IGP Extensions for Segment Routing Service Segment
draft-lz-lsr-igp-sr-service-segments-04
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Liu Yao
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Zheng Zhang
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Yongqing Zhu
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2021-01-21
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LSR Working Group Yao. Liu
Internet-Draft Zheng. Zhang
Intended status: Standards Track ZTE Corporation
Expires: July 25, 2021 Yongqing. Zhu
China Telecom
January 21, 2021
IGP Extensions for Segment Routing Service Segment
draft-lz-lsr-igp-sr-service-segments-04
Abstract
This document defines extensions to the link-state routing protocols
(IS-IS and OSPF) in order to carry service segment information via
IGP.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 25, 2021.
Copyright Notice
Copyright (c) 2021 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IGP Extensions for Service Segments . . . . . . . . . . . . . 4
3.1. IS-IS Extensions . . . . . . . . . . . . . . . . . . . . 4
3.2. OSPFv2 and OSPFv3 Extensions . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Segments are introduced in the SR architecture [RFC8402]. Segment
Routing (SR) allows for a flexible definition of end-to-end paths by
encoding paths as sequences of topological sub-paths, called
"segments".
Service Function Chaining (SFC) [RFC7665] provides support for the
creation of composite services that consist of an ordered set of
Service Functions (SF) that are to be applied to packets and/or
frames selected as a result of classification.
[I-D.ietf-spring-sr-service-programming] describes how a service can
be associated with a SID and how to achieve service funtion chaining
in SR-enabled MPLS and IPv6 networks. It also defines SR-aware and
SR-unaware services. For a SR-unaware service ,there has to be a SR
proxy handling the SR processing on behalf of the service .
[I-D.dawra-idr-bgp-ls-sr-service-segments] propose extensions to BGP-
LS for Service Chaining to distribute the service segment information
to SR Controller.
The reference network topology is shown in figure 1.
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SR-C
A----1----2----3----4----5----B
| |
| |
S1 S2
Figure 1: Network with Services
Node 1-5 are nodes capital of segment routing. A and B are two end
hosts. S1 is an SR-aware Service. S2 is an SR-unaware Service and
node 4 act as an SR proxy. The path from A to B needs to pass
through service function S1 and S2. SR Controller (SR-C) is capable
of receiving BGP-LS updates to discover topology, and calculating
constrained paths between 1 and 5. To provision and maintain service
function path, the SR-C needs to collect the SID-related service
information as well.
If the service segment information can only be transmitted through
BGP-LS, the BGP protocol needs to be enabled on all the service
function nodes or SFFs, and BGP neighbors should be established
between these nodes and the SR-C or the node selected to have a BGP
session with the controller.
A common scenario is that IGP is enabled on each node in the network
to distributed SIDs and SID-related information(e.g reachability,
behavior, structure,etc) within the domain and a small amout of nodes
are connected to the controller/PCE via BGP-LS to report SID-related
information along with the topology. This document proposes
extensions for IGP to advertise service segment information along
with SIDs to support such scenario.
2. Conventions used in this document
2.1. 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.
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2.2. Acronyms
SFC: Service Function Chain
SFF: Service Function Forwarder
SF: Service Function
SFP: Service Function Path
3. IGP Extensions for Service Segments
If an service function node like S1 supports IGP function, it
advertises the service information to other SR nodes through IGP
itself. Otherwise, SFFs like node 2 or node 4 are responsible to
advertise the service information through IGP. How can SFFs get the
service segment information from SFs is outside of scope of this
document.
3.1. IS-IS Extensions
This document introduces new sub-sub-TLVs for SRv6 End SID sub-TLV
[I-D.ietf-lsr-isis-srv6-extensions] and Prefix Segment Identifier
(Prefix-SID) Sub-TLV [RFC8667] for SR-MPLS to associate the Service
SID Value with Service-related Information.
One of the new TLVs is Service Chaining (SC) TLV, the TLV is defined
as follows :
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 | Service Info |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Traffic Type | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2:Service Chaining (SC) TLV
where:
Type: 8 bit field. TBD
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Length: 8 bit field indicating the length of the remainder of the TLV
The Flags, Traffic Type and RESERVED fields are the same as in the SC
TLV defined in [I-D.dawra-idr-bgp-ls-sr-service-segments] chapter 2.
Flags: 8 bit field. Bits SHOULD be 0 on transmission and MUST be
ignored on reception.
Traffic Type: 8 Bit field. A bit to identify if Service is IPv4 OR
IPv6 OR L2 Ethernet Capable.
Bit 0(LSB): Set to 1 if Service is IPv4 Capable
Bit 1: Set to 1 if Service is IPv6 Capable
Bit 2: Set to 1 if Service is Ethernet Capable
RESERVED: 16bit field. SHOULD be 0 on transmission and MUST be
ignored on reception.
