





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].






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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.

















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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.


















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














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   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.























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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].




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      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



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   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.



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   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".










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   IANA maintains and registers values for ORF-Type field as follows:

      - ORF-Type value 0 is reserved.

      - 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].

      - ORF-Type values 64 through 127 are to be assigned by IANA, using
        the "First Come First Served" policy defined in RFC 5226
        [RFC5226].

      - 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.



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   [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


















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