Network Working Group D. Trossen Internet-Draft D. Purkayastha Intended status: Informational A. Rahman Expires: June 14, 2019 InterDigital Communications, LLC December 11, 2018 Name-Based Service Function Forwarder (nSFF) component within SFC framework draft-trossen-sfc-name-based-sff-02 Abstract Many stringent requirements are imposed on today's network, such as low latency, high availability and reliability in order to support several use cases such as IoT, Gaming, Content distribution, Robotics etc. Adoption of cloud and fog technology at the edge of the network allows operator to deploy a single "Service Function" to multiple "Execution locations". The decision to steer traffic to a specific location may change frequently based on load, proximity etc. Under the current SFC framework, steering traffic dynamically to the different execution end points require a specific 're-chaining', i.e., a change in the service function path reflecting the different IP endpoints to be used for the new execution points. In order to address this, we discuss separating the logical Service Function Path from the specific execution end points. This can be done by identifying the Service Functions using a name rather than a routable IP endpoint (or Layer 2 address). This draft describes the necessary extensions, additional functions and protocol details in SFF (Service Function Forwarder) to handle name based relationships. 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 https://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 June 14, 2019. Trossen, et al. Expires June 14, 2019 [Page 1] Internet-Draft Name Based SFF December 2018 Copyright Notice Copyright (c) 2018 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 (https://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. Example use case: 5G control plane services . . . . . . . . . 4 3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Relevant part of SFC architecture . . . . . . . . . . . . 6 3.2. Challenges with current framework . . . . . . . . . . . . 6 4. Name based operation in SFF . . . . . . . . . . . . . . . . . 7 4.1. General Idea . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Name-Based Service Function Path (nSFP) . . . . . . . . . 8 4.3. Name Based Network Locator Map (nNLM) . . . . . . . . . . 9 4.4. Name-based Service Function Forwarder (nSFF) . . . . . . 11 4.5. High Level Architecture . . . . . . . . . . . . . . . . . 12 4.6. Operational Steps . . . . . . . . . . . . . . . . . . . . 13 5. nSFF Forwarding Operations . . . . . . . . . . . . . . . . . 15 5.1. nSFF Protocol Layers . . . . . . . . . . . . . . . . . . 15 5.2. nSFF Operations . . . . . . . . . . . . . . . . . . . . . 17 5.2.1. Forwarding between nSFFs and nSFF-NR . . . . . . . . 17 5.2.2. SF Registration . . . . . . . . . . . . . . . . . . . 18 5.2.3. Local SF Forwarding . . . . . . . . . . . . . . . . . 19 5.2.4. Remote SF Forwarding . . . . . . . . . . . . . . . . 20 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 7. Security Considerations . . . . . . . . . . . . . . . . . . . 23 8. Informative References . . . . . . . . . . . . . . . . . . . 23 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 1. Introduction The requirements on today's networks are very diverse, enabling multiple use cases such as IoT, Content Distribution, Gaming and Network functions such as Cloud RAN and 5G control planes based on a service-based architecture . These network services are deployed, Trossen, et al. Expires June 14, 2019 [Page 2] Internet-Draft Name Based SFF December 2018 provisioned and managed using Cloud based techniques as seen in the IT world. Virtualization of compute and storage resources is at the heart of providing (often web) services to end users with the ability to quickly provisioning such virtualized service endpoints through, e.g., container based techniques. This creates a dynamicity with the capability to dynamically compose new services from available services as well as move a service instance in response to user mobility or resource availability where desirable. When moving from a pure 'distant cloud' model to one of localized micro data centers with regional, metro or even street level, often called 'edge' data centers, such virtualized service instances can be instantiated in topologically different locations with the overall 'distant' data center now being transformed into a network of distributed ones. The Service Function Chaining (SFC) framework [RFC7665] allows network operators as well as service providers to compose new services by chaining individual "Service Functions (SFs)". Such chains are expressed through explicit relationships of functional components (the service functions), realized through their direct Layer 2 (e.g., MAC address) or Layer 3 (e.g., IP address) relationship as defined through next hop information that is being defined by the network operator, see Section 3 for more background on SFC. In a dynamic service environment of distributed data centers as the one outlined above, with the ability to create and recreate service endpoints frequently, the SFC framework requires to reconfigure the existing chain through information based on the new relationships, causing overhead in a number of components, specifically the orchestrator that initiates the initial service function chain and any possible reconfiguration. This document describes how such changes can be handled without involving the initiation of new and reconfigured SFCs by lifting the chaining relationship from Layer 2 and 3 information to that of service function 'names', such as names for instance being expressed as URIs. In order to transparently support such named relationships, we propose to embed the necessary functionality directly into the Service Function Forwarder (SFF, see [RFC7665]). With that, the SFF described in this document allows for keeping an existing SFC intact, as described by its service function path (SFP), while enabling the selection of an appropriate service function endpoint(s) during the traversal of packets through the SFC. Trossen, et al. Expires June 14, 2019 [Page 3] Internet-Draft Name Based SFF December 2018 2. Example use case: 5G control plane services We exemplify the need for chaining service functions at the level of a service name through a use case stemming from the current 3GPP Rel 16 work on Service Based Architecture (SBA) [_3GPP_SBA], [_3GPP_SBA_ENHANCEMENT]. In this work, mobile