Service Function Chaining S. Homma Internet-Draft K. Naito Intended status: Informational NTT Expires: July 27, 2015 D. R. Lopez Telefonica I+D M. Stiemerling NEC/H-DA D. Dolson Sandvine January 23, 2015 Analysis on Forwarding Methods for Service Chaining draft-homma-sfc-forwarding-methods-analysis-01 Abstract Some working groups of the IETF and other Standards Developing Organizations are now discussing use cases of a technology that enables data packets to traverse appropriate service functions located remotely through networks. This is called Service Chaining in this document. (Also, in Network Functions Virtualisation (NFV), a subject that forwarding packets to required service functions in appropriate order is called VNF Forwarding Graph.) This draft does not focus only on SFC method, and thus, use the term "Service Chaining". SFC may be one of approaches to realize Service Chaining. There are several Service Chaining methods to forward data packets to service functions, and the applicable methods will vary depending on the service requirements of individual networks. This document presents the results of analyzing packet forwarding methods and path selection patterns for achieving Service Chaining. For forwarding data packets to the appropriate service functions, distribution of route information and steering data packets following the route information, are required. Examples of route information are packet identifier and the routing configurations based on the identifier. Also, forwarding functions are required to decide the path according to the route information. 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/. Homma, et al. Expires July 27, 2015 [Page 1] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 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 July 27, 2015. Copyright Notice Copyright (c) 2015 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4 3. Classification of Forwarding Methods and SP Decision Patterns 5 3.1. Forwarding Methods . . . . . . . . . . . . . . . . . . . 5 3.1.1. Method 1: Forwarding Based on Flow Identifiable Information . . . . . . . . . . . . . . . . . . . . . 5 3.1.2. Method 2: Forwarding with Stacked Transport Headers . 6 3.1.3. Method 3: Forwarding Based on Service Chain Identifiable Tags . . . . . . . . . . . . . . . . . . 8 3.2. Service Path Selection Patterns . . . . . . . . . . . . . 9 3.2.1. Pattern 1: Static Selection of End to End Service Path . . . . . . . . . . . . . . . . . . . . . . . . 10 3.2.2. Pattern 2: Dynamic Selection of Segmented Service Path . . . . . . . . . . . . . . . . . . . . . . . . 12 4. Consideration of Service Chaining Methods and Architecture Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.1. Analysis of 3.1. Forwarding Methods . . . . . . . . . . . 18 4.1.1. Analysis of Method 1 . . . . . . . . . . . . . . . . 18 4.1.2. Analysis of Method 2 . . . . . . . . . . . . . . . . 18 4.1.3. Analysis of Method 3 . . . . . . . . . . . . . . . . 19 4.2. Analysis of 3.2. Service Paths Selection Patterns . . . . 19 4.2.1. Analysis of Pattern 1 . . . . . . . . . . . . . . . . 19 4.2.2. Analysis of Pattern 2 . . . . . . . . . . . . . . . . 20 4.3. Example of selecting Methods and Patterns . . . . . . . . 24 Homma, et al. Expires July 27, 2015 [Page 2] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 4.3.1. Example A: Datacenter Network . . . . . . . . . . . . 24 4.3.2. Example B: Current Mobile Carrier's Network . . . . . 24 4.3.3. Example C: Fixed and Mobile Converged Network . . . . 25 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 1. Introduction Service Chaining is a technology that enables data packets to traverse the appropriate service functions deployed in networks. This draft assumes that Service Chaining is achieved in the following steps: a. A classification function identifies data packets and determines the set of services that will be provided for the packets and in which order. b. The path, that the packets will traverse for reaching the required service functions, is established based on the result of step a. c. Forwarding functions determine the appropriate destination and forward each packet to the next hop according to the path. d. A service function provides services to received packets and return each packet to the forwarding function. e. Steps c and d are repeated until each packet has been transferred to all required service functions. f. After a packet has been transferred to all required Service Functions, it is forwarded to its original destination. There are several forwarding methods for Service Chaining, and they can be classified into certain categories in terms of distribution of information for setting the paths and decision of the paths. The methods used to distribute the information and the patterns used to decide the paths will affect the mechanism of Service Chaining as well as service flexibility. The applicable methods vary depending on network requirements, and thus, classifying and determining forwarding methods will be important in designing the architecture of Service Function Chaining (SFC). This document provides the results of analyzing forwarding methods for Service Chaining. Homma, et al. Expires July 27, 2015 [Page 3] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 OAM, security, and redundancy are outside the scope of this draft. 