Internet DRAFT - draft-irtf-nfvrg-service-verification

draft-irtf-nfvrg-service-verification



 



NFV Research Group                                         M-K. Shin, Ed.
Internet-Draft                                                       ETRI
Intended status: Informational                                     K. Nam
Expires: April 29, 2018                                           Friesty
                                                                  S. Pack
                                                                       KU
                                                                   S. Lee
                                                                     ETRI
                                                              R. Krishnan
                                                                     Dell
                                                         October 29, 2017


    Verification of NFV Services : Problem Statement and Challenges
                draft-irtf-nfvrg-service-verification-05

Abstract         

   NFV relocates network functions from dedicated hardware appliances to
   generic servers, so they can run in software. However, incomplete or
   inconsistent configuration of virtualized network functions (VNFs)
   and forwarding graph (FG, aka service chain) could cause break-down
   of the supporting infrastructure. In this sense, verification is
   critical for network operators to check their requirements and
   network properties are correctly enforced in the supporting
   infrastructures. Recognizing these problems, we discuss key
   properties to be checked on NFV services. Also, we present
   challenging issues related to verification in NFV environments.  

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 27, 2017.

Copyright Notice

 


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   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . .  . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Problem statement . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1. Dependencies of network service components in NFV framework .3
     2.2. Invariant and error check in VNF FGs . . . . . . . . . . . . 4 
     2.3. Load Balancing and optimization among VNF Instances  . . . . 4
     2.4. Policy and state consistency on NFV services . . . . . . . . 4
     2.5. Performance  . . . . . . . . . . . . . . . . . . . . . . . . 5 
     2.6. Security . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   3.  Examples - NS policy conflict with NFVI policy  . . . . . . . . 6 
   4.  Requirements of verification framework  . . . . . . . . . . . . 7
   5.  Challenging issues  . . . . . . . . . . . . . . . . . . . . . . 8
     5.1. Consistency check in distributed state .   . . . . . . . . . 8
     5.2. Intent-based service composition . . . . . . . . . . . . . . 8 
     5.3. Finding infinite loops in VNF FGs . .  . . . . . . . . . . . 8
     5.4. Complexity of live traffic verification  . . . . . . . . . . 9
     5.5. Languages and their semantics  . . . . . . . . . . . . . . . 9
     5.6. Stateful VNFs with multiple physical views . . . . . . . . . 9   
   6.  Gap analysis - open source projects . . . . . . . . . . . . . .10
     6.1. OPNFV  . . . . . . . . . . . . . . . . . . . . . . . . . . .10
     6.2. ODL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.3. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 13  
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16






 


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1. Introduction

   NFV is a network architecture concept that proposes using IT
   virtualization related technologies, to virtualize entire classes of
   network service functions into building blocks that may be connected,
   or chained, together to create end-to-end network services. NFV
   service is defined as a composition of network functions and
   described by its functional and behavioral specification, where
   network functions (i.e., firewall, DPI, SSL, load balancer, NAT, AAA,
   etc.) are well-defined, hence both their functional behavior as well
   as their external interfaces are described in each specifications. 

   In NFV, a VNF is a software package that implements such network
   functions. A VNF can be decomposed into smaller functional modules or
   APIs for scalability, reusability, and/or faster response [ETSI-NFV-
   Arch],[ETSI-NFV-MANO]. These modular updates or composition for a
   network function may lead to many other verification or security
   issues. In addition, a set of ordered network functions which build
   FGs may be connected, or chained, together to create an end-to-end
   network service. Multiple VNFs can be composed together to reduce the
   complexity of management and VNF FGs. While autonomic networking
   techniques could be used to automate the configuration process
   including FG updates, it is important to take into account that
   incomplete and/or inconsistent configuration may lead to verification
   issues. Moreover, automation of NFV process with integration of SDN
   may lead the network services to be more error-prone. In this sense,
   we need to identify and verify key properties to be correct before
   VNFs and FGs are physically placed and realized in the supporting
   infrastructure.

1.1.  Terminology

   This document draws freely on the terminology defined in [ETSI-NFV-
   Arch].


