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RFC 7543

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Covering Prefixes Outbound Route Filter for BGP-4

 


Top       ToC       Page 1 
Internet Engineering Task Force (IETF)                           H. Jeng
Request for Comments: 7543                                          AT&T
Category: Standards Track                                       L. Jalil
ISSN: 2070-1721                                                  Verizon
                                                               R. Bonica
                                                        Juniper Networks
                                                                K. Patel
                                                           Cisco Systems
                                                                 L. Yong
                                                     Huawei Technologies
                                                                May 2015


           Covering Prefixes Outbound Route Filter for BGP-4

Abstract

   This document defines a new Outbound Route Filter (ORF) type, called
   the Covering Prefixes ORF (CP-ORF).  CP-ORF is applicable in Virtual
   Hub-and-Spoke VPNs.  It also is applicable in BGP/MPLS Ethernet VPN
   (EVPN) networks.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7543.

Page 2 
Copyright Notice

   Copyright (c) 2015 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.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  CP-ORF Encoding . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Processing Rules  . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Applicability in Virtual Hub-and-Spoke VPNs . . . . . . . . .  10
     4.1.  Multicast Considerations  . . . . . . . . . . . . . . . .  13
   5.  Applicability in BGP/MPLS Ethernet VPN (EVPN) . . . . . . . .  13
   6.  Clean-up  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  18
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  20
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

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1.  Introduction

   A BGP [RFC4271] speaker can send Outbound Route Filters (ORFs)
   [RFC5291] to a peer.  The peer uses ORFs to filter routing updates
   that it sends to the BGP speaker.  Using ORF, a BGP speaker can
   realize a "route pull" paradigm in which the BGP speaker, on demand,
   pulls certain routes from the peer.

   This document defines a new ORF-type, called the Covering Prefixes
   ORF (CP-ORF).  A BGP speaker sends a CP-ORF to a peer in order to
   pull routes that cover a specified host address.  A prefix covers a
   host address if it can be used to forward traffic towards that host
   address.  Section 3 provides a more complete description of covering
   prefix selection criteria.

   CP-ORF is applicable in Virtual Hub-and-Spoke VPNs [RFC7024]
   [RFC4364].  It also is applicable BGP/MPLS Ethernet VPN (EVPN)
   [RFC7432] networks.

1.1.  Terminology

   This document uses the following terms:

   o  Address Family Identifier (AFI) - defined in [RFC4760]

   o  Subsequent Address Family Identifier (SAFI) - defined in [RFC4760]

   o  Route Target (RT) - defined in [RFC4364]

   o  VPN-IP Default Route - defined in [RFC7024]

   o  Virtual Hub (V-hub) - defined in [RFC7024]

   o  Virtual Spoke (V-spoke) - defined in [RFC7024]

   o  BGP/MPLS Ethernet VPN (EVPN) - defined in [RFC7432]

   o  EVPN Instance (EVI) - defined in [RFC7432]

   o  MAC - Media Access Control

   o  Unknown MAC Route (UMR) - A regular EVPN MAC/IP Advertisement
      route where the MAC Address Length is set to 48 and the MAC
      address to 00:00:00:00:00:00

   o  Default MAC Gateway (DMG) - An EVPN Provider Edge (PE) that
      advertises a UMR

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1.2.  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.  CP-ORF Encoding

   RFC 5291 augments the BGP ROUTE-REFRESH message so that it can carry
   ORF entries.  When the ROUTE-REFRESH message carries ORF entries, it
   includes the following fields:

   o  AFI [IANA.AFI]

   o  SAFI [IANA.SAFI]

   o  When-to-refresh (IMMEDIATE or DEFERRED)

   o  ORF Type

   o  Length (of ORF entries)

   The ROUTE-REFRESH message also contains a list of ORF entries.  Each
   ORF entry contains the following fields:

   o  Action (ADD, REMOVE, or REMOVE-ALL)

   o  Match (PERMIT or DENY)

   The ORF entry may also contain Type-specific information.  Type-
   specific information is present only when the Action is equal to ADD
   or REMOVE.  It is not present when the Action is equal to REMOVE-ALL.

