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
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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
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This document and the information contained herein are provided on an
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12. Expiration Date
This memo is filed as <draft-nalawade-bgp-soft-notify-01.txt> expires
January, 2006.
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