Network Working Group                                             Y. Liu
Internet-Draft                                              China Mobile
Intended status: Informational                                  D. Voyer
Expires: 7 November 2025                                     Bell Canada
                                                                 T. Graf
                                                                Swisscom
                                                               Z. Miklos
                                                                     MTN
                                                            L. Contreras
                                                              Telefonica
                                                              N. Leymann
                                                        Deutsche Telekom
                                                                 L. Song
                                                            Alibaba, Inc
                                                           S. Matsushima
                                                                SoftBank
                                                                  C. Xie
                                                           China Telecom
                                                                   X. Yi
                                                            China Unicom
                                                              6 May 2025


             SRv6 Deployment and Operation Problem Summary
                  draft-liu-srv6ops-problem-summary-05

Abstract

   This document aims to provide a concise overview of the common
   problems encountered during SRv6 deployment and operation, which
   provides foundations for further work, including for example of
   potential solutions and best practices to navigate deployment.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."




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   This Internet-Draft will expire on 7 November 2025.

Copyright Notice

   Copyright (c) 2025 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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  SRv6 Upgrade and Evolution  . . . . . . . . . . . . . . . . .   3
   3.  SRv6 Network Visualization  . . . . . . . . . . . . . . . . .   4
   4.  SRv6 Address Planning . . . . . . . . . . . . . . . . . . . .   5
   5.  Traffic steering to SRv6  . . . . . . . . . . . . . . . . . .   5
   6.  Deployment Practice for SRv6 Protection . . . . . . . . . . .   6
   7.  Challenges of Different Network Types . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Segment Routing over IPv6 (SRv6) is a new technology that builds upon
   the existing IPv6 infrastructure to offer programmable data plane
   capabilities.  This allows for more granular control over traffic
   forwarding, enabling flexible and scalable network designs.  While
   SRv6 presents numerous potential benefits, such as improved traffic
   engineering, optimized resource utilization, its deployment and
   operation come with certain challenges.









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   This document aims to provide a concise overview of the common
   problems encountered during SRv6 deployment and operation, which
   provides foundations for further work, including for example
   potential solutions and best practices to navigate deployment . By
   understanding these challenges and exploring mitigation strategies,
   network administrators can make informed decisions when implementing
   and managing SRv6 networks.

   This document identifies a number of Deployment and Operation
   Problems (DOPs) that require additional work within IETF.

1.1.  Requirements Language

   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.

2.  SRv6 Upgrade and Evolution

   In the evolution from non-SRV6 networks to SRv6 networks, the upgrade
   from MPLS to SRv6 represents the most typical and common scenario,
   which requires consideration of two cases:

   For SRv6 and MPLS coexistence, a smooth transition from an MPLS
   network to an SRv6 network is required, avoiding service
   interruptions.  For instance, deploy dual-stack tunnels for VPN over
   MPLS and VPN over SRv6, with MPLS and SRv6 sharing VPN instances.
   When the next hop of the route is an IPv4 address, iterate through
   the MPLS tunnel; when the next hop is an IPv6 address, iterate
   through the SRv6 tunnel.  Prefer VPN routes based on SRv6.  Once the
   transition is complete, remove the MPLS tunnel.

   For SRv6 and MPLS integration, the legacy MPLS network and the newly
   established SRv6 network coexist, ensuring intercommunication between
   the two networks.  For instance, configure route regeneration and
   route re-advertisement functions between two address families (EVPN,
   VPN) on edge nodes.

   In some cases, SRv6 needs to traverse third-party networks that may
   not natively support SRv6 even IPv6.  One of the possible methods is
   to establish tunnels between nodes that support SRv6, and create SRv6
   BE (Bandwidth Engineering) or SRv6 TE (Traffic Engineering) Policy
   across the tunnels as overlay network.






