(a). A large enough label range is preallocated to accommodate
all the systems you might ever want to add to the
VPLS/VPWS (assuming that service interruption is not
acceptable), and
(b). There is no per-wire information other than labels that
needs to distributed
In these cases, the label range approach can reduce the size of the
setup messages as analyzed above. However, the counter argument is
that any such reduction will become a second-order effect as soon as
some other piece of per-wire status or configuration (e.g., MTU)
information must be distributed. In addition, the idea of pre-
allocating a large enough label range to accommodate future
expansion, while saving bits in the setup messages, has other costs
which may be large. In particular:
(a). Until the future expansion takes place (if it ever does),
one may be wasting quite a lot of labels (noting that
that each label you distribute requires you to allocate a
piece of high-speed memory in your forwarding engine;
putting some of it aside for possible later use seems
very costly. Each one you put aside is, e.g., one less
RFC2547 route you can support).
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However, if you don't preallocate enough contiguous label
space for future expansion, then if the expansion occurs
you must start adding additional labels or label ranges,
and your setup messages start getting longer anyway (in
theory, you could just carve a new set of label ranges,
instead of adding new ones; counter-position: if you did
that, you'd have to bring down your whole VPWS (and
possibly VPLS) every time you add a new endpoint).
(b). Fragmentation of the label space, which can result from
this preallocation, has real impact on label switching
implementations (as the MPLS architecture explicitly
leaves it to the implementation to develop its own label
assignment strategies). So if, for example, a hardware
designer thinks s/he can improve performance by using,
say, prime numbered labels first, s/he should have the
ability to design her/his system in this way. If an
application is going to come along and demand that labels
be assigned in contiguous groups, implementations which
are perfectly conformant to the architecture may not be
able to support that application.
(c). For diagnosis of network problems, the label-range
approach may have the additional issue that the operator
may not know (a priori) which label(s) were assigned to
which endpoint(s).
(d). Finally, one may argue that label-range allocation is
sub-optimal for non-full mesh topologies, since all peers
of the VPN must hear about the a label-range withdraw, and
(in a non-full mesh topology), not all peers need to know
about it.
In any event, one may argue that the scaling benefits of using a RR
in routing is that the RR pre-digests all the received info; it runs
the (BGP) decision process, and only forwards the results of the
decision process, rather than forwarding all the raw data. In the
case of VPWS (and possibly VPLS), the argument is that this advantage
is absent (i.e., we don't run BGP path selection), and as a result,
the RR doesn't help with scaling in the same way it does with
routing. Of course, the counter position is that some form of BGP
path selection is used; see discussion above). Finally, one may argue
that using the RR will introduce some latency into the label withdraw
procedure.
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8.3. VPWS and Per-Wire Attributes
While several per-wire attributes have been defined (see [L2TPV3],
for example), the need for per-wire attributes for VPWS remains
controversial. The following sections examine those controversies.
8.3.1. Assertion #4
Assertion #4 is that VPWS requires various per-wire parameters. These
may include (but are not limited to) MTU, whether to use sequencing
capabilities, bandwidth capabilities, and QoS. In addition, during
the lifetime of a pseudo-wire, there are per-wire status indications
that may need to be passed to the other endpoint.
8.3.2. Counter-Assertion #4:
Counter-Assertion #4 states that it has not been demonstrated that
VPWS needs per-wire attributes as few (per-wire attributes) have as
yet been defined (see, e.g., [MARTINI]).
8.3.3. Assertion #5
Assertion #5 states that passing per-wire attributes through an RR
will likely be inefficient. The argument here is that in the event
that per-wire attributes are required, passing these (per-wire)
attributes through a RR will be sub-optimal as the RR will forward
the status to all the VPWS members, not just to the one endpoint that
is interested in it. For attributes like sequence numbers, it may
even more difficult as one has to make sure the sequence numbers
resynchronize properly when the pseudo-wire flaps. This seems
somewhat difficult to achieve through a BGP RR.
