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Versions: (draft-filsfils-spring-segment-routing-central-epe) 00 01 02 03 04 05 06 07 08 09 10 Draft is active
In: MissingRef
Network Working Group                                   C. Filsfils, Ed.
Internet-Draft                                           S. Previdi, Ed.
Intended status: Informational                       Cisco Systems, Inc.
Expires: March 17, 2017                                         E. Aries
                                                                Facebook
                                                             D. Ginsburg
                                                            D. Afanasiev
                                                                  Yandex
                                                      September 13, 2016


            Segment Routing Centralized BGP Peer Engineering
            draft-ietf-spring-segment-routing-central-epe-02

Abstract

   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.  A segment can represent any
   instruction topological or service-based.  SR allows to enforce a
   flow through any topological path and service chain while maintaining
   per-flow state only at the ingress node of the SR domain.

   The Segment Routing architecture can be directly applied to the MPLS
   dataplane with no change on the forwarding plane.  It requires minor
   extension to the existing link-state routing protocols.

   This document illustrates the application of Segment Routing to solve
   the BGP Peer Engineering (BGP-PE) requirement.  The SR-based BGP-PE
   solution allows a centralized (SDN) controller to program any egress
   peer policy at ingress border routers or at hosts within the domain.
   This document is on the informational track.

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 http://datatracker.ietf.org/drafts/current/.



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   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 March 17, 2017.

Copyright Notice

   Copyright (c) 2016 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
   (http://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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Segment Routing Documents . . . . . . . . . . . . . . . .   3
     1.2.  Problem Statement . . . . . . . . . . . . . . . . . . . .   4
   2.  BGP Peering Segments  . . . . . . . . . . . . . . . . . . . .   6
   3.  Distribution of External Topology and TE Information using
       BGP-LS  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  BGP-PE Router advertising the Peer D and its PeerNode SID   7
     3.2.  BGP-PE Router advertising the Peer E and its PeerNode SID   7
     3.3.  BGP-PE Router advertising the Peer F and its PeerNode SID   8
     3.4.  BGP-PE Router advertising a first PeerAdj to Peer F . . .   8
     3.5.  BGP-PE Router advertising a second PeerAdj to Peer F  . .   9
     3.6.  Fast Reroute (FRR)  . . . . . . . . . . . . . . . . . . .   9
   4.  BGP-PE Controller . . . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Valid Paths From Peers  . . . . . . . . . . . . . . . . .  10
     4.2.  Intra-Domain Topology . . . . . . . . . . . . . . . . . .  11
     4.3.  External Topology . . . . . . . . . . . . . . . . . . . .  11
     4.4.  SLA characteristics of each peer  . . . . . . . . . . . .  11
     4.5.  Traffic Matrix  . . . . . . . . . . . . . . . . . . . . .  12
     4.6.  Business Policies . . . . . . . . . . . . . . . . . . . .  12
     4.7.  BGP-PE Policy . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Programming an input policy . . . . . . . . . . . . . . . . .  13
     5.1.  At a Host . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.2.  At a router - SR Traffic Engineering tunnel . . . . . . .  13
     5.3.  At a Router - RFC3107 policy route  . . . . . . . . . . .  13



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     5.4.  At a Router - VPN policy route  . . . . . . . . . . . . .  14
     5.5.  At a Router - Flowspec route  . . . . . . . . . . . . . .  14
   6.  IPv6  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   7.  Benefits  . . . . . . . . . . . . . . . . . . . . . . . . . .  15
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     12.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   The document is structured as follows:

   o  Section 1 states the BGP-PE problem statement and provides the key
      references.

   o  Section 2 defines the different BGP Peering Segments and the
      semantic associated to them.

   o  Section 3 describes the automated allocation of BGP Peering SID's
      by the BGP-PE enabled egress border router and the automated
      signaling of the external peering topology and the related BGP
      Peering SID's to the collector
      [I-D.ietf-idr-bgpls-segment-routing-epe].

   o  Section 4 overviews the components of a centralized EPE
      controller.  The definition of the EPE controller is outside the
      scope of this document.

   o  Section 5 overviews the methods that could be used by the
      centralized BGP-PE controller to implement a BGP-PE policy at an
      ingress border router or at a source host within the domain.  The
      exhaustive definition of all the means to program an BGP-PE input
      policy is outside the scope of this document.

