draft-ietf-mpls-rsvp-tunnel-applicability-00.txt   draft-ietf-mpls-rsvp-tunnel-applicability-01.txt 
Internet Engineering Task Force Internet Engineering Task Force
INTERNET-DRAFT INTERNET-DRAFT
MPLS Working Group Daniel O. Awduche MPLS Working Group Daniel O. Awduche
Expiration Date: March 2000 UUNET (MCI Worldcom) Expiration Date: October 2000 UUNET (MCI Worldcom)
Alan Hannan Alan Hannan
Xipeng Xiao Xipeng Xiao
Frontier Globalcenter Frontier Globalcenter
September, 1999 April, 2000
Applicability Statement for Extensions to RSVP for LSP-Tunnels Applicability Statement for Extensions to RSVP for LSP-Tunnels
draft-ietf-mpls-rsvp-tunnel-applicability-00.txt draft-ietf-mpls-rsvp-tunnel-applicability-01.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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Service providers and users have indicated that there is a great need Service providers and users have indicated that there is a great need
for traffic engineering capabilities in IP networks. These traffic for traffic engineering capabilities in IP networks. These traffic
engineering capabilities can be based on Multiprotocol Label engineering capabilities can be based on Multiprotocol Label
Switching (MPLS) and can be implemented on label switching routers Switching (MPLS) and can be implemented on label switching routers
(LSRs) from different vendors that interoperate using a common (LSRs) from different vendors that interoperate using a common
signaling and label distribution protocol. A description of the signaling and label distribution protocol. A description of the
requirements for traffic engineering in MPLS based IP networks can be requirements for traffic engineering in MPLS based IP networks can be
found in [2]. There is, therefore, a requirement for an open, non- found in [2]. There is, therefore, a requirement for an open, non-
proprietary, standards based signaling and label distribution proprietary, standards based signaling and label distribution
protocol for the MPLS traffic engineering application that may be protocol for the MPLS traffic engineering application that will allow
available from all label switching router vendors, which allow such label switching routers from different vendors to interoperate.
devices to interoperate.
The "Extensions to RSVP for LSP tunnels" (RSVP-Tunnel) specification The "Extensions to RSVP for LSP tunnels" (RSVP-TE) specification [1]
[1] was developed by the IETF MPLS working group to address this was developed by the IETF MPLS working group to address this
requirement. RSVP-Tunnel is a composition of several related requirement. RSVP-TE is a composition of several related proposals
proposals submitted to the IETF MPLS working group. It contains all submitted to the IETF MPLS working group. It contains all the
the necessary objects, packet formats, and procedures required to necessary objects, packet formats, and procedures required to
establish and maintain explicit label switched paths (LSPs). Explicit establish and maintain explicit label switched paths (LSPs). Explicit
LSPs are foundational to the traffic engineering application in MPLS LSPs are foundational to the traffic engineering application in MPLS
based IP networks. Besides the traffic engineering application, the based IP networks. Besides the traffic engineering application, the
RSVP-Tunnel specification may have other uses within the Internet. RSVP-TE specification may have other uses within the Internet.
This memo describes the applicability of the RSVP-Tunnel
specifications [1]. The protocol's principles of operation are
highlighted, the network context for which it was developed is
described, guidelines for deployment are offered, and known protocol
limitations are indicated.
Two fundamental aspects distinguish the RSVP-Tunnel specification [1]
from the original RSVP protocol [3].
The first distinguishing aspect is the fact that the RSVP-Tunnel
specification [1] 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 is the fact that the RSVP-Tunnel This memo describes the applicability of the RSVP-TE specifications
specification generalizes the concept of "RSVP flow." The RSVP-Tunnel [1]. The protocol's principles of operation are highlighted, the
specification essentially allows an RSVP session to consist of an network context for which it was developed is described, guidelines
arbitrary aggregation of traffic (based on local policies) between for deployment are offered, and known protocol limitations are
the origination node of an LSP-tunnel and the egress node of the indicated.
tunnel. To be definite, in the original RSVP protocol [3], a session
was defined as a data flow with a particular destination and
transport layer protocol. In the RSVP-Tunnel specification, however,
a session is implicitly defined as the set of packets that are
assigned the same MPLS label value at the origination node of an
LSP-tunnel. The assignment of labels 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-Tunnel 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 to manage reservations and maintain state for potentially
thousands or even millions of RSVP sessions at the micro-flow
granularity.