2. Problem statement 

   The verification services should be able to check the following
   properties:

2.1. Dependencies of network service components in NFV framework

   In NFV framework, there exist several network service components
   including NFVI, VNFs, MANO, etc. as well as network controller and
   switches to realize end-to-end network services. Unfortunately, these
   components have intricate dependencies that make operation incorrect.
   In this case, there is inconsistency between states stored and
 


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   managed in VNF FGs and network tables (e.g., flow tables), due to
   communication delays and/or configuration errors. For example, if a
   VNF is replicated into the other same one for the purpose of load
   balance and a new FG is established through the copied one, but all
   the state/DBs replication is not finished yet due to delays, this can
   lead to unexpected behaviors or errors of the network service.
   Therefore, these dependencies make it difficult to correctly compose
   NFV-enabled end-to-end network services.

2.2. Invariant and error check in VNF FGs  

   In VNF FGs, an infinite loop construction should be avoided and
   verified. Let us consider the example. Two VNF A and VNF B are
   located in the same service node X whereas another VNF C resides in
   other service node Y [SIGCOMM-Gember]. Also, the flow direction is
   from X to Y, and the given forwarding rule is A->C->B. In such a
   case, service node Y can receive two ambiguous flows from VNF A: 1)
   one flow processed by VNF A and 2) another flow processed by VNF A,
   B, and C. For the former case, the flow should be processed by VNF C
   whereas the latter flow should be further routed to next service
   nodes. If these two flows cannot be distinguished, service node Y can
   forward the flow to service node X even for the latter case and a
   loop can be formed. To avoid the infinite loop formation, the
   forwarding path over VNF FG should be checked in advance with the
   consideration of physical placement of VNF among service nodes. Also,
   reactive verification may be necessary, since infinite loop formation
   may not be preventable in cases where configuration change is
   happening with live traffic. 

   In addition, isolation between VNFs (e.g. confliction of properties
   or interference between VNFs) and consistent ordering of VNF FGs
   should be always checked and maintained. 

2.3. Load balancing among VNF instances

   In VNF FG, different number of VNF instances can be activated on
   several service nodes to carry out the given task. In such a
   situation, load balancing among the VNF instances is one of the most
   important considerations. In particular, the status in resource usage
   of each service node can be different and thus an appropriate amount
   of jobs should be distributed to the VNF instances. To guarantee
   well-balanced load among VNF instances, the correctness of hash
   functions for load balancing needs to be verified. Moreover, when VNF
   instances locate in physically different service nodes, simple
   verification of load balancing in terms of resource usage is not
   sufficient because different service nodes experience diverse network
   conditions (e.g., different levels of network congestion)[ONS-
   Gember]. Therefore, it is needed to monitor global network condition
 


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   as well as local resource condition to achieve the network-wide load
   balancing in VNF FGs. Also, whether the monitoring function for
   network/compute/storage resources is correctly working should be
   checked.

2.4. Policy and state consistency on NFV services

   In VNF FG, policy to specific users can be dynamically changed. For
   example, a DPI VNF can be applied only in the daytime in order to
   prohibit from watching adult contents while no DPI VNFs applied
   during the nighttime. When the policy is changed, the changed policy
   should be reconfigured in VNF service nodes as soon as possible. If
   the reconfiguration procedure is delayed, inconsistent policies may
   exist in service nodes. Consequently, policy inconsistency or
   confliction needs to be checked. Also in some situations, states for
   VNF instances may be conflicted or inconsistent. Especially when a
   new VNF instance is instantiated for scale-up and multiple VNF
   instances are running, these multiple VNF instances may have
   inconsistent states owing to inappropriate instantiation procedure
   [SIGCOMM-Gember]. In particular, since the internal states of VNF
   instances (e.g., the instantaneous state of CPU, register, and memory
   in virtual machine) are not easily-visible, a new way to check the
   VNF internal states should be devised. 

2.5. Performance 

   In VNF FG, VNF instances can be located in different service nodes
   and these service nodes have different load status and network
   conditions. Consequently, the overall throughput of VNF FG is
   severely affected by the service nodes running VNF instances. For
   example, if a VNF instance locates in a heavily loaded service node,
   the service time at the service node will be increased. In addition,
   when a VNF FG includes a bottleneck link experiencing congestion, the
   end-to-end performance (e.g., latency and throughput) in the VNF FG
   can be degraded. Furthermore, policies on the performance such as
   minimum bandwidth or latency can be given to VNFs or their FGs.
   Therefore, the identification of bottleneck link and node is the
   first step for performance verification or guarantee of the VNF FG
   [ONS-Gember]. After detecting the bottleneck link/node, the VNF
   requiring scale up or down can be identified and the relocation of
   VNF instance among service nodes can be determined.