8.3.4. Counter-Assertion #5
The counter assertion here is that, since few (or no) per-wire
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attributes have been defined (counter-assertion #4), the fact that it
is inefficient to use a RR for distribution is irrelevant.
8.3.5. Assertion #6
Assertion #6 states that, while still an open issue, pseudo-wire
congestion control may require regular point-to-point control message
exchanges, something which BGP would seem ill-equipped to handle.
8.3.6. Counter-Assertion #6
In this case, the counter assertion is that since few (or no) per-
wire attributes have been defined (see counter-assertion #4), and
further, since congestion control for pseudo-wires is still an open
issue, arguing fit is premature.
8.3.7. Assertion #7:
Assertion #7 states that the primary motivation for VPWS is to
deliver existing service models (i.e., Frame Relay and ATM) over a
packet infrastructure (this is as opposed to some new service). In
this case, common deployments involve partial mesh topologies (more
specifically multiple hub and spoke connections, with some hub to hub
connectivity that makes sense for the enterprise traffic profile). In
addition, some of the connections in such deployments require per-
wire characteristics (e.g., guaranteed throughput for voice, etc).
In other words, the argument here is that a VPWS service designed to
support so-called legacy services (Frame Relay and ATM) will require
point-to-point signaling due to existing topologies and the need for
per-wire attributes. Further, for new VPWS services that require
full-mesh auto-provisioning, the "Colored Pools PW Provisioning
Model" [L2VPN] suggests a method to support such provisioning while
retaining the point-to-point signaling required to support per-wire
attributes.
Meyer, et. al. Section 8.3.7. [Page 28]
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8.3.8. Counter-Assertion #7:
<what is the counter-assertion here?>
8.4. VPLS
A VPLS service connects a number of sites by an emulated LAN segment.
In the next sections, we examine whether VPLS maybe be considered to
be a routing application, and hence whether BGP is a good fit for its
distribution requirements.
8.4.1. Assertion #8
Assertion #8 states that VPLS is a routing application, since the
notion of "VPLS site identification" is analogous to a VPN site
identifier for VPWS (which this camp also views as a routing
application). As a result, the analysis of the distribution needs of
these five items is exactly as for RFC 2547 VPNs, and the conclusion
is that BGP is reasonably well-suited for this application, and with
the addition of [RTCONST] and [REFRESH], the fit is even better.
Finally, note that existing BGP path selection mechanisms can be used
as is for VPLS, and can prove useful for multi-homed sites.
8.4.2. Counter-Assertion #8
Counter-Assertion #8 states that VPLS is not a routing application.
In particular, the contention here is that while the VPLS NLRI are
used to identify that a particular PE belongs to a particular VPLS
instance (as described in Assertion #8),the path which data traffic
follows will depend on the route to that PE, and that route is
determined by the ordinary IP routing. As a result, it is not
relevant which neighbor a VPLS NLRI was received from, and hence is
not routing.
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8.4.3. Assertion #9
Assertion #9 is that constrained or true broadcast is not valuable
for VPLS, since the same label can not be used by all peers. In
particular, the same label can not be used by all peers since MAC
address learning is performed in the data plane.
8.4.4. Counter-Assertion #9
<what is the counter-assertion here? label ranges?>
9. Operational Implications
In this section we examine the operational implications of the
various choices in the design spaces described in this document.
9.1. OAM Functionality
A service provider (SP) may want to know exactly where a particular
pseudo-wire leaves its domain, and in addition may want to keep
various counts and bits of status at that point. Further, the SP may
want to be able to do data path testing to that point. That is, a SP
may want point-to-point pseudo-wire state to be maintained at its
border routers.
9.1.1. Assertion #10:
Assertion #10 states that it may be difficult for service providers
to maintain point-to-point pseudo-wire state at their border routers
with the proposed BGP signaling mechanisms. This is because those
mechanisms provide no way to ensure that a pseudo-wire data path will
leave the network at a node which has state information for that
pseudo-wire.
