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Versions: (draft-sreekantiah-idr-segment-routing-te) 00 01 02 03 04 05 06 07 draft-ietf-idr-segment-routing-te-policy

Network Working Group                                    S. Previdi, Ed.
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                          A. Sreekantiah
Expires: September 19, 2016                                 S. Sivabalan
                                                     Cisco Systems, Inc.
                                                               P. Mattes
                                                               Microsoft
                                                          March 18, 2016


    Advertising Segment Routing Traffic Engineering Policies in BGP
             draft-previdi-idr-segment-routing-te-policy-00

Abstract

   This document defines a new BGP SAFI with a new NLRI in order to
   advertise a Segment Routing Traffic Engineering Policy (SR TE
   Policy).  The SR TE Policy is advertised along with the Tunnel
   Encapsulation Attribute for which this document also defines new sub-
   TLVs.  An SR TE policy is advertised with the information that will
   be used by the node receiving the advertisement in order to
   instantiate the policy in its forwarding table and to steer traffic
   according to the policy.

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/.

   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 September 19, 2016.

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



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   (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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  SR TE Policy Encoding . . . . . . . . . . . . . . . . . . . .   4
     2.1.  SR TE Policy SAFI and NLRI  . . . . . . . . . . . . . . .   4
       2.1.1.  SR TE Policies and Add-Paths  . . . . . . . . . . . .   5
     2.2.  SR TE Policy and Tunnel Encapsulation Attribute . . . . .   5
     2.3.  Remote Endpoint and Color . . . . . . . . . . . . . . . .   6
     2.4.  SR TE Policy Sub-TLVs . . . . . . . . . . . . . . . . . .   7
       2.4.1.  SR TE Binding SID Sub-TLV . . . . . . . . . . . . . .   7
       2.4.2.  Weight Sub-TLV  . . . . . . . . . . . . . . . . . . .   8
       2.4.3.  Segment List Sub-TLV  . . . . . . . . . . . . . . . .   9
       2.4.4.  Segment Sub-TLV . . . . . . . . . . . . . . . . . . .   9
   3.  SR TE Policy Operations . . . . . . . . . . . . . . . . . . .  11
     3.1.  Multipath Operation . . . . . . . . . . . . . . . . . . .  12
     3.2.  Binding SID TLV . . . . . . . . . . . . . . . . . . . . .  12
     3.3.  Reception of an SR TE Policy  . . . . . . . . . . . . . .  13
     3.4.  Announcing BGP SR TE Policies . . . . . . . . . . . . . .  14
     3.5.  Flowspec and SR TE Policies . . . . . . . . . . . . . . .  14
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     7.2.  Informational References  . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Segment Routing (SR) technology leverages the source routing and
   tunneling paradigms.  [I-D.ietf-spring-segment-routing] describes the
   SR architecture.  [I-D.ietf-spring-segment-routing-mpls] describes
   its instantiation on the MPLS data plane and
   [I-D.ietf-6man-segment-routing-header] describes the Segment Routing
   instantiation over the IPv6 data plane.

   This document defines the Segment Routing Traffic Engineering Policy
   (SR TE Policy) as a set of weighted equal cost multi path (WECMP)




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   segment lists (representing explicit paths) as well as the mechanism
   allowing a router to steer traffic into an SR TE Policy.

   The SR TE Policy is advertised in the Border Gateway Protocol (BGP)
   by the BGP speaker being a router or a controller and using
   extensions defined in this document.  Among the information encoded
   in the BGP message and representing the SR TE Policy, the steering
   mechanism makes also use of the Extended Color Community currently
   defined in [I-D.ietf-idr-tunnel-encaps]

   Typically, a controller defines the set of policies and advertise
   them to BGP routers (typically ingress routers).  The policy
   advertisement uses BGP extensions defined in this document.  The
   policy advertisement is, in most but not all of the cases, tailored
   for the receiver.  In other words, a policy advertised to a given BGP
   speaker has significance only for that particular router and is not
   intended to be propagated anywhere else.  Then, the receiver of the
   policy instantiate the policy in its routing and forwarding tables
   and steer traffic into it based on both the policy and destination
   prefix color and next-hop.

