Network working group X. Xu Internet Draft Huawei Category: Informational S.Sivabalan Cisco Expires: August 2014 February 8, 2014 Connecting SPRING Islands over IP Networks draft-xu-spring-islands-connection-over-ip-00 Abstract Segment Routing (SR) architecture [SR-ARCH] introduces a new MPLS paradigm in which a sender of a packet is allowed to partially or completely specify the route the packet takes through the network by using stacked MPLS labels. The current SR architecture requires an end-to-end MPLS Label Switched Path (LSP) between any two SR-enabled routers (e.g., two adjacent hops of a given explicit path). In order to enable SR to be deployed even when there are non-MPLS routers along the path between two SR-enabled routers, it is desirable to have an alternative, which allows the use of IP-based tunnels (e.g., GRE tunnels) to connect two SR-enabled routers. This document describes a mechanism for such usage. 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 http://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 8, 2014. Xu, et al. Expires August 8, 2014 [Page 1] Internet-Draft Connecting SPRING Islands over IP February 2014 Copyright Notice Copyright (c) 2013 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 (http://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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Conventions used in this document 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 [RFC2119]. Table of Contents 1. Introduction ................................................ 3 2. Terminology ................................................. 3 3. Packet Forwarding Process ................................... 3 4. Security Considerations ..................................... 4 5. IANA Considerations ......................................... 4 6. Acknowledgements ............................................ 4 7. References .................................................. 4 7.1. Normative References ................................... 4 7.2. Informative References ................................ 4 Authors' Addresses ............................................. 4 Xu, et al. Expires August 8, 2014 [Page 2] Internet-Draft Connecting SPRING Islands over IP February 2014 1. Introduction Segment Routing (SR) architecture [SR-ARCH] introduces a new MPLS paradigm in which a sender of a packet is allowed to partially or completely specify the route the packet takes through the network by using stacked MPLS labels. In other words, this new paradigm could support source routing by using the MPLS label stack where each MPLS label represents a given hop that the packet must go through. Here the MPLS label could be either locally significant or globally significant. The current SR architecture requires an end-to-end MPLS Label Switched Path (LSP) between any two SR-enabled routers (e.g., any two adjacent hops of a given explicit path). This means that SR cannot be implemented if there is a part of the path between those two SR- enabled routers that does not support MPLS. In order to enable SR to be deployed even when there are non-MPLS routers along the path between two SR-enabled routers, it is desirable to have an alternative, which allows the use of IP-based tunnels (e.g., GRE tunnels) to connect two SR-enabled routers which are specified as adjacent hops of a given explicit path. The tunnel destination address would be the address of next-hop SR-enabled router along the explicit path, and this would cause the packet to be delivered to the next explicit hop. In this procedure, the ingress and egress of IP-based tunnel themselves must support SR features including the MPLS forwarding capability, whereas the transit routers along the path between them don't need to support MPLS and SR. The above mechanism is beneficial for incrementally deployment of the SR technology, especially in the case where only a few specific routers (e.g., service function nodes) in addition to Provider Edge (PE) routers are actually required to be specified as explicit hops of the loose explicit path. 2. Terminology This memo makes use of the terms defined in [RFC1195] and [SR-ARCH]. 3. Packet Forwarding Process Assume a SR-enabled router X prepares to forward a MPLS packet to the next node segment Y which is identified by the top label of the MPLS packet, if the next-hop router Z which is physically adjacent to X is a non-SR router, X would pop the top label (if required) and then encapsulate the remaining MPLS packet into an IP-based tunnel(e.g., Xu, et al. Expires August 8, 2014 [Page 3] Internet-Draft Connecting SPRING Islands over IP February 2014 GRE) where the tunnel destination is an IP address of Y and the tunnel source is an IP address of X. The IP encapsulated packet would be forwarded according to the IP forwarding table. Upon receipt of that IP encapsulated packet, Y would decapsulate it and then process the decapsulated MPLS packet accordingly. As for which tunnel encapsulation type should be used by X, it can be manually specified on X or dynamically learnt from Y's advertisement of its tunnel encapsulation capability. How to advertise tunnel encapsulation capability is outside of the scope of this document. 4. Security Considerations TBD. 5. IANA Considerations No action is required for IANA. 6. Acknowledgements Thanks to. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [SR-ARCH] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment Routing Architecture", draft-filsfils-rtgwg- segment-routing-00 (work in progress), June 2013. 7.2. Informative References [RFC4023] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating MPLS in IP or GRE", RFC4023, March 2005. Authors' Addresses Xiaohu Xu Huawei Technologies, Beijing, China Xu, et al. Expires August 8, 2014 [Page 4] Internet-Draft Connecting SPRING Islands over IP February 2014 Phone: +86-10-60610041 Email: xuxiaohu@huawei.com Siva Sivabalan Cisco Systems Email: msiva@cisco.com