





Internet Engineering Task Force (IETF)                    P. Psenak, Ed.
Request for Comments: 8444                                      N. Kumar
Category: Standards Track                                   IJ. Wijnands
ISSN: 2070-1721                                                    Cisco
                                                             A. Dolganow
                                                                   Nokia
                                                           T. Przygienda
                                                                J. Zhang
                                                  Juniper Networks, Inc.
                                                               S. Aldrin
                                                            Google, Inc.
                                                           November 2018


      OSPFv2 Extensions for Bit Index Explicit Replication (BIER)

Abstract

   Bit Index Explicit Replication (BIER) is an architecture that
   provides optimal multicast forwarding through a "BIER domain" without
   requiring intermediate routers to maintain multicast-related, per-
   flow state.  BIER also does not require an explicit tree-building
   protocol for its operation.  A multicast data packet enters a BIER
   domain at a Bit-Forwarding Ingress Router (BFIR) and leaves the BIER
   domain at one or more Bit-Forwarding Egress Routers (BFERs).  The
   BFIR adds a BIER packet header to the packet.  The BIER packet header
   contains a BitString in which each bit represents exactly one BFER to
   forward the packet to.  The set of BFERs to which the multicast
   packet needs to be forwarded is expressed by the set of bits in the
   BIER packet header.

   This document describes the OSPF protocol extension (from RFC 2328)
   that is required for BIER with MPLS encapsulation (which is defined
   in RFC 8296).  Support for other encapsulation types and the use of
   multiple encapsulation types are outside the scope of this document.
















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Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc8444.

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.























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Table of Contents

   1. Introduction ....................................................3
   2. Flooding of the BIER Information in OSPF ........................4
      2.1. BIER Sub-TLV ...............................................4
      2.2. BIER MPLS Encapsulation Sub-TLV ............................5
      2.3. Flooding Scope of BIER Information .........................7
   3. Security Considerations .........................................8
   4. IANA Considerations .............................................9
   5. References ......................................................9
      5.1. Normative References .......................................9
      5.2. Informative References ....................................10
   Acknowledgments ...................................................11
   Authors' Addresses ................................................11

1.  Introduction

   Bit Index Explicit Replication (BIER) is an architecture that
   provides optimal multicast forwarding through a "BIER domain" without
   requiring intermediate routers to maintain any multicast-related,
   per-flow state.  Neither does BIER explicitly require a tree-building
   protocol for its operation.  A multicast data packet enters a BIER
   domain at a Bit-Forwarding Ingress Router (BFIR) and leaves the BIER
   domain at one or more Bit-Forwarding Egress Routers (BFERs).  The
   BFIR router adds a BIER packet header to the packet.  The BIER packet
   header contains a BitString in which each bit represents exactly one
   BFER to forward the packet to.  The set of BFERs to which the
   multicast packet needs to be forwarded is expressed by the set of
   bits in the BIER packet header.

   The BIER architecture requires routers participating in BIER to
   exchange BIER-related information within a given domain and permits
   link-state routing protocols to perform distribution of such
   information.  This document describes extensions to OSPF necessary to
   advertise BIER-specific information in the case where BIER uses MPLS
   encapsulation as described in [RFC8296].

   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.









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2.  Flooding of the BIER Information in OSPF

   All BIER-specific information that a Bit-Forwarding Router (BFR)
   needs to advertise to other BFRs is associated with a BFR-prefix.  A
   BFR-prefix is a unique (within a given BIER domain) routable IP
   address that is assigned to each BFR as described in detail in
   Section 2 of [RFC8279].

   Given that BIER information must be associated with a BFR-prefix, the
   OSPFv2 Extended Prefix Opaque LSA [RFC7684] has been chosen for
   advertisement.

2.1.  BIER Sub-TLV

   A sub-TLV of the OSPFv2 Extended Prefix TLV (defined in [RFC7684]) is
   defined for distributing BIER information.  The sub-TLV is called the
   BIER Sub-TLV.  Multiple BIER Sub-TLVs may be included in the OSPFv2
   Extended Prefix TLV.