   Alternatively, a router (i.e.: an BGP egress router) advertises SR TE
   Policies representing paths to itself.  These advertisements are sent
   to BGP ingress nodes who instantiate these policies and steer traffic
   into them according to the color and endpoint/BGP next-hop of both
   the policy and the destination prefix.

   An SR TE Policy being intended only for the receiver of the
   advertisement, the SR TE Policies are sent directly to each receiver
   and, in most of the cases will not traverse any Route Reflector (RR,
   [RFC4456]).

   However, in the case where the same SR TE Policy is intended for a
   group of nodes, nothing prevents the originator to rely on one or
   more RRs in order to distribute the SR TE Policy to multiple
   receivers.  The encoding of the SR TE Policy defined in this document
   supports both propagation schemes: direct BGP session and Route
   Reflectors.

   The BGP extensions for the advertisement of SR TE Policies include
   following components:

   o  A new Subsequent Address Family Identifier (SAFI) identifying the
      content of the BGP message (i.e.: the SR TE Policy).

   o  A new NLRI identifying the SR TE Policy.





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   o  A set of new TLVs to be inserted into the Tunnel Encapsulation
      Attribute (as defined in [I-D.ietf-idr-tunnel-encaps]) and
      describing the SR TE Policy.

   o  The Extended Color Community (as defined in
      [I-D.ietf-idr-tunnel-encaps]) and used in order to steer traffic
      into an SR TE Policy.

1.1.  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].

2.  SR TE Policy Encoding

2.1.  SR TE Policy SAFI and NLRI

   A new SAFI is defined: the SR TE Policy SAFI (codepoint suggested
   value 73, to be assigned by IANA).

   The SR TE Policy SAFI uses a new NLRI defined as follows:

   +-----------------------------------------------+
   |           Policy Color (4 octets)             |
   +-----------------------------------------------+
   |           Endpoint (4 or 16 octets)           |
   +-----------------------------------------------+

   where:

   o  Policy Color: 4-octet value identifying (with the endpoint) the
      policy.  The color is used to match the color of the destination
      prefixes in order to steer traffic into the SR TE Policy.

   o  Endpoint: identifies the endpoint of a policy.  The Endpoint may
      represent a single node or a set of nodes (e.g.: an anycast
      address or a summary address).  The Endpoint may be an IPv4
      (4-octet) address or an IPv6 (16-octet) address according to the
      AFI of the NLRI.

   The NLRI containing the SR TE Policy is carried in a BGP UPDATE
   message [RFC4271] using BGP multiprotocol extensions [RFC4760] with
   an AFI of 1 or 2 (IPv4 or IPv6) and with a SAFI of 73 (suggested
   value, to be assigned by IANA).

   An update message that carries the MP_REACH_NLRI or MP_UNREACH_NLRI
   attribute with the SR TE Policy SAFI MUST also carry the BGP



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   mandatory attributes: NEXT_HOP, ORIGIN, AS_PATH, and LOCAL_PREF (for
   IBGP neighbors), as defined in [RFC4271].  In addition, the BGP
   update message MAY also contain any of the BGP optional attributes.

   The NEXT_HOP attribute of the SR TE Policy SAFI NLRI is set based on
   the AFI.  For example, if the AFI is set to IPv4 (1), then the
   nexthop is encoded as a 4-byte IPv4 address.  If the AFI is set to
   IPv6 (2), then the nexthop is encoded as a 16-byte IPv6 address of
   the router.  It is important to note that any BGP speaker receiving a
   BGP message with an SR TE Policy NLRI, will process it only if the
   NLRI is a best path as per the BGP best path selection algorithm.

   The NEXT_HOP attribute of the SR TE Policy SAFI NLRI MUST be set as
   one of the local addresses of the BGP speaker originating and
   advertising the SR TE Policy (either the controller or the BGP egress
   node).

2.1.1.  SR TE Policies and Add-Paths

   The SR TE Policy SAFI NLRI MAY use the Add Paths extension
   ([I-D.ietf-idr-add-paths]) when the same policy (identified by the
   same Color and Endpoint) is to be advertised by multiple originators
   (e.g.: multiple controllers) and all advertisements need to be
   advertised to a group of receivers (hence these advertisements need
   to be preserved from a RR selection process).

