BGP trigger Segment Routing ODN
draft-su-bgp-trigger-segment-routing-odn-00
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| Author | Yuanchao Su | ||
| Last updated | 2018-10-01 | ||
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draft-su-bgp-trigger-segment-routing-odn-00
Network Working Group Yuanchao Su
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track October 1,2018
Expires: January 3, 2019
BGP trigger Segment Routing ODN
draft-su-bgp-trigger-segment-routing-odn-00
Abstract
This document defines an extension to the BGP SR Policy NLRI
(draft-ietf-idr-segment-routing-te-policy) in order to use BGP to trigger
Segment Routing ODN, without using PCEP.
The goal is to consolidate the SR Policy provision(BGP-TE), collection(BGP-LS)
and ODN-trigger protocol for device to be BGP only, thus remove the need
for PCEP and reduce the network complexity and potential bugs cause by
different protocol interactions.
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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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 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
(https://trustee.ietf.org/license-info) in effect on the date of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction
Segment Routing (SR) allows a headend node to steer a packet flow
along any path. Intermediate per-flow states are eliminated thanks
to source routing [I-D.ietf-spring-segment-routing].
The headend node is said to steer a flow into a Segment Routing
Policy (SR Policy).
The header of a packet steered in an SR Policy is augmented with the
ordered list of segments associated with that SR Policy.
[I-D.ietf-spring-segment-routing-policy] details the concepts of SR
Policy and steering into an SR Policy. These apply equally to the
MPLS and SRv6 instantiations of segment routing.
[I-D.ietf-idr-segment-routing-te-policy] specifies the way to use BGP
to distribute one or more of the candidate paths of an SR Policy to the
headend of that policy.
This document specifies a way for headend to trigger SR ODN with BGP SR Policy NLRI UPDATE messages.
BGP can then be used to replace PCEP as the signal protocol for ODN.
This special UPDATE message SHOULD NOT be used for BGP best path selection.
When controller receives this specific UPDATE message from headend, it checks whether it's PCE,
if yes, it processed the payload of the message, otherwise it drops the message.
If controller is PCE, it retrieves the color, link affinity, association
information from the message and starts the path calculation.
Once the path calculation is done, the controller uses BGP SR Policy NLRI UPDATE message
to distribute the candidate path to headend.If the calculation is failed,
for example, the constrains expressed by the link affinity TLV can't be met,
the controller MUST sends a BGP SR Policy NLRI with Segment List TLV empty and Bing-SID empty.
When headend receives the update from controller, it processed the update
as specified in [I-D.ietf-idr-segment-routing-te-policy]
The extensions to SR Policy NLRI include:
o Distinguisher field SR Policy NLRI: special address FF:FF:FF:FF as the signal for ODN
o Two new sub-TLVs belong to Tunnel Encaps Attribute with Tunnel-Type set to 15(SR Policy)
o Metric sub-TLV to specify the metric that the PCE should use for the path calculation
o Link Affinity sub-TLV to specify the link constrains
o Association sub-TLV to specify the disjointness and protection constrains
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. BGP trigger ODN Encoding
2.1. Extension to SR Policy NLRI
[I-D.ietf-idr-segment-routing-te-policy] defines the SR Policy NLRI as below:
+------------------+
| NLRI Length | 1 octet
+------------------+
| Distinguisher | 4 octets
+------------------+
| Policy Color | 4 octets
+------------------+
| Endpoint | 4 or 16 octets
+------------------+
where:
o NLRI Length: 1 octet of length expressed in bits as defined in
[RFC4760].
o Distinguisher: 4-octet value uniquely identifying the policy in
the context of <color, endpoint> tuple. The distinguisher has no
semantic value and is solely used by the SR Policy originator to
make unique (from an NLRI perspective) multiple occurrences of the
same SR Policy.
o Policy Color: 4-octet value identifying (with the endpoint) the
policy. The color is used to match the color of the destination
prefixes to steer traffic into the SR Policy
[I-D.ietf-spring-segment-routing-policy].
o Endpoint: identifies the endpoint of a policy. The Endpoint may
represent a single node or a set of nodes (e.g., an anycast
address). The Endpoint is an IPv4 (4-octet) address or an IPv6
(16-octet) address according to the AFI of the NLRI.
NLRI Length, Policy Color,Endpoint field remains unchanged, while the
Distinguisher field will be set to FF:FF:FF:FF to signal the ODN request
to controller.
2.2. New SR Policy Sub-TLVs
The content of the SR Policy is encoded in the Tunnel Encapsulation
Attribute originally defined in [I-D.ietf-idr-tunnel-encaps] using a
new Tunnel-Type TLV (codepoint is 15, assigned by IANA.
