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Network Working Group                                 Gargi Nalawade
Internet Draft                                        Keyur Patel
Expires: January 2006                                  John Scudder
                                                      David Ward

                                                      Cisco Systems



                     BGPv4 Soft-Notification Message

                 draft-nalawade-bgp-soft-notify-01.txt




Status of this Memo


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Abstract

   This document defines a new message type, the BGP SOFT-NOTIFICATION
   message that can notify a peer of an error-condition for a particular
   AFI/SAFI and soft-reset the AFI/SAFI, without terminating the BGP
   session and without impacting the other AFI/SAFIs exchanged with the
   peer.




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1. Introduction

   Currently there is no mechanism available for two BGP Speakers to
   communicate the occurrence of an error-condition other than through a
   BGP NOTIFICATION Message. The problem is that a NOTIFICATION message
   resets the peering session and terminates the connection. If a peer
   wants to gracefully recover from an error or wants to warn its peer
   about the occurrence of a BGP-related event, there is no mechanism
   currently available to do that.

   The proposed BGP SOFT-NOTIFICATION message is a mechanism to notify a
   remote peer of an error-condition or an event without resetting or
   terminating the BGP session. The purpose of this message is to
   provide the ability to soft-reset a particular AFI/SAFI without
   disrupting other BGP AFI/SAFIs or sections.


2. Definition of the BGP SOFT-NOTIFICATION Message

   The BGP SOFT-NOTIFICATION message is a BGP message with type TBD. A
   BGP SOFT-NOTIFICATION message may be sent to notify a peer of an
   error condition within a particular AFI/SAFI.

   In addition to the fixed-size BGP header, the SOFT-NOTIFICATION
   message contains the following fields:



          0                   1
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       AFI                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       SAFI    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Type-code               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Sub-code                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Length                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Variable Data TLV       |
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







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   where :

   AFI/SAFI : as defined in [IANA-AFI] [IANA-SAFI]

   Type-code : is a 2 octet field indicating the error-condition or
   event for the respective AFI/SAFI.

   Sub-code : is a 2-octet field that may define a sub-code related to
   the error-condition or event that this message carries.

   Length : is a 2-octet field that contains the length of the remaining
   message that may contain an optional Variable length Data TLV.

   Variable Data TLV : is a variable-length field that contains a
   Variable Data TLV that may be used to carry additional data to
   provide more information about the error-condition or event.

2.1 AFI-SAFI

   The AFI-SAFI fields indicate the AFI/SAFI for which the error-
   condition or event has occured and needs to be soft-reset. A Reserved
   Value [TBD] will indicate that this message is for all AFI/SAFIs. A
   Reserved Value [TBD] in only the SAFI field will indicate that this
   message applies to all SAFIs under a particular AFI.

2.2 Type-code

   The following Type-codes have been defined :

              Error Code       Symbolic Name

                 1         UPDATE Message Error

                 2         Cease

                 3         Event


2.3 Sub-code

   The following Sub-codes have been defined :

   UPDATE Message Error subcodes:

      1 - Malformed Attribute List.
      2 - Unrecognized Well-known Attribute.
      3 - Missing Well-known Attribute.
      4 - Attribute Flags Error.



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      5 - Invalid Attribute Length.
      6 - Invalid ORIGIN Attribute.
      7 - Invalid NEXT_HOP Attribute.
      8 - Optional Attribute Error.
      9 - Invalid Network Field.
     10 - Bad ASPATH.
     11 - Invalid Update-Message Type.


   CEASE Message Error subcodes:

      1 - Maximum Number of Prefixes Reached
      2 - Administratively Shutdown
      3 - Peer Unconfigured
      4 - Administratively Reset
      5 - Other Configuration Change

   Event Message subcodes :

      1 - ACK Soft-Notification
      2 - Peer Administratively unshut
      3 - Peer Configured
      4 - Timer Expired
      5 - Dampening routes
      6 - Undampened routes

2.4. Variable Data TLV

   The Variable Data TLV MAY be used to carry additional information
   about the Error or Event. It is of the following form :



   +------------------------+
   | Type (1 octet)         |
   +------------------------+
   | Length (2 octets)      |
   +------------------------+
   | Value (variable)       |
   +------------------------+


