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rfc:rfc5291

Network Working Group E. Chen Request for Comments: 5291 Cisco Systems Category: Standards Track Y. Rekhter

                                                      Juniper Networks
                                                           August 2008
           Outbound Route Filtering Capability for BGP-4

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 This document defines a BGP-based mechanism that allows a BGP speaker
 to send to its BGP peer a set of Outbound Route Filters (ORFs) that
 the peer would use to constrain/filter its outbound routing updates
 to the speaker.

1. Introduction

 Currently, it is not uncommon for a BGP speaker [BGP-4] to receive,
 and then filter out some unwanted routes from its peers based on its
 local routing policy.  Since the generation and transmission of
 routing updates by the sender, as well as the processing of routing
 updates by the receiver consume resources, it may be beneficial if
 the generation of such unwanted routing updates can be avoided in the
 first place.
 This document defines a BGP-based mechanism that allows a BGP speaker
 to send to its BGP peer a set of Outbound Route Filters (ORFs).  The
 peer would then apply these filters, in addition to its locally
 configured outbound filters (if any), to constrain/filter its
 outbound routing updates to the speaker.

2. Specification of Requirements

 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].

Chen & Rekhter Standards Track [Page 1] RFC 5291 ORF Capability for BGP-4 August 2008

3. Outbound Route Filter (ORF)

 This document uses the terms "Address Family Identifier (AFI)" and
 "Subsequent Address Family Identifier (SAFI)".  In the context of
 this document, the meaning of these terms is the same as in [BGP-MP].
 Conceptually, an ORF entry is a tuple of the form <AFI/SAFI, ORF-
 Type, Action, Match, ORF-value>; an ORF consists of one or more ORF
 entries that have a common AFI/SAFI and ORF-Type.  An ORF is
 identified by <AFI/SAFI, ORF-Type>.
 The "AFI/SAFI" component provides a coarse granularity control by
 limiting the ORF to only the routes whose Network Layer Reachability
 Information (NLRI) matches the "AFI/SAFI" component of the ORF.
 The "ORF-Type" component determines the content of the ORF-value.
 The "Action" component controls handling of the ORF Request by the
 remote peer.  Action can be one of ADD, REMOVE, REMOVE-ALL.  ADD adds
 an ORF entry to the ORF on the remote peer; REMOVE deletes a
 previously installed ORF entry on the remote peer; REMOVE-ALL deletes
 the previously installed entries in the specified ORF on the remote
 peer.
 The "Match" component is used to support matching granularity on a
 per ORF entry basis.  It can be either PERMIT or DENY.  The semantics
 of PERMIT is to ask the peer to pass updates for the set of routes
 that match the ORF entry.  The semantics of DENY is to ask the peer
 not to pass updates for the set of routes that match the ORF entry.
 When an ORF is defined, an ORF-specific matching rule MUST be
 specified so that there is no ambiguity regarding which ORF entry is
 considered as the matching entry in the ORF when a route is passed
 through the ORF.

Chen & Rekhter Standards Track [Page 2] RFC 5291 ORF Capability for BGP-4 August 2008

4. Carrying ORF Entries in BGP

 ORF entries are carried in the BGP ROUTE-REFRESH message [BGP-RR].
 A BGP speaker can distinguish an incoming ROUTE-REFRESH message that
 carries one or more ORF entries from an incoming plain ROUTE-REFRESH
 message by using the Message Length field in the BGP message header.
 A single ROUTE-REFRESH message MAY carry multiple ORF entries in one
 or more ORFs, as long as all these entries share the same AFI/SAFI.
 From the encoding point of view, each ORF entry consists of a common
 part and type-specific part, as shown in Figures 1 and 2.
 The common part consists of <AFI/SAFI, ORF-Type, Action, Match>, and
 is encoded as follows:
    The AFI/SAFI component of an ORF entry is encoded in the AFI/SAFI
    field of the ROUTE-REFRESH message.
    Following the AFI/SAFI component is the one-octet When-to-refresh
    field.  The value of this field can be either IMMEDIATE (0x01) or
    DEFER (0x02).  The semantics of IMMEDIATE and DEFER are discussed
    in the "Operation" section of this document.
    Following the When-to-refresh field is a collection of one or more
    ORFs, grouped by ORF-Type.
    The ORF-Type component is encoded as a one-octet field.
    The "Length of ORF entries" component is a two-octet field that
    contains the total length (in octets) of the ORF entries that
    follows for the specified ORF type.