   In such case, each controller will use a different path identifier in
   the advertisement of the SR TE Policy.

   When Add-Paths extensions is to be used, it MUST be signaled in the
   BGP capability according to ([I-D.ietf-idr-add-paths]).

2.2.  SR TE Policy and Tunnel Encapsulation Attribute

   The content of the SR TE Policy is encoded in the Tunnel
   Encapsulation Attribute originally defined in
   [I-D.ietf-idr-tunnel-encaps] using a new Tunnel-Type TLV (suggested
   codepoint is 14, to be assigned by IANA).

   The SR TE Policy Encoding structure is as follows:











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   SR TE Policy SAFI NLRI: <Policy-Color, Endpoint>
   Attributes:
      Tunnel Encaps Attribute (23)
         Tunnel Type: SR TE Policy
             Binding SID
             Segment List
                 Weight
                 Segment (sid/nai/flags)
                 Segment (sid/nai/flags)
                 ...
             ...
         ...
   where:

   o  SR TE Policy SAFI NLRI is defined in Section 2.1.

   o  Tunnel Encapsulation Attribute is defined in
      [I-D.ietf-idr-tunnel-encaps].

   o  Tunnel-Type is set to a suggested value of 14 (to be assigned by
      IANA).

   o  Binding SID, Weight, Segment and Segment-List are new sub-TLVs
      defined in this document.

   o  Additional sub-TLVs may be defined in the future.

   A single occurrence of "Tunnel Type: SR TE Policy" MUST be encoded
   within the same Tunnel Encapsulation Attribute.

   Multiple occurrences of "Segment List" MAY be encoded within the same
   SR TE Policy.

   Multiple occurrences of "Segment" MAY be encoded within the same
   Segment List.

2.3.  Remote Endpoint and Color

   The Remote Endpoint and Color sub-TLVs, as defined in
   [I-D.ietf-idr-tunnel-encaps], MAY also be present in the SR TE Policy
   encodings.

   If present, the Remote Endpoint sub-TLV MUST match the Endpoint of
   the SR TE Policy SAFI NLRI.  If they don't match, the SR TE Policy
   advertisement MUST be considered as invalid.






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   If present, the Color sub-TLV MUST match the Policy Color of the SR
   TE Policy SAFI NLRI.  If they don't match, the SR TE Policy
   advertisement MUST be considered as invalid.

2.4.  SR TE Policy Sub-TLVs

   This section defines the SR TE Policy sub-TLVs.

2.4.1.  SR TE Binding SID Sub-TLV

   The Binding SID sub-TLV requests the allocation of a Binding Segment
   identifier associated with the SR TE Policy.  The Binding SID 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              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Binding SID (variable, optional)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o  Type: to be assigned by IANA (suggested value is 6).

   o  Length: specifies the length of the value field not including Type
      and Length fields.  Can be 0 or 4 or 16.

   o  Binding SID: if length is 0, then no field is present.  If length
      is 4 then the Binding SID contains a 4-octet SID.  If length is 16
      then the Binding SID contains a 16-octet IPv6 SID.

   The Binding SID sub-TLV is used to instruct the receiver of the BGP
   message to allocate a Binding SID to the SR TE Policy.  The
   allocation of the Binding SID in the receiver is done according to
   following rules:

   o  If length is 0 (no value field is present), then the receiver MUST
      allocate a local Binding SID whose value is chosen by the
      receiver.

   o  If length is 4, then the value field contains the 4-octet Binding
      SID value the receiver SHOULD allocate.

   o  If length is 16, then the value field contains the 16-octet
      Binding SID value the receiver SHOULD allocate.




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   The Binding SID sub-TLV is mandatory and MUST NOT appear more than
   once on an SR TE Policy Advertisement.

   When a controller is used in order to define and advertise SR TE
   Policies and when the Binding SID is allocated by the receiver, such
   Binding SID SHOULD be reported to the controller.  The mechanisms
   and/or APIs used for the reporting of the Binding SID are outside the
   scope of this document.

