BGP Shutdown Message: Extended BGP Administrative Shutdown Communication
Lets a BGP router explain, in up to 255 bytes of UTF-8 text, why it is closing a session.
Snijders, J., Heitz, J., Scudder, J., and A. Azimov, "Extended BGP Administrative Shutdown Communication", RFC 9003, DOI 10.17487/RFC9003, January 2021, <https://www.rfc-editor.org/info/rfc9003>.
@misc{rfc9003,
series = {Request for Comments},
number = 9003,
howpublished = {RFC 9003},
publisher = {RFC Editor},
doi = {10.17487/RFC9003},
url = {https://www.rfc-editor.org/info/rfc9003},
author = {J. Snijders and J. Heitz and J. Scudder and A. Azimov},
title = {{Extended BGP Administrative Shutdown Communication}},
pagetotal = 7,
year = 2021,
month = jan,
} RFC text
Contents
Internet Engineering Task Force (IETF) J. Snijders
Request for Comments: 9003 NTT
Obsoletes: 8203 J. Heitz
Updates: 4486 Cisco
Category: Standards Track J. Scudder
ISSN: 2070-1721 Juniper
A. Azimov
Yandex
January 2021
Extended BGP Administrative Shutdown Communication
Abstract
This document enhances the BGP Cease NOTIFICATION message
"Administrative Shutdown" and "Administrative Reset" subcodes for
operators to transmit a short free-form message to describe why a BGP
session was shut down or reset. This document updates RFC 4486 and
obsoletes RFC 8203 by defining an Extended BGP Administrative
Shutdown Communication of up to 255 octets to improve communication
using multibyte character sets.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9003.
Copyright Notice
Copyright (c) 2021 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
(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
1.1. Requirements Language
2. Shutdown Communication
3. Operational Considerations
4. Error Handling
5. IANA Considerations
6. Security Considerations
7. References
7.1. Normative References
7.2. Informative References
Appendix A. Changes to RFC 8203
Acknowledgements
Authors' Addresses
1. Introduction
It can be troublesome for an operator to correlate a BGP-4 [RFC4271]
session teardown in the network with a notice that was transmitted
via offline methods, such as email or telephone calls. This document
updates [RFC4486] by specifying a mechanism to transmit a short free-
form UTF-8 [RFC3629] message as part of a Cease NOTIFICATION message
[RFC4271] to inform the peer why the BGP session is being shut down
or reset. This document obsoletes [RFC8203]; the specific
differences and rationale are discussed in detail in Appendix A.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Shutdown Communication
If a BGP speaker decides to terminate its session with a BGP
neighbor, and it sends a NOTIFICATION message with the Error Code
"Cease" and Error Subcode "Administrative Shutdown" or
"Administrative Reset" [RFC4486], it MAY include a UTF-8-encoded
string. The contents of the string are at the operator's discretion.
The Cease NOTIFICATION message with a Shutdown Communication is
encoded as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code 6 | Subcode | Length | ... \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ /
\ \
/ ... Shutdown Communication ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
Subcode: The Error Subcode value MUST be one of the following
values: 2 ("Administrative Shutdown") or 4 ("Administrative
Reset").
Length: This 8-bit field represents the length of the Shutdown
Communication field in octets. When the length value is zero, no
Shutdown Communication field follows.
Shutdown Communication: To support international characters, the
Shutdown Communication field MUST be encoded using UTF-8. A
receiving BGP speaker MUST NOT interpret invalid UTF-8 sequences.
Note that when the Shutdown Communication contains multibyte
characters, the number of characters will be less than the length
value. This field is not NUL terminated. UTF-8 "Shortest Form"
encoding is REQUIRED to guard against the technical issues
outlined in [UTR36].
Mechanisms concerning the reporting of information contained in the
Shutdown Communication are implementation specific but SHOULD include
methods such as syslog [RFC5424].
3. Operational Considerations
Operators are encouraged to use the Shutdown Communication to inform
their peers of the reason for the shutdown of the BGP session and
include out-of-band reference materials. An example of a useful
Shutdown Communication would be:
"[TICKET-1-1438367390] software upgrade; back in 2 hours"
"[TICKET-1-1438367390]" is a ticket reference with significance to
both the sender and receiver, followed by a brief human-readable
message regarding the reason for the BGP session shutdown followed by
an indication about the length of the maintenance. The receiver can
now use the string 'TICKET-1-1438367390' to search in their email
archive to find more details.
If a Shutdown Communication longer than 128 octets is sent to a BGP
speaker that implements [RFC8203], then that speaker will treat it as
an error, the consequence of which should be a log message.