Chen & Rekhter Standards Track [Page 3] RFC 5291 ORF Capability for BGP-4 August 2008

       +--------------------------------------------------+
       | Address Family Identifier (2 octets)             |
       +--------------------------------------------------+
       | Reserved (1 octet)                               |
       +--------------------------------------------------+
       | Subsequent Address Family Identifier (1 octet)   |
       +--------------------------------------------------+
       | When-to-refresh (1 octet)                        |
       +--------------------------------------------------+
       | ORF Type (1 octet)                               |
       +--------------------------------------------------+
       | Length of ORF entries (2 octets)                 |
       +--------------------------------------------------+
       | First ORF entry (variable)                       |
       +--------------------------------------------------+
       | Second ORF entry (variable)                      |
       +--------------------------------------------------+
       | ...                                              |
       +--------------------------------------------------+
       | N-th ORF entry (variable)                        |
       +--------------------------------------------------+
       | ORF Type (1 octet)                               |
       +--------------------------------------------------+
       | Length of ORF entries (2 octets)                 |
       +--------------------------------------------------+
       | First ORF entry (variable)                       |
       +--------------------------------------------------+
       | Second ORF entry (variable)                      |
       +--------------------------------------------------+
       | ...                                              |
       +--------------------------------------------------+
       | N-th ORF entry (variable)                        |
       +--------------------------------------------------+
       | ...                                              |
       +--------------------------------------------------+
       Figure 1: Carrying ORF Entries in the ROUTE-REFRESH Message

Chen & Rekhter Standards Track [Page 4] RFC 5291 ORF Capability for BGP-4 August 2008

 The rest of the components in the common part are encoded in the
 first octet of each ORF-entry (from the most significant to the least
 significant bit) as shown in Figure 2:
    Action is a two-bit field.  The value of this field is 0 for ADD,
    1 for REMOVE, and 2 for REMOVE-ALL.
    Match is a one-bit field.  The value of this field is 0 for PERMIT
    and 1 for DENY.  This field is significant only when the value of
    the Action field is either ADD or REMOVE.
    Reserved is a 5-bit field.  It is set to 0 on transmit and ignored
    on receipt.
       +---------------------------------+
       |   Action (2 bit)                |
       +---------------------------------+
       |   Match (1 bit)                 |
       +---------------------------------+
       |   Reserved (5 bits)             |
       +---------------------------------+
       |   Type specific part (variable) |
       +---------------------------------+
           Figure 2: ORF Entry Encoding
    When the Action component of an ORF entry specifies REMOVE-ALL,
    the entry consists of only the common part.

Chen & Rekhter Standards Track [Page 5] RFC 5291 ORF Capability for BGP-4 August 2008

5. Outbound Route Filtering Capability

 A BGP speaker that is willing to receive ORF entries from its peer,
 or a BGP speaker that would like to send ORF entries to its peer,
 advertises this to the peer by using the Outbound Route Filtering
 Capability, as described below.
 The Outbound Route Filtering Capability is a new BGP Capability
 [BGP-CAP] defined as follows:
    Capability code: 3
    Capability length: variable
    Capability value: one or more of the entries as shown in Figure 3.
       +--------------------------------------------------+
       | Address Family Identifier (2 octets)             |
       +--------------------------------------------------+
       | Reserved (1 octet)                               |
       +--------------------------------------------------+
       | Subsequent Address Family Identifier (1 octet)   |
       +--------------------------------------------------+
       | Number of ORFs (1 octet)                         |
       +--------------------------------------------------+
       | ORF Type (1 octet)                               |
       +--------------------------------------------------+
       | Send/Receive (1 octet)                           |
       +--------------------------------------------------+
       | ...                                              |
       +--------------------------------------------------+
       | ORF Type (1 octet)                               |
       +--------------------------------------------------+
       | Send/Receive (1 octet)                           |
       +--------------------------------------------------+
       Figure 3: Outbound Route Filtering Capability Encoding
 The use and meaning of these fields are as follows:
    Address Family Identifier (AFI):
       This field is the same as the one used in [BGP-MP].
    Subsequent Address Family Identifier (SAFI):
       This field is the same as the one used in [BGP-MP].

