draft-ietf-teas-te-express-path-00.txt   draft-ietf-teas-te-express-path-01.txt 
TEAS Working Group A. Atlas TEAS Working Group A. Atlas
Internet-Draft J. Drake Internet-Draft J. Drake
Intended status: Informational Juniper Networks Intended status: Informational Juniper Networks
Expires: August 1, 2015 S. Giacalone Expires: September 27, 2015 S. Giacalone
Thomson Reuters Thomson Reuters
D. Ward D. Ward
S. Previdi S. Previdi
C. Filsfils C. Filsfils
Cisco Systems Cisco Systems
January 28, 2015 March 26, 2015
Performance-based Path Selection for Explicitly Routed LSPs using TE Performance-based Path Selection for Explicitly Routed LSPs using TE
Metric Extensions Metric Extensions
draft-ietf-teas-te-express-path-00 draft-ietf-teas-te-express-path-01
Abstract Abstract
In certain networks, it is critical to consider network performance In certain networks, it is critical to consider network performance
criteria when selecting the path for an explicitly routed RSVP-TE criteria when selecting the path for an explicitly routed RSVP-TE
LSP. Such performance criteria can include latency, jitter, and loss LSP. Such performance criteria can include latency, jitter, and loss
or other indications such as the conformance to link performance or other indications such as the conformance to link performance
objectives and non-RSVP TE traffic load. This specification uses objectives and non-RSVP TE traffic load. This specification uses
network performance data, such as is advertised via the OSPF and ISIS network performance data, such as is advertised via the OSPF and ISIS
TE metric extensions (defined outside the scope of this document) to TE metric extensions (defined outside the scope of this document) to
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 1, 2015. This Internet-Draft will expire on September 27, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8 6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 9 6.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
In certain networks, such as financial information networks, network In certain networks, such as financial information networks, network
performance information is becoming as critical to data path performance information is becoming as critical to data path
selection as other existing metrics. Network performance information selection as other existing metrics. Network performance information
can be obtained via either the TE Metric Extensions in OSPF can be obtained via either the TE Metric Extensions in OSPF [RFC7471]
[I-D.ietf-ospf-te-metric-extensions] or ISIS or ISIS [I-D.ietf-isis-te-metric-extensions] or via a management
[I-D.ietf-isis-te-metric-extensions] or via a management system. As system. As with other TE information flooded via OSPF or ISIS, the
with other TE information flooded via OSPF or ISIS, the TE metric TE metric extensions have a flooding scope limited to the local area
extensions have a flooding scope limited to the local area or level. or level. This document describes how a path computation function,
This document describes how to use that information for path whether in an ingress LSR or a PCE[RFC4655] , can use that
selection for explicitly routed LSPs signaled via RSVP-TE [RFC3209]. information for path selection for explicitly routed LSPs. The
Methods of optimizing path selection for multiple parameters are selected path may be signaled via RSVP-TE [RFC3209] or simply used by
generally computationally complex. However, there are good the ingress with segment routing
[I-D.ietf-spring-segment-routing-mpls] to properly forward the
packet. Methods of optimizing path selection for multiple parameters
are generally computationally complex. However, there are good
heuristics for the delay-constrained lowest-cost (DCLC) computation heuristics for the delay-constrained lowest-cost (DCLC) computation
problem [k-Paths_DCLC] that can be applied to consider both path cost problem [k-Paths_DCLC] that can be applied to consider both path cost
and a maximum delay bound. Some of the network performance and a maximum delay bound. Some of the network performance
information can also be used to prune links from a topology before information can also be used to prune links from a topology before
computing the path. computing the path.
The path selection mechanisms described in this document apply to The path selection mechanisms described in this document apply to
paths that are fully computed by the head-end of the LSP and then paths that are fully computed by the head-end of the LSP and then
signaled in an ERO where every sub-object is strict. This allows the signaled in an ERO where every sub-object is strict. This allows the
head-end to consider IGP-distributed performance data without head-end to consider IGP-distributed performance data without
requiring the ability to signal the performance constraints in an requiring the ability to signal the performance constraints in an
object of the RSVP Path message. object of the RSVP Path message.
When considering performance-based data, it is obvious that there are When considering performance-based data, it is obvious that there are
additional contributors to latency beyond just the links. Clearly additional contributors to latency beyond just the links. Clearly
end-to-end latency is a combination of router latency (e.g. latency end-to-end latency is a combination of router latency (e.g. latency
from traversing a router without queueing delay), queuing latency, from traversing a router without queueing delay), queuing latency,
physical link latency and other factors. While traversing a router physical link latency and other factors. While traversing a router
can cause delay, that router latency can be included in the can cause delay, that router latency can be included in the
advertised link delay. As described in advertised link delay. As described in [RFC7471] and
[I-D.ietf-ospf-te-metric-extensions] and
[I-D.ietf-isis-te-metric-extensions], queuing delay must not be [I-D.ietf-isis-te-metric-extensions], queuing delay must not be
included in the measurements advertised by OSPF or ISIS. included in the measurements advertised by OSPF or ISIS.
