Network Working Group R. Browne Internet-Draft A. Chilikin Intended status: Standards Track B. Ryan Expires: April 20, 2016 Intel October 19 2015 Network Service Header Time Stamping draft-browne-ietf-sfc-nsh-timestamp-00 Abstract This draft describes a method of time-stamping Network Service Header (NSH) encapsulated packets or frames on service chains in order to measure accurately hop by hop performance delays of application flows carried within the chain. This method may be used to monitor performance and highlight problems with virtual links (vlinks) VNFs or PNFs on the rendered service path (RSP). 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]. 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 April 20, 2016. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. Browne Expires April 20, 2016 [Page 1] Internet-Draft Network Service Header Time Stamping August 2015 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1. Definition of Terms . . . . . . . . . . . . . . . . . . 3 3. NSH Time stamping . . . . . . . . . . . . . . . . . . . . . 5 3.1 Prerequisites . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 Operation . . . . . . . . . . . . . . . . . . . . . . . 7 3.3 Implementation . . . . . . . . . . . . . . . . . . . . . . 8 4. NSH Time stamping Encapsulation . . . . . . . . . . . . . . . 9 5. Hybrid Models . . . . . . . . . . . . . . . . . . . . . . . 11 5.1 Targeted VNF Time Stamp . . . . . . . . . . . . . . . . . 12 6. Fragmentation Considerations . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8. Open Items for WG Discussion . . . . . . . . . . . . . . . . 12 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 13 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction Network Service Header (NSH) as defined by draft-ietf-sfc-nsh-00 defines a method to insert a service-aware header in between payload and transport headers. This allows a great deal of flexibility and programmability in the forwarding plane allowing user flows to be programmed on the fly for the appropriate service functions (SFs). Whilst NSH promises a compelling vista of operational agility for Service Providers, many service providers are concerned about losing service visibility in the transition from physical appliance SFs to virtualized SFs running in the NFV domain. This concern increases when we consider that many service providers wish to run their networks seamlessly in 'hybrid' mode: - that is, whereby they wish to mix physical and virtual SFs and run services seamlessly between the two domains. Browne Expires April 20, 2016 [Page 2] Internet-Draft Network Service Header Time Stamping August 2015 This draft describes a generic method to monitor and debug service chains and application performance of the flows within a service chain. This method is compliant with hybrid architectures in which VNFs and PNFs are freely mixed in the service chain. This method also is flexible to monitor an entire chain performance or part thereof as desired. Please refer to draft-ietf-sfc-nsh-00.txt as background architecture for the method described in this document. The method described in this draft is not an OAM protocol like Y.1731 or Y.1564 for example. As such it does not define new OAM packet types or operation. Rather it monitors the service chain performance for subscriber payloads and indicates subscriber QoE rather than out-of-band infrastructure metrics. 2.1. Definition of Terms Classification: Locally instantiated policy and customer/network/service profile matching of traffic flows for identification of appropriate outbound forwarding actions. First TS Node (FTSN) - Must mark packet correctly. Must understand 5 tuple information in order to match TS Controller flow table. Last TS Node (LTSN) - must read all MD & export to system performance statistics agent or repository. Should also send NSH header - the SI will indicate if a PNF(s) was at the end of the chain. The LTSN changes the SPI in order that the underlay routes the metadata back directly to the TSDB. Network Node/Element: Device that forwards packets or frames based on outer header information. In most cases is not aware of the presence of NSH. Network Overlay: Logical network built on top of existing network (the underlay). Packets are encapsulated or tunneled to create the overlay network topology. Network Service Header: Data plane header added to frames/packets. The header contains information required for service chaining, as well as metadata added and consumed by network nodes and service elements. NSH Proxy: Acts as a gateway: removes and inserts SH on behalf of a service function that is not NSH aware. PNF: Physical Network Function Browne Expires April 20, 2016 [Page 3] Internet-Draft Network Service Header Time Stamping August 2015 Service Classifier: Function that performs classification and