Internet DRAFT - draft-hegde-idr-bgp-ls-epe-inter-as

draft-hegde-idr-bgp-ls-epe-inter-as







SPRING                                                          S. Hegde
Internet-Draft                                                 S. Sangli
Intended status: Standards Track                   Juniper Networks Inc.
Expires: October 21, 2019                                          X. Xu
                                                            Alibaba Inc.
                                                          April 19, 2019


      BGP-LS Extensions for Inter-AS TE using EPE based mechanisms
                 draft-hegde-idr-bgp-ls-epe-inter-as-01

Abstract

   In certain network deployments, a single operator has multiple
   Autonomous Systems(AS) to facilitate ease of management.  A multiple
   AS network design could also be a result of network mergers and
   acquisitions.  In such scenarios, a centralized Inter-domain TE
   approach could provide most optimal allocation of resources and the
   most controlled path placement.  BGP-LS-EPE
   [I-D.ietf-idr-bgpls-segment-routing-epe] describes an extension to
   BGP Link State (BGP-LS) for the advertisement of BGP Peering Segments
   along with their BGP peering node and inter-AS link information, so
   that efficient BGP Egress Peer Engineering (EPE) policies and
   strategies can be computed based on Segment Routing.  This document
   describes extensions to the BGP-LS EPE to enable it to be used for
   inter-AS Traffic-Engineering (TE) purposes.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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."




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   This Internet-Draft will expire on October 21, 2019.

Copyright Notice

   Copyright (c) 2019 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
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   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.  Reference Topology  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Fast Reroute Label  . . . . . . . . . . . . . . . . . . . . .   4
   4.  TE Link attributes of PeerNode SID  . . . . . . . . . . . . .   5
   5.  Example Advertisements  . . . . . . . . . . . . . . . . . . .   6
   6.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Segment Routing (SR) leverages source routing.  A node steers a
   packet through a controlled set of instructions, called segments, by
   prepending the packet with an SR header with segment identifiers
   (SID).  A SID can represent any instruction, topological or service-
   based.  SR segments allows to enforce a flow through any topological
   path or service function while maintaining per-flow state only at the
   ingress node of the SR domain.

   As there is no per-path state in the network, the bandwidth
   management for the paths is expected to be handled by a centralized
   entity which has a complete view of:

      1.  Up-to-date topology of the network



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      2.  Resources, States and Attributes of links and nodes of the
      network

      3.  Run-time utilization/availability of resources

   The BGP Link-State extensions provide mechanisms whereby link-state
   and TE information can be propagated n a network and a consumer of
   such BGP LS updates may build topology, provide bandwidth calendering
   and other traffic engineering services.  The centralized entity can
   be such a consumer (also referred to as controller).  In the case of
   multi-AS networks, the controller needs to learn the per-AS network
   information and the inter-AS link information thus arriving at a
   consolidated Traffic Engineering Database which can be used to
   compute end-to-end Traffic Engineering Path.  The controller can
   learn the topology, link-state and TE information from each of the AS
   networks either by participating in their IGPs or by listening to BGP
   LS updates [RFC7752].  Similar information about the inter-AS links
   can be learnt via BGP-LS EPE [I-D.ietf-idr-bgpls-segment-routing-epe]
   along with extensions defined in this documet.

2.  Reference Topology

   The controller learns TE attributes of all the links, including the
   inter-AS links and uses the attributes to compute constrained paths.
   The controller should be able to correlate the inter-AS links for
   bidirectional connectivity from both ASes.


           +----------+
           |Controller|
           +----------+
                |
            |----------|
      +---------+      +------+
      |         |      |      |
      |    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




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   The reference diagram from
   [I-D.ietf-spring-segment-routing-central-epe] represents multiple
   Autonomous Systems connected to each other.  When the Multiple ASes
   belong to same operator and are organised into separate domains for
   operational purposes, it is advantageous to support Traffic-
   Engineering across the ASes including the inter-AS links.  The
   controller has visibility of all of the ASes by means of IGP topology
   exported via BGP-LS [RFC7752], or other means.  In addition, the
   inter-AS links and the labels associated with the inter-AS links are
   exported via [I-D.ietf-idr-bgpls-segment-routing-epe].  The
   controller needs to correlate the information acquired from all of
   the ASes, including the inter-AS links in order to get a view of the
   unified topology so that it can build end-to-end Traffic-Engineered
   paths.

3.  Fast Reroute Label

   [I-D.ietf-spring-segment-routing-central-epe] section 3.6 describes
   mechanisms to provide Fast Reroute (FRR) protection for the EPE
   Labels.  The BGP-LS EPE [I-D.ietf-idr-bgpls-segment-routing-epe]
   describes "B" bit to indicate that a PeerNodeSID or PeerAdjSID is
   eligible for backup.  However, it does not specify what is the
   behaviour when the failure kicks-in.  The controller needs to know
   which links are used for protection so that admission control and
   failure simulation can be done effectively and appropriate inter-AS
   links used for path construction.

