BGP Cease subcodes: Subcodes for BGP Cease Notification Message
Eight reason codes that explain why a BGP speaker is ending a peering session.
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>.
@misc{rfc4486,
series = {Request for Comments},
number = 4486,
howpublished = {RFC 4486},
publisher = {RFC Editor},
doi = {10.17487/RFC4486},
url = {https://www.rfc-editor.org/info/rfc4486},
author = {E. Chen and V. Gillet},
title = {{Subcodes for BGP Cease Notification Message}},
pagetotal = 6,
year = 2006,
month = apr,
} RFC text
Contents
Network Working Group E. Chen
Request for Comments: 4486 Cisco Systems
Category: Standards Track V. Gillet
France Telecom
April 2006
Subcodes for BGP Cease Notification Message
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.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document defines several subcodes for the BGP Cease NOTIFICATION
message that would provide more information to aid network operators
in correlating network events and diagnosing BGP peering issues.
1. Introduction
This document defines several subcodes for the BGP Cease NOTIFICATION
message that would provide more information to aid network operators
in correlating network events and diagnosing BGP peering issues. It
also recommends that a BGP speaker implement a backoff mechanism in
re-trying a BGP connection after the speaker receives a NOTIFICATION
message with certain CEASE subcode.
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 [RFC-2119].
3. Subcode Definition
The following subcodes are defined for the Cease NOTIFICATION
message:
Subcode Symbolic Name
1 Maximum Number of Prefixes Reached
2 Administrative Shutdown
3 Peer De-configured
4 Administrative Reset
5 Connection Rejected
6 Other Configuration Change
7 Connection Collision Resolution
8 Out of Resources
4. Subcode Usage
If a BGP speaker decides to terminate its peering with a neighbor
because the number of address prefixes received from the neighbor
exceeds a locally configured upper bound (as described in [BGP-4]),
then the speaker MUST send to the neighbor a NOTIFICATION message
with the Error Code Cease and the Error Subcode "Maximum Number of
Prefixes Reached". The message MAY optionally include the Address
Family information [BGP-MP] and the upper bound in the "Data" field,
as shown in Figure 1, where the meaning and use of the <AFI, SAFI>
tuple is the same as defined in [BGP-MP], Section 7.
+-------------------------------+
| AFI (2 octets) |
+-------------------------------+
| SAFI (1 octet) |
+-------------------------------+
| Prefix upper bound (4 octets) |
+-------------------------------+
Figure 1: Optional Data Field
If a BGP speaker decides to administratively shut down its peering
with a neighbor, then the speaker SHOULD send a NOTIFICATION message
with the Error Code Cease and the Error Subcode "Administrative
Shutdown".
If a BGP speaker decides to de-configure a peer, then the speaker
SHOULD send a NOTIFICATION message with the Error Code Cease and the
Error Subcode "Peer De-configured".
If a BGP speaker decides to administratively reset the peering with a
neighbor, then the speaker SHOULD send a NOTIFICATION message with
the Error Code Cease and the Error Subcode "Administrative Reset".
If a BGP speaker decides to disallow a BGP connection (e.g., the peer
is not configured locally) after the speaker accepts a transport
protocol connection, then the BGP speaker SHOULD send a NOTIFICATION
message with the Error Code Cease and the Error Subcode "Connection
Rejected".
If a BGP speaker decides to administratively reset the peering with a
neighbor due to a configuration change other than the ones described
above, then the speaker SHOULD send a NOTIFICATION message with the
Error Code Cease and the Error Subcode "Other Configuration Change".
If a BGP speaker decides to send a NOTIFICATION message with the
Error Code Cease as a result of the collision resolution procedure
(as described in [BGP-4]), then the subcode SHOULD be set to
"Connection Collision Resolution".
If a BGP speaker runs out of resources (e.g., memory) and decides to
reset a session, then the speaker MAY send a NOTIFICATION message
with the Error Code Cease and the Error Subcode "Out of Resources".
It is RECOMMENDED that a BGP speaker behave as though the
DampPeerOscillations attribute [BGP-4] were true for this peer when
re-trying a BGP connection after the speaker receives a Cease
NOTIFICATION message with a subcode of "Administrative Shutdown",
"Peer De-configured", "Connection Rejected", or "Out of Resources".
An implementation SHOULD impose an upper bound on the number of
consecutive automatic retries. Once this bound is reached, the
implementation would stop re-trying any BGP connections until some
administrative intervention, i.e., set the AllowAutomaticStart
attribute [BGP-4] to FALSE.
