draft-ietf-mpls-crldp-applic-01.txt   rfc3213.txt 
MPLS Working Group Jerry Ash, AT&T Network Working Group J. Ash
Internet Draft Request for Comments: 3213 AT&T
Expiration Date: January 2001 Muckai Girish, Atoga Systems Category: Informational M. Girish
Atoga Systems
Eric Gray, Zaffire, Inc. E. Gray
Sandburst
Bilel Jamoussi, Gregory Wright, B. Jamoussi
G. Wright
Nortel Networks Corp. Nortel Networks Corp.
January 2002
July 2000
Applicability Statement for CR-LDP Applicability Statement for CR-LDP
draft-ietf-mpls-crldp-applic-01.txt
Status of this Memo Status of this Memo
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Abstract Abstract
This Internet-Draft discusses the applicability of Constraint-Based This document discusses the applicability of Constraint-Based LSP
LSP Setup using LDP [1]. It discusses possible network applications, Setup using LDP. It discusses possible network applications,
extensions to Label Distribution Protocol (LDP) [2] required to extensions to Label Distribution Protocol (LDP) required to implement
implement constraint-based routing, guidelines for deployment and constraint-based routing, guidelines for deployment and known
known limitations of the protocol. This document is a prerequisite limitations of the protocol. This document is a prerequisite to
to advancing CR-LDP on the standards track. advancing CR-LDP on the standards track.
1. Introduction 1. Introduction
As the Internet evolves, additional capabilities are required to As the Internet evolves, additional capabilities are required to
ensure proper treatment of data [3], voice, video and other delay ensure proper treatment of data [3], voice, video and other delay
sensitive traffic [4]. MPLS enhances source routing and allows for sensitive traffic [4]. MPLS enhances source routing and allows for
certain techniques, used in circuit switching, in IP networks. This certain techniques, used in circuit switching, in IP networks. This
permits a scalable approach to handling these diverse transmission permits a scalable approach to handling these diverse transmission
requirements. CR-LDP is a simple, scalable, open, non-proprietary, requirements. CR-LDP [1] is a simple, scalable, open, non-
traffic engineering signaling protocol for MPLS IP networks. proprietary, traffic engineering signaling protocol for MPLS IP
networks.
CR-LDP provides mechanisms for establishing explicitly routed Label CR-LDP provides mechanisms for establishing explicitly routed Label
Switched Paths (LSPs). These mechanisms are defined as extensions Switched Paths (LSPs). These mechanisms are defined as extensions to
to LDP [1]. Because LDP is a peer-to-peer protocol based on the LDP [2]. Because LDP is a peer-to-peer protocol based on the
establishment and maintenance of TCP sessions, the following natural establishment and maintenance of TCP sessions, the following natural
benefits exist: benefits exist:
CR-LDP messages are reliably delivered by the underlying TCP, CR-LDP messages are reliably delivered by the underlying TCP, and
and State information associated with explicitly routed LSPs State information associated with explicitly routed LSPs does not
does not require periodic refresh. require periodic refresh.
CR-LDP messages are flow controlled (throttled) through TCP. CR-LDP messages are flow controlled (throttled) through TCP.
CR-LDP is defined for the specific purpose of establishing and CR-LDP is defined for the specific purpose of establishing and
maintaining explicitly routed LSPs. Additional optional maintaining explicitly routed LSPs. Additional optional capabilities
capabilities included have minimal impact on system performance and included have minimal impact on system performance and requirements
requirements when not in use for a specific explicitly routed LSP. when not in use for a specific explicitly routed LSP. Optional
Optional capabilities provide for negotiation of LSP services and capabilities provide for negotiation of LSP services and traffic
traffic management parameters over and above best-effort packet management parameters over and above best-effort packet delivery
delivery including bandwidth allocation, setup and holding including bandwidth allocation, setup and holding priorities. CR-LDP
priorities. CR-LDP optionally allows these parameters to be optionally allows these parameters to be dynamically modified without
dynamically modified without disruption of the operational (in- disruption of the operational (in-service) LSP [4].
service) LSP [4].