   For editorial reasons, the solution is described for IPv4.  A later
   section describes how the same solution is applicable to IPv6.

1.1.  Segment Routing Documents

   The main references for this document are:

   o  SR Problem Statement: [I-D.ietf-spring-problem-statement].




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   o  SR Architecture: [I-D.ietf-spring-segment-routing].

   o  Distribution of External Topology and TE Information using BGP:
      [I-D.ietf-idr-bgpls-segment-routing-epe].

   The SR instantiation in the MPLS dataplane is described in
   [I-D.ietf-spring-segment-routing-mpls].

   The SR IGP protocol extensions are defined in
   [I-D.ietf-isis-segment-routing-extensions],
   [I-D.ietf-ospf-segment-routing-extensions] and
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions].

   The Segment Routing PCE protocol extensions are defined in
   [I-D.ietf-pce-segment-routing].

1.2.  Problem Statement

   The BGP-PE problem statement is defined in
   [I-D.ietf-spring-problem-statement].

   A centralized controller should be able to instruct an ingress
   Provider Edge router (PE) or a content source within the domain to
   use a specific egress PE and a specific external interface/neighbor
   to reach a particular destination.

   We call this solution "BGP-PE" for "BGP Peer Engineering".  The
   centralized controller is called the "BGP-PE Controller".  The egress
   border router where the BGP-PE traffic-steering functionality is
   implemented is called a BGP-PE-enabled border router.  The input
   policy programmed at an ingress border router or at a source host is
   called a BGP-PE policy.

   The requirements that have motivated the solution described in this
   document are listed here below:

   o  The solution MUST apply to the Internet use-case where the
      Internet routes are assumed to use IPv4 unlabeled or IPv6
      unlabeled.  It is not required to place the Internet routes in a
      VRF and allocate labels on a per route, or on a per-path basis.

   o  The solution MUST NOT make any assumption on the currently
      deployed iBGP schemes (RRs, confederations or iBGP full meshes)
      and MUST be able to support all of them.

   o  The solution MUST be applicable to iBGP as well as eBGP peerings.





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   o  The solution SHOULD minimize the need for new BGP capabilities at
      the ingress PEs.

   o  The solution MUST accommodate an ingress BGP-PE policy at an
      ingress PE or directly at an source host within the domain.

   o  The solution MUST support automated Fast Reroute (FRR) and fast
      convergence mechanisms.

   The following reference diagram is used throughout this document.

   +---------+      +------+
   |         |      |      |
   |    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

   IPv4 addressing:

   o  C's interface to D: 198.51.100.1/30, D's interface:
      198.51.100.2/30

   o  C's interface to E: 198.51.100.5/30, E's interface:
      198.51.100.6/30

   o  C's upper interface to F: 198.51.100.9/30, F's interface:
      198.51.100.10/30

   o  C's lower interface to F: 198.51.100.13/30, F's interface:
      198.51.100.14/30

   o  Loopback of F used for eBGP multi-hop peering to C: 192.0.2.2/32

   o  C's loopback is 203.0.113.3/32 with SID 64

   C's BGP peering:

   o  Single-hop eBGP peering with neighbor 198.51.100.2 (D)

   o  Single-hop eBGP peering with neighbor 198.51.100.6 (E)



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   o  Multi-hop eBGP peering with F on IP address 192.0.2.2 (F)

   C's resolution of the multi-hop eBGP session to F:

   o  Static route 192.0.2.2/32 via 198.51.100.10

   o  Static route 192.0.2.2/32 via 198.51.100.14

   C is configured with local policy that defines a BGP PeerSet as the
   set of peers (198.51.100.6 and 192.0.2.2)

   X is the BGP-PE controller within AS1 domain.

   H is a content source within AS1 domain.

2.  BGP Peering Segments

   As defined in [I-D.ietf-spring-segment-routing], certain segments are
   defined by BGP-PE capable node and corresponding to its attached
   peers.  These segments are called BGP peering segments or BGP Peering
   SIDs.  They enable the expression of source-routed inter-domain
   paths.

   An ingress border router of an AS may compose a list of segments to
   steer a flow along a selected path within the AS, towards a selected
   egress border router C of the AS and through a specific peer.  At
   minimum, a BGP Peering Engineering policy applied at an ingress PE
   involves two segments: the Node SID of the chosen egress PE and then
   the BGP Peering Segment for the chosen egress PE peer or peering
   interface.