network control planes are proposed to be realized by replacing the traditional network function interfaces with a fully service-based one. HTTP was chosen as the application layer protocol for exchanging suitable service requests [_3GPP_SBA]. With this in mind, the exchange between, say the 3GPP (Rel. 15) defined Session Management Function (SMF) and the Access and Mobility management Function (AMF) in a 5G control plane is being described as a set of web service like requests which are in turn embedded into HTTP requests. Hence, interactions in a 5G control plane can be modelled based on service function chains where the relationship is between the specific (IP-based) service function endpoints that implement the necessary service endpoints in the SMF and AMF. The service functions are exposed through URIs with work ongoing to define the used naming conventions for such URIs. This move from a network function model (in pre-Rel 15 systems of 3GPP) to a service-based model is motivated through the proliferation of data center operations for mobile network control plane services. In other words, typical IT-based methods to service provisioning, in particular that of virtualization of entire compute resources, are envisioned to being used in future operations of mobile networks. Hence, operators of such future mobile networks desire to virtualize service function endpoints and direct (control plane) traffic to the most appropriate current service instance in the most appropriate (local) data centre, such data centre envisioned as being interconnected through a software-defined wide area network (SD-WAN). 'Appropriate' here can be defined by topological or geographical proximity of the service initiator to the service function endpoint. Alternatively, network or service instance compute load can be used to direct a request to a more appropriate (in this case less loaded) instance to reduce possible latency of the overall request. Such data center centric operation is extended with the trend towards regionalization of load through a 'regional office' approach, where micro data centers provide virtualizable resources that can be used in the service execution, creating a larger degree of freedom when choosing the 'most appropriate' service endpoint for a particular incoming service request. While the move to a service-based model aligns well with the framework of SFC, choosing the most appropriate service instance at runtime requires so-called 're-chaining' of the SFC since the relationships in said SFC are defined through Layer 2 or 3 identifiers, which in turn are likely to be different if the chosen Trossen, et al. Expires June 14, 2019 [Page 4] Internet-Draft Name Based SFF December 2018 service instances reside in different parts of the network (e.g., in a regional data center). Hence, when a traffic flow is forwarded over a service chain expressed as an SFC-compliant Service Function Path (SFP), packets in the traffic flow are processed by the various service function instances, with each service function instance applying a service function prior to forwarding the packets to the next network node. It is a Service layer concept and can possibly work over any Virtual network layer and an Underlay network, possibly IP or any Layer 2 technology. At the service layer, Service Functions are identified using a path identifier and an index. Eventually this index is translated to an IP address (or MAC address) of the host where the service function is running. Because of this, any change of service function instance is likely to require a change of the path information since either IP address (in the case of changing the execution from one data centre to another) or MAC address will change due to the newly selected service function instance. Returning to our 5G Control plane example, a user's connection request to access an application server in the internet may start with signaling in the Control Plane to setup user plane bearers. The connection request may flow through service functions over a service chain in the Control plane, as deployed by network operator. Typical SFs in a 5G control plane may include "RAN termination / processing", "Slice Selection Function", "AMF" and "SMF". The Classifier, as described in SFC architecture, may reside in the user terminal or at the eNB. These service functions can be configured to be part of a Service Function Chain. We can also say that some of the configurations of the Service Function Path may change at the execution time. E.g. SMF may be relocated as user moves and a new SMF may be included in the Service Function Path based on user location. The following diagram in Figure 1 shows the example Service Function Chain described here. +------+ +---------+ +-----+ +-----+ | User | | Slice | | | | | | App |-->| Control |->| AMF |-->| SMF |--> | Fn | | Function| | | | | +------+ +---------+ +-----+ +-----+ Figure 1: Mapping SFC onto Service Function Execution Points along a Service Function Path Trossen, et al. Expires June 14, 2019 [Page 5] Internet-Draft Name Based SFF December 2018 3. Background [RFC7665] describes an architecture for the specification, creation, and ongoing maintenance of Service Function Chains (SFCs). It includes architectural concepts, principles, and components used in the construction of composite services through deployment of SFCs. In the following, we outline the parts of this SFC architecture relevant for our proposed extension, followed by the challenges with this current framework in the light of our example use case. 3.1. Relevant part of SFC architecture SFC Architecture [RFC7665], describes architectural components such as Service Function (SF), Classifier, and Service Function Forwarder (SFF). It describes the Service Function Path (SFP) as the logical path of an SFC. Forwarding traffic along such SFP is the responsibility of the SFF. For this, the SFFs in a network maintain the requisite SFP forwarding information. Such SFP forwarding information is associated with a service path identifier (SPI) that is used to uniquely identify an SFP. The service forwarding state is represented by the Service Index (SI) and enables an SFF to identify which SFs of a given SFP should be applied, and in what order. The SFF also has information that allows it to forward packets to the next SFF after applying local service functions. The operational steps to forward traffic are then as follows: Traffic arrives at an SFF from the network. The SFF determines the appropriate SF the traffic should be forwarded to via information contained in the SFC encapsulation. After SF processing, the traffic is returned to the SFF, and, if needed, is forwarded to another SF associated with that SFF. If there is another non-local hop (i.e., to an SF with a different SFF) in the SFP, the SFF further encapsulates the traffic in the appropriate network transport protocol and delivers it to the network for delivery to the next SFF along the path. Related to this forwarding responsibility, an SFF should be able to interact with metadata. 