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Versions: (draft-keyupate-idr-bgp-gr-notification) 00 01 03 04 05 06 07 08 09 10 11 12 13 15

Internet Engineering Task Force                                 K. Patel
Internet-Draft                                                    Arrcus
Updates: 4724 (if approved)                                  R. Fernando
Intended status: Standards Track                           Cisco Systems
Expires: October 12, 2018                                     J. Scudder
                                                                 J. Haas
                                                        Juniper Networks
                                                          April 10, 2018


         Notification Message support for BGP Graceful Restart
               draft-ietf-idr-bgp-gr-notification-15.txt

Abstract

   The BGP Graceful Restart mechanism defined in RFC 4724 limits the
   usage of BGP Graceful Restart to BGP protocol messages other than a
   BGP NOTIFICATION message.  This document updates RFC 4724 by defining
   an extension that permits the Graceful Restart procedures to be
   performed when the BGP speaker receives a BGP NOTIFICATION Message or
   the Hold Time expires.  This document also defines a new BGP
   NOTIFICATION Cease Error subcode whose effect is to request a full
   session restart instead of a Graceful Restart.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 October 12, 2018.

Copyright Notice

   Copyright (c) 2018 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



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   (https://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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Modifications to BGP Graceful Restart Capability  . . . . . .   3
   3.  BGP Hard Reset Subcode  . . . . . . . . . . . . . . . . . . .   3
     3.1.  Sending a Hard Reset  . . . . . . . . . . . . . . . . . .   4
     3.2.  Receiving a Hard Reset  . . . . . . . . . . . . . . . . .   4
   4.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Rules for the Receiving Speaker . . . . . . . . . . . . .   5
   5.  Use of Hard Reset . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  When to Send Hard Reset . . . . . . . . . . . . . . . . .   6
     5.2.  Interaction With Other Specifications . . . . . . . . . .   7
   6.  Management Considerations . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   For many classes of errors, the BGP protocol must send a NOTIFICATION
   message and reset the peering session to handle the error condition.
   The BGP Graceful Restart extension defined in [RFC4724] requires that
   normal BGP procedures defined in [RFC4271] be followed when a
   NOTIFICATION message is sent or received.  This document defines an
   extension to BGP Graceful Restart that permits the Graceful Restart
   procedures to be performed when the BGP speaker receives a
   NOTIFICATION message or the Hold Time expires.  This permits the BGP
   speaker to avoid flapping reachability and continue forwarding while
   the BGP speaker restarts the session to handle errors detected in the
   BGP protocol.

   At a high level, this document can be summed up as follows.  When a
   BGP session is reset, both speakers operate as "Receiving Speakers"
   according to [RFC4724], meaning they retain each other's routes.
   This is also true for HOLDTIME expiration.  The functionality can be
   defeated using a "Hard Reset" subcode for the BGP NOTIFICATION Cease




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   Error code.  If a Hard Reset is used, a full session reset is
   performed.

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.  Modifications to BGP Graceful Restart Capability

   The BGP Graceful Restart Capability is augmented to signal the
   Graceful Restart support for BGP NOTIFICATION messages.  The Restart
   Flags field is augmented as follows (following the diagram from
   section 3 of [RFC4724]):

    Restart Flags:

            This field contains bit flags relating to restart.

                0 1 2 3
               +-+-+-+-+
               |R|N|   |
               +-+-+-+-+

   The most significant ("Restart State", or "R") bit is defined in
   [RFC4724].

   The second most significant bit ("N") is defined as the BGP Graceful
   Notification bit, which is used to indicate Graceful Restart support
   for BGP NOTIFICATION messages.  A BGP speaker indicates support for
   the procedures of this document, by advertising a Graceful Restart
   Capability with its Graceful NOTIFICATION bit set (value 1).  This
   also implies support for the format for a BGP NOTIFICATION Cease
   message defined in [RFC4486].

   If a BGP speaker that previously advertised a given set of Graceful
   Restart parameters opens a new session with a different set of
   parameters, these new parameters apply once the session has
   transitioned into ESTABLISHED state.

3.  BGP Hard Reset Subcode

   We define a new BGP NOTIFICATION Cease message subcode, called the
   BGP Hard Reset Subcode.  The value of this subcode is discussed in
   Section 8.  We refer to a BGP NOTIFICATION Cease message with the
   Hard Reset subcode as a Hard Reset message, or just a Hard Reset.




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   When the "N" bit has been exchanged by two peers, to distinguish them
   from Hard Reset we refer to any NOTIFICATION messages other than Hard
   Reset as "Graceful", since such messages invoke Graceful Restart
   semantics.

3.1.  Sending a Hard Reset

   A Hard Reset message is used to indicate to a peer with which the
   Graceful Notification bit has been exchanged, that the session is to
   be fully terminated.