Meyer, et. al. Section 9.1.1. [Page 30]
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9.1.2. Counter-Assertion #10:
<counter assertion?>
9.2. Full-Mesh Issues
10. Conclusions and Recommendations
11. Intellectual Property
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11 [RFC2028].
Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementors or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
12. Design Team
The design team that produced this document consisted of Daniel
Awduche (awduche@awduche.com), Ron Bonica (Ronald.P.Bonica@mci.com),
Hank Kilmer (hank@rem.com), Kireeti Kompella (kireeti@juniper.net),
Chris Lewis (chrlewis@cisco.com), Danny McPherson (danny@tcb.net),
David Meyer (dmm@1-4-5.net) and Peter Whiting
Meyer, et. al. Section 12. [Page 31]
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(pwhiting@vericenter.com).
13. Acknowledgments
David Ball, Peter Gutierrez, Susan Harris, Pedro Marques, Eric Rosen,
Pekka Savola, and Mark Townsley have all made many insightful
comments on earlier versions of this document.
Meyer, et. al. Section 13. [Page 32]
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14. Security Considerations
This document specifies neither a protocol nor an operational
practice, and as such, it creates no new security considerations.
15. IANA Considerations
This document creates a no new requirements on IANA namespaces
[RFC2434].
Meyer, et. al. Section 15. [Page 33]
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16. References
16.1. Normative References
[AFI] http://www.iana.org/assignments/address-family-numbers
[BGP] Rekhter, Y, T.Li, and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", draft-ietf-idr-bgp4-23.txt.
Work in progress.
[BGPVPN] Ould-Brahim, H., E. Rosen, and Y. Rekhter, "Using
BGP as an Auto-Discovery Mechanism for
Provider-provisioned VPNs",
draft-ietf-l3vpn-bgpvpn-auto-00.txt. Work in
progress.
[CLARK] Clark, D., "Design Philosophy of the DARPA Internet
Protocols", Computer Communication Review, volume
25, number 1, January 1995. ISSN # 0146-4833.
[EXTCOMM] Sangali, S., D. Tappan, and Y. Rekhter, "BGP
Extended Communities Attribute",
draft-ietf-idr-bgp-ext-communities-06.txt. Work
in progress.
[FLOW] Marques, P, et. al., "Dissemination of flow
specification rules",
draft-marques-idr-flow-spec-00.txt. Work in
progress.
[LABELRANGE] What is the cite here?
[L2VPN] Andersson, L. and E. Rosen, "L2VPN Framework",
draft-ietf-l2vpn-l2-framework-03.txt. Work in
Progress.
[L2VPNSIG] Rosen, E. and V. Rodoaca, "Provisioning Models
and Endpoint Identifiers in L2VPN Signaling",
draft-ietf-l2vpn-signaling-00.txt. Work in
Progress.
[L2VPNT] Kompella, K. (Editor), "Layer 2 VPNs Over
Tunnels", draft-kompella-l2vpn-l2vpn-00.txt.
Work in Progress.
Meyer, et. al. Section 16.1. [Page 34]
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[L2TPv3] Lau, J., M. Townsley and I. Goyret (Editors),
"Layer Two Tunneling Protocol (Version
3)", draft-ietf-l2tpext-l2tp-base-11.txt. Work in
Progress.
[MARTINI] Martini, L., E.Rosen, and T. Smith, "Pseudowire
Setup and Maintenance using LDP",
draft-ietf-pwe3-control-protocol-05.txt. Work in
progress.
[MULLER1999] Muller, R. et. al., "Control System Reliability
Requires Careful Software Installation
Procedures", International Conference on
Accelerator and Largeand Large Experimental
Physics Systems, 1999, Trieste, Italy.
[MULTISESSION] Scudder, J. and C. Appanna, "Multisession BGP,
draft-scudder-bgp-multisession-00.txt. Work in
progress.