3.2. Challenges with current framework As outlined in previous section, the Service Function Path defines an ordered sequence of specific Service Functions instances being used for the interaction between initiator and service functions along the SFP. These service functions are addressed by IP (or any L2/MAC) addresses and defined as next hop information in the network locator maps of traversing SFF nodes. As outlined in our use case, however, the service provider may want to provision SFC nodes based on dynamically spun up service function Trossen, et al. Expires June 14, 2019 [Page 6] Internet-Draft Name Based SFF December 2018 instances so that these (now virtualized) service functions can be reached in the SFC domain using the SFC underlay layer. Following the original model of SFC, any change in a specific execution point for a specific Service Function along the SFP will require a change of the SFP information (since the new service function execution point likely carries different IP or L2 address information) and possibly even the Next Hop information in SFFs along the SFP. In case the availability of new service function instances is rather dynamic (e.g., through the use of container-based virtualization techniques), the current model and realization of SFC could lead to reducing the flexibility of service providers and increasing the management complexity incurred by the frequent changes of (service) forwarding information in the respective SFF nodes. This is because any change of the SFP (and possibly next hop info) will need to go through suitable management cycles. To address these challenges through a suitable solution, we identify the following requirements: o Relations between Service Execution Points MUST be abstracted so that, from an SFP point of view, the Logical Path never changes. o Deriving the Service Execution Points from the abstract SFP SHOULD be fast and incur minimum delay. o Identification of the Service Execution Points SHOULD not use a combination of Layer 2 or Layer 3 mechanisms. The next section outlines a solution to address the issue, allowing for keeping SFC information (represented in its SFP) intact while addressing the desired flexibility of the service provider. 4. Name based operation in SFF 4.1. General Idea The general idea is two-pronged. Firstly, we elevate the definition of a Service Function Path onto the level of 'name-based interactions' rather than limiting SFPs to Layer 3 or Layer 2 information only. Secondly, we extend the operations of the SFF to allow for forwarding decisions that take into account such name-based interaction while remaining backward compatible to the current SFC architecture [RFC7665]. In the following sections, we outline these two components of our solution. If the next hop information in the Network Locator Map is described using L2/L3 identifier, the nSFF MAY operate as described in Trossen, et al. Expires June 14, 2019 [Page 7] Internet-Draft Name Based SFF December 2018 [RFC7665]. On the other hand, if the next hop information in the NLM is described as a name, then the nSFF operates as described in the following sections. In the following sections, we outline the two components of our solution. 4.2. Name-Based Service Function Path (nSFP) In the existing SFC framework [RFC7665], as outlined in Section 3, the SFP information is representing path information based on Layer 2 or 3 information, i.e., MAC or IP addresses , causing the aforementioned frequent adaptations in cases of execution point changes. Instead, we introduce the notion of a 'name-based service function path (nSFP)' In today's networking terms, any identifier can be treated as a name but we will illustrate the realization of a "Name based SFP" through extended SFF operations (see Section 5) based on URIs as names and HTTP as the protocol of exchanging information . Here, URIs are being used to name for a Service Function along the nSFP. It is to be noted that the Name based SFP approach is not restricted to HTTP (as the protocol) and URIs (as next hop identifier within the SFP). Other identifiers such as an IP address itself can also be used and are interpreted as a 'name' in the nSFP . With this, our notion of the nSFP goes beyond the initial proposals made in [I-D.purkayastha-sfc-service-indirection], which limited the notion of a 'name' to a URL (uniform resource locator), commonly used in the addressing of HTTP requests. In other words, IP addresses as well as fully qualified domain names forming complex URIs (uniform resource identifiers), such as www.foo.com/service_name1, are all captured by the notion of 'name' in this draft. Generally, nSFPs are defined as an ordered sequence of the "name" of Service Functions (SF) and a typical name-based Service Function Path may look like: 192.168.x.x -> www.foo.com -> www.foo2.com/service1 -> www.foo2.com/service2 Our use case in Section 2 can then be represented as an ordered named sequence. An example for a session initiation that involves an authentication procedure, this could look like 192.168.x.x -> smf.3gpp.org/session_initiate -> amf.3gpp.org/auth -> smf.3gpp.org/ session_complete -> 192.168.x.x [Note that this example is only a conceptual one, since the exact nature of any future SBA-based exchange of 5G control plane functions is yet to be defined by standardization bodies such as 3GPP] Trossen, et al. Expires June 14, 2019 [Page 8] Internet-Draft Name Based SFF December 2018 In accordance with our use case in Section 2, any of these named services can potentially be realized through more than one replicated SF instances. This leads to make dynamic decision on where to send packets along the SAME service function path information, being provided during the execution of the SFC. Through elevating the SFP onto the notion of name-based interactions, the SFP will remain