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diff --git a/doc/rfc/rfc8426.txt b/doc/rfc/rfc8426.txt new file mode 100644 index 0000000..8a9fd61 --- /dev/null +++ b/doc/rfc/rfc8426.txt @@ -0,0 +1,675 @@ + + + + + + +Internet Engineering Task Force (IETF) H. Sitaraman, Ed. +Request for Comments: 8426 V. Beeram +Category: Informational Juniper Networks +ISSN: 2070-1721 I. Minei + Google, Inc. + S. Sivabalan + Cisco Systems, Inc. + July 2018 + + + Recommendations for RSVP-TE and Segment Routing (SR) + Label Switched Path (LSP) Coexistence + +Abstract + + Operators are looking to introduce services over Segment Routing (SR) + Label Switched Paths (LSPs) in networks running Resource Reservation + Protocol - Traffic Engineering (RSVP-TE) LSPs. In some instances, + operators are also migrating existing services from RSVP-TE to SR + LSPs. For example, there might be certain services that are well + suited for SR and need to coexist with RSVP-TE in the same network. + Such introduction or migration of traffic to SR might require + coexistence with RSVP-TE in the same network for an extended period + of time, depending on the operator's intent. The following document + provides solution options for keeping the traffic engineering + database consistent across the network, accounting for the different + bandwidth utilization between SR and RSVP-TE. + +Status of This Memo + + This document is not an Internet Standards Track specification; it is + published for informational purposes. + + This document is a product of the Internet Engineering Task Force + (IETF). It represents the consensus of the IETF community. It has + received public review and has been approved for publication by the + Internet Engineering Steering Group (IESG). Not all documents + approved by the IESG are candidates for any level of Internet + Standard; see Section 2 of RFC 7841. + + Information about the current status of this document, any errata, + and how to provide feedback on it may be obtained at + https://www.rfc-editor.org/info/rfc8426. + + + + + + + + +Sitaraman, et al. Informational [Page 1] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + +Copyright Notice + + Copyright (c) 2018 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (https://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. Code Components extracted from this document must + include Simplified BSD License text as described in Section 4.e of + the Trust Legal Provisions and are provided without warranty as + described in the Simplified BSD License. + +Table of Contents + + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 + 3. Solution Options . . . . . . . . . . . . . . . . . . . . . . 3 + 3.1. Static Partitioning of Bandwidth . . . . . . . . . . . . 4 + 3.2. Centralized Management of Available Capacity . . . . . . 4 + 3.3. Flooding SR Utilization in IGP . . . . . . . . . . . . . 5 + 3.4. Running SR over RSVP-TE . . . . . . . . . . . . . . . . . 5 + 3.5. TED Consistency by Reflecting SR Traffic . . . . . . . . 5 + 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 + 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 + 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 6.1. Normative References . . . . . . . . . . . . . . . . . . 9 + 6.2. Informative References . . . . . . . . . . . . . . . . . 9 + Appendix A. Multiplier Value Range . . . . . . . . . . . . . . . 11 + Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11 + Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 11 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 + +1. Introduction + + Introduction of SR [RFC8402] in the same network domain as RSVP-TE + [RFC3209] presents the problem of accounting for SR traffic and + making RSVP-TE aware of the actual available bandwidth on the network + links. RSVP-TE is not aware of how much bandwidth is being consumed + by SR services on the network links; hence, both at computation time + (for a distributed computation) and at signaling time, RSVP-TE LSPs + will incorrectly place loads. This is true where RSVP-TE paths are + distributed or centrally computed without a common entity managing + both SR and RSVP-TE computation for the entire network domain. + + + + + +Sitaraman, et al. Informational [Page 2] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + + The problem space can be generalized as a dark bandwidth problem to + cases where any other service exists in the network that runs in + parallel across common links and whose bandwidth is not reflected in + the available and reserved values in the Traffic Engineering Database + (TED). In most practical instances, given the static nature of the + traffic demands, limiting the reservable bandwidth available to RSVP- + TE has been an