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   While traditional inter-domain implementations in service provider
   networks often rely on MPLS and leverage Option A.  Option A approach
   has scalability limitations and presents relatively higher complexity
   in both deployment and maintenance.  The ASBR needs to manage the
   routing of all VPNs and create VPN instances for each VPN.  At the
   same time, it requests associating separate interfaces and
   corresponding VLANs for each inter-domain VPN.  SRv6 presents an
   alternative approach with E2E inter-domain solution, potentially
   leading to simplification and improved scalability.  SRv6 naturally
   support end-to-end inter-domain by utilizing IPv6 route reachability
   and IPv6 route aggregation reduces the number of SRv6 locators
   distribution for inter-domain deployment.

   DOP-1 Upgrading (migration) from existing MPLS networks to SRv6, how
   to ensure interoperability, simplify deployment complexity, minimize
   network disruption, and maintain existing services with minimal
   impact.

3.  SRv6 Network Visualization

   The existing IETF data collection frameworks can be applied to SRv6
   for both data plane and control plane monitoring, but currently lack
   critical capabilities for measuring SRv6-specific path performance
   metrics and granular traffic statistics.  This significant visibility
   gap fundamentally limits the ability to conduct meaningful SRv6
   network analysis, either making it completely impossible or severely
   compromising the effectiveness of such analysis, particularly for
   service chain validation, predictive traffic engineering, and
   microsecond-level performance troubleshooting in SRv6 deployments and
   operations.

   DOP-2 The collection of SRv6 network data is incomplete and
   inefficient, making it challenging to visualize the information
   effectively.

   Network data is collected through multiple channels such as BMP,
   IPFIX, and YANG push, but the lack of correlation among these
   datasets hinders effective network performance analysis and
   optimization.  While various techniques can be applied to utilize the
   collected data for SRv6 network analysis and performance optimization
   (particularly for traffic engineering) once it's gathered in defined
   formats, current limitations result in delayed fault detection and
   recovery, as well as inconsistencies between traffic patterns and
   routing behaviors.  Furthermore, the diversity of applicable data
   models for SRv6 creates integration challenges, compounded by the
   absence of effective methods to interpret and present data using
   existing models.




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   DOP-3 Multi-source network data (BMP/IPFIX/YANG etc.) lacks
   correlation and model integration, hindering SRv6 performance
   analysis and causing delayed fault detection and recovery etc.
   challenges.

4.  SRv6 Address Planning

   Existing IPv6 address planning approach ensures efficient address
   utilization and simplifies network management for IPv6 netowrk, which
   can't satisfy the SRv6 SID planning for service provider, especially
   considering the complexities introduced by advanced features like
   SRv6 compression.  The allocation of SRv6 SID blocks should be
   strategically planned by holistically considering administrative
   division management and route aggregation requirements, while the
   distribution of NodeID and function segments needs to balance
   administrative convenience with optimal address space utilization
   based on the SRv6 SID structure.  Some initial work could refer to
   [I-D.liu-srv6ops-sid-address-assignment].  In summary:

   DOP-4 Traditional IPv6 address planning proves inadequate for SRv6
   due to its SID structure, which introduces additional complexity in
   IPv6 architecture and complicates network planning.

   DOP-5 In inter-domain scenarios, SRv6 address allocation may cause
   address space wastage, prevent route aggregation, and fail to ensure
   compression efficiency.

5.  Traffic steering to SRv6

   The general purpose of traffic steering is to optimize the allocation
   and transmission of network resources, ensure a balanced distribution
   of network traffic, improve network performance, reduce congestion,
   and increase available bandwidth to provide users with a better
   network experience.  There are various SRv6 traffic steering methods,
   each with its own unique advantages and challenges.  It is essential
   to choose the appropriate traffic steering method to SRv6 based on
   specific application scenarios to ensure efficient operation.  Some
   initial work could refer to
   [I-D.geng-srv6ops-traffic-steering-to-srv6].  In summary:

   DOP-6 There are various methods for SRv6 traffic steering, making it
   difficult to select the appropriate method for different scenarios,
   leading to deployment complexity.








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6.  Deployment Practice for SRv6 Protection

   Implementing reliability practices can significantly enhance the
   stability and performance of networks based on SRv6.  Network
   failures are inevitable in the real world.  Reliability practices can
   help network engineers quickly identify, isolate, and fix faults,
   thus minimizing impact on services.