If a Shutdown Communication of any length is sent to a BGP speaker
that implements neither [RFC8203] nor this specification, then that
speaker will treat it as an error, the consequence of which should be
a log message.
In any case, a receiver of a NOTIFICATION message is unable to
acknowledge the receipt and correct understanding of any Shutdown
Communication.
Operators should not rely on Shutdown Communications as their sole
form of communication with their peers for important events.
If it is known that the peer BGP speaker supports this specification,
then a Shutdown Communication that is not longer than 255 octets MAY
be sent. Otherwise, a Shutdown Communication MAY be sent, but it
SHOULD NOT be longer than 128 octets.
4. Error Handling
If a Shutdown Communication with an invalid UTF-8 sequence is
received, a message indicating this event SHOULD be logged for the
attention of the operator. An erroneous or malformed Shutdown
Communication itself MAY be logged in a hexdump format.
5. IANA Considerations
IANA has referenced this document at subcodes "Administrative
Shutdown" and "Administrative Reset" in the "BGP Cease NOTIFICATION
message subcodes" registry under the "Border Gateway Protocol (BGP)
Parameters" group in addition to [RFC4486].
6. Security Considerations
This document uses UTF-8 encoding for the Shutdown Communication.
There are a number of security issues with Unicode. Implementers and
operators are advised to review Unicode Technical Report #36 [UTR36]
to learn about these issues. UTF-8 "Shortest Form" encoding is
REQUIRED to guard against the technical issues outlined in [UTR36].
As BGP Shutdown Communications are likely to appear in syslog output,
there is a risk that carefully constructed Shutdown Communication
might be formatted by receiving systems in a way to make them appear
as additional syslog messages. The 255-octet length limit on the BGP
Shutdown Communication may help limit the ability to mount such an
attack.
Users of this mechanism should be aware that unless a transport that
provides integrity is used for the BGP session in question, a
Shutdown Communication message could be forged. Unless a transport
that provides confidentiality is used, a Shutdown Communication
message could be snooped by an attacker. These issues are common to
any BGP message, but they may be of greater interest in the context
of this proposal since the information carried in the message is
generally expected to be used for human-to-human communication.
Refer to the related considerations in [RFC4271] and [RFC4272].
Users of this mechanism should consider applying data minimization
practices as outlined in Section 6.1 of [RFC6973] because a received
Shutdown Communication may be used at the receiver's discretion.
7. References
7.1. 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>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424,
DOI 10.17487/RFC5424, March 2009,
<https://www.rfc-editor.org/info/rfc5424>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
[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>.
[UTR36] Davis, M., Ed. and M. Suignard, Ed., "Unicode Security
Considerations", Unicode Technical Report #36, August
2010, <http://unicode.org/reports/tr36/>.
Appendix A. Changes to RFC 8203
The maximum permitted length was changed from 128 to 255.
Feedback from operators based in regions that predominantly use
multibyte character sets showed that messages similar in meaning to
what can be sent in other languages using single-byte encoding failed
to fit within the length constraints as specified by [RFC8203]. For
example, the phrase "Planned work to add switch to stack. Completion
time - 30 minutes" has a length of 65 bytes. Its translation in
Russian has a length of 139 bytes.
If a Shutdown Communication message longer than 128 octets is sent to
a BGP speaker that implements [RFC8203], then that speaker will bring
it to the attention of an operator but will otherwise process the
NOTIFICATION message as normal.
Acknowledgements
The authors would like to gratefully acknowledge Tom Scholl, David
Freedman, Jared Mauch, Jeff Haas, Peter Hessler, Bruno Decraene, John
Heasley, Peter van Dijk, Arjen Zonneveld, James Bensley, Susan Hares,
Saku Ytti, Lou Berger, Alvaro Retana, and Adam Roach.
The authors would like to thank Enke Chen and Vincent Gillet for
their work on [RFC4486] and granting the related BCP 78 rights to the
IETF Trust.
The authors would like to acknowledge Misha Grishin (MSK-IX) for
raising awareness that the length specification of [RFC8203] was
insufficient in context of multibyte character sets.
Authors' Addresses
Job Snijders
NTT Ltd.
Theodorus Majofskistraat 100
1065 SZ Amsterdam
Netherlands
Email: job@ntt.net
Jakob Heitz
Cisco
170 West Tasman Drive
San Jose, CA 95134
United States of America
Email: jheitz@cisco.com
John Scudder
Juniper Networks
1133 Innovation Way
Sunnyvale, CA 94089
United States of America
Email: jgs@juniper.net
Alexander Azimov
Yandex
Ulitsa Lva Tolstogo 16
Moscow
119021
Russian Federation
Email: a.e.azimov@gmail.com
AI ELI5
On this page
§1Why a Shutdown Message
It can be troublesome for an operator to match a BGP-4 session teardown in the network with a notice sent by offline means such as email or telephone calls. RFC 9003 updates RFC 4486 by specifying a way to send a short free-form UTF-8 message inside a Cease NOTIFICATION message, telling the peer why the session is being shut down or reset.
