Network Working Group X. Xu, Ed.
Internet-Draft S. Bryant, Ed.
Intended status: Standards Track Huawei
Expires: December 30, 2017 R. Raszuk
Bloomberg LP
U. Chunduri
Huawei
L. Contreras
Telefonica I+D
L. Jalil
Verizon
H. Assarpour
Broadcom
G. Van De Velde
Nokia
J. Tantsura
Individual
S. Ma
Juniper
June 28, 2017

Unified Source Routing Instruction using MPLS Label Stack
draft-xu-mpls-unified-source-routing-instruction-02

Abstract

MPLS-SPRING (a.k.a., MPLS Segment Routing) is an MPLS data plane-based source routing paradigm in which a sender of a packet is allowed to partially or completely specify the route the packet takes through the network by imposing stacked MPLS labels to the packet. MPLS-SPRING could be leveraged to realize a unified source routing mechanism across MPLS, IPv4 and IPv6 data planes by using a unified source routing instruction set while preserving backward compatibility with MPLS-SPRING.

Status of This Memo

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This Internet-Draft will expire on December 30, 2017.

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Table of Contents

1. Introduction

MPLS-SPRING [I-D.ietf-spring-segment-routing-mpls] (a.k.a., MPLS Segment Routing) is an MPLS data plane-based source routing paradigm in which a sender of a packet is allowed to partially or completely specify the route the packet takes through the network by imposing stacked MPLS labels to the packet. MPLS-SPRING could be leveraged to realize a unified source routing mechanism across MPLS, IPv4 and IPv6 data planes by using a unified source routing instruction set while preserving backward compatibility with MPLS-SPRING. More specifically, the source routing instruction set information contained in a source routed packet could be uniformly encoded as an MPLS label stack no matter the underlay is IPv4, IPv6 or MPLS. Although the source routing instructions are encoded as MPLS labels, this is a hardware convenience rather than an indication that the whole MPLS protocol stack and in particular the MPLS control protocols need to be deployed. Note that the complexity associated with the whole MPLS protocol stack is largely due to the complex control plane protocols.

The traditional IPv4 and IPv6 source routing mechanisms by use of IPv4 Source Routing Options and IPv6 Route Header Type 0 Extension respectively have been deprecated due to their obvious security vulnerabilities. IPv6 SPRING (a.k.a., SRv6) [I-D.ietf-6man-segment-routing-header] is a newly proposed IPv6 source routing mechanism in which the source route instruction information is encoded as an ordered list of 128-bit long IPv6 addresses and contained in the Source Routing Header (SRH). Although it has overcome the security vulnerability issues associated with the traditional IPv6 source routing mechanism as claimed in [I-D.ietf-6man-segment-routing-header], it still has the following obvious drawbacks which need to be addressed: 1) the encapsulation overhead is significant especially when the list of the explicit routing hops is very long; 2) for those transit IPv6 routers that don't support the flow label-based load-balancing mechanism yet, the ECMP load-balancing effect may be impacted seriously if they could not recognize the SRH and therefore could not obtain the five tuple of the source routed IPv6 packet; 3) it requires a totally new forwarding logic on basis of the SRH and the forwarding performance associated with the IPv6 SRH may still be a big concern for some hardware platforms; 4) the SRH-based souring routing mechanism could not be applied to IPv4 networks.

Section 3 describes various use cases for the unified source routing instruction mechanism and Section 4 describes a typical application scenario and how the packet forwarding happens.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

2. Terminology

This memo makes use of the terms defined in [RFC3031] and [I-D.ietf-spring-segment-routing-mpls].

3. Use Cases

The unified source routing mechanism across IPv4, IPv6 and MPLS is useful at least in the following use cases:

4. Packet Forwarding Procedures

 +-----+       +-----+       +-----+        +-----+        +-----+
 |  A  +-------+  B  +-------+  C  +--------+  D  +--------+  H  |
 +-----+       +--+--+       +--+--+        +--+--+        +-----+
                  |             |              |
                  |             |              |
               +--+--+       +--+--+        +--+--+
               |  E  +-------+  F  +--------+  G  |
               +-----+       +-----+        +-----+