the same even if those specific execution points change for a specific service interaction. The following diagram in Figure 2, describes this name-based SFP concept and the resulting mapping of those named interactions onto (possibly) replicated instances. +---------------------------------------------------------------+ |SERVICE LAYER | | 192.168.x.x --> www.foo.com --> www.foo2.com --> www.fooN.com | | || || | +----------------------||--------------||-----------------------+ || || || || +----------------------||--------------||-----------------------+ | Underlay network \/ \/ | | +--+ +--+ +--+ +--+ +--+ +--+ | | | | | | | | | | | | | | | | +--+ +--+ +--+ +--+ +--+ +--+ | | Compute and Compute and | | storage nodes storage nodes | +---------------------------------------------------------------+ Figure 2: Mapping SFC onto Service Function Execution Points along a Service Function Path based on Virtualized Service Function Instance 4.3. Name Based Network Locator Map (nNLM) In order to forward a packet within a name-based SFP, we need to extend the network locator map as originally defined in [RFC8300] with the ability to consider name relations based on URIs as well as high-level transport protocols such as HTTP for means of SFC packet forwarding. Another example for SFC packet forwarding could be that of CoAP. The extended Network Locator Map or name-based Network Locator Map (nNLM) is shown in Figure 3 as an example for www.foo.com being part of the nSFP. Such extended nNLM is stored at each SFF throughout the SFC domain with suitable information populated to the nNLM during the configuration phase Trossen, et al. Expires June 14, 2019 [Page 9] Internet-Draft Name Based SFF December 2018 +------+------+---------------------+-------------------------+ | SPI | SI | Next Hop(s) | Transport Encapsulation | +------+------+---------------------+-------------------------+ | 10 | 255 | 192.0.2.1 | VXLAN-gpe | | | | | | | 10 | 254 | 198.51.100.10 | GRE | | | | | | | 10 | 253 | www.foo.com | HTTP | ----------------------------------------------------------- | | | | | | 40 | 251 | 198.51.100.15 | GRE | | | | | | | 50 | 200 | 01:23:45:67:89:ab | Ethernet | | | | | | | 15 | 212 | Null (end of path) | None | +------+------+---------------------+-------------------------+ Figure 3: Name-based Network Locator Map Alternatively, the extended network locator map may be defined with implicit name information rather than explicit URIs as in Figure 3. In the example of Figure 4 below, the next hop is represented as a generic HTTP service without a specific URI being identified in the extended network locator map. In this scenario, the SFF forwards the packet based on parsing the HTTP request in order to identify the host name or URI. It retrieves the URI and may apply policy information to determine the destination host/service. Trossen, et al. Expires June 14, 2019 [Page 10] Internet-Draft Name Based SFF December 2018 +------+------+---------------------+-------------------------+ | SPI | SI | Next Hop(s) | Transport Encapsulation | +------+------+---------------------+-------------------------+ | 10 | 255 | 192.0.2.1 | VXLAN-gpe | | | | | | | 10 | 254 | 198.51.100.10 | GRE | | | | | | | 10 | 253 | HTTP Service | HTTP | ----------------------------------------------------------- | | | | | | 40 | 251 | 198.51.100.15 | GRE | | | | | | | 50 | 200 | 01:23:45:67:89:ab | Ethernet | | | | | | | 15 | 212 | Null (end of path) | None | +------+------+---------------------+-------------------------+ Figure 4: Name-based Network Locator Map with Implicit Name information 4.4. Name-based Service Function Forwarder (nSFF) While [I-D.purkayastha-sfc-service-indirection] outlined the realization of forwarding packets in URL-based interaction through HTTP via a specific function (called Service Request Routing (SRR) in [I-D.purkayastha-sfc-service-indirection] ), it is desirable to extend the SFF of the SFC underlay in order to handle nSFPs transparently and without the need to insert a special (SRR) service function into the nSFP. Such extended name-based SFF would then be responsible for forwarding a packet in the SFC domain as per the definition of the (extended) nSFP. In our exemplary realization for an extended SFF, the solution described in this document uses HTTP as the protocol of forwarding SFC packets to the next (name-based) hop in the nSFP. The URI in the HTTP transaction are the names in our nSFP information, which will be used for name based forwarding. Following our reasoning so far, HTTP requests (and more specifically the plain text encoded requests above) are the equivalent of Packets that enter the SFC domain. In the existing SFC framework, typically an IP payload is assumed to be a packet entering the SFC domain. This packet is forwarded to destination nodes using the L2 encapsulation. Any layer 2 network can be used as an underlay network. This notion is now extended to packets being possibly part of a entire higher layer application, such as HTTP requests. The handling of any intermediate layers such as TCP, IP is left to the Trossen, et al. Expires June 14, 2019 [Page 11] Internet-Draft Name Based SFF December 2018 realization of the (extended) SFF operations towards the next (named) hop. For this, we will first outline the general lifecycle of an SFC packet in the following subsection, followed by two examples for determining next hop information in Section 5.2.3, finalized by a layered view on the realization of the nSFF in Section 5.2.4 4.5. High Level Architecture +----------+ | SF1 | +--------+ +------+ | instance |\ | NR | | SF2 | +----------+ \ +--------+ +------+ \ || || +------------+ \ +-------+ +---------+ +---------+ +-------+ | Classifier |---| nSFF1 |---|Forwarder|---|Forwarder|---| nSFF2 | +------------+ +-------+ +---------+ +---------+ +-------+ || +----------+ | Boundary | | node | +----------+ Figure 5: High-level architecture The high-level architecture for name based operation shown in Figure 5 is very similar to the SFC architecture, as described in [RFC7665]. Two new functions are introduced, as shown in the above diagram, namely the name-based Service Function Forwarder (nSFF) and the Name Resolver (NR). The former is an extension of the existing SFF and is capable of processing SFC packets based on name-based network locator map (nNLM) information, determining the next SF, where the packet should be forwarded and the required transport encapsulation. Like