2. Definition of Terms Term "Classification", "Classifier" referred to [I-D.ietf-sfc-architecture]. Term "Service Function", "Service Node" referred to [I-D.ietf-sfc-dc-use-cases]. Service Chaining: A technology that lets data packets traverse a series of service functions. Classification: Locally instantiated policy and customer/network/ service profile matching of traffic flows for identification of appropriate outbound forwarding actions. Classifier (CF): The entity that performs classification. Service Function (SF): A function that is responsible for specific treatment of received packets. A Service Function can act at various layers of a protocol stack (e.g. at the network layer or other OSI layers). A Service Function can be a virtual element or be embedded in a physical network element. One of multiple Service Functions can be embedded in the same network element. Multiple occurrences of the Service Function can be enabled in the same administrative domain. One or more Service Functions can be involved in the delivery of added-value services. A non-exhaustive list of Service Functions includes: firewalls. WAN and application acceleration, Deep Packet Inspection (DPI), LI (Lawful Intercept) module, server load balancers, NAT44 [RFC3022], NAT64 [RFC6146], NPTv6 [RFC6296], HOST_ID injection, HTTP Header Enrichment functions, TCP optimizer, etc. Service Node (SN): A virtual or physical device that hosts one or more service functions, which can be accessed via the network location associated with it. Forwarder (FWD): The entity, responsible for forwarding data packets along the service path, which includes delivery of traffic to the connected service functions. FWD handles Forwarding Tables, which is used for forwarding packets. Control Entity (CE): The entity responsible for managing service topology and indicating forwarding configurations to Forwarders. Service Chain (SC): A service chain defines an ordered list of service functions that must be applied to user packets selected as Homma, et al. Expires July 27, 2015 [Page 4] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 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. Service Path (SP): The instantiation of a service chain in the network. Packets follow a service path through the requisite service functions. Service path shows a specific path of traversing SF instance. For example, SC is written as SF#1 -> SF#2 -> SF#3 (This shows an ordered list of SFs), and SP is written as SF#1_1(1_1 means instance 1 of SF1) -> SF#2_1 -> SF#3_1. Service Chaining Domain (SC Domain): The domain managed by one or a set of CEs. Service Path Information (SPI): The information used to forward packets to The appropriate SFs based on the selected service. Examples of SPI include routing configurations for Forwarders, transport headers for forwarding packets to required SFs, and service/flow identifiable tags. 3. Classification of Forwarding Methods and SP Decision Patterns 3.1. Forwarding Methods In Service Chaining, data packets are transferred to service functions, which can be located outside the regular computed path to the original destination. Therefore, a routing mechanism that is different from general L2/L3 switching/routing may be required. The routing mechanism can be classified into three methods in terms of distribution of SPI and packet forwarding. 3.1.1. Method 1: Forwarding Based on Flow Identifiable Information The mechanism of method 1 is shown in Figure 1. In this method, routing configurations based on flow identifiable information, such as 5-tuple (e.g. dst IP, src IP, dst port, src port, tcp) are indicated to the CF and each FWD. There may be an CE to handle this. The flow identifiable information can be constructed with some fields of L2 or L3 or combination of those. The information can be configured either before packets arrive, or at the time packets arrive at CF and FWD. Each FWD identifies the packets with flow identifiable information and forwards the packets to the SFs according to the configuration. This method does not require changing any fields of the original packet frame. Homma, et al. Expires July 27, 2015 [Page 5] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 *Distribution model of SPI* +----------------+ | Control Entity | +----------------+ ^ | indication of routing configuration | | based on packet identifiable information | +---------------+-------------------------------+---------> | | | | | | | | | v v v +--------+ +-------+ +------+ +-------+ ------>| CF |------> | FWD |------> | SF#1 |------>| FWD |-----> +--------+ +-------+ +------+ +-------+ //////////////////////////////////////////////////////////////////////// *Forwarding Tables* Locate: [CF] [FWD] [FWD] Table: 192.168.1.1 192.168.1.1 192.168.1.1 ->FWD#1 ->SF#1 ->SF#2 10.0.1.1 10.0.1.1 10.0.1.1 ->FWD#1 ->FWD#2 ->SF#2 ... ... ... //////////////////////////////////////////////////////////////////////// *Condition of Packet* Locate: [CF] [FWD] [SF#1] [FWD] +-------+ +-------+ +-------+ +-------+ Packet: | PDU | | PDU | | PDU | | PDU | +-------+ +-------+ +-------+ +-------+ Figure 1: Forwarding Based on Flow Identifiable Information 3.1.2. Method 2: Forwarding with Stacked Transport Headers The mechanism of method 2 is shown in Figure 2. In this method, the CF classifies packets and stacks transport headers in which actual network address is included, e.g., MPLS or GRE headers, onto the packets based on the classification. This method does not require any forwarding function for forwarding packets based on the service information. Forwarding functions of underlay networks forward the packets to SFs following the outermost header. The outermost header Homma, et al. Expires July 27, 2015 [Page 6] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 is removed after service process of the SF. The actions are repeated until all