CR-LDP allows the specification of a set of parameters to be CR-LDP allows the specification of a set of parameters to be signaled
signaled along with the LSP setup request. Moreover, the network can along with the LSP setup request. Moreover, the network can be
be provisioned with a set of edge traffic conditioning functions provisioned with a set of edge traffic conditioning functions (which
(which could include marking, metering, policing and shaping). This could include marking, metering, policing and shaping). This set of
set of parameters along with the specification of edge conditioning parameters along with the specification of edge conditioning
functions can be shown to be adequate and powerful enough to functions can be shown to be adequate and powerful enough to
describe, characterize and parameterize a wide variety of QoS describe, characterize and parameterize a wide variety of QoS
scenarios and services including IP differentiated services [5], scenarios and services including IP differentiated services [5],
integrated services [6], ATM service classes [7], and frame relay integrated services [6], ATM service classes [7], and frame relay
[8]. [8].
CR-LDP is designed to adequately support the various media types CR-LDP is designed to adequately support the various media types that
that MPLS was designed to support (ATM, FR, Ethernet, PPP, etc.). MPLS was designed to support (ATM, FR, Ethernet, PPP, etc.). Hence,
Hence, it will work equally well for Multi-service switched it will work equally well for Multi-service switched networks, router
networks, router networks, or hybrid networks. networks, or hybrid networks.
This applicability statement does not preclude the use of other This applicability statement does not preclude the use of other
signaling and label distribution protocols for the traffic signaling and label distribution protocols for the traffic
engineering application in MPLS based networks. Service providers engineering application in MPLS based networks. Service providers
are free to deploy whatever signaling protocol meets their needs. are free to deploy whatever signaling protocol meets their needs.
In particular CR-LDP and RSVP-TE [9] are two signaling protocols In particular CR-LDP and RSVP-TE [9] are two signaling protocols that
that perform similar functions in MPLS networks. There is currently perform similar functions in MPLS networks. There is currently no
no consensus on which protocol is technically superior. Therefore, consensus on which protocol is technically superior. Therefore,
network administrators should make a choice between the two based network administrators should make a choice between the two based
upon their needs and particular situation. Applicability of RSVP-TE upon their needs and particular situation. Applicability of RSVP-TE
is described in [10]. is described in [10].
2. Applicability of extensions to LDP 2. Applicability of extensions to LDP
To provide support of additional LSP services, CR-LDP extensions are To provide support of additional LSP services, CR-LDP extensions are
defined in such a way as to be directly translatable to objects and defined in such a way as to be directly translatable to objects and
messages used in other protocols defined to provide similar services messages used in other protocols defined to provide similar services
[9]. Implementations can take advantage of this fact to: [9]. Implementations can take advantage of this fact to:
Setup LSPs for provision of an aggregate service associated Setup LSPs for provision of an aggregate service associated with
with the services being provided via these other protocols. the services being provided via these other protocols.
Directly translate protocol messages to provide services Directly translate protocol messages to provide services defined
defined in a non-CR-LDP portion of the network. in a non-CR-LDP portion of the network.
Describe, characterize and parameterize a wide variety of QoS Describe, characterize and parameterize a wide variety of QoS
scenarios and services including IP differentiated services, scenarios and services including IP differentiated services,
integrated services, ATM service classes, and frame relay. integrated services, ATM service classes, and frame relay.
Steady state information required for proper maintenance of an LSP Steady state information required for proper maintenance of an LSP
may be as little as 200 bytes or less. It is not unreasonable to may be as little as 200 bytes or less. It is not unreasonable to
anticipate that CR-LDP implementations may support in excess of one anticipate that CR-LDP implementations may support in excess of one
hundred thousand or one million LSPs switched through a single Label hundred thousand or one million LSPs switched through a single Label
Switching Router (LSR) under fairly stable conditions. Switching Router (LSR) under fairly stable conditions.