   When the BGP ROUTE-REFRESH message carries CP-ORF entries, the
   following conditions MUST be true:

   o  The ORF Type MUST be equal to CP-ORF (65).

   o  The AFI MUST be equal to IPv4, IPv6, or Layer 2 VPN (L2VPN).

   o  If the AFI is equal to IPv4 or IPv6, the SAFI MUST be equal to
      MPLS-labeled VPN address.

   o  If the AFI is equal to L2VPN, the SAFI MUST be equal to BGP EVPN.

   o  The Match field MUST be equal to PERMIT.

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   Figure 1 depicts the encoding of the CP-ORF Type-specific
   information.

                     +--------------------------------+
                     |  Sequence (32 bits)            |
                     +--------------------------------+
                     |  Minlen   (8 bits)             |
                     +--------------------------------+
                     |  Maxlen   (8 bits)             |
                     +--------------------------------+
                     |  VPN Route Target (64 bits)    |
                     +--------------------------------+
                     |  Import Route Target (64 bits) |
                     +--------------------------------+
                     |  Route Type (8 bits)           |
                     +--------------------------------+
                     |  Host Address                  |
                     |    (0, 32, 48, or 128 bits)    |
                     |           ....                 |
                     +--------------------------------+

                  Figure 1: CP-ORF Type-Specific Encoding

   The CP-ORF recipient uses the following fields to select routes
   matching the CP-ORF:

   o  Sequence: the relative position of a CP-ORF entry among other
      CP-ORF entries

   o  Minlen: the minimum length of the selected route (measured in
      bits)

   o  Maxlen: the maximum length of the selected route (measured in
      bits)

   o  VPN Route Target: the VPN Route Target carried by the selected
      route

   o  Route Type: the type of the selected route

   o  Host Address: the address covered by the selected route

   See Section 3 for details.

   The CP-ORF recipient marks routes that match CP-ORF with the Import
   Route Target before advertising those routes to the CP-ORF
   originator.  See Section 3 for details.

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   If the ROUTE-REFRESH AFI is equal to IPv4,

   o  the value of Minlen MUST be less than or equal to 32;

   o  the value of Maxlen MUST be less than or equal to 32;

   o  the value of Minlen MUST be less than or equal to the value of
      Maxlen;

   o  the value of Route Type MUST be 0 (i.e., RESERVED); and

   o  the Host Address MUST contain exactly 32 bits.

   If the ROUTE-REFRESH AFI is equal to IPv6,

   o  the value of Minlen MUST be less than or equal to 128;

   o  the value of Maxlen MUST be less than or equal to 128;

   o  the value of Minlen MUST be less than or equal to the value of
      Maxlen;

   o  the value of Route Type MUST be 0 (i.e., RESERVED); and

   o  the Host Address MUST contain exactly 128 bits.

   If the ROUTE-REFRESH AFI is equal to L2VPN, the value of Route Type
   MUST be one of the following values taken from the IANA EVPN Registry
   [IANA.EVPN]:

   o  1 - Ethernet Autodiscovery Route

   o  2 - MAC/IP Advertisement Route

   o  3 - Inclusive Multicast Route

   o  4 - Ethernet Segment

   If the ROUTE-REFRESH AFI is equal to L2VPN and the value of Route
   Type is equal to Ethernet Autodiscovery Route, Inclusive Multicast
   Route, or Ethernet Segment,

   o  the value of Minlen MUST be equal to 0;

   o  the value of Maxlen MUST be equal to 0; and

   o  the Host Address MUST be absent (i.e., contain 0 bits).

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   If the ROUTE-REFRESH AFI is equal to L2VPN and the value of Route
   Type is equal to MAC/IP Advertisement Route,

   o  the value of Minlen MUST be less than or equal to 48;

   o  the value of Maxlen MUST be less than or equal to 48;

   o  the value of Minlen MUST be less than or equal to the value of
      Maxlen; and

   o  the Host Address MUST contain exactly 48 bits.

