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Versions: 00 01 02 03 04 05 06 07 draft-ietf-mpls-sr-epe-oam

Routing area                                                    S. Hegde
Internet-Draft                                                  K. Arora
Intended status: Standards Track                           M. Srivastava
Expires: December 5, 2020                          Juniper Networks Inc.
                                                                S. Ninan
                                                  Individual Contributor
                                                                   X. Xu
                                                            Alibaba Inc.
                                                            June 3, 2020


   Label Switched Path (LSP) Ping/Traceroute for Segment Routing (SR)
Egress Peer Engineering Segment Identifiers (SIDs) with MPLS Data Planes
                   draft-hegde-mpls-spring-epe-oam-07

Abstract

   Egress Peer Engineering (EPE) is an application of Segment Routing to
   Solve the problem of egress peer selection.  The Segment Routing
   based BGP-EPE solution allows a centralized controller, e.g. a
   Software Defined Network (SDN) controller to program any egress peer.
   The EPE solution requires a node to program the PeerNode Segment
   Identifier(SID) describing a session between two nodes, the PeerAdj
   SID describing the link (one or more) that is used by sessions
   between peer nodes, and the PeerSet SID describing an arbitrary set
   of sessions or links between a local node and its peers.  This
   document provides new sub-TLVs for EPE Segment Identifiers (SID) that
   would be used in the MPLS Target stack TLV (Type 1), in MPLS Ping and
   Traceroute procedures.

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."

   This Internet-Draft will expire on December 5, 2020.





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Copyright Notice

   Copyright (c) 2020 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   4.  FEC Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  PeerAdj SID Sub-TLV . . . . . . . . . . . . . . . . . . .   4
     4.2.  PeerNode SID Sub-TLV  . . . . . . . . . . . . . . . . . .   6
     4.3.  PeerSet SID Sub-TLV . . . . . . . . . . . . . . . . . . .   9
   5.  EPE-SID FEC validation  . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Egress Peer Engineering (EPE) as defined in
   [I-D.ietf-spring-segment-routing-central-epe] is an effective
   mechanism to select the egress peer link based on different criteria.
   The EPE-SIDs provide means to represent egress peer links.  Many
   network deployments have built their networks consisting of multiple
   Autonomous Systems either for ease of operations or as a result of
   network mergers and acquisitons.  The inter-AS links connecting the
   two Autonomous Systems could be traffic engineered using EPE-SIDs in
   this case as well.It is important to be able to validate the control
   plane to forwarding plane synchronization for these SIDs so that any
   anomaly can be detected easily by the operator.





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      +---------+      +------+
      |         |      |      |
      |    H    B------D      G
      |         | +---/| AS 2 |\  +------+
      |         |/     +------+ \ |      |---L/8
      A   AS1   C---+            \|      |
      |         |\\  \  +------+ /| AS 4 |---M/8
      |         | \\  +-E      |/ +------+
      |    X    |  \\   |      K
      |         |   +===F AS 3 |
      +---------+       +------+


                        Figure 1: Reference Diagram

   In this reference diagram, EPE-SIDs are advertised from AS1 to AS2
   and AS3.  In certain cases the EPE-SIDs advertised by the control
   plane may not be in synchronization with label programmed in data-
   plane.  For example, on C a PeerAdj SID could be advertised to
   indicate it is for the link C->D.  Due to some software anomaly the
   actual data forwarding on this PeerAdj SID could be happening over
   C->E link.  If E had relevant data paths for further forwarding the
   packet, this kind of anomalies will go unnoticed by the operator.  A
   FEC definition for the EPE-SIDs will define the details of the
   control plane association of the SID and the data plane validation of
   the SID will be done during the MPLS trace route procedure.  When
   there is a multi-hop EBGP session between the ASBRs, PeerNode SID is
   advertised and traffic would be load-balanced between the interfaces
   connecting two nodes.  In the reference diagram C and F could have a
   PeerNode-SID advertised.  When the OAM packet is received on F, it
   needs to validate if the packet came on one of the two interfaces
   connected to C.

