SRv6 for Inter-Layer Network Programming
draft-dong-spring-srv6-inter-layer-programming-10
This document is an Internet-Draft (I-D).
Anyone may submit an I-D to the IETF.
This I-D is not endorsed by the IETF and has no formal standing in the
IETF standards process.
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Liuyan Han , Jie Dong , Minxue Wang , Ran Chen , Zongpeng Du | ||
| Last updated | 2024-12-17 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-dong-spring-srv6-inter-layer-programming-10
SPRING Working Group L. Han
Internet-Draft China Mobile
Intended status: Standards Track J. Dong
Expires: 20 June 2025 Huawei Technologies
M. Wang
China Mobile
R. Chen
ZTE Corporation
Z. Du
China Mobile
17 December 2024
SRv6 for Inter-Layer Network Programming
draft-dong-spring-srv6-inter-layer-programming-10
Abstract
The Segment Routing over IPv6 (SRv6) Network Programming framework
enables a network operator or an application to specify a packet
processing program by encoding a sequence of instructions in the IPv6
packet header.
Following the SRv6 Network Programming concept, this document defines
SRv6 based mechanisms for inter-layer network programming, which can
help to integrate the packet network layer with its underlying layers
efficiently. For inter-layer path programming, a new SRv6 behavior
is defined for steering packets to underlay network connections. The
applicability of this new SRv6 behavior in typical scenarios is
illustrated.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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 20 June 2025.
Han, et al. Expires 20 June 2025 [Page 1]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
Copyright Notice
Copyright (c) 2024 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 publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Use Cases of Inter-Layer Network Programming . . . . . . . . 3
2.1. IP and Optical Inter-layer Path Programming . . . . . . . 3
2.2. IP and MTN Inter-layer Path Programming . . . . . . . . . 3
3. SRv6 Behavior for Inter-Layer Programming . . . . . . . . . . 4
4. Application of SRv6 Inter-Layer Programming . . . . . . . . . 6
4.1. IP and Optical Integration . . . . . . . . . . . . . . . 6
4.2. IP and MTN Integration . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
In many network scenarios, the operator owns a multi-layered network.
In layer-3, the technology has converged to IP, while there can be
different technologies in layer-2 and below. In such networks, the
cross-layer planning and optimization is considered more efficient
than independent planning and operation of the layer-3 and the
underlying networks in terms of resource utilization and SLA
assurance, but it is also considered more complicated. Thus a
mechanism for flexible and efficient inter-layer network integration
is desired.
Segment Routing over IPv6 (SRv6) [RFC8986] enables a network operator
or an application to specify a packet processing program by encoding
a sequence of instructions in the IPv6 packet header. Currently SRv6
Han, et al. Expires 20 June 2025 [Page 2]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
does not consider about the network layers under the IP layer.
However, with the capability of SRv6 network programming, it is
possible to achieve seamless integration between IP (layer-3) and the
underlying (layer-2 and below) networks.
Following the SRv6 network programming concept, this document defines
a new SRv6 behavior, which can be used for steering packets to
underlay network connections, so that the packet network layer can be
integrated with the underlying layers efficiently. The applicability
of this new SRv6 behavior in typical inter-layer network programming
scenarios is also illustrated. The proposed mechanism is applicable
to networks in which the IP layer and its underlay network are under
the same administration, and the necessary information of the
underlay connections is allowed to be exposed to the IP layer for
inter-layer path programming.
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. Use Cases of Inter-Layer Network Programming
2.1. IP and Optical Inter-layer Path Programming
In many network scenarios, the underlay of the IP network is an
optical network. The IP network and optical network are usually
managed separately, the optical network works as an underlay which is
normally invisible to the IP network. In some cases, the optical
path resources and the IP path resources may not be one-to-one
mapping, which makes the redundant optical paths not fully used by
the IP layer. In some other cases, there may be optical paths
between non-adjacent IP nodes thus they are not visible in the L3
topology, thus they can not be used for carrying traffic based on IP
routing. However, such optical paths may be used for inter-layer
traffic engineering.
