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Versions: (draft-keyur-idr-enhanced-gr) 00 01 02 03 04 05 06

Internet Engineering Task Force                                 K. Patel
Internet-Draft                                                   E. Chen
Intended status: Informational                               R. Fernando
Expires: December 9, 2016                                  Cisco Systems
                                                              J. Scudder
                                                        Juniper Networks
                                                            June 7, 2016


        Accelerated Routing Convergence for BGP Graceful Restart
                   draft-ietf-idr-enhanced-gr-06.txt

Abstract

   In this document we specify extensions to BGP graceful restart in
   order to avoid unnecessary transmission of the routing information
   preserved across a session restart, thus accelerating the routing
   convergence.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 9, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Version Numbers for Routing Entities  . . . . . . . . . . . .   3
   3.  UPDATE-VERSION Message  . . . . . . . . . . . . . . . . . . .   3
   4.  Enhanced Graceful Restart Capability  . . . . . . . . . . . .   4
   5.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Currently the BGP graceful restart (GR) mechanism specified in
   [RFC4724] requires a complete re-advertisement of the routing
   information across a session restart, even though the routing
   information may have been preserved.  For example, as described in
   [RFC4724], the "Receiving Speaker" temporarily maintains the routes
   received from its neighbor with the GR Capability.  In addition, the
   "Restarting Speaker" may also be able to preserve routing information
   across a BGP restart by check-pointing routing information to a
   standby or secondary facility.

   Clearly the routing re-convergence post a session restart would be
   faster if we can avoid unnecessary transmission of the routing
   information preserved across a session restart.  That is the goal of
   this document.

   In this document we specify extensions to BGP graceful restart in
   order to avoid unnecessary transmission of the routing information
   preserved across a session restart, thus accelerating the routing
   convergence.  More specifically, we describe a "version number" based
   mechanism for keeping track of the routing information across a
   session restart.  A new BGP message type, UPDATE-VERSION, is
   introduced for checkpointing the update version maintained for a
   neighbor.  We also introduce the Enhanced Graceful Restart
   Capability, and specify procedures for handling routing update across
   a session restart.






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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Version Numbers for Routing Entities

   In order to avoid unnecessary transmission of the routing information
   preserved across a session restart, a BGP speaker will need to
   identify exactly "what" has been preserved by a remote speaker.

   The approach described here is "version number" (or "sequence
   number") based, and it consists of (a) assigning a unique,
   monotonically increasing number as the version number for each
   routing entity (e.g., route or message) when it is created or
   modified; and (b) maintaining an update version (for each neighbor)
   calculated as the maximum of the version numbers of all the routing
   entities that have been sent to the neighbor.

   A BGP speaker can tell whether a given routing entity has been sent
   to a neighbor by comparing the version number of the entity with the
   update version for the neighbor.  Thus by checkpointing the update
   version for a neighbor across a session restart, a BGP speaker would
   be able to identify exactly "what" has been preserved by a remote
   speaker, and also "what" remains to be sent.

   In this document a version number is a 8-octet unsigned integer.
   Value 0 is used to indicate the beginning (or "epoch") of the update
   generation.  The version number is not expected to wrap.  However, in
   the unlikely scenario that it does wrap, the sender MUST maintain its
   internal consistency, and also MUST perform a route refresh
   [RFC2918], [RFC7313] toward the receiver.

   The number space for the version numbers should be AFI/SAFI [RFC4760]
   specific.  Version numbers are also assigned (from the same number
   space) to other AFI/SAFI specific, non-update information (such as
   ROUTE-REFRESH [RFC2918]), and are included in the calculation of the
   update version for a neighbor.

3.  UPDATE-VERSION Message

   The UPDATE-VERSION message is a new BGP message type with type code
   <TBD>.  In addition to the fixed-size BGP header [RFC4271], the
   UPDATE-VERSION message contains the following fields:






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                +------------------------------------------------+
                | Address Family Identifier (2 octets)           |
                +------------------------------------------------+
                | Subsequent Address Family Identifier (1 octet) |
                +------------------------------------------------+
                | Message Subtype (1 octet)                      |
                +------------------------------------------------+
                | Version (8 octets)                             |
                +------------------------------------------------+

   The "Address Family Identifier" (AFI) field and the "Subsequent
   Address Family Identifier" (SAFI) field are the same as the ones used
   in [RFC4760].

   The "Message Subtype" field indicates whether the sender is (a)
   sending an update version (value 1), (b) acknowledging the receipt of
   an update version (value 2), or (c) requesting updates from the very
   last update version the sender has acknowledged (value 3).

