



rtgwg                                                           Q. Xiong
Internet-Draft                                                    X. Zhu
Intended status: Standards Track                         ZTE Corporation
Expires: 21 November 2026                                    20 May 2026


                 Indication of Load-balancing Strategy
              draft-xz-rtgwg-load-balancing-indication-01

Abstract

   This document proposes the encoding of the indication for load-
   balancing strategies which can be encapsulated into a variety of
   protocols such as MPLS, IPv6 and SRv6 networks.  It also provides the
   considerations for load-balancing configuration in control plane as
   well.

Status of This Memo

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

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   This Internet-Draft will expire on 21 November 2026.

Copyright Notice

   Copyright (c) 2026 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
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   provided without warranty as described in the Revised BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Load Balancing Strategies . . . . . . . . . . . . . . . . . .   3
   4.  Encapsulation for Load-balancing Indication . . . . . . . . .   4
     4.1.  Indication of Load-balancing Strategies . . . . . . . . .   4
     4.2.  MPLS MNA Encapsulation  . . . . . . . . . . . . . . . . .   4
     4.3.  IPv6 Header Encapsulation . . . . . . . . . . . . . . . .   5
   5.  Considerations for Load-balancing Policy in Control Plane . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The load balancing serves as a critical mechanism for achieving high-
   performance transmission in wide-area networks (WANs), with diverse
   implementation strategies such as flow-level and packet-level load
   balancing, some approaches include:

   *Equal-Cost Multi-Path (ECMP) and Weighted ECMP (WCMP): these
   mechanisms preserve the transmission order of packets within a data
   stream.  When the network guarantees transmission and link
   reliability, packets typically arrive at the receiver in sequence.
   This eliminates the need for complex packet reordering at the
   receiver end, allowing simplified Go-Back-N (GBN)retransmission
   mechanisms to be adopted, thereby reducing device complexity and
   cost.

   *Flowlet-based Load Balancing: this mechanism segments packets into
   micro-flowlets, which may be divided based on time intervals, message
   granularity, or fixed lengths.  While these fragments are transmitted
   across different paths to maintain intra-flowlet ordering, they may
   cause inter-flowlet disorder, significantly increasing the receiver's
   buffer and reordering requirements.

   *Packet Spraying: by randomly or load-aware proportionally
   distributing packets across multiple paths, this mechanism maximizes
   load balancing efficiency.  However, it results in the highest packet
   disorder level, imposing the most stringent demands on the receiver's
   reordering capabilities.



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   In WANs with dynamic topologies, the load balancing strategy requires
   host-to-network collaboration to adapt to varying transmission
   scenarios.  The selection of load balancing strategies should
   consider:

   *traffic characteristics (e.g., flow size, burstiness, sensitivity to
   delay)

   *path characteristics (e.g., latency, bandwidth, loss rate, and
   reliability)

   *receiver's reordering capability (e.g., buffer size, reordering
   algorithm efficiency)

   This document proposes the encoding of the indication for load-
   balancing strategies which can be encapsulated into a variety of
   protocols such as MPLS, IPv6 and SRv6 networks.  It also provides the
   considerations for load-balancing configuration in control plane as
   well.

2.  Conventions Used in This Document

2.1.  Abbreviations

2.2.  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.

3.  Load Balancing Strategies

   The reordering capabilities of incoming traffic flows may differ
   across servers.  For example, standard RDMA NICs (Network Interface
   Cards) almost lack out-of-order reordering capabilities, while
   advanced DPU NICs achieve reordering through high-speed caches.  The
   TCP receiving end can also perform out-of-order reordering based on
   caching.  At network nodes, load balancing for flows is a local
   behavior and cannot perceive whether the server has the corresponding
   out-of-order recovery capability.  The information from host-and-
   network collaboration may help to select the best load-balancing
   strategy.







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          Traffic 1/2/3            Apply the load-balancing strategy
+--------+        +---------+      +-------+     +--------+      +---+---+     +-------+
|Client A|------->|Edge Node|----->|Node X |---->| Node A |----->|Node Y |<--->|Server |
+--------+        +---------+      +-------+  |  +--------+  ^   +-------+     +-------+
                 Insert the indication        |  +--------+  |
                 of load-balancing strategies +->| Node B |--+
                                              |  +--------+  ^
                                              |  +--------+  |
                                              +->| Node C |--+
                                                 +--------+
    Figure 1: Selection of Load-balancing Strategies

   As shown in Figure 1, at the edge node, the information can be
   carried in packets to indicate the preferred load-balancing
   strategies.  The indication may be carried in data packets throughout
   the network path.  And the network node can route the packets based
   on the indication of load-balancing strategy, allowing the network to
   apply different strategies for different types of flows.

4.  Encapsulation for Load-balancing Indication

4.1.  Indication of Load-balancing Strategies


       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |  Flag   |F|L|P|
      +---------------+

       Figure 2: Indication Flag of Load-balancing Strategies

   F: 1 bit, when F is set to 1, it indicates the flow-based load-
   balancing mechanism.

   L: 1 bit, when L is set to 1, it indicates the flowlet-based load-
   balancing mechanism.

   P: 1 bit, when P is set to 1, it indicates the packet-based load-
   balancing mechanism.

4.2.  MPLS MNA Encapsulation

   The indication flag could be encapsulated into MPLS MNA header as per
   MNA encapsulation specified in [I-D.ietf-mpls-mna-hdr].







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4.3.  IPv6 Header Encapsulation

   The indication flag can be encapsulated into an IPv6 HbH EH as per
   [RFC8200] since it may be processed by transit nodes along the path
   in IPv6 networks.

   The indication flag can also be encapsulated into an DOH EH as per
   [RFC8200] before an SRH since it may be processed by the forwarding
   nodes of the SRv6 segment list in SRv6 networks.

5.  Considerations for Load-balancing Policy in Control Plane

   The client or the server may notify the out-of-order recovery
   capability to the edge node or the controller in control plane.  The
   controller can also sense the characteristics of a flow and decide
   the best load-balancing strategy and configure the indication to the
   edge node.  And the edge node can encode the information into the
   encapsulation of the packets.

6.  Security Considerations

   To be discussed in future versions of this document.

7.  IANA Considerations

   TBA.

8.  Contributors

   The following people have substantially contributed to this document:


   Qinghua Shao
   ZTE Corporation
   Email: shao.qinghua@zte.com.cn

9.  References

9.1.  Normative References

   [I-D.ietf-mpls-mna-hdr]
              Rajamanickam, J., Gandhi, R., Zigler, R., Song, H., and K.
              Kompella, "MPLS Network Action (MNA) Sub-Stack
              Specification including In-Stack Network Actions and
              Data", Work in Progress, Internet-Draft, draft-ietf-mpls-
              mna-hdr-21, 24 February 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
              mna-hdr-21>.



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   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/rfc/rfc8200>.

9.2.  Informative 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/rfc/rfc2119>.

   [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/rfc/rfc768>.

   [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/rfc/rfc8174>.

Authors' Addresses

   Quan Xiong
   ZTE Corporation
   Email: xiong.quan@zte.com.cn


   Xiangyang Zhu
   ZTE Corporation
   Email: zhu.xiangyang@zte.com.cn





















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