   When sending a Hard Reset, the data portion of the NOTIFICATION is
   encoded as follows:

       +--------+--------+--------
       | ErrCode| Subcode| Data
       +--------+--------+--------

   ErrCode is a BGP Error Code (as documented in the IANA BGP Error
   Codes registry) that indicates the reason for the Hard Reset.
   Subcode is a BGP Error Subcode (as documented in the IANA BGP Error
   Subcodes registry) as appropriate for the ErrCode.  Similarly, Data
   is as appropriate for the ErrCode and Subcode.  In short, the Hard
   Reset encapsulates another NOTIFICATION message in its data portion.

3.2.  Receiving a Hard Reset

   Whenever a BGP speaker receives a Hard Reset, the speaker MUST
   terminate the BGP session following the standard procedures in
   [RFC4271].

4.  Operation

   A BGP speaker that is willing to receive and send BGP NOTIFICATION
   messages according to the procedures of this document MUST advertise
   the BGP Graceful Notification "N" bit using the Graceful Restart
   Capability as defined in [RFC4724].

   When such a BGP speaker has received the "N" bit from its peer, and
   receives from that peer a BGP NOTIFICATION message other than a Hard
   Reset, it MUST follow the rules for the Receiving Speaker mentioned
   in Section 4.1.  The BGP speaker generating the BGP NOTIFICATION
   message MUST also follow the rules for the Receiving Speaker.

   When a BGP speaker resets its session due to a HOLDTIME expiry, it
   should generate the relevant BGP NOTIFICATION message as mentioned in
   [RFC4271], but subsequently it MUST follow the rules for the
   Receiving Speaker mentioned in Section 4.1.



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   A BGP speaker SHOULD NOT send a Hard Reset to a peer from which it
   has not received the "N" bit.  We note, however, that if it did so
   the effect would be as desired in any case, since according to
   [RFC4271] and [RFC4724] any NOTIFICATION message, whether recognized
   or not, results in a session reset.  Thus the only negative effect to
   be expected from sending the Hard Reset to a peer that hasn't
   advertised compliance to this specification would be that the peer
   would be unable to properly log the associated information.

   Once the session is re-established, both BGP speakers SHOULD set
   their "Forwarding State" bit to 1.  If the "Forwarding State" bit is
   not set, then according to the procedures of [RFC4724] section 4.2,
   the relevant routes will be flushed, defeating the goals of this
   specification.

4.1.  Rules for the Receiving Speaker

   [RFC4724] section 4.2 defines rules for the Receiving Speaker.  These
   are modified as follows.

   The sentence "To deal with possible consecutive restarts, a route
   (from the peer) previously marked as stale MUST be deleted" only
   applies when the "N" bit has not been exchanged with the peer:

   OLD: When the Receiving Speaker detects termination of the TCP
        session for a BGP session with a peer that has advertised the
        Graceful Restart Capability, it MUST retain the routes received
        from the peer for all the address families that were previously
        received in the Graceful Restart Capability and MUST mark them
        as stale routing information.  To deal with possible consecutive
        restarts, a route (from the peer) previously marked as stale
        MUST be deleted.  The router MUST NOT differentiate between
        stale and other routing information during forwarding.

   NEW: When the Receiving Speaker detects termination of the TCP
        session for a BGP session with a peer that has advertised the
        Graceful Restart Capability, it MUST retain the routes received
        from the peer for all the address families that were previously
        received in the Graceful Restart Capability and MUST mark them
        as stale routing information.  The router MUST NOT differentiate
        between stale and other routing information during forwarding.
        If the "N" bit has not been exchanged with the peer, then to
        deal with possible consecutive restarts, a route (from the peer)
        previously marked as stale MUST be deleted.

   The stale timer is given a formal name and made mandatory:





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   OLD: To put an upper bound on the amount of time a router retains the
        stale routes, an implementation MAY support a (configurable)
        timer that imposes this upper bound.

   NEW: To put an upper bound on the amount of time a router retains the
        stale routes, an implementation MUST support a (configurable)
        timer, called the "stale timer", that imposes this upper bound.
        A suggested default value for the stale timer is 180 seconds.
        An implementation MAY provide the option to disable the timer
        (i.e., to provide an infinite retention time) but MUST NOT do so
        by default.

5.  Use of Hard Reset

5.1.  When to Send Hard Reset

   Although when to send a Hard Reset is an implementation-specific
   decision, we offer some advice.  Many Cease notification subcodes
   represent permanent or long-term rather than transient session
   termination, and as such it's appropriate to use Hard Reset with
   them.  At time of publication, Cease subcodes 1-9 were defined.