   [I-D.ietf-spring-segment-routing] defines three types of BGP peering
   segments/SID's: PeerNodeSID, PeerAdjSID and PeerSetSID.

   The BGP extensions to signal these BGP peering segments are outlined
   in the following section.

3.  Distribution of External Topology and TE Information using BGP-LS

   In ships-in-the-night mode with respect to the pre-existing iBGP
   design, a BGP-LS session is established between the BGP-PE enabled
   border router and the BGP-PE controller.

   As a result of its local configuration and according to the behavior
   described in [I-D.ietf-idr-bgpls-segment-routing-epe], node C
   allocates the following BGP Peering Segments
   ([I-D.ietf-spring-segment-routing]):




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   o  A PeerNode segment for each of its defined peer (D, E and F).

   o  A PeerAdj segment for each recursing interface to a multi-hop peer
      (e.g.: the upper and lower interfaces from C to F in figure 1).

   o  A PeerSet segment to the set of peers (E and F).

   C programs its forwarding table accordingly:

   Incoming             Outgoing
   Label     Operation  Interface
   ------------------------------------
   1012          POP    link to D
   1022          POP    link to E
   1032          POP    upper link to F
   1042          POP    lower link to F
   1052          POP    load balance on any link to F
   1060          POP    load balance on any link to E or to F

   C signals the related BGP-LS NLRI's to the BGP-PE controller.  Each
   such BGP-LS route is described in the following subsections according
   to the encoding details defined in
   [I-D.ietf-idr-bgpls-segment-routing-epe].

3.1.  BGP-PE Router advertising the Peer D and its PeerNode SID

   Descriptors:

   o  Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1

   o  Peer Descriptors (peer ASN): AS2

   o  Link Descriptors (IPv4 interface address, neighbor IPv4 address):
      198.51.100.1, 198.51.100.2

   Attributes:

   o  PeerNode-SID: 1012

3.2.  BGP-PE Router advertising the Peer E and its PeerNode SID

   Descriptors:

   o  Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1

   o  Peer Descriptors (peer ASN): AS3





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   o  Link Descriptors (IPv4 interface address, neighbor IPv4 address):
      198.51.100.5, 198.51.100.6

   Attributes:

   o  PeerNode-SID: 1022

   o  PeerSetSID: 1060

   o  Link Attributes: see section 3.3.2 of [RFC7752]

3.3.  BGP-PE Router advertising the Peer F and its PeerNode SID

   Descriptors:

   o  Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1

   o  Peer Descriptors (peer ASN): AS3

   o  Link Descriptors (IPv4 interface address, neighbor IPv4 address):
      203.0.113.3, 192.0.2.2

   Attributes:

   o  PeerNode-SID: 1052

   o  PeerSetSID: 1060

3.4.  BGP-PE Router advertising a first PeerAdj to Peer F

   Descriptors:

   o  Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1

   o  Peer Descriptors (peer ASN): AS3

   o  Link Descriptors (IPv4 interface address, neighbor IPv4 address):
      198.51.100.9, 198.51.100.10

   Attributes:

   o  PeerAdj-SID: 1032

   o  LinkAttributes: see section 3.3.2 of [RFC7752]







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3.5.  BGP-PE Router advertising a second PeerAdj to Peer F

   Descriptors:

   o  Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1

   o  Peer Descriptors (peer ASN): AS3

   o  Link Descriptors (IPv4 interface address, neighbor IPv4 address):
      198.51.100.13, 198.51.100.14

   Attributes:

   o  PeerAdj-SID: 1042

   o  LinkAttributes: see section 3.3.2 of [RFC7752]

3.6.  Fast Reroute (FRR)

   An BGP-PE enabled border router should allocate a FRR backup entry on
   a per BGP Peering SID basis:

   o  PeerNode SID

      1.  If multi-hop, backup via the remaining PeerADJ SIDs to the
          same peer.

      2.  Else backup via local PeerNode SID to the same AS.

      3.  Else pop the PeerNode SID and perform an IP lookup.

   o  PeerAdj SID

      1.  If to a multi-hop peer, backup via the remaining PeerADJ SIDs
          to the same peer.

      2.  Else backup via PeerNode SID to the same AS.

      3.  Else pop the PeerNode SID and perform an IP lookup.

   o  PeerSet SID

      1.  Backup via remaining PeerNode SIDs in the same PeerSet.

      2.  Else pop the PeerNode SID and IP lookup.

   We illustrate the different types of possible backups using the
   reference diagram and considering the Peering SIDs allocated by C.



