Internet Engineering Task Force
INTERNET-DRAFT
MPLS Working Group Daniel O. Awduche
Expiration Date: October 2000 UUNET (MCI Worldcom)
Alan Hannan
Xipeng Xiao
Frontier Globalcenter
April, 2000A new Request for Comments is now available in online RFC libraries.
RFC 3210
Title: Applicability Statement for Extensions to RSVP for
LSP-Tunnels
draft-ietf-mpls-rsvp-tunnel-applicability-01.txt
Status of this Memo
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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
Author(s): D. Awduche, A. Hannan, X. Xiao
Status: Informational
Date: December 2001
Mailbox: awduche@movaz.com, alan@routingloop.com,
xxiao@photuris.com
Pages: 8
Characters: 17691
Updates/Obsoletes/SeeAlso: None
I-D Tag: draft-ietf-mpls-rsvp-tunnel-applicability-02.txt
URL: ftp://ftp.rfc-editor.org/in-notes/rfc3210.txt
This memo discusses the applicability of "Extensions to RSVP (Resource
ReSerVation Protocol) for LSP
Tunnels" [1]. Tunnels". It highlights the protocol's
principles of operation and describes the network context for which it
was designed. Guidelines for deployment are offered and known
protocol limitations are indicated. This document is intended to
accompany the submission of "Extensions to RSVP for LSP Tunnels" onto
the Internet standards track.
1.0 Introduction
Service providers and users have indicated that there
This document is a great need
for traffic engineering capabilities in IP networks. These traffic
engineering capabilities can be based on product of the Multiprotocol Label Switching (MPLS) and can be implemented on label switching routers
(LSRs) from different vendors that interoperate using a common
signaling and label distribution protocol. A description of the
requirements for traffic engineering in MPLS based IP networks can be
found in [2]. There is, therefore, a requirement for an open, non-
proprietary, standards based signaling and label distribution
protocol for the MPLS traffic engineering application that will allow
label switching routers from different vendors to interoperate.
The "Extensions to RSVP for LSP tunnels" (RSVP-TE) specification [1]
was developed by the IETF MPLS working group to address this
requirement. RSVP-TE is a composition
Working Group of several related proposals
submitted to the IETF MPLS working group. It contains all the
necessary objects, packet formats, and procedures required to
establish and maintain explicit label switched paths (LSPs). Explicit
LSPs are foundational to the traffic engineering application in MPLS
based IP networks. Besides the traffic engineering application, the
RSVP-TE specification may have other uses within the Internet. IFTF.
This memo describes the applicability of the RSVP-TE specifications
[1]. The protocol's principles of operation are highlighted, the
network context for which it was developed is described, guidelines provides information for deployment are offered, and known protocol limitations are
indicated.
This applicability statement concerns only the use of RSVP to set up
unicast LSP-tunnels. Internet community. It is noted that not all of the features
described in RFC2205 [3] are required to support the instantiation
and maintenance of LSP-tunnels. Aspects related to the support of
other features and capabilities of RSVP by an implementation that
also supports LSP-tunnels are beyond the scope of this document.
However, support of such additional features and capabilities should
not introduce new security vulnerabilities in environments that only
use RSVP to set up LSP-tunnels.
This applicability statement does
not preclude the use of other
signaling and label distribution protocols for the traffic
engineering application in MPLS based networks. Service providers
are free to deploy whatever signaling protocol that meets their
needs.
In particular, CR-LDP [7] and RSVP-TE [1] are two signaling protocols
that perform similar functions in MPLS networks. There is currently
no consensus on which protocol is technically superior. Therefore,
network administrators should make a choice between the two based
upon their needs and particular situation.
2.0 Technical Overview of Extensions to RSVP for LSP Tunnels
The RSVP-TE specification extends the original RSVP protocol by
giving it new capabilities that support the following functions in specify an
MPLS domain:
(1) downstream-on-demand label distribution
(2) instantiation of explicit label switched paths
(3) allocation of network resources (e.g., bandwidth) to
explicit LSPs
(4) rerouting of established LSP-tunnels in a smooth fashion
using the concept of make-before-break
(5) tracking of the actual route traversed by an LSP-tunnel
(6) diagnostics on LSP-tunnels
(7) the concept of nodal abstraction
(8) preemption options that are administratively controllable
The RSVP-TE specification introduces several new RSVP objects,
including the LABEL-REQUEST object, the RECORD-ROUTE object, the
LABEL object, the EXPLICIT-ROUTE object, and new SESSION objects. New
error messages are defined to provide notification of exception
conditions. All Internet standard of the new objects defined in RSVP-TE are optional
with respect to the RSVP protocol, except the LABEL-REQUEST and LABEL
objects, which are both mandatory for the establishment any kind. Distribution of LSP-
tunnels.