   This document provides Target Forwarding Equivalence Class (FEC)
   stack TLV definitions for EPE-SIDs.  Other procedures for MPLS Ping
   and Traceroute as defined in [RFC8287] section 7 and clarified by
   [RFC8690] are applicable for EPE-SIDs as well.

2.  Theory of Operation

   [I-D.ietf-idr-bgpls-segment-routing-epe] provides mechanisms to
   advertise the EPE-SIDs in BGP-LS.  These EPE-SIDs may be used to
   build Segment Routing paths as described in
   [I-D.ietf-spring-segment-routing-policy] or using Path Computation
   Element Protocol (PCEP) extensions as defined in [RFC8664].  Data
   plane monitoring for such paths which consist of EPE-SIDs will use
   extensions defined in this document to build the Taget FEC stack TLV.
   The MPLS Ping and Traceroute procedures MAY be initaited by the head-



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   end of the Segment Routing path or a centralized topology-aware data
   plane monitoring system as described in [RFC8403].  The extensions in
   [I-D.ietf-spring-segment-routing-policy] and [RFC8664] do not define
   the details of the SID and such extensions are out of scope for this
   document.  The node initiating the data plane monitoring may acquire
   the details of EPE-SIDs through BGP-LS advertisements as described in
   [I-D.ietf-idr-bgpls-segment-routing-epe].  There may be other
   possible mechanisms to learn the definition of the SID from
   controller.  Details of such mechanisms are out of scope for this
   document.

   The EPE-SIDs are advertised for inter-AS links which run EBGP
   sessions.  The procedures to operate EBGP sessions in a scenario with
   unnumbered interfaces is not very well defined and hence out of scope
   for this document.  During AS migration scenario procedures described
   in [RFC7705] may be in force.  In these scenarios, if the local and
   remote AS fields in the FEC as described in Section 4carries the
   global AS and not the "local AS" as defined in [RFC7705], the FEC
   validation procedures may fail.

3.  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.

4.  FEC Definitions

   Three new sub-TLVs are defined for the Target FEC Stack TLV (Type 1),
   the Reverse-Path Target FEC Stack TLV (Type 16), and the Reply Path
   TLV (Type 21).

               Sub-Type    Sub-TLV Name
               --------  ---------------
                TBD1      PeerAdj SID Sub-TLV
                TBD2      PeerNode SID Sub-TLV
                TBD3      PeerSet SID Sub-TLV


                        Figure 2: New sub-TLV types

4.1.  PeerAdj SID Sub-TLV







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        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 = TBD                     |          Length               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local AS Number (4  octets)                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote As Number (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local BGP router ID (4 octets)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote BGP Router ID (4 octets)                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local Interface address (4/16 octets)            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote Interface address (4/16 octets)           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




                       Figure 3: PeerAdj SID Sub-TLV

   Type : TBD

   Length : variable based on IPV4/IPV6 interface address.  Length
   excludes the length of Type and length field.For IPV4 interface
   addresses length will be 24.  In case of IPV6 address length will be
   48

   Local AS Number :

   4 octet unsigned integer representing the Member ASN inside the
   Confederation.[RFC5065].  The AS number corresponds to the AS to
   which PeerAdj SID advertising node belongs to.

   Remote AS Number :

   4 octet unsigned integer representing the Member ASN inside the
   Confederation.[RFC5065].  The AS number corresponds to the AS of the
   remote node for which the PeerAdj SID is advertised.

   Local BGP Router ID :

   4 octet unsigned integer of the advertising node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Remote BGP Router ID :



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   4 octet unsigned integer of the receiving node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Local Interface Address :

   In case of PeerAdj SID Local interface address corresponding to the
   PeerAdj SID should be apecified in this field.  For IPV4,this field
   is 4 octets; for IPV6, this field is 16 octets.  Link Local IPV6
   addresses are for further study.

   Remote Interface Address :

   In case of PeerAdj SID Remote interface address corresponding to the
   PeerAdj SID should be apecified in this field.  For IPV4,this field
   is 4 octets; for IPV6, this field is 16 octets.Link Local IPv6
   addresses are for further study.