Service Info: 16-bits field. The right most 12 bits categorize the
Service Type: (such as "Firewall", "Classifier" etc).
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| P FLAG| Service Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Service Info Field
The first 4 bits are P FLAG which is used to indicate the SR proxy
type with the following values:
0000:SR-aware function.
0001:Static proxy.
0010:Dynamic proxy.
0011:Masquerading proxy(for SRv6 only).
0100:Shared memory proxy.
Other values are reserved.
The P FLAG is mainly defined for SR-MPLS.
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In SRv6, although the SR proxy type can be represented by the END
functions[I-D.ietf-spring-sr-service-programming] which can be
advertised in Endpoint Behavior field of End SID sub-TLV
[I-D.ietf-lsr-isis-srv6-extensions], there may be situations that the
proxy with certain type cannot be associated with a network
programming function(for example, Shared memory proxy),or an user
want to define a new type of proxy for private use, or the SR proxy
node does not support network programming, so the P flag is still
useful.
In the IS-IS notification message, when both SR proxy END function
and P FLAG exist, the proxy type represented by P FLAG shall prevail.
Another Optional Opaque Metadata(OM) TLV is defined in figure 4. The
definition and structure are the same as the OM TLV defined in
[I-D.dawra-idr-bgp-ls-sr-service-segments] chapter 2.
+---------------------------------------+
| Type (1 octet) |
+---------------------------------------+
| Length (1 octet) |
+---------------------------------------+
| Opaque Type (2 octet) |
+---------------------------------------+
| Flags (1 octet) |
+---------------------------------------+
| Value (variable) |
+---------------------------------------+
Figure 4:Opaque Metadata(OM) TLV
3.2. OSPFv2 and OSPFv3 Extensions
This document introduces new sub-sub-TLVs for SRv6 End SID sub-TLV
[I-D.li-ospf-ospfv3-srv6-extensions] and Prefix-SID Sub-TLV [RFC8665]
[RFC8665] for SR-MPLS to associate the Service SID Value with
Service-related Information.
One of the new TLVs is Service Chaining (SC) TLV,
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Info | Flags | Traffic Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5:Service Chaining (SC) TLV
where:
Type: 16 bit field. TBD
Length: 16 bit field indicating the length of the remainder of the
TLV
Flags, Traffic Type and RESERVED are the same as that in SC TLV
defined in [I-D.dawra-idr-bgp-ls-sr-service-segments] chapter 2.
The definition and use principle of the Service Type field is the
same as that defined in the IS-IS extension above.
Another Optional Opaque Metadata(OM) TLV is defined in figure 6. The
definition and structure are the same as the OM TLV defined in
[I-D.dawra-idr-bgp-ls-sr-service-segments] chapter 2.
+---------------------------------------+
| Type (2 octet) |
+---------------------------------------+
| Length (2 octet) |
+---------------------------------------+
| Opaque Type (2 octet) |
+---------------------------------------+
| Flags (1 octet) |
+---------------------------------------+
| Value (variable) |
+---------------------------------------+
Figure 6:Opaque Metadata(OM) TLV
4. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the IS-IS and OSPF security model
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5. IANA Considerations
TBD
6. References
6.1. Normative References
[I-D.dawra-idr-bgp-ls-sr-service-segments]
Dawra, G., Filsfils, C., Talaulikar, K., Clad, F.,
daniel.bernier@bell.ca, d., Uttaro, J., Decraene, B.,
Elmalky, H., Xu, X., Guichard, J., and C. Li, "BGP-LS
Advertisement of Segment Routing Service Segments", draft-
dawra-idr-bgp-ls-sr-service-segments-04 (work in
progress), August 2020.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11
(work in progress), October 2020.
[I-D.ietf-spring-sr-service-programming]
Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
Henderickx, W., and S. Salsano, "Service Programming with
Segment Routing", draft-ietf-spring-sr-service-
programming-03 (work in progress), September 2020.
[I-D.li-ospf-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
"OSPFv3 Extensions for SRv6", draft-li-ospf-
ospfv3-srv6-extensions-07 (work in progress), November
2019.
[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>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[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>.
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[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
December 2019, <https://www.rfc-editor.org/info/rfc8666>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
6.2. Informative References
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
Authors' Addresses
Liu Yao
ZTE Corporation
Nanjing
China
Email: liu.yao71@zte.com.cn
Zhang Zheng
ZTE Corporation
Nanjing
China
Email: zzhang_ietf@hotmail.com
Zhu Yongqing
China Telecom
China
Email: zhuyq8@chinatelecom.cn
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