This applicability statement concerns only the use of RSVP to set up This applicability statement concerns only the use of RSVP to set up
unicast LSP-tunnels. It is noted that not all of the features unicast LSP-tunnels. It is noted that not all of the features
described in RFC2205 [3] are required to support the instantiation described in RFC2205 [3] are required to support the instantiation
and maintenance of LSP-tunnels. Aspects related to the support of and maintenance of LSP-tunnels. Aspects related to the support of
other features and capabilities of RSVP by an implementation that other features and capabilities of RSVP by an implementation that
also supports LSP-tunnels are beyond the scope of this document. also supports LSP-tunnels are beyond the scope of this document.
However, support of such additional features and capabilities should However, support of such additional features and capabilities should
not introduce new security vulnerabilities in environments that only not introduce new security vulnerabilities in environments that only
use RSVP to set up LSP-tunnels. use RSVP to set up LSP-tunnels.
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 IP networks. Service providers engineering application in MPLS based networks. Service providers
are free to deploy whatever signaling protocol that meets their are free to deploy whatever signaling protocol that meets their
needs. 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 2.0 Technical Overview of Extensions to RSVP for LSP Tunnels
The RSVP-Tunnel specification extends the original RSVP protocol by The RSVP-TE specification extends the original RSVP protocol by
giving it new capabilities that support the following functions in an giving it new capabilities that support the following functions in an
MPLS domain: MPLS domain:
(1) downstream-on-demand label distribution (1) downstream-on-demand label distribution
(2) instantiation of explicit label switched paths (2) instantiation of explicit label switched paths
(3) allocation of network resources (e.g., bandwidth) to explicit (3) allocation of network resources (e.g., bandwidth) to
LSPs explicit LSPs
(4) rerouting of established LSP-tunnels in a smooth fashion using (4) rerouting of established LSP-tunnels in a smooth fashion
the concept of make-before-break using the concept of make-before-break
(5) tracking of the actual route traversed by an LSP-tunnel (5) tracking of the actual route traversed by an LSP-tunnel
(6) diagnostics on LSP-tunnels (6) diagnostics on LSP-tunnels
(7) the concept of nodal abstraction (7) the concept of nodal abstraction
(8) preemption options that are administratively controllable (8) preemption options that are administratively controllable
The RSVP-Tunnel specification introduces several new RSVP objects,
The RSVP-TE specification introduces several new RSVP objects,
including the LABEL-REQUEST object, the RECORD-ROUTE object, the including the LABEL-REQUEST object, the RECORD-ROUTE object, the
LABEL object, the EXPLICIT-ROUTE object, and new SESSION objects. New LABEL object, the EXPLICIT-ROUTE object, and new SESSION objects. New
error messages are defined to provide notification of exception error messages are defined to provide notification of exception
conditions. All of the new objects defined in RSVP-Tunnel are conditions. All of the new objects defined in RSVP-TE are optional
optional with respect to the RSVP protocol, except the LABEL-REQUEST with respect to the RSVP protocol, except the LABEL-REQUEST and LABEL
and LABEL objects, which are both mandatory for the establishment of objects, which are both mandatory for the establishment of LSP-
LSP-tunnels. tunnels.
Informally, establishment of an LSP-tunnel proceeds in the following Two fundamental aspects distinguish the RSVP-TE specification [1]
way: First, the origination node of the LSP-tunnel creates an RSVP from the original RSVP protocol [3].
Path message and inserts a LABEL-REQUEST object into it. Optionally,
an EXPLICIT-ROUTE object, a RECORD-ROUTE object, and a
SESSION_ATTRIBUTE object may also be inserted into the path message.
The LABEL-REQUEST object indicates that a label binding is requested;
the EXPLICIT-ROUTE object depicts the explicit route for the LSP-
tunnel as a sequence of abstract nodes; the RECORD-ROUTE object
specifies that a path vector record of the route traversed is
required; finally, the SESSION_ATTRIBUTE object is used for session
identification and diagnosis.
