SPRING C. Filsfils, Ed.
Internet-Draft P. Camarillo, Ed.
Intended status: Standards Track Cisco Systems, Inc.
Expires: August 16, 2020 D. Cai
D. Voyer
Bell Canada
I. Meilik
K. Patel
Arrcus, Inc.
W. Henderickx
P. Jonnalagadda
Barefoot Networks
D. Melman
February 13, 2020

Network Programming extension: SRv6 uSID instruction


The SRv6 "micro segment" (SRv6 uSID or uSID for short) instruction is defined and illustrated.

It is a straightforward extension to the SRv6 Network Programming model and its SRH encapsulation.

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.

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 August 16, 2020.

Copyright Notice

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Table of Contents

1. Introduction

SRv6 Network Programming [I-D.ietf-spring-srv6-network-programming] defines a mechanism to build a network program with topological and service segments. It leverages the SRH [I-D.ietf-6man-segment-routing-header] to encode a network program together with optional metadata shared among the different SIDs.

This draft extends SRv6 Network Programming with a new type of SRv6 SID behavior: SRv6 uN. This is combined with the rest of instructions of the network program and the SRH encapsulation to build programs in a scalable and efficient way.

2. Terminology

The SRv6 Network Programming [I-D.ietf-spring-srv6-network-programming] and SRH [I-D.ietf-6man-segment-routing-header] terminology is leveraged and extended with the following terms:

uSID carrier: a 128bit SRv6 SID of format <uSID-Block><Active-uSID><Next-uSID>...<Last-uSID><End-of-Carrier>...<End-of-Carrier>. A uSID carrier can be encoded in the Destination Address of an IPv6 header or at any position in the Segment List of an SRH.

uSID block: A block of uSID's

uSID: in this document a 16-bit ID. A different uSID length may be used.

Active uSID: first uSID after the uSID block

Next uSID: next uSID after the Active uSID

Last uSID: from left to right, the last uSID before the first End-of-Carrier uSID

End-of-Carrier: reserved ID used to mark the end of a uSID carrier. The value 0000 is selected as End-of-Carrier. All of the empty uSID carrier positions must be filled with the End-of-Carrier ID. Hence, the End-of-Carrier can be present more than once in a uSID carrier.

Parent (node): the node at which an uSID is instantiated. The uSIDs are instantiated on a per-parent node basis.

Behavior of an uSID: the SRv6 function associated with a given ID. Section 3 defines them.

2.1. Notation for human readability

For human readability, the examples in this document follow this notation:

3. SRv6 behaviors associated with a uSID

The SRv6 SRH encapsulation and its network programming model are extended with the following functions:

3.1. uN

The uN behavior is a variant of the endpoint behavior.

This behavior takes a 80b argument, "Arg", which contains the next uSIDs in the uSID carrier.

When N receives a packet whose IPv6 DA is S and S is a local uN SID, N does:

1.   IF DA[48..63] != 0                                       ;; Ref1
2.      Copy DA[48..127] into DA[32..111]
3.      Set DA[112..127] to 0x0000
4.      Forward the packet to the new DA
5.   ELSE
6.      Execute the End pseudocode                            ;; Ref2

Ref 1: DA[X..Y] refers to the bits from position X to Y (included) in the IPv6 Destination Address of the received packet. The bit 0 is the MSB, while the bit 127 is the LSB.

Ref 2: This refers to the End behavior as defined in Section 4.1 of [I-D.ietf-spring-srv6-network-programming]. The End behavior may be combined with the PSP, USP and USD flavours.

4. Routing

If N is configured with a uN SID 2001:db8::/32 then the operator must ensure that N advertises 2001:db8::/32 in routing.

5. Illustration

This section extends the illustrations for SRv6 Network Programming [I-D.filsfils-spring-srv6-net-pgm-illustration] to cover uSID. The reference topology is the same with the addition of link 6-8.

5.1. Reference diagram

Nodes 1 to 8 are considered within the network domain.

Nodes X and Y are outside the domain.

Nodes 1 and 8 act as PE respectively to nodes X and Y.

All the links within the domain have the same IGP metric. The IGP-metric shortest-path from 1 to 8 is 1-2-7-8 while the latency-metric shortest-path from 1 to 8 is 1-2-3-4-5-6-7-8.

            |       \ /
            |        6 
            |       / \
       1--- 2------7---8
      /                 \
     X                   Y 
Tenant100            Tenant100 with
                       IPv4 20/8 

Figure 1: Reference topology

5.2. SRv6 overlay with underlay optimization

Let us illustrate a low-latency SR-L3VPN service delivered to a packet (X,Y).

PE 1 encapsulates (X, Y) in an outer IPv6 header with DA = 2001:db8:0300:0500:0700:: and SRH (B:8:D0::; SL=1; NH=4). Leveraging the illustration conventions from SRv6 network programming, the following resulting packet leaves node 1 in the direction of node 3:

2001:db8:0300:0500:0700:: is a uSID carrier encoding a source routed stateless path via node 3 then 5 then 7.

B:8:D0:: is an End.DT4 SID instantiated at node 8.

1 sends this packet to 2, as 2 is on the shortest-path to 2001:db8:0300::/48 advertised by 3.

When 2 receives the packet, 2 performs a regular IPv6 FIB lookup. It finds a FIB entry for 2001:db8:0300::/48 and forwards along the shortest path to 3.

When 3 receives the packet, 3 matches 2001:db8:0300::/48 in its "My SID Table" and executes the uN behavior. The updated DA becomes 2001:db8:0500:0700::. Node 3 then performs a lookup on the updated DA and forwards the packet to 5 along the shortest path to 2001:db8:0500::/48.