2.2. IP and MTN Inter-layer Path Programming
The architecture of Metro Transport Network (MTN) is defined in
[ITU-T_G.8310]. In an MTN based network, network nodes can support
two forwarding modes: per-hop IP packet forwarding and the MTN Path
(MTNP) layer cross-connect. An MTN path is a multi-hop underlay
transport path which may be established between any two nodes in the
MTN network, and the intermediate nodes on the MTN path will forward
Han, et al. Expires 20 June 2025 [Page 3]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
the traffic based on the pre-established MTN cross-connect without IP
table lookup. Thus an MTN path is considered as an underlay
connection between two remote MTN nodes. Although in some cases it
is possible to set up a layer-3 adjacency between the two endpoints
of the MTN path, it will make the provisioning of MTN path
complicated. Moreover, in some cases the two endpoints may reside in
different IGP areas or ASes, which makes a layer-3 adjacency between
them more challenging. Last but not the least, the MTN path may be
provisioned unidirectionally, which cannot pass the bidirectional
connectivity check required for a layer-3 link. Since the MTN paths
are usually not visible in the L3 topology, it is difficult to
compute and establish an end-to-end inter-layer path which consists
of both the layer-3 network segments and the MTN paths.
3. SRv6 Behavior for Inter-Layer Programming
In this section, a new SRv6 Endpoint Behavior called SRv6 END.IL
Behavior is proposed, which can be used for SRv6 based inter-layer
path programming.
The "Endpoint with inter-layer connection" behavior ("End.IL" for
short) is a variant of the SRv6 End behavior as defined in [RFC8986].
Its main use is for SRv6 based inter-layer path programming and
traffic engineering. The End.IL behavior steers packets to a remote
network node via underlay network connections.
The underlay network connections may be realized using Metro
Transport Network (MTN) paths [ITU-T_G.8310], ODUk or DWDM
connections, or other technologies which work as the underlay of the
IP network. Usually the underlay connections are invisible in the L3
topology and are not considered in IP distributed route computation
(e.g. SPF). However, this is just the expected behavior in some
inter-layer programming scenarios, where the underlay connections are
provisioned for traffic engineering of specific types of services.
The SRv6 End.IL SIDs can be used together with other types of SRv6
SIDs to build SRv6 SID lists for inter-layer path programming.
Any SID instance of this behavior is associated with an underlay
network connection, which connects to a remote network node.
When node N receives a packet destined to S and S is a local End.IL
SID, N does the following:
Han, et al. Expires 20 June 2025 [Page 4]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
S01. When an SRH is processed {
S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S11. }
S12. Decrement IPv6 Hop Limit by 1
S13. Decrement Segments Left by 1
S14. Update IPv6 DA with Segment List[Segments Left]
S15. Send the packet through the underlay network connection
identified by S.
S16. }
Note that the underlay network connection in step 15 SHOULD be
established before the associated End.IL SID is announced into the
network.
When forwarding packets through the underlay network connection
towards the remote endpoint node, depending on the type of
connection, layer-2 encapsulation may be required. The information
needed for layer-2 encapsulation may be provisioned via mechanisms
such as static Neighbor Discovery (ND) cache or using specific MAC
address. In some network scenarios where there is only one underlay
network connection between two layer-3 nodes, the use of End.IL SID
could be optional. In some implementations, the End.IL SID may
optionally contain the arguments field, which can be used to encode
the type and identifier information of the underlay connection. The
details are out of the scope of this document.
End.IL SIDs MAY be allocated by the network nodes and announced to
the network controller with the information of the underlay
connections using IGP [RFC1195] [RFC2328] or BGP-LS [RFC9552].
Alternatively, End.IL SIDs MAY be assigned by a centralized network
controller and advertised to the network nodes through Netconf/YANG
Han, et al. Expires 20 June 2025 [Page 5]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
[RFC6241] [RFC6020], BGP [RFC4271], or PCEP [RFC5440]. The detailed
protocol extensions are out of the scope of this document, and will
be described in separate documents. With the information of End.IL
SIDs, the network controller or headend nodes could use End.IL SIDs
together with other types of SRv6 SIDs to build SRv6 SID lists for
inter-layer TE path programming.
4. Application of SRv6 Inter-Layer Programming
4.1. IP and Optical Integration
Assuming that an operator owns both the IP and optical network, and
the operator needs to deploy E2E service across IP and optical
network, with traditional approaches the planning and service
provisioning would be complex and time consuming due of the manual
synergy needed between the operator's IP team and optical team. With
the introduction of SRv6 and the new SRv6 behaviors defined in this
document, one simplified approach for IP and optical integration is
to build a SRv6 SID list that integrates the path in both the IP
layer and the optical layer.
As the optical layer is not packet based, source routing mechanism
can not be directly used in the optical network. However, the
abstracted optical paths (e.g., with ODUk or DWDM) could be exposed
to the control system of the IP network using the SRv6 End.IL SIDs,
and some of the attributes of the optical paths may also be provided.
Based on this information, IP-optical inter-layer paths can be
computed and programmed using SRv6 SID lists to meet some specific
service requirements, such as low latency.