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   PeerNode SID 1052, allocated by C for peer F:

   o  Upon the failure of the upper connected link CF, C can reroute all
      the traffic onto the lower CF link to the same peer (F).

   PeerNode SID 1022, allocated by C for peer E:

   o  Upon the failure of the connected link CE, C can reroute all the
      traffic onto the link to PeerNode SID 1052 (F).

   PeerNode SID 1012, allocated by C for peer D:

   o  Upon the failure of the connected link CD, C can pop the PeerNode
      SID and lookup the IP destination address in its FIB and route
      accordingly.

   PeerSet SID 1060, allocated by C for the set of peers E and F:

   o  Upon the failure of a connected link in the group, the traffic to
      PeerSet SID 1060 is rerouted on any other member of the group.

   For specific business reasons, the operator might not want the
   default FRR behavior applied to a PeerNode SID or any of its
   dependent PeerADJ SID.

   The operator should be able to associate a specific backup PeerNode
   SID for a PeerNode SID: e.g., 1022 (E) must be backed up by 1012 (D)
   which overrules the default behavior which would have preferred F as
   a backup for E.

4.  BGP-PE Controller

   In this section, we provide a non-exhaustive set of inputs that an
   BGP-PE controller would likely collect such as to perform the BGP-PE
   policy decision.

   The exhaustive definition is outside the scope of this document.

4.1.  Valid Paths From Peers

   The BGP-PE controller should collect all the paths advertised by all
   the engineered peers.

   This could be realized by setting an iBGP session with the BGP-PE
   enabled border router, with "add-path all" and the original next-hop
   preserved.





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   In this case, C would advertise the following Internet routes to the
   BGP-PE controller:

   o  NLRI <L/8>, nhop 198.51.100.2, AS Path {AS 2, 4}

      *  X (i.e.: the BGP-PE controller) knows that C receives a path to
         L/8 via neighbor 198.51.100.2 of AS2.

   o  NLRI <L/8>, nhop 198.51.100.6, AS Path {AS 3, 4}

      *  X knows that C receives a path to L/8 via neighbor 198.51.100.6
         of AS2.

   o  NLRI <L/8>, nhop 192.0.2.2, AS Path {AS 3, 4}

      *  X knows that C has an eBGP path to L/8 via AS3 via neighbor
         192.0.2.2

   An alternative option would be for an BGP-PE collector to use BGP
   Monitoring Protocol (BMP) to track the Adj-RIB-In of BGP-PE enabled
   border routers.

4.2.  Intra-Domain Topology

   The BGP-PE controller should collect the internal topology and the
   related IGP SIDs.

   This could be realized by collecting the IGP LSDB of each area or
   running a BGP-LS session with a node in each IGP area.

4.3.  External Topology

   Thanks to the collected BGP-LS routes described in the section 2
   (BGP-LS advertisements), the BGP-PE controller is able to maintain an
   accurate description of the egress topology of node C.  Furthermore,
   the BGP-PE controller is able to associate BGP Peering SIDs to the
   various components of the external topology.

4.4.  SLA characteristics of each peer

   The BGP-PE controller might collect SLA characteristics across peers.
   This requires an BGP-PE solution as the SLA probes need to be steered
   via non-best-path peers.

   Unidirectional SLA monitoring of the desired path is likely required.
   This might be possible when the application is controlled at the
   source and the receiver side.  Unidirectional monitoring dissociates
   the SLA characteristic of the return path (which cannot usually be



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   controlled) from the forward path (the one of interest for pushing
   content from a source to a consumer and the one which can be
   controlled).

   Alternatively, Extended Metrics, as defined in
   [I-D.ietf-isis-te-metric-extensions] could also be advertised using
   new BGP-LS attributes.

4.5.  Traffic Matrix

   The BGP-PE controller might collect the traffic matrix to its peers
   or the final destinations.  IPFIX is a likely option.

   An alternative option consists in collecting the link utilization
   statistics of each of the internal and external links, also available
   in the current definition of [RFC7752].

4.6.  Business Policies

   The BGP-PE controller should collect business policies.

