Unified Identifier in IPv6 Segment Routing Networks
draft-mirsky-6man-unified-id-sr-03
The information below is for an old version of the document.
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|---|---|---|---|
| Authors | Weiqiang Cheng , Greg Mirsky , Shaofu Peng , Aihua Liu , XiaoLan Wan , Cheng Wei | ||
| Last updated | 2019-07-25 (Latest revision 2019-04-03) | ||
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draft-mirsky-6man-unified-id-sr-03
Network C. Weiqiang
Internet-Draft China Mobile
Intended status: Standards Track G. Mirsky
Expires: January 26, 2020 ZTE Corp.
P. Shaofu
L. Aihua
ZTE Corporation
W. Xiaolan
New H3C Technologies Co. Ltd
C. Wei
Centec
July 25, 2019
Unified Identifier in IPv6 Segment Routing Networks
draft-mirsky-6man-unified-id-sr-03
Abstract
Segment Routing architecture leverages the paradigm of source
routing. It can be realized in a network data plane by prepending
the packet with a list of instructions, a.k.a. segments. A segment
can be encoded as a Multi-Protocol Label Switching (MPLS) label, IPv4
address, or IPv6 address. Segment Routing can be applied in MPLS
data plane by encoding segments in MPLS label stack. It also can be
applied to IPv6 data plane by encoding a list of segment identifiers
in IPv6 Segment Routing Extension Header (SRH). This document
extends the use of the SRH to unified identifiers encoded as MPLS
label and IPv4 address, to support interworking between SR-MPLS and
SRv6.
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 26, 2020.
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Copyright Notice
Copyright (c) 2019 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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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Segment Routing Extension Header: Benefits and Challenges . . 4
3. Support of Multiple SID Lengths in IPv6 Segment Routing
Extension Header . . . . . . . . . . . . . . . . . . . . . . 4
4. The Use Case of Unified Segment Identifier . . . . . . . . . 6
4.1. Interworking Scenario Between SR-MPLS and SRv6 . . . . . 6
5. Operations with Unified Segment Identifier . . . . . . . . . 8
5.1. Egress SR Tunnel Node . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Segment Routing architecture [RFC8402] leverages the paradigm of
source routing. It can be realized in a network data plane by
prepending the packet with a list of instructions, a.k.a. segment
identifiers (SIDs). A segment can be encoded as a Multi-Protocol
Label Switching (MPLS) label, IPv4 address, or IPv6 address. Segment
Routing can be applied in MPLS data plane by encoding 20-bits SIDs in
MPLS label stack [I-D.ietf-spring-segment-routing-mpls]. It also can
be applied to IPv6 data plane by encoding a list of 128-bits SIDs in
IPv6 Segment Routing Extension Header (SRH)
[I-D.ietf-6man-segment-routing-header]. Applicability of 32-bits SID
that may represent an IPv4 address has not been defined.
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SR extensions to Interior Gateway Protocols (IGP), IS-IS
[I-D.ietf-isis-segment-routing-extensions], OSPF
[I-D.ietf-ospf-segment-routing-extensions], and OSPFv3
[I-D.ietf-ospf-ospfv3-segment-routing-extensions], defined how
20-bits and 32-bits SIDs advertised and bound to SR objects and/or
instructions. Extensions to BGP link-state address family
[I-D.ietf-idr-bgp-ls-segment-routing-ext] enabled propagation of
segment information of variable length via BGP.
This document extends the use of the SRH
[I-D.ietf-6man-segment-routing-header] to SIDs for unified identifier
encoded as MPLS label and IPv4 address to support interworking
between SR-MPLS and SRv6.
