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rfc:rfc8444

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.

Psenak, et al. Standards Track [Page 1] RFC 8444 OSPFv2 Extensions for BIER November 2018

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.

Psenak, et al. Standards Track [Page 2] RFC 8444 OSPFv2 Extensions for BIER November 2018

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.

Psenak, et al. Standards Track [Page 3] RFC 8444 OSPFv2 Extensions for BIER November 2018

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].

Psenak, et al. Standards Track [Page 4] RFC 8444 OSPFv2 Extensions for BIER November 2018

 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.

Psenak, et al. Standards Track [Page 5] RFC 8444 OSPFv2 Extensions for BIER November 2018

 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.

Psenak, et al. Standards Track [Page 6] RFC 8444 OSPFv2 Extensions for BIER November 2018

 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

Psenak, et al. Standards Track [Page 7] RFC 8444 OSPFv2 Extensions for BIER November 2018

    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

Psenak, et al. Standards Track [Page 8] RFC 8444 OSPFv2 Extensions for BIER November 2018

 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>.

Psenak, et al. Standards Track [Page 9] RFC 8444 OSPFv2 Extensions for BIER November 2018

 [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/>.

Psenak, et al. Standards Track [Page 10] RFC 8444 OSPFv2 Extensions for BIER November 2018

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

Psenak, et al. Standards Track [Page 11] RFC 8444 OSPFv2 Extensions for BIER November 2018

 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

Psenak, et al. Standards Track [Page 12]

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