The following packet leaves node 3:

4 forwards along the shortest path to 2001:db8:0500::/48.

When 5 receives the packet, 5 matches 2001:db8:0500::/48 in its "My SID Table" and executes the uN behavior. The updated DA becomes 2001:db8:0700::. 5 performs a lookup on the updated DA and forwards the packet to 7 along the shortest path to 2001:db8:0700::/48.

The following packet leaves node 5:

6 forwards along the shortest path to 2001:db8:0700::/48.

When 7 receives the packet, 7 matches 2001:db8:0700::/48 in its "My SID Table" and finds the bound function uN. As a result, Node 7 executes the "End with PSP and USD support" pseudocode, decrementing the SL value in the SRH, and updating the DA with the next SID B:8:D0::. Since the SL value is zero the SRH is removed. Node 7 performs a lookup on the updated DA and forwards along the shortest path.

The following packet leaves node 7:

8 receives it, performs the End.DT4 function and sends the IP packet (X, Y) towards its VPN destination.

This example illustrates the benefits highlighted in the next section.

6. Benefits

7. Running code

The hardware and software platforms listed below have demonstrated support for the uN instruction defined in this document.

Further on, all these implementations have participated in a joint interoperability testing.

Hardware implementations (in alphabetical order):

Software open-source implementations (in alphabetical order):

8. Security

The security rules defined in Section 7 of [I-D.ietf-spring-srv6-network-programming], protect intra-domain deployments that includes SRv6 uSID.

9. Work in progress

Future version of this document will include other uSID behaviors related to TE, VPN and service programming.

10. Acknowledgements

The authors would like to acknowledge Francois Clad, Peter Psenak, Ketan Talaulikar, Jakub Horn, Swadesh Agrawal, Zafar Ali, Darren Dukes, Kiran Sadshiran, Junaid Israr, Lakshmanan Srikanth, Asif Islam, Saleem Hafeez, Michael MacKenzie, Sushek Shekar, YuanChao Su, Alexander Preusche, Alberto Donzelli, Miya Kohno, David Smith, Ianik Semco, Bertrand Duvivier, Frederic Trate, Kris Michielsen, Eyal Dagan, Eli Stein, Ofer Iny, Elad Naor, Aviad Behar, Joseph Chin.

11. Contributors

Jisu Bhattacharyaa
Cisco Systems, Inc.
United States of America

Email: jisu@cisco.com

Kamran Raza
Cisco Systems, Inc.

Email: skraza@cisco.com

John Bettink
Cisco Systems, Inc.
United States of America

Email: jbettink@cisco.com

Tomonobu Niwa

Email: to-niwa@kddi.com

Luay Jalil
United States of America

Email: luay.jalil@one.verizon.com

Zhichun Jiang

Email: zcjiang@tencent.com

Ahmed Shawky
Saudi Telecom Company
Saudi Arabia

Email: ashawky@stc.com.sa

Nic Leymann
Deutsche Telekom

Email: N.Leymann@telekom.de

Dirk Steinberg
Lapishills Consulting Limited

Email: dirk@lapishills.com

Shawn Zandi
United States of America

Email: szandi@linkedin.com

Gaurav Dawra
United States of America

Email: gdawra@linkedin.com

Jim Uttaro
United States of America

Email: ju1738@att.com

Ning So
United States of America

Email: Ning.So@ril.com

Michael Fiumano
United States of America

Email: michael.f.fiumano@sprint.com

Mazen Khaddam
United States of America

Email: Mazen.Khaddam@cox.com

Jichun Ma
China Unicom

Email: majc16@chinaunicom.cn

Satoru Matsushima

Email: satoru.matsushima@g.softbank.co.jp

Francis Ferguson
United States of America

Email: Francis.Ferguson@centurylink.com

Takuya Miyasaka

Email: ta-miyasaka@kddi.com

Kentaro Ebisawa
Toyota Motor Corporation

Email: ebisawa@toyota-tokyo.tech

Yukito Ueno
NTT Communications Corporation

Email: yukito.ueno@ntt.com

12. References

12.1. Normative References

[I-D.ietf-6man-segment-routing-header] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S. and D. Voyer, "IPv6 Segment Routing Header (SRH)", Internet-Draft draft-ietf-6man-segment-routing-header-26, October 2019.
[I-D.ietf-spring-srv6-network-programming] Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., Matsushima, S. and Z. Li, "SRv6 Network Programming", Internet-Draft draft-ietf-spring-srv6-network-programming-09, February 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.

12.2. Informative References

[I-D.filsfils-spring-srv6-net-pgm-illustration] Filsfils, C., Camarillo, P., Li, Z., Matsushima, S., Decraene, B., Steinberg, D., Lebrun, D., Raszuk, R. and J. Leddy, "Illustrations for SRv6 Network Programming", Internet-Draft draft-filsfils-spring-srv6-net-pgm-illustration-01, August 2019.

Authors' Addresses

Clarence Filsfils (editor) Cisco Systems, Inc. Belgium EMail: cf@cisco.com
Pablo Camarillo Garvia (editor) Cisco Systems, Inc. Spain EMail: pcamaril@cisco.com
Dennis Cai Alibaba China EMail: d.cai@alibaba-inc.com
Daniel Voyer Bell Canada Canada EMail: daniel.voyer@bell.ca
Israel Meilik Broadcom Israel EMail: israel.meilik@broadcom.com
Keyur Patel Arrcus, Inc. United States of America EMail: keyur@arrcus.com
Wim Henderickx Nokia Belgium EMail: wim.henderickx@nokia.com
Prem Jonnalagadda Barefoot Networks United States of America EMail: prem@barefootnetworks.com
David Melman Marvell Israel EMail: davidme@marvell.com