draft-ietf-idr-add-paths-13.txt   draft-ietf-idr-add-paths-14.txt 
Network Working Group D. Walton Network Working Group D. Walton
Internet-Draft Cumulus Networks Internet-Draft Cumulus Networks
Intended status: Standards Track A. Retana Intended status: Standards Track A. Retana
Expires: June 13, 2016 E. Chen Expires: November 1, 2016 E. Chen
Cisco Systems, Inc. Cisco Systems, Inc.
J. Scudder J. Scudder
Juniper Networks Juniper Networks
December 11, 2015 April 30, 2016
Advertisement of Multiple Paths in BGP Advertisement of Multiple Paths in BGP
draft-ietf-idr-add-paths-13 draft-ietf-idr-add-paths-14
Abstract Abstract
This document defines a BGP extension that allows the advertisement This document defines a BGP extension that allows the advertisement
of multiple paths for the same address prefix without the new paths of multiple paths for the same address prefix without the new paths
implicitly replacing any previous ones. The essence of the extension implicitly replacing any previous ones. The essence of the extension
is that each path is identified by a path identifier in addition to is that each path is identified by a path identifier in addition to
the address prefix. the address prefix.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on June 13, 2016. This Internet-Draft will expire on November 1, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 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 Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Specification of Requirements . . . . . . . . . . . . . . 2 1.1. Specification of Requirements . . . . . . . . . . . . . . 2
2. How to Identify a Path . . . . . . . . . . . . . . . . . . . 3 2. How to Identify a Path . . . . . . . . . . . . . . . . . . . 3
3. Extended NLRI Encodings . . . . . . . . . . . . . . . . . . . 3 3. Extended NLRI Encodings . . . . . . . . . . . . . . . . . . . 3
4. ADD-PATH Capability . . . . . . . . . . . . . . . . . . . . . 3 4. ADD-PATH Capability . . . . . . . . . . . . . . . . . . . . . 3
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Applications . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 5
7. Deployment Considerations . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 10.1. Normative References . . . . . . . . . . . . . . . . . . 6
11.1. Normative References . . . . . . . . . . . . . . . . . . 6 10.2. Informative References . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
The BGP specification [RFC4271] defines an Update-Send Process to The BGP specification [RFC4271] defines an Update-Send Process to
advertise the routes chosen by the Decision Process to other BGP advertise the routes chosen by the Decision Process to other BGP
speakers. No provisions are made to allow the advertisement of speakers. No provisions are made to allow the advertisement of
multiple paths for the same address prefix, or Network Layer multiple paths for the same address prefix, or Network Layer
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.
This document defines a BGP extension that allows the advertisement This document defines a BGP extension that allows the advertisement
of multiple paths for the same address prefix without the new paths of multiple paths for the same address prefix without the new paths
implicitly replacing any previous ones. The essence of the extension implicitly replacing any previous ones. The essence of the extension
is that each path is identified by a path identifier in addition to is that each path is identified by a path identifier in addition to
the address prefix. the address prefix.
The availability of the additional paths can help reduce or eliminate
persistent route oscillations [RFC3345]. It can also help with
optimal routing and routing convergence in a network by providing
potential alternate or backup paths, respectively.
1.1. 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].
2. 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
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needs to be introduced so that a particular path for an address needs to be introduced so that a particular path for an address
prefix can be identified by the combination of the address prefix and prefix can be identified by the combination of the address prefix and
the Path Identifier. the Path Identifier.
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.
value.
3. Extended NLRI Encodings 3. Extended NLRI Encodings
In order to carry the Path Identifier in an UPDATE message, the NLRI In order to carry the Path Identifier in an UPDATE message, the NLRI
encoding MUST be extended by prepending the Path Identifier field, encoding MUST be extended by prepending the Path Identifier field,
which is of four-octets. which is of four-octets.
For example, the NLRI encoding specified in [RFC4271] is extended as For example, the NLRI encoding specified in [RFC4271] is extended as
the following: the following:
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+--------------------------------+ +--------------------------------+
| Length (1 octet) | | Length (1 octet) |
+--------------------------------+ +--------------------------------+
| Prefix (variable) | | Prefix (variable) |
+--------------------------------+ +--------------------------------+
The usage of the extended NLRI encodings is specified in Section 5. The usage of the extended NLRI encodings is specified in Section 5.
4. 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], with
Capability Code for this capability is specified in the IANA Capability Code 69. The Capability Length field of this capability
Considerations section of this document. The Capability Length field is variable. The Capability Value field consists of one or more of
of this capability is variable. The Capability Value field consists the following tuples:
of one or more of the following tuples:
+------------------------------------------------+ +------------------------------------------------+
| Address Family Identifier (2 octets) | | Address Family Identifier (2 octets) |
+------------------------------------------------+ +------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) | | Subsequent Address Family Identifier (1 octet) |
+------------------------------------------------+ +------------------------------------------------+
| Send/Receive (1 octet) | | Send/Receive (1 octet) |
+------------------------------------------------+ +------------------------------------------------+
The meaning and use of the fields are as follows: The meaning and use of the fields are as follows:
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If any other value is received, then the capability SHOULD be If any other value is received, then the capability SHOULD be
treated as not understood and ignored [RFC5492]. treated as not understood and ignored [RFC5492].