   +-------+------------------------------------+----------------------+
   | Value |                Name                |  Suggested Behavior  |
   +-------+------------------------------------+----------------------+
   |   1   | Maximum Number of Prefixes Reached |      Hard Reset      |
   |   2   |      Administrative Shutdown       |      Hard Reset      |
   |   3   |         Peer De-configured         |      Hard Reset      |
   |   4   |        Administrative Reset        | Provide user control |
   |   5   |        Connection Rejected         |    Graceful Cease    |
   |   6   |     Other Configuration Change     |    Graceful Cease    |
   |   7   |  Connection Collision Resolution   |    Graceful Cease    |
   |   8   |          Out of Resources          |    Graceful Cease    |
   |   9   |             Hard Reset             |      Hard Reset      |
   +-------+------------------------------------+----------------------+

                  Suggestions for Cease Subcode Behavior

   These suggestions are only that, suggestions, not requirements.  It's
   the nature of BGP implementations that the mapping of internal states
   to BGP NOTIFICATION codes and subcodes is not always perfect.  The
   guiding principle for the implementor should be that if there is no
   realistic hope that forwarding can continue or that the session will
   be re-established within the deadline, Hard Reset should be used.

   For all other NOTIFICATION codes other than Cease, use of Hard Reset
   does not appear to be indicated.




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5.2.  Interaction With Other Specifications

   "BGP Administrative Shutdown Communication" [RFC8203] specifies use
   of the data portion of the Administrative Shutdown or Administrative
   Reset Cease to convey a short message.  When [RFC8203] is used in
   conjunction with Hard Reset, the subcode of the outermost Cease MUST
   be Hard Reset, with the Administrative Shutdown or Reset Cease
   encapsulated within.  The encapsulated administrative shutdown
   message MUST subsequently be processed according to [RFC8203].

6.  Management Considerations

   When reporting a Hard Reset to network management, the error code and
   subcode reported MUST be Cease, Hard Reset.  If the network
   management layer in use permits it, the information carried in the
   Data portion SHOULD be reported as well.

7.  Acknowledgements

   The authors would like to thank Jim Uttaro for the suggestion, and
   Emmanuel Baccelli, Bruno Decraene, Chris Hall, Paul Mattes, Robert
   Raszuk, and Alvaro Retana for their review and comments.

8.  IANA Considerations

   IANA has temporarily assigned subcode 9, named "Hard Reset", in the
   "BGP Cease NOTIFICATION message subcodes" registry.  Upon publication
   of this document as an RFC, IANA is requested to make this allocation
   permanent.

   IANA is requested to establish a registry within the "Border Gateway
   Protocol (BGP) Parameters" grouping, to be called "BGP Graceful
   Restart Flags".  The Registration Procedure should be Standards
   Action, the reference this document and [RFC4724], and the initial
   values as follows:

       +--------------+---------------+------------+---------------+
       | Bit Position |      Name     | Short Name |   Reference   |
       +--------------+---------------+------------+---------------+
       |      0       | Restart State |     R      |   [RFC4724]   |
       |      1       |  Notification |     N      | this document |
       |     2, 3     |   unassigned  |            |               |
       +--------------+---------------+------------+---------------+

   IANA is requested to establish a registry within the "Border Gateway
   Protocol (BGP) Parameters" grouping, to be called "BGP Graceful
   Restart Flags for Address Family".  The Registration Procedure should




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   be Standards Action, the reference this document and [RFC4724], and
   the initial values as follows:

       +--------------+------------------+------------+-----------+
       | Bit Position |       Name       | Short Name | Reference |
       +--------------+------------------+------------+-----------+
       |      0       | Forwarding State |     F      | [RFC4724] |
       |     1-7      |    unassigned    |            |           |
       +--------------+------------------+------------+-----------+

9.  Security Considerations

   This specification doesn't change the basic security model inherent
   in [RFC4724], with the exception that the protection against repeated
   resets is relaxed.  To mitigate the consequent risk that an attacker
   could use repeated session resets to prevent stale routes from ever
   being deleted, we make the stale routes timer mandatory (in practice
   it is already ubiquitous).  To the extent [RFC4724] might be said to
   help defend against denials of service by making the control plane
   more resilient, this extension may modestly increase that resilience;
   however, there are enough confounding and deployment-specific factors
   that no general claims can be made.

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,
              <https://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,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4486]  Chen, E. and V. Gillet, "Subcodes for BGP Cease
              Notification Message", RFC 4486, DOI 10.17487/RFC4486,
              April 2006, <https://www.rfc-editor.org/info/rfc4486>.

   [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,
              <https://www.rfc-editor.org/info/rfc4724>.

   [RFC8203]  Snijders, J., Heitz, J., and J. Scudder, "BGP
              Administrative Shutdown Communication", RFC 8203,
              DOI 10.17487/RFC8203, July 2017,
              <https://www.rfc-editor.org/info/rfc8203>.



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Authors' Addresses

   Keyur Patel
   Arrcus

   Email: keyur@arrcus.com


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

   Email: rex@cisco.com


   John Scudder
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA  94089
   USA

   Email: jgs@juniper.net


   Jeff Haas
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA  94089
   USA

   Email: jhaas@juniper.net


















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