Chen & Rekhter Standards Track [Page 6] RFC 5291 ORF Capability for BGP-4 August 2008

    Number of ORF Types:
       This field contains the number of Filter Types to be listed in
       the following fields.
    ORF Type:
       This field contains the value of an ORF Type.
    Send/Receive:
       This field indicates whether the sender is (a) willing to
       receive ORF entries from its peer (value 1), (b) would like to
       send ORF entries to its peer (value 2), or (c) both (value 3)
       for the ORF Type.

6. Operation

 A BGP speaker that is willing to receive ORF entries from its peer,
 or would like to send ORF entries to its peer SHOULD advertise the
 Outbound Route Filtering Capability to the peer using BGP
 Capabilities advertisement [BGP-CAP].
 A BGP speaker that implements the Outbound Route Filtering Capability
 MUST support the BGP ROUTE-REFRESH message, as defined in [BGP-RR].
 A BGP speaker that advertises the Outbound Route Filtering Capability
 to a peer using BGP Capabilities advertisement [BGP-CAP] does not
 have to advertise the BGP Route Refresh Capability to that peer.
 Consider a BGP speaker that advertises the Outbound Route Filtering
 Capability indicating its willingness to receive a particular set of
 <AFI/SAFI, ORF-Type> from its peer, and that receives the Outbound
 Route Filtering Capability indicating the desire of the peer to send
 a particular set <AFI/SAFI, ORF-Type> to the speaker.  If for a given
 AFI/SAFI the intersection between these two sets is non-empty, the
 speaker SHOULD NOT advertise to the peer any routes with that
 AFI/SAFI prior to receiving from the peer any ROUTE-REFRESH message
 carrying that AFI/SAFI, where the message could be either without any
 ORF entries, or with one or more ORF entry and the When-to-refresh
 field set to IMMEDIATE.  If, on the other hand, for a given AFI/SAFI
 the intersection between these two sets is empty, the speaker MUST
 follow normal BGP procedures.
 A BGP speaker may send a ROUTE-REFRESH message with one or more ORF
 entries to its peer only if the peer advertises to the speaker the
 Outbound Route Filtering Capability indicating its willingness to
 receive ORF entries from the speaker, and the speaker advertises to
 the peer the Outbound Route Filtering Capability indicating its

Chen & Rekhter Standards Track [Page 7] RFC 5291 ORF Capability for BGP-4 August 2008

 desire to send ORF entries to the peer.  The message may contain only
 ORF entries of <AFI/SAFI, ORF-type> that the peer is willing to
 receive, as advertised to the speaker in the Outbound Route Filtering
 Capability.
 When a BGP speaker receives a ROUTE-REFRESH message with one or more
 ORF entries from its peer, then the speaker performs the following
 actions.  If an <AFI/SAFI, ORF-type> carried by the message does not
 match <AFI/SAFI, ORF-type> that the speaker is willing to receive
 from the peer (as advertised to the peer in the Outbound Route
 Filtering Capability), the specified ORF entries in the message are
 ignored.  Otherwise, the speaker modifies the specified ORF
 previously received, according to the ORF entries carried in the
 message.  If any of the fields of an ORF entry in the message
 contains an unrecognized value, the whole specified ORF previously
 received is removed.
 If the Action component of an ORF entry is REMOVE, but the ORF
 previously received does not contain the specified entry, the ORF
 entry in the message is ignored.
 ORF entries with either REMOVE or REMOVE-ALL cannot remove locally
 configured outbound route filters.
 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.
 If the When-to-refresh indicates DEFER, then after processing all the
 ORF entries carried in the message the speaker defers re-
 advertisement 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 received from
 the peer until the speaker receives a subsequent ROUTE-REFRESH
 message for the same AFI/SAFI either without any ORF entries, or with
 one or more ORF entries and When-to-refresh set to IMMEDIATE.
 If the speaker receives from the peer a ROUTE-REFRESH message without
 any ORF entries, then the speaker sends to the peer all routes from
 the Adj-RIB-Out associated with the peer whose AFI/SAFI is the same
 as what is carried in the message and taking into account the ORFs
 (if any) previously received from the peer.

