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Network Working Group                                         D. Trossen
Internet-Draft                                            D. Purkayastha
Intended status: Informational                                 A. Rahman
Expires: April 20, 2019                 InterDigital Communications, LLC
                                                        October 17, 2018

   Name-Based Service Function Forwarder (nSFF) component within SFC


   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 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 April 20, 2019.

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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
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   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 . . . . . . . . .   3
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     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) . . . . . . . . .   7
     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 . . . . . . . . . . . . . . . . . . . . .  16
       5.2.1.  Forwarding between nSFFs and nSFF-NR  . . . . . . . .  16
       5.2.2.  SF Registration . . . . . . . . . . . . . . . . . . .  18
       5.2.3.  Local SF Forwarding . . . . . . . . . . . . . . . . .  19
       5.2.4.  Remote SF Forwarding  . . . . . . . . . . . . . . . .  19
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   8.  Informative References  . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

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 services are deployed, provisioned
   and managed using Cloud based techniques as seen in the IT world.

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   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".  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).  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.

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

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   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 session management function (SMF) and the authentication
   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
   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

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   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 and 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
   configuration 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 3 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

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.

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   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 (i.e.,
   different SFF) hop 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 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
   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 points for a specific Service Function along the SFP will
   require a change of the SFP information (since the new service

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   function execution points 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 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 mechanism.

   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.

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 afore
   mentioned frequent adaptations in cases of execution point changes.
   Instead, we introduce the notion of a 'name-based service function
   path (nSFP)'

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   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 ->

   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]

   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 describes this name-based SFP concept and the
   resulting mapping of those named interactions onto (possibly)
   replicated instances.

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     |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 name-based SFC, 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

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         | SPI  | SI   | Next Hop(s)         | Transport Encapsulation |
         | 10   | 255  |           | VXLAN-gpe               |
         |      |      |                     |                         |
         | 10   | 254  |       | GRE                     |
         |      |      |                     |                         |
         | 10   | 253  | www.foo.com         | HTTP                    |
         |      |      |                     |                         |
         | 40   | 251  |       | 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.

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         | SPI  | SI   | Next Hop(s)         | Transport Encapsulation |
         | 10   | 255  |           | VXLAN-gpe               |
         |      |      |                     |                         |
         | 10   | 254  |       | GRE                     |
         |      |      |                     |                         |
         | 10   | 253  | HTTP Service        | HTTP                    |
         |      |      |                     |                         |
         | 40   | 251  |       | 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

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 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
   entire higher layer application, such as HTTP requests.  The handling
   of any intermediate layers such as TCP, IP is left to the realization

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   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 Forwarder shown in
   the above diagram are Layer 2 switches.

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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  |           | VXLAN-gpe               |
         |      |      |                     |                         |
         | 10   | 254  |       | GRE                     |
         |      |      |                     |                         |
         | 10   | 253  | www.foo.com         | HTTP                    |
         |      |      |                     |                         |
         | 10   | 252  | www.foo2.com        | HTTP                    |
         |      |      |                     |                         |
         | 40   | 251  |       | 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.

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      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 the
      routing/forwarding information 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.

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         | SPI  | SI   | Next Hop(s)         | Transport Encapsulation |
         |      |      |                     |                         |
         | 10   | 252  | www.foo2.com        | HTTP                    |
         |      |      |                     |                         |
         | 40   | 251  |       | 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.

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   +-------+  +------+----+                              +----+-----+
   |App    |  |      |    |   +--------+                 |    |     |
   |HTTP   |  |-------->  |   |  NR    |                 |nSFF----->|--
   |TCP    |->| TCP  |nSFF|   +---/\---+                 |    | TCP | |
   |IP     |  | IP   |    |       ||                     |    | IP  | |
   +-------+  +------+----+  +---------+   +---------+   +----------+ |
   |   L2  |  |      L2   |->|Forwarder|-->|Forwarder|-->|   L2     | |
   +-------+  +------+----+  +---------+   +---------+   +----------+ |
     SF1           nSFF1                                     nSFF2    |
                                                 +-------+            |
                                                 | App   |/           |
                                                 | HTTP  | -----------+
                                                 | TCP   |\
                                                 | IP    |
                                                 | L2    |

                         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.

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

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   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

   |         |                 |                       //             |
   | 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
   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

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   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].  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
   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 SR
   (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

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   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

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
   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 handles the case of suitable forwarding
   information to the remote nSFF not existing, therefore consulting the
   NR to obtain suitable information, while Section describes

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   the maintenance of forwarding information at the local nSFF, while
   Section 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 and SR components.  Ultimately,
   Section describes the forwarding to the remote nSFF via the
   forwarder network  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 being
   served at the nSFF (or for an FQDN whose pathID information has been
   flushed as a result of the update operations in Section,
   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  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 and the suitable entry is locally created upon

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   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.  Updating Forwarding Information at nSFF

   The forwarding information maintained at each nSFF (see
   Section 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.

   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

   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

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   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  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.  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 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

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              3GPP, "Technical Realization of Service Based
              Architecture", 3GPP TS 29.500 0.4.0, January 2018,

              3GPP, "New SID for Enhancements to the Service-Based 5G
              System Architecture", 3GPP S2-182904 , February 2018, <htt

              Purkayastha, D., Rahman, A., and D. Trossen, "Multicast
              HTTP using BIER", draft-purkayastha-bier-multicast-http-00
              (work in progress), March 2018.

              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.

              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,

Authors' Addresses

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   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

   Email: Debashish.Purkayastha@InterDigital.com

   Akbar Rahman
   InterDigital Communications, LLC

   Email: Akbar.Rahman@InterDigital.com

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