Queuing latency is specifically excluded to insure freedom from Queuing latency is specifically excluded to insure freedom from
oscillations and stability issues that have plagued prior attempts to oscillations and stability issues that have plagued prior attempts to
use delay as a routing metric. If application traffic follows a path use delay as a routing metric. If application traffic follows a path
based upon latency constraints, the same traffic might be in an based upon latency constraints, the same traffic might be in an
Expedited Forwarding Per-Hop-Behavior [RFC3246] with minimal queuing Expedited Forwarding Per-Hop-Behavior [RFC3246] with minimal queuing
delay or another PHB with potentially very substantial per-hop delay or another PHB with potentially very substantial per-hop
queuing delay. Only traffic which experiences relatively low queuing delay. Only traffic which experiences relatively low
congestion, such as Expedited Forwarding traffic, will experience congestion, such as Expedited Forwarding traffic, will experience
delays very close to the sum of the reported link delays. delays very close to the sum of the reported link delays.
This document does not specify how a router determines what values to This document does not specify how a router determines what values to
advertise by the IGP; it does assume that the constraints specified advertise by the IGP; it does assume that the constraints specified
in [I-D.ietf-ospf-te-metric-extensions] and in [RFC7471] and [I-D.ietf-isis-te-metric-extensions] are followed.
[I-D.ietf-isis-te-metric-extensions] are followed. Additionally, the Additionally, the end-to-end performance that is computed for an LSP
end-to-end performance that is computed for an LSP path should be path should be built from the individual link data. Any end-to-end
built from the individual link data. Any end-to-end characterization characterization used to determine an LSP's performance compliance
used to determine an LSP's performance compliance should be fully should be fully reflected in the Traffic Engineering Database so that
reflected in the Traffic Engineering Database so that a path a path calculation can also determine whether a path under
calculation can also determine whether a path under consideration consideration would be in compliance.
would be in compliance.
1.1. Basic Requirements 1.1. Basic Requirements
The following are the requirements that motivate this solution. The following are the requirements that motivate this solution.
1. Select a TE tunnel's path based upon a combination of existing 1. Select a TE tunnel's path based upon a combination of existing
constraints as well as on link-latency, packet loss, jitter, link constraints as well as on link-latency, packet loss, jitter, link
performance objectives conformance, and bandwidth consumed by performance objectives conformance, and bandwidth consumed by
non-RSVP-TE traffic. non-RSVP-TE traffic.
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layer or measurements made at a queuing priority higher than any layer or measurements made at a queuing priority higher than any
significant traffic (such as DSCP CS7 or CS6 [RFC4594], but not CS2 significant traffic (such as DSCP CS7 or CS6 [RFC4594], but not CS2
if traffic levels at CS3 and higher or EF and AF can affect the if traffic levels at CS3 and higher or EF and AF can affect the
measurement). Making delay measurements at the same priority as the measurement). Making delay measurements at the same priority as the
traffic on affected paths is likely to cause oscillations. traffic on affected paths is likely to cause oscillations.
2. Using Performance Data Constraints 2. Using Performance Data Constraints
2.1. End-to-End Constraints 2.1. End-to-End Constraints
The per-link performance data available in the IGP The per-link performance data available in the IGP [RFC7471]
[I-D.ietf-ospf-te-metric-extensions]
[I-D.ietf-isis-te-metric-extensions] includes: unidirectional link [I-D.ietf-isis-te-metric-extensions] includes: unidirectional link
delay, unidirectional delay variation, and link loss. Each (or all) delay, unidirectional delay variation, and link loss. Each (or all)
of these parameters can be used to create the path-level link-based of these parameters can be used to create the path-level link-based
parameter. parameter.
It is possible to compute a CSPF where the link latency values are It is possible to compute a CSPF where the link latency values are
used instead of TE metrics, this results in ignoring the TE metrics used instead of TE metrics, this results in ignoring the TE metrics
and causing LSPs to prefer the lowest-latency paths. In practical and causing LSPs to prefer the lowest-latency paths. In practical
scenarios, latency constraints are typically a bound constraint scenarios, latency constraints are typically a bound constraint
rather than a minimization objective. An end-to-end latency upper rather than a minimization objective. An end-to-end latency upper
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latter is exactly the delay-constrained lowest-cost (DCLC) problem to latter is exactly the delay-constrained lowest-cost (DCLC) problem to
which good heuristics have been proposed in the literature (e.g. which good heuristics have been proposed in the literature (e.g.