   Further use of the Binding SID is described in a subsequent section.

2.4.2.  Weight Sub-TLV

   The Weight sub-TLV specifies the weight associated to a given path
   (i.e.: a given segment list).  The weight is used in order to apply
   weighted-ECMP mechanism when steering traffic into a policy that
   includes multiple paths (i.e.: multiple segment lists).

   The Weight 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                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Weight                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   Type: to be assigned by IANA (suggested value is 7).

   Length: 4.

   The Weight sub-TLV is optional and MAY appear only once in the
   Segment List sub-TLV.

   When present, the Weight sub-TLV specifies a weight to be associated
   with the corresponding Segment List, for use in unequal-cost multi
   path.  Weights are applied by summing the total value of all of the
   weights for all Segment Lists, and then assigning a fraction of the
   forwarded traffic to each Segment List in proportion its weight's
   fraction of the total.








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2.4.3.  Segment List Sub-TLV

   The Segment List sub-TLV is used in order to encode a single explicit
   path towards the endpoint.  The Segment List sub-TLV includes the
   elements of the paths (i.e.: segments) as well as an optional Weight
   TLV.

   The Segment List 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-TLVs                          //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o  Type: to be assigned by IANA (suggested value is 8).

   o  Length: the total length (not including the Type and Length
      fields) of the sub-TLVs encoded within the Segment List sub-TLV.

   o  sub-TLVs:

      *  An optional single Weight sub-TLV.

      *  One or more Segment sub-TLVs.

   The Segment List sub-TLV is mandatory.

   Multiple occurrences of the Segment List sub-TLV MAY appear in the SR
   TE Policy.

   When multiple occurrences of the Segment List sub-TLV appear in the
   SR TE Policy, the traffic is load-balanced across them either through
   an ECMP scheme (if no Weight sub-TLV is present) or through a W-ECMP
   scheme according to Section 2.4.2.

2.4.4.  Segment Sub-TLV

   The Segment sub-TLV describes a single segment in a segment list
   (i.e.: a single element of the explicit path).  Multiple Segment sub-
   TLVs constitute an explicit path of the SR TE Policy.

   The encoding format of the Segment sub-TLV is based on the ERO sub-
   object definition described in [I-D.ietf-pce-segment-routing]):



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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                     |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ST   |                 Flags                     |I|L|F|S|C|M|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                        SID (32 bits or 128 bits)            //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                        NAI (variable)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o  Type: to be assigned by IANA (suggested value is 9).

   o  Length: the length of the Segment sub-TLV not including the Type
      and Length fields.

   SID Type (ST) indicates the type of the information associated with
   the SID and NAI contained in the sub-TLV.  ST is defined in
   [I-D.ietf-pce-segment-routing].

   SID is the Segment Identifier as defined in
   [I-D.ietf-pce-segment-routing].

   NAI (Node and Adjacency Identifier) contains the NAI associated with
   the SID.  Depending on the value of ST, the NAI can have different
   formats as described in [I-D.ietf-pce-segment-routing].

   Flags carry any additional information related to the SID.
   Currently, the following flags are defined:

      I-Flag: IPv6 SID flag.  When set, it indicates that the SID is
      encoded as a 16-octet IPv6 SID (IPv6 SIDs are defined in
      [I-D.ietf-6man-segment-routing-header]).  When clear, the SID is
      encoded as a 4-octet SID.

      L-Flag: Loose flag.  Indicates whether the encoding represents a
      loose-hop in the LSP ([RFC3209]).  If L-Flag is clear, a BGP
      speaker MUST NOT overwrite the SID value present in the Segment
      sub-TLV.  Otherwise, a BGP speaker, based on local policy, MAY
      expand or replace the SID value in the received Segment sub-TLV.

      F-flag: when set, the NAI value in the object body is null.

      S-Flag: when set, the SID value in the object body is null.  In
      this case, the receiving BGP speaker is responsible for choosing



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      the SID value, e.g., by looking up its Tunnel DB using the NAI
      which, in this case, MUST be present in the object.