3.  Processing Rules

   According to [RFC4271], every BGP speaker maintains a single Loc-RIB.
   For each of its peers, the BGP speaker also maintains an Outbound
   Filter and an Adj-RIB-Out.  The Outbound Filter defines policy that
   determines which Loc-RIB entries are processed into the corresponding
   Adj-RIB-Out.  Mechanisms such as RT-Constrain [RFC4684] and ORF
   [RFC5291] enable a router's peer to influence the Outbound Filter.
   Therefore, the Outbound Filter for a given peer is constructed using
   a combination of the locally configured policy and the information
   received via RT-Constrain and ORF from the peer.

   Using this model, we can describe the operations of CP-ORF as
   follows:

   When a BGP speaker receives a ROUTE-REFRESH message that contains a
   CP-ORF and that ROUTE-REFRESH message violates any of the encoding
   rules specified in Section 2, the BGP speaker MUST ignore the entire
   ROUTE-REFRESH message.  It SHOULD also log the event.  However, an
   implementation MAY apply logging thresholds to avoid excessive
   messaging or log file overflow.

   Otherwise, the BGP speaker processes each CP-ORF entry as indicated
   by the Action field.  If the Action is equal to ADD, the BGP speaker
   adds the CP-ORF entry to the Outbound Filter associated with the peer
   in the position specified by the Sequence field.  If the Action is
   equal to REMOVE, the BGP speaker removes the CP-ORF entry from the
   Outbound Filter.  If the Action is equal to REMOVE-ALL, the BGP
   speaker removes all CP-ORF entries from the Outbound Filter.

   Whenever the BGP speaker applies an Outbound Filter to a route
   contained in its Loc-RIB, it evaluates the route in terms of the
   CP-ORF entries first.  It then evaluates the route in terms of the
   remaining non-CP-ORF entries.  The rules for the former are described
   below.  The rules for the latter are outside the scope of this
   document.

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   The following route types can match a CP-ORF:

   o  IPv4-VPN

   o  IPv6-VPN

   o  L2VPN

   In order for an IPv4-VPN route or IPv6-VPN route to match a CP-ORF,
   all of the following conditions MUST be true:

   o  the route carries an RT whose value is the same as the CP-ORF VPN
      Route Target;

   o  the route prefix length is greater than or equal to the CP-ORF
      Minlen plus 64 (i.e., the length of a VPN Route Distinguisher);

   o  the route prefix length is less than or equal to the CP-ORF Maxlen
      plus 64 (i.e., the length of a VPN Route Distinguisher);

   o  ignoring the Route Distinguisher, the leading bits of the route
      prefix are identical to the leading bits of the CP-ORF Host
      Address, and CP-ORF Minlen defines the number of bits that must be
      identical; and

   o  Loc-RIB does not contain a more specific route that also satisfies
      all of the above listed conditions.

   The BGP speaker ignores Route Distinguishers when determining whether
   a prefix matches a host address.  For example, assume that a CP-ORF
   carries the following information:

   o  Minlen equal to 1

   o  Maxlen equal to 32

   o  Host Address equal to 192.0.2.1

   Assume also that Loc-RIB contains routes for the following IPv4-VPN
   prefixes and that all of these routes carry an RT whose value is the
   same as the CP-ORF VPN Route Target:

   o  1:0.0.0.0/64.

   o  2:192.0.2.0/88

   o  3:192.0.2.0/89

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   Only the prefix 3:192.0.2.0/89 matches the CP-ORF.  The prefix
   1:0.0.0.0/64 does not match, because its length (64) is less than the
   CP-ORF Minlen (1) plus the length of an L3VPN Route Distinguisher
   (64).  If Loc-RIB did not contain the prefix 3:192.0.2.0/89,
   2:192.0.2.0/88 would match the CP-ORF.  However, because Loc-RIB also
   contains a more specific covering route (3:192.0.2.0/89),
   2:192.0.2.0/88 does not match.  Only 3:192.0.2.0/89 satisfies all of
   the above listed match criteria.  Note that the matching algorithm
   ignored Route Distinguishers.

   In order for an EVPN route to match a CP-ORF, all of the following
   conditions MUST be true:

   o  the EVPN route type is equal to the CP-ORF Route Type; and

   o  the route carries an RT whose value is equal to the CP-ORF VPN
      Route Target.