[k-Paths_DCLC]). [k-Paths_DCLC]).
An end-to-end bound on delay variation can be used similarly as a An end-to-end bound on delay variation can be used similarly as a
constraint in the path computation on what links to explore where the constraint in the path computation on what links to explore where the
path's delay variation is the sum of the used links' delay path's delay variation is the sum of the used links' delay
variations. variations.
For link loss, the path loss is not the sum of the used links' For link loss, the path loss is not the sum of the used links'
losses. Instead, the path loss percentage is 100 - (100 - losses. Instead, the path loss fraction is 1 - (1 - loss_L1)*(1 -
loss_L1)*(100 - loss_L2)*...*(100 - loss_Ln), where the links along loss_L2)*...*(1 - loss_Ln), where the links along the path are L1 to
the path are L1 to Ln. The end-to-end link loss bound, computed in Ln with loss_Li in fractions. This computation is discussed in more
this fashion, can also be used as a constraint in the path detail in Sections 5.1.4 and 5.1.5 in [RFC6049]. The end-to-end link
computation. loss bound, computed in this fashion, can also be used as a
constraint in the path computation.
The heuristic algorithms for DCLC only address one constraint bound The heuristic algorithms for DCLC only address one constraint bound
but having a CSPF that limits the paths explored (i.e. based on hop- but having a CSPF that limits the paths explored (i.e. based on hop-
count) can be combined [hop-count_DCLC]. count) can be combined [hop-count_DCLC].
2.2. Link Constraints 2.2. Link Constraints
In addition to selecting paths that conform to a bound on performance In addition to selecting paths that conform to a bound on performance
data, it is also useful to avoid using links that do not meet a data, it is also useful to avoid using links that do not meet a
necessary constraint. Naturally, if such a parameter were a known necessary constraint. Naturally, if such a parameter were a known
fixed value, then resource attribute flags could be used to express fixed value, then resource attribute flags could be used to express
this behavior. However, when the parameter associated with a link this behavior. However, when the parameter associated with a link
may vary dynamically, there is not currently a configuration-time may vary dynamically, there is not currently a configuration-time
mechanism to enforce such behavior. An example of this is described mechanism to enforce such behavior. An example of this is described
in Section 2.3, where links may move in and out of conformance for in Section 2.3, where links may move in and out of conformance for
link performance objectives with regards to latency, delay variation, link performance objectives with regards to latency, delay variation,
and link loss. and link loss.
When doing path selection for TE tunnels, it has not been possible to When doing path selection for TE tunnels, it has not been possible to
know how much actual bandwidth is available that includes the know how much actual bandwidth is available that includes the
bandwidth used by non-RSVP-TE traffic. In bandwidth used by non-RSVP-TE traffic. In [RFC7471]
[I-D.ietf-ospf-te-metric-extensions]
[I-D.ietf-isis-te-metric-extensions], the Unidirectional Available [I-D.ietf-isis-te-metric-extensions], the Unidirectional Available
Bandwidth is advertised as is the Residual Bandwidth. When computing Bandwidth is advertised as is the Residual Bandwidth. When computing
the path for a TE tunnel, only links with at least a minimum amount the path for a TE tunnel, only links with at least a minimum amount
of Unidirectional Available Bandwidth might be permitted. of Unidirectional Available Bandwidth might be permitted.
Similarly, only links whose loss is under a configurable value might Similarly, only links whose loss is under a configurable value might
be acceptable. For these constraints, each link can be tested be acceptable. For these constraints, each link can be tested
against the constraint and only explored in the path computation if against the constraint and only explored in the path computation if
the link passes. In essence, a link that fails the constraint test the link passes. In essence, a link that fails the constraint test
is treated as if it contained a resource attribute in the exclude-any is treated as if it contained a resource attribute in the exclude-any
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a. Should the link be trusted and used for the setup of new LSPs? a. Should the link be trusted and used for the setup of new LSPs?
b. Should LSPs using this link automatically be moved to a secondary b. Should LSPs using this link automatically be moved to a secondary
path? path?