   The BIER Sub-TLV has the following format:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | sub-domain-id |     MT-ID     |              BFR-id           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    BAR        |    IPA        |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Sub-TLVs (variable)                      |
   +-                                                             -+
   |                                                               |

   Type:  9

   Length:  Variable, dependent on sub-TLVs.

   sub-domain-id:  Unique value identifying the BIER sub-domain within
      the BIER domain, as described in Section 1 of [RFC8279].

   MT-ID:  Multi-Topology ID (as defined in [RFC4915]) that identifies
      the topology that is associated with the BIER sub-domain.

   BFR-id:  A 2-octet field encoding the BFR-id, as documented in
      Section 2 of [RFC8279].  If the BFR is not locally configured with
      a valid BFR-id, the value of this field is set to 0, which is
      defined as illegal in [RFC8279].



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   BAR:  Single-octet BIER Algorithm used to calculate underlay paths to
      reach other BFRs.  Values are allocated from the "BIER Algorithm"
      registry defined in [RFC8401].

   IPA:  Single-octet IGP Algorithm used to either modify, enhance, or
      replace the calculation of underlay paths to reach other BFRs as
      defined by the BAR value.  Values are defined in the "IGP
      Algorithm Types" registry [IANA-IGP].

   Each BFR sub-domain MUST be associated with one and only one OSPF
   topology that is identified by the MT-ID.  If the association between
   the BIER sub-domain and OSPF topology advertised in the BIER Sub-TLV
   by other BFRs is in conflict with the association locally configured
   on the receiving router, the BIER Sub-TLV for such conflicting sub-
   domains MUST be ignored.

   If the MT-ID contains an invalid value as specified in [RFC4915], the
   BIER Sub-TLV for such subdomains with conflict MUST be ignored.

   If a BFR advertises the same sub-domain-id in multiple BIER Sub-TLVs,
   the BFR MUST be treated as if it did not advertise a BIER Sub-TLV for
   such sub-domain.

   All BFRs MUST detect advertisement of duplicate valid BFR-ids for a
   given MT-ID and sub-domain-id.  When such duplication is detected by
   the BFR, it MUST behave as described in Section 5 of [RFC8279].

   The supported BAR and IPA algorithms MUST be consistent for all
   routers supporting a given BFR sub-domain.  If a router receives a
   BIER Sub-TLV advertisement with a value in the BAR or IPA fields that
   does not match the locally configured value for a given BFR sub-
   domain, the router MUST report a misconfiguration for such BIER sub-
   domain and MUST ignore the BIER Sub-TLV containing the error.

   The use of non-zero values in either the BAR field or the IPA field
   is outside the scope of this document.

2.2.  BIER MPLS Encapsulation Sub-TLV

   The BIER MPLS Encapsulation Sub-TLV is a sub-TLV of the BIER Sub-TLV.
   The BIER MPLS Encapsulation Sub-TLV is used in order to advertise
   MPLS-specific information used for BIER.  It MAY appear multiple
   times in the BIER Sub-TLV.








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   The BIER MPLS Encapsulation Sub-TLV has the following format:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Max SI    |                     Label                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |BS Len |                     Reserved                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:  10

   Length:  8 octets

   Max SI:  A 1-octet field encoding the maximum Set Identifier (SI)
      (see Section 1 of [RFC8279]) used in the encapsulation for this
      BIER sub-domain for this BitString length.

   Label:  A 3-octet field, where the 20 rightmost bits represent the
      first label in the label range.  The 4 leftmost bits MUST be
      ignored.

   BS Len (BitString Length):  A 4-bit field encoding the supported
      BitString length associated with this BFR-prefix.  The values
      allowed in this field are specified in Section 2 of [RFC8296].

   Reserved:  SHOULD be set to 0 on transmission and MUST be ignored on
      reception.

   The "label range" is the set of labels beginning with the Label and
   ending with (Label + (Max SI)).  A unique label range is allocated
   for each BitString length and sub-domain-id.  These labels are used
   for BIER forwarding as described in [RFC8279] and [RFC8296].