2.6. Security 

   How to verify security holes in VNF FG is another important
   consideration. In terms of security services, authentication, data
   integrity, confidentiality, and replay protection should be provided.
   On the other hand, several VNFs (e.g., NAT) can modify or update
 


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   packet headers and payload. In these environments, it is difficult to
   protect the integrity of flows traversing such VNFs. Another security
   concern in the VNF FG is distributed denial of service (DDoS) to a
   specific service node. If an attacker floods packets to a target
   service node, the target service node cannot perform its functions
   correctly. Therefore, such security attacks in the VNF FG should be
   detected and handled in an efficient manner. In the case of DDoS,
   adding a DDoS appliance as the first element in the service chain
   would help alleviate the problem. Moreover, unknown or unauthorized
   VNFs can run and thus how to identify those problems is another
   security challenge. 


3.  Examples - NS policy conflict with NFVI policy

   Another target of NFV verification is conflict of Network Service
   (NS) policies against global network policy, called NFVI policy.

   NFV allocates and manages NFVI resources for a network service
   according to an NS policy given in the network service descriptor
   (NSD), which describes how to govern NFVI resources for VNF instances
   and VL instances to support KPIs of the network service. Example
   factors of the NS policy are resource constraints (or deployment
   flavor), affinity/anti-affinity, scaling, fault and performance
   management, NS topology, etc. 

   For a network-wide (or NS-wide) management of NFVI, NFVI policy (or
   global network policy) can be provided to describe how to govern the
   NFVI resources for optimized use of the infrastructure resources
   (e.g., energy efficiency and load balancing) rather than optimized
   performance of a single network service. Example factors of the NFVI
   policy are NFVI resource access control, reservation and/or
   allocation policies, placement optimization based on affinity and/or
   anti-affinity rules, geography and/or regulatory rules, resource
   usage, etc.

   While both of the policies define the requirements for resource
   allocation, scheduling, and management, the NS policy is about a
   single network service; and the NFVI policy is about the shared NFVI
   resources, which may affect all of the given network services
   globally. Thus, some of NS and NFVI policies may be inconsistent with
   each other when they have contradictive resource constraints on the
   shared NFVI resources. Examples of the policy conflicts are as
   follows:

   <Example conflict case #1>

    o NS policy of NS_A (composed of VNF_A and VNF_B)
 


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      - Resource constraints: 3 CPU core for VNF_A and 2 CPU core for VNF_B
      - Affinity rule between VNF_A and VNF_B

    o NFVI policy
      - No more than 4 CPU cores per physical host

    o Conflict case
      - The NS policy cannot be met within the NFVI policy

   <Example conflict case #2>

    o NS policy of NS_B (composed of VNF_A and VNF_B)
      - Affinity rule between VNF_A and VNF_B

    o NFVI policy
      - Place VM whose outbound traffic is larger than 100Mbps at POP_A
      - Place VM whose outbound traffic is smaller than 100Mbps at POP_B

    o Conflict case
      - If VNF_A and VNF_B generate traffic in 150Mbps and 50Mbps, 
        respectively, 
      - VNF_A and VNF_B need to be placed at POP_A and POP_B, respectively 
        according to the NFVI policy
      - But it will violate the affinity rule given in the NS policy

   <Example conflict case #3>

    o NS policy of NS_C (composed of VNF_A and VNF_B)
      - Resource constraints: VNF_A and VNF_B exist in the same POP
      - Auto-scaling policy: if VNF_A has more than 300K CPS, scale-out

    o NFVI policy
     - No more than 10 VMs per physical host in POP_A

    o Conflict case
     - If CPS of VNF_A in POP_A gets more than 300K CPS,
     - and if there is no such physical host in the POP_A whose VMs are 
       smaller than 10,
     - VNF_A need to be scaled-out to other POP than POP_A according to 
       the NFVI policy
     - But it will violate the NS policy


4. Requirements of verification framework

   The verification framework addressed in this document follows [ETSI-
   NFV-Testing]. [ETSI-NFV-Testing] covers the following aspects of pre-
   deployment testing: 1) assessing the performance of the NFVI and its
 


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   ability to fulfil the performance and reliability requirements of the
   VNFs executing on the NFVI, 2) data and control plane testing of VNFs
   and their interactions with the NFV Infrastructure and the NFV MANO,
   and 3) validating the performance, reliability and scaling
   capabilities of network services.