   This document defines a new flag "F" in the Peering SIDs TLV to
   indicate a SID as an FRR SID.  With the "F" flag set, the protection
   for any peering SID can be specified using another PeerAdjSID,
   PeerNodeSID or PeerSetSID to the controller.  If the protection is
   achieved by fallback to local IP lookup, FRR SID SHOULD not be
   advertised.  The link(s) represented by the FRR SID will carry the
   traffic when there is a failure.  These SIDs are included as an FRR
   SIDs in the peerAdjSID, PeerNodeSID and PeerSetSID advertisements.


         0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |V|L|B|P|F|Rsvd |
      +-+-+-+-+-+-+-+-+


                  Figure 2: Peering SID TLV Flags Format

   * F-Flag: FRR Label Flag: If set, the peer SID where the FRR Label
   appears is using backup links represented by FRR Label.




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4.  TE Link attributes of PeerNode SID

   In any eBGP deployment, the peering session can be either single-hop
   of multi-hop.  For single-hop eBGP sessions, the peering address is
   that of the directly attached interface to which the session is
   pinned down.  For multi-hop eBGP session, the peering adress is
   reachable over more than one interface and that the peering session
   is not pinned down to any of the directly attached interfaces.

   A Peer Node Segment is a segment describing a peer, including the SID
   (PeerNodeSID) allocated to it.  The link descriptors for the
   PeerNodeSID include the addresses used by the BGP session encoded
   using TLVs as defined in [RFC7752].  Since the eBGP session can be
   either single-hop or multi-hop, the IP address used by BGP session as
   local/neigbour is not sufficient to identify the underlaying
   interface(s).  Also, the controller needs to know the links
   associated with the PeerNodeSID, to be able derive TE link
   attributes.  This can be achieved by including the interface local
   and remote addresses in the Link attributes in PeerNodeSID NLRI.

   PeerAdjSID MUST be advertised for each inter-AS link for the purposes
   of inter-AS TE.  The PeerAdjSID should contain link TE attributes
   such as bandwidth, admin-group etc.  The PeerAdjSID should also
   contain the local and remote interface IPv4/IPv6 addresses which is
   used for correlating the links.  PeerNodeSID SHOULD contain the
   additional attribute of link local address which is used by the
   controller to find corresponding PeerAdjSID and hence the
   corresponding link TE attributes.

   A peerAdj segment carries mandatory link descriptors as local and
   remote link id.  Remote link id of the neighboring ASBR is not
   readily available.  [I-D.ietf-idr-bgpls-segment-routing-epe] suggests
   to carry the value '0' for the remote link id.  The Controller needs
   to associate the links in both directions to effectively handle
   failure notifications and for this purpose a unque remote link is
   necessary.  The remote link ID cannot be manually configured on the
   router as the link-ids generally change over router reboot etc and
   hence manual configuration is operationally very difficult to manage.
   This document mandates advertisement of local and remote iterface
   addresses for the inetr-AS TE purposes.

   The Unnumbered interface is not in the scope of this document.









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   +-----------+---------------------+--------------+------------------+
   |  TLV Code | Description         |  IS-IS TLV   | Reference        |
   |   Point   |                     |   /Sub-TLV   | (RFC/Section)    |
   +-----------+---------------------+--------------+------------------+
   |    259    | IPv4 Local interface|    22/6      | [RFC5305]/3.2    |
   |           | Address             |              |                  |
   |    261    | IPv6 Local interface|   22/12      | [RFC6119]/4.2    |
   |           | Address             |              |                  |
   +-------------------------------------------------------------------+



              Figure 3: Link Addresses carried as attributes

5.  Example Advertisements

   The below diagram represents two ASBR routers and inter-AS links
   between them.  The inter-AS links could be connected via switches L1
   and L2 as shown in the diagram or via Point-to-point links A2->B2,
   A3->B3 as shown in the diagram below.  In the below example, lets
   assume peerNodeSID 1 is configured to use peerAdjSID 10002 then
   PeerNodeSID 1 will have the B bit set which means the PeerNodeSID 1
   is eligible for backup.  Label 10002 is added to the PeerNodeSID with
   a "F" bit set, which means 10002 is a backup for PeerNodeSID 1.