Because CR-LDP provides for low overhead per LSP - both in terms of Because CR-LDP provides for low overhead per LSP - both in terms of
needed state information and control traffic - CR-LDP is applicable needed state information and control traffic - CR-LDP is applicable
in those portions of the Internet where very large numbers of LSPs in those portions of the Internet where very large numbers of LSPs
may need to be switched at each LSR. An example of this would be may need to be switched at each LSR. An example of this would be
large backbone networks using MPLS exclusively to transport very large backbone networks using MPLS exclusively to transport very
large numbers of traffic streams between a moderately large number large numbers of traffic streams between a moderately large number of
of MPLS edge nodes. MPLS edge nodes.
CR-LDP may also be applicable as a mediating service between CR-LDP may also be applicable as a mediating service between networks
networks providing similar service extensions using widely varying providing similar service extensions using widely varying signaling
signaling models. models.
3. Implementation and deployment considerations in relation to LDP 3. Implementation and deployment considerations in relation to LDP
LDP specifies the following label distribution and management modes LDP specifies the following label distribution and management modes
(which can be combined in various logical ways described in LDP): (which can be combined in various logical ways described in LDP):
. Downstream On Demand label distribution . Downstream On Demand label distribution
. Downstream Unsolicited label distribution . Downstream Unsolicited label distribution
. Independent Label Distribution Control . Independent Label Distribution Control
. Ordered Label Distribution Control . Ordered Label Distribution Control
skipping to change at page 6, line ? skipping to change at page 3, line 51
LDP specifies the following label distribution and management modes LDP specifies the following label distribution and management modes
(which can be combined in various logical ways described in LDP): (which can be combined in various logical ways described in LDP):
. Downstream On Demand label distribution . Downstream On Demand label distribution
. Downstream Unsolicited label distribution . Downstream Unsolicited label distribution
. Independent Label Distribution Control . Independent Label Distribution Control
. Ordered Label Distribution Control . Ordered Label Distribution Control
. Conservative Label Retention Mode . Conservative Label Retention Mode
. Liberal Label Retention Mode . Liberal Label Retention Mode
The applicability of LDP is described in [11]. The applicability of LDP is described in [11].
In networks where only Traffic Engineered LSPs are required, the CR- In networks where only Traffic Engineered LSPs are required, the CR-
LDP implementation and deployment does NOT require all the LDP implementation and deployment does NOT require all the
functionality defined in the LDP specification. The basic Discovery, functionality defined in the LDP specification. The basic Discovery,
Session, and Notification messages are required. However, CR-LDP Session, and Notification messages are required. However, CR-LDP
requires one specific combination of the label distribution modes: requires one specific combination of the label distribution modes:
. Downstream On Demand Ordered label distribution and . Downstream On Demand Ordered label distribution and
conservative Label Retention Mode conservative Label Retention Mode
Although CR-LDP is defined as an extension to LDP, support for Although CR-LDP is defined as an extension to LDP, support for
Downstream Unsolicited Label Advertisement and Independent Control Downstream Unsolicited Label Advertisement and Independent Control
modes is not required for support of Strict Explicit Routes. In modes is not required for support of Strict Explicit Routes. In
addition, implementations of CR-LDP MAY be able to support Loose addition, implementations of CR-LDP MAY be able to support Loose
Explicit Routes via the use of `Abstract Nodes' and/or `Hierarchical Explicit Routes via the use of 'Abstract Nodes' and/or 'Hierarchical
Explicit Routing', without using LDP for hop-by-hop LSP setup. Explicit Routing', without using LDP for hop-by-hop LSP setup.