headers are removed. *Distribution model of SPI* +----------------+ | Control Entity | +----------------+ ^ | | | indication of | | stacking headers | v +--------+ +-------+ +------+ +------+ -------->| CF |------>| SF#1 |------>| SF#2 |------>| SF#3 |------> +--------+ +-------+ +------+ +------+ //////////////////////////////////////////////////////////////////////// *Forwarding Tables* Locate: [CF] Table: 192.168.1.1 __/__/__/__/__/__/__/__/__/__/__/__/__/ ->Stack #1,2,3 __/ Packets are forwarded to SFs by __/ 10.0.1.1 FWD1 __/ the outermost transport header. __/ ->Stack #1,3 __/__/__/__/__/__/__/__/__/__/__/__/__/ ... //////////////////////////////////////////////////////////////////////// *Condition of Packet* Locate: [CF] [SF#1] [SF#2] [SF#3] +--------+ Header: |To SF#1 | +--------+ +--------+ |To SF#2 | |To SF#2 | +--------+ +--------+ +--------+ |To SF#3 | |To SF#3 | |To SF#3 | +--------+ +--------+ +--------+ : : : : +--------+ +--------+ +--------+ +--------+ Packet: | PDU | | PDU | | PDU | | PDU | +--------+ +--------+ +--------+ +--------+ Figure 2: Forwarding with Stacked Multiple Transport Headers Homma, et al. Expires July 27, 2015 [Page 7] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 3.1.3. Method 3: Forwarding Based on Service Chain Identifiable Tags The mechanism of this method is shown in Figure 3. In this method, a CF classifies each packet and attaches a tag for identifying the service or flow on the packets based on the classification. The routing configuration based on the tags is sent to each FWD (from some CE) in advance. Each FWD forwards packets to the SFs following the configuration and the tag. After a packet has traversed all SFs, the tag is removed and the packet is transported to the original destination. Homma, et al. Expires July 27, 2015 [Page 8] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 *Distribution model of SPI* +----------------+ | Control Entity | +----------------+ ^ | indication of attached tag | | and routing configuration based on tags | +----------------+------------------------------+---------> | | | | | | | | | v v v +--------+ +-------+ +------+ +-------+ ----->| CF |------> | FWD |------>| SF#1 |------>| FWD |-----> +--------+ +-------+ +------+ +-------+ ////////////////////////////////////////////////////////////////////// *Forwarding Tables* Locate: [CF] [FWD] [FWD] Table: 192.168.1.1 IF ID#1,3 IF ID#1,2,5 ->Stack ID#1 ->SF#1 ->SF#2 10.0.1.1 FWD1 ->Stack ID#2 ... ... ... ////////////////////////////////////////////////////////////////////// *Condition of Packet* Locate: [CF] [FWD] [SF#1] [FWD] +-------+ +-------+ +-------+ +-------+ Tag: | ID#1 | | ID#1 | | ID#1 | | ID#1 | +-------+ +-------+ +-------+ +-------+ Packet:| PDU | | PDU | | PDU | | PDU | +-------+ +-------+ +-------+ +-------+ Figure 3: Forwarding Based on Service Chain Identifiable Tags 3.2. Service Path Selection Patterns Since SC contains only logical information (e.g. series of services that are applied to flows and their sequences), the actual instances, which are called SPs, are needed in order for the forwarding process to work. In this process, an instance of SP is created at certain points during a packet's delivery. Therefore, to forward packets, the SC needs to be turned into an SP, which indicates specific FWDs Homma, et al. Expires July 27, 2015 [Page 9] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 (or switches, routers) and SFs that the packets will be forwarded to. In the points translating SC to SP, the paths that determine the Service Chaining are classified into two patterns. 3.2.1. Pattern 1: Static Selection of End to End Service Path The translation point is only a CF; that is, the SP is statically pre-established as an end-to-end path and a CF inserts packets into the appropriate path based on the result of the classification. Each FWD on the route has a routing table to uniquely determine the next destination of packets, and each FWD statically forwards the received packets to the next destination. FWD requires only a function to receive indications of routing configurations from the CE. Pattern 1 can be achieved in the following ways. 3.2.1.1. SF Shared Model Figure 4 shows the mechanism of this way. An SF is shared by multiple SPs. In this way, the FWDs require a function to identify SP for each packet and insert the packets into the next appropriate hop. Homma, et al. Expires July 27, 2015 [Page 10] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 *Path Structure* +----+ +-----+ +----+ +-----+ +------+ +-----+ +----+ | |SC#1| FWD | |SF#1| | FWD | |SF#2_1| | FWD | |SF#3| SP#1 | |================================================================> | |SC#2| | | | | | +------+ | | | | SP#2 | |===============================# +------+ #=====================> | | | | +----+ | | # |SF#2_2| # | | +----+ | | | | | | #==========# | | ->| CF | +-----+ +-----+ +------+ +-----+ | | . . . . . . +-----+ +----+ +-----+ +----+ | |SC#n| FWD | |SF#4| | FWD | |SF#5| SP#n | |================================================================> +----+ +-----+ +----+ +-----+ +----+ SC:Service Chain ///////////////////////////////////////////////////////////////////////// *Packet Flow* Service Chain#1: SP#1 [ CF ]--->[ FWD ]-->[SF#1]-->[ FWD ]-->[SF#2_1]-->[ FWD ]-->[SF#3]--> Service Chain#2: SP#2 [ CF ]--->[ FWD ]-->[SF#1]-->[ FWD ]-->[SF#2_2]-->[ FWD ]-->[SF#3]--> : Service Chain#n: SP#n [ CF ]--->[ FWD ]-->[SF#4]----------------------->[ FWD ]-->[SF#5]--> Figure 4: SF Shared Model 3.2.1.2. SF Dedicated Model Figure 5 shows the mechanism of this style. An SF (instance) is used by