      +--------+
      |IP(A->E)|
      +--------+                 +--------+
      |  L(G)  |                 |IP(E->G)|
      +--------+                 +--------+        +--------+
      |  L(H)  |                 |  L(H)  |        |IP(G->H)|
      +--------+                 +--------+        +--------+
      | Packet |     --->        | Packet |  --->  | Packet |
      +--------+                 +--------+        +--------+
                         Figure 1

[RFC7510] or MPLS-over-GRE [RFC4023]) towards router E and then send it out. In other words, router A would pop the top label and then encapsulate the MPLS packet with an IP-based tunnel towards router E. When the IP-encapsulated MPLS packet arrives at router E, router E would strip the IP-based tunnel header and then process the decapsulated MPLS packet accordingly. Since there is no LSP towards router G which is indicated by the current top label of the decapsulated MPLS packet, router E would replace the current top label with an IP-based tunnel towards router G and send it out. When the packet arrives at router G, router G would strip the IP-based tunnel header and then process the decapsulated MPLS packet. Since there is no LSP towards router H, router G would replace the current top label with an IP-based tunnel towards router H. Now the packet encapsulated with the IP-based tunnel towards router H is exactly the original packet that router A had intended to send towards router H. If the packet is an MPLS packet, router G could use any IP-based tunnel for MPLS (e.g., MPLS-over-UDP [RFC7510] or MPLS-over-GRE [RFC4023]). If the packet is an IP packet, router G could use any IP tunnel for IP (e.g., IP-in-UDP [I-D.xu-intarea-ip-in-udp] or GRE [RFC2784]). That original IP or MPLS packet would be forwarded towards router H via an IP-based tunnel. When the encapsulated packet arrives at router H, router H would decapsulate it into the original packet and then process it accordingly.

Note that in the above description, it's assumed that the label associated with each prefix-SID advertised by the owner of the prefix-SID is a Penultimate Hop Popping (PHP) label (e.g., the NP-flag [I-D.ietf-ospf-segment-routing-extensions] associated with the corresponding prefix SID is not set). Figure 2 demostrates the packet walk in the case where the label associated with each prefix-SID advertised by the owner of the prefix-SID is not a Penultimate Hop Popping (PHP) label (e.g., the NP-flag [I-D.ietf-ospf-segment-routing-extensions] associated with the corresponding prefix SID is set). Although the above description is based on the use of prefix-SIDs, the unified source routing instruction approach is actually applicable to the use of adj-SIDs as well. For instance, when the top label of a received MPLS packet indicates an given adj-SID and the corresponding adjacent node to that adj-SID is not MPLS-capable, the top label would be replaced by an IP-based tunnel towards that adjacent node and then forwarded over the correponding link indicated by that adj-SID.

 +-----+       +-----+       +-----+        +-----+        +-----+
 |  A  +-------+  B  +-------+  C  +--------+  D  +--------+  H  |
 +-----+       +--+--+       +--+--+        +--+--+        +-----+
                  |             |              |
                  |             |              |
               +--+--+       +--+--+        +--+--+
               |  E  +-------+  F  +--------+  G  |
               +-----+       +-----+        +-----+

      +--------+
      |IP(A->E)|
      +--------+                 +--------+
      |  L(E)  |                 |IP(E->G)|
      +--------+                 +--------+        +--------+
      |  L(G)  |                 |  L(G)  |        |IP(G->H)|
      +--------+                 +--------+        +--------+
      |  L(H)  |                 |  L(H)  |        |  L(H)  |
      +--------+                 +--------+        +--------+
      | Packet |     --->        | Packet |  --->  | Packet |
      +--------+                 +--------+        +--------+
                         Figure 2

Note that as for which tunnel encapsulation type should be used, it could be manually specified on tunnel ingress routers or be learnt from the tunnel egress routers' advertisements of its tunnel encapsulation capability. How to advertise the tunnel encapsulation capability using IS-IS or OSPF are specified in [I-D.ietf-isis-encapsulation-cap] and [I-D.ietf-ospf-encapsulation-cap] respectively.

5. Acknowledgements

Thanks Joel Halpern, Bruno Decraene and Loa Andersson for their insightful comments on this draft.

6. IANA Considerations

No IANA action is required.

7. Security Considerations

TBD.

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.