   A verification framework for NFV-based services also needs to satisfy
   the following requirements:.

     o R1 : It should be able to check global and local properties and
            invariants. Global properties and invariants relate to the 
            entire VNFs, and local properties and invariants relates to 
            the specific domain or resources that some of the VNFs are   
            using. For example, Loop-freeness and isolation between 
            VNFs can be regarded as global. The policies that are 
            related only to the specific network controllers or devices 
            are local.

     o R2 : It should be able to access to information on the entire 
            network states and resource usage whenever verification 
            tasks are started. It can directly manage the states of 
            network and NFV-based services through databases or any 
            solution that specializes in dealing with the network 
            topology and configurations, or can utilize the functions 
            provided by NFV M&O and VNFI solutions to get or set the 
            states at any time.

     o R3 : It should be independent from specific solutions and
            frameworks, and provide standard APIs.

     o R4 : It should able to process standard protocols such as 
            NetConf, YANG, OpenFlow, and northbound and southbound 
            interfaces that are related network configurations, and 
            used by OSS.


5. Challenging issues 

   There are emerging challenges that the verification services face
   with.

5.1. Consistency check in distributed state

   Basically, NFV states as well as SDN controllers are distributed.
   Writing code that works correctly in a distributed setting is very
   hard. Therefore, distributed state management and consistency check
   has challenging issues. Some open source projects such as ONOS offers
   a core set of primitives to manage this complexity. RAFT algorithm
 


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   [RAFT] is used for distribution and replication. Similarly, Open
   daylight project has a clustering concept to management distributed
   state. There is no "one-size-fits-all" solution for control plane
   data consistency.

5.2. Intent-based service composition

   Recently, Intent-based policing feature/approach/mechanism has been
   added in open source projects [ODL],[ONOS]. The Intent allows for a
   descriptive way to get what is desired from the infrastructure,
   unlike the current NFV description and SDN interfaces which are based
   on describing how to provide different services. This Intent will
   accommodate orchestration services and network and business oriented
   SDN/NFV applications, including OpenStack Neutron, Service Function
   Chaining, and Group Based Policy. A Intent compiler translates and
   compiles it into low level instructions (e.g., SDN
   controller/OpenStack primitives) for network service components. In
   this sense, error checking and debugging are critical for reliable
   Intent-based service composition. 

5.3. Finding infinite loops 

   General solutions for the infinite loop can lead to intractable
   problem (e.g. the halting problem). To make the verification
   practical and minimize the complexity, some restrictions are
   required. Finding cycle can be processed in polynomial time but the
   restriction could be too much for some cases that service functions
   or network flows requires finite loops.

5.4. Complexity of live traffic verification

   It is a known fact that the complexity of verification tasks for the
   real and big problem is high. A few invariants can be checked in
   real-time but it would be impossible if the size of VNFs increases or
   properties to be checked are complex.

5.5. Languages and their semantics

   For the verification, all the information on VNFs including
   configurations, dynamic states and their temporal orderings need to
   be precisely expressed in platform independent languages based on
   formal semantics. The languages and their semantic models should be
   optimized to the verification frameworks as well as the NFV
   infrastructures.

5.6. Stateful VNFs with multiple physical views

   The correctness of VNFs whose behaviors depend on the previous states
 


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   (packets, actions, etc) and whose physical entities are multiple
   should be checked differently than the stateless ones. Such VNFs
   include firewall, load balancer, NAT, flow rules with counter or soft
   timeout.

     o Case 1: 
       If a firewall service is implemented over two physical OpenFlow 
       switches, there could be two paths that the client-server 
       packets go through. If the packets between client and server go 
       through the same switch, the firewall functions correctly. 
       However if packets from client to server go through S1 but 
       packets from server to client come back through S2, those flows 
       could be blocked and lead to false-negative result.

       To mitigate the situation, states of all instances for one 
       logical VNF must be considered to verify the correctness.

                    ~-----------------------~
                    |Enterprise/private nets|
                    |  +----+               |
        +------+  |----| S1 |<--|  +------+ |
        |Server|<-+ |  +----+   +--|Client| |
        |      |--+ |  +----+   +->|      | |
        +------+  |--->| S2 |---|  +------+ |
                    |  +----+               |
                    ~-----------------------~

     o Case 2: 
       If there are VNFs whose behavior depend on the previous VNF, 
       those dependency must be considered as well. 

       For example, if firewall and load balancer gets packets go 
       through NAT service, they need to know the header mapping 
       information that the NAT have set to correctly process their 
       functions. If the FG consists of IPS followed by DPI and those 
       functions are connected different switches, the switch 
       connecting DPI must know if the incomming packets should be 
       forwarded to DPI or not. Port knocking is also well-known 
       example of stateful function.