   In addition, if the CP-ORF Route Type is equal to MAC/IP
   Advertisement Route, the following conditions also MUST be true:

   o  the EVPN Route MAC Address Length is greater than or equal to the
      CP-ORF Minlen plus 64 (i.e., the length of a VPN Route
      Distinguisher);

   o  the EVPN Route MAC Address Length is less than or equal to the CP-
      ORF Maxlen plus 64 (i.e., the length of a VPN Route
      Distinguisher); and

   o  ignoring the Route Distinguisher, the leading bits of the EVPN
      Route MAC Address are identical to the leading bits of the CP-ORF
      Host Address.  CP-ORF Minlen defines the number of bits that must
      be identical.

   If a route matches the selection criteria of a CP-ORF entry and it
   does not violate any subsequent rule specified by the Outbound Filter
   (e.g., rules that reflect local policy or rules that are due to
   RT-Constrains), the BGP speaker places the route into the Adj-RIB-
   Out.  In Adj-RIB-Out, the BGP speaker adds the CP-ORF Import Route
   Target to the list of RTs that the route already carries.  The BGP
   speaker also adds a Transitive Opaque Extended Community [RFC4360]
   with the sub-type equal to CP-ORF (0x03).  As a result of being
   placed in Adj-RIB-Out, the route is advertised to the peer associated
   with the Adj-RIB-Out.

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   Receiving CP-ORF entries with REMOVE or REMOVE-ALL Actions may cause
   a route that has previously been installed in a particular Adj-RIB-
   Out to be excluded from that Adj-RIB-Out.  In this case, as specified
   in [RFC4271], "the previously advertised route in that Adj-RIB-Out
   MUST be withdrawn from service by means of an UPDATE message".

   RFC 5291 states that a BGP speaker should respond to a ROUTE REFRESH
   message as follows:

      If the When-to-refresh indicates IMMEDIATE, then after processing
      all the ORF entries carried in the message the speaker
      re-advertises to the peer routes from the Adj-RIB-Out associated
      with the peer that have the same AFI/SAFI as what is carried in
      the message, and taking into account all the ORF entries for that
      AFI/SAFI received from the peer.  The speaker MUST re-advertise
      all the routes that have been affected by the ORF entries carried
      in the message, but MAY also re-advertise the routes that have not
      been affected by the ORF entries carried in the message.

   When the ROUTE-REFRESH message includes only CP-ORF entries, the BGP
   speaker MUST re-advertise routes that have been affected by these
   CP-ORF entries.  It is RECOMMENDED not to re-advertise the routes
   that have not been affected by the CP-ORF entries.

   When the ROUTE-REFRESH message includes one or more CP-ORF entries
   and one or more ORF entries of a different type, the behavior remains
   unchanged from that described in RFC 5291.

4.  Applicability in Virtual Hub-and-Spoke VPNs

   In a Virtual Hub-and-Spoke environment, VPN sites are attached to PE
   routers.  For a given VPN, a PE router acts in exactly one of the
   following roles:

   o  as a V-hub

   o  as a V-spoke

   o  as neither a V-hub nor a V-spoke

   To illustrate CP-ORF operation in conjunction with Virtual Hub-and-
   Spoke, assume the following:

   o  One of the sites in a particular VPN, RED-VPN, is connected to a
      PE that acts as neither a V-hub nor a V-spoke for RED-VPN.  We
      refer to this PE as PE1.

Top      ToC       Page 11 
   o  Another site in RED-VPN is connected to another PE, and that PE
      acts as a V-hub for RED-VPN.  We refer to this PE as V-hub1.

   o  Yet another site in RED-VPN is connected to another PE, and that
      PE acts as a V-spoke for RED-VPN.  We refer to this PE as
      V-spoke1.

   All of these PEs advertise RED-VPN routes to a Route Reflector (RR).
   They mark these routes with an RT, which we will call RT-RED.  In
   particular, PE1 advertises a RED-VPN route to a prefix that we will
   call P.  P covers a host address that we will call H.