only one single SP; in other words, there is an SF instance per SP. At each FWD, incoming packets are statically routed to a single predefined next hop. Homma, et al. Expires July 27, 2015 [Page 11] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 *Path Structure* +----+ +-----+ +------+ +-----+ +------+ +-----+ +------+ | |SC#1| FWD | |SF#1_1| | FWD | |SF#2_1| | FWD | |SF#3_1| SP#1 | |================================================= =============> | | +-----+ +------+ +-----+ +------+ +-----+ +------+ | | +-----+ +------+ +-----+ +------+ +-----+ +------+ | |SC#2| FWD | |SF#1_2| | FWD | |SF#2_2| | FWD | |SF#3_2| SP#2 | |===============================================================> ->| CF | +-----+ +------+ +-----+ +------+ +-----+ +------+ | | . . . . . . +-----+ +------+ +-----+ +------+ | |SC#n| FWD | | SF#4 | | FWD | | SF#5 | SP#n | |===============================================================> +----+ +-----+ +------+ +-----+ +------+ SC:Service Chain //////////////////////////////////////////////////////////////////////// *How packets traverse* Service Chain#1: SP#1 [ CF ]--->[ FWD ]->[SF#1_1]->[ FWD ]->[SF#2_1]->[ FWD ]->[SF#3_1]--> Service Chain#2: SP#2 [ CF ]--->[ FWD ]->[SF#1_2]->[ FWD ]->[SF#2_2]->[ FWD ]->[SF#3_2]--> : Service Chain#n: SP#n [ CF ]--->[ FWD ]->[ SF#4 ]-------------------->[ FWD ]->[ SF#5 ]--> Figure 5: SF Dedicated Model 3.2.2. Pattern 2: Dynamic Selection of Segmented Service Path The mechanism of this style is shown in Figure 6. The translation points are a CF and some FWDs. The SP is established by a series of multiple paths, which are sectioned by CFs and FWDs. The path, which is sectioned by CFs and FWDs, is referred to as a segmented path in this draft. CFs or FWDs that select the next segmented path may require notification of routing configurations from the CE. Moreover, some FWDs require functions to select the destination of packets from various alternatives and to retrieve the information for Homma, et al. Expires July 27, 2015 [Page 12] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 selecting the next path. For example, each FWD obtains metric information or load conditions of servers and selects an optimal segmented path based on the information. The CE may have the selection mechanism and may notify CFs or FWDs of it. *Path Structure* +----+ +-----+ +----+ +-----+ +------+ +-----+ +----+ | |SC#1| FWD | |SF#1| | FWD | |SF#2_1| | FWD | |SF#3| SP#1 | |==========================*=====================================> | | | | | | | # | +------+ | | | | SP#2 | | | | | | | # | +------+ #=====================> | | | | +----+ | # | |SF#2_2| # | | +----+ | | | | | #===============# | | ->| CF | +-----+ +-----+ +------+ +-----+ | | . . . . . . +-----+ +----+ +-----+ +----+ | |SC#n| FWD | |SF#4| | FWD | |SF#5| SP#m | |================================================================> +----+ +-----+ +----+ +-----+ +----+ SC:Service Chain ///////////////////////////////////////////////////////////////////////// *How packets traverse* Service Chain#1: SP#1 [ CF ]--->[ FWD ]-->[SF#1]-->[ FWD ]-->[SF#2_1]-->[ FWD ]-->[SF#3]--> SP#2 [ CF ]--->[ FWD ]-->[SF#1]-->[ FWD ]-->[SF#2_2]-->[ FWD ]-->[SF#3]--> : Service Chain#n: SP#m [ CF ]--->[ FWD ]-->[SF#4]----------------------->[ FWD ]-->[SF#5]--> Figure 6: Dynamic Selection of Segmented Service Path In addition, this pattern accepts establishment of hierarchical domains as following: Homma, et al. Expires July 27, 2015 [Page 13] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 3.2.2.1. Hierarchical Service Path Domains Complex problems often become manageable with a hierarchical approach. This pattern allows network-wide orchestration of Service Chaining to be relatively simple, while hiding the complexities of fine-grained policy-based path selection within sub-domains. Each sub-domain can be independently administered and orchestrated. Figure 7 shows two levels of hierarchy in a service provider's network. At the top level in the hierarchy, Service Chaining components are: 1. Edge-classifiers (Edge CF) that reside near the edge of a service provider's domain and 2. SF sub-domains that reside in data centers. 3. SF Domain Proxies that reside in data centers, linking together the levels of the hierarchy. To the higher level, this is an SF. To the lower level, this is a classifier and FWD. Homma, et al. Expires July 27, 2015 [Page 14] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 *How packets traverse* +----+ +-----+ +----------------------+ +-----+ | |SC#1| FWD | |SF Domain Proxy #1 | | FWD | ->| |================* *===============> | | +-----+ | # (in DC#1) # | +-----+ | | | V # | |Edge| |+---+ +---+| Top domain | CF | * * * * *||CF | * * * * * *|FWD|| * * * * * | | * |+---+ +-+-+| * | | * | | | | | | Sub * | | * +-o-o--------------o-o-+ domain* | | * SC#1.2 | |SC#1.1 ^ ^ #1 * | | * +-----+ | | | * | | * | V | | * | | * | +---+ +------+ | | * | | * | |FWD|->|SF#1_1|--+ | * | | * | +---+ +------+ | * | | * V | * | | * +---+ +------+ +---+ +------+ * | | * |FWD|->|SF#1_2|->|FWD|->|SF#2_1| * | | * +---+ +------+ +---+ +------+ * . * * * * * * * * * * * * * * * * * * * * * * . | | +-----+ +-------------------+ +-----+ | |SC#n| FWD | | SF Domain Proxy#q | | FWD | | |=======================================================> | | +-----+ | (in DC#m) | +-----+ +----+ +-------------------+ (Details of sub-domain #q not shown) Figure 7: Service Chain Hierarchy in Service Provider Network The components within an SF sub-domain are opaque at the top level; each SF domain proxy acts as a single SF node in the top-level domain. A service path