       To mitigate the situation, the states of all VNFs having 
       behavioral dependency must be considered when they are verified.


6. Gap analysis - open source projects 

   Recently, the Open Platform for NFV (OPNFV) community is
   collaborating on a carrier-grade, integrated, open source platform to
 


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   accelerate the introduction of new NFV products and services [OPNFV].
   Open Daylight (ODL) is also being tightly coupled with this OPNFV
   platform to integrate SDN controller into NFV framework [ODL].   

   This clause analyzes the existing open source projects including
   OPNFV and ODL related to verification of NFV services.

6.1. OPNFV 

6.1.1. Doctor 

   The Doctor project provides a NFVI fault management and maintenance
   framework on top of the virtualized infrastructure. The key feature
   is to notify unavailability of virtualized resources and to recover
   unavailable VNFs.

   While the Doctor project focuses only on faults in NFVI including
   compute, network, and storage resources, the document discusses
   broader fault management issues such as break-down of the supporting
   infrastructure due to incomplete or inconsistent configuration of NFV
   services.

6.1.2. Moon

   The Moon project implements a security  management system for the
   cloud computing infrastructure. The project also enforces the
   security managers through various mechanisms, e.g., authorization for
   access control, firewall for networking, isolation for storage, and
   logging for tractability.

   Note that the main interest of the Moon project is the DDoS attack to
   a service node and the IDS management for VNFs. A wider range of
   security issues in the NFV service verification need to be
   discussed.

6.1.3 Bottlenecks

   The Bottlenecks project aims to find system bottlenecks by testing
   and verifying OPNFV infrastructure in a staging environment before
   committing it to a production environment. Instead of debugging the
   deployment in production environment, an automatic method for
   executing benchmarks to validate the deployment during staging is
   adopted. For example, the system measures the performance of each VNF
   by generating workload on VNFs. The Bottlenecks project does not
   consider incomplete or inconsistent configurations on NFV services
   that might cause the system bottlenecks. Furthermore, the Bottlenecks
   project aims to find system bottlenecks before committing it to a
   production environment. Meanwhile, the draft also considers how to
 


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   find bottlenecks in real time. 

6.1.4 VSPerf

   The VSPerf projects provides an automated testing framework and
   comprehensive test suite based on industry standards for measuring
   data-plane performance. The architecture of VSPerf is agnostic to
   switch and traffic generator and test scenarios can be customized. 

   The VSPerf can be used for developing switching technologies as well
   as for evaluation and optimization of the data-path performance.

6.2. ODL

6.2.1. Network Intent Composition

   The Network Intent Composition project enables the controller to
   manage and direct network services and network resources based on
   intent for network behaviors and network policies. Intents are
   described to the controller through a new northbound interface, which
   provides generalized and abstracted policy semantics. Also, the
   Network Intent Composition project aims to provide advanced
   composition logic for identifying and resolving intent conflicts
   across the network applications.

   When the reconfiguration upon the policy (i.e, intent) is delayed,
   policy inconsistency in service nodes may occur after the policy is
   applied to service nodes. While the Network Intent Composition
   project resolves such intent conflicts only before they are
   translated into service nodes, this document covers intent conflicts
   and inconsistency issues in a broader sense.

6.2.2. Controller Shield 

   The Controller Shield project proposes to create a repository called
   unified-security plugin (USecPlugin). The unified-security plugin is
   a general purpose plugin to provide the controller security
   information to northbound applications. The security information
   could be for various purposes such as collating source of different
   attacks reported in southbound plugins and suspected controller
   intrusions. Information collected at this plugin can also be used to
   configure firewalls and create IP blacklists for the network.

   In terms of security services, the document covers authentication,
   data integrity, confidentiality, and replay protection. However, the
   Controller Shield project only covers authentication, data integrity,
   and replay protection services where the confidentiality service is
   not considered.
 


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6.2.3. Defense4All 

   The Defense4All project proposes a SDN application for detecting and
   mitigating DDoS attacks. The application communicates with ODL
   controller via the northbound interface and performs the two main
   tasks; 1) Monitoring behavior of protected traffic and 2) Diverting
   attacked traffic to selected attack mitigation systems (AMSs).

   While the Defense4All project only focuses on defense system at the
   controller, this document includes broader defense issues at the
   service node as well as the controller.