8.2. Informative References

[I-D.ietf-6man-segment-routing-header] Previdi, S., Filsfils, C., Raza, K., Leddy, J., Field, B., daniel.voyer@bell.ca, d., daniel.bernier@bell.ca, d., Matsushima, S., Leung, I., Linkova, J., Aries, E., Kosugi, T., Vyncke, E., Lebrun, D., Steinberg, D. and R. Raszuk, "IPv6 Segment Routing Header (SRH)", Internet-Draft draft-ietf-6man-segment-routing-header-06, March 2017.
[I-D.ietf-isis-encapsulation-cap] Xu, X., Decraene, B., Raszuk, R., Chunduri, U., Contreras, L. and L. Jalil, "Advertising Tunnelling Capability in IS-IS", Internet-Draft draft-ietf-isis-encapsulation-cap-01, April 2017.
[I-D.ietf-mpls-spring-entropy-label] Kini, S., Kompella, K., Sivabalan, S., Litkowski, S., Shakir, R. and j. jefftant@gmail.com, "Entropy label for SPRING tunnels", Internet-Draft draft-ietf-mpls-spring-entropy-label-06, May 2017.
[I-D.ietf-ospf-encapsulation-cap] Xu, X., Decraene, B., Raszuk, R., Contreras, L. and L. Jalil, "Advertising Tunneling Capability in OSPF", Internet-Draft draft-ietf-ospf-encapsulation-cap-04, June 2017.
[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", Internet-Draft draft-ietf-ospf-segment-routing-extensions-17, June 2017.
[I-D.ietf-spring-segment-routing-ldp-interop] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B. and S. Litkowski, "Segment Routing interworking with LDP", Internet-Draft draft-ietf-spring-segment-routing-ldp-interop-08, June 2017.
[I-D.ietf-spring-segment-routing-mpls] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing with MPLS data plane", Internet-Draft draft-ietf-spring-segment-routing-mpls-10, June 2017.
[I-D.xu-intarea-ip-in-udp] Xu, X., Lee, Y. and F. Yongbing, "Encapsulating IP in UDP", Internet-Draft draft-xu-intarea-ip-in-udp-04, December 2016.
[I-D.xu-mpls-service-chaining] Xu, X., Bryant, S., Assarpour, H., Shah, H., Contreras, L., daniel.bernier@bell.ca, d., jefftant@gmail.com, j. and S. Ma, "Service Chaining using an Unified Source Routing Instruction", Internet-Draft draft-xu-mpls-service-chaining-02, May 2017.
[I-D.xu-mpls-spring-islands-connection-over-ip] Xu, X., Raszuk, R., Chunduri, U., Contreras, L. and L. Jalil, "Connecting MPLS-SPRING Islands over IP Networks", Internet-Draft draft-xu-mpls-spring-islands-connection-over-ip-00, October 2016.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D. and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, DOI 10.17487/RFC2784, March 2000.
[RFC3031] Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001.
[RFC4023] Worster, T., Rekhter, Y. and E. Rosen, "Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005.
[RFC4817] Townsley, M., Pignataro, C., Wainner, S., Seely, T. and J. Young, "Encapsulation of MPLS over Layer 2 Tunneling Protocol Version 3", RFC 4817, DOI 10.17487/RFC4817, March 2007.
[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R. and D. Black, "Encapsulating MPLS in UDP", RFC 7510, DOI 10.17487/RFC7510, April 2015.
[RFC7665] Halpern, J. and C. Pignataro, "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015.

Authors' Addresses

Xiaohu Xu (editor) Huawei EMail: xuxiaohu@huawei.com
Stewart Bryant (editor) Huawei EMail: stewart.bryant@gmail.com
Robert Raszuk Bloomberg LP EMail: robert@raszuk.net
Uma Chunduri Huawei EMail: uma.chunduri@gmail.com
Luis M. Contreras Telefonica I+D EMail: luismiguel.contrerasmurillo@telefonica.com
Luay Jalil Verizon EMail: luay.jalil@verizon.com
Hamid Assarpour Broadcom EMail: hamid.assarpour@broadcom.com
Gunter Van De Velde Nokia Antwerp Belgium EMail: gunter.van_de_velde@nokia.com
Jeff Tantsura Individual EMail: jefftant.ietf@gmail.com
Shaowen Ma Juniper EMail: mashao@juniper.net