SFC WG T. Ao Internet-Draft ZTE Corporation Intended status: Informational G. Mirsky Expires: September 14, 2017 ZTE Corp. March 13, 2017 Analysis of the SFC scalability draft-ao-sfc-scalability-analysis-02 Abstract SFC is an ordered set of service function, should be scalable to meet numerous requirements. The scalability of SFC can be interpreted as ability of the SFC to accommodate one or more SFs joining the SFC , or leaving the SFC without significant impact to SFC performance. This document presents four use cases on SFC scale-out and scale-in, and analysis of the requirements to support such capability. 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/. 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Code Components extracted from this document must Ao & Mirsky Expires September 14, 2017 [Page 1] Internet-Draft Analysis of the SFC scalability March 2017 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Four Use cases for scale-out/scale-in . . . . . . . . . . . . 3 3.1. Join . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2. Redundancy . . . . . . . . . . . . . . . . . . . . . . . 3 3.3. By-pass . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.4. Failure or Remove . . . . . . . . . . . . . . . . . . . . 4 4. Data Plane Requirements . . . . . . . . . . . . . . . . . . . 4 5. Control Plane Requirements . . . . . . . . . . . . . . . . . 5 5.1. Centralized CP . . . . . . . . . . . . . . . . . . . . . 5 5.2. Distributed CP . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Information References . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction Service Function Chain (SFC) is the chain with a series of ordered Service Functions(SF). The SFC maybe changed because of load balance , failure, or other management requirement. We call it SFC scalability. The SFC being scalable means that the Service Functions can be added or removed from the path of this SFC. With this capability, SFC is more flexible and elastic to adapt all kinds of requirements. In this document, we will present four use cases on SFC scale-out and scale-in, and analysis some requirements to support such capability. 2. Terminology SFC(Service Function Chain): An ordered set of some abstract SFs. SFC Scale-out: One or more SFs are added into the path of the SFC for the sake of load balance, protection or other new services requirement. SFC Scale-in: One or more SFs are removed from the path of the SFC for the sake of the SFs are by-passed or the SFs are failed. Ao & Mirsky Expires September 14, 2017 [Page 2] Internet-Draft Analysis of the SFC scalability March 2017 3. Four Use cases for scale-out/scale-in Following describe four use cases to illustrate the scalability of the SFC. 3.1. Join This is SFC horizontal scale-out use case. One or more new SFs must be added to a certain SFC for the traffic that has been classified to require application of new SF(s). This case is the reverse scenario to the by-pass. In this case one or more SFs that were by-passed need to be re-inserted into the SFC. And the SFC itself can be characterized as being scaled out. There are two sub-cases of an SF joining the SFC. One when both the SF and corresponding SFF are new to the SFC. The second is when the SF attaches to an existing SFF. In the first scenario, control plane needs to notify the upstream SFF to modify its next hop to point to the new SFF and configure the new SFF's forwarding information. In the second scenario control plane needs to configure the existing SFF's forwarding information. In this scenario, SFF forwards the packets not only according to the SFPID but also according to the metadata in the SFC header. 3.2. Redundancy This is an example of SFC vertical scale-out use case. One or more SFs are added into the SFC to meet the redundancy or load balance requirements. This case is different with the Join case (section 3.1) in that the SF is the same with one of the SF that is on the path of the SFC. The new SF have the same function with the existing SF, and the new SF is added into the SFC to protect the existing corresponding SF and to load balance the existing corresponding SF. In this case, control plane need to notify the upstream SFF that the new SF joins the SFC as a redundancy SF for protection or load balance, and its next hop should be a protection group or ECMP group. For the purpose of load balance to ensure proper forwarding, the Flow Id field MUST be present in the NSH as expression of entropy so that SFF can select an SF from the group according to the Flow Id. 3.3. By-pass This is a horizontal scale-in case. In this scenario some SFs are not removed from the SFC but just by-passed by the traffic so that the packets will not be processed by these SFs. Use cases for this scenario are described in [draft-ietf-sfc-long-lived-flow-use-cases] and [draft-kumar-sfc-offloads] . In these two drafts, the SF is Ao & Mirsky Expires September 14, 2017 [Page 3] Internet-Draft Analysis of the SFC scalability March 2017 offloaded because it is not necessary to steer the traffic to the SFs to improve the forwarding performance. The corresponding solution is also provided in the above drafts. 