   This document defines TLVs summarized below:

   Type    Name     Length         Value
   ----    -----    -------        -----
   1     String     variable       A text string whose length is
                                   given by the length field. Not



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                                   null-terminated.
   2     PDU        variable       A copy of the PDU which
                                   triggered the SOFT-NOTIFICATION
                                   message. May be truncated.
   3     Attribute  variable       A copy of the path attribute
                                   which triggered the SOFT-NOTIFICATION
                                   message.  May be truncated.
   4     Integer    4 octets       A four-octet integer

   No TLV may appear in the SOFT-NOTIFICATION message more than once.




3. Operation

   A BGP Speaker may generate a SOFT-NOTIFICATION for the relevant
   AFI/SAFIs in lieu of the NOTIFICATION Message [BGP-4] [BGP-CEASE] for
   the relevant Type-codes and sub-codes in [BGP-4] [and BGP-CEASE], as
   redefined in section 2.2 for SOFT-NOTIFICATIONS. A BGP Speaker may
   also generate a SOFT-NOTIFICATION in case of an Event that is listed
   in the Event sub-codes above.

   The following rules apply to the processing of the BGP SOFT-
   NOTIFICATION Message.

   When a peer receives a BGP SOFT-NOTIFICATION Message, it will take an
   action based on the Type-code contained in the message. The sending
   peer will also take an action after it has sent the SOFT-
   NOTIFICATION out to its peer.

   In the sections below the BGP Speaker sending the SOFT-NOTIFICATION
   is refered to as the Sending Speaker and the BGP Speaker receiving
   the SOFT-NOTIFICATION is refered to as the Receiving Speaker. A
   SOFT-NOTIFICATION Message with Type-Code "Event" and sub-code "Soft-
   Notify-ACK" is refered to simply as the "Soft-Notify-ACK".

3.1 Update Error Type-code

   The Sending Speaker, upon sending a SOFT-NOTIFICATION message, will
   start a timer for the receipt of a Soft-Notify-ACK, and will discard
   any updates received from the Receiving Speaker after this, until a
   Soft-Notify-ACK is received. The Sending Speaker will then flush the
   routes of the Receiving Speaker for that AFI/SAFI and start sending
   out new updates to the Receiving Speaker. When the Sending Speaker
   receives the Soft-Notify-ACK, it will resume accepting updates from
   the Receiving Speaker. If the Soft-Notification Timer expires before
   receiving the Soft-Notify-ACK, the Sending Speaker will terminate the



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   BGP session.

   If the SOFT-NOTIFICATION message received by the Receiving Speaker,
   contains an Update Error Type-code, the Receiving Speaker must send a
   Soft-Notify-ACK back to the Sending Speaker. The Receiving Speaker
   will also flush the routes of the Sending Speaker for that AFI/SAFI
   and then proceed to re-advertise its own routes to the Sending
   Speaker.


   The exact hand-shaking mechanism is described in the diagram below.




        sender                       receiver
        ------                       --------

        tx soft-notification
        start soft-notification timer
        soft-reset peer for that safi
        tx new updates
                       --------> rx soft-notification
                       <-------- tx soft-notify-ack
                                 soft-reset-peer for that safi
                       <-------> rx/tx new updates

        rx updates
            |
            |
        rx Soft-Notify-ACK ?
            |             \
            | N            \  Y
            |               \
            |       rx all pending Soft-Notify-ACKs ?
            |         |        \
            | N       | N       \
            |         |          \
        soft-notification         \ Y
        timer expired ?            \
            |         \            \
            | N        \ Y          \
            |           \            \
        Discard     Hard-Reset   Start accepting
        Update      BGP peer     BGP Updates






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3.2 Cease Type-code

   The Sending Speaker, upon sending a SOFT-NOTIFICATION message with a
   Type-code Cease, must flush the routes of the Receiving Speaker for
   that AFI/SAFI and put the AFI/SAFI in a shutdown state for that peer.