Two fundamental aspects distinguish the RSVP-TE specification [1]
from the original RSVP protocol [3].
The first distinguishing aspect is the fact that the RSVP-TE
specification [1] this
memo is intended for use by label switching routers (as
well as hosts) to establish and maintain LSP-tunnels and to reserve
network resources for such LSP-tunnels. The original RSVP
specification [3], on the other hand, was intended for use by hosts
to request and reserve network resources for micro-flows.
The second distinguishing aspect unlimited.
This announcement is the fact that the RSVP-TE
specification generalizes the concept of "RSVP flow." The RSVP-TE
specification essentially allows an RSVP session sent to consist of an
arbitrary aggregation of traffic (based on local policies) between
the originating node of an LSP-tunnel and the egress node of the
tunnel. To be definite, in the original RSVP protocol [3], a session
was defined as a data flow with a particular destination IETF list and
transport layer protocol. In the RSVP-TE specification, however, a
session is implicitly defined as the set of packets that are assigned
the same MPLS label value at the originating node of an LSP-tunnel.
The assignment of labels RFC-DIST list.
Requests to packets can be based on various criteria,
and may even encompass all packets (or subsets thereof) between the
endpoints of the LSP-tunnel. Because traffic is aggregated, the
number of LSP-tunnels (hence the number of RSVP sessions) does not
increase proportionally with the number of flows in the network.
Therefore, the RSVP-TE specification [1] addresses a major scaling
issue with the original RSVP protocol [3], namely the large amount of
system resources that would otherwise be required added to manage
reservations and maintain state for potentially thousands or even
millions of RSVP sessions at the micro-flow granularity.
The reader is referred to [1] for a technical description of deleted from the
RSVP-TE protocol specification.
3.0 Applicability of Extensions IETF distribution list
should be sent to RSVP for LSP Tunnels
Use of RSVP-TE is appropriate in contexts where it is useful IETF-REQUEST@IETF.ORG. Requests to
establish and maintain explicit label switched paths in an MPLS
network. LSP-tunnels may be instantiated for measurement purposes
and/or for routing control purposes. They may also be instantiated
for other administrative reasons.
For the measurement application, an LSP-tunnel can be used
added to capture
various path statistics between its endpoints. This can be
accomplished by associating various performance management and fault
management functions with an LSP-tunnel, such as packet and byte
counters. For example, an LSP-tunnel can be instantiated, with or
without bandwidth allocation, solely for the purpose of monitoring
traffic flow statistics between two label switching routers.
For the routing control application, LSP-tunnels can be used to
forward subsets of traffic through paths that are independent of
routes computed by conventional Interior Gateway Protocol (IGP)
Shortest Path First (SPF) algorithms. This feature introduces
significant flexibility into the routing function and allows policies
to be implemented that can result in the performance optimization of
operational networks. For example, using LSP-tunnels, traffic can be
routed away deleted from congested network resources onto relatively
underutilized ones. More generally, load balancing policies can be
actualized that increase the effective capacity of the network.
To further enhance the control application, RSVP-TE may RFC-DIST distribution list should
be augmented
with an ancillary constraint-based routing entity. This entity may
compute explicit routes based sent to RFC-DIST-REQUEST@RFC-EDITOR.ORG.
Details on certain traffic attributes, while
taking network constraints into account. Additionally, IGP link state
advertisements obtaining RFCs via FTP or EMAIL may be extended to propagate new topology state
information. This information can be used obtained by the constraint-based
routing entity to compute feasible routes. Furthermore, the IGP
routing algorithm may itself be enhanced to take pre-established
LSP-tunnels into consideration while building the routing table. All
these augmentations are useful, but not mandatory. In fact, the
RSVP-TE specification may be deployed in certain contexts without any
of these additional components.
The capability to monitor point to point traffic statistics between
two routers and the capability to control the forwarding paths of
subsets of traffic through a given network topology together make the
RSVP-TE specifications applicable and useful for traffic engineering
within service provider networks.
These capabilities also make the RSVP-TE applicable, in some
contexts, as a component of sending
an MPLS based VPN provisioning framework.
It is significant that the MPLS architecture [4] states clearly that
no single label distribution protocol is assumed for the MPLS
technology. Therefore, as noted in the introduction, this
applicability statement does not (and should not be construed to)
prevent a label switching router from implementing other signaling
and label distribution protocols that also support establishment of
explicit LSPs and traffic engineering in MPLS networks.
