Internet DRAFT - draft-wmsaxw-6man-usid-id-use
draft-wmsaxw-6man-usid-id-use
Network C. Weiqiang
Internet-Draft China Mobile
Intended status: Informational P. Shaofu
Expires: May 6, 2020 L. Aihua
ZTE Corporation
G. Mirsky
ZTE Corp.
W. Xiaolan
New H3C Technologies Co. Ltd
C. Wei
Centec
S. Zadok
Broadcom
November 3, 2019
Unified Identifier in IPv6 Segment Routing Networks
draft-wmsaxw-6man-usid-id-use-00
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 the MPLS
data plane by encoding segments in an MPLS label stack. It also can
be applied to the IPv6 data plane by encoding a list of segment
identifiers in IPv6 Segment Routing Extension Header (SRH). In this
document is described the use of unified segment identifiers in use
cases where interworking between SR-MPLS and SRv6 is required.
Status of This Memo
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This Internet-Draft will expire on May 6, 2020.
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Copyright Notice
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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. Requirements for Using SRv6 in Backhaul . . . . . . . . . . . 4
3. Using SRv6 U-SID in Backhaul . . . . . . . . . . . . . . . . 4
3.1. Smoothly Upgrading to SRv6 from SR-MPLS . . . . . . . . . 4
3.2. Interworking Between SRv6 and SR-MPLS . . . . . . . . . . 5
3.3. Compressing SRv6 Header Effectively . . . . . . . . . . . 6
3.4. Support a Super-large-scale Networking and Flexibility in
Assigning Addresses . . . . . . . . . . . . . . . . . . . 6
4. Operations with Unified Segment Identifier . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
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 the Source Routing
Extension Header (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
[I-D.ietf-spring-segment-routing-mpls], also referred to as SR-MPLS.
On the other hand, the size of the IPv6 segment identifier (SID)
presents a scaling challenge to use topological instructions that
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define a strict explicitly routed path in combination with service-
based instructions. At the same time, that is where the SR-MPLS
approach provides better results due to smaller SID length.
SR-MPLS currently, more often than SRv6, is used in metro networks.
With the gradual deployment of SRv6 in the core networks, it becomes
necessary to support interworking between SR-MPLS and SRv6.
Operationally it would be more efficient and straightforward if SRv6
can use the same size SIDs as in SR-MPLS. The SRH can be extended to
use the same as in SR-MPLS SID length to support the unified segment
identifier (U-SID) [I-D.mirsky-6man-unified-id-sr]. As a result of
using this approach, U-SIDs can be used end-to-end across a tunnel
that spans over SR-MPLS and SRv6 domains.
In this document is described the use of unified segment identifiers,
encoded as MPLS label and/or 32 bits-long address, in use cases when
interworking between SR-MPLS and SRv6 networks is required.
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 data plane
SID: Segment Identifier
IGP: Interior Gateway Protocol
OAM: Operation, Administration and Maintenance
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. Requirements for Using SRv6 in Backhaul
2G/3G/4G backhaul networks widely deploy MPLS to connect wireless
services. Many operators are already deploying 5G networks. To
optimize the operation of the network, many operators intent to adopt
the segment routing. Currently, given maturity of SR-MPLS, it has
been deployed on a large scale. Meanwhile the requirements of 5G
super-large-scale number of connections accelerate the deployment of
IPv6 networks. Thus, logically, operators consider SRv6 solution to
fulfill the 5G backhaul requirement. But the backhaul network could
not deploy SRv6 in one day, especially if it has already been using
MPLS and SR-MPLS. It might be reasonable to upgrade from MPLS to SR-
MPLS and then to SRv6. There are several essential operational
requirements for the deployment of SRv6 in 5G backhaul network:
1. Ensure the ability to transform the existing SR-MPLS backhaul
network into an SRv6 5G backhaul network incrementally.
2. Support interworking between SRv6 and SR-MPLS domains in the
network.
3. Support SRv6 header compressing.
4. Support super-large-scale networking and address planning
3. Using SRv6 U-SID in Backhaul
U-SID provides a solution that complies to the 5G backhaul
requirements.
3.1. Smoothly Upgrading to SRv6 from SR-MPLS
SR-MPLS uses a segment encoded as a label in an MPLS label stack to
simplify the backhaul network. It leverages the advantages of both
source-routing and MPLS. Existing backhaul networks that use MPLS
can be first updated to use SR-MPLS. SRv6 uses the segment encoded
as an identifier in IPv6 SRH. The SR-MPLS and SRv6 protocol stacks
are illustrated in Figure 1.