standard SFF operation, it adds transport encapsulation to the SFC packet and forwards it. The Name Resolver is a new functional component, capable of identifying the execution end points, where a "named SF" is running, triggered by suitable resolution requests sent by the nSFF. The other functional components such as Classifier, SF are same as described in SFC architecture [RFC7665], while the Forwarders shown in the above diagram are traditional Layer 2 switches. Trossen, et al. Expires June 14, 2019 [Page 12] Internet-Draft Name Based SFF December 2018 4.6. Operational Steps In the proposed solution, the operations are realized by the name- based SFF, called nSFF. We utilize the high-level architecture in Figure 5 to describe the traversal between two service function instances of an nSFP-based transactions in an example chain of : 192.168.x.x -> SF1 (www.foo.com) -> SF2 (www.foo2.com) -> SF3 -> ... According to the SFC lifecycle [RFC7665] and based on our example chain above, the traffic originates from a Classifier or another SFF on the left. The traffic is processed by the incoming nSFF1 (on the left side) through the following steps. The traffic exits at nSFF2. o Step 1: At nSFF1 the following nNLM is assumed +------+------+---------------------+-------------------------+ | SPI | SI | Next Hop(s) | Transport Encapsulation | +------+------+---------------------+-------------------------+ | 10 | 255 | 192.0.2.1 | VXLAN-gpe | | | | | | | 10 | 254 | 198.51.100.10 | GRE | | | | | | | 10 | 253 | www.foo.com | HTTP | | | | | | | 10 | 252 | www.foo2.com | HTTP | | | | | | | 40 | 251 | 198.51.100.15 | GRE | | | | | | | 50 | 200 | 01:23:45:67:89:ab | Ethernet | | | | | | | 15 | 212 | Null (end of path) | None | +------+------+---------------------+-------------------------+ Figure 6: nNLM at nSFF1 o Step 2: nSFF1 removes the previous transport encapsulation (TE) for any traffic originating from another SFF or classifier (traffic from an SF instance does not carry any TE and is therefore directly processed at the nSFF). o Step 3: nSFF1 then processes the NSH information to identify the next SF at the nSFP level by mapping the NSH information to the appropriate entry in its nNLM (see Figure 6) based on the provided SPI/SI information in the NSH (see Section 3) in order to determine the name-based identifier of the next hop SF. With such nNLM in mind, the nSFF searches the map for SPI = 10 and SI = 253. Trossen, et al. Expires June 14, 2019 [Page 13] Internet-Draft Name Based SFF December 2018 It identifies the next hop as = www.foo.com and HTTP as the protocol to be used. Given the next hop resides locally , the SFC packet is forwarded to the SF1 instance of www.foo.com. Note that the next hop could also be identified from the provided HTTP request, if the next hop information was identified as a generic HTTP service, as defined in Section 5.3. o Step 4: The SF1 instance then processes the received SFC packet according to its service semantics and modifies the NSH by setting SPI = 10, SI = 252 for forwarding the packet along the SFP. It then forwards the SFC packet to its local nSFF, i.e., nSFF1. o Step 5: nSSF1 processes the NSH of the SFC packet again, now with the NSH modified (SPI = 10, SI = 252) by the SF1 instance. It retrieves the next hop information from its nNLM in Figure 6, to be www.foo2.com. Due to this SF not being locally available , the nSFF consults any locally available information regarding routing/ forwarding towards a suitable nSFF that can serve this next hop. o Step 6: If such information exists, the Packet (plus the NSH information) is marked to be sent towards the nSFF serving the next hop based on such information in step 8. o Step 7: If such information does not exist, nSFF1 consults the Name Resolver (NR) to determine the suitable routing/forwarding information towards the identified nSFF serving the next hop of the SFP. For future SFC packets towards this next hop, such resolved information may be locally cached , avoiding to contact the Name Resolver for every SFC packet forwarding. The packet is now marked to be sent via the network in step 8. o Step 8: Utilizing the forwarding information determined in steps 6 or 7, nSFF1 adds the suitable transport encapsulation (TE) for the SFC packet before forwarding via the forwarders in the network towards the next nSFF22. o Step 9: When the Packet (+NSH+TE) arrives at the outgoing nSFF2, i.e., the nSFF serving the identified next hop of the SFP, removes the TE and processes the NSH to identify the next hop information. At nSFF2 the nNLM in Figure 7 is assumed. Based on this nNLM and NSH information where SPI = 10 and SI = 252, nSFF2 identifies the next SF as www.foo2.com. Trossen, et al. Expires June 14, 2019 [Page 14] Internet-Draft Name Based SFF December 2018 +------+------+---------------------+-------------------------+ | SPI | SI | Next Hop(s) | Transport Encapsulation | +------+------+---------------------+-------------------------+ | | | | | | 10 | 252 | www.foo2.com | HTTP | | | | | | | 40 | 251 | 198.51.100.15 | GRE | | | | | | | 50 | 200 | 01:23:45:67:89:ab | Ethernet | | | | | | | 15 | 212 | Null (end of path) | None | +------+------+---------------------+-------------------------+ Figure 7: nNLM at SFF2 o Step 10: If the next hop is locally registered at the nSFF, it forwards the packet (+NSH) to the service function instance, using suitable IP/MAC methods for doing so. o Step 11: Otherwise, the outgoing nSFF adds a new TE information to the packet and forwards the packet (+NSH+TE) to the next SFF or boundary node, as shown in Figure 7. 5. nSFF Forwarding Operations This section outlines the realization of various nSFF forwarding operations in Section 4.6. Although the operations in Section 4 utilize the notion of name-based transactions in general, we exemplify the operations here in Section 5 specifically for HTTP- based transactions to ground our description into a specific protocol for such name-based transaction. We will refer to the various steps in each of the following sub-sections. 