   [I-D.ietf-idr-bgpls-segment-routing-epe] mandates sending local
   interface ID and remote interface ID in the Link Descriptors and
   allows a value of 0 in the remote descriptors.  It is useful to
   validate the incoming interface for a OAM packet and if the remote
   descriptor is 0 this validation is not possible.
   [I-D.ietf-idr-bgpls-segment-routing-epe] allows optional link
   descriptors of local and remote interface addresses as described in
   section 4.2.  This document recommends sending these optional
   descriptors and use them to validate incoming interface.  When these
   local and remote interface addresses are not available, an ingress
   node can send 0 in the local and/or remote interface address field.
   The receiver SHOULD skip the validation for the incoming interface if
   the address field contains 0.

4.2.  PeerNode SID Sub-TLV



















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        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 = TBD                     |          Length               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local AS Number (4  octets)                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote As Number (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local BGP router ID (4 octets)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote BGP Router ID (4 octets)                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   No.of IPV4 interface pairs  |   No.of IPV6 interface pairs  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local Interface address1 (4/16 octets)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote Interface address1 (4/16 octets)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local Interface address2 (4/16 octets)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              ......                                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






                      Figure 4: PeerNode SID Sub-TLV

   Type : TBD

   Length : variable based on IPV4/IPV6 interface address.  There could
   be multiple pairs of local and remote interface pairs.  The length
   includes all the pairs.  Type and Length field are not included in
   the actual length carried in the packet.

   Local AS Number :

   4 octet unsigned integer representing the Member ASN inside the
   Confederation.[RFC5065].  The AS number corresponds to the AS to
   which PeerNode SID advertising node belongs to.

   Remote AS Number :






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   4 octet unsigned integer representing the Member ASN inside the
   Confederation.[RFC5065].  The AS number corresponds to the AS of the
   remote node for which the PeerNode SID is advertised.

   Local BGP Router ID :

   4 octet unsigned integer of the advertising node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Remote BGP Router ID :

   4 octet unsigned integer of the receiving node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Number of IPV4 interface pairs:

   Total number of IPV4 local and remote interface address pairs.

   Number of IPV6 interface pairs:

   Total number of IPV6 local and remote interface address pairs.

   There can be multiple Layer 3 interfaces on which a peerNode SID
   loadbalances the traffic.  All such interfaces local/remote address
   MUST be included in the FEC.

   When a PeerNode SID load-balances over few interfaces with IPV4 only
   address and few interfaces with IPV6 address then the FEC definition
   should list all IPV4 address pairs together followed by IPV6 address
   pairs.

   Local Interface Address :

   In case of PeerNode SID, the interface local address IPV4/IPV6 which
   corresponds to the PeerNode SID MUST be specified.  For IPV4,this
   field is 4 octets; for IPV6, this field is 16 octets.Link Local IPV6
   addresses are for further study.

   Remote Interface Address :

   In case of PeerNode SID, the interface remote address IPV4/IPV6 which
   corresponds to the PeerNode SID MUST be specified.  For IPV4,this
   field is 4 octets; for IPV6, this field is 16 octets.  Link Local
   IPV6 addresses are for further study.

   When there is a multi-hop EBGP session between two ASBRs, PeerNode
   SID is advertised for this session and traffic can be load balanced
   across these interfaces.  An EPE controller that does bandiwdth



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   management for these links should be aware of the links on which the
   traffic will be load-balanced.  [I-D.hegde-idr-bgp-ls-epe-inter-as]
   provides extensions to advertise attributes that will provide details
   of links that the traffic will be load-balanced for a Peer Node SID.
   It is useful to validate the incoming interface for an OAM packet
   received on a remote ASBR.  When the interface information for a
   PeerNode SID is not available an ingress node can choose to send 0
   pairs of interface addresses in which case, incoming interface
   validation SHOULD be skipped by the remote ASBR.