6.3. Summary

   The verification functions should spread over the platforms to
   accomplish the requirements mentioned in clause 3. The correctness of
   NFV- based services and their network configurations can be checked
   in the NFV MANO layer which has the entire states of the VNFs. Each
   NFVI needs to provide verification layer which composed of policy
   manager, network database and interfaces (e.g. REST APIs). Local
   properties and invariants can be verified inside the specific NFVI,
   and the global properties and invariants can be checked by merging
   local verification results from the related NFVIs.

   The verification service provides verification functions to NFV MANO,
   NFVI, and any other low-level modules such as SDN controllers. For
   the platform independency, it provides standard APIs to process the
   verification tasks. It also uses standard APIs provided by OSS such
   as OpenStack (Neutron) and Open Daylight. The compiler and
   interpreter translate standard description languages and protocols
   into the internal model which optimized to the verification tasks. It
   can process user-defined properties to be checked as well. The
   properties to be checked whether they are user-defined or pre-defined
   invariants are managed by property library. The verifier maintains a
   set of verification algorithms to check the properties. The network
   database inside the verification service manages the global network
   states directly or indirectly.

   A PoC can be implemented using OpenStack (Neutron) and Open Daylight.
   The modules related to verification framework can reside in between
   network virtualization framework (e.g. OpenStack Neutron) and SDN
   controller (e.g. Open Daylight). Neutron and Open Daylight uses
   standard APIs provided by verification service to accomplish
   verification tasks. The initial use case for the PoC could be, in
   particular, any of security, performance, etc as mentioned in clause
   2.


 


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7. Security Considerations

   As already described in clause 2.6, how to verify security holes in
   VNF FG is very important consideration. In terms of security
   services, authentication, data integrity, confidentiality, and replay
   protection should be provided. On the other hand, potential security
   concern should be also carefully checked since several VNFs (e.g.,
   NAT) can modify or update packet headers and payload. 


8. Acknowledgements 

   The authors would like to thank formal methods lab members in Korea
   University for their verification theory support. Also thank Jose
   Saldana for his useful comments.



9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.


9.2.  Informative References

   [ETSI-NFV-Arch] ETSI, "Network Function Virtualisation (NFV);
              Architectural Framework," 2014.

   [ETSI-NFV-MANO] ETSI, "Network Function Virtualiztion (NFV)
              Management and Orchestration," 2014.

   [ETSI-NFV-Testing] ETSI, "Network Function Virtualiztion (NFV) Pre-
              deployment Testing; Report on Validation of NFV
              Environments and Services," 2016.

   [SIGCOMM-Qazi] Z. Qazi, C. Tu, L. Chiang, R. Miao, V. Sekar, and M.
              Yu, "SIMPLE-fying Middlebox Policy Enforcement Using SDN,"
              in Proc. ACM SIGCOMM 2013, August 2013.

   [ONS-Gember] A. Gember, R. Grandl, A. Anand, T. Benson, and A.
              Akella, "Stratos: Virtual Middleboxes as First-Class
              Entities," ONS 2013 and TR.

   [SIGCOMM-Gember] A. Gember, R. Viswanathan, C. Prakash, R. Grandl, J.
              Khalid, S. Das, and A. Akella, "OpenNF: Enabling
 


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              Innovation in Network Function Control," in Proc. ACM
              SIGCOMM 2014, August 2014.

   [HOTSDN-Ghorbani] S. Ghorbani, B. Godfrey, "Towards Correct Network
              Virtualization", HOTSDN 2014.

   [RAFT] https://raftconsensus.github.io/.

   [ODL] "OpenDaylight SDN Controller, "http://www.opendaylight.org/

   [ONOS] "Open Network Operating System, "http://onosproject.org/

   [OPNFV] "Open Platform for NFV, "https://www.opnfv.org/



































 


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Authors' Addresses

      Myung-Ki Shin
      ETRI
      161 Gajeong-dong Yuseng-gu
      Daejeon, 305-700
      Korea

      Phone: +82 42 860 4847
      Email: mkshin@etri.re.kr


      Ki-Hyuk Nam
      Friesty

      Email: nam@friesty.com


      Sangheon Pack
      Korea University 

      Email: shpack@korea.ac.kr


      Seungik Lee
      ETRI
      161 Gajeong-dong Yuseng-gu
      Daejeon, 305-700
      Korea

      Phone: +82 42 860 1483
      Email: seungiklee@etri.re.kr


      Ramki Krishnan 
      Dell     

      Email: Ramki_Krishnan@dell.com













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