imposes an NSH. Creates a service path. Non-initial (i.e. subsequent) classification can occur as needed and can alter, or create a new service path. Service Function (SF): A function that is responsible for specific treatment of received packets. A service function can act at the network layer or other OSI layers. A service function can be virtual instance or be embedded in a physical network element. One of multiple service functions can be embedded in the same network element. Multiple instances of the service function can be enabled in the same administrative domain. Service Function Chain (SFC): A service function chain defines an ordered set of service functions that must be applied to packets and/or frames selected as a result of classification. The implied order may not be a linear progression as the architecture allows for nodes that copy to more than one branch. The term service chain is often used as shorthand for service function chain. Service Function Path (SFP): The instantiation of a SFC in the network. Packets follow a service function path from a classifier through the requisite service functions. TS Controller: The TS Controller may be part of the service chaining application, SDN controller, NFVO or any MANO entity. For clarity we define the TS Controller separately here as the central logic that decides what packets to timestamp and how. The TS Controller instructs the classifier on how to mark the NSH header. Time Stamp Control Plane (TSCP) - the control plane between the FTSN and the TS Controller. Time Stamp Database (TSDB) - external storage of Metadata for reporting, trend analysis etc. UTC: Real Time Clock VNF: Virtual Network Function Browne Expires April 20, 2016 [Page 4] Internet-Draft Network Service Header Time Stamping August 2015 3. NSH Time stamping As a generic architecture, please refer to figure 1 below:- TS Controller | TSDB | TSCP Interface | ,---. ,---. ,---. ,---. / \ / \ / \ / \ ( SCL )-------->( SF1 )--------->( SF2 )--------->( SFN ) \ FTSN/ \ / \ / \ LTSN/ `---' `---' `---' `---' Figure 1: Logical roles in NSH Time Stamping The TS Controller will most probably be part of the SFC controller but is explained separately in this document for clarity. The TS Controller is responsible for initiating start/stop timestamp requests to the SCL or FTSN, and also for distributing timestamp NSH policy into the service chain via the Time Stamping Control Plane (TSCP) interface. The First Time Stamp Node (FTSN) will typically be part of the service classifier but again is called out as separate logical entity for clarity. The FTSN is responsible for marking NSH MD Type 0x2 fields for the correct flow with the appropriate NSH fields. This tells all upstream nodes how to behave in terms of time stamping at VNF ingress,egress or both, or ignoring the timestamp NSH metadata completely. The FTSN also writes the UTC value into the header so the chain:flow performance can be compared to previous samples for offline analysis. The FTSN should return an error to the TS Controller if not synchronized to time-of-day and forward the packet along the service-chain unchanged. SF1, SF2 timestamp the packets as dictated by the FTSN and process the payload as per normal. Note 1: The exact location of the timestamp creation may not be in the VNF itself as referenced in section 3.3. Note 2: Special cases exist where some of the SFs (PNFs or VNFs) are NSH-unaware. This is covered in section 6. The Last Time Stamp Node (LTSN) should export all NSH time stamp metadata to the Time stamp Database (TSDB) for offline analysis, strip the entire header and forward the packet to the IP next hop. In fully virtualized environments the LTSN will be co-located with the VNF that decrements NSH SI to zero. Corner cases exist whereby this is not the case and is covered in section 6. Browne Expires April 20, 2016 [Page 5] Internet-Draft Network Service Header Time Stamping August 2015 3.1 Prerequisites In order to guarantee metadata accuracy, all servers hosting VNFs should be synchronized from a centralized stable clock. As PNFs do not time stamp there is no need for synchronize. There are two types of synchronization required. A) Low accuracy time-of-day as described in 1 below and B) High accuracy (sub-microsecond) as described by 2 or 3 below. 1. Each platform (including the TS Controller) should synch their system real-time-clock from an NTP server. This is used to mark the metadata in the chain. The UTC format is written by the first SF in the chain to apply a timestamp. NTP accuracy can vary by several milliseconds between locations. This is not an issue as the UTC stamp is merely being used as a reference inserted into the TSDB for performance monitoring. It is not a reference for the timestamp itself. 