When the Path message reaches the egress node of the LSP-tunnel, a The first distinguishing aspect is the fact that the RSVP-TE
Resv message is created and a LABEL object containing an MPLS label specification [1] is intended for use by label switching routers (as
is inserted into the Resv message. As the Resv message propagates to well as hosts) to establish and maintain LSP-tunnels and to reserve
the origination node (in the reverse direction along the path network resources for such LSP-tunnels. The original RSVP
traversed by the Path message), each node uses the MPLS label in the specification [3], on the other hand, was intended for use by hosts
LABEL object from its downstream neighbor as outgoing label for the to request and reserve network resources for micro-flows.
LSP-tunnel. Each node inserts its own LABEL object before propagating
the Resv message upstream. This way, labels are allocated The second distinguishing aspect is the fact that the RSVP-TE
sequentially all the way from the egress node of the LSP-tunnel to specification generalizes the concept of "RSVP flow." The RSVP-TE
the origination node. It is when the Resv message reaches the specification essentially allows an RSVP session to consist of an
origination node that the LSP-tunnel becomes established. 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 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 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 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 the
RSVP-TE protocol specification.
3.0 Applicability of Extensions to RSVP for LSP Tunnels 3.0 Applicability of Extensions to RSVP for LSP Tunnels
Use of RSVP-Tunnel is appropriate in contexts where it is useful to Use of RSVP-TE is appropriate in contexts where it is useful to
establish and maintain explicit label switched paths in an MPLS establish and maintain explicit label switched paths in an MPLS
network. LSP-tunnels may be instantiated for measurement purposes network. LSP-tunnels may be instantiated for measurement purposes
and/or for control purposes. They may also be instantiated for other and/or for routing control purposes. They may also be instantiated
administrative reasons. for other administrative reasons.
For the measurement application, an LSP-tunnel can be used to capture For the measurement application, an LSP-tunnel can be used to capture
various path statistics between its endpoints. This can be various path statistics between its endpoints. This can be
accomplished by associating various performance management and fault accomplished by associating various performance management and fault
management functions with an LSP-tunnel, such as packet and byte management functions with an LSP-tunnel, such as packet and byte
counters. For example, an LSP-tunnel can be instantiated, with or counters. For example, an LSP-tunnel can be instantiated, with or
without bandwidth allocation, solely for the purpose of monitoring without bandwidth allocation, solely for the purpose of monitoring
traffic flow statistics between two label switching routers. traffic flow statistics between two label switching routers.
For the control application, LSP-tunnels can be used to forward For the routing control application, LSP-tunnels can be used to
subsets of traffic through paths that are independent of routes forward subsets of traffic through paths that are independent of
computed by conventional Interior Gateway Protocol (IGP) Shortest routes computed by conventional Interior Gateway Protocol (IGP)
Path First (SPF) algorithms. This feature provides significant Shortest Path First (SPF) algorithms. This feature introduces
control over the routing function and allows policies to be significant flexibility into the routing function and allows policies
implemented that result in the performance optimization of to be implemented that can result in the performance optimization of
operational networks. For example, using LSP-tunnels, traffic can be operational networks. For example, using LSP-tunnels, traffic can be
routed away from congested network resources onto relatively routed away from congested network resources onto relatively
underutilized ones. More generally, load balancing policies can be underutilized ones. More generally, load balancing policies can be
actualized that increase the effective capacity of the network. actualized that increase the effective capacity of the network.
To further enhance the control application, RSVP-Tunnel may be To further enhance the control application, RSVP-TE may be augmented
augmented with an ancillary constraint-based routing entity. This with an ancillary constraint-based routing entity. This entity may
entity may compute explicit routes based on certain traffic compute explicit routes based on certain traffic attributes, while
attributes, while taking network constraints into account. taking network constraints into account. Additionally, IGP link state
Additionally, IGP link state advertisements may be extended to advertisements may be extended to propagate new topology state
propagate new topology state information. This information can be information. This information can be used by the constraint-based
used by the constraint-based routing entity to compute feasible routing entity to compute feasible routes. Furthermore, the IGP
routes. Furthermore, the IGP routing algorithm may itself be enhanced routing algorithm may itself be enhanced to take pre-established
to take pre-established LSP-tunnels into consideration while building LSP-tunnels into consideration while building the routing table. All
the routing table. All these augmentations are useful, but not these augmentations are useful, but not mandatory. In fact, the
mandatory. In fact, the RSVP-Tunnel specification may be deployed in RSVP-TE specification may be deployed in certain contexts without any
certain contexts without any of these additional components. of these additional components.