4.3.  PeerSet SID Sub-TLV


        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 = TBD                     |          Length               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local AS Number (4  octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local BGP router ID (4 octets)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   No.of elements in set       |          Reserved             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote As Number (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote BGP Router ID (4 octets)                  |
       ++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
       |   No.of IPV4 interface pairs  |   No.of IPV6 interface pairs  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local Interface address1 (4/16 octets)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote Interface address1 (4/16 octets)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local Interface address2 (4/16 octets)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              ......                                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        One element in set consists of below details
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote As Number (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote BGP Router ID (4 octets)                  |
       ++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++
       |   No.of IPV4 interface pairs  |   No.of IPV6 interface pairs  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local Interface address1 (4/16 octets)          |



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       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote Interface address1 (4/16 octets)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              ......                                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+









                       Figure 5: PeerSet SID Sub-TLV

   Type : TBD

   Length : variable based on IPV4/IPV6 interface address and number of
   elements in the set.  The length field does not include the length of
   Type and Length fields.

   Local AS Number :

   4 octet unsigned integer representing the Member ASN inside the
   Confederation.[RFC5065].  The AS number corresponds to the AS to
   which PeerSet SID advertising node belongs to.

   Remote AS Number :

   4 octet unsigned integer representing the Member ASN inside the
   Confederation.[RFC5065].  The AS number corresponds to the AS of the
   remote node for which the PeerSet SID is advertised.

   Advertising BGP Router ID :

   4 octet unsigned integer of the advertising node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Receiving BGP Router ID :

   4 octet unsigned integer of the receiving node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   No.of elements in set:




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   Number of remote ASes, the set SID load-balances on.

   PeerSet SID may be associated with a number of PeerNode SIDs and
   PeerAdj SIDs.  Link address details of all these SIDs should be
   included in the peerSet SID FEC so that the data-plane can be
   correctly verified on the remote node.

   Number of IPV4 interface pairs:

   Total number of IPV4 local and remote interface address pairs.

   Number of IPV6 interface pairs:

   Total number of IPV6 local and remote interface address pairs.

   There can be multiple Layer 3 interfaces on which a peerNode SID
   loadbalances the traffic.  All such interfaces local/remote address
   MUST be included in the FEC.

   When a PeerSet SID load-balances over few interfaces with IPV4 only
   address and few interfaces with IPV6 address then the Link address
   TLV should list all IPV4 address pairs together followed by IPV6
   address pairs.

   Local Interface Address :

   In case of PeerNodeSID/PeerAdj SID, the interface local address IPV4/
   IPV6 which corresponds to the PeerNode SID/PeerAdj SID MUST be
   specified.  For IPV4,this field is 4 octets; for IPV6, this field is
   16 octets.  Link Local IPV6 addresses are for further study.

   Remote Interface Address :

   In case of PeerNodeSID/PeerAdj SID, the interface remote address
   IPV4/IPV6 which corresponds to the PeerNode SID/PeerAdj SID MUST be
   specified.  For IPV4,this field is 4 octets; for IPV6, this field is
   16 octets.  Link Local IPV6 addresses are for further study.

   The details on how to obtain interface addresses in described for
   PeerAdj SID and PeerNode SID in previous sections and the same is
   applicable for PeerSet SID.

5.  EPE-SID FEC validation

   When a remote ASBR of the EPE-SID advertisement receives the MPLS OAM
   packet with top FEC being the EPE-SID, it SHOULD perform validity
   checks on the content of the EPE-SID FEC sub-TLV.  The basic length
   check should be performed on the received FEC.



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    PeerAdj SID
    -----------
    Length = 24 or 48

    Peer Node SID
    -------------
    Length = 20 + "No.of IPv4 interface pairs" * 8 +
             "No.of IPv6 interface pairs " * 32

    PeerSet SID
    -----------
    Length = 9 + no.of elements in the set *
             (8 + "No.of IPv4 interface pairs" * 8 +
              "No.of IPv6 interface pairs " * 32)


                        Figure 6: Length Validation

   If a malformed FEC sub-TLV is received, then a return code of 1,
   "Malformed echo request received" as defined in [RFC8029] SHOULD be
   sent.  The below section augments the section 7.4 of [RFC8287]