in the top-level domain may visit multiple sub-domains. At the lower level in the hierarchy, each sub-domain contains an independently administrated Service Chaining network, generally comprised of multiple instances of multiple types of hosts, most likely (but not necessarily) within the same data center. There is no need for knowledge of the "big picture" at the level of the SF- sub-domain except as required to forward packets to the other SFs that are the next hop of each chain. Note that different encapsulation methods can be used at each layer in the hierarchy, provided the SF domain-Proxy can translate between Homma, et al. Expires July 27, 2015 [Page 15] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 them. For example, MPLS could be used to deliver packets from network edge to the SF clusters within data centers, and NSH [I-D.quinn-sfc-nsh] could be used within the data center. Details of Top Level of Hierarchy In this pattern, referring to Figure 8, network-wide Service Chaining orchestration is only concerned with creating service paths from network edge points to sub-domains within data centers and configuring classifiers at a coarse level to get the correct hosts' traffic onto paths that will arrive at appropriate sub-domains. The figure shows one possible service chain passing from edge, through two sub-domains, to network egress. This top level of orchestration may attach meta-data to provide context from the network edge into the data center. +------------+ |Sub-domain#1| | in DC1 | +----+-------+ | .------+---------. +--+ +--+ / / | \--|CF| --->|CF|--/---->' | \ +--+ +--+ / SC#1 | \ | | | | | .------>|---> | / / | \ | / / +--+ \ | / / +--+ |CF|---\ V / /---|CF| +--+ '------+---------' +--+ | +----+-------+ |Sub-domain#2| | in DC2 | +------------+ Figure 8: Network-wide view of Top Level of Hierarchy The orchestration at this top level must ensure bidirectional path symmetry so that inbound packets traverse sub-domains in the reverse order as outbound packets. Because classifiers must have rules to handle any traffic passing through the network, we believe that a useful approach to classification will be to assign traffic to service function paths on Homma, et al. Expires July 27, 2015 [Page 16] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 the basis of coarse classification like subscriber tier, tenant or VRF identifier. These classification rules could be relatively static, changing in response to provisioning but not in response to traffic. In some networks it might be possible to create a rule per residential subscriber, resulting in rule updates when subscribers are assigned IP addresses. However, with judicious allocation of IP blocks, entire classes of subscribers could be classified with IP- prefix rules. Similarly, in a mobile network path selection could be based on APN. Hence, there are methods of globally managing very large networks by choosing a suitable classification granularity. Details of Lower Level of Hierarchy Within each SF sub-domain, there are: 1. An SF domain-proxy to receive incoming data packets on any of the configured service chains and load-balance (if necessary) traffic to classifiers, 2. Classifier(s) to select internal service chain to use, potentially based on stateful flow analysis, DPI, etc. 3. Service components comprised of FWD and SF. Local Service Chaining orchestration is concerned with providing viable paths to various functions, providing failure recovery, NFV elasticity, etc. Classification within each sub-domain can be concerned with determining the local service paths for individual transport-layer flows based on ports, DPI and meta-data provided by the higher-level chain. For any classifier that is transport-layer-stateful, it is most efficient for the same classifier instance to handle traffic in both directions of a bidirectional connection. State tracking may require that service function paths begin and end at the same node with the flow state, where the same classifier instance can be used for both directions of traffic. Homma, et al. Expires July 27, 2015 [Page 17] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 4. Consideration of Service Chaining Methods and Architecture Patterns This chapter presents the results of analyzing the forwarding methods and architecture patterns in chapter 3. 4.1. Analysis of 3.1. Forwarding Methods 4.1.1. Analysis of Method 1 This method can achieve Service Chaining without adding any headers to packets, so it may not cause any increase in packet size or be subject to MTU restrictions. Furthermore, this method does not require additional functions within SFs to be applied to any headers because data packets are transported in original format. Therefore, it will be easier to use legacy SFs for network operators. However, forwarding entries or static configuration for flows at each FWD is required. For example, if there are 10,000 flows to be handled at a CF/FWD, the routing table for each CF/FWD uses 10,000 flow entries at most. Therefore, it might not be feasible for large- scale networks such as carrier networks that handle a SC per user (which means that individual users have their own policies), because some large carriers have over a million users and even more flows. Another concern is the traffic increase in the control plane because route setting is required for each flow. Moreover, it may be hard to use this method if some service functions modify header fields of a packet or frame, for example, NAT/NAPT, in a chain. For example, if a NAT changes the IP address of packets dynamically, the FWDs that follow need to renew their routing tables. The results of the above analysis suggest that this method may be suitable for networks with a limited number of flows. 