The document obsoletes RFC 8203. The differences and their rationale are in Appendix A.
Instead of a router just hanging up, it can say a few words first, so the other side knows it was on purpose and why.
§2The Shutdown Communication Format
A BGP speaker that ends a session sends a NOTIFICATION with Error Code 6 (Cease) and Error Subcode Administrative Shutdown (2) or Administrative Reset (4). It MAY then include a UTF-8 string, whose contents are at the operator's discretion.
- Length: an 8-bit field giving the length of the Shutdown Communication in octets. A value of zero means no Shutdown Communication follows.
- Shutdown Communication: MUST be encoded in UTF-8. It is not NUL terminated, and UTF-8 shortest-form encoding is REQUIRED.
Multibyte characters mean the number of characters will be less than the length value. A receiving speaker MUST NOT interpret invalid UTF-8 sequences. Reporting is implementation specific but SHOULD include methods such as syslog.
The note has a little label saying how long it is, followed by the words themselves. If the label says zero, there is no note.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
ERROR-CODE | Error Code | 1 byte | 6 | Cease. |
SUBCODE | Subcode | 1 byte | 2 (Administrative Shutdown) or 4 (Administrative Reset). | |
LENGTH | Length | 1 byte | Length of the Shutdown Communication in octets; zero means none follows. | |
TEXT | Shutdown Communication | 1 byte | UTF-8 text, up to 255 octets, not NUL terminated; continues past this row. |
§3Using It in Practice
Operators are encouraged to use the Shutdown Communication to give the reason for the shutdown and to include out-of-band reference materials. The RFC's example is [TICKET-1-1438367390] software upgrade; back in 2 hours: a ticket reference meaningful to both sides, a brief reason, and the expected length of the maintenance.
Length matters for compatibility. A speaker implementing RFC 8203 treats a message longer than 128 octets as an error, with a log message as the likely consequence. A speaker that implements neither RFC 8203 nor this specification treats a message of any length as an error, again with a log message as the consequence.
So a message of up to 255 octets MAY be sent if the peer is known to support this specification. Otherwise a message MAY be sent but SHOULD NOT be longer than 128 octets.
A receiver cannot acknowledge that it received and understood a Shutdown Communication, so operators should not rely on it as their sole way of communicating important events.
Short notes are safe for everyone. Long notes are only for neighbors you know can read them, and you should not count on the note being read.
§4Error Handling
If a Shutdown Communication containing an invalid UTF-8 sequence is received, a message indicating this event SHOULD be logged for the operator's attention. The erroneous or malformed text itself MAY be logged in hexdump format.
If the note is garbled, the router writes in its logbook that it got a garbled note, so a person can look at it.
§5Security Considerations
Unicode has a number of security issues, so implementers and operators are advised to read Unicode Technical Report #36. Shortest-form UTF-8 is REQUIRED to guard against the problems it outlines.
Because Shutdown Communications are likely to appear in syslog output, a carefully constructed message might be formatted so that it looks like extra syslog messages. The 255-octet limit may help limit such an attack.
Unless the BGP session uses a transport that provides integrity, the message could be forged; unless it provides confidentiality, it could be snooped. These issues are common to any BGP message. Users should also consider data minimization practices as outlined in Section 6.1 of RFC 6973.
Anyone could write a fake note or peek at a real one, and a sneaky note could try to look like something else in the logbook. So keep notes short and do not put secrets in them.
§6IANA Actions
IANA has referenced this document at the subcodes Administrative Shutdown and Administrative Reset in the 'BGP Cease NOTIFICATION message subcodes' registry, under the 'Border Gateway Protocol (BGP) Parameters' group, in addition to RFC 4486.
The official list of codes now also points to this document for these two entries.
§7Changes from RFC 8203
The maximum permitted length changed from 128 to 255 octets. Operators in regions that predominantly use multibyte character sets reported that messages with the same meaning as in single-byte languages did not fit in the old limit. The RFC's example: the phrase 'Planned work to add switch to stack. Completion time - 30 minutes' is 65 bytes, while its Russian translation is 139 bytes.
If a message longer than 128 octets reaches a speaker implementing RFC 8203, that speaker brings it to the operator's attention but otherwise processes the NOTIFICATION as normal.
Some languages need more bytes for the same sentence, like needing a bigger envelope for the same letter. So the envelope was made bigger.