      4a. Segment Routing EPE-SID Validation:

    If the Label-stack-depth is 0 and the Target FEC Stack sub-TLV
         at FEC-stack-depth is TBD1 (PeerAdj SID sub-TLV)

            Set the Best-return-code to 10, "Mapping for this FEC is not
            the given label at stack-depth  if any below
            conditions fail:



               o  Validate that the Receiving Node BGP Local AS matches
                  with the remote AS field in the received PeerAdj SID
                  FEC sub-TLV.

               o  Validate that the Receiving Node BGP Router-ID matches
                  with the Remote Router ID field in the received
                  PeerAdj SID FEC.

               o  Validate that there is a EBGP session with a peer
                  having local As number and BGP Router-ID as
                  specified in the Local AS number and Local Router-ID
                  field in the received PeerAdj SID FEC sub-TLV.

            If the Remote interface address is not zero, validate the



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            incoming interface.
            Set the Best-return-code to 35 "Mapping for this FEC is not
            associated with the incoming interface"  (RFC8287) if any below
            conditions fail:

               o  Validate the incoming interface on which the OAM packet
                  was receieved, matches with the remote interface
                  specified in the PeerAdj SID FEC sub-TLV

            If all above validations have passed, set the return code to 3
            "Replying router is an egress for the FEC at stack-depth"

    Else, if the Target FEC sub-TLV at FEC-stack-depth is TBD2
         (PeerNode SID sub-TLV),

            Set the Best-return-code to 10, "Mapping for this FEC is not
            the given label at stack-depth  if any below
            conditions fail:


               o  Validate that the Receiving Node BGP Local AS matches with
                  the remote AS field in the
                  received PeerNode SID FEC sub-TLV.

               o  Validate that the Receiving Node BGP Router-ID matches
                  with the Remote Router ID field in the received
                  PeerNode SID FEC.

               o  Validate that there is a EBGP session with a peer
                  having local As number and BGP Router-ID as
                  specified in the Local AS number and Local Router-ID
                  field in the received PeerNode SID FEC sub-TLV.

            If the Remote interface address is not zero, validate the
            incoming interface.
            Set the Best-return-code to 35 "Mapping for this FEC is not
            associated with the incoming interface"  (RFC8287) if any below
            conditions fail:

               o  Validate the incoming interface on which the OAM packet
                  was receieved, matches with the any of the
                  remote interfaces specified in the PeerNode SID FEC sub-TLV

            If all above validations have passed, set the return code to 3
            "Replying router is an egress for the FEC at stack-depth"

    Else, if the Target FEC sub-TLV at FEC-stack-depth is TBD3
         (PeerSet SID sub-TLV),



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            Set the Best-return-code to 10, "Mapping for this FEC is not
            the given label at stack-depth"  if any below
            conditions fail:


               o  Validate that the Receiving Node BGP Local AS matches
                  with one of the remote AS field in the received PeerSet
                  SID FEC sub-TLV.

               o  Validate that the Receiving Node BGP Router-ID matches
                  with one of the  Remote Router ID field in the received
                  PeerSet SID FEC sub-TLV.

               o  Validate that there is a EBGP session with a peer having
                  local As number and BGP Router-ID as
                  specified in the Local AS number and Local Router-ID
                  field in the received PeerSet SID FEC sub-TLV.

            If the Remote interface address is not zero, validate the
            incoming interface.
            Set the Best-return-code to 35 "Mapping for this FEC is not
            associated with the incoming interface"  (RFC8287) if any below
            conditions fail:

               o  Validate the incoming interface on which the OAM packet
                  was receieved, matches with the any of the
                  remote interfaces specified in the PeerSet SID FEC sub-TLV

            If all above validations have passed, set the return code to 3
            "Replying router is an egress for the FEC at stack-depth"

                     Figure 7: EPE-SID FEC validiation

6.  IANA Considerations

   New Target FEC stack sub-TLV from the "sub-TLVs for TLV types 1,16
   and 21" subregistry of the "Multi-Protocol Label switching (MPLS)
   Label Switched Paths (LSPs) Ping parameters" registry