2. Synchronous Ethernet. Each platform should be synchronized to a primary reference clock (PRC) and use G.8261, G.8262 and G.8264 ITU specifications. 3. IEEE 1588: Each platform should be frequency-synchronized to a primary reference clock (PRC) and use IEEE 1588-2008 for frequency distribution. If a SF is not synchronized at the moment of time stamping, it should indicate synch status in the NSH header. This is described in more detail in section 5. By synchronizing the network in this way, the time stamping operation is independent of the current RSP, whether the entire chain is served by one NFVI-PoP or by multiple. Indeed the time stamp MD can indicate where a chain has been moved due to a resource starvation event as indicated in the figure 2 below, between VNF 3 and VNF 4 at time B. Delay | v | v | x | x x = UTC time A | xv v = UTC time B | xv | xv |______|______|______|______|______|_____ VNF1 VNF2 VNF3 VNF4 VNF5 Figure 2: Flow performance in a service chain Browne Expires April 20, 2016 [Page 6] Internet-Draft Network Service Header Time Stamping August 2015 Regarding draft-ietf-sfc-nsh-00, section 3.2. We would request that the text is changed to reflect that MD-Type 0x2 MUST be supported to aid methods like the one outlined in this draft. 3.2 Operation Section 3.5 of draft-ietf-sfc-nsh-00.txt defines NSH metadata type 2 encapsulation as per the figure below. Please refer to the draft for detailed explanation. Time stamed flows will use this format. 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver|O|C|R|R|R|R|R|R| Length | MD-type=0x2 | Next Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Path ID | Service Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLV Class | Type |R|R|R| Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Variable Metadata | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: NSH MD type 2 Encapsulation Flow Selection The TS Controller should maintain a list of flows within each service chain to be monitored. This flow table should be in the format SPI:5 tuple ID. The TS Controller should map these pairs to unique Flow IDs per service chain within the extended NSH header specified in this draft. The TS Controller should instruct the FTSN node initiate timestamping on flow table match. The TS Controller should also tell the classifier the duration of the time stamping operation, either by number of packets in the flow or a duration in UTC format. In this way the system can monitor the performance of an individual subscriber in a chain or just a specific application the subscriber is running. The TS Controller should write the list of monitored flows into the TSDB for correlation of performance data. Thus when the TSDB receives data from the LTSN it understands to which flow the data pertains. The association of source IP to subscriber identity is outside the scope of this draft and will vary by network application. For example the method of association of a source IP to IMSI in mobile cores will be different to how a CPE with NAT function may be chained in an enterprise NFV application. Browne Expires April 20, 2016 [Page 7] Internet-Draft Network Service Header Time Stamping August 2015 TSCP Interface A new timestamp control plane (TSCP) interface is required between the TS Controller and the FTSN or classifier. This interface:- - Communicates which chains:flows to timestamp. This can be a specific chain:flow combination or include wildcards for monitoring subscribers across multiple chains or multiple flows within one chain. - How the timestamp should be applied (ingress, egress, both or specific) - When to stop time stamping Exact specification of TSCP is for further study. 3.3 Implementation Whilst applying and operating on the timestamps themselves incur an additional small delay in the service chain it can be assumed that these additional delays are all relative for the flow in question. Thus whist the absolute timestamps may not be fully accurate for normal non-time stamped traffic they can be assumed to be relative. It is assumed that the method described in this document would only operate on a small percentage of user flows. The service provider may choose a flexible policy in the TS Controller to time stamp a selection of user-plane every minute for example to highlight any performance issues. Of course the TS Controller can stress test an individual flow or chain should a deeper analysis be required. We can expect that this type of deep analysis has an impact on the performance of the chain itself whilst under investigation. The impact will be dependent on vendor implementation and outside the scope of this document. The timestamp may be applied at various parts of the NFV architecture. The VNF, hypervisor (assuming no SRIOV pass-through), vSwitch or NIC are all potential locations that's can append the packet with the requested timestamp. Whilst it is desirable to timestamp