   The Version field contains an update version associated with the
   message subtypes 1 and 2.  The value of this field is irrelevant for
   the message subtype 3.  This value of the field is opaque to the
   receiver.

   As detailed in the Operation section, the UPDATE-VERSION message can
   be used by a BGP speaker to either carry an update version, or
   acknowledge the receipt of an update version, or request updates from
   the very last update version acknowledged.

4.  Enhanced Graceful Restart Capability

   The Enhanced Graceful Restart (GR) Capability is a new BGP capability
   [RFC5492].  The Capability Code for this capability is specified in
   the IANA Considerations section of this document.  The Capability
   Length field of this capability is 0.

   By advertising the Enhanced GR Capability to a peer, a BGP speaker
   conveys to the peer that the speaker is capable of receiving and
   properly handling the UPDATE-VERSION message from the peer, as well
   as recognizing the two new bit flags defined below for the GR
   Capability.

   The two new bit flags for the "Flags for Address Family" field of the
   GR Capability are defined as follows:







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                           0 1 2 3 4 5 6 7
                          +-+-+-+-+-+-+-+-+
                          | | |R|T|       |
                          +-+-+-+-+-+-+-+-+

   The third most significant bit (R) is defined as the "RX Routing
   State", which is used to indicate whether during the previous session
   restart the routes of the given AFI/SAFI that were received have
   indeed been preserved up to the update version acknowledged by the
   speaker previously.  When set (value 1), the bit indicates that the
   routes have been preserved.

   The fourth most significant bit (T) is defined as the "TX Routing
   State", which is used to indicate whether the speaker has indeed
   preserved enough state to resume advertising routes of the given AFI/
   SAFI from the update version acknowledged by the neighbor previously.
   When set (value 1), the bit indicates that the state has been
   preserved.

5.  Operation

   In order for a BGP speaker to be able to resume sending routing
   information for an AFI/SAFI from the last update version that was
   previously acknowledged by a peer, the speaker MUST maintain enough
   state for all the routing information that has been sent until their
   acknowledgment is received by the speaker.  The routing information
   includes reachable / unreachable information as well as other AFI/
   SAFI specific, non-update information.  Furthermore, the route
   advertisement state needs to be maintained properly in order to
   minimize spurious route withdraws across a session restart.

   An implementation SHOULD impose an upper bound on how much state it
   would maintain in the case that a receiver ("slow peer") is not able
   to generate an acknowledgment in a timely manner.  The upper bound
   might be based on a number of factors such as the number of pending
   unacknowledged withdraws or more generally, the volume of
   unacknowledged state, and a timer.  Once the acknowledgment from a
   peer is not received within the specified upper bound, and the
   maintained state is compromised, then the speaker MUST clear the "TX
   Routing State" in the GR Capability to be advertised to the peer in
   the next session restart.

   A BGP speaker MAY advertise the Enhanced GR Capability to its peer if
   the speaker is capable of receiving and properly handling the UPDATE-
   VERSION message from the peer, and also recognizing the two new bit
   flags in the GR Capability.  If the GR Capability is to be sent by
   the speaker, the "RX Routing State" for an AFI/SAFI in the GR
   Capability SHOULD be set if the speaker has preserved the routing



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   information from the peer up to the update version that the speaker
   acknowledged previously.  In addition, the "TX Routing State" for an
   AFI/SAFI in the GR Capability SHOULD be set if the speaker has
   preserved enough routing state to resume sending messages from the
   update version acknowledged by the peer previously.

   When both the GR Capability and the Enhanced GR Capability are to be
   included in an OPEN message, it is RECOMMENDED (though not required)
   that the Enhanced GR Capability be placed ahead of the GR Capability.

   In processing the GR Capability in an OPEN message from a peer, a BGP
   speaker MUST NOT examine the two new bit flags defined in this
   document for the GR Capability unless the Enhanced GR Capability is
   also present in the OPEN message.

   A BGP speaker MAY send an UPDATE-VERSION message to a peer only if
   the Enhanced GR Capability is received from the peer.

   Once a BGP speaker receives the Enhanced GR Capability from its peer,
   the speaker SHOULD send an UPDATE-VERSION message carrying the update
   version after sending significant amount of routing information
   (including non-UPDATE messages) for an AFI/SAFI.  This SHALL continue
   as long as routing information is being sent.  To reduce the overhead
   by excessive number of UPDATE-VERSION messages, we highly recommend
   the "batching" approach, that is, use one UPDATE-VERSION message to
   cover a number of routing updates, and/or a meaningful duration of
   time.

