Network Working Group                                              X. Xu
Internet-Draft                                               Alibaba Inc
Intended status: Standards Track                                 S. Kini
Expires: November 15, 2019 March 6, 2020
                                                               P. Psenak
                                                             C. Filsfils
                                                            S. Litkowski
                                                            May 14,
                                                       September 3, 2019

  Signaling Entropy Label Capability and Entropy Readable Label Depth
                              Using IS-IS


   Multiprotocol Label Switching (MPLS) has defined a mechanism to load-
   balance traffic flows using Entropy Labels (EL).  An ingress Label
   Switching Router (LSR) cannot insert ELs for packets going into a
   given Label Switched Path (LSP) unless an egress LSR has indicated
   via signaling that it has the capability of processing to process ELs, referred to
   as Entropy Label Capability (ELC), on that tunnel.  In addition, it
   would be useful for ingress LSRs to know each LSR's capability of for
   reading the maximum label stack depth and performing EL-based load-
   balancing, referred to as Entropy Readable Label Depth (ERLD).  This
   document defines a mechanism to signal these two capabilities using
   IS-IS.  These mechanisms are particularly useful, where label
   advertisements are done via protocols like IS-IS.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on November 15, 2019. March 6, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Advertising ERLD Using IS-IS  . . . . . . . . . . . . . . . .   3
   4.  Advertising ELC Using IS-IS . . . . . . . . . . . . . . . . .   3
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations  BGP-LS Extension  . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   4   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [RFC6790] describes a method to load-balance Multiprotocol Label
   Switching (MPLS) traffic flows using Entropy Labels (EL).  "The Use
   of Entropy Labels in MPLS Forwarding" [RFC6790] introduces the
   concept of Entropy Label Capability (ELC) and defines the signalings
   of this capability via MPLS signaling protocols.  Recently,
   mechanisms have been defined to signal labels via link-state Interior
   Gateway Protocols (IGP) such as IS-IS
   [I-D.ietf-isis-segment-routing-extensions].  In such scenario, scenarios, the
   defined signaling mechanisms are inadequate.  This draft defines a
   mechanism to signal the ELC using IS-IS.  This mechanism is useful
   when the label advertisement is also done via IS-IS.

   In addition, in the cases where stacked LSPs are used for whatever reasons
   (e.g., SR-MPLS [I-D.ietf-spring-segment-routing-mpls]), it would be
   useful for ingress LSRs to know each intermediate LSR's capability of
   reading the maximum label stack depth and performing EL-based load-balancing. load-
   balancing.  This capability, referred to as Entropy Readable Label
   Depth (ERLD) as defined in [I-D.ietf-mpls-spring-entropy-label] may
   be used by ingress LSRs to determine the position of the EL label in
   the stack, and whether it's necessary to insert an EL for a given LSP in
   the case where there has already been multiple ELs at least one EL
   different positions in the label
   stack [I-D.ietf-mpls-spring-entropy-label]. stack.

2.  Terminology

   This memo makes use of the terms defined in [RFC6790] and [RFC4971].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.  Advertising ERLD Using IS-IS

   A new MSD-type of the Node MSD sub-TLV [RFC8491], called ERLD is
   defined to advertise the ERLD of a given router.  As shown in
   Figure 2, it is formatted as described in [RFC8491] with a new MSD-
   Type code to be assigned by IANA (the type code of 2 is desired) and
   the Value field is set to the ERLD in the range between 0 to 255.
   The scope of the advertisement depends on the application.  If a
   router has multiple linecards line-cards with different capabilities of reading
   the maximum label stack depth, the router MUST advertise the smallest

         0                   1                   2                   3
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        | MSD-Type=TBD2 |     ERLD      |
                         Figure 2: ERLD MSD-Type Format

4.  Advertising ELC Using IS-IS

   Even though ELC is a property of the node, in some cases it is
   advantageous to associate and advertise the ELC with a prefix.  In a
   multi-area network, routers may not know the identity of the prefix
   originator in the a remote area, or may not know the capabilities of such
   originator.  Similarly in a multi-domain network, the identity of the
   prefix originator and its capabilities may not be known to the
   ingress LSR.