A BGP speaker that wishes to indicate support for multiple AFI/SAFI A BGP speaker that wishes to indicate support for multiple AFI/SAFI
MUST do so by including the information in a single instance of the MUST do so by including the information in a single instance of the
ADD-PATH Capability. ADD-PATH Capability.
5. Operation 5. Operation
The Path Identifier specified in the previous section can be used to The Path Identifier specified in Section 3 can be used to advertise
advertise multiple paths for the same address prefix without multiple paths for the same address prefix without subsequent
subsequent advertisements replacing the previous ones. Apart from advertisements replacing the previous ones. Apart from the fact that
the fact that this is now possible, the route advertisement rules of this is now possible, the route advertisement rules of [RFC4271] are
[RFC4271] are not changed. In particular, a new advertisement for a not changed. In particular, a new advertisement for a given address
given address prefix and a given path identifier replaces a previous prefix and a given path identifier replaces a previous advertisement
advertisement for the same address prefix and path identifier. If a for the same address prefix and path identifier. If a BGP speaker
BGP speaker receives a message to withdraw a prefix with a path receives a message to withdraw a prefix with a path identifier not
identifier not seen before, it SHOULD silently ignore it. seen before, it SHOULD silently ignore it.
For a BGP speaker to be able to send multiple paths to its peer, that For a BGP speaker to be able to send multiple paths to its peer, that
BGP speaker MUST advertise the ADD-PATH capability with the Send/ BGP speaker MUST advertise the ADD-PATH capability with the Send/
Receive field set to either 2 or 3, and MUST receive from its peer Receive field set to either 2 or 3, and MUST receive from its peer
the ADD-PATH capability with the Send/Receive field set to either 1 the ADD-PATH capability with the Send/Receive field set to either 1
or 3, for the corresponding <AFI, SAFI>. or 3, for the corresponding <AFI, SAFI>.
A BGP speaker MUST follow the procedures defined in [RFC4271] when A BGP speaker MUST follow the procedures defined in [RFC4271] when
generating an UPDATE message for a particular <AFI, SAFI> to a peer generating an UPDATE message for a particular <AFI, SAFI> to a peer
unless the BGP speaker advertises the ADD-PATH Capability to the peer unless the BGP speaker advertises the ADD-PATH Capability to the peer
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A BGP speaker SHOULD include the bestpath when more than one path are A BGP speaker SHOULD include the bestpath when more than one path are
advertised to a neighbor unless the bestpath is a path received from advertised to a neighbor unless the bestpath is a path received from
that neighbor. that neighbor.
As the Path Identifiers are locally assigned, and may or may not be As the Path Identifiers are locally assigned, and may or may not be
persistent across a control plane restart of a BGP speaker, an persistent across a control plane restart of a BGP speaker, an
implementation SHOULD take special care so that the underlying implementation SHOULD take special care so that the underlying
forwarding plane of a "Receiving Speaker" as described in [RFC4724] forwarding plane of a "Receiving Speaker" as described in [RFC4724]
is not affected during the graceful restart of a BGP session. is not affected during the graceful restart of a BGP session.
6. Applications 6. Deployment Considerations
The BGP extension specified in this document can be used by a BGP
speaker to advertise multiple paths in certain applications. The
availability of the additional paths can help reduce or eliminate
persistent route oscillations [RFC3345]. It can also help with
optimal routing and routing convergence in a network. The
applications are detailed in separate documents.
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 [I-D.ietf-idr-add-paths-guidelines].
separate application documents.
The only explicit indication that the encoding described in Section 3
is in use in a particular BGP session is the exchange of Capabilities
Section 4. If the negotiation is successful [RFC5492], then the BGP
speakers will be able to process all BGP UPDATES properly, as
described in Section 5. However, if, for example, a packet analyzer
is used on the wire to examine an active BGP session, it may not be
able to properly decode the BGP UPDATES because it lacks prior
knowledge of the negotiated Capabilities.
When deployed as a provider edge router or a peering router that When deployed as a provider edge router or a peering router that
interacts with external neighbors, a BGP speaker usually advertises interacts with external neighbors, a BGP speaker usually advertises
at most one path to the internal neighbors in a network. In the case at most one path to the internal neighbors in a network. In the case
the speaker is configured to advertise multiple paths to the internal the speaker is configured to advertise multiple paths to the internal
neighbors, and additional information is needed for the application, neighbors, and additional information is needed for the application,
the speaker could use attributes such as the Edge_Discriminator the speaker could use attributes such as the Edge_Discriminator
attribute [I-D.pmohapat-idr-fast-conn-restore]. The use of that type attribute [I-D.pmohapat-idr-fast-conn-restore]. The use of that type
of additional information is outside the scope of this document. of additional information is outside the scope of this document.
8. IANA Considerations 7. IANA Considerations
IANA has assigned capability number 69 for the ADD-PATH Capability IANA has assigned capability number 69 for the ADD-PATH Capability
described in this document. This registration is in the BGP described in this document. This registration is in the BGP
Capability Codes registry. Capability Codes registry.
