draft-ietf-idr-add-paths-01.txt   draft-ietf-idr-add-paths-02.txt 
Network Working Group D. Walton Network Working Group D. Walton
Internet Draft A. Retana Internet Draft A. Retana
Intended Status: Standards Track E. Chen Intended Status: Standards Track E. Chen
Expiration Date: December 2009 Cisco Systems Expiration Date: February 2010 Cisco Systems
J. Scudder J. Scudder
Juniper Networks Juniper Networks
July 27, 2009 August 3, 2009
Advertisement of Multiple Paths in BGP Advertisement of Multiple Paths in BGP
draft-ietf-idr-add-paths-01.txt draft-ietf-idr-add-paths-02.txt
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Drafts. Drafts.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on December 28, 2009. This Internet-Draft will expire on February 4, 2010.
Abstract Abstract
In this document we propose a BGP extension that allows the In this document we propose a BGP extension that allows the
advertisement of multiple paths for the same address prefix without advertisement of multiple paths for the same address prefix without
the new paths implicitly replacing any previous ones. The essence of the new paths implicitly replacing any previous ones. The essence of
the extension is that each path is identified by a path identifier in the extension is that each path is identified by a path identifier in
addition to the address prefix. addition to the address prefix.
1. Introduction 1. Introduction
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Reachability Information (NLRI). In fact, a route with the same NLRI Reachability Information (NLRI). In fact, a route with the same NLRI
as a previously advertised route implicitly replaces the previous as a previously advertised route implicitly replaces the previous
advertisement. advertisement.
In this document we propose a BGP extension that allows the In this document we propose a BGP extension that allows the
advertisement of multiple paths for the same address prefix without advertisement of multiple paths for the same address prefix without
the new paths implicitly replacing any previous ones. The essence of the new paths implicitly replacing any previous ones. The essence of
the extension is that each path is identified by a path identifier in the extension is that each path is identified by a path identifier in
addition to the address prefix. addition to the address prefix.
2. Specification of Requirements 1.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. How to Identify a Path 2. How to Identify a Path
As defined in [RFC4271], a path refers to the information reported in As defined in [RFC4271], a path refers to the information reported in
the path attribute field of an UPDATE message. As the procedures the path attribute field of an UPDATE message. As the procedures
specified in [RFC4271] allow only the advertisement of one path for a specified in [RFC4271] allow only the advertisement of one path for a
particular address prefix, a path for an address prefix from a BGP particular address prefix, a path for an address prefix from a BGP
peer can be keyed on the address prefix. peer can be keyed on the address prefix.
In order for a BGP speaker to advertise multiple paths for the same In order for a BGP speaker to advertise multiple paths for the same
address prefix, a new identifier (termed "Path Identifier" hereafter) address prefix, a new identifier (termed "Path Identifier" hereafter)
needs to be introduced so that a particular path for an address needs to be introduced so that a particular path for an address
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The assignment of the Path Identifier for a path by a BGP speaker is The assignment of the Path Identifier for a path by a BGP speaker is
purely a local matter. However, the Path Identifier MUST be assigned purely a local matter. However, the Path Identifier MUST be assigned
in such a way that the BGP speaker is able to use the (prefix, path in such a way that the BGP speaker is able to use the (prefix, path
identifier) to uniquely identify a path advertised to a neighbor. A identifier) to uniquely identify a path advertised to a neighbor. A
BGP speaker that re-advertises a route MUST generate its own Path BGP speaker that re-advertises a route MUST generate its own Path
Identifier to be associated with the re-advertised route. A BGP Identifier to be associated with the re-advertised route. A BGP
speaker that receives a route SHOULD NOT assume that the identifier speaker that receives a route SHOULD NOT assume that the identifier
carries any particular semantics; it SHOULD be treated as an opaque carries any particular semantics; it SHOULD be treated as an opaque
value. value.
4. Extended NLRI Encodings 3. Extended NLRI Encodings
In order to carry the Path Identifier in an UPDATE message, the In order to carry the Path Identifier in an UPDATE message, the
existing NLRI encodings are extended by prepending the Path existing NLRI encodings are extended by prepending the Path
Identifier field, which is of four-octets. Identifier field, which is of four-octets.