Chen & Rekhter Standards Track [Page 8] RFC 5291 ORF Capability for BGP-4 August 2008

 The set of ORF entries that the speaker sends to the peer expresses
 the speaker's local preference, that the peer may or may not decide
 to honor.
 During a single BGP session, the speaker MAY pass multiple ORF
 entries to the peer.
 After a BGP speaker makes changes to the ORF entries previously sent
 to a peer, the speaker MUST send to the peer the updated ORF entries
 with either (a) When-to-refresh set to IMMEDIATE, or (b) When-to-
 refresh set to DEFER followed by a plain ROUTE-REFRESH message.  The
 latter MUST be used by the speaker when there are other policy
 changes (in addition to the ORF entries) that require the peer to
 re-advertise all the routes.
 The lifetime of an ORF is the duration of the BGP session during
 which the ORF is exchanged.
 An ORF is removed when the last ORF entry is removed (either via
 REMOVE-ALL, or via a sequence of REMOVE).
 If a particular route maintained by a BGP speaker does not match any
 of the ORF entries of any of the (non-empty) ORFs associated with a
 particular peer, then this route SHOULD NOT be advertised to the
 peer.
 If a BGP speaker maintains multiple ORFs of different ORF-Types for a
 particular peer, then the decision by the speaker to advertise a
 route to the peer is determined by passing the route through each
 such ORF, and combining the results (combining of PERMIT and DENY
 results in DENY).

7. IANA Considerations

 This document defines a new BGP Capability - Outbound Route Filtering
 Capability.  The Capability Code for the Outbound Route Filtering
 Capability is 3.
 As specified in this document, an ORF entry contains the ORF-Type
 field for which IANA has created and now maintains a registry
 entitled "BGP Outbound Route Filtering (ORF) Types".

Chen & Rekhter Standards Track [Page 9] RFC 5291 ORF Capability for BGP-4 August 2008

 IANA maintains and registers values for ORF-Type field as follows:
  1. ORF-Type value 0 is reserved.
  1. ORF-Type values 1 through 63 are to be assigned by IANA using

either the Standards Action process defined in RFC 5226

      [RFC5226], or the Early IANA Allocation process defined in RFC
      4020 [RFC4020].
  1. ORF-Type values 64 through 127 are to be assigned by IANA, using

the "First Come First Served" policy defined in RFC 5226

      [RFC5226].
  1. ORF-Type values 128 through 255 are vendor-specific, and values

in this range are not to be assigned by IANA.

8. Manageability Considerations

 The management objects for BGP ORFs will be defined separately,
 outside this document.  However, it is suggested that the following
 management objects be defined:
 The ORF Capability object, which describes the ORF Capability
 exchanged over a BGP session, should include the ORF types and the
 Send/Receive values advertised and received for a BGP peer.
 The ORF entry object should contain the ORF entries of each ORF sent
 and received for a BGP peer.

9. Security Considerations

 This extension to BGP does not change the underlying security issues
 [BGP-4].

10. Acknowledgments

 Some of the material in the document is adapted from a proposal for
 selective updates by Yakov Rekhter, Kannan Varadhan, and Curtis
 Villamizar.

11. Normative References

 [BGP-4]   Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border
           Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006.
 [BGP-MP]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
           "Multiprotocol Extensions for BGP-4", RFC 4760, January
           2007.

Chen & Rekhter Standards Track [Page 10] RFC 5291 ORF Capability for BGP-4 August 2008

 [BGP-CAP] Chandra, R. and J. Scudder, "Capabilities Advertisement
           with BGP-4", RFC 3392, November 2002.
 [BGP-RR]  Chen, E., "Route Refresh Capability for BGP-4", RFC 2918,
           September 2000.
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4020] Kompella, K. and A. Zinin, "Early IANA Allocation of
           Standards Track Code Points", BCP 100, RFC 4020, February
           2005.
 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
           IANA Considerations Section in RFCs", BCP 26, RFC 5226, May
           2008.

Authors' Addresses

 Enke Chen
 Cisco Systems, Inc.
 170 W. Tasman Dr.
 San Jose, CA 95134
 Email: enkechen@cisco.com
 Yakov Rekhter
 Juniper Networks
 1194 N. Mathilda Ave
 Sunnyvale, CA 94089
 Email: yakov@juniper.net

Chen & Rekhter Standards Track [Page 11] RFC 5291 ORF Capability for BGP-4 August 2008

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Chen & Rekhter Standards Track [Page 12]

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