   For the purpose of illustration, also assume that the PEs and the RRs
   use RT-Constrain [RFC4684].

   V-hub1 serves the RED-VPN.  Therefore, V-hub1 advertises a VPN-IP
   default route for the RED-VPN to the RR, carrying the route target
   RT-RED-FROM-HUB1.

   V-spoke1 establishes a BGP session with the RR, negotiating the
   CP-ORF capability as well as the Multiprotocol Extensions capability
   [RFC4760].  Upon establishment of the BGP session, the RR does not
   advertise any routes to V-spoke1.  The RR will not advertise any
   routes until it receives either a ROUTE-REFRESH message or a BGP
   UPDATE message containing a Route Target Membership Network Layering
   Reachability Information (NLRI) [RFC4684].

   Immediately after the BGP session is established, V-spoke1 sends the
   RR a BGP UPDATE message containing a Route Target Membership NLRI.
   The Route Target Membership NLRI specifies RT-RED-FROM-HUB1 as its
   RT.  In response to the BGP-UPDATE message, the RR advertises the VPN
   IP default route for the RED-VPN to V-spoke1.  This route carries the
   route target RT-RED-FROM-HUB1.  V-spoke1 subjects this route to its
   import policy and accepts it because it carries the route target
   RT-RED-FROM-HUB1.

   Now, V-spoke1 begins normal operation, sending all of its RED-VPN
   traffic through V-hub1.  At some point, V-spoke1 determines that it
   might benefit from a more direct route to H.  (Note that criteria by
   which V-spoke1 determines that it needs a more direct route to H are
   beyond the scope of this document.)

Top      ToC       Page 12 
   In order to discover a more direct route, V-spoke1 assigns a unique
   numeric identifier to H.  V-spoke1 then sends a ROUTE-REFRESH message
   to the RR, which contains the following information:

   o  AFI is equal to IPv4 or IPv6, as appropriate

   o  SAFI is equal to "MPLS-labeled VPN address"

   o  When-to-refresh is equal to IMMEDIATE

   o  Action is equal to ADD

   o  Match is equal to PERMIT

   o  ORF Type is equal to CP-ORF

   o  CP-ORF Sequence is equal to the identifier associated with H

   o  CP-ORF Minlen is equal to 1

   o  CP-ORF Maxlen is equal to 32 or 128, as appropriate

   o  CP-ORF VPN Route Target is equal to RT-RED

   o  CP-ORF Import Route Target is equal to RT-RED-FROM-HUB1

   o  CP-ORF Route Type is equal to 0 (i.e., undefined)

   o  CP-ORF Host Address is equal to H

   Upon receipt of the ROUTE-REFRESH message, the RR MUST ensure that it
   carries all routes belonging to the RED-VPN.  In at least one special
   case, where all of the RR clients are V-spokes and none of the RR
   clients are V-hubs, the RR will lack some or all of the required
   RED-VPN routes.  So, the RR sends a BGP UPDATE message containing a
   Route Target Membership NLRI for VPN-RED to all of its peers.  This
   causes the peers to advertise VPN-RED routes to the RR if they have
   not done so already.

   Next, the RR adds the received CP-ORF to the Outbound Filter
   associated with V-spoke1.  Using the procedures in Section 3, the RR
   determines whether any of the routes in its Loc-RIB satisfy the
   selection criteria of the newly updated Outbound Filter.  If any
   routes satisfy the match criteria, they are added to the Adj-RIB-Out
   associated with V-spoke1.  In Adj-RIB-Out, the RR adds
   RT-RED-FROM-HUB1 to the list of RTs that the route already carries.
   The RR also adds a Transitive Opaque Extended Community [RFC4360]

Top      ToC       Page 13 
   with the sub-type equal to CP-ORF.  Finally, RR advertises the newly
   added routes to V-spoke1.  In this example, the RR advertises P to
   V-spoke1 with a next-hop of PE1.

   V-spoke1 subjects the advertised routes to its import policy and
   accepts them because they carry the route target RT-RED-FROM-HUB1.

   V-spoke1 may repeat this process whenever it discovers another flow
   that might benefit from a more direct route to its destination.