The SR Policy Encoding structure is as follows:
SR Policy SAFI NLRI: <Distinguisher, Policy-Color, Endpoint>
Attributes:
Tunnel Encaps Attribute (23)
Tunnel Type: SR Policy
Binding SID
Preference
Priority
Policy Name
Explicit NULL Label Policy (ENLP)
Segment List
Weight
Segment
Segment
...
...
where:
o SR Policy SAFI NLRI is defined in [I-D.ietf-idr-segment-routing-te-policy]
o Tunnel Encapsulation Attribute is defined in
[I-D.ietf-idr-tunnel-encaps].
o Tunnel-Type is set to 15.
o Preference, Binding SID, Priority, Policy Name, ENLP, Segment-
List, Weight and Segment sub-TLVs are defined in [I-D.ietf-idr-segment-routing-te-policy].
o Additional sub-TLVs may be defined in the future.
In this document, 3 new SR Policy sub-TLVs are defined.
2.3. New SR Policy Sub-TLVs
This section defines the new SR Policy sub-TLVs.
o Metric sub-TLV to specify the metric that the PCE should use for the path calculation
o LSPA sub-TLV to specify the link constrains
o Association sub-TLV to specify the disjointness and protection constrains
2.3.1. Metric Sub-TLV
The Metric sub-TLV carries the same content as Metric Object defined in
[RFC5440] and [I-D.ietf-pce-segment-routing].
The Metric sub-TLV has following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |C|B| T |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| metric-value (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TBD
o Length: specifies the length of the value field not including Type
and Length fields.
o T (Type - 8 bits): Specifies the metric type.
Four values are currently defined:
* T=1: IGP metric
* T=2: TE metric
* T=3: Hop Counts
* T=11: Maximum SID Depth of the requested path
Flags (8 bits): Two flags are currently defined:
* B (Bound - 1 bit): When set in a BGP UPDATE message, the metric-
value indicates a bound (a maximum) for the path metric that
must not be exceeded for the headend to consider the computed path
as acceptable. The path metric must be less than or equal to
the value specified in the metric-value field. When the B flag
is cleared, the metric-value field is not used to reflect a
bound constraint.
* C (Computed Metric - 1 bit): When set in a BGP UPDATE message, this
indicates that the controller MUST provide the computed path metric
value (should a path satisfying the constraints be found) in
the PCRep message for the corresponding metric.
Unassigned flags MUST be set to zero on transmission and MUST be
ignored on receipt.
Metric-value (32 bits): metric value encoded in 32 bits in IEEE
floating point format (see [IEEE.754.1985]).
2.3.2. LSPA Sub-TLV
The LSPA sub-TLV carries the same content as Metric Object defined in
[RFC5440] and [I-D.ietf-pce-segment-routing].
The LSPA sub-TLV has following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |L| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Exclude-any sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-any sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-all sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TBD
o Length: specifies the length of the value field not including Type
and Length fields.
Flags (8 bits)
L flag: Corresponds to the "Local Protection Desired" bit
([RFC3209]) of the SESSION-ATTRIBUTE Object. When set, this
means that the computed path must include links protected with
Fast Reroute as defined in [RFC4090].
Unassigned flags MUST be set to zero on transmission and MUST be
ignored on receipt.
Reserved (8 bits): This field MUST be set to zero on transmission
and MUST be ignored on receipt.
Exclude-any, Include-any, Include-all sub-TLV's format is the same as
subobjects defined in [RFC3209].
2.3.3. Association Sub-TLV
The Association sub-TLV carries the same content as Association Object defined in
[RFC5440] and [I-D.ietf-pce-segment-routing].
The Association sub-TLV has following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Association type | Association ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Association Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional sub-TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TBD
o Length: specifies the length of the value field not including Type
and Length fields.
Flags (8 bits)
R (Removal - 1 bit): when set, the requesting PCEP peer requires the
removal of an LSP from the association group. When unset, the
PCEP peer indicates that the LSP is added or retained as part of
the association group. This flag is used for the ASSOCIATION
object in the PCRpt and the PCUpd message, the flag is ignored in
other PCEP messages.
Association type,Association ID, IPv4 Association Source format
is the same as definition in [I-D.ietf-pce-association-group].
3. BGP trigger ODN Operations
3.1. Configure BGP trigger ODN
Headend use color template to initiate ODN. To use BGP trigger ODN instead of PCEP,
a new CLI knob to specify this new mechanism, something like below:
on-demand color 30
candidate-paths
preference 100
dynamic
*bgp*
metric
type te
With the key word "bgp" configured, the headend MUST initiate ODN by
sending SR Policy NLRI UPDATE messages with Distinguisher field set to
FF.FF.FF.FF, also SHOULD set the Metric sub-TLV, LSPA sub-TLV and Association sub-TLV.