   +------------------------------------------------------------------+
   |         PeerNodeSID                          PeerAdjSID          |
   |                                                                  |
   |+-+----------------------------+ +-+-----------------------------+|
   ||N|Loc Node Descr:     AS1:A   | |N|Loc Node Descr:         AS1:A||
   ||L|Rmt Node Descr:     AS2:B   | |L|Rmt Node Descr:         AS2:B||
   ||R|Link Descr:         lo1:lo1 | |R|Link Descr LinkLocRmtID: 1:0 ||
   ||I|                            | |I|Link IP (mandatory):    A1:B1||
   |+-+----------------------------+ +-+-----------------------------+|
   ||A|Link IP (new):  A1:B1       | |A|PeerAdjSID: 10001            ||
   ||T|Link IP (new):  A2:B2       | |T|SRLG                         ||
   ||T|PeerNodeSID: 1              | |T|affinity group               ||
   ||R|PeerSetSID (optional)       | |R|MaxB/W                       ||
   |+-+----------------------------+ +-+-----------------------------+|
   |+-+----------------------------+ +-+-----------------------------+|
   ||N|Loc Node Descr:     AS1:A   | |N|Loc Node Descr:         AS1:A||
   ||L|Rmt Node Descr:     AS2:B   | |L|Rmt Node Descr:         AS2:B||
   ||R|Link Descr:         lo2:lo2 | |R|Link Descr LinkLocRmtID: 2:0 ||
   ||I|                            | |I|Link IP (mandatory):    A2:B2||
   |+-+----------------------------+ +-+-----------------------------+|
   ||A|Link IP (new):  A1:B1       | |A|PeerAdjSID: 10002            ||
   ||T|Link IP (new):  A3:B3       | |T|SRLG                         ||



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   ||T|PeerNodeSID: 2              | |T|affinity group               ||
   ||R|PeerSetSID (optional)       | |R|MaxB/W                       ||
   || |                            | | |Unused B/W                   ||
   |+-+----------------------------+ +-+-----------------------------+|
   |+-+----------------------------+ +-+-----------------------------+|
   ||N|Loc Node Descr:     AS1:A   | |N|Loc Node Descr:         AS1:A||
   ||L|Rmt Node Descr:     AS2:B   | |L|Rmt Node Descr:         AS2:B||
   ||R|Link Descr:         A3:B3   | |R|Link Descr LinkLocRmtID: 2:0 ||
   ||I|                            | |I|Link IP (mandatory):    A3:B3||
   |+-+----------------------------+ +-+-----------------------------+|
   || |PeerNodeSID: 3              | |A|PeerAdjSID: 10103            ||
   ||A|SRLG                        | |T|SRLG                         ||
   ||T|affinity group              | |T|affinity group               ||
   ||T|MaxB/W                      | |R|MaxB/W                       ||
   ||R|Unused B/W                  | | |Unused B/W                   ||
   || |...                         | | |                             ||
   |+-+----------------------------+ +-+-----------------------------+|
   +------------------------------------------------------------------+
                                     ^
                 BGP-LS EPE          |
   +----------> w/ InerDomain -------+
   |             extensions
   |
   |  +---------------------------------mh-eBGP--------------------+
   |  |                                                            |
   |  |   +-----------------------------mh-eBGP----------------+   |
   |  |   |                                                    |   |
   +--+---+-----+ static lo1 -->   +-----+    +-----+    +-----+---+--+
   |  v   v     | static lo2 -->   | L2  |    | L2  |    |     v   v  |
   | lo1 lo2  A1*------------------| swt |--->| swt |----*B1  lo2 lo1 |
   |            |                  +-----+    +-----+    |            |
   |            |                                        |            |
   |            |                                        |            |
   |   RtR A    | static lo1 -->                         |   RtR B    |
   |          A2*----------------------------------------*B2          |
   |            |                                        |            |
   |            | static lo2 -->                         |            |
   |          A3*----------------------------------------*B3          |
   |            |                                        |            |
   +-----------+^                                        ^+-----------+
                |                                        |
                |                                        |
                +-------------------eBGP-----------------+


                     Figure 4: Example Advertisements





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6.  Backward Compatibility

   The extension proposed in this document is backward compatible with
   procedures described in [I-D.ietf-idr-bgpls-segment-routing-epe] and
   [I-D.ietf-spring-segment-routing-central-epe]

7.  Security Considerations

   TBD

8.  IANA Considerations

   No new TLV code points are needed.

9.  Acknowledgements

   Thanks to Julian Lucek and Rafal Jan Szarecki for careful review and
   suggestions.

10.  References

10.1.  Normative References

   [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-18 (work in progress), March 2019.

   [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.

   [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>.

   [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,
              <https://www.rfc-editor.org/info/rfc7752>.






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10.2.  Informative References

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

Authors' Addresses

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

   Email: shraddha@juniper.net


   Srihari Sangli
   Juniper Networks Inc.
   Exora Business Park
   Bangalore, KA  560103
   India

   Email: ssangli@juniper.net


   Xiaohu Xu
   Alibaba Inc.
   Beijing
   China

   Email: xiaohu.xxh@alibaba-inc.com


















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