1.1. Conventions used in this document
1.1.1. Terminology
SR: Segment Routing
SRH: Segment Routing Extension Header
MPLS: Multiprotocol Label Switching
SR-MPLS: Segment Routing using MPLS dataplane
SID: Segment Identifier
IGP: Interior Gateway Protocol
OAM: Operation, Administration and Maintenance
TE: Traffic Engineering
SRv6: Segment Routing in IPv6
U-SID: Unified Segment Identifier
1.1.2. 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. Segment Routing Extension Header: Benefits and Challenges
Many functions related to Operation, Administration and Maintenance
(OAM) require identification of the SR tunnel ingress and the path,
constructed by segments, between the ingress and the egress SR nodes.
Combination of IPv6 encapsulation [RFC8200] and SRH
[I-D.ietf-6man-segment-routing-header], referred to as SRv6, comply
with these requirements while it is challenging when applying SR in
MPLS networks, also referred to as SR-MPLS.
On the other hand, the size of IPv6 SID presents a scaling challenge
to use topological instructions that define strict explicit traffic
engineered (TE) path in combination with service-based instructions.
At the same time, that is where SR-MPLS approach provides better
results due to smaller SID length.
SR-MPLS is currently larger-scale used to metro networks than SRv6.
With the gradual deployment of SRv6 in the core networks, it becomes
necessary to support interworking between SR-MPLS and SRv6. It's
operationally more efficient and straightforward if SRv6 can use the
same size SIDs as in SR-MPLS. The SRH can be extended to define the
same as in SR-MPLS SID length to support the unified segment
identifier (U-SID). As a result, end-to-end SR tunnel may use U-SIDs
across SR-MPLS and SRv6 domains.
3. Support of Multiple SID Lengths in IPv6 Segment Routing Extension
Header
In section 3 of [I-D.ietf-6man-segment-routing-header] SRH format has
been defined as presented in Figure 1
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flags | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
...
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SRH format
This document defines the new field Size in the SRH Flags field as a
two-bits field with the following values:
0b00 - 128-bits SID;
0b01 - 20-bits SID;
0b10 - 32-bits SID
0b11 - reserved for future use.
0b01 and 0b10 can be used as an indication for the U-SID length.
When the value of the S field is 0b01 the 20-bit SID may be encoded
as 20-bit label-only or in four octets then occupies the 20 rightmost
bits.
Entries of the segment list in the SRH MUST be of the same length.
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4. The Use Case of Unified Segment Identifier
The U-SID can be used for interworking between SR-MPLS and SRv6. The
SR-MPLS is large-scale used to the metro network, such as, for
example, the backhaul metro network of CMCC. When the core network
uses SRv6, such as, for example, the core network of CMCC, it can use
the U-SID to interworking with SR-MPLS in the metro network for end-
to-end tunnel.
4.1. Interworking Scenario Between SR-MPLS and SRv6
SR-MPLS uses SR SIDs as MPLS label in MPLS stack over IPv4 or IPv6,
and the SIDs are 20-bits long. SRv6 uses SR SIDs as IPv6 extension
header in SRH over IPv6, and the SIDs are 128-bits long.
The U-SID uses the same length SIDs in MPLS stack and SRH, and the
SID is either 20-bits or 32-bits long. There can be put six 20-bit
USIDs and left 8-bit reserved or four 32-bits long USIDs in the space
of the single 128-bits long header. The encapsulation is illustrated
in Figure 2 and Figure 3.
+---------+ +------------------------------------+
| | | IPv6 header |
|IPv4/IPv6| +------------------------------------+
| | | SRH |
+---------+ +------------------------------------+
| USID1 | | USID1 | USID2 | ... | USID6 | Res |
+---------+ +------------------------------------+
| USID2 | | USID7 |... | USIDn| Null | Res |
+---------+ +------------------------------------+
| ... | + Payload |
+---------+ +------------------------------------+
| USIDn |
+---------+
| Payload |
+---------+
Figure 2: 20-bits long U-SIDs Encapsulation
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+---------+ +----------------------------------+
| | | IPv6 header |
|IPv4/IPv6| +----------------------------------+
| | | SRH |
+---------+ +----------------------------------+
| USID1 | | USID1 | USID2 | ... | USID4 |
+---------+ +----------------------------------+
| USID2 | | USID5 |... | USIDn | Null |
+---------+ +----------------------------------+
| ... | + Payload |
+---------+ +----------------------------------+
| USIDn |
+---------+
| Payload |
+---------+
Figure 3: 32-bits long U-SIDs Encapsulation
The SR-MPLS and SRv6 interworking is illustrated in Figure 4. An
end-to-end SR tunnel from A to F crosses the SR-MPLS and SRv6
domains. The SRv6 border nodes (E/G) receive SR-MPLS packets and
forward them into the SRv6 domain using U-SIDs.