[ORF] Chen, E., and Rekhter, Y., "Cooperative Route
Filtering Capability for BGP-4",
draft-ietf-idr-route-filter-09.txt. Work in
progress.
[RTCONST] Bonica, R. et al, "Constrained VPN route
distribution",
draft-marques-ppvpn-rt-constrain-01.txt. Work in
progress.
[SOFTNOTIFY} Nalawade, G., K. Patel, J. Scudder, and D. Ward,
"BGPv4 Soft-Notification Message",
draft-nalawade-bgp-soft-notify-00.txt., Work in
progress.
[RFC1075] Waitzman, D., C. Partridge, and S. Deering,
"Distance Vector Multicast Routing Protocol", RFC
1075, November, 1988.
[RFC1142] Oran, D. Editor, "OSI IS-IS Intra-domain Routing
Protocol", RFC 1142, February, 1990.
[RFC1771] Rekhter, Y., and T. Li, "A Border Gateway
Protocol 4 (BGP-4)", RFC 1771, March 1995.
Meyer, et. al. Section 16.1. [Page 35]
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[RFC1958] Carpenter, B., "Architectural principles of the
Internet", Editor. RFC 1958, June 1996.
[RFC1997] Chandra, R., P. Traina, and T. Li, "BGP
Communities Attribute", RFC 1997, August, 1996.
[RFC2138] Rigney, C., et. al., "Remote Authentication Dial
In User Service (RADIUS)", RFC 2138, April, 1997.
[RFC2328] Moy, J., "OSPF Version 2", RFC 2328, April, 1998.
[RFC2453] Malkin, G., "RIP Version 2", RFC 2453, November,
1998.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol,
Version 6 (IPv6) Specification", RFC 2460,
December, 1998.
[RFC2547BIS] Rosen, E., et. al., "BGP/MPLS IP VPNs",
draft-ietf-l3vpn-rfc2547bis-00.txt. Work in
progress.
[RFC2858] Bates, T., et. al., "Multiprotocol Extensions
for BGP-4", RFC 2858, June 2000.
[RFC2918] Chen, E., "Route Refresh Capability for BGP-4",
RFC 2918, September 2000.
[RFC3036] Anderson, L., et. al., "LDP Specification", RFC
3036, January 2001.
[RFC3439] Bush, R. and D. Meyer, "Some Internet
Architectural Guidelines and Philosophy", RFC
3439, December, 2002.
[SAFI] http://www.iana.org/assignments/safi-namespace
[VPLS] Kompella, K., et. al. "Virtual Private LAN
Service", draft-ietf-l2vpn-vpls-bgp-01.txt.
Work in progress.
[VPWS] Kompella, K. et.al. "Layer 2 VPNs Over Tunnels",
draft-kompella-ppvpn-l2vpn-04.txt. Work in
progress.
Meyer, et. al. Section 16.1. [Page 36]
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16.2. Informative References
[IETFOL] https://www1.ietf.org/mailman/listinfo/routing-discussion
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", RFC 2119, March,
1997.
[RFC2026] Bradner, S., "The Internet Standards Process --
Revision 3", RFC 2026/BCP 9, October, 1996.
[RFC2028] Hovey, R. and S. Bradner, "The Organizations
Involved in the IETF Standards Process", RFC
2028/BCP 11, October, 1996.
[RFC2434] Narten, T., and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in RFCs",
RFC 2434/BCP 26, October 1998.
[RVBIB] http://www.routeviews.org/papers
[WILLINGER2002] Willinger, W., and J. Doyle, "Robustness and the
Internet: Design and evolution", 2002.
Meyer, et. al. Section 16.2. [Page 37]
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17. Editor's Address
David Meyer
Email: dmm@1-4-5.net
18. Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Meyer, et. al. Section 18. [Page 38]
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Meyer, et. al. Section 18. [Page 39]