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+-----------------+ +-----------------+
| Ethernet | | Ethernet |
+-----------------+ +-----------------+
| | | |
| SR-MPLS | | SRv6 |
| | | |
+-----------------+ +-----------------+
| Payload | | Payload |
+-----------------+ +-----------------+
Figure 1: SR-MPLS and SRv6 Protocol Stacks
A segment identifier in SR-MPLS occupies 32 bits, and in SRv6 - 128
bits. As the backhaul infrastructure being upgraded to IPv6,
operators are looking for technology that would reuse SR-MPLS by re-
mapping the label table. But the namespace in SR-MPLS is limited and
couldn't build the new segment identifiers to the global network.
Using U-SID with SRv6 allows the reuse of the 32-bit SIDs, which are
the same as in SR-MPLS. Thus, U-SID with SRv6 can be reused in
backhaul to minimize the impact on existing SR-MPLS services and
support smooth rollout of SRv6. The only additional task is to
assign U-SIDs to the SRv6 domain. The controller could create an
end-to-end SR tunnel using 32bit-long segments identifiers to stitch
the SR-MPLS and SRv6 domains.
3.2. Interworking Between SRv6 and SR-MPLS
For a 5G backhaul network, the operators want to try their best to
reuse the existing transport network. Consequently, they must
consider the SRv6 interworking with SR-MPLS while deploying SRv6.
Using U-SID offers a practical approach to native interworking
between SR-MPLS and SRv6 domains because an operator in both domains
can use segment identifiers of the same format, U-SID.
Using U-SID interworking between SRv6 and SR-MPLS brings some
significant advantages:
1. An end-to-end LSP can be created across the access/aggregation
network with SR-MPLS and core network with SRv6.
2. An end-to-end OAM and protection mechanism can be supported
reusing SR-MPLS
The SR-MPLS and SRv6 interworking is illustrated in Figure 2. An
end-to-end SR tunnel from A to F crosses the SR-MPLS and SRv6
domains. Using U-SID end-to-end LSP can reuse SR-MPLS forwarding,
and support end-to-end OAM and protection.
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+-----+ +-----+ +-----+ +-----+
LSP-->| A +-------+ B +-------+ E +-------+ F |-->
+-----+ +--+--+ +--+--+ +--+--+
| SR-MPLS | | SRv6 |
| Access/Agg | | Core |
+-----+ +--+--+ +--+--+ +--+--+
| C |-------| D +-------+ G +-------+ H |
+-----+ +-----+ +-----+ +-----+
Figure 2: SR-MPLS and SRv6 Interworking
3.3. Compressing SRv6 Header Effectively
While deploying SRv6 in the backhaul network, the SRv6 header
overhead must be considered. Typically there a maximum of ten hops
for an end-to-end transport path. The header overhead is 1280 bits
(10*128 bit SRH) using SRH with the 128-bit SID without OAM and
protection. It will be reduced to 320 bits (3*128 bit SRH) using
U-SID SRv6 with 32-bit SID. So the compressing rate is more than 70%
(from at least 10*128 bit SRH to 3*128 bit SRH).
3.4. Support a Super-large-scale Networking and Flexibility in
Assigning Addresses
The scale of the backhaul network is up to 10K nodes. A network of
such size needs to support to address up to 10K nodes. U-SID SRv6
can support the 2^20 labels as the same with MPLS, and it's enough
for a super-large-scale backhaul networking. Since IPv6 solves the
problem of a shortage of IPv4 addresses, it should not be using a
shorter IPv6 address, i.e., a shorter prefix plus a shorter offset.
That will violate the original IPv6 design. On the other hand, using
SRv6 should not require the assignment of special addresses for the
operator's network. U-SID can preserve the full 128-bit addresses by
re-mapping the table. To use U-SID in SRv6 doesn't require the IPv6
address and SRv6 segments planning, such as the address prefix
allocation. The operator would reuse the current address assignment
and planning, thus minimizing the impact on the backhaul network.
4. 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.
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5. IANA Considerations
This document has no requests to IANA. This section can be removed
before the publication.
6. Security Considerations
This specification inherits all security considerations of [RFC8402]
and [I-D.ietf-6man-segment-routing-header].
7. Acknowledgements
TBD
8. 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-26 (work in progress), October 2019.
[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.
[I-D.mirsky-6man-unified-id-sr]
Cheng, W., Mirsky, G., Peng, S., Aihua, L., Wan, X., and
C. Wei, "Unified Identifier in IPv6 Segment Routing
Networks", draft-mirsky-6man-unified-id-sr-03 (work in
progress), July 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>.
[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>.
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[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
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
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
Wan Xiaolan
New H3C Technologies Co. Ltd
No.8, Yongjia Road, Haidian District
Beijing
China
Email: wxlan@h3c.com
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Cheng Wei
Centec
Building B, No.5 Xing Han Street, Suzhou Industrial Park
Suzhou
China
Email: Chengw@centecnetworks.com
Shay
Broadcom
Israel
Email: shay.zadok@broadcom.com
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