   When a BGP speaker receives an UPDATE-VERSION message carrying an
   update version, if the AFI/SAFI carried by the message does not match
   any AFI/SAFI that the speaker is willing to receive from the peer,
   the UPDATE-VERSION message SHALL be ignored.  Otherwise, the speaker
   MUST send an UPDATE-VERSION message back promptly acknowledging the
   receipt of the update version.  The UPDATE-VERSION messages carrying
   the acknowledgments MUST be sent in the same order as the received
   UPDATE-VERSION messages carrying the update versions.

   When a BGP speakers receives an UPDATE-VERSION message acknowledging
   an update version, the speaker MUST record this latest update version
   being acknowledged for future use.

   Consider the case that both the GR Capability and the Enhanced GR
   Capability are exchanged between Speaker A and Speaker B, and for an
   AFI/SAFI the "TX Routing State" is set in the GR advertised by A, and
   the "RX Routing State" is also set in the GR received from B.  Then
   Speaker A SHALL send routing information from the last update version
   that was previously acknowledged by Speaker B.  Note that it may be
   advantageous for Speaker B to send an UPDATE-VERSION message



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   acknowledging the most recent update version immediately after the
   session is established.  Also, Speaker B MUST NOT follow the
   procedures described in [RFC4724] for purging stale routes.  If the
   conditions specified in this paragraph are not satisfied, then the
   procedures described in [RFC4724] remain unchanged.

   During the lifetime of an established session, if needed, a BGP
   speaker MAY use the UPDATE-VERSION message to request updates from
   the last update version that was previously acknowledged as long as
   the speaker has received the Enhanced GR Capability from its peer.

   When a BGP speaker receives such a request, it SHALL try to send
   routing information from the last acknowledged update version that
   the speaker has recorded.  If the speaker is unable to do so for some
   reason (e.g., "slow peer"), then it SHOULD perform a route refresh
   using mechanism defined in [RFC7313] if possible.  Otherwise, the BGP
   speaker SHOULD reset the session.

6.  Error Handling

   This document defines a new NOTIFICATION error code:

               +------------+------------------------------+
               | Error Code |        Symbolic Name         |
               +------------+------------------------------+
               |    TBD     | UPDATE-VERSION Message Error |
               +------------+------------------------------+

   The following error subcodes are defined as well:

                   +--------+-------------------------+
                   | Subode |      Symbolic Name      |
                   +--------+-------------------------+
                   |   1    |  Invalid Message Length |
                   |   2    | Invalid Message Subtype |
                   +--------+-------------------------+

   If a BGP speaker detects an error while processing an UPDATE-VERSION
   message, it MUST send a NOTIFICATION message with Error Code UPDATE-
   VERSION Message Error.  The Data field of the NOTIFICATION message
   MUST contain the complete UPDATE-VERSION message.

   If the Length field for the UPDATE-VERSION message is incorrect, then
   the error subcode is set to "Invalid Message Length".

   If the Message Subtype in the UPDATE-VERSION message is not any of
   the defined value, then the error subcode is set to "Invalid Message
   Subtype".



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7.  Acknowledgements

   Thanks to Jonathan Looney for valuable review and suggestions.

8.  IANA Considerations

   This document introduces the Enhanced Graceful Restart Capability.
   The capability code needs to be assigned by IANA per [RFC5492].

   This document introduce a new BGP message type, UPDATE-VERSION.  The
   type code needs to be assigned by IANA.

   In addition, this document defines an NOTIFICATION error code and
   several error subcodes for the UPDATE-VERSION message.  They need to
   be registered with the IANA.

9.  Security Considerations

   This extension to BGP does not change the underlying security issues
   inherent in the existing BGP [RFC4271] [RFC4724].

10.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2918]  Chen, E., "Route Refresh Capability for BGP-4", RFC 2918,
              DOI 10.17487/RFC2918, September 2000,
              <http://www.rfc-editor.org/info/rfc2918>.

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

   [RFC4724]  Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
              Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
              DOI 10.17487/RFC4724, January 2007,
              <http://www.rfc-editor.org/info/rfc4724>.

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





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   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <http://www.rfc-editor.org/info/rfc5492>.

   [RFC7313]  Patel, K., Chen, E., and B. Venkatachalapathy, "Enhanced
              Route Refresh Capability for BGP-4", RFC 7313,
              DOI 10.17487/RFC7313, July 2014,
              <http://www.rfc-editor.org/info/rfc7313>.

Authors' Addresses

   Keyur Patel
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: keyupate@cisco.com


   Enke Chen
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: enkechen@cisco.com


   Rex Fernando
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: rex@cisco.com


   John Scudder
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA  94089
   USA

   Email: jgs@juniper.net






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