4.1.  Multicast Considerations

   When applying Multicast VPN [RFC6513] [RFC6514] procedures, routes
   bearing a Transitive Opaque Extended Community [RFC4360] with the
   sub-type equal to CP-ORF MUST NOT be used to determine Eligible
   Upstream Multicast Hops (UMH).

5.  Applicability in BGP/MPLS Ethernet VPN (EVPN)

   In an EVPN environment, Customer Edge (CE) devices are attached to PE
   routers.  A CE can be a host, a router, or a switch.  For a given
   EVI, a PE router acts in exactly one of the following roles:

   o  as a DMG

   o  as a Spoke

   o  as neither a DMG nor a Spoke

   To illustrate CP-ORF operation in the EVPN environment, assume the
   following:

   o  A CE device in a particular EVI, RED-EVI, is connected to a PE
      that acts as neither a DMG nor a Spoke for RED-EVI.  We refer to
      this PE as PE1.

   o  Another CE device in RED-EVI is connected to another PE, and that
      PE acts as a DMG for RED-EVI.  We refer to this PE as DMG1.

   o  Yet another CE device in RED-EVI is connected to another PE, and
      that PE acts as a Spoke for RED-EVI.  We refer to this PE as
      Spoke1.

   All of these PEs advertise RED-EVI routes to a RR.  They mark these
   routes with an RT, which we will call RT-RED.  In particular, PE1
   advertises a RED-EVI route to a MAC Address that we will call M.

Top      ToC       Page 14 
   The RED-EVI VPN Routing and Forwarding tables (VRFs) on all of these
   PEs are provisioned to import EVPN routes that carry RT-RED.

   Since DMG1 acts as a DMG for RED-EVI, DMG1 advertises a UMR for the
   RED-EVI to the RR, carrying the route target RT-RED.  The UMR is
   characterized as follows:

   o  EVPN Route Type is equal to MAC/IP Advertisement Route

   o  MAC address length is equal to 0

   o  IP address length is equal to 0

   Spoke1 establishes a BGP session with the RR, negotiating the CP-ORF
   capability as well as the Multiprotocol Extensions capability
   [RFC4760].  Upon establishment of the BGP session, the RR does not
   advertise any routes to Spoke1.  The RR will not advertise any routes
   until it receives a ROUTE-REFRESH message.

   Immediately after the BGP session is established, Spoke1 sends the RR
   a ROUTE REFRESH message containing the following information:

   o  AFI is equal to L2VPN

   o  SAFI is equal to BGP EVPN

   o  When-to-refresh is equal to IMMEDIATE

   o  Action is equal to ADD

   o  Match is equal to PERMIT

   The ROUTE REFRESH message also contains four ORF entries.  The first
   ORF entry contains the following information:

   o  ORF Type is equal to CP-ORF

   o  CP-ORF Sequence is equal to 1

   o  CP-ORF Minlen is equal to 0

   o  CP-ORF Maxlen is equal to 0

   o  CP-ORF VPN Route Target is equal to RT-RED

   o  CP-ORF Import Route Target is equal to RT-RED

   o  CP-ORF Route Type is equal to 1 (Ethernet Autodiscovery Route)

Top      ToC       Page 15 
   The second ORF entry contains the following information:

   o  ORF Type is equal to CP-ORF

   o  CP-ORF Sequence is equal to 2

   o  CP-ORF Minlen is equal to 0

   o  CP-ORF Maxlen is equal to 0

   o  CP-ORF VPN Route Target is equal to RT-RED

   o  CP-ORF Import Route Target is equal to RT-RED

   o  CP-ORF Route Type is equal to 2 (MAC/IP Advertisement Route)

   The third ORF entry contains the following information:

   o  ORF Type is equal to CP-ORF

   o  CP-ORF Sequence is equal to 3

   o  CP-ORF Minlen is equal to 0

   o  CP-ORF Maxlen is equal to 0

   o  CP-ORF VPN Route Target is equal to RT-RED

   o  CP-ORF Import Route Target is equal to RT-RED

   o  CP-ORF Route Type is equal to 3 (Inclusive Multicast Route)