   The size of the label range is determined by the number of SIs
   (Section 1 of [RFC8279]) that are used in the network.  Each SI maps
   to a single label in the label range: the first label is for SI=0,
   the second label is for SI=1, etc.

   If the label associated with the Maximum Set Identifier exceeds the
   20-bit range, the BIER MPLS Encapsulation Sub-TLV containing the
   error MUST be ignored.

   If the BitString length is set to a value that does not match any of
   the allowed values specified in [RFC8296], the BIER MPLS
   Encapsulation Sub-TLV containing the error MUST be ignored.



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   If the same BitString length is repeated in multiple BIER MPLS
   Encapsulation Sub-TLVs inside the same BIER Sub-TLV, the whole BIER
   Sub-TLV containing the conflicts MUST be ignored.

   Label ranges within all BIER MPLS Encapsulation Sub-TLVs advertised
   by the same BFR MUST NOT overlap.  If an overlap is detected, all
   BIER sub-TLVs advertised by such a router MUST be ignored.

2.3.  Flooding Scope of BIER Information

   The flooding scope of the OSPFv2 Extended Prefix Opaque LSA [RFC7684]
   that is used for advertising the BIER Sub-TLV is set to area-local.
   To allow BIER deployment in a multi-area environment, OSPF must
   propagate BIER information between areas.

                 (  )         (  )         (  )
               (      )     (      )     (      )
            R1  Area 1   R2  Area 0   R3  Area 2  R4
               (      )     (      )     (      )
                 (  )         (  )         (  )

                 Figure 1: BIER Propagation between Areas

   The following procedure is used in order to propagate BIER-related
   information between areas:

      When an OSPF Area Border Router (ABR) advertises a Type-3 Summary
      LSA from an intra-area or inter-area prefix to all its attached
      areas, it will also originate an OSPFv2 Extended Prefix Opaque
      LSA, as described in [RFC7684].  The flooding scope of the OSPFv2
      Extended Prefix Opaque LSA type will be set to area-local.  The
      route-type in the OSPFv2 Extended Prefix TLV is set to inter-area.
      When determining whether a BIER Sub-TLV should be included in this
      LSA, an OSPF ABR will:

      *  Examine its best path to the prefix in the source area and find
         the advertising router associated with the best path to that
         prefix.

      *  Determine if the advertising router advertised a BIER Sub-TLV
         for the prefix.  If yes, the ABR will copy the information from
         that BIER Sub-TLV when advertising the BIER Sub-TLV to each
         attached area.

      In Figure 1, R1 advertises a prefix 192.0.2.1/32 in Area 1.  It
      also advertises an OSPFv2 Extended Prefix Opaque LSA for prefix
      192.0.2.1/32 and includes a BIER Sub-TLV in it.  ABR R2 calculates
      the reachability for prefix 192.0.2.1/32 inside Area 1 and



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      propagates it to Area 0.  When doing so, it copies the entire BIER
      Sub-TLV (including all of its Sub-TLVs) that it received from R1
      in Area 1 and includes it in the OSPFv2 Extended Prefix Opaque LSA
      it generates for 192.0.2.1/32 in Area 0.  ABR R3 calculates the
      reachability for prefix 192.0.2.1/32 inside Area 0 and propagates
      it to Area 2.  When doing so, it copies the entire BIER Sub-TLV
      (including all of its sub-TLVs) that it received from R2 in Area 0
      and includes it in the OSPFv2 Extended Prefix Opaque LSA it
      generates for 192.0.2.1/32 in Area 2.

3.  Security Considerations

   This document introduces new sub-TLVs for the existing OSPFv2
   Extended Prefix TLV.  It does not introduce any new security risks to
   OSPF.  Existing security extensions as described in [RFC2328] and
   [RFC7684] apply.

   It is assumed that both the BIER and OSPF layers are under a single
   administrative domain.  There can be deployments where potential
   attackers have access to one or more networks in the OSPF routing
   domain.  In these deployments, stronger authentication mechanisms
   such as those specified in [RFC7474] SHOULD be used.