   One bit of the "Bit Values for Prefix Attribute Flags Sub-TLV"
   registry defined in [RFC7794] (Bit 3 is desired) is to be assigned by
   the IANA for the ELC.  If a router has multiple line cards, the
   router MUST NOT announce the ELC for any prefixes that are locally
   attached unless all of its linecards line-cards are capable of processing ELs.

   If a router supports ELs on all of its linecards, line-cards, it SHOULD set the
   ELC for every local host prefix it advertises in IS-IS.

   When a router leaks a prefix between two levels (upwards or
   downwards), it MUST preserve the ELC signalling signaling for this prefix.

          0 1 2 3 4 5 6 7...
         |X|R|N|E|        ...

   When redistributing a prefix between two IS-IS protocol instances or
   redistributing from another protocol to an IS-IS protocol instance, a
   router SHOULD preserve the ELC signalling signaling for that prefix.  The exact
   mechanism on how used to exchange ELC between protocol instances running on
   an ASBR is outside of the scope of this document and is
   implementation specific.

5.  Acknowledgements

   The authors would like to thank Yimin Shen, George Swallow, Acee
   Lindem, Les Ginsberg, Ketan Talaulikar, Jeff Tantsura, Bruno Decraene
   Carlos Pignataro, Wim Hendrickx, and Gunter Van De Velde for their
   valuable comments.

6.  BGP-LS Extension

   The IS-IS extensions defined in this document can be advertised via
   BGP-LS [RFC7752] using existing BGP-LS TLVs.

   The ELC Flag included in the Prefix Attribute Flags sub-TLV, as
   defined in Section 4, is advertised using the Prefix Attribute Flags
   TLV (TLV 1170) of the BGP-LS IPv4/IPv6 Prefix NLRI Attribute as
   defined in section 2.3.2 of

   The ERLD MSD-type introduced for IS-IS in Section 3 is advertised
   using the Node MSD TLV (TLV 266) of the BGP-LS Node NLRI Attribute as
   defined in section 3 of [I-D.ietf-idr-bgp-ls-segment-routing-ext].

7.  IANA Considerations

   IANA is requested to allocate the E-bit (bit position 3 is desired)
   from the "Bit Values for Prefix Attribute Flags Sub-TLV" registry.

   IANA is requested to allocate a MSD type (the type code of 2 is
   desired) from the "IGP MSD Types" registry for ERLD.


8.  Security Considerations

   The security considerations as described in [RFC4971] nd
   [I-D.ietf-mpls-spring-entropy-label] are applicable to this document.  This document does not introduce any new security


   Incorrectly setting the E flag (ELC capable) (during origination,
   leaking or redistribution) may lead to black-holing of the traffic on
   the egress node.

9.  Normative References

              Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
              and M. Chen, "BGP Link-State extensions for Segment
              Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
              (work in progress), June 2019.

              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., and B. Decraene, "IS-IS Extensions for
              Segment Routing", draft-ietf-isis-segment-routing-
              extensions-25 (work in progress), April May 2019.

              Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
              Shakir, R., and J. Tantsura, "Entropy label for SPRING
              tunnels", draft-ietf-mpls-spring-entropy-label-12 (work in
              progress), July 2018.

              Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-22
              (work in progress), May 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC4971]  Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
              "Intermediate System to Intermediate System (IS-IS)
              Extensions for Advertising Router Information", RFC 4971,
              DOI 10.17487/RFC4971, July 2007,

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,

   [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,

   [RFC7794]  Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
              U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
              and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
              March 2016, <>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8491]  Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,

Authors' Addresses

   Xiaohu Xu
   Alibaba Inc


   Sriganesh Kini


   Peter Psenak


   Clarence Filsfils

   Stephane Litkowski