SPRING Working Group W. Cheng
Internet Draft China Mobile
Intended status: Standards Track P. Ma
Expires: July 10, 2024 China Telecom
F. Ren
China Unicom
C. Lin
New H3C Technologies
L. Gong
China Mobile
S. Zadok
Broadcom
M.Wu
CentecNetworks
X. Wang
Ruijie Networks Co., Ltd.
January 10, 2024
Encoding Network Slice Identification for SRv6
draft-cheng-spring-srv6-encoding-network-sliceid-08
Abstract
This document describes a method to encode network slicing
identifier within SRv6 domain.
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Table of Contents
1. Introduction...................................................3
1.1. Requirements Language.....................................3
2. Slice Identifier...............................................3
3. SLID Assignment................................................3
4. Per-Slice Forwarding...........................................5
5. Example........................................................5
6. Backward Compatibility.........................................6
7. Acknowledgements...............................................7
8. Security Considerations........................................7
9. IANA Considerations............................................7
10. References....................................................7
10.1. Normative References.....................................7
10.2. Informative References...................................7
Authors' Addresses................................................9
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1. Introduction
SRv6 Network Programming [RFC8986] enables the creation of overlays
with underlay optimization to be deployed in an SR domain [RFC8402].
As defined in [RFC8754], all inter-domain packets are encapsulated
for the part of the packet journey that is within the SR domain. The
outer IPv6 header [RFC8200] is originated by a node of the SR domain
and is destined to a node of the SR domain.
This document describes a novel method to encode slice identifier in
the outer IPv6 header of an SR domain. Unlike other proposed methods
before, which will bring side effects on existed functions, by
encoding network slicing identifier in the source IPv6 address of
the outer header, this method avoids the drawbacks which previous
proposals incur.
1.1. 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.
2. Slice Identifier
The Slice identifier (SLID) is a network slicing identifier encoded
within the IPv6 packet that allows transit routers to apply the
proper forwarding treatment with associated network resources.
[I-D.ietf-teas-ietf-network-slices] defines the network resource
mapped to the network slice as NRP (Network Resource Partition). A
NRP may be associated with a unique IETF network slice or a group of
slices. In this document, SLID also refers to NRP-ID, which is used
to identify the network resource used in the forwarding process.
3. SLID Assignment
When an SR domain enables network slicing, the ingress PE should
reserve least significant bits in a local IPv6 address for slicing
use. The number of bits used to encode SLID is governed by local
policy and uniform within the SR domain.
When a packet enters the SR domain from an ingress PE, the ingress
PE encapsulates the packet in an outer IPv6 header and optional SRH
as defined in [RFC8754]. The ingress PE MAY also classify the packet
into a slice and set the slice identifier as follows:
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o Write this SLID in the least significant bits of source address
of the outer IPv6 header.
o Set the SLID Presence Indicator (SPI) in the outer IPv6 header.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| SPI (Option A)| Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI (Option B) ~ |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- +
| |
+ Source Address +
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ SLID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Encoding of SLID and SPI
The SPI is used to inform transit routers that a SLID is encoded in
the packet. There are two possible places in the outer IPv6 header
that may be used to encode SPI:
o SPI Option A - Traffic Class: The SPI is encoded as a specific
bit in the Traffic Class field. The choice of the SPI bit is
governed by local policy and uniform within the SR domain.
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Traffic Class
+---------------+
| .....SPI Bit. |
+---------------+
o SPI Option B - Source Address: The SPI is encoded as a specific
prefix covering the Source Address. The assignment of the SPI
prefix is governed by local policy and uniform within the SR
domain. Furthermore, some bits in the SPI prefix can be masked,
which provides greater flexibility for network administrators to
plan IPv6 addresses.
Source Address
+------------+---------+---------+------+
| SPI Prefix | Node ID | Padding | SLID |
+------------+---------+---------+------+
4. Per-Slice Forwarding
Any router within the SR domain that forwards a packet with SPI set
uses the SLID to select a slice and apply per-slice policies.