      C-Flag: when this flag as well as the M-flag are set, then the SID
      value represents an MPLS label stack entry as specified in
      [RFC5462], where all the entry's fields (Label, TC, S, and TTL)
      are specified by the sending BGP speaker.  However, a receiving
      BGP speaker MAY choose to override TC, S, and TTL values according
      its local policy and MPLS forwarding rules.

      M-Flag: when this bit is set, the SID value represents an MPLS
      label stack entry as specified in [RFC5462] where only the label
      value is specified by the BGP speaker.  Other label fields (i.e:
      TC, S, and TTL) fields MUST be ignored, and receiving BGP speaker
      MUST set these fields according to its local policy and MPLS
      forwarding rules.

      Other flags may be defined in the future.

   The NAI encoding is as per corresponding sub-TLV definition in
   [I-D.ietf-pce-segment-routing]

3.  SR TE Policy Operations

   SR TE Policies are advertised in the Tunnel Encapsulation Attribute
   defined in [I-D.ietf-idr-tunnel-encaps].  The SR TE Policy TLVs
   specify one (or more for load balancing purposes) list of segment
   identifiers (SIDs), that define the set of explicit SR TE paths
   towards the endpoint address encoded in the NLRI.

   The Color field of the NLRI allows association of destination
   prefixes with a given SR TE Policy.  The BGP speaker SHOULD then
   attach a Color Extended Community (as defined in [RFC5512]) to
   destination prefixes (e.g.: IPv4/IPv6 unicast prefixes) in order to
   allow the receiver of the SR TE Policy and of the destination prefix
   to steer traffic into the SR TE Policy if the destination prefix:

   o  Has a BGP next-hop attribute matching the SR TE Policy SAFI NLRI
      Endpoint and

   o  Has an attached Extended Color Community with the same value as
      the color of the SR TE Policy NLRI Color.

   A SR TE Policy MAY also be sent by a controller, in lieu of the
   originating speaker.  The controller sends the SR TE Policy SAFI NLRI
   with a Policy Color and an Endpoint identifying the Policy, where:





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      The Policy Color is to be used in order to steer traffic into the
      policy in the node receiving the SR TE Policy.

      The Endpoint (with the Color) identifies the policy.  Endpoint is
      used to match the BGP next-hop attribute of the destination prefix
      when steering traffic in the node receiving the SR TE Policy.

   On reception of an SR TE Policy, a BGP speaker SHOULD instantiate the
   SR TE Policy in its routing and forwarding table with the set of
   segment lists (i.e.: explicit paths) included in the policy and
   taking into account the Binding SID and Weight sub-TLVs.

   On the receiving BGP speaker, all destination prefixes that share the
   same Extended Color Community value and the same BGP next-hop
   attribute are steered to the corresponding SR TE Policy that has been
   instantiated and which matches the Color and Endpoint NLRI values.

   Similarly, different destination prefixes can be steered into
   distinct SR TE Policies by coloring them differently.

3.1.  Multipath Operation

   The SR TE Policy MAY contain multiple Segment Lists which, in the
   absence of the Weight TLV, signifies equal cost load balancing
   amongst them.

   When a weight sub-TLV is encoded in each Segment List TLV, then the
   weight value SHOULD be used in order to perform an unequal cost load
   balance amongst the Segment Lists as specified in Section 2.4.2.

3.2.  Binding SID TLV

   When the optional Binding SID sub-TLV is present, it indicates an
   instruction, to the receiving BGP speaker to allocate a Binding SID
   for the list of SIDs the Binding sub-TLV is related to.

   Any incoming packet with the Binding SID as active segment (according
   to the terminology described in [I-D.ietf-spring-segment-routing])
   will then have the Binding SID swapped with the list of SIDs
   specified in the Segment List sub-TLVs on the allocating BGP speaker.
   The allocated Binding SID MAY be then advertised by the BGP speaker
   that created it, through, e.g., BGP-LS in order to, typically, feed a
   controller with the updated topology and SR TE Policy information.