4.1.2. Analysis of Method 2 In this method, none of the FWDs require any specific routing tables for Service Chaining, but they require a function to forward packets based on header information, and to remove the outermost header from the received packets. Therefore, the control plane would be simple because the SC controller would not be required to manage the routing configuration of FWDs. Also, there are already several technologies proposed that can be used to achieve this method, such as MPLS. However, the more the SFs packets traverse, the more headers have to be added to the packet and this in turn means that the packet size increases. But packet sizes are restricted by the minimal available MTU of any link in the network path and exceeding the MTU will require to fragment the original packet before starting to add more headers required to the service chaining. This requires more Homma, et al. Expires July 27, 2015 [Page 18] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 complexity in processing due to the fragmentation, adds a new source of errors, as fragments of packets can get lost and so the whole original packet will get discarded, and also will cause an increase in traffic as more packets have to be processed by the network. Moreover, from a hardware point of view, it might be challenging for FWDs or SFs to process packets with variable length headers. In terms of SF equipment, if fragmented packets need to be reassembled at every SF, this would be very wasteful of CPU resources, and some equipment has restricted resources and memory for reassembly. The results of the above analysis indicate that this method would be appropriate when the number of SFs in an SC is small, or most packets are forwarded to a static SP. On the other hand, it may be unsuitable in cases where there are many SFs in a chain. 4.1.3. Analysis of Method 3 In this method, a tag is defined for each Service Chain. By adopting single fixed-length tags, this method can prevent an increase in the amount of traffic in the data plane, and can provide an upper bound on packet size. (Problems which happen as a result of exceeding MTU are stated in 4.1.2.) This method also enables FWDs to save resources for flow tables and all SPs may be established in advance in most of cases. It enables CFs and FWDs which are located on the SP to change the following SP, because the CFs and FWDs have only to change the tag attached on the packet. Therefore, this method has many advantages in terms of scalability, and it might be appropriate for use in large-scale networks. However, this method might require renewal of equipment, or Operating Systems (OSes) installed in hardware, or software, or any other components to realize the method in network which includes SFs, if this tag handling is an entirely new mechanism. Furthermore discussion might be required to deploy such standardized technologies. 4.2. Analysis of 3.2. Service Paths Selection Patterns 4.2.1. Analysis of Pattern 1 In this pattern, the mechanism of FWDs would be simpler than the one in pattern 2 because FWDs do not require any functions to select paths or retrieve any information for determination of the next hop. Moreover, it is not necessary to maintain the state of each flow. Therefore, existing protocols for virtualizing networks, such as VxLAN or MPLS, can be used to achieve Service Chaining in this pattern. Homma, et al. Expires July 27, 2015 [Page 19] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 However, this pattern will impact the flexibility of the SCs, as adding new SFs to a SC, removing SFs from a SC, or migrating SFs to other locations requires an update or new creation of a path in the Service Path. Furthermore, unified management of FWDs and SFs in an SC domain would be required in setting end-to-end paths. Therefore, the management system of SPs, for example, a CE, for wide-area networks that include several segments may be massive and complex. Figure 9 shows the case in which SPs are established across multiple datacenters in pattern 1. In Figure 9, a CE manages multiple datacenters as a single SC domain for establishing SPs across multiple datacenters. In pattern 4.2.1.2 (SF Dedicated Model), the number of flow entries that FWDs hold can be extremely small, as FWDs hold only static next- hop information. Also, the CF function would be simple, as the CF only determines the gateway of each SP. However, because the SF (instance) is settled for each SP, resource usage would be high if there were many SPs. +--------------+ . . . . . . . . . . |Control Entity| . . . . . . . +--------------+ . . . . * * . * * * * . * * * * * * * * * * * * * * * * . * * * * * * * * * * . . . * * . . . * * . .-----. .-----------. .