      PeerAdj SID Sub-TLV : TBD1

      PeerNode SID Sub-TLV: TBD2

      PeerSet SID Sub-TLV : TBD3







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7.  Security Considerations

   The EPE-SIDs are advertised for egress links for Egress Peer
   Engineering purposes or for inter-As links between co-operating ASes.
   When co-operating domains are involved, they can allow the packets
   arriving on trusted interfaces to reach the control plane and get
   processed.  When EPE-SIDs which are created for egress TE links where
   the neighbor AS is an independent entity, it may not allow packets
   arriving from external world to reach the control plane.  In such
   deployments MPLS OAM packets will be dropped by the neighboring AS
   that receives the MPLS OAM packet.  In MPLS traceroute applications,
   when the AS boundary is crossed with the EPE-SIDs, the FEC stack is
   changed.  [RFC8287] does not mandate that the initiator upon
   receiving an MPLS Echo Reply message that includes the FEC Stack
   Change TLV with one or more of the original segments being popped
   remove a corresponding FEC(s) from the Target FEC Stack TLV in the
   next (TTL+1) traceroute request.  If an initiator does not remove the
   FECs belonging to the previous AS that has traversed, it MAY expose
   the internal AS information to the following AS being traversed in
   traceroute.

8.  Acknowledgments

   Thanks to Loa Andersson, Dhruv Dhody, Ketan Talaulikar, Italo Busi
   and Alexander Vainshtein for careful review and comments.

9.  References

9.1.  Normative References

   [I-D.hegde-idr-bgp-ls-epe-inter-as]
              Hegde, S., Ramachandra, S., Srivastava, M., and X. Xu,
              "BGP-LS Extensions for Inter-AS TE using EPE based
              mechanisms", draft-hegde-idr-bgp-ls-epe-inter-as-03 (work
              in progress), June 2020.

   [I-D.ietf-idr-bgpls-segment-routing-epe]
              Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
              S., and J. Dong, "BGP-LS extensions for Segment Routing
              BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
              segment-routing-epe-19 (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,
              <https://www.rfc-editor.org/info/rfc2119>.





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   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [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>.

   [RFC8287]  Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
              N., Kini, S., and M. Chen, "Label Switched Path (LSP)
              Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
              IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
              Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
              <https://www.rfc-editor.org/info/rfc8287>.

   [RFC8690]  Nainar, N., Pignataro, C., Iqbal, F., and A. Vainshtein,
              "Clarification of Segment ID Sub-TLV Length for RFC 8287",
              RFC 8690, DOI 10.17487/RFC8690, December 2019,
              <https://www.rfc-editor.org/info/rfc8690>.

9.2.  Informative References

   [I-D.ietf-spring-segment-routing-central-epe]
              Filsfils, C., Previdi, S., Dawra, G., Aries, E., and D.
              Afanasiev, "Segment Routing Centralized BGP Egress Peer
              Engineering", draft-ietf-spring-segment-routing-central-
              epe-10 (work in progress), December 2017.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-07 (work in progress),
              May 2020.

   [RFC7705]  George, W. and S. Amante, "Autonomous System Migration
              Mechanisms and Their Effects on the BGP AS_PATH
              Attribute", RFC 7705, DOI 10.17487/RFC7705, November 2015,
              <https://www.rfc-editor.org/info/rfc7705>.

   [RFC8403]  Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
              Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
              Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
              2018, <https://www.rfc-editor.org/info/rfc8403>.






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   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

Authors' Addresses

   Shraddha Hegde
   Juniper Networks Inc.
   Exora Business Park
   Bangalore, KA  560103
   India

   Email: shraddha@juniper.net


   Kapil Arora
   Juniper Networks Inc.

   Email: kapilaro@juniper.net


   Mukul Srivastava
   Juniper Networks Inc.

   Email: msri@juniper.net


   Samson Ninan
   Individual Contributor

   Email: samson.cse@gmail.com


   Xiaohu Xu
   Alibaba Inc.
   Beijing
   China

   Email: xiaohu.xxh@alibaba-inc.com










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