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3.3.  Reception of an SR TE Policy

   When a BGP speaker receives an SR TE Policy from a neighbor it has to
   determine if the SR TE Policy advertisement is acceptable.  The
   following applies:

   o  The SR TE Policy NLRI MUST have a color value and MAY have an
      Endpoint value.

   o  The Tunnel Encapsulation Attribute MUST be attached to the BGP
      Update and MUST have the Tunnel Type set to SR TE Policy (value to
      be assigned by IANA).

   o  Within the SR TE Policy, at least one Segment List sub-TLV MUST be
      present.

   o  Within the Segment List sub-TLV at least one Segment sub-TLV MUST
      be present.

   o  Within Segment sub-TLV it is not required that both SID and NAI
      are encoded however, at least one of the two MUST be present.

   Any segment (in the segment list sub-TLV) being advertised with an
   NAI MUST be validated by the receiver.  The validation consists of
   resolving the SID using the NAI information, i.e., the receiver does
   a lookup in its local table and finds the SID value corresponding to
   the NAI information.  The type of information carried in the NAI is
   related to the settings of the ST bits in the segment sub-TLV and
   described in [I-D.ietf-pce-segment-routing].

   When a BGP speaker receives an SR TE Policy from a neighbor and
   according to [I-D.ietf-pce-segment-routing], the receiver MUST check
   the validity of the first SID of each Segment List sub-TLV of the SR
   TE Policy.  The first SID MUST be known in the receiver local table
   either as a label (in the case the SID encodes a label value) or as
   an IPv6 address.

   When a BGP speaker receives an SR TE Policy from a neighbor with an
   acceptable SR TE Policy SAFI NLRI and with the I-flag clear, it
   SHOULD compute the segment list and equivalent MPLS label from the
   Segment List sub-TLVs and program them in the MPLS data plane.

   When a BGP speaker receives an SR TE Policy from a neighbor with an
   acceptable SR TE Policy SAFI NLRI and with the I-flag set, it SHOULD
   compute the segment list and equivalent IPv6 segment list from the
   Segment List sub-TLVs and program them in the IPv6 data plane
   according to [I-D.ietf-6man-segment-routing-header].




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   Also, the receiver SHOULD program its MPLS or IPv6 data planes so
   that BGP destination prefixes matching their Extended Color Community
   and BGP next-hop with the SR TE Policy SAFI NLRI Color and Endpoint
   are steered into the SR TE Policy and forwarded accordingly.

   When building the MPLS label stack or the IPv6 Segment list from the
   Segment List sub-TLV, the receiving BGP speaker MUST interpret the
   set of Segment sub-TLVs as follows:

   o  The first Segment sub-TLV represents the topmost label or the
      first IPv6 segment.  In the receiving BGP speaker, it identifies
      the first segment the traffic will be directed towards to (along
      the SR TE explicit path).

   o  The last Segment sub-TLV represents the bottommost label or the
      last IPv6 segment.

3.4.  Announcing BGP SR TE Policies

   Typically, the value of the SIDs encoded in the Segment sub-TLVs is
   determined by configuration/provisioning either in the controller or
   in the node originating the SR TE Policy.

   A BGP speaker SHOULD follow normal iBGP/eBGP rules to propagate the
   SR TE Policy.  The Add-Paths capability in the SR TE Policy SAFI NLRI
   allows the propagation of each individual policy through one or more
   Route Reflectors (RR) without incurring the case where one or more
   policies are dropped due to RR selection process.

   Since the SR TE Policies are unique within an SR domain and intended
   only for the receiver of the SR TE Policy advertisement, a BGP
   speaker receiving an SR TE Policy, by default, MUST NOT propagate
   such policy unless explicitly configured to do so.

   In order to prevent propagation of SR TE Policy advertisement, BGP
   filters MAY be deployed in addition to the use of the NO_ADVERTISE
   community ([RFC1997]) that MAY be attached to the advertisement.

3.5.  Flowspec and SR TE Policies

   The SR TE Policy can be carried in context of a Flowspec NLRI
   ([RFC5575]).  In this case, when the redirect to IP nexthop is
   specified as in [I-D.ietf-idr-flowspec-redirect-ip], the tunnel to
   the nexthop is specified by the segment list in the Segment List sub-
   TLVs.  The Segment List (e.g..: label stack or IPv6 segment list) is
   imposed to flows matching the criteria in the Flowspec route in order
   to steer them towards the nexthop as specified in the SR TE Policy
   SAFI NLRI.