-----. * * +----+ / DC#1 \ / WAN \ / DC#2 \ * * | |=====================================================> SP#1 * * | CF |=====================================================> SP#2 * * : : : * * | |=====================================================> SP#n * * +----+ \ / \ / \ / * * '-----' '-----------' '-----' * * * * SC Domain * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Figure 9: Establishment of SPs Across Multiples DCs in Pattern 1 4.2.2. Analysis of Pattern 2 In this pattern, SPs are established with a combination of segmented paths, so it enables SPs to be established flexibly (which means, CEs do not need to constantly manage the entire end-to-end SP) based on additional information such as the load condition of SFs. Homma, et al. Expires July 27, 2015 [Page 20] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 Furthermore, as it is described in the previous section, in cases where some SPs traverse multiple datacenters across a WAN, SPs could be established with a combination of segmented paths that each datacenter determines independently based on the Service Chain information. Therefore, it might be possible to separate SC domains into several small areas for WANs, which would enable a simpler configuration of each CE. Figure 10 shows the case in which SPs are established across multiple datacenters in pattern 2. In Figure 10, each CE manages a single datacenter independently, and the CEs synchronize the Service Chain information for establishing and determining the appropriate segmented SPs in each domain. However, the (fault) monitoring of the whole SC can get harder as multiple domains are part of the SC. On the other hand each domain can perform its fault management as required (and probably better as it is more specific). This will require an overarching (fault) monitoring where information from multiple SC domains is collected and aggregated to get a full view of the end-to-end service of the SC. Moreover, in this pattern, some FWDs may require additional mechanisms to select the next segmented path, and the FWDs must maintain the states of each flow because some SFs require a stateful process, and the FWDs need to insert packets into the same SF instances in the same session. In case that SC information is conveyed to some components via data plane as any encapsulation, a new protocol such as SFC [I-D.ietf-sfc-architecture] will be required. Homma, et al. Expires July 27, 2015 [Page 21] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 Synchronization of Service Chain info. +--------------------------------------+ | | v v +--------+ +--------+ | CE#1 | | CE#2 | +--------+ +--------+ . . * * * * * * . * * * * * * * * * * * * . * * * * * * * . * * . * * .-------------. * * .------------. * * / DC#1 \ * .------. * / DC#2 \ * * +----+ +-----+ * / WAN \ * +-----+ | * * | |=========>| | * | | * | CF/ |==========> SP#1 * * | CF |=========>| FWD |===============>| FWD |==========> SP#2 * * : : : * | | * : : : * * | |=========>| | * \ / * | |==========> SP#n * * +----+ +-----+ * '------' * +-----+ | * * \ / * * \ / * * '-------------' * * '-----------' * * SC Domain#1 * * SC Domain#2 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Figure 10: Establishment of SPs Across Multiples DCs in pattern 2 Also, the detail analysis of establishment of "Hierarchical Service Path domains" is shown in the following section. 4.2.2.1. Analysis of Hierarchical Service Path domains The dynamic selection of SPs pattern allows multiple independent domains of administration. (In the example, two levels were shown, but the pattern could be extended to multiple levels.) This pattern allows even the largest networks to implement SC from the edges of the network by using coarse-grained classification. Classification choices can be made that are feasible within the constraints of the edge classifiers and FWDs. There is no need to maintain flow state or react to traffic at the top level. This pattern allows control of sub-domains to be delegated to different owners. Each domain is simpler to comprehend than would be the case by dealing with a single flat network. Furthermore, failures and errors are localized. (See Figure 11.) Homma, et al. Expires July 27, 2015 [Page 22] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 +----------+ |Top-level | . . . . . . . . . . . . . . . . . . . . . |Control | . |Entity | +------------+ +--------+ . +----------+ |sub-domain#1|. . .| CE#1 | . . +-----+------+ +--------+ . . | . . .------+---------. +---+ . . +---+ / \--|CF |. . . . . . . .|CF |--/ \ |FWD| . . |FWD| / \+---+ . . +---+ | | . . | | . . | | . . +---+ \ / . . |CF | \ / +---+ . . . . .|FWD|---\ /---|CF | . . . +---+ '------+---------' |FWD| | +---+ +--------+ +------------+ | CE#2 |. . .|sub-domain#2| +--------+ +-----+------+ Figure 11: Multiple Control Entities in Hierarchical Service Chaining This hierarchical model supports management of large networks by adhering to these principles: 1. At higher levels of hierarchy packet classification is coarse, to minimize state and control-plane chatter. 2. At lower levels of hierarchy packet classification can be more granular because classifiers in the lower levels deal with a subset of the entire network: fewer flows, lower bit-rate and a subset of network policy. However, in this model, a new component that can proxy between the different domains, termed "SF Domain Proxy," will be required. It has some commonality with the legacy SF proxy discussed in [I-D.song-sfc-legacy-sf-mapping]. This model also requires some coordination of path information within the SF Domain Proxy component, since the proxy must map packets back and forth between domains. Solving this probably requires sharing metadata dictionaries among controllers and inventing a scheme that provides a level of indirection by naming path identifiers and metadata values. Homma, et al. Expires July 27, 2015 [Page 23] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 4.3. Example of selecting Methods and Patterns In this section, clarifications about the most suitable method and pattern are made for the following example networks based on the results of the above analysis. 4.3.1. Example A: Datacenter Network The conditions of network A are as follows: 1. The network is used for several business offices as a single DC. 2. Service Chain varies per office (not per user). 