Han, et al. Expires 20 June 2025 [Page 6]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
----- ----- -----
| P1 |--------| P2 |--------| P3 |
----- ----- -----
/ |. |. |. \
----- / | . | . | . \ -----
| P7 | | . | . | . | P8 |
----- \ | . | . | ./ -----
\ | . | . | / .
----- . ----- . ----- .
| P4 |-------| P5 |--------| P6 | .
----- . ----- . ----- .
. . . . . .
. ===== . ===== . =====
. | O1 |----------| O2 |--------| O3 |
. ===== . ===== . =====
. | . | . |
. | . | . |
. | . | . |
. | . | . |
.| .| .|
===== ===== =====
| O4 |----------| O5 |--------| O6 |
===== ===== =====
Figure 1. IP and Optical Layered Network Topology
In Figure 1, P1 to P8 are IP nodes, and O1 to O6 are optical nodes.
Assume the operator needs to deploy a low latency path between P7 and
P8. With normal segment routing, an IP layer path with the segment
list {P7, P1, P2, P3, P8} can be used. If an optical path from O1 to
O3 exists, the End.IL SID as defined in this document can be used to
announce this optical path as an underlay interface or connection
with specific attributes into the IP network. The headend node or
the controller in IP layer can program an inter-layer TE path along
{P7, P1, (O1, O2, O3), P3, P8} or {P7, P1, (O4, O5, O6, O3), P3, P8}
which could provide lower latency.
The underlay optical path between O1 and O3 may be created in advance
or as a result of the request from the IP layer. The creation should
be done by the optical network controller (not shown in the figure).
The details of the process are out of scope of this document, and may
refer to [I-D.ietf-teas-actn-poi-applicability].
There is also another case of IP and Optical integration. Assume
there are two optical paths between P1 and P2. One is {P1, O1, O2,
P2} , and the other is {P1, O1, O4, O5, O2, P2}. With SRv6 inter-
layer programming, two separate SRv6 inter-layer SIDs can be
allocated for these two underlay connections respectively. One is
Han, et al. Expires 20 June 2025 [Page 7]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
P1::C2 for the underlay path {P1, O1, O2, P2}, and the other is
P1::C45 for the path {P1, O1, O4, O5, O2, P2}. The headend P7 or the
IP network controller will be informed about these two SRv6 SIDs and
the associated path attributes, so that the headend or the controller
can program different end-to-end inter-layer paths using SRv6 SID
lists with different SRv6 inter-layer SIDs for services with
different SLA requirements.
4.2. IP and MTN Integration
Assuming that an operator owns both an MTN network domain and an IP
network domain. In the MTN network, each MTN node has both the
layer-3 functionality and the MTN Path layer functionality. In
layer-3, all the MTN nodes are in a layer-3 network topology, which
connects to the IP network domain. In the MTN Path Layer, a set of
MTN paths are provisioned between the selected pairs of MTN nodes for
traffic engineering. In the MTN network, different types of services
may be carried using either a layer-3 path, an end-to-end MTN path,
or an inter-layer path comprising of both the layer-3 links and the
MTN paths as segments. In addition, For some type of services, end-
to-end paths across the IP domain and the MTN domain are needed,
which is comprised of both the layer-3 paths and the MTN path as
different segments.
Han, et al. Expires 20 June 2025 [Page 8]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
.......................................... ...........................
. . . .
. +----+ +----+ +----+ . . +----+ +----+ .
. | M1 |-----| M2 |-----| M3 |------| P1 |-----| P2 | .
. +----+ +----+ +----+ . . +----+ +----+ .
. / | | | . . | | \ .
. +----+ / | | | . . | | \+----+.
. | M7 |/ | | | . . | | | P5 |.
. +----+\ | | | . . | | /+----+.
. \ | | | . . | | / .
. \+----+ +----+ +----+ . . +----+ +----+ .
. | M4 |-----| M5 |-----| M6 |------| P3 |-----| P4 | .
. +----+ +----+ +----+ . . +----+ +----+ .
. . . .
. Layer-3 Topology MTN Network . . IP Network .
. . ...........................
----------------------------------------------------------------------
. MTN Path Layer Topology .
. .
. +----+ +----+ +----+ .
. | M1'|################| M3'| .
. +----+ ## +----+ ## +----+ .
. ## ## .
. +----+ ## ## .
. | M7'| ## .
. +----+ ## ## .
. ## ## .
. +----+ ## +----+ ## +----+ .
. | M4'|################| M6'| .
. +----+ +----+ +----+ .
. .
. .
..........................................
.