The most significant bit of SLID may be used to carry an S-flag,
which is used to indicate whether the packet MUST be forwarded
strictly using the network resource associated with the SLID. When
the network resource associated with the SLID does not exist or is
not available, if the S-flag is set to 1, the packet MUST be
discarded, otherwise the packet SHOULD be forwarded using the
default network resource or ignoring the SLID.
+------------+
|S| SLID |
+------------+
5. Example
Figure 2 shows an example of network slice packet forwarding using
the proposed encoding method. Assume the SPI is encoded using option
B as the SPI prefix in Source Address.
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SPI prefix: AA::/64
+--------------+--------------+
| | |
v v v
+---+ +---+ +---+ +---+ +---+
|CE1|------|PE1|----------|P1 |----------|PE2|-----|CE2|
+---+ +---+ +---+ +---+ +---+
^
|
IPv6 Addr: AA::1:0:0 (Lowest 32 bits reserved for SLID)
+------------+ +------------+
| IPv6 | | IPv6 |
|SA=AA::1:0:5| |SA=AA::1:0:5|
+------------+ +------------+
| SRH | | SRH |
+-------+ +------------+ +------------+ +-------+
|Payload| --> | Payload | --> | Payload | --> |Payload|
+-------+ PE1 +------------+ P1 +------------+ PE2 +-------+
Figure 2: Packet Forwarding for Network Slice
The PE and P routers are configured to use the prefix AA::/64 as
SPI. The IPv6 address AA::1:0:0 is assigned to PE1 as the source
address used for network slicing. And the lowest 32 bits of the
address is reserved for SLID.
PE1 encapsulates the network slice packet with an outer IPv6 header
along with an SRH. The Source Address in the outer header is
AA::1:0:5, in which the lowest 32 bits carries the SLID 5. P1 checks
the Source Address and finds it matching the SPI prefix AA::/64. So,
P1 parses SLID 5 from the Source Address, and uses the network
resources associated with SLID 5 to forward the packet. PE2
decapsulates the outer IPv6 header and SRH.
6. Backward Compatibility
PE routers that do not set the SPI do not enable the SLID semantic
of the IPv6 source address bits. Hence, SLID-aware routers would not
attempt to classify these packets into a slice.
Any router that does not process the SPI nor the SLID forwards
packets as usual.
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7. Acknowledgements
The authors would like to thank AAAA, BBBB and CCCC for their
insightful feedback on this document.
8. Security Considerations
TBD
9. IANA Considerations
TBD
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, May 2017
[RFC8200] Deering, S., and Hinden, D., "Internet Protocol, Version 6
(IPv6) Specification", 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>.
10.2. Informative References
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986, DOI
10.17487/RFC8986, February 2021, <https://www.rfc-
editor.org/info/rfc8986>.
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[I-D.ietf-teas-ietf-network-slices] Farrel, A., Drake, J., Rokui,
R., Homma, S., Makhijani, K., Contreras, L. M., and J.
Tantsura, "Framework for IETF Network Slices", Work
inProgress, Internet-Draft, draft-ietf-teas-ietf-network-
slices-21, June 2023,
<https://www.ietf.org/archive/id/draft-ietf-teas-ietf-
network-slices-21.txt>.
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Authors' Addresses
Weiqiang Cheng
China Mobile
Beijing
China
Email: chengweiqiang@chinamobile.com
Peiyong Ma
China Telecom
Guangzhou
China
Email: mapeiy@chinatelecom.cn
Fenghua Ren
China Unicom
Beijing
China
Email: renfh3@chinaunicom.cn
Changwang Lin
New H3C Technologies
Beijing
China
Email: linchangwang.04414@h3c.com
Liyan Gong
China Mobile
Beijing
China
Email: gongliyan@chinamobile.com
Shay Zadok
Broadcom
Israel
Email: shay.zadok@broadcom.com
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Mingyu Wu
CentecNetworks
Suzhou Industrial Park
China
Email: wumy@centec.com
Xuewei Wang
Ruijie Networks Co., Ltd.
Beijing
China
Email: wangxuewei1@ruijie.com.cn
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