   In summary, the necessity of SRv6 reliability practices is evident in
   several aspects, including improving network stability and
   performance, enhancing fault handling capabilities, ensuring
   security, improving compatibility and interoperability, optimizing
   management and monitoring, and enhancing deployment experience.

   SRv6 offers multiple protection mechanisms, with different
   applications requiring different protection needs.  It is challenging
   to select the most suitable protection mechanism, or a combination of
   mechanisms.  When multiple protection mechanisms coexist, achieving
   the desired protection outcome becomes difficult, and there is a lack
   of effective coordination methods.  Some initial work could refer to
   [I-D.liu-srv6ops-sr-protection].

   DOP-7 SRv6 provides diverse protection mechanisms, but selecting
   optimal solutions for specific applications remains challenging,
   especially when coordinating multiple coexisting mechanisms
   effectively.

7.  Challenges of Different Network Types

   SRv6 deployment faces various challenges across different network
   environments, including not only carrier networks but also data
   centers and campus networks.  Specifically, clos (Spine-Leaf)
   architecture of data center requires SRv6 path control (e.g.,
   explicit paths) compatible with ECMP to ensure traffic balance, while
   addressing performance impacts from SRv6 overhead and enabling
   automated large-scale deployment.  Campus networks require SRv6
   integration with legacy protocols (e.g., OSPF/VLAN), IPv4-IPv6
   transition support, enhanced security for source routing risks, and
   automated deployment to reduce operational complexity.

   For instance, in the power grid, SRv6 is supposed to provide Quality
   of Service (QoS) guarantees, performance optimization, and other
   specialized features to meet specific demands based on the power
   application scenario.

   DOP-8 It is difficult to apply a single deployment guideline to meet
   the diverse SRv6 requirements of different network types.




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8.  Security Considerations

   TBD.

9.  IANA Considerations

   TBD

10.  References

10.1.  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>.

   [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>.

10.2.  Informative References

   [I-D.geng-srv6ops-traffic-steering-to-srv6]
              Geng, G., Liu, Y., Xie, C., and C. Lin, "Best practices
              for traffic steering to SRv6", Work in Progress, Internet-
              Draft, draft-geng-srv6ops-traffic-steering-to-srv6-00, 4
              March 2024, <https://datatracker.ietf.org/doc/html/draft-
              geng-srv6ops-traffic-steering-to-srv6-00>.

   [I-D.liu-srv6ops-sid-address-assignment]
              Liu, Y. and Y. Zhu, "IPv6 Address Assignment for SRv6",
              Work in Progress, Internet-Draft, draft-liu-srv6ops-sid-
              address-assignment-01, 25 February 2025,
              <https://datatracker.ietf.org/doc/html/draft-liu-srv6ops-
              sid-address-assignment-01>.

   [I-D.liu-srv6ops-sr-protection]
              Liu, Y., Wenying, J., Lin, C., Geng, X., and Y. Liu,
              "Operational Guidance for Protection mechanisms in SRv6
              Networks", Work in Progress, Internet-Draft, draft-liu-
              srv6ops-sr-protection-03, 20 March 2025,
              <https://datatracker.ietf.org/doc/html/draft-liu-srv6ops-
              sr-protection-03>.

Authors' Addresses





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   Yisong Liu
   China Mobile
   Email: liuyisong@chinamobile.com


   Daniel Voyer
   Bell Canada
   Email: Danvoyer@gmail.com


   Thomas Graf
   Swisscom
   Email: Thomas.Graf@swisscom.com


   Zoltan Miklos
   MTN
   Email: Zoltan.Miklos@mtn.com


   Luis Contreras
   Telefonica
   Email: luismiguel.contrerasmurillo@telefonica.com


   Nicolai Leymann
   Deutsche Telekom
   Email: N.Leymann@telekom.de


   Linjian Song
   Alibaba, Inc
   Email: linjian.slj@alibaba-inc.com


   Satoru Matsushima
   SoftBank
   Email: satoru.matsushima@g.softbank.co.jp


   Chongfeng Xie
   China Telecom
   Email: xiechf@chinatelecom.cn


   Xinxin Yi
   China Unicom
   Email: yixx3@chinaunicom.cn



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