5.1. nSFF Protocol Layers Figure 8 shows the protocol layers, based on the high-level architecture in Figure 5. Trossen, et al. Expires June 14, 2019 [Page 15] Internet-Draft Name Based SFF December 2018 +-------+ +------+----+ +----+-----+ |App | | | | +--------+ | | | |HTTP | |--------> | | NR | |nSFF----->|-- |TCP |->| TCP |nSFF| +---/\---+ | | TCP | | |IP | | IP | | || | | IP | | +-------+ +------+----+ +---------+ +---------+ +----------+ | | L2 | | L2 |->|Forwarder|-->|Forwarder|-->| L2 | | +-------+ +------+----+ +---------+ +---------+ +----------+ | SF1 nSFF1 nSFF2 | +-------+ | | App |/ | | HTTP | -----------+ | TCP |\ | IP | | L2 | +-------+ SF2 Figure 8: Protocol layers The nSFF component here is shown as implementing a full incoming/ outgoing TCP/IP protocol stack towards the local service functions, while implementing the nSFF-NR and nSFF-nSFF protocols based on the descriptions in Section 5.2.3. For the exchange of HTTP-based service function transactions, the nSFF terminates incoming TCP connections from as well as outgoing TCP connections to local SFs, e.g., the TCP connection from SF1 terminates at nSFF1, and nSFF1 may store the connection information, such as socket information. It also maintains the mapping information for the HTTP request such as originating SF, destination SF and socket ID. nSFF1 may implement sending keep-alive messages over the socket to maintain the connection to SF1. Upon arrival of an HTTP request from SF1, nSFF1 extracts the HTTP Request and forwards it towards the next node, as outlined in Section 5.2. Any returning response is mapped onto the suitable open socket (for the original request) and send towards SF1. At the outgoing nSFF2, the destination SF2/Host is identified from the HTTP request message. If no TCP connection exists to the SF2, a new TCP connection is opened towards the destination SF2 and the HTTP request is sent over said TCP connection. The nSFF2 may also save the TCP connection information (such as socket information) and maintain the mapping of the socket information to the destination SF2. When an HTTP response is received from SF2 over the TCP connection, nSFF2 extracts the HTTP response, which is forwarded to Trossen, et al. Expires June 14, 2019 [Page 16] Internet-Draft Name Based SFF December 2018 the next node. nSFF2 may maintain the TCP connection through keep- alive messages. 5.2. nSFF Operations In this section, we present three key aspects of operations for the realization of the steps in Section 4.6, namely (i) the registration of local SFs (for step 3 in Section 4.6), (ii) the forwarding of SFC packets to and from local SFs (for step 3 and 4 as well as 10 in Section 4.6), (iii) the forwarding to a remote SF (for steps 5, 6., and 7 in Section 4.6) and to the NR as well as (iv) for the lookup of a suitable remote SF (for step 7 in Section 4.6). We also cover aspects of maintaining local lookup information for reducing lookup latency and others issues. 5.2.1. Forwarding between nSFFs and nSFF-NR Forwarding between the distributed nSFFs as well as between nSFF and NR is realized over the operator network via a path-based approach. A path-based approach utilizes path information provided by the source of the packet for forwarding said packet in the network. This is similar to segment routing albeit differing in the type of information provided for such source-based forwarding, as described in this section. In this approach, the forwarding information to a remote nSFF or the NR is defined as a 'path identifier' (pathID) of a defined length where said length indicate the overall pathID length as the 2 to the power of 'length', i.e., maximum 2^16 bits as path information. The payload of the packet is defined by the various operations outlined in the following sub-sections, resulting in an overall packet being transmitted. With this, the generic forwarding format (GFF) for transport over the operator network is defined in Figure 9 with the length field defining the length of the pathID provided. +---------+-----------------+------------------------//------------+ | | | // | | Length | Path ID | Payload // | | (4 bit) | | // | +---------+-----------------+--------------------//----------------+ Figure 9: Generic Forwarding Format(GFF) For the pathID information, solutions such as those in [Reed2016] can be used. Here, the IPv6 source and destination addresses are used to realize a so-called path-based forwarding from the incoming to the Trossen, et al. Expires June 14, 2019 [Page 17] Internet-Draft Name Based SFF December 2018 outgoing nSFF or the NR. The forwarders in Figure 8 are realized via SDN (software-defined networking) switches, implementing an AND/CMP operation based on arbitrary wildcard matching over the IPv6 source and destination addresses, as outlined in [Reed2016]. Note that in the case of using IPv6 address information for path-based forwarding, the step of removing the transport encapsulation at the outgoing nSFF in Figure 8 is realized by utilizing the provided (existing) IP header (which was used for the purpose of the path-based forwarding in [Reed2016]) for the purpose of next hop forwarding, such as that of IP-based routing. As described in step 8 of the extended nSFF operations, this forwarding information is used as traffic encapsulation. With the forwarding information utilizing existing IPv6 information, IP headers are utilized as TE in this case. The next hop nSFF (see Figure 8) will restore the IP header of the packet with the relevant IP information used to forward the SFC packet to SF2 or it will create a suitable TE (Transport Encapsulation) information to forward the information to another nSFF or boundary node. Forwarding operations at the intermediary forwarders, i.e., SDN switches, examine the pathID information through a flow matching rule in which a specific switch-local output port is represented through the specific assigned bit position in the pathID. Upon a positive match in said rule, the packet is forwarded on said output port. Alternatively, the solution in [I-D.purkayastha-bier-multicast-http] suggests using a so-called BIER (Binary Indexed Explicit Replication) underlay. Here, the nSFF would be realized at the ingress to the BIER underlay, injecting the SFC packet (plus the NSH) header with BIER-based traffic encapsulation into the BIER underlay with each of the forwarders in Figure 8 being realized as a so-called Bit- Forwarding Router (BFR) [RFC8279]. 