For example, the NLRI encodings specified in [RFC4271, RFC4760] are For example, the NLRI encodings specified in [RFC4271, RFC4760] are
extended as the following: extended as the following:
+--------------------------------+ +--------------------------------+
| Path Identifier (4 octets) | | Path Identifier (4 octets) |
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| Label (3 octets) | | Label (3 octets) |
+--------------------------------+ +--------------------------------+
| ... | | ... |
+--------------------------------+ +--------------------------------+
| Prefix (variable) | | Prefix (variable) |
+--------------------------------+ +--------------------------------+
The usage of the extended NLRI encodings is specified in the The usage of the extended NLRI encodings is specified in the
Operation section. Operation section.
5. ADD-PATH Capability 4. ADD-PATH Capability
The ADD-PATH Capability is a new BGP capability [RFC5492]. The The ADD-PATH Capability is a new BGP capability [RFC5492]. The
Capability Code for this capability is specified in the IANA Capability Code for this capability is specified in the IANA
Considerations section of this document. The Capability Length field Considerations section of this document. The Capability Length field
of this capability is variable. The Capability Value field consists of this capability is variable. The Capability Value field consists
of one or more of the following tuples: of one or more of the following tuples:
+------------------------------------------------+ +------------------------------------------------+
| Address Family Identifier (2 octets) | | Address Family Identifier (2 octets) |
+------------------------------------------------+ +------------------------------------------------+
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This field is the same as the one used in [RFC4760]. This field is the same as the one used in [RFC4760].
Send/Receive: Send/Receive:
This field indicates whether the sender is (a) willing to This field indicates whether the sender is (a) willing to
receive multiple paths from its peer (value 1), (b) would receive multiple paths from its peer (value 1), (b) would
like to send multiple paths to its peer (value 2), or (c) like to send multiple paths to its peer (value 2), or (c)
both (value 3) for the <AFI, SAFI>. both (value 3) for the <AFI, SAFI>.
6. Operation 5. Operation
The Path Identifier specified in the previous section can be used to The Path Identifier specified in the previous section can be used to
advertise multiple paths for the same address prefix without advertise multiple paths for the same address prefix without
subsequent advertisements replacing the previous ones. Apart from subsequent advertisements replacing the previous ones. Apart from
the fact that this is now possible, the route advertisement rules of the fact that this is now possible, the route advertisement rules of
[RFC4271] are not changed. In particular, a new advertisement for a [RFC4271] are not changed. In particular, a new advertisement for a
given address prefix and a given path identifier replaces a previous given address prefix and a given path identifier replaces a previous
advertisement for the given address prefix and the given path advertisement for the given address prefix and the given path
identifier. identifier.
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speaker advertises the ADD-PATH Capability to the peer indicating its speaker advertises the ADD-PATH Capability to the peer indicating its
desire to send multiple paths for the <AFI, SAFI>, and also receives desire to send multiple paths for the <AFI, SAFI>, and also receives
the ADD-PATH Capability from the peer indicating its willingness to the ADD-PATH Capability from the peer indicating its willingness to
receive multiple paths for the <AFI, SAFI>, in which case the speaker receive multiple paths for the <AFI, SAFI>, in which case the speaker
MUST generate a route update for the <AFI, SAFI> based on the MUST generate a route update for the <AFI, SAFI> based on the
combination of the address prefix and the Path Identifier, and use combination of the address prefix and the Path Identifier, and use
the extended NLRI encodings specified in this document. The peer the extended NLRI encodings specified in this document. The peer
SHALL act accordingly in processing an UPDATE message related to a SHALL act accordingly in processing an UPDATE message related to a
particular <AFI, SAFI>. particular <AFI, SAFI>.
7. Applications As the Path Identifiers are locally assigned, and may or may not be
persistent across a control plane restart of a BGP speaker, an
implementation SHOULD take special care so that the underlying
forwarding plane of a "Receiving Speaker" as described in [RFC4724]
is not affected during the graceful restart of a BGP session.
6. Applications
The BGP extension specified in this document can be used by a BGP The BGP extension specified in this document can be used by a BGP
speaker to advertise multiple paths in certain applications. The speaker to advertise multiple paths in certain applications. The
availability of the additional paths can help reduce or eliminate availability of the additional paths can help reduce or eliminate
persistent route oscillations [RFC3345]. It can also help with persistent route oscillations [RFC3345]. It can also help with
optimal routing and routing convergence in a network. The optimal routing and routing convergence in a network. The
applications are detailed in separate documents. applications are detailed in separate documents.