The capability to monitor point to point traffic statistics between The capability to monitor point to point traffic statistics between
two routers and the capability to control the forwarding paths of two routers and the capability to control the forwarding paths of
subsets of traffic through a given network topology together make the subsets of traffic through a given network topology together make the
RSVP-Tunnel specifications applicable and useful for traffic RSVP-TE specifications applicable and useful for traffic engineering
engineering within service provider networks. within service provider networks.
These capabilities also make the RSVP-Tunnel applicable, in some These capabilities also make the RSVP-TE applicable, in some
contexts, as a component of an MPLS based VPN provisioning framework. contexts, as a component of an MPLS based VPN provisioning framework.
It is significant that the MPLS architecture [4] states clearly that It is significant that the MPLS architecture [4] states clearly that
no single label distribution protocol is assumed for the MPLS no single label distribution protocol is assumed for the MPLS
technology. Therefore, this applicability statement does not (and technology. Therefore, as noted in the introduction, this
should not be construed to) prevent a label switching router from applicability statement does not (and should not be construed to)
implementing other signaling and label distribution protocols that prevent a label switching router from implementing other signaling
also support establishment of explicit LSPs and traffic engineering and label distribution protocols that also support establishment of
in MPLS networks. explicit LSPs and traffic engineering in MPLS networks.
4.0 Deployment and Policy Considerations 4.0 Deployment and Policy Considerations
When deploying RSVP-Tunnel, there should be well defined When deploying RSVP-TE, there should be well defined administrative
administrative policies governing the selection of nodes that will policies governing the selection of nodes that will serve as
serve as endpoints for LSP-tunnels. Furthermore, when devising a endpoints for LSP-tunnels. Furthermore, when devising a virtual
virtual topology for LSP-tunnels, special consideration should be topology for LSP-tunnels, special consideration should be given to
given to the tradeoff between the operational complexity associated the tradeoff between the operational complexity associated with a
with a large number of LSP-tunnels and the control granularity that large number of LSP-tunnels and the control granularity that large
large numbers of LSP-tunnels allow. Stated otherwise, a large number numbers of LSP-tunnels allow. Stated otherwise, a large number of
of LSP-tunnels allows greater control over the distribution of LSP-tunnels allows greater control over the distribution of traffic
traffic across the network, but increases network operational across the network, but increases network operational complexity. In
complexity. In large networks, it may be advisable to start with a large networks, it may be advisable to start with a simple LSP-tunnel
simple LSP-tunnel virtual topology and then introduce additional virtual topology and then introduce additional complexity based on
complexity based on observed or anticipated traffic flow patterns. observed or anticipated traffic flow patterns.
Administrative policies should also guide the amount of bandwidth to Administrative policies may also guide the amount of bandwidth to be
be allocated (if any) to each LSP-tunnel. Policies of this type may allocated (if any) to each LSP-tunnel. Policies of this type may take
take into consideration traffic statistics derived from the into consideration empirical traffic statistics derived from the
operational network in addition to other factors. operational network in addition to other factors.
5.0 Limitations 5.0 Limitations
The RSVP-Tunnel specification supports only unicast LSP-tunnels. The RSVP-TE specification supports only unicast LSP-tunnels.
Multicast LSP-tunnels are not supported. Multicast LSP-tunnels are not supported.
The RSVP-Tunnel specification supports only unidirectional LSP- The RSVP-TE specification supports only unidirectional LSP- tunnels.
tunnels. Bidirectional LSP-tunnels are not supported. Bidirectional LSP-tunnels are not supported.
The soft state nature of RSVP remains a source of concern because of The soft state nature of RSVP remains a source of concern because of
the need to generate refresh messages periodically to maintain the the need to generate refresh messages periodically to maintain the
state of established LSP-tunnels. This issue is addressed in several state of established LSP-tunnels. This issue is addressed in several
proposals that have been submitted to the RSVP working group (see proposals that have been submitted to the RSVP working group (see
e.g. [6]). e.g. [6]).