2.3.1. Use of Anomalous Links for New Paths 2.3.1. Use of Anomalous Links for New Paths
If the answer to (a) is no for link latency performance objectives, If the answer to (a) is no for link latency performance objectives,
then any link which has the Anomalous bit set in the Unidirectional then any link which has the Anomalous bit set in the Unidirectional
Link Delay sub-TLV[I-D.ietf-ospf-te-metric-extensions] Link Delay sub-TLV[RFC7471] [I-D.ietf-isis-te-metric-extensions]
[I-D.ietf-isis-te-metric-extensions] should be removed from the should be removed from the topology before a path calculation is used
topology before a path calculation is used to compute a new path. In to compute a new path. In essence, the link should be treated
essence, the link should be treated exactly as if it fails the exactly as if it fails the exclude-any resource attributes
exclude-any resource attributes filter.[RFC3209]. filter.[RFC3209].
Similarly, if the answer to (a) is no for link loss performance Similarly, if the answer to (a) is no for link loss performance
objectives, then any link which has the Anomalous bit set in the Link objectives, then any link which has the Anomalous bit set in the Link
Los sub-TLV should be treated as if it fails the exclude-any resource Los sub-TLV should be treated as if it fails the exclude-any resource
attributes filter. If the answer to (a) is no for link jitter attributes filter. If the answer to (a) is no for link jitter
performance objectives, then any link that has the Anomalous bit set performance objectives, then any link that has the Anomalous bit set
in the Unidirectional Delay Variation sub- in the Unidirectional Delay Variation sub-
TLV[I-D.ietf-isis-te-metric-extensions] should be treated as if it TLV[I-D.ietf-isis-te-metric-extensions] should be treated as if it
fails the exclude-any resource attributes filter. fails the exclude-any resource attributes filter.
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4. Security Considerations 4. Security Considerations
This document is not currently believed to introduce new security This document is not currently believed to introduce new security
concerns. concerns.
5. Acknowledgements 5. Acknowledgements
The authors would like to thank Curtis Villamizar for his extensive The authors would like to thank Curtis Villamizar for his extensive
detailed comments and suggested text in the Section 1 and detailed comments and suggested text in the Section 1 and
Section 1.2. The authors would also like to thank Xiaohu Xu and Section 1.2. The authors would like to thank Dhruv Dhody for his
Sriganesh Kini for their review. useful comments, and his care and persistence in making sure that
these important corrections weren't missed. The authors would also
like to thank Xiaohu Xu and Sriganesh Kini for their review.
6. References 6. References
6.1. Normative References 6.1. Normative References
[I-D.ietf-isis-te-metric-extensions] [I-D.ietf-isis-te-metric-extensions]
Previdi, S., Giacalone, S., Ward, D., Drake, J., Atlas, Previdi, S., Giacalone, S., Ward, D., Drake, J., Atlas,
A., Filsfils, C., and W. Wu, "IS-IS Traffic Engineering A., Filsfils, C., and W. Wu, "IS-IS Traffic Engineering
(TE) Metric Extensions", draft-ietf-isis-te-metric- (TE) Metric Extensions", draft-ietf-isis-te-metric-
extensions-04 (work in progress), October 2014. extensions-04 (work in progress), October 2014.
[I-D.ietf-ospf-te-metric-extensions]
Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", draft-ietf-ospf-te-metric-extensions-11 (work
in progress), January 2015.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001. Tunnels", RFC 3209, December 2001.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, March 2015.
6.2. Informative References 6.2. Informative References
[I-D.ietf-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
and E. Crabbe, "Segment Routing with MPLS data plane",
draft-ietf-spring-segment-routing-mpls-00 (work in
progress), December 2014.
[RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec, [RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
J., Courtney, W., Davari, S., Firoiu, V., and D. J., Courtney, W., Davari, S., Firoiu, V., and D.
Stiliadis, "An Expedited Forwarding PHB (Per-Hop Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, March 2002. Behavior)", RFC 3246, March 2002.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594, August Guidelines for DiffServ Service Classes", RFC 4594, August
2006. 2006.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC6049] Morton, A. and E. Stephan, "Spatial Composition of
Metrics", RFC 6049, January 2011.
[hop-count_DCLC] [hop-count_DCLC]
Agrawal, H., Grah, M., and M. Gregory, "Optimization of Agrawal, H., Grah, M., and M. Gregory, "Optimization of
QoS Routing", 6th IEEE/AACIS International Conference on QoS Routing", 6th IEEE/AACIS International Conference on
Computer and Information Science 2007, 2007, Computer and Information Science 2007, 2007,
<http://ieeexplore.ieee.org/xpl/ <http://ieeexplore.ieee.org/xpl/
articleDetails.jsp?arnumber=4276447>. articleDetails.jsp?arnumber=4276447>.
[k-Paths_DCLC] [k-Paths_DCLC]
Jia, Z. and P. Varaiya, "Heuristic methods for delay Jia, Z. and P. Varaiya, "Heuristic methods for delay
constrained least cost routing using k-shortest-paths", constrained least cost routing using k-shortest-paths",
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