3.4. Failure or Remove This is a vertical SFC scale-in case. This happens when the SFC is being protected or load balanced. When SF in one SFC has failed or needs to be removed because it is no longer needed the ability of the SFC to scale-in is excercised. For this case the upstream SFF must be notified that its next hop must be changed to the next SF of the SF. From the cases described we can conclude that no matter if is SFC scale-out case or scale-in cases, there are some requirements to SFC control protocol. And for some cases, there are requirements to data plane as well. 4. Data Plane Requirements For the cases of load balancing or protection switch it is highly beneficial to have an entropy field in the SFC header to be used by the. The entropy field can be named as Flow ID which should be in SFC header. This means that Classifier not only classifies the traffic based on different SFPID, but using Flow ID as well. According to the NSH draft in draft--ietf-sfc-nsh-12, we propose to extend NSH to include the entropy field. Two options can be considered. One is to use existing field, for example, some reserved bits. Extended field in NSH Service Path Header is showed below as an example. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service Path Identifier (SPI) | Service Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flow ID | +-----------------------------------------------+---------------+ Another is to extend a new metadata to meet the requirement. Which has been described in draft draft-quinn-sfc-nsh-tlv-02 section 8. Ao & Mirsky Expires September 14, 2017 [Page 4] Internet-Draft Analysis of the SFC scalability March 2017 5. Control Plane Requirements Another is to extend a new metadata to meet the requirement. Which has been described in draft draft-quinn-sfc-nsh-tlv-02 section 8. 5.1. Centralized CP Controller is required to: a) Send a message to SFF that the joined SF connected to set the correct SFPID and its next hop. b) Send register message to previous SFF with some information. Such information not only includes next hop locator, but also includes an indicator that if the next hop is a new joined SF or the next hop is a new SF that added into a group. If the indicator is a new joined SF, it means a new SF will join the SFC. If the indicator is a group SF, it means a new SF will be added into a group for load balance or protection. c) Send de-register message to previous SFF with some information. Such information not only includes next hop locator, but also includes an indicator that if the next hop is the next SF because the current SF is by-passed, or the next hop is the SF that is removed from a group. If the indicator is the by-passed SF, it means the current SF is by-passed or is leaving from the SFC. If the indicator is group SF, it means the current SF will be removed into a protection group that is for load balance or protection. 5.2. Distributed CP Distributed CP can be used in Plug-and-Play scenario. Distributed CP requires: a) The SF that needs to join the SFC or by-pass from the SFC should notify the SFF it connects by a message. b) The SFF should send a register message to the previous SFF with some information. Such information not only includes next hop locator, but also includes an indicator that if the next hop is a new joined SF or the next hop is a new SF that added into a group. If the indicator is a new joined SF, it means a new SF will join the SFC. If the indicator is a group SF, it means a new SF will be added into a group for load balance or protection. c) The SFF send de-register message to previous SFF with some information. Such information not only includes next hop locator, but also includes an indicator that if the next hop is the next SF Ao & Mirsky Expires September 14, 2017 [Page 5] Internet-Draft Analysis of the SFC scalability March 2017 because the current SF is by-passed, or the next hop is the SF that is removed from a group. If the indicator is the by-passed SF, it means the current SF is by-passed or is leaving from the SFC. If the indicator is group SF, it means the current SF will be removed into a protection group that is for load balance or protection. 6. Security Considerations For the scalability of the SFC, security is very important to be considered. Before allow the SF to join to the SFC, it is required to make sure the SF's security first. 7. IANA Considerations TBD 8. Information References [I-D.ietf-sfc-architecture] Halpern, J. and C. Pignataro, "Service Function Chaining (SFC) Architecture", draft-ietf-sfc-architecture-11 (work in progress), July 2015. [I-D.ietf-sfc-nsh] Quinn, P. and U. Elzur, "Network Service Header", draft- ietf-sfc-nsh-12 (work in progress), February 2017. [RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for Service Function Chaining", RFC 7498, DOI 10.17487/RFC7498, April 2015, . Authors' Addresses Ting Ao ZTE Corporation No.889, BiBo Road Shanghai 201203 China Phone: +86 21 68897642 Email: ao.ting@zte.com.cn Ao & Mirsky Expires September 14, 2017 [Page 6] Internet-Draft Analysis of the SFC scalability March 2017 Greg Mirsky ZTE Corp. 1900 McCarthy Blvd. #205 Milpitas, CA 95035 USA Email: gregimirsky@gmail.com Ao & Mirsky Expires September 14, 2017 [Page 7]