CR-LDP also includes support for loose explicit routes. Use of this CR-LDP also includes support for loose explicit routes. Use of this
capability allows the network operator to define an 'explicit path' capability allows the network operator to define an 'explicit path'
through portions of their network with imperfect knowledge of the through portions of their network with imperfect knowledge of the
entire network topology. Proper use of this capability may also entire network topology. Proper use of this capability may also
allow CR-LDP implementations to inter-operate with 'vanilla' LDP allow CR-LDP implementations to inter-operate with 'vanilla' LDP
implementations - particularly if it is desired to set up an implementations - particularly if it is desired to set up an
explicitly routed LSP for best-effort packet delivery via a loosely explicitly routed LSP for best-effort packet delivery via a loosely
defined path. defined path.
Finally, in networks where both Routing Protocol-driven LSPs (a.k.a. Finally, in networks where both Routing Protocol-driven LSPs (a.k.a.
hop-by-hop LSPs) and Traffic Engineered LSPs are required, a single hop-by-hop LSPs) and Traffic Engineered LSPs are required, a single
protocol (LDP, with the extensions defined in CR-LDP) can be used protocol (LDP, with the extensions defined in CR-LDP) can be used for
for both TE and Hop-by-Hop LSPs. New protocols do not have to be both TE and Hop-by-Hop LSPs. New protocols do not have to be
introduced in the network to provide TE-LSP signaling. introduced in the network to provide TE-LSP signaling.
4. Limitations 4. Limitations
CR-LDP specification only supports point-to-point LSPs. Multi-point- CR-LDP specification only supports point-to-point LSPs. Multi-
to-point and point-to-multi-point are FFS. point-to-point and point-to-multi-point are for further study (FFS).
CR-LDP specification only supports unidirectional LSP setup. Bi- CR-LDP specification only supports unidirectional LSP setup. Bi-
directional LSP setup is FFS. directional LSP setup is FFS.
CR-LDP specification only supports a unique label allocation per LSP CR-LDP specification only supports a unique label allocation per LSP
setup. Multiple label allocations per LSP setup are FFS. setup. Multiple label allocations per LSP setup are FFS.
5. Security Considerations 5. Security Considerations
No additional security issues are introduced in this draft. As an No additional security issues are introduced in this document. As an
extension to LDP, CR-LDP shares the security concerns associated extension to LDP, CR-LDP shares the security concerns associated with
with LDP. LDP.
6. Acknowledgements 6. Acknowledgements
The authors would like to thank the following people for their The authors would like to thank the following people for their
careful review of the draft and their comments: Loa Andersson, Peter careful review of the document and their comments: Loa Andersson,
Ashwood-Smith, Anoop Ghanwani, Juha Heinanen, Jon Weil, and Adrian Peter Ashwood-Smith, Anoop Ghanwani, Juha Heinanen, Jon Weil and
Farrel. Adrian Farrel.
7. References 7. References
1 B. Jamoussi, et., al., "Constraint-based LSP Setup Using LDP", [1] Jamoussi, B., Andersson, L., Callon, R., Dantu, R., Wu, L.,
work in progress, June 2000. Doolan, P., Worster, T., Feldman, N., Fredette, A., Girish, M.,
Gray, E., Heinanen, J., Kilty, T. and A. Malis, "Constraint-
based LSP Setup Using LDP", RFC 3212, January 2002.
2 L. Andersson, et., al., "LDP Specification", work in progress, [2] Andersson, L., Doolan, P., Feldman, N., Fredette, A. and B.
June 2000. Thomas, "LDP Specification", RFC 3036, January 2001.
3 D. Awduche et., al., "Requirements for Traffic Engineering Over [3] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and J.
MPLS", RFC 2702, September 1999. McManus, "Requirements for Traffic Engineering Over MPLS", RFC
2702, September 1999.
4 G. Ash, et., al.,"LSP Modification using CR-LDP," work in [4] Ash, B., Lee, Y., Ashwood-Smith, P., Jamoussi, B., Fedyk, D.,
progress, February 2000. Skalecki, D. and L. Li, "LSP Modification using CR-LDP", RFC
3214, January 2002.