5.2.1.1. Transport Protocol Considerations Given that the proposed solution operates at the 'named transaction' level, particularly for HTTP transactions, forwarding between nSFFs and/or NR SHOULD be implemented via a transport protocol between nSFFs and/or NR in order to provide reliability, segmentation of large GFF packets, and flow control. The details of this protocol will be outlined at a later stage, with the GFF in Figure 9 being the basic forwarding format for this. 5.2.2. SF Registration As outlined in step 3 and 10 of Section 4.6, the nSFF needs to determine if the SF derived from the nNLM is locally reachable or whether the packet needs forwarding to a remote SFF. For this, a Trossen, et al. Expires June 14, 2019 [Page 18] Internet-Draft Name Based SFF December 2018 registration mechanism is provided for such local SF with the local nSFF. Two mechanisms can be used for this: 1. SF-initiated: We assume that the SF registers its FQDN to the local nSFF. As local mechanisms, we foresee that either a REST-based interface over the link-local link or configuration of the nSFF (through configuration files or management consoles) can be utilized. Such local registration event leads to the nSFF to register the given FQDN with the NR in combination with a system-unique nSFF identifier that is being used for path computation purposes in the NR. For the registration, the packet format in Figure 10 is used (inserted as the payload in the GFF of Figure 9 with the pathID towards the NR), with a hash over the FQDN being conveyed in the registration and the R/D bit set to 0 (for registration). We assume that the pathID towards the NR is known to the nSFF through configuration means. +---------+-----------------+------------------+ | | | | | R/D | hash(FQDN) | nSFF_ID | | (1 bit) | (16 bit) | (8 bit) | +---------+-----------------+------------------+ Figure 10: Registration packet format The NR maintains an internal table that associates the hash(FQDN), the nSFF_id information as well as the pathID information being used for communication between nSFF and NR. The nSFF locally maintains a mapping of registered FQDNs to IP addresses, for the latter using link-local private IP addresses. 2. Orchestration-based: in this mechanism, we assume that SFC to be orchestrated and the chain being provided through an orchestration template with FQDN information associated to a compute/storage resource that is being deployed by the orchestrator. We also assume knowledge at the orchestrator of the resource topology. Based on this, the orchestrator can now use the same REST-based protocol defined in option 1 to instruct the NR to register the given FQDN, as provided in the template, at the nSFF it has identified as being the locally servicing nSFF, provided as the system-unique nSFF identifier. 5.2.3. Local SF Forwarding There are two cases of local SF forwarding, namely the SF sending an SFC packet to the local nSFF (incoming requests) or the nSFF sending a packet to the SF (outgoing requests) as part of steps 3 and 10 in Trossen, et al. Expires June 14, 2019 [Page 19] Internet-Draft Name Based SFF December 2018 Section 4.6. In the following, we outline the operation for HTTP as an example named transaction. As shown in Figure 8, incoming HTTP requests from SFs are extracted by terminating the incoming TCP connection at their local nSFFs at the TCP level. The nSFF MUST maintain a mapping of open TCP sockets to HTTP requests for HTTP response association. For outgoing HTTP requests, the nSFF utilizes the maintained mapping of locally registered FQDNs to link-local IP addresses (see Section 5.2.2 option 1). Hence, upon receiving an SFC packet from a remote nSFF (in step 9 of Section 4.6), the nSFF determines the local existence of the SF through the registration mechanisms in Section 5.2.2. If said SF does exist locally, the HTTP (+NSH) packet, after stripping the TE, is sent to the local SF as step 10 in Section 4.6 via a TCP-level connection. Outgoing nSFF SHOULD keep TCP connections open to local SFs for improving SFC packet delivery in subsequent transactions. 5.2.4. Remote SF Forwarding In steps 5, 6, 7, and 8 of Section 4.6, an SFC packet is forwarded to a remote nSFF based on the nNLM information for the next hop of the nSFP. Section 5.2.4.1 handles the case of suitable forwarding information to the remote nSFF not existing, therefore consulting the NR to obtain suitable information, while Section 5.2.4.2 describes the maintenance of forwarding information at the local nSFF, while Section 5.2.4.3 describes the update of stale forwarding information. Note that the forwarding described in Section 5.2.1 is used for the actual forwarding to the various nSFF components. Ultimately, Section 5.2.4.4 describes the forwarding to the remote nSFF via the forwarder network 5.2.4.1. Remote SF Discovery The nSFF communicates with the NR for two purposes, namely the registration and discovery of FQDNs. The packet format for the former was shown in Figure 10 in Section 5.2.2, while Figure 11 outlines the packet format for the discovery request. A path to a specific FQDN is requested by sending a hash of the FQDN to the NR together with its nSFF_id, receiving as a response a pathID with a length identifier. The NR should maintain a table of discovery requests that map discovered (hash of) FQDN to the nSFF_id that requested it and the pathID that is being calculated as a result of the discovery request. The discovery request for an FQDN that has not previously been served at the nSFF (or for an FQDN whose pathID information has been flushed Trossen, et al. Expires June 14, 2019 [Page 20] Internet-Draft Name Based SFF December 2018 as a result of the update operations in Section 5.2.4.3), results in an initial latency incurred by this discovery through the NR, while any SFC packet sent over the same SFP in a subsequent transaction will utilize the nSFF local mapping table. Such initial latency can be avoided by pre-populating the FQDN-pathID mapping proactively as part of the overall orchestration procedure, e.g., alongside the distribution of the nNLM information to the nSFF. +--------------+-------------+ +--------+-----------------//--------+ | | | | | // | | hash(FQDN) | nSFF_ID | | Length | pathID // | | (16 bit) | (8 bit) | | (4 bit)| // | +--------------+-------------+ +--------+-------------//------------+ Path Request Path Response Figure 11: Discovery packet format 5.2.4.2. Maintaining Forwarding Information at Local nSFF Each nSFF MUST maintain an internal table that maps the (hash of the) FQDN information to a suitable pathID information. As outlined in step 7 of Section 4.6, if a suitable entry does not exist for a given FQDN, the pathID information is requested with the operations in Section 5.2.4.1 and the suitable entry is locally created upon receiving a reply with the forwarding operation being executed as described in Section 5.2.1. If such entry does exist (i.e., step 6 of Section 4.6) the pathID is locally retrieved and used for the forwarding operation in Section 5.2.1. 