Figure 2. A network with MTN Domain and IP Domain
Han, et al. Expires 20 June 2025 [Page 9]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
Figure 2 gives an example of a network with a MTN domain and an IP
domain. M1 to M7 are MTN nodes, and P1 to P4 are IP nodes. The same
set of MTN nodes builds two separate network layers. The topology in
the IP layer shows the layer-3 connectivity between the MTN nodes and
the connectivity with the IP network domain, while the topology in
the MTN Path layer shows the MTN paths between the selected pair of
MTN nodes. An end-to-end path from M7 to P5 can be established in
layer-3 using an SRv6 SID list representing the layer-3 path {M7, M1,
M2, M3, P1, P2, P5}. While for services which require low latency,
with SRv6 inter-layer programming, an end-to-end path consisting of
both the layer-3 segments and MTN paths could be established using an
SRv6 SID list representing the inter-layer path {M7, M1::C3, P1, P2,
P5}, where the SRv6 SID M1::C3 represents the underlay MTN path M1'-
M3'.
This shows that it is convenient to use integrated SRv6 SID lists to
program inter-layer TE paths both within the MTN domain, and across
the IP and MTN domain using the combination of SRv6 L3 SIDs and the
SRv6 inter-layer SID.
5. Security Considerations
The security considerations of SRv6 in [RFC8754] [RFC8986] apply to
this document.
6. IANA Considerations
This document defines a new SRv6 Endpoint behavior called END.IL.
IANA has allocated the following code points for different flavors of
End.IL from the "SRv6 Endpoint Behaviors" sub-registry in the
"Segment-routing with IPv6 data plane (SRv6) Parameters" registry:
+------+--------+------------------------------------------+-----------+
| Value| Hex | Endpoint Behavior | Reference |
+------+--------+------------------------------------------+-----------+
| 150 | 0x0096 | End.IL | [This ID] |
| 151 | 0x0097 | End.IL with PSP | [This ID] |
| 152 | 0x0098 | End.IL with USP | [This ID] |
| 153 | 0x0099 | End.IL with USD | [This ID] |
| 154 | 0x009A | End.IL with PSP, USP & USD | [This ID] |
| 155 | 0x009B | End.IL with REPPLACE-CSID | [This ID] |
| 156 | 0x009C | End.IL with REPPLACE-CSID & PSP | [This ID] |
| 157 | 0x009D | End.IL with REPPLACE-CSID, PSP, USP & USD| [This ID] |
+------+--------+------------------------------------------+-----------+
Han, et al. Expires 20 June 2025 [Page 10]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
7. Acknowledgements
The authors would like to thank Xiaodong Chang, Yongjian Hu,
Alexander Vainshtein, Ketan Talaulikar and Zhibo Hu for their review
and comments.
8. References
8.1. Normative References
[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>.
[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>.
8.2. Informative References
[I-D.ietf-teas-actn-poi-applicability]
Peruzzini, F., Bouquier, J., Busi, I., King, D., and D.
Ceccarelli, "Applicability of Abstraction and Control of
Traffic Engineered Networks (ACTN) to Packet Optical
Integration (POI)", Work in Progress, Internet-Draft,
draft-ietf-teas-actn-poi-applicability-12, 5 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
actn-poi-applicability-12>.
[ITU-T_G.8310]
ITU-T, "ITU-T G.8310: Architecture of the metro transport
network", https://www.itu.int/rec/T-REC-
G.8310-202012-I/en, December 2020.
Han, et al. Expires 20 June 2025 [Page 11]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and
Traffic Engineering Information Using BGP", RFC 9552,
DOI 10.17487/RFC9552, December 2023,
<https://www.rfc-editor.org/info/rfc9552>.
Authors' Addresses
Liuyan Han
China Mobile
No.32 XuanWuMen West Street
Beijing, 100053
China
Email: hanliuyan@chinamobile.com
Jie Dong
Huawei Technologies
Huawei Campus, No.156 Beiqing Road
Beijing, 100095
China
Han, et al. Expires 20 June 2025 [Page 12]
Internet-Draft SRv6 Inter-Layer Network Programming December 2024
Email: jie.dong@huawei.com
Minxue Wang
China Mobile
No.32 XuanWuMen West Street
Beijing, 100053
China
Email: wangminxue@chinamobile.com
Ran Chen
ZTE Corporation
Nanjing
China
Email: chen.ran@zte.com.cn
Zongpeng Du
China Mobile
No.32 XuanWuMen West Street
Beijing, 100053
China
Email: duzongpeng@foxmail.com
Han, et al. Expires 20 June 2025 [Page 13]