5. IANA Considerations
This document defines the subcodes 1 - 8 for the BGP Cease
NOTIFICATION message. Future assignments are to be made using either
the Standards Action process defined in [RFC-2434], or the Early IANA
Allocation process defined in [RFC-4020]. Assignments consist of a
name and the value.
6. Security Considerations
This extension to BGP does not change the underlying security issues
inherent in the existing BGP.
7. Acknowledgements
The authors would like to thank Yakov Rekhter, Pedro Marques, Andrew
Lange, and Don Goodspeed for their review and suggestions.
8. References
8.1. Normative References
[BGP-4] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[BGP-MP] Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 2858, June 2000.
[RFC-2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[RFC-4020] Kompella, K. and A. Zinin, "Early IANA Allocation of
Standards Track Code Points", BCP 100, RFC 4020, February
2005.
Authors' Addresses
Enke Chen
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
USA
EMail: enkechen@cisco.com
Vincent Gillet
France Telecom Longues Distances
61, rue des Archives
75003 Paris FRANCE
EMail: vgi@opentransit.net
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ISO Plain Language
On this page
§1Why Cease Messages Need More Detail
A BGP speaker that ends a peering session sends a NOTIFICATION with the Cease error code. The code says the session is closing but does not identify the cause.
RFC 4486 defines subcodes that provide more information for correlating network events and diagnosing BGP peering issues. It also recommends backoff when retrying after certain Cease notifications.
The Cease code tells a neighbor that a session is closing. A subcode gives the neighbor a more specific reason for the closure.
§3The Eight Cease Subcodes
RFC 4486 assigns subcodes 1 through 8: Maximum Number of Prefixes Reached, Administrative Shutdown, Peer De-configured, Administrative Reset, Connection Rejected, Other Configuration Change, Connection Collision Resolution and Out of Resources.
The names cover operator actions, protocol events and resource conditions. For the maximum-prefixes subcode, the notification may also include the address family and the configured upper bound in its Data field.
Each of the eight numbers represents a different cause, such as an operator shutdown or a prefix limit. The neighbor can use the reason to diagnose the session event.
- 1Maximum Number of Prefixes Reached — Received prefixes exceeded a locally configured upper bound.
- 2Administrative Shutdown — The speaker administratively shuts down the peering.
- 3Peer De-configured — The speaker de-configures the peer.
- 4Administrative Reset — The speaker administratively resets the peering.
- 5Connection Rejected — A connection is disallowed after transport acceptance.
- 6Other Configuration Change — Reset due to another configuration change.
- 7Connection Collision Resolution — Cease results from collision resolution.
- 8Out of Resources — The speaker resets a session after resource exhaustion.
§4When a Speaker Sends Each Code
If a speaker terminates a peering because received prefixes exceed a locally configured upper bound, it MUST send Maximum Number of Prefixes Reached. The optional data can contain the AFI, SAFI and prefix upper bound.
A speaker SHOULD use Administrative Shutdown, Peer De-configured, Administrative Reset, Connection Rejected or Other Configuration Change for the corresponding local action. It SHOULD use Connection Collision Resolution when a session ends because of BGP's collision-resolution procedure. Out of Resources MAY be used when the speaker runs out of resources, such as memory, and resets a session.
A speaker must report a prefix-limit closure with its matching subcode. For administrative actions and other listed conditions, the RFC says which subcode the speaker should use.
§4.1Retrying After Selected Cease Reasons
After receiving Administrative Shutdown, Peer De-configured, Connection Rejected or Out of Resources, a speaker should use a backoff approach when retrying the connection. The recommendation is to behave as though the BGP DampPeerOscillations attribute were true for that peer.
An implementation should set an upper limit on consecutive automatic retries. After reaching that limit, it stops retrying until an administrator intervenes.
Some Cease reasons signal that an immediate reconnect may not succeed. The speaker should wait between attempts and stop automatic retries after a configured limit.
§5Assigning Future Subcodes
The document defines Cease subcodes 1-8. Future assignments use either Standards Action or Early IANA Allocation, following the procedures in RFC 2434 and RFC 4020.
Each assignment consists of a name and a value. This keeps the numeric code and its stated reason associated in the registry.
Future subcodes need an approved assignment and a name. This prevents two reasons from being assigned the same number.
§6Security Considerations
The security considerations section states that this extension does not change the security issues inherent in BGP. It adds reason codes and retry guidance, not a new security mechanism.
The new subcodes do not change BGP's underlying security properties. They explain why a speaker ended a session.