5 S. Blake et., al., "An Architecture for Differentiated Services", [5] Blake S., Black, D., Carlson, M., Davies, E., Wang, Z. and W.
RFC-2495, December 1998. Weiss, "An Architecture for Differentiated Services", RFC 2475,
December 1998.
6 S. Shenker, J. Wroclawski, "General Characterization Parameters [6] Shenker, S. and J. Wroclawski, "General Characterization
for Integrated Service Network Elements" RFC-2215 Parameters for Integrated Service Network Elements", RFC 2215,
September 1997.
7 ATM Forum Traffic Management Specification Version 4.1 (AF-TM- [7] ATM Forum Traffic Management Specification Version 4.1 (AF-TM-
0121.000), March 1999. 0121.000), March 1999.
8 CONGESTION MANAGEMENT FOR THE ISDN FRAME RELAYING BEARER [8] CONGESTION MANAGEMENT FOR THE ISDN FRAME RELAYING BEARER
SERVICE, ITU (CCITT) Recommendation I.370, 1991. SERVICE, ITU (CCITT) Recommendation I.370, 1991.
9 D. Awduche, L. Berger, D. Gan, T. Li, G. Swallow, V. Srinivasan, [9] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V. and G.
"Extensions to RSVP for LSP Tunnels," work in progress, February Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC
2000. 3209, December 2001.
10 D. Awduche, A. Hannan, X. Xiao, "Applicability Statement for [10] Awduche, D., Hannan, A. and X. Xiao, "Applicability Statement
Extensions to RSVP for LSP-Tunnels_, work in progress, April for Extensions to RSVP for LSP-Tunnels", RFC 3210, December
2000. 2001.
11 B. Thomas, E. Gray, "LDP Applicability", Work in Progress, June [11] Thomas, B. and E. Gray, "LDP Applicability", RFC 3037, January
2000. 2001.
8. Author's Addresses 8. Author's Addresses
Gerald R. Ash M. K. Girish Gerald R. Ash
AT&T Atoga Systems AT&T
Room MT E3-3C37 49026 Milmont Drive Room MT D5-2A01
200 Laurel Avenue Fremont, CA 94538 200 Laurel Avenue
Middletown, NJ 07748 E-mail: muckai@atoga.com Middletown, NJ 07748
USA USA
Phone: 732-420-4578 Phone: 732-420-4578
Fax: 732-440-6687 Fax: 732-368-8659
Email: gash@att.com EMail: gash@att.com
Eric Gray
Sandburst
600 Federal Drive
Andover, MA 01810
Phone: (978) 689-1610
EMail: eric.gray@sandburst.com
Eric W Gray Bilel Jamoussi
Zaffire, Inc Nortel Networks Corp.
2630 Orchard Parkway, 600 Technology Park Drive
San Jose, CA 95134-2020 Billerica, MA 01821
Phone: 408-894-7362 USA
egray@zaffire.com phone: +1 978-288-4506
Jamoussi@nortelnetworks.com
Gregory Wright Gregory Wright
Nortel Networks Corp. Nortel Networks Corp.
P O Box 3511 Station C P O Box 3511 Station C
Ottawa, ON K1Y 4H7 Ottawa, ON K1Y 4H7
Canada Canada
Phone: +1 613 765-7912 Phone: +1 613 765-7912
gwright@nortelnetworks.com EMail: gwright@nortelnetworks.com
Full Copyright Statement M. K. Girish
Atoga Systems
49026 Milmont Drive
Fremont, CA 94538
EMail: muckai@atoga.com
Bilel Jamoussi
Nortel Networks Corp.
600 Technology Park Drive
Billerica, MA 01821
USA
phone: +1 978-288-4506
EMail: Jamoussi@nortelnetworks.com
9. Full Copyright Statement
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"Copyright (C) The Internet Society (date). All Rights Reserved.
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
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