acceptable solution. However, in the case of SR + traffic, there is assumed to be very dynamic traffic demands, and + there is considerable risk associated with stranding capacity or + overbooking service traffic resulting in traffic drops. + + The high-level requirements to consider are: + + 1. Placement of SR LSPs in the same domain as RSVP-TE LSPs must not + introduce inaccuracies in the TED used by distributed or + centralized path computation engines. + + 2. Engines that compute RSVP-TE paths may have no knowledge of the + existence of the SR paths in the same domain. + + 3. Engines that compute RSVP-TE paths should not require a software + upgrade or change to their path-computation logic. + + 4. Protocol extensions should be avoided or be minimal as, in many + cases, this coexistence of RSVP-TE and SR may be needed only + during a transition phase. + + 5. Placement of SR LSPs in the same domain as RSVP-TE LSPs that are + computed in a distributed fashion must not require migration to a + central controller architecture for the RSVP-TE LSPs. + +2. Conventions Used in This Document + + The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", + "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and + "OPTIONAL" in this document are to be interpreted as described in + BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all + capitals, as shown here. + +3. Solution Options + + The following section lists SR and RSVP coexistence solution options. + A specific solution is not recommended as all solutions are valid, + even though some may not satisfy all the requirements. If a solution + is acceptable for an operator based on their deployment model, then + such a solution can be chosen. + + + + + +Sitaraman, et al. Informational [Page 3] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + +3.1. Static Partitioning of Bandwidth + + In this model, the static reservable bandwidth of an interface can be + statically partitioned between SR and RSVP-TE; each one can operate + within that bandwidth allocation and SHOULD NOT preempt the other. + + While it is possible to configure RSVP-TE to only reserve up to a + certain maximum link bandwidth and manage the remaining link + bandwidth for other services, this is a deployment where SR and RSVP- + TE are separated in the same network (ships in the night) and can + lead to suboptimal link bandwidth utilization not allowing each to + consume more, if required and constraining the respective + deployments. + + The downside of this approach is the inability to use the reservable + bandwidth effectively and the inability to use bandwidth left unused + by the other protocol. + +3.2. Centralized Management of Available Capacity + + In this model, a central controller performs path placement for both + RSVP-TE and SR LSPs. The controller manages and updates its own view + of the in-use and available capacity. As the controller is a single + common entity managing the network it can have a unified and + consistent view of the available capacity at all times. + + A practical drawback of this model is that it requires the + introduction of a central controller managing the RSVP-TE LSPs as a + prerequisite to the deployment of any SR LSPs. Therefore, this + approach is not practical for networks where distributed TE with + RSVP-TE LSPs is already deployed, as it requires a redesign of the + network and is not backwards compatible. This does not satisfy + requirement 5. + + Note that it is not enough for the controller to just maintain the + unified view of the available capacity, it must also perform the path + computation for the RSVP-TE LSPs, as the reservations for the SR LSPs + are not reflected in the TED. + + + + + + + + + + + + + +Sitaraman, et al. Informational [Page 4] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + +3.3. Flooding SR Utilization in IGP + + Using techniques in [RFC7810], [RFC7471], and [RFC7823], the SR + utilization information can be flooded in IGP-TE, and the RSVP-TE + path computation engine (Constrained Shortest Path First (CSPF)) can + be changed to consider this information. This requires changes to + the RSVP-TE path computation logic and would require upgrades in + deployments where distributed computation is done across the network. + + This does not fit with requirements 3 and 4 mentioned earlier. + +3.4. Running SR over RSVP-TE + + SR can run over dedicated RSVP-TE LSPs that carry only SR traffic. + In this model, the LSPs can be one-hop or multi-hop and can provide + bandwidth reservation for the SR traffic based on functionality such + as auto-bandwidth. The model of deployment would be similar in + nature to running LDP over RSVP-TE. This would allow the TED to stay + consistent across the network and any other RSVP-TE LSPs will also be + aware of the SR traffic reservations. In this approach, non-SR + traffic MUST NOT take the SR-dedicated RSVP-TE LSPs, unless required + by policy. + + The drawback of this solution is that it requires SR to rely on RSVP- + TE for deployment. Furthermore, the accounting accuracy/frequency of + this method is dependent on performance of auto-bandwidth for RSVP- + TE. Note that, for this method to work, the SR-dedicated RSVP-TE + LSPs must be set up with the best setup and hold priorities in the + network. + +3.5. TED Consistency by Reflecting SR Traffic + + The solution relies on dynamically measuring SR traffic utilization + on each TE interface and reducing the bandwidth allowed for use by + RSVP-TE. It is assumed that SR traffic receives precedence in terms + of the placement on the path over RSVP traffic (that is, RSVP traffic + can be preempted from the path in case of insufficient resources). + This is logically equivalent to SR traffic having the best preemption + priority in the network. Note that this does not necessarily mean + that SR traffic has higher QoS priority; in fact, SR and RSVP traffic + may be in the same QoS class. + + + + + + + + + + +Sitaraman, et al. Informational [Page 5] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + + Reducing the bandwidth allowed for use by RSVP-TE can be explored + using the three parameters available in IGP-TE ([RFC5305] [RFC3630]), + namely Maximum-Link-Bandwidth, Maximum-Reservable-Bandwidth, and + Unreserved-Bandwidth. + + o Maximum-Link-Bandwidth: This parameter can be adjusted to + accommodate the bandwidth required for SR traffic with cascading + impacts on Maximum-Reservable-Bandwidth and Unreserved-Bandwidth. + However, changing the maximum bandwidth for the TE link will + prevent any compute engine for SR or RSVP from determining the + real static bandwidth of the TE link. Further, when the Maximum- + Reservable-Bandwidth is derived from the Maximum-Link-Bandwidth, + its definition changes since Maximum-Link-Bandwidth will account + for the SR traffic. + + o Unreserved-Bandwidth: SR traffic could directly adjust the + Unreserved-Bandwidth, without impacting Maximum-Link-Bandwidth or + Maximum-Reservable-Bandwidth. This model is equivalent to the + option described in Section 3.4. Furthermore this would result in + overloading IGP-TE advertisements to directly reflect both RSVP-TE + bandwidth bookings and SR bandwidth measurements. + + o Maximum-Reservable-Bandwidth: As the preferred option, SR traffic + could adjust the Maximum-Reservable-Bandwidth, with cascading + impact on the Unreserved-Bandwidth. + + The following methodology can be used at every TE node for this + solution, using the following parameters: + + o T: Traffic statistics collection time interval. + + o k: The number of traffic statistics samples that can provide a + smoothing function to the statistics collection. The value of k + is a constant integer multiplier greater or equal to 1. + + o N: Traffic averaging calculation (adjustment) interval such that N + = k * T. + + o Maximum-Reservable-Bandwidth: The maximum available bandwidth for + RSVP-TE. + + o If Diffserv-aware MPLS Traffic Engineering (DS-TE) [RFC4124] is + enabled, the Maximum-Reservable-Bandwidth SHOULD be interpreted as + the aggregate bandwidth constraint across all Class-Types + independent of the Bandwidth Constraints model. + + + + + + +Sitaraman, et al. Informational [Page 6] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + + o Initial Maximum-Reservable-Bandwidth: The Maximum-reservable- + bandwidth for TE when no SR traffic or RSVP-TE reservations exist + on the interface. + + o RSVP-unreserved-bandwidth-at-priority-X: Maximum-Reservable- + Bandwidth - sum of (existing reservations at priority X and all + priorities better than X). + + o SR traffic threshold percentage: The percentage difference of + traffic demand that, when exceeded, can result in a change to the + RSVP-TE Maximum-Reservable-Bandwidth. + + o IGP-TE update threshold: Specifies the frequency at which IGP-TE + updates should be triggered based on TE bandwidth updates on a + link. + + o M: An optional multiplier that can be applied to the SR traffic + average. This multiplier provides the ability to grow or shrink + the bandwidth used by SR. Appendix A offers further guidance on + M. + + At every interval T, each node SHOULD collect the SR traffic + statistics for each of its TE interfaces. The measured SR traffic + includes all labeled SR traffic and any traffic entering the SR + network over that TE interface. Further, at every interval N, given + a configured SR traffic threshold percentage and a set of collected + SR traffic statistics samples across the interval N, the SR traffic + average (or any other traffic metric depending on the algorithm used) + over this period is calculated. This method of sampling traffic + statistics and adjusting bandwidth reservation accordingly is similar + to how bandwidth gets adjusted for auto-bandwidth RSVP-TE LSPs. + + If the difference between the new calculated SR traffic average and + the current SR traffic average (that was computed in the prior + adjustment) is at least SR traffic threshold percentage, then two + values MUST be updated: + + o New Maximum-Reservable-Bandwidth = Initial Maximum-Reservable- + Bandwidth - (new SR traffic average * M) + + o New RSVP-unreserved-bandwidth-at-priority-X = New Maximum- + Reservable-Bandwidth - sum of (existing reservations at priority X + and all priorities better than X) + + A DS-TE LSR that advertises a Bandwidth Constraints TLV should update + the bandwidth constraints for class-types based on operator policy. + For example, when Russian Dolls Model (RDM) [RFC4127] is in use, then + + + + +Sitaraman, et al. Informational [Page 7] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + + only BC0 may be updated. Whereas, when Maximum Allocation Model + (MAM) [RFC4125] is in use, then all Bandwidth Constraints (BCs) may + be updated equally such that the total value updated is equal to the + newly calculated SR traffic average. + + Note that the computation of the new RSVP-unreserved-bandwidth-at- + priority-X MAY result in RSVP-TE LSPs being hard or soft preempted. + Such preemption will be based on relative priority (e.g., low to + high) between RSVP-TE LSPs. The IGP-TE update threshold SHOULD allow + for more frequent flooding of unreserved bandwidth. From an + operational point of view, an implementation SHOULD be able to expose + both the configured and the actual values of the Maximum-Reservable- + Bandwidth. + + If LSP preemption is not acceptable, then the RSVP-TE Maximum- + Reservable-Bandwidth cannot be reduced below what is currently + reserved by RSVP-TE on that interface. This may result in bandwidth + not being available for SR traffic. Thus, it is required that any + external controller managing SR LSPs SHOULD be able to detect this + situation (for example, by subscribing to TED updates [RFC7752]) and + SHOULD take action to reroute existing SR paths. + + Generically, SR traffic (or any non-RSVP-TE traffic) should have its + own priority allocated from the available priorities. This would + allow SR to preempt other traffic according to the preemption + priority order. + + In this solution, the logic to retrieve the statistics, calculating + averages and taking action to change the Maximum-Reservable-Bandwidth + is an implementation choice, and all changes are local in nature. + However, note that this is a new network trigger for RSVP-TE + preemption and thus is a consideration for the operator. + + The above solution offers the advantage of not introducing new + network-wide mechanisms especially during scenarios of migrating to + SR in an existing RSVP-TE network and reusing existing protocol + mechanisms. + +4. IANA Considerations + + This document has no IANA actions. + +5. Security Considerations + + This document describes solution options for the coexistence of RSVP- + TE and SR LSPs in the same administrative domain. The security + considerations for SR are described in [RFC8402]. The security + considerations pertaining to RSVP-TE are described in [RFC5920]. The + + + +Sitaraman, et al. Informational [Page 8] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + + security considerations of each architecture are typically unaffected + by the presence of the other. However, when RSVP-TE and SR LSPs + coexist, it is possible for a hijacked SR traffic stream to + maliciously consume sufficient bandwidth and cause disruption to + RSVP-TE LSPs. With the solution option specified in Section 3.5, the + impact to RSVP-TE traffic can be controlled and paths re-routed. + Some latent risk of disruption still remains because this solution + option relies on taking statistics samples and adopting to new + traffic flows only after the adjustment period. The defensive + mechanisms described in the base SR security framework should be + employed to guard against situations that result in SR traffic + hijacking or denial of service. + +6. References + +6.1. Normative References + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, + DOI 10.17487/RFC2119, March 1997, + <https://www.rfc-editor.org/info/rfc2119>. + + [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., + and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP + Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, + <https://www.rfc-editor.org/info/rfc3209>. + + [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC + 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, + May 2017, <https://www.rfc-editor.org/info/rfc8174>. + + [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., + Decraene, B., Litkowski, S., and R. Shakir, "Segment + Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, + July 2018, <https://www.rfc-editor.org/info/rfc8402>. + +6.2. Informative References + + [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering + (TE) Extensions to OSPF Version 2", RFC 3630, + DOI 10.17487/RFC3630, September 2003, + <https://www.rfc-editor.org/info/rfc3630>. + + [RFC4124] Le Faucheur, F., Ed., "Protocol Extensions for Support of + Diffserv-aware MPLS Traffic Engineering", RFC 4124, + DOI 10.17487/RFC4124, June 2005, + <https://www.rfc-editor.org/info/rfc4124>. + + + + +Sitaraman, et al. Informational [Page 9] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + + [RFC4125] Le Faucheur, F. and W. Lai, "Maximum Allocation Bandwidth + Constraints Model for Diffserv-aware MPLS Traffic + Engineering", RFC 4125, DOI 10.17487/RFC4125, June 2005, + <https://www.rfc-editor.org/info/rfc4125>. + + [RFC4127] Le Faucheur, F., Ed., "Russian Dolls Bandwidth Constraints + Model for Diffserv-aware MPLS Traffic Engineering", + RFC 4127, DOI 10.17487/RFC4127, June 2005, + <https://www.rfc-editor.org/info/rfc4127>. + + [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic + Engineering", RFC 5305, DOI 10.17487/RFC5305, October + 2008, <https://www.rfc-editor.org/info/rfc5305>. + + [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS + Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010, + <https://www.rfc-editor.org/info/rfc5920>. + + [RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S. + Previdi, "OSPF Traffic Engineering (TE) Metric + Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015, + <https://www.rfc-editor.org/info/rfc7471>. + + [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and + S. Ray, "North-Bound Distribution of Link-State and + Traffic Engineering (TE) Information Using BGP", RFC 7752, + DOI 10.17487/RFC7752, March 2016, + <https://www.rfc-editor.org/info/rfc7752>. + + [RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and + Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", + RFC 7810, DOI 10.17487/RFC7810, May 2016, + <https://www.rfc-editor.org/info/rfc7810>. + + [RFC7823] Atlas, A., Drake, J., Giacalone, S., and S. Previdi, + "Performance-Based Path Selection for Explicitly Routed + Label Switched Paths (LSPs) Using TE Metric Extensions", + RFC 7823, DOI 10.17487/RFC7823, May 2016, + <https://www.rfc-editor.org/info/rfc7823>. + + + + + + + + + + + + +Sitaraman, et al. Informational [Page 10] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + +Appendix A. Multiplier Value Range + + The following is a suggestion for the range of values for M: + + M is a per-node positive real number that ranges from 0 to 2 with a + default of 1 and may be expressed as a percentage. + + o If M < 1, then the SR traffic average is being understated, which + can result in the link getting full even though Maximum- + Reservable-Bandwidth does not reach zero. + + o If M > 1, then the SR traffic average is overstated, thereby + resulting in the Maximum-Reservable-Bandwidth reaching zero before + the link gets full. If the reduction of Maximum-Reservable- + Bandwidth becomes a negative value, then a value of zero SHOULD be + used and advertised. + +Acknowledgements + + The authors would like to thank Steve Ulrich for his detailed review + and comments. + +Contributors + + Chandra Ramachandran + Juniper Networks + Email: csekar@juniper.net + + Raveendra Torvi + Juniper Networks + Email: rtorvi@juniper.net + + Sudharsana Venkataraman + Juniper Networks + Email: sudharsana@juniper.net + + Martin Vigoureux + Nokia + Email: martin.vigoureux@nokia.com + + + + + + + + + + + + +Sitaraman, et al. Informational [Page 11] + +RFC 8426 RSVP-TE and SR LSP Coexistence July 2018 + + +Authors' Addresses + + Harish Sitaraman (editor) + Juniper Networks + 1133 Innovation Way + Sunnyvale, CA 94089 + United States of America + + Email: hsitaraman@juniper.net + + + Vishnu Pavan Beeram + Juniper Networks + 10 Technology Park Drive + Westford, MA 01886 + United States of America + + Email: vbeeram@juniper.net + + + Ina Minei + Google, Inc. + 1600 Amphitheatre Parkway + Mountain View, CA 94043 + United States of America + + Email: inaminei@google.com + + + Siva Sivabalan + Cisco Systems, Inc. + 2000 Innovation Drive + Kanata, Ontario K2K 3E8 + Canada + + Email: msiva@cisco.com + + + + + + + + + + + + + + + +Sitaraman, et al. Informational [Page 12] + |