3.2. Reception of an SR Policy NLRI with Distinguisher field set to
FF.FF.FF.FF
On reception of an SR Policy NLRI Distinguisher field set to
FF.FF.FF.FF, a controller(BGP speaker) MUST determine if
it's first acceptable, then it determines if it is usable.
3.2.1. Acceptance of an SR Policy NLRI
When a BGP speaker receives an SR Policy NLRI from a neighbor it has
to determine if it's acceptable. The following applies:
o The SR Policy NLRI MUST include a distinguisher, color and
endpoint field which implies that the length of the NLRI MUST be
either 12 or 24 octets (depending on the address family of the
endpoint).
o The SR Policy update MUST have either the NO_ADVERTISE community
or at least one route-target extended community in IPv4-address
format. If a router supporting this document receives an SR
policy update with no route-target extended communities and no
NO_ADVERTISE community, the update MUST NOT be sent to the SRPM.
Furthermore, it SHOULD be considered to be malformed, and the
"treat-as-withdraw" strategy of [RFC7606] is applied.
o The Tunnel Encapsulation Attribute MUST be attached to the BGP
Update and MUST have a Tunnel Type TLV set to SR Policy (
codepoint is 15.
A router that receives an SR Policy update that is not valid
according to these criteria MUST treat the update as malformed. The
route MUST NOT be passed to the SRPM, and the "treat-as-withdraw"
strategy of [RFC7606] is applied.
A unacceptable SR Policy update that has a valid NLRI portion with
invalid attribute portion MUST be considered as a withdraw of the SR
Policy.
3.2.2. Usable SR Policy NLRI
If one or more route-targets are present, then at least one route-
target MUST match one of the BGP Identifiers of the neighbor in order
for the update to be considered usable. The BGP Identifier is
defined in [RFC4271] as a 4 octet IPv4 address. Therefore the route-
target extended community MUST be of the same format.
If one or more route-targets are present and no one matches any of
the neighbors' BGP Identifiers, then, while the SR Policy NLRI is
acceptable, it is not usable on the receiver node.
3.2.3. Passing a usable SR Policy NLRI to calculation engine
Once BGP has determined that the SR Policy NLRI is usable, BGP passes
the SR Policy candidate path to calculation engine.Calculation engine will
use its own algorithm and parameters retrieved from the SR Policy NLRI to calculate.
The result will pass back the result to headend as defined in
[I-D.ietf-idr-segment-routing-te-policy]
4. Contributors
Yuanchao Su (editor)
Cisco Systems, Inc.
China
Email: yuasu@cisco.com
5. Acknowledgments
The authors of this document would like to thank for their comments and review of this document.
7. Implementation Status
Note to RFC Editor: Please remove this section prior to publication,
as well as the reference to RFC 7942.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
When IANA-assigned values are available, implementations will be
updated to use them.
8. IANA Considerations
This document defines new Sub-TLVs in following existing registries:
o BGP Tunnel Encapsulation Attribute sub-TLV
Value Description Reference
---------------------------------------------------------------------------------
XX Metric sub-TLV This document
XX LSPA sub-TLV This document
XX Association sub-TLV This document
9. Security Considerations
TBD.
10. References
10.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy]
S. Previdi, Ed., C. Filsfils,D. Jain, Ed., P. Mattes,E. Rosen,
S. Lin,"Advertising Segment Routing Policies in BGP",
draft-ietf-idr-segment-routing-te-policy-04.txt(work in progress),
July,2018
[I-D.ietf-idr-tunnel-encaps]
Rosen, E., Patel, K., and G. Velde, "The BGP Tunnel
Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-09
(work in progress), February 2018.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing",
draft-ietf-pce-segment-routing-12 (work in progress), June
2018.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-01 (work in progress), June 2018.
[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>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[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>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
and D. McPherson, "Dissemination of Flow Specification
Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
<https://www.rfc-editor.org/info/rfc5575>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
10.2. Informational References
[I-D.filsfils-spring-sr-policy-considerations]
Filsfils, C., Talaulikar, K., Krol, P., Horneffer, M., and
P. Mattes, "SR Policy Implementation and Deployment
Considerations", draft-filsfils-spring-sr-policy-
considerations-01 (work in progress), June 2018.
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-14 (work in
progress), June 2018.
[I-D.ietf-idr-flowspec-redirect-ip]
Uttaro, J., Haas, J., Texier, M., Andy, A., Ray, S.,
Simpson, A., and W. Henderickx, "BGP Flow-Spec Redirect to
IP Action", draft-ietf-idr-flowspec-redirect-ip-02 (work
in progress), February 2015.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<https://www.rfc-editor.org/info/rfc4456>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
Authors' Addresses
Yuanchao Su (editor)
Cisco Systems, Inc.
China
Email: yuasu@cisco.com