as close as possible to the VNF for performance accuracy, the exact location of the timestamp application is outside the scope of this document, but should be consistent across the individual TS Controller domain. Browne Expires April 20, 2016 [Page 8] Internet-Draft Network Service Header Time Stamping August 2015 4. NSH Time stamping Encapsulation NSH time stamping encapsulation is shown below in figure 4:- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver|O|C|R|R|R|R|R|R| Length | MD-type=0x2 | NextProto=0x0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Path ID | Service Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLV Class=0x10 | Type=0x01 |R|R|R| Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | UTC Reference | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Syn |R|E|I|TSI|TS Service Indx| Flow ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Ingress Timestamp (I bit is set)(FTSN) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Egress Timestamp (E bit is set)(FTSN) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Syn |R|E|I|TSI|TS Service Indx| Flow ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Ingress Timestamp (I bit is set) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Egress Timestamp (E bit is set) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Syn |R|E|I|TSI|TS Service Indx| Flow ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | Ingress Timestamp (I bit is set) (LTSN) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Egress Timestamp (E bit is set) (LTSN) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: NSH Time Stamp Encapsulation Relevant fields in header that the FTSN must implement: The O bit should not be set as we are operating on subscriber packets The C bit should be set indicating critical metadata exists Browne Expires April 20, 2016 [Page 9] Internet-Draft Network Service Header Time Stamping August 2015 The MD type must be set to 0x2 TLV Class must be set to 0x10 (General KPI Monitoring) as requested in section 11, and in addition that we define the timestamp type to be 0x01. Type = 0x00 Reserved. Type = 0x01 Timestamp. The MSB of the Type field must be set to zero. Thus if a receiver along the path does not understand the time stamping protocol it will pass the packet transparently and not drop. This scheme allows for extensibility to the mechanism described in this document to other KPI collections and operations. FTSN timestamp metadata contains Timestamp Service Index (TSI) field which must be set as follows: 0x0 Timestamp mode, no Service index specified in the TS Service Index field. 0x1 Timestamp Hybrid mode is selected, Time Stamp Service Index contains LTSN Service index. This is used when PNFs or NSH-unaware SFs are used at the tail of the chain. If TSI=0x1, then the value in the type field informs the chain which SF should act as the LTSN. 0x2 Timestamp Specific mode is selected, Time Stamp Service Index contains the targeted Service Index. In this case the Time Stamp Service Index field indicates which SF is to be time stamped. Both ingress and egress timestamps are performed when the SI=TSSI on the chain. In this mode the FTSN will also apply UTC and ingress time stamp. This will indicate the delay along the entire service chain to the targeted SF. This method may also be used as a light implementation to monitor end-to-end service chain performance whereby the targeted SF is the LTSN. The Flow ID is a unique 16 bit identifier written into the header by the classifier. This allow 65536 flows to be concurrently timestamped on any given NSH service chain (SPI). Flow IDs are not written by subsequent SFs in the chain. The FTSN exports monitored flow IDs to the TSDB for correlation. The E bit should be set if Egress timestamp is requested. The I bit should be set if Ingress timestamp is requested. UTC reference is the wall clock of the FTSN, and may be used for historical comparison of SC performance. If the FTSN is not time-of-day synched it should inform the TS controller over the TSCP interface. Browne Expires April 20, 2016 [Page 10] The Syn bits are an indication of the synchronization status of the node performing the time stamp and must be set as follows: In Synch: 0x00 In holdover: 0x01 In free run: 0x02 Out of Synch: 0x03 If the network node is out of synch or in free run no timestamp is applied by the node (but other timestamp MD is applied) and the packet is processed normally. If FTSN is out of synch or in free run timestamp request rejected and not propagated though the chain. The FTSN should inform the TS controller in such an event over the TSCP interface. The Outer service index value is copied into the timestamp metadata to help cater for hybrid chains that's are a mix of VNFs and PNFs or through SFs that do not understand NSH. Thus if a flow transits through a PNF or a NSH-unaware node the delta in the inner service index between time stamps will indicate this. Timestamps are applied in PTP format (64 bit) and corresponding bits (I and E) reported in the timestamp metadata header. 