4.7.  BGP-PE Policy

   On the basis of all these inputs (and likely others), the BGP-PE
   Controller decides to steer some demands away from their best BGP
   path.

   The BGP-PE policy is likely expressed as a two-entry segment list
   where the first element is the IGP prefix SID of the selected egress
   border router and the second element is a BGP Peering SID at the
   selected egress border router.

   A few examples are provided hereafter:

   o  Prefer egress PE C and peer AS AS2: {64, 1012}.

   o  Prefer egress PE C and peer AS AS3 via eBGP peer 198.51.100.6:
      {64, 1022}.

   o  Prefer egress PE C and peer AS AS3 via eBGP peer 192.0.2.2: {64,
      1052}.

   o  Prefer egress PE C and peer AS AS3 via interface 198.51.100.14 of
      multi-hop eBGP peer 192.0.2.2: {64, 1042}.

   o  Prefer egress PE C and any interface to any peer in the group
      1060: {64, 1060}.




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   Note that the first SID could be replaced by a list of segments.
   This is useful when an explicit path within the domain is required
   for traffic-engineering purposes.  For example, if the Prefix SID of
   node B is 60 and the BGP-PE controller would like to steer the
   traffic from A to C via B then through the external link to peer D
   then the segment list would be {60, 64, 1012}.

5.  Programming an input policy

   The detailed/exhaustive description of all the means to implement an
   BGP-PE policy are outside the scope of this document.  A few examples
   are provided in this section.

5.1.  At a Host

   A static IP/MPLS route can be programmed at the host H.  The static
   route would define a destination prefix, a next-hop and a label stack
   to push.  The global property of the IGP Prefix SID is particularly
   convenient: the same policy could be programmed across hosts
   connected to different routers.

5.2.  At a router - SR Traffic Engineering tunnel

   The BGP-PE controller can configure the ingress border router with an
   SR traffic engineering tunnel T1 and a steering-policy S1 which
   causes a certain class of traffic to be mapped on the tunnel T1.

   The tunnel T1 would be configured to push the required segment list.

   The tunnel and the steering policy could be configured via PCEP
   according to [I-D.ietf-pce-segment-routing] and
   [I-D.ietf-pce-pce-initiated-lsp] or via Netconf ([RFC6241]).

   Example: at A

   Tunnel T1: push {64, 1042}
   IP route L/8 set nhop T1

5.3.  At a Router - RFC3107 policy route

   The BGP-PE Controller could build a RFC3107 ([RFC3107]) route (from
   scratch) and send it to the ingress router:

   o  NLRI: the destination prefix to engineer: e.g., L/8.

   o  Next-Hop: the selected egress border router: C.

   o  Label: the selected egress peer: 1042.



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   o  AS path: reflecting the selected valid AS path.

   o  Some BGP policy to ensure it will be selected as best by the
      ingress router.

   This RFC3107 policy route "overwrites" an equivalent or less-specific
   "best path".  As the best-path is changed, this EPE input policy
   option influences the path propagated to the upstream peer/customers.

5.4.  At a Router - VPN policy route

   The EPE Controller could build a VPNv4 route (from scratch) and send
   it to the ingress router:

   o  NLRI: the destination prefix to engineer: e.g., L/8.

   o  Next-Hop: the selected egress border router: C.

   o  Label: the selected egress peer: 1042.

   o  Route-Target: selecting the appropriate VRF at the ingress router.

   o  AS path: reflecting the selected valid AS path.

   o  Some BGP policy to ensure it will be selected as best by the
      ingress router in the related VRF.

   The related VRF must be preconfigured.  A VRF fallback to the main
   FIB might be beneficial to avoid replicating all the "normal"
   Internet paths in each VRF.

5.5.  At a Router - Flowspec route

   An EPE Controller builds a FlowSpec route and sends it to the ingress
   router to engineer:

   o  Dissemination of Flow Specification Rules ([RFC5575].

   o  Destination/Source IP Addresses, IP Protocol, Destination/Source
      port (+1 component).

   o  ICMP Type/Code, TCP Flags, Packet length, DSCP, Fragment.

