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rfc:rfc7543

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.

Jeng, et al. Standards Track [Page 1] RFC 7543 Covering Prefixes ORF May 2015

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

Jeng, et al. Standards Track [Page 2] RFC 7543 Covering Prefixes ORF May 2015

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

Jeng, et al. Standards Track [Page 3] RFC 7543 Covering Prefixes ORF May 2015

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.

Jeng, et al. Standards Track [Page 4] RFC 7543 Covering Prefixes ORF May 2015

 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.

Jeng, et al. Standards Track [Page 5] RFC 7543 Covering Prefixes ORF May 2015

 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).

Jeng, et al. Standards Track [Page 6] RFC 7543 Covering Prefixes ORF May 2015

 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.

Jeng, et al. Standards Track [Page 7] RFC 7543 Covering Prefixes ORF May 2015

 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

Jeng, et al. Standards Track [Page 8] RFC 7543 Covering Prefixes ORF May 2015

 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.

Jeng, et al. Standards Track [Page 9] RFC 7543 Covering Prefixes ORF May 2015

 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.

Jeng, et al. Standards Track [Page 10] RFC 7543 Covering Prefixes ORF May 2015

 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.)

Jeng, et al. Standards Track [Page 11] RFC 7543 Covering Prefixes ORF May 2015

 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]

Jeng, et al. Standards Track [Page 12] RFC 7543 Covering Prefixes ORF May 2015

 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.

Jeng, et al. Standards Track [Page 13] RFC 7543 Covering Prefixes ORF May 2015

 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)

Jeng, et al. Standards Track [Page 14] RFC 7543 Covering Prefixes ORF May 2015

 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)

Jeng, et al. Standards Track [Page 15] RFC 7543 Covering Prefixes ORF May 2015

 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

Jeng, et al. Standards Track [Page 16] RFC 7543 Covering Prefixes ORF May 2015

 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) |
  +------------------------------------------------+---------------+

Jeng, et al. Standards Track [Page 17] RFC 7543 Covering Prefixes ORF May 2015

 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>.

Jeng, et al. Standards Track [Page 18] RFC 7543 Covering Prefixes ORF May 2015

 [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>.

Jeng, et al. Standards Track [Page 19] RFC 7543 Covering Prefixes ORF May 2015

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

Jeng, et al. Standards Track [Page 20] RFC 7543 Covering Prefixes ORF May 2015

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

Jeng, et al. Standards Track [Page 21]

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