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4.  Acknowledgments

   The authors of this document would like to thank Eric Rosen for his
   review of this document.

5.  IANA Considerations

   This document defines:

   o  a new SAFI in the registry "Subsequent Address Family Identifiers
      (SAFI) Parameters":

           Suggested         Description            Reference
             Value
           -----------------------------------------------------
              73        SR TE Policy SAFI         This document

   o  a new Tunnel-Type in the registry "BGP Tunnel Encapsulation
      Attribute Tunnel Types":

          Suggested         Description            Reference
            Value
          -----------------------------------------------------
             14          SR TE Policy Type         This document

   o  new sub-TLVs in the registry "BGP Tunnel Encapsulation Attribute
      sub-TLVs":

          Suggested         Description            Reference
            Value
          -----------------------------------------------------
              6           Binding SID sub-TLV      This document
              7           Weight sub-TLV           This document
              8           Segment List sub-TLV     This document
              9           Segment sub-TLV          This document

6.  Security Considerations

   TBD.

7.  References

7.1.  Normative References

   [I-D.ietf-idr-tunnel-encaps]
              Rosen, E., Patel, K., and G. Velde, "The BGP Tunnel
              Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-01
              (work in progress), December 2015.



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   [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-06 (work in progress), August 2015.

   [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>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <http://www.rfc-editor.org/info/rfc3209>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <http://www.rfc-editor.org/info/rfc4271>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <http://www.rfc-editor.org/info/rfc4364>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <http://www.rfc-editor.org/info/rfc4760>.

   [RFC5462]  Andersson, L. and R. Asati, "Multiprotocol Label Switching
              (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
              Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
              2009, <http://www.rfc-editor.org/info/rfc5462>.

   [RFC5512]  Mohapatra, P. and E. Rosen, "The BGP Encapsulation
              Subsequent Address Family Identifier (SAFI) and the BGP
              Tunnel Encapsulation Attribute", RFC 5512,
              DOI 10.17487/RFC5512, April 2009,
              <http://www.rfc-editor.org/info/rfc5512>.

   [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>.






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7.2.  Informational References

   [I-D.ietf-6man-segment-routing-header]
              Previdi, S., Filsfils, C., Field, B., Leung, I., Linkova,
              J., Kosugi, T., Vyncke, E., and D. Lebrun, "IPv6 Segment
              Routing Header (SRH)", draft-ietf-6man-segment-routing-
              header-00 (work in progress), December 2015.

   [I-D.ietf-idr-add-paths]
              Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", draft-ietf-idr-
              add-paths-13 (work in progress), December 2015.

   [I-D.ietf-idr-flowspec-redirect-ip]
              Uttaro, J., Haas, J., Texier, M., Andy, A., Ray, S.,
              Simpson, A., and W. Henderickx, "BGP Flow-Spec Redirect to
              IP Action", draft-ietf-idr-flowspec-redirect-ip-02 (work
              in progress), February 2015.

   [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-07 (work in progress), December
              2015.

   [I-D.ietf-spring-segment-routing-mpls]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
              and E. Crabbe, "Segment Routing with MPLS data plane",
              draft-ietf-spring-segment-routing-mpls-03 (work in
              progress), February 2016.

   [RFC1997]  Chandra, R., Traina, P., and T. Li, "BGP Communities
              Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
              <http://www.rfc-editor.org/info/rfc1997>.

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <http://www.rfc-editor.org/info/rfc4456>.

Authors' Addresses









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

   Email: sprevidi@cisco.com


   Clarence Filsfils
   Cisco Systems, Inc.
   Brussels
   BE

   Email: cfilsfil@cisco.com


   Arjun Sreekantiah
   Cisco Systems, Inc.
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: asreekan@cisco.com


   Siva Sivabalan
   Cisco Systems, Inc.
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: msiva@cisco.com


   Paul Mattes
   Microsoft
   One Microsoft Way
   Redmond, WA  98052
   USA

   Email: pamattes@microsoft.com









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