6.  IPv6

   The described solution is applicable to IPv6, either with MPLS-based
   or IPv6-Native segments.  In both cases, the same three steps of the
   solution are applicable:



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   o  BGP-LS-based signaling of the external topology and BGP Peering
      Segments to the BGP-PE controller.

   o  Collection of various inputs by the BGP-PE controller to come up
      with a policy decision.

   o  Programming at an ingress router or source host of the desired
      BGP-PE policy which consists in a list of segments to push on a
      defined traffic class.

7.  Benefits

   The BGP-PE solutions described in this document have the following
   benefits:

   o  No assumption on the iBGP design within AS1.

   o  Next-Hop-Self on the Internet routes propagated to the ingress
      border routers is possible.  This is a common design rule to
      minimize the number of IGP routes and to avoid importing external
      churn into the internal routing domain.

   o  Consistent support for traffic-engineering within the domain and
      at the external edge of the domain.

   o  Support both host and ingress border router BGP-PE policy
      programming.

   o  BGP-PE functionality is only required on the BGP-PE enabled egress
      border router and the BGP-PE controller: an ingress policy can be
      programmed at the ingress border router without any new
      functionality.

   o  Ability to deploy the same input policy across hosts connected to
      different routers (avail the global property of IGP prefix SIDs).

8.  IANA Considerations

   This document does not request any IANA allocations.

9.  Manageability Considerations

   TBD








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10.  Security Considerations

   TBD

11.  Acknowledgements

   The authors would like to thank Acee Lindem for his comments and
   contribution.

12.  References

12.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3107]  Rekhter, Y. and E. Rosen, "Carrying Label Information in
              BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001,
              <http://www.rfc-editor.org/info/rfc3107>.

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
              <http://www.rfc-editor.org/info/rfc5575>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

12.2.  Informative References

   [I-D.ietf-idr-bgpls-segment-routing-epe]
              Previdi, S., Filsfils, C., Ray, S., Patel, K., Dong, J.,
              and M. Chen, "Segment Routing BGP Egress Peer Engineering
              BGP-LS Extensions", draft-ietf-idr-bgpls-segment-routing-
              epe-05 (work in progress), May 2016.

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
              Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
              Extensions for Segment Routing", draft-ietf-isis-segment-
              routing-extensions-07 (work in progress), June 2016.






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   [I-D.ietf-isis-te-metric-extensions]
              Previdi, S., Giacalone, S., Ward, D., Drake, J., and W.
              Wu, "IS-IS Traffic Engineering (TE) Metric Extensions",
              draft-ietf-isis-te-metric-extensions-11 (work in
              progress), February 2016.

   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3
              Extensions for Segment Routing", draft-ietf-ospf-ospfv3-
              segment-routing-extensions-06 (work in progress), July
              2016.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-09 (work in progress), July 2016.

   [I-D.ietf-pce-pce-initiated-lsp]
              Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
              Extensions for PCE-initiated LSP Setup in a Stateful PCE
              Model", draft-ietf-pce-pce-initiated-lsp-07 (work in
              progress), July 2016.

   [I-D.ietf-pce-segment-routing]
              Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E.,
              Lopez, V., Tantsura, J., Henderickx, W., and J. Hardwick,
              "PCEP Extensions for Segment Routing", draft-ietf-pce-
              segment-routing-07 (work in progress), March 2016.

   [I-D.ietf-spring-problem-statement]
              Previdi, S., Filsfils, C., Decraene, B., Litkowski, S.,
              Horneffer, M., and R. Shakir, "SPRING Problem Statement
              and Requirements", draft-ietf-spring-problem-statement-08
              (work in progress), April 2016.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing-09 (work in progress), July 2016.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Shakir, R.,
              jefftant@gmail.com, j., and E. Crabbe, "Segment Routing
              with MPLS data plane", draft-ietf-spring-segment-routing-
              mpls-05 (work in progress), July 2016.



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

Authors' Addresses

   Clarence Filsfils (editor)
   Cisco Systems, Inc.
   Brussels
   BE

   Email: cfilsfil@cisco.com


   Stefano Previdi (editor)
   Cisco Systems, Inc.
   Via Del Serafico, 200
   Rome  00142
   Italy

   Email: sprevidi@cisco.com


   Ebben Aries
   Facebook
   1 Hacker Way
   Menlo Park, CA  94025
   US

   Email: exa@fb.com


   Daniel Ginsburg
   Yandex
   RU

   Email: dbg@yandex-team.ru


   Dmitry Afanasiev
   Yandex
   RU

   Email: fl0w@yandex-team.ru





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