6.0 Conclusion 6.0 Conclusion
The applicability of the "Extensions to RSVP for LSP Tunnels" The applicability of the "Extensions to RSVP for LSP Tunnels"
specification has been discussed in this document. The specification specification has been discussed in this document. The specification
introduced several enhancements to the RSVP protocol, which make it introduced several enhancements to the RSVP protocol, which make it
applicable in contexts in which the original RSVP protocol would have applicable in contexts in which the original RSVP protocol would have
been inappropriate. One context in which the RSVP-Tunnel been inappropriate. One context in which the RSVP-TE specification is
specification is particularly applicable is in traffic engineering in particularly applicable is in traffic engineering in MPLS based IP
MPLS based IP networks. networks.
7.0 Security Considerations 7.0 Security Considerations
This document does not introduce new security issues. The RSVP-Tunnel This document does not introduce new security issues. The RSVP-TE
specification adds new opaque objects to RSVP and so the security specification adds new opaque objects to RSVP. Therefore, the
considerations pertaining to the original RSVP protocol remain security considerations pertaining to the original RSVP protocol
relevant. When deployed in service provider networks, it is mandatory remain relevant. When deployed in service provider networks, it is
to ensure that only authorized entities are permitted to initiate mandatory to ensure that only authorized entities are permitted to
establishment of LSP-tunnels. initiate establishment of LSP-tunnels.
8.0 Acknowledgments 8.0 Acknowledgments
The authors gratefully acknowledge the useful comments received from The authors gratefully acknowledge the useful comments received from
the following individuals during initial review of this memo in the the following individuals during initial review of this memo in the
MPLS WG mailing list: Eric Gray, John Renwick, and George Swallow. MPLS WG mailing list: Eric Gray, John Renwick, and George Swallow.
9.0 References 9.0 References
[1] D. Awduche, L. Berger, D. Gan, T. Li, G. Swallow, [1] D. Awduche, L. Berger, D. Gan, T. Li, G. Swallow,
skipping to change at page 7, line 40 skipping to change at page 7, line 40
[3] Braden, R. et al., "Resource ReSerVation Protocol (RSVP) -- [3] Braden, R. et al., "Resource ReSerVation Protocol (RSVP) --
Version 1, Functional Specification", RFC 2205, September 1997. Version 1, Functional Specification", RFC 2205, September 1997.
[4] E. Rosen, A. Viswanathan, R. Callon, "A Proposed Architecture [4] E. Rosen, A. Viswanathan, R. Callon, "A Proposed Architecture
for MPLS", Work in Progress. for MPLS", Work in Progress.
[5] R. Callon, P. Doolan, N. Feldman, A. Fredette, G. Swallow, [5] R. Callon, P. Doolan, N. Feldman, A. Fredette, G. Swallow,
A. Viswanathan, "A Framework for Multiprotocol Label A. Viswanathan, "A Framework for Multiprotocol Label
Switching", Work in Progress. Switching", Work in Progress.
[6] L. Berger, D. Gan, G. Swallow, "RSVP Refresh Reduction [6] L. Berger, D. Gan, G. Swallow, P. Pan, F. Tommasi, "RSVP
Extensions," Work in Progress. Refresh Reduction Extensions," Work in Progress.
[7] B. Jamoussi et al, "Constraint-Based LSP Setup using
LDP," Work in Progress
10.0 AUTHORS' ADDRESSES 10.0 AUTHORS' ADDRESSES
Daniel O. Awduche Daniel O. Awduche
UUNET (MCI Worldcom) UUNET (MCI Worldcom)
3060 Williams Drive 22001 Loudoun County Parkway
Fairfax, VA 22031 Ashburn, VA 20147
Email: awduche@uu.net Email: awduche@uu.net
Voice: +1 703-208-5277 Voice: +1 703-886-5277
Alan Hannan Alan Hannan
Frontier Globalcenter Frontier Globalcenter
141 Caspian Court, 141 Caspian Court,
Sunnyvale, CA 94089 Sunnyvale, CA 94089
Email: alan@globalcenter.net, Email: alan@globalcenter.net,
Voice: +1 408-543-4891 Voice: +1 408-543-4891
Xipeng Xiao Xipeng Xiao
Frontier Globalcenter Frontier Globalcenter
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