5. Hybrid Models A hybrid chain may be defined as a chain whereby there is a mix of NSH-aware and NSH-unaware SFs. This may be the case is some PNFs are used in the chain or if VNFs are used that do not support NSH. Example 1: PNF in the middle TS Controller | TSDB | TSCP Interface | ,---. ,---. ,---. ,---. / \ / \ / \ / \ ( SCL )-------->( SF1 )--------->( SF2 )--------->( SFN ) \ FTSN/ \ / \ PNF1/ \ LTSN/ `---' `---' `---' `---' Figure 5: Hybrid chain with PNF in middle In this example the FTSN begins operation and sets the SI to 3, SF1 decrements this to 2 and passes the flow to a SFC proxy (not shown). The proxy strips the NSH header and passes to the PNF. On receipt back from the PNF the Proxy decrements the SI and passes the packet onto the LTSN with a SI=1. Browne Expires April 20, 2016 [Page 11] After the LTSN processes the traffic it knows it is the last node on the chain from the SI value and exports the entire NSH header and all metadata to the TSDB. The payload is forwarded to the next hop on the underlay minus the NSH header. The TS information packet is given a new SPI which acts as a homing tag to transport the timestamp data back to the TSDB. Example 2: PNF at the end TS Controller | TSDB | TSCP Interface | ,---. ,---. ,---. ,---. / \ / \ / \ / \ ( SCL )-------->( SF1 )--------->( SF2 )--------->( PNFN ) \ FTSN/ \ / \ LTSN/ \ / `---' `---' `---' `---' Figure 6: Hybrid Chain with PNF at end In this example the FTSN begins operation and sets the SI to 3, the TSI field set to 0x1, and the type to 1. Thus when SF2 receives the packet with SI=1, it understands that it is expected to take on the role of the LTSN as it is the last NSH-aware node in the chain. 5.1 Targeted VNF Time Stamp For the majority of flows within the service chain, time stamps (ingress,egress or both) will be carried out at each hop until the SI decrements to zero and the NSH header and TS MD is exported to the TSDB. There may exist however the need to just test a particular VNF (perhaps after a scale out operation or software upgrade for example). In this case the FTSN should mark the NSH header as follows:- TSI field is set to 0x2. Type is set to the expected SI at the SF in question. When outer SI = type. Timestamps are applied at SF ingress, egress and the NSH header and MD exported to the TSDB. Browne Expires April 20, 2016 [Page 12] 6. Fragmentation Considerations The method described in this draft does not support fragmentation. The TS Controller should return an error should a time stamping request from an external system exceed MTU limits and require fragmentation. Depending on the length of the payload and the type of timestamp and chain length, this will vary for each packet. In most service provider architectures we would expect a SI << 10, and that may include some PNFs in the chain which do not add overhead. Thus for typical IMIX packet sizes we expect to able to perform time stamping on the vast majority of flows without fragmenting. 7. Security Considerations TBD 8. Open Items for WG Discussion 1. Specification and operation of TSCP 2. AOB 9. Acknowledgments The authors would like to thank Ron Parker of Affirmed Networks and Seungik Lee of ETRI for their reviews of this draft. 10. IANA Considerations TLV Class Registry IANA is requested to set up a registry of "TLV Types". These are 16-bit values. Registry entries are assigned by using the "IETF Review" policy defined in RFC 5226 [RFC5226]. One new type is required for KPI General Monitoring and time stamping type as discussed above. Browne Expires April 20, 2016 [Page 13] 11. References 11.1. 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, . [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 11.2. Informative References [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC6071] Frankel, S. and S. Krishnan, "IP Security (IPsec) and Internet Key Exchange (IKE) Document Roadmap", RFC 6071, February 2011. [SFC-PS] Quinn, P., Ed. and T. Nadeau, Ed., "Service Function Chaining Problem Statement", 2014, . [SFC-arch] Quinn, P., Ed. and J. Halpern, Ed., "Service Function Chaining (SFC) Architecture", 2014, . [dcalloc] Guichard, J., Smith, M., and S. Kumar, "Network Service Header (NSH) Context Header Allocation (Data Center)", 2014, . [moballoc] Napper, J. and S. Kumar, "NSH Context Header Allocation -- Mobility", 2014, . Browne Expires April 20, 2016 [Page 14] Author's Address Rory Browne Email: rory.browne@intel.com Andrey Chilikin Email: andrey.chilikin@intel.com Brendan Ryan Email: brendan.ryan@intel.com Intel Dromore House Shannon Co.Clare Ireland Browne Expires April 20, 2016 [Page 15]