9. Security Considerations 8. Security Considerations
This document defines a BGP extension that allows the advertisement This document defines a BGP extension that allows the advertisement
of multiple paths for the same address prefix without the new paths of multiple paths for the same address prefix without the new paths
implicitly replacing any previous ones. As a result, multiple paths implicitly replacing any previous ones. As a result, multiple paths
for a large number of prefixes may be received by a BGP speaker for a large number of prefixes may be received by a BGP speaker
potentially depleting memory resources or even causing network-wide potentially depleting memory resources or even causing network-wide
instability. The use of the ADD-PATH Capability is intended to instability. The use of the ADD-PATH Capability is intended to
address specific needs related to, for example, eliminating the MED- address specific needs related to, for example, eliminating the MED-
induced route oscillations in a network induced route oscillations in a network
[I-D.ietf-idr-route-oscillation-stop]. While the applications for [I-D.ietf-idr-route-oscillation-stop]. While describing the
the ADD-PATH Capability are outside the scope of this document, the applications for the ADD-PATH Capability is outside the scope of this
users are encouraged to examine their behavior and potential impact document, users are encouraged to examine their behavior and
by studying the best practices described in potential impact by studying the best practices described in
[I-D.ietf-idr-add-paths-guidelines]. [I-D.ietf-idr-add-paths-guidelines].
This document introduces no new security concerns in the base This document introduces no new security concerns in the base
operation of BGP [RFC4271]. operation of BGP [RFC4271].
10. Acknowledgments 9. 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. contributions to the design and development of the extension.
Many people have made valuable comments and suggestions, including Many people have made valuable comments and suggestions, including
Rex Fernando, Eugene Kim, Danny McPherson, Dave Meyer, Pradosh Rex Fernando, Eugene Kim, Danny McPherson, Dave Meyer, Pradosh
Mohapatra, Keyur Patel, Robert Raszuk, Eric Rosen, Srihari Sangli, Mohapatra, Keyur Patel, Robert Raszuk, Eric Rosen, Srihari Sangli,
Dan Tappan, Mark Turner, Jeff Haas, Jay Borkenhagen and Mach Chen. Dan Tappan, Mark Turner, Jeff Haas, Jay Borkenhagen, Mach Chen, Denis
Ovsienko, Carlos Pignataro and Meral Shirazipour.
11. References 10. References
11.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>. <http://www.rfc-editor.org/info/rfc4271>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760, "Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007, DOI 10.17487/RFC4760, January 2007,
<http://www.rfc-editor.org/info/rfc4760>. <http://www.rfc-editor.org/info/rfc4760>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <http://www.rfc-editor.org/info/rfc5492>. 2009, <http://www.rfc-editor.org/info/rfc5492>.
11.2. Informative References 10.2. Informative References
[I-D.ietf-idr-add-paths-guidelines] [I-D.ietf-idr-add-paths-guidelines]
Uttaro, J., Francois, P., Patel, K., Mohapatra, P., Haas, Uttaro, J., Francois, P., Patel, K., Haas, J., Simpson,
J., Simpson, A., and R. Fragassi, "Best Practices for A., and R. Fragassi, "Best Practices for Advertisement of
Advertisement of Multiple Paths in IBGP", draft-ietf-idr- Multiple Paths in IBGP", draft-ietf-idr-add-paths-
add-paths-guidelines-07 (work in progress), December 2014. guidelines-08 (work in progress), April 2016.
[I-D.ietf-idr-route-oscillation-stop] [I-D.ietf-idr-route-oscillation-stop]
Walton, D., Retana, A., Chen, E., and J. Scudder, "BGP Walton, D., Retana, A., Chen, E., and J. Scudder, "BGP
Persistent Route Oscillation Solutions", draft-ietf-idr- Persistent Route Oscillation Solutions", draft-ietf-idr-
route-oscillation-stop-01 (work in progress), October route-oscillation-stop-02 (work in progress), April 2016.
2015.
[I-D.pmohapat-idr-fast-conn-restore] [I-D.pmohapat-idr-fast-conn-restore]
Mohapatra, P., Fernando, R., Filsfils, C., and R. Raszuk, Mohapatra, P., Fernando, R., Filsfils, C., and R. Raszuk,
"Fast Connectivity Restoration Using BGP Add-path", draft- "Fast Connectivity Restoration Using BGP Add-path", draft-
pmohapat-idr-fast-conn-restore-03 (work in progress), pmohapat-idr-fast-conn-restore-03 (work in progress),
January 2013. January 2013.
[RFC3345] McPherson, D., Gill, V., Walton, D., and A. Retana, [RFC3345] McPherson, D., Gill, V., Walton, D., and A. Retana,
"Border Gateway Protocol (BGP) Persistent Route "Border Gateway Protocol (BGP) Persistent Route
Oscillation Condition", RFC 3345, DOI 10.17487/RFC3345, Oscillation Condition", RFC 3345, DOI 10.17487/RFC3345,
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