   The Receiving Speaker, upon receiving a SOFT-NOTIFICATION message
   with a Type-code Cease, must send a Soft-Notify-ACK to the Sending
   Speaker, flush the routes of the Sending Speaker for that AFI/SAFI
   and put the AFI/SAFI in a shutdown state for that peer. A shutdown
   state of a SAFI for a peer is a state in which the BGP Speaker will
   not accept and process any updates from the peer.


3.3 Event Type-code

   The Sending Speaker, upon sending a SOFT-NOTIFICATION message with a
   Type-Code "Event" and subcode "Administratively unshut", must
   transition out of the shutdown state for that AFI/SAFI for that peer.
   It will then readvertise its routes for that AFI/SAFI to the
   Receiving Speaker.

   The Receiving Speaker, upon receiving a SOFT-NOTIFICATION message
   with Type-Code "Event" and subcode "Administratively unshut", must
   send a Soft-Notify-ACK to the Sending Speaker and transition out of
   the shutdown state for that AFI/SAFI. The Receiving Speaker will then
   re-advertise its routes for the relevant AFI/SAFI to the Sending
   Speaker.

   If the SOFT-NOTIFICATION message received contains any Event Type-
   code other then "Administratively unshut" and "Soft-Notify-ACK", the
   Receiving Speaker must send a Soft-Notify-ACK to the Sending Speaker
   and MAY choose to log the message.


3.4 Multiple Soft-Notifications

   The sending of SOFT-NOTIFICATION Messages and soft-reset of the peer
   for an AFI/SAFI, should be rate-limited and some mechanism for
   exponential backoff should be implemented. The exact mechanism to be
   used is beyond the scope of this document.

   If a Sending Speaker sends multiple SOFT-NOTIFICATION Messages, it
   must remember how many such Messages have not yet been acknowledged.
   When it receives a Soft-Notify-ACK, it must associate it with the
   earliest SOFT-NOTIFICATION message pending a Soft-Notify-ACK.

4. Capability



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   A new capability [BGP-CAP] code (TBD) is defined for the BGP SOFT-
   NOTIFICATION messages. A BGP SOFT-NOTIFICATION message can only be
   sent to peers that have advertised this capability.

5. Deployment considerations

   This draft does not affect the deployment considerations for BGP.

6. Intellectual Property Considerations

   Cisco Systems may seek patent or other intellectual property
   protection for some of all of the technologies disclosed in this
   document. If any standards arising from this document are or become
   protected by one or more patents assigned to Cisco Systems, Cisco
   intends to disclose those patents and license them on reasonable and
   non-discriminatory terms.

7. Security Considerations

   This extension to BGP does not change the underlying security issues.

8. Acknowledgements

The authors would like to thank Nehal Bahu, Shyam Suri, David Ball,
Srihari R. Sangli and Pedro Marquez for their review and comments.

9. Normative References

   [IANA-AFI] http://www.iana.org/assignments/address-family-numbers

   [IANA-SAFI] http://www.iana.org/assignments/safi-namespace

   [BGP-4]  Rekhter, Y. and T. Li (editors), "A Border Gateway Protocol
   4 (BGP-4)", Internet Draft draft-ietf-idr-bgp4-21.txt, March 2004.

   [BGP-CAP] Chandra, R., Scudder, J., "Capabilities Advertisement with
   BGP-4", draft-ietf-idr-rfc2842bis-02.txt, April 2002.

   [BGP-CEASE] Chen, E., Gillett V., "Subcodes for BGP Cease
   Notification Message", draft-ietf-idr-cease-subcode-03.txt, May 2003.

   [BGP-INFORM] Nalawade, G., Scudder, J., Ward, D., "BGPv4 Inform
   message", draft-nalawade-bgp-inform-02.txt, August 2002.


10. Author's Addresses

   Gargi Nalawade mailto:gargi@cisco.com



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   Keyur Patel mailto:keyupate@cisco.com

   John Scudder mailto:jgs@cisco.com

   David Ward mailto:dward@cisco.com

   Cisco Systems, Inc 170 West Tasman Drive San Jose, CA 95134

11. Full Copyright Statement

   Copyright (C) The Internet Society (2005).  All Rights Reserved.

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


12. Expiration Date

   This memo is filed as <draft-nalawade-bgp-soft-notify-01.txt> expires
   January, 2006.






















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