+-----+ +-----+ +-----+ +-----+
| A +-------+ B +-------+ E +-------+ F |
+-----+ +--+--+ +--+--+ +--+--+
| SR-MPLS | | SRv6 |
| | | |
+-----+ +--+--+ +--+--+ +--+--+
| C |-------| D +-------+ G +-------+ H |
+-----+ +-----+ +-----+ +-----+
Figure 4: SR-MPLS and SRv6 interworking
The SRv6 edge node is assigned two U-SIDs (e.g., E1 and E2), one for
SR- MPLS and the other for SRv6. Figure 5 demonstrates an example of
the packet forwarding.
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+--------+
|IP(A->F)|
+--------+
| USID(A)|
+--------+ +--------+
| USID(B)| |IP(E->F)|
+--------+ +--------+ +----------------+
|USID(E1)| |USID(E1)| |IP(E->F) |
+--------+ +--------+ +----------------+
|USID(E2)| |USID(E2)| | SRH |
+--------+ +--------+ +----------------+
| USID(F)| | USID(F)| | SID(E2)| SID(F)|
+--------+ +--------+ +----------------+
| Payload| ---> | Payload| ---> | payload |
+--------+ +--------+ +----------------+
Figure 5: An Example of Packe Forwarding Based on U-SID
The controller may assign the end-to-end SR tunnel U-SIDs, and
another method is out of the scope for this document.
5. Operations with Unified Segment Identifier
When the SRH is used to include 20-bits or 32-bits U-SIDs the ingress
and transit nodes of an SR tunnel act as described in Section 5.1 and
Section 5.2 of [I-D.ietf-6man-segment-routing-header] respectively.
5.1. Egress SR Tunnel Node
TBD
6. IANA Considerations
IANA is requested to allocate from the Segment Routing Header Flags
registry the two-bits long field referred to as Size.
7. Security Considerations
This specification inherits all security considerations of [RFC8402]
and [I-D.ietf-6man-segment-routing-header].
8. Acknowledgements
TBD
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9. Normative References
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
Routing Header (SRH)", draft-ietf-6man-segment-routing-
header-21 (work in progress), June 2019.
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), June 2019.
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
Gredler, H., and B. Decraene, "IS-IS Extensions for
Segment Routing", draft-ietf-isis-segment-routing-
extensions-25 (work in progress), May 2019.
[I-D.ietf-ospf-ospfv3-segment-routing-extensions]
Psenak, P. and S. Previdi, "OSPFv3 Extensions for Segment
Routing", draft-ietf-ospf-ospfv3-segment-routing-
extensions-23 (work in progress), January 2019.
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-27 (work in progress), December 2018.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 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>.
[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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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[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
Cheng Weiqiang
China Mobile
Beijing
China
Email: chengweiqiang@chinamobile.com
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
Peng Shaofu
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing
China
Email: peng.shaofu@zte.com.cn
Liu Aihua
ZTE Corporation
Zhongxing Industrial Park, Nanshan District
Shenzhen
China
Email: liu.aihua@zte.com.cn
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Wan Xiaolan
New H3C Technologies Co. Ltd
No.8, Yongjia Road, Haidian District
Beijing
China
Email: wxlan@h3c.com
Cheng Wei
Centec
Building B, No.5 Xing Han Street, Suzhou Industrial Park
Suzhou
China
Email: Chengw@centecnetworks.com
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