   The fourth ORF entry contains the following information:

   o  ORF Type is equal to CP-ORF

   o  CP-ORF Sequence is equal to 4

   o  CP-ORF Minlen is equal to 0

   o  CP-ORF Maxlen is equal to 0

   o  CP-ORF VPN Route Target is equal to RT-RED

   o  CP-ORF Import Route Target is equal to RT-RED

   o  CP-ORF Route Type is equal to 4 (Ethernet Segment)

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   In response to the ROUTE REFRESH message, the RR advertises the
   following to V-spoke1:

   o  All Ethernet Autodiscovery Routes belonging to RED-EVI

   o  A UMR advertised by DMG1 and belonging to RED-EVI

   o  All Inclusive Multicast Routes belonging to RED-EVI

   o  All Ethernet Segment Routes belonging to RED-EVI

   All of these routes carry the route target RT-RED.  Spoke1 subjects
   these routes to its import policy and accepts them because they carry
   the route target RT-RED.

   Now, Spoke1 begins normal operation, sending all of its RED-VPN
   traffic through DMG1.  At some point, Spoke1 determines that it might
   benefit from a more direct route to M.  (Note that criteria by which
   Spoke1 determines that it needs a more direct route to M are beyond
   the scope of this document.)

   In order to discover a more direct route, Spoke1 assigns a unique
   numeric identifier to M.  V-spoke1 then sends a ROUTE-REFRESH message
   to the RR, containing the following information:

   o  AFI is equal to L2VPN

   o  SAFI is equal to BGP EVPN

   o  When-to-refresh is equal to IMMEDIATE

   o  Action is equal to ADD

   o  Match is equal to PERMIT

   o  ORF Type is equal to CP-ORF

   o  CP-ORF Sequence is equal to the identifier associated with M

   o  CP-ORF Minlen is equal to 1

   o  CP-ORF Maxlen is equal to 48

   o  CP-ORF VPN Route Target is equal to RT-RED

   o  CP-ORF Import Route Target is equal to RT-RED

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   o  CP-ORF Route Type is equal to 2 (i.e., MAC/IP Advertisement Route)

   o  CP-ORF Host Address is equal to M

   Next, the RR adds the received CP-ORF to the Outbound Filter
   associated with Spoke1.  Using the procedures in Section 3, the RR
   determines whether any of the routes in its Loc-RIB satisfy the
   selection criteria of the newly updated Outbound Filter.  If any
   routes satisfy the match criteria, they are added to the Adj-RIB-Out
   associated with Spoke1.  The RR adds a Transitive Opaque Extended
   Community [RFC4360] with the sub-type equal to CP-ORF.  Note that as
   these routes are added to the Adj-RIB-Out, the RR does not change the
   list of RTs that the route already carries.  Finally, RR advertises
   the newly added routes to V-spoke1.  In this example, the RR
   advertises M to V-spoke1 with a next-hop of PE1.

   Spoke1 subjects the advertised routes to its import policy and
   accepts them because they carry the route target RT-RED.

   Spoke1 may repeat this process whenever it discovers another flow
   that might benefit from a more direct route to its destination.

   Note that, in general, an EVI may have more than one DMG, in which
   case each spoke would receive a UMR from each of them.  The spoke
   should follow its local route selection procedures to select one of
   them as the "best" and use the selected one.

6.  Clean-up

   Each CP-ORF consumes memory and compute resources on the device that
   supports it.  Therefore, in order to obtain optimal performance, BGP
   speakers periodically evaluate all CP-ORFs that they have originated
   and remove unneeded CP-ORFs.  The criteria by which a BGP speaker
   identifies unneeded CP-ORF entries is a matter of local policy and is
   beyond the scope of this document.

7.  IANA Considerations

   This memo uses code points from the First Come First Served [RFC5226]
   range of the following registries:

    +------------------------------------------------+---------------+
    | Registry                                       | Code Point    |
    +------------------------------------------------+---------------+
    | BGP Outbound Route Filtering (ORF) Types       | CP-ORF (65)   |
    | Transitive Opaque Extended Community Sub-Types | CP-ORF (0x03) |
    +------------------------------------------------+---------------+

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   IANA has updated the above-mentioned registry entries so that they
   reference this memo.