3. The number of SF included in for each Service Chain is few. (e.g. within 5.) 4. SF (instance) cost is not so high. 5. MTU should not be restricted. 6. Service Chains do not fork paths through end-to-end. (As monitoring, or controlling will be harder, some operators may not want to change paths after packets got into a service chain.) On the basis of conditions 4 and 6, Pattern 1 (SF Dedicated Model) would be selected. In this case, any method would be applicable. (Even if method 2 is selected, only one header that shows the gateway to the specific SC is stacked on packets. This does not restrict the MTU.) 4.3.2. Example B: Current Mobile Carrier's Network The conditions of network B are as follows: 1. The network handles millions of users. 2. Service Chain (SF set and order) is predefined and limited. 3. The number of SF, included in for each Service Chain, is few. (e.g. within 5.) 4. The user chooses or the provider can choose for the user a predefined Service Chain to adopt to their traffic. 5. SFs are located in (S)Gi-LAN.(Term referred to [I-D.ietf-sfc-use-case-mobility]) Homma, et al. Expires July 27, 2015 [Page 24] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 6. Service Chains do not require to fork paths through end-to-end. On the basis of conditions 1, 2, and 5, Pattern 1 (SF Shared Model) would be selected because the architecture would be simple. On the basis of conditions 3 and 4, method 1 (unless the configuration or forwarding table does not increase explosively) or 3 would be applicable. 4.3.3. Example C: Fixed and Mobile Converged Network Conditions of the network A is as follows: 1. The network handles millions of users. 2. The user chooses or the provider can choose for the user multiple SFs to adopt to their traffic. 3. Many SFs (e.g. 5 or more,) are included in for each Service Chain. 4. SFs are located in multiple DCs.(e.g. Some delay sensitive SFs, or SFs which should be placed near users' locations are installed in DCs located locally, and added-value SFs are installed in DCs located centrally.) 5. There are some expansive SFs (instance) that should be shared by several SPs. 6. Service Chains may be forked according to the process of SF. On the basis of conditions 1, 2, 3, 4, and 5, Method 3 would be applicable in terms of scalability. Pattern 2 should be selected based on conditions 1 and 6. Although the operation would be complex, there may be a case in which some carriers set multiple DCs and separate SC domains according to their network or service policy. The use case and architecture pattern is introduced in [I-D.ietf-sfc-dc-use-cases]. 5. Acknowledgements The authors would like to thank Konomi Mochizuki and Lily Guo for their reviews and comments. 6. Contributors The following people are active contributors to this document and have provided review, content and concepts (listed alphabetically by surname): Homma, et al. Expires July 27, 2015 [Page 25] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 Hiroshi Dempo NEC Ron Parker Affirmed Networks Paul Quinn Cisco Systems 7. IANA Considerations This memo includes no request to IANA. 8. References [I-D.ietf-sfc-architecture] Halpern, J. and C. Pignataro, "Service Function Chaining (SFC) Architecture", draft-ietf-sfc-architecture-04 (work in progress), January 2015. [I-D.ietf-sfc-dc-use-cases] Surendra, S., Tufail, M., Majee, S., Captari, C., and S. Homma, "Service Function Chaining Use Cases In Data Centers", draft-ietf-sfc-dc-use-cases-02 (work in progress), January 2015. [I-D.ietf-sfc-problem-statement] Quinn, P. and T. Nadeau, "Service Function Chaining Problem Statement", draft-ietf-sfc-problem-statement-10 (work in progress), August 2014. [I-D.ietf-sfc-use-case-mobility] Haeffner, W., Napper, J., Stiemerling, M., Lopez, D., and J. Uttaro, "Service Function Chaining Use Cases in Mobile Networks", draft-ietf-sfc-use-case-mobility-03 (work in progress), January 2015. [I-D.quinn-sfc-nsh] Quinn, P., Guichard, J., Surendra, S., Smith, M., Henderickx, W., Nadeau, T., Agarwal, P., Manur, R., Chauhan, A., Majee, S., Elzur, U., Melman, D., Garg, P., McConnell, B., Wright, C., and K. Kevin, "Network Service Header", draft-quinn-sfc-nsh-04 (work in progress), December 2014. Homma, et al. Expires July 27, 2015 [Page 26] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 [I-D.song-sfc-legacy-sf-mapping] Song, H., You, J., Yong, L., Jiang, Y., Dunbar, L., Bouthors, N., and D. Dolson, "SFC Header Mapping for Legacy SF", draft-song-sfc-legacy-sf-mapping-04 (work in progress), December 2014. [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, January 2001. [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, April 2011. [RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix Translation", RFC 6296, June 2011. Authors' Addresses Shunsuke Homma NTT, Corp. 3-9-11, Midori-cho Musashino-shi, Tokyo 180-8585 Japan Email: homma.shunsuke@lab.ntt.co.jp Kengo Naito NTT, Corp. 3-9-11, Midori-cho Musashino-shi, Tokyo 180-8585 Japan Email: naito.kengo@lab.ntt.co.jp Diego R. Lopez Telefonica I+D. Don Ramon de la Cruz, Street Madrid 28006 Spain Phone: +34 913 129 041 Email: diego.r.lopez@telefonica.com Homma, et al. Expires July 27, 2015 [Page 27] Internet-Draft draft-homma-sfc-forwarding-methods-analysis January 2015 Martin Stiemerling NEC Laboratories Europe / Hochschule Darmstadt Kurfuerstenanlage 36 Heidelberg 69115 Germany URI: ietf.stiemerling.org David Dolson Sandvine 408 Albert Street Waterloo, Ontario N2L 3V3 Canada Email: ddolson@sandvine.com Homma, et al. Expires July 27, 2015 [Page 28]