8. Deployment Considerations 7. Deployment Considerations
The extension proposed in this document provides a mechanism for a The extension proposed in this document provides a mechanism for a
BGP speaker to advertise multiple paths over a BGP session. Care BGP speaker to advertise multiple paths over a BGP session. Care
needs to be taken in its deployment to ensure consistent routing and needs to be taken in its deployment to ensure consistent routing and
forwarding in a network, the details of which will be described in forwarding in a network, the details of which will be described in
separate application documents. separate application documents.
9. IANA Considerations 8. IANA Considerations
IANA needs to assign a capability number for the ADD-PATH Capability IANA has assigned capability number <TBD> for the ADD-PATH Capability
described in this document. described in this document. This registration is in the BGP
Capability Codes registry.
10. Security Considerations 9. Security Considerations
This document introduces no new security concerns to BGP or other This document introduces no new security concerns to BGP or other
specifications referenced in this document. specifications referenced in this document.
11. Acknowledgments 10. Acknowledgments
We would like to thank David Cook and Naiming Shen for their We would like to thank David Cook and Naiming Shen for their
contributions to the design and development of the extension, and for contributions to the design and development of the extension.
co-authoring drafts that lead to the current document.
Many people have made valuable comments and suggestions, including Many people have made valuable comments and suggestions, including
Dave Meyer, Srihari Sangli, Eric Rosen, Dan Tappan, Robert Raszuk, Rex Fernando, Eugene Kim, Danny McPherson, Dave Meyer, Pradosh
Mark Turner, Danny McPherson, Eugene Kim, Pradosh Mohapatra, Rex Mohapatra, Keyur Patel, Robert Raszuk, Eric Rosen, Srihari Sangli,
Fernando, and Keyur Patel. Dan Tappan, and Mark Turner.
12. Normative References 11. References
11.1. Normative References
[RFC4271] Rekhter, Y., T. Li, and S. Hares, "A Border Gateway [RFC4271] Rekhter, Y., T. Li, and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)," RFC 4271, January 2006. Protocol 4 (BGP-4)," RFC 4271, January 2006.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, February 2009. with BGP-4", RFC 5492, February 2009.
[RFC4760] Bates, T., Chandra, R., Rekhter, Y., and D. Katz, [RFC4760] Bates, T., Chandra, R., Rekhter, Y., and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 4760, January 2007. "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007.
[RFC3107] Rekhter, R. and E. Rosen, "Carrying Label Information in [RFC3107] Rekhter, R. and E. Rosen, "Carrying Label Information in
BGP-4," RFC 3107, May 2001. BGP-4," RFC 3107, May 2001.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," RFC 2119, BCP 14, March 1997. Requirement Levels," RFC 2119, BCP 14, March 1997.
13. Informative References [RFC4724] Sangli, S., E. Chen, R. Fernando, J. Scudder, and Y.
Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, January
2007.
11.2. Informative References
[RFC3345] McPherson, D., V. Gill, D. Walton, and A. Retana, "Border [RFC3345] McPherson, D., V. Gill, D. Walton, and A. Retana, "Border
Gateway Protocol (BGP) Persistent Route Oscillation Condition", RFC Gateway Protocol (BGP) Persistent Route Oscillation Condition", RFC
3345, August 2002. 3345, August 2002.
14. Authors' Addresses 12. Authors' Addresses
Daniel Walton Daniel Walton
Cisco Systems, Inc. Cisco Systems, Inc.
7025 Kit Creek Rd. 7025 Kit Creek Rd.
Research Triangle Park, NC 27709 Research Triangle Park, NC 27709
Email: dwalton@cisco.com Email: dwalton@cisco.com
Alvaro Retana Alvaro Retana
Cisco Systems, Inc. Cisco Systems, Inc.
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170 W. Tasman Dr. 170 W. Tasman Dr.
San Jose, CA 95134 San Jose, CA 95134
Email: enkechen@cisco.com Email: enkechen@cisco.com
John Scudder John Scudder
Juniper Networks Juniper Networks
Email: jgs@juniper.net Email: jgs@juniper.net
15. Copyright Notice 13. Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info). publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. and restrictions with respect to this document.
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