Internet Engineering Task Force K. Patel
Internet-Draft Arrcus
Intended status: Standards Track R. Fernando
Expires: September 28, 2017 Cisco Systems
J. Scudder
J. Haas
Juniper Networks
March 27, 2017
Notification Message support for BGP Graceful Restart
draft-ietf-idr-bgp-gr-notification-10.txt
Abstract
The current BGP Graceful Restart mechanism limits the usage of BGP
Graceful Restart to BGP protocol messages other than a BGP
NOTIFICATION message. This document defines an extension to the BGP
Graceful Restart 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
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 28, 2017.
Copyright Notice
Copyright (c) 2017 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 . . . . . . . . . . . . . . . . . . . 4
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. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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
Error code. If a Hard Reset is used, a full session reset is
performed.
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1.1. Requirements Language
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 [RFC2119].
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:
+--------------------------------------------------+
| Restart Flags (4 bits) |
+--------------------------------------------------+
| Restart Time in seconds (12 bits) |
+--------------------------------------------------+
| Address Family Identifier (16 bits) |
+--------------------------------------------------+
| Subsequent Address Family Identifier (8 bits) |
+--------------------------------------------------+
| Flags for Address Family (8 bits) |
+--------------------------------------------------+
| ... |
+--------------------------------------------------+
| Address Family Identifier (16 bits) |
+--------------------------------------------------+
| Subsequent Address Family Identifier (8 bits) |
+--------------------------------------------------+
| Flags for Address Family (8 bits) |
+--------------------------------------------------+
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
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the procedures of this document, by advertising a Graceful Restart
Capability with its Graceful NOTIFICATION bit set (value 1). This
also implies support for the format for a BGP NOTIFICATION Cease
message defined in [RFC4486].
3. BGP Hard Reset Subcode
A new BGP NOTIFICATION Cease message subcode is defined known as the
BGP Hard Reset Subcode. The value of this subcode is discussed in
Section 6. We refer to a BGP NOTIFICATION Cease message with the
Hard Reset subcode as a Hard Reset message, or just a Hard Reset.
3.1. Sending a Hard Reset
A Hard Reset message is used to indicate to a peer with which the
Graceful Notification flag 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.
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 in Graceful mode 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
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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.
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] S. 4.2, the
relevant routes will be flushed, defeating the goals of this
specification.
4.1. Rules for the Receiving Speaker
[RFC4724] S. 4.2 defines rules for the Receiving Speaker. These are
modified as follows.
As part of this extension, routes from the peer previously marked as
stale MUST NOT be deleted, until and unless the optional timer
mentioned in the final paragraph of [RFC4724] S. 4.2 expires, or
unless a Hard Reset is performed. This supersedes the "consecutive
restarts" requirement in the third paragraph of [RFC4724] S. 4.2.
In addition to the rules already specified in [RFC4724] S. 4.2 for
how variations in the received Graceful Restart Capability should be
interpreted (the paragraph that begins "Once the session is re-
established..."), if the Graceful Notification ("N") bit is not set
in the newly received Graceful Restart Capability, no new actions are
triggered on the Receiving Speaker -- in particular, a clear "N" bit
does not trigger deletion of stale routes.
Other than these modifications, the rules for the Receiving Speaker
are as specified in [RFC4724] S. 4.2.
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5. Acknowledgements
The authors would like to thank Jim Uttaro for the suggestion, and
Emmanuel Baccelli, Bruno Decraene, Chris Hall, Paul Mattes and Robert
Raszuk for their review and comments.
6. IANA Considerations
IANA is requested to assign a new subcode in the "BGP Cease
NOTIFICATION message subcodes" registry. The suggested name for the
code point is "Hard Reset".
7. Security Considerations
This extension to BGP does not change the underlying security issues
inherent in the existing [RFC4724] and [RFC4271].
8. 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,
<http://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,
<http://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, <http://www.rfc-editor.org/info/rfc4486>.
[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,
<http://www.rfc-editor.org/info/rfc4724>.
Authors' Addresses
Keyur Patel
Arrcus
Email: keyur@arrcus.com
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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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