8.  Security Considerations

   Each CP-ORF consumes memory and compute resources on the device that
   supports it.  Therefore, a device supporting CP-ORF takes the
   following steps to protect itself from oversubscription:

   o  When negotiating the ORF capability, advertise willingness to
      receive the CP-ORF only to known, trusted Internal BGP (iBGP)
      peers.  See Section 5 of RFC 5291 for negotiation details.

   o  Enforce a per-peer limit on the number of CP-ORFs that can be
      installed at any given time.  Ignore all requests to add CP-ORFs
      beyond that limit

   Security considerations for BGP are presented in [RFC4271] while
   further security analysis of BGP is found in [RFC6952].

9.  References

9.1.  Normative References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997,
               <http://www.rfc-editor.org/info/rfc2119>.

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

   [RFC4360]   Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
               Communities Attribute", RFC 4360, February 2006,
               <http://www.rfc-editor.org/info/rfc4360>.

   [RFC4684]   Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
               R., Patel, K., and J. Guichard, "Constrained Route
               Distribution for Border Gateway Protocol/MultiProtocol
               Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
               Private Networks (VPNs)", RFC 4684, November 2006,
               <http://www.rfc-editor.org/info/rfc4684>.

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

Top      ToC       Page 19 
   [RFC5291]   Chen, E. and Y. Rekhter, "Outbound Route Filtering
               Capability for BGP-4", RFC 5291, August 2008,
               <http://www.rfc-editor.org/info/rfc5291>.

   [RFC6513]   Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
               BGP IP VPNs", RFC 6513, February 2012,
               <http://www.rfc-editor.org/info/rfc6513>.

   [RFC6514]   Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
               Encodings and Procedures for Multicast in MPLS/BGP IP
               VPNs", RFC 6514, February 2012,
               <http://www.rfc-editor.org/info/rfc6514>.

   [RFC7024]   Jeng, H., Uttaro, J., Jalil, L., Decraene, B., Rekhter,
               Y., and R. Aggarwal, "Virtual Hub-and-Spoke in BGP/MPLS
               VPNs", RFC 7024, October 2013,
               <http://www.rfc-editor.org/info/rfc7024>.

   [RFC7432]   Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
               Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
               Ethernet VPN", RFC 7432, February 2015,
               <http://www.rfc-editor.org/info/rfc7432>.

9.2.  Informative References

   [IANA.AFI]  IANA, "Address Family Numbers",
               <http://www.iana.org/assignments/address-family-numbers>.

   [IANA.EVPN] IANA, "Ethernet VPN (EVPN)",
               <http://www.iana.org/assignments/evpn>.

   [IANA.SAFI] IANA, "Subsequent Address Family Identifiers (SAFI)
               Parameters",
               <http://www.iana.org/assignments/safi-namespace>.

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

   [RFC5226]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
               IANA Considerations Section in RFCs", BCP 26, RFC 5226,
               May 2008, <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6952]   Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
               BGP, LDP, PCEP, and MSDP Issues According to the Keying
               and Authentication for Routing Protocols (KARP) Design
               Guide", RFC 6952, May 2013,
               <http://www.rfc-editor.org/info/rfc6952>.

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Acknowledgements

   The authors wish to acknowledge Han Nguyen, James Uttaro, and Alvaro
   Retana for their comments and contributions.

Contributors

   The following individuals contributed to the development of this
   document:

   o  Yakov Rekhter

   o  Xiaohu Xu

Top      ToC       Page 21 
Authors' Addresses

   Huajin Jeng
   AT&T

   EMail: hj2387@att.com


   Luay Jalil
   Verizon

   EMail: luay.jalil@verizon.com


   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, Virginia  20170
   United States

   EMail: rbonica@juniper.net


   Keyur Patel
   Cisco Systems
   170 W. Tasman Drive
   San Jose, California  95134
   United States

   EMail: keyupate@cisco.com


   Lucy Yong
   Huawei Technologies
   Austin, Texas
   United States

   EMail: lucy.yong@huawei.com