5.2.4.3. Updating Forwarding Information at nSFF The forwarding information maintained at each nSFF (see Section 5.2.4.2) might need to be updated for three reasons: o An existing SF is no longer reachable: In this case, the nSFF with which the SF is locally registered, deregisters the SF explicitly at the NR by sending the packet in Figure 10 with the hashed FQDN and the R/D bit set to 1 (for deregister). o Another SF instance has become reachable in the network (and therefore might provide a better alternative to the existing SF): in this case, the NR has received another packet with format defined in Figure 11 but a different nSFF_id value. Trossen, et al. Expires June 14, 2019 [Page 21] Internet-Draft Name Based SFF December 2018 o Links along paths might no longer be reachable: the NR might use suitable southbound interface to transport networks to detect link failures, which it associates to the appropriate pathID bit position For this purpose, the packet format in Figure 12 is sent from the NR to all affected nSFFs, using the generic format in Figure 9. The pathID to the affected nSFFs is computed as the binary OR over all pathIDs to those nSFF_ids affected where the pathID information to the affected nSFF_id values is determined from the NR-local table maintained in the registration/deregistration operation of Section 5.2.2. +---------+-----------------+--------------//----+ | | | // | | Type | #IDs | IDs // | | (1 bit) | (8 bit) | // | +---------+-----------------+----------//--------+ Figure 12: Path update format In case 1 and 2, the Type bit is set to 1 (type nSFF_id) and the affected nSFFs are determined by those nSFFs that have previously sent SF discovery requests, utilizing the optional table mapping previously registered FQDNs to nSFF_id values. If no table mapping the (hash of) FQDN to nSFF_id is maintained, the update is sent to all nSFFs. Upon receiving the path update at the affected nSFF, all appropriate nSFF-local mapping entries to pathIDs for the hash(FQDN) identifiers provided will be removed, leading to a new NR discovery request at the next remote nSFF forwarding to the appropriate FQDN. In case 3, the Type bit is set to 0 (type linkID) and the affected nSFFs are determined by those nSFFs whose discovery requests have previously resulted in pathIDs which include the affected link, utilizing the optional table mapping previously registered FQDNs to pathID values (see Section 5.2.4.1). Upon receiving the path update, the affected nSFF will check its internal table that maps FQDNs to pathIDs to determine those pathIDs affected by the link problems. For this, the pathID entries of said table are checked against the linkID values provided in the ID entry of the path update through a binary AND/CMP operation to check the inclusion of the link in the pathIDs to the FQDNs. If any pathID is affected, the FQDN-pathID entry is removed, leading to a new NR discovery request at the next remote nSFF forwarding to the appropriate FQDN. Trossen, et al. Expires June 14, 2019 [Page 22] Internet-Draft Name Based SFF December 2018 5.2.4.4. Forwarding to remote nSFF Once step 5, 6, and 7 in Section 4.6 are being executed, step 8 finally sends the SFC packet to the remote nSFF, utilizing the pathID returned in the discovery request (Section 5.2.4.1) or retrieved from the local pathID mapping table. The SFC packet is placed in the payload of the generic forwarding format in Figure 14 together with the pathID and the nSFF eventually executes the forwarding operations in Section 5.2.1. 6. IANA Considerations This document requests no IANA actions. 7. Security Considerations The operations in Section 4 and 5 consider the forwarding of SFC packets between named SFs based on HTTP. The support for HTTPS is foreseen to ensure suitable encryption capability of such exchanges. Future updates to this draft will outline the support for such HTTPS- based SFC exchanges. 8. Informative References [_3GPP_SBA] 3GPP, "Technical Realization of Service Based Architecture", 3GPP TS 29.500 0.4.0, January 2018, . [_3GPP_SBA_ENHANCEMENT] 3GPP, "New SID for Enhancements to the Service-Based 5G System Architecture", 3GPP S2-182904 , February 2018, . [I-D.purkayastha-bier-multicast-http] Purkayastha, D., Rahman, A., and D. Trossen, "Multicast HTTP using BIER", draft-purkayastha-bier-multicast-http-00 (work in progress), March 2018. [I-D.purkayastha-sfc-service-indirection] Purkayastha, D., Rahman, A., Trossen, D., Despotovic, Z., and R. Khalili, "Alternative Handling of Dynamic Chaining and Service Indirection", draft-purkayastha-sfc-service- indirection-02 (work in progress), March 2018. Trossen, et al. Expires June 14, 2019 [Page 23] Internet-Draft Name Based SFF December 2018 [Reed2016] Reed, M., Al-Naday, M., Thomas, N., Trossen, D., and S. Spirou, "Stateless multicast switching in software defined networks", ICC 2016, 2016. [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015, . [RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., Przygienda, T., and S. Aldrin, "Multicast Using Bit Index Explicit Replication (BIER)", RFC 8279, DOI 10.17487/RFC8279, November 2017, . [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, January 2018, . Appendix A. Change Log [Note to Editor: Please remove this section before publication.] Changes from 01 version: o Added this Change Log in Appendix A. o Addressed Editorial Comments (nits) throughout the document from Dirk Hugo, DT. o Section 4.1, added a paragraph to clarify the execution path of nSFF when the next hop is identified by L2/L3 identifier or by using Name. o Section 5.1, added paragraphs to clarify how TCP connection is terminated and handled at the ingress nSFF and egress nSFF. Authors' Addresses Trossen, et al. Expires June 14, 2019 [Page 24] Internet-Draft Name Based SFF December 2018 Dirk Trossen InterDigital Communications, LLC 64 Great Eastern Street, 1st Floor London EC2A 3QR United Kingdom Email: Dirk.Trossen@InterDigital.com URI: http://www.InterDigital.com/ Debashish Purkayastha InterDigital Communications, LLC Conshohocken USA Email: Debashish.Purkayastha@InterDigital.com Akbar Rahman InterDigital Communications, LLC Montreal Canada Email: Akbar.Rahman@InterDigital.com Trossen, et al. Expires June 14, 2019 [Page 25]