   The Security Considerations section of [RFC8279] discusses the
   possibility of performing a Denial-of-Service (DoS) attack by setting
   too many bits in the BitString of a BIER-encapsulated packet.
   However, this sort of DoS attack cannot be initiated by modifying the
   OSPF BIER advertisements specified in this document.  A BFIR decides
   which systems are to receive a BIER-encapsulated packet.  In making
   this decision, it is not influenced by the OSPF control messages.
   When creating the encapsulation, the BFIR sets one bit in the
   encapsulation for each destination system.  The information in the
   OSPF BIER advertisements is used to construct the forwarding tables
   that map each bit in the encapsulation into a set of next hops for
   the host that is identified by that bit, but the information is not
   used by the BFIR to decide which bits to set.  Hence, an attack on
   the OSPF control plane cannot be used to cause this sort of DoS
   attack.

   While a BIER-encapsulated packet is traversing the network, a BFR
   that receives a BIER-encapsulated packet with n bits set in its
   BitString may have to replicate the packet and forward multiple
   copies.  However, a given bit will only be set in one copy of the
   packet.  This means that each transmitted replica of a received
   packet has fewer bits set (i.e., is targeted to fewer destinations)
   than the received packet.  This is an essential property of the BIER
   forwarding process as defined in [RFC8279].  While a failure of this




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   process might cause a DoS attack (as discussed in the Security
   Considerations section of [RFC8279]), such a failure cannot be caused
   by an attack on the OSPF control plane.

   Implementations MUST ensure that malformed BIER and BIER MPLS
   Encapsulation Sub-TLVs as defined in this document are detected and
   that they do not provide a vulnerability for attackers to crash the
   OSPF router or routing process.  Reception of malformed TLVs or sub-
   TLVs SHOULD be counted and/or logged for further analysis.  Logging
   of malformed TLVs and sub-TLVs SHOULD be rate-limited to prevent a
   DoS attack (distributed or otherwise) from overloading the OSPF
   control plane.

4.  IANA Considerations

   IANA has allocated the following from the "OSPFv2 Extended Prefix TLV
   Sub-TLVs" registry defined in [RFC7684].

      BIER Sub-TLV: 9

      BIER MPLS Encapsulation Sub-TLV: 10

5.  References

5.1.  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>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
              <https://www.rfc-editor.org/info/rfc7474>.







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   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [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>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8296]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
              for Bit Index Explicit Replication (BIER) in MPLS and Non-
              MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
              2018, <https://www.rfc-editor.org/info/rfc8296>.

   [RFC8401]  Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
              Zhang, "Bit Index Explicit Replication (BIER) Support via
              IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,
              <https://www.rfc-editor.org/info/rfc8401>.

5.2.  Informative References

   [IANA-IGP] IANA, "IGP Algorithm Types",
              <https://www.iana.org/assignments/igp-parameters/>.





















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Acknowledgments

   The authors would like to thank Rajiv Asati, Christian Martin, Greg
   Shepherd, and Eric Rosen for their contributions.

Authors' Addresses

   Peter Psenak (editor)
   Cisco
   Apollo Business Center
   Mlynske nivy 43
   Bratislava  821 09
   Slovakia

   Email: ppsenak@cisco.com


   Nagendra Kumar
   Cisco
   7200 Kit Creek Road
   Research Triangle Park, NC  27709
   United States of America

   Email: naikumar@cisco.com


   IJsbrand Wijnands
   Cisco
   De Kleetlaan 6a
   Diegem  1831
   Belgium

   Email: ice@cisco.com


   Andrew Dolganow
   Nokia
   750 Chai Chee Rd
   06-06 Viva Business Park
   Singapore  469004
   Singapore

   Email: andrew.dolganow@nokia.com








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   Tony Przygienda
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford, MA  01886
   United States of America

   Email: prz@juniper.net


   Jeffrey Zhang
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford, MA  01886
   United States of America

   Email: zzhang@juniper.net


   Sam Aldrin
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA
   United States of America

   Email: aldrin.ietf@gmail.com


























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