Internet DRAFT - draft-ietf-idr-bgp-gr-notification
draft-ietf-idr-bgp-gr-notification
Internet Engineering Task Force K. Patel
Internet-Draft Arrcus
Updates: 4724 (if approved) R. Fernando
Intended status: Standards Track Cisco Systems
Expires: May 31, 2019 J. Scudder
J. Haas
Juniper Networks
November 27, 2018
Notification Message support for BGP Graceful Restart
draft-ietf-idr-bgp-gr-notification-16.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
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This Internet-Draft will expire on May 31, 2019.
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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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. Operational Considerations . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11. 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", "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. 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).
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 9. 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. Operational Considerations
Note that long (or infinite) retention time may cause operational
issues, and should be enabled with care.
8. Acknowledgements
The authors would like to thank Jim Uttaro for the suggestion, and
Emmanuel Baccelli, Bruno Decraene, Chris Hall, Warren Kumari, Paul
Mattes, Robert Raszuk, and Alvaro Retana for their review and
comments.
9. 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:
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+--------------+---------------+------------+---------------+
| Bit Position | Name | Short Name | Reference |
+--------------+---------------+------------+---------------+
| 0 | Restart State | R | [RFC4724] |
| 1 | Notification | N | this document |
| 2, 3 | unassigned | | this document |
+--------------+---------------+------------+---------------+
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
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 | | this document |
+--------------+------------------+------------+---------------+
10. 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.
11. 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>.
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[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>.
[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>.
[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>.
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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