4.0 Deployment and Policy Considerations
When deploying RSVP-TE, there should be well defined administrative
policies governing the selection of nodes that will serve as
endpoints for LSP-tunnels. Furthermore, when devising a virtual
topology for LSP-tunnels, special consideration should be given EMAIL message to
the tradeoff between the operational complexity associated rfc-info@RFC-EDITOR.ORG with a
large number of LSP-tunnels and the control granularity that large
numbers of LSP-tunnels allow. Stated otherwise, a large number of
LSP-tunnels allows greater control over the message body
help: ways_to_get_rfcs. For example:
To: rfc-info@RFC-EDITOR.ORG
Subject: getting rfcs
help: ways_to_get_rfcs
Requests for special distribution of traffic
across the network, but increases network operational complexity. In
large networks, it may be advisable to start with a simple LSP-tunnel
virtual topology and then introduce additional complexity based on
observed or anticipated traffic flow patterns.
Administrative policies may also guide the amount of bandwidth to should be
allocated (if any) to each LSP-tunnel. Policies of this type may take
into consideration empirical traffic statistics derived from the
operational network in addition to other factors.
5.0 Limitations
The RSVP-TE specification supports only unicast LSP-tunnels.
Multicast LSP-tunnels are not supported.
The RSVP-TE specification supports only unidirectional LSP- tunnels.
Bidirectional LSP-tunnels are not supported.
The soft state nature of RSVP remains a source of concern because of
the need to generate refresh messages periodically to maintain the
state of established LSP-tunnels. This issue is addressed in several
proposals that have been submitted to either the RSVP working group (see
e.g. [6]).
6.0 Conclusion
The applicability
author of the "Extensions to RSVP for LSP Tunnels"
specification has been discussed in this document. The specification
introduced several enhancements to the RSVP protocol, which make it
applicable in contexts in which the original RSVP protocol would have
been inappropriate. One context in which the RSVP-TE specification is
particularly applicable is in traffic engineering RFC in MPLS based IP
networks.
7.0 Security Considerations
This document does not introduce new security issues. The RSVP-TE
specification adds new opaque objects to RSVP. Therefore, the
security considerations pertaining question, or to RFC-Manager@RFC-EDITOR.ORG. Unless
specifically noted otherwise on the original RSVP protocol
remain relevant. When deployed in service provider networks, it is
mandatory to ensure that only authorized entities RFC itself, all RFCs are permitted to
initiate establishment of LSP-tunnels.
8.0 Acknowledgments
The authors gratefully acknowledge the useful comments received from
the following individuals during initial review of this memo in the
MPLS WG mailing list: Eric Gray, John Renwick, and George Swallow.
9.0 References
[1] D. Awduche, L. Berger, D. Gan, T. Li, G. Swallow,
V. Srinivasan, "Extensions to RSVP for LSP Tunnels,"
Work in Progress.
[2] D. Awduche, J. Malcolm, J. Agogbua, M. O'Dell, J. McManus,
"Requirements
unlimited distribution.echo
Submissions for Traffic Engineering Over MPLS," Requests for Comments should be sent to
RFC-EDITOR@RFC-EDITOR.ORG. Please consult RFC 2702, September 1999.
[3] Braden, R. et al., "Resource ReSerVation Protocol (RSVP) --
Version 1, Functional Specification", 2223, Instructions to RFC 2205, September 1997.
[4] E. Rosen, A. Viswanathan, R. Callon, "A Proposed Architecture
for MPLS", Work in Progress.
[5] R. Callon, P. Doolan, N. Feldman, A. Fredette, G. Swallow,
A. Viswanathan, "A Framework
Authors, for Multiprotocol Label
Switching", Work in Progress.
[6] L. Berger, D. Gan, G. Swallow, P. Pan, F. Tommasi, "RSVP
Refresh Reduction Extensions," Work in Progress.
[7] B. Jamoussi et al, "Constraint-Based LSP Setup using
LDP," Work in Progress
10.0 AUTHORS' ADDRESSES
Daniel O. Awduche
UUNET (MCI Worldcom)
22001 Loudoun County Parkway
Ashburn, VA 20147
Email: awduche@uu.net
Voice: +1 703-886-5277
Alan Hannan
Frontier Globalcenter
141 Caspian Court,
Sunnyvale, CA 94089
Email: alan@globalcenter.net,
Voice: +1 408-543-4891
Xipeng Xiao
Frontier Globalcenter
141 Caspian Court,
Sunnyvale, CA 94089
Email: xipeng@globalcenter.net,
Voice: +1 408-543-4801 further information.