Network Working Group S. Kini, Ed. Internet-Draft Ericsson Intended status: Informational K. Kompella Expires: February 20, 2014 Juniper August 19, 2013 Entropy labels for source routed stacked tunnels draft-kini-mpls-entropy-label-src-stacked-tunnels-00 Abstract Source routed tunnel stacking is a technique that can be leveraged to provide a method to steer a packet through a controlled set of segments. This can be applied to the Multi Protocol Label Switching (MPLS) data plane. Entropy label (EL) is a technique used in MPLS to improve load balancing. This document examines how ELs are to be applied to source routed stacked tunnels. 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 February 20, 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 Kini & Kompella Expires February 20, 2014 [Page 1] Internet-Draft EL for source routed stacked tunnels August 2013 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 2. Abbreviations and Terminology . . . . . . . . . . . . . . . . 2 3. Entropy Labels for source routed stacked tunnels . . . . . . 3 3.1. Single EL at the bottom of the stack of tunnels . . . . . 4 3.2. An EL per tunnel in the stack . . . . . . . . . . . . . . 4 3.3. A re-usable EL for a stack of tunnels . . . . . . . . . . 4 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction The source routed stacked tunnels paradigm is leveraged by techniques such as Segment Routing (SR) [I-D.filsfils-rtgwg-segment-routing] to steer a packet through a set of segments. This can be directly applied to the MPLS data plane. Entropy labels (EL) [RFC6790] is a technique used by the MPLS data plane to do load balancing. Applying ELs to stacked tunnels brings up some issues and these are documented in Section 3. 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 [RFC2119]. 2. Abbreviations and Terminology EL - Entropy Label ELI - Entropy Label Identifier SR - Segment Routing ECMP - Equal Cost Multi Paths MPLS - Multi Protocol Label Switching Kini & Kompella Expires February 20, 2014 [Page 2] Internet-Draft EL for source routed stacked tunnels August 2013 SID - Segment Identifier 3. Entropy Labels for source routed stacked tunnels Stacked tunnels have several use-cases, one of which is service chaining [I-D.filsfils-rtgwg-segment-routing-use-cases]. Consider a service-chaining network in Figure 1. The source LSR S wants to send traffic to destination LSR D. This traffic is required to go through service nodes S1 and S2 to produce the service chain S-S1-S2-D. Segment Routing can be used to achieve this. Load balancing is required across the parallel links between P1 and S1. Load balancing is also required between the ECMP paths from S1 to S2, S1-P1-P2-P3-S2 and S1-P1-P2-P4-S2. The source LSR wants the intermediate LSRs P1 and P2 to take local load balancing decisions and does not specify the Segment Identifiers (SIDs) of specific interfaces. Entropy labels should be used to achieve the desired load balancing. Two possible ways to use the entropy labels and their associated tradeoffs are discussed below. We denote SN to be the node segment identifier (SID) of LSR N and SN{L1,L2,...} to denote the SID of the adjacency set for links {L1,L2,...} of LSR N and S-N to denote the SID for a service at service node N. The label stack that the source LSR S uses for the service chain can be or . The issues discussed in this document are equally applicable to both of these options. +-----+ +-----+ | S1 | +------| P3 |------+ +-----+ | +-----+ | L1| |L2 | | +-----+ +-----+ +-----+ +-----+ | S |-----| P1 |-----| P2 | | S2 | +-----+ +-----+ +-----+ +-----+ | | | +-----+ | +------| P4 |------+ +-----+ | +-----+ | D | +-----+ S=Source LSR, D=Destination LSR, S1,S2=service-nodes, L1,L2=links, P1,P2,P3,P4=Transit LSRs Figure 1: Service chaining use-case Kini & Kompella Expires February 20, 2014 [Page 3] Internet-Draft EL for source routed stacked tunnels August 2013 3.1. Single EL at the bottom of the stack of tunnels In this option a single EL is used for the entire label stack. The source LSR S encodes the entropy label (EL) below the labels of all the stacked tunnels. In Figure 1 label stack at LSR S would look like . Note that the notation in [RFC6790] is used to describe the label stack. An issue with this approach is that as the label stack grows due an increase in the number of SIDs, the EL correspondingly goes deeper in the label stack. As a result, intermediate LSRs (such as P1) that have to walk the label stack at least until the EL to perform load balancing decisions have to access a larger number of bytes in the packet header when making forwarding decisions. A network design using this approach, should ensure that all intermediate LSRs have the capability to traverse the maximum label stack depth in order to do effective load balancing. The use- case for which the tunnel stacking is applied would determine the maximum label stack depth. 3.2. An EL per tunnel in the stack In this option each tunnel in the stack can be given its own EL. The source LSR pushes an before pushing a tunnel label when load balancing is required to direct traffic on that tunnel. For the same Figure 1 above, the source LSR S encoded label stack would be where all the ELs would typically have the same value. Accessing the EL at an intermediate LSR is independent of the depth of the label stack and hence independent of the specific use-case to which the stacked tunnels are applied. A drawback is that the depth of the label stack grows significantly, almost 3 times as the number of labels in the label stack. The network design should ensure that source LSRs should have the capability to push such a deep label stack. Also, the bandwidth overhead and potential MTU issues of deep label stacks should be accounted for in the network design. 3.3. A re-usable EL for a stack of tunnels In this option an LSR that terminates a tunnel re-uses the EL of the terminated tunnel for the next inner tunnel. It does this by storing the EL from the outer tunnel when that tunnel is terminated and re- inserting it below the next inner tunnel label during the label swap operation. The LSR that stacks tunnels SHOULD insert an EL below the outermost tunnel. It SHOULD NOT insert ELs for any inner tunnels. For the same Figure 1 above, the source LSR S encoded label stack would be . At P1 the outgoing label stack would be after it has load balanced to one of the links L1 or L2. At S1 the outgoing Kini & Kompella Expires February 20, 2014 [Page 4] Internet-Draft EL for source routed stacked tunnels August 2013 label stack would be . At P2 the outgoing label stack would be and it would load balance to one of the nexthop LSRs P3 or P4. Accessing the EL at an intermediate LSR is independent of the depth of the label stack and hence independent of the specific use-case to which the stacked tunnels are applied. 4. Acknowledgements The authors would like to thank Rob Shakir and TBD for their comments. 5. IANA Considerations This memo includes no request to IANA. 6. Security Considerations 7. References 7.1. Normative References [I-D.filsfils-rtgwg-segment-routing-use-cases] Filsfils, C., Francois, P., Previdi, S., Decraene, B., Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment Routing Use Cases", draft-filsfils-rtgwg-segment- routing-use-cases-01 (work in progress), July 2013. [I-D.filsfils-rtgwg-segment-routing] 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. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, November 2012. 7.2. Informative References [I-D.previdi-isis-segment-routing-extensions] Kini & Kompella Expires February 20, 2014 [Page 5] Internet-Draft EL for source routed stacked tunnels August 2013 Previdi, S., Filsfils, C., Bashandy, A., Gredler, H., and S. Litkowski, "IS-IS Extensions for Segment Routing", draft-previdi-isis-segment-routing-extensions-02 (work in progress), July 2013. [I-D.psenak-ospf-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., and R. Shakir, "OSPF Extensions for Segment Routing", draft- psenak-ospf-segment-routing-extensions-02 (work in progress), July 2013. Authors' Addresses Sriganesh Kini (editor) Ericsson Email: sriganesh.kini@ericsson.com Kireeti Kompella Juniper Email: kireeti@juniper.net Kini & Kompella Expires February 20, 2014 [Page 6]