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Versions: (draft-mglt-i2rs-security-environment-reqs) 00 01 02 03 04 05

I2RS WG                                                       D. Migault
Internet-Draft                                                J. Halpern
Intended status: Informational                                  Ericsson
Expires: September 29, 2017                                     S. Hares
                                                                  Huawei
                                                          March 28, 2017


                 I2RS Environment Security Requirements
              draft-ietf-i2rs-security-environment-reqs-05

Abstract

   This document provides environment security requirements for the I2RS
   architecture.  Environment security requirements are independent of
   the protocol used for I2RS.  The security environment requirements
   are the good security practices to be used during implementation and
   deployment of the code related to the new interface to routing system
   (I2RS) so that I2RS implementations can be securely deployed and
   operated.

   Environmental security requirements do not specify the I2RS protocol
   seecurity requirements.  This is done in another document (draft-
   ietf-i2rs-protocol-security-requirements).

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 September 29, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology and Acronyms  . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements notation . . . . . . . . . . . . . . . . . .   4
   3.  I2RS Plane Isolation  . . . . . . . . . . . . . . . . . . . .   4
     3.1.  I2RS Plane and Management plane . . . . . . . . . . . . .   5
     3.2.  I2RS Plane and Forwarding Plane . . . . . . . . . . . . .   7
     3.3.  I2RS Plane and Control Plane  . . . . . . . . . . . . . .   8
     3.4.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   9
   4.  I2RS Access Control for Routing System Resources  . . . . . .  11
     4.1.  I2RS Access Control Architecture  . . . . . . . . . . . .  11
       4.1.1.  Access control Enforcement Scope  . . . . . . . . . .  14
       4.1.2.  Notification Requirements . . . . . . . . . . . . . .  14
       4.1.3.  Trust . . . . . . . . . . . . . . . . . . . . . . . .  15
       4.1.4.  Sharing access control Information  . . . . . . . . .  15
       4.1.5.  Sharing Access Control in Groups of I2RS Clients and
               Agents  . . . . . . . . . . . . . . . . . . . . . . .  17
       4.1.6.  Managing Access Control Policy  . . . . . . . . . . .  19
     4.2.  I2RS Agent Access Control Policies  . . . . . . . . . . .  20
       4.2.1.  I2RS Agent Access Control . . . . . . . . . . . . . .  20
       4.2.2.  I2RS Client Access Control Policies . . . . . . . . .  21
       4.2.3.  Application and Access Control Policies . . . . . . .  22
   5.  I2RS Application Isolation  . . . . . . . . . . . . . . . . .  23
     5.1.  Robustness Toward Programmability . . . . . . . . . . . .  23
     5.2.  Application Isolation . . . . . . . . . . . . . . . . . .  24
       5.2.1.  DoS . . . . . . . . . . . . . . . . . . . . . . . . .  24
       5.2.2.  Application Logic Control . . . . . . . . . . . . . .  26
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  26
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  27
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28






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1.  Introduction

   This document provides environment security requirements for the I2RS
   architecture.  Environment security requirements are independent of
   the protocol used for I2RS.  The I2RS protocol security requirements
   [section 4.3)">I-D.ietf-i2rs-protocol-security-requirements] define the security
   for the communication between I2RS client and agent.  The security
   environment requirements are good security practices to be used
   during implementation and deployment of the I2RS protocol so that
   I2RS protocol implementations can be securely deployed and operated.
   These environment security requirements address the security
   considerations described in the I2RS Architecture [RFC7921] required
   to provide a stable and secure environment in which the dynamic
   programmatic interface to the routing system (I2RS) should operates.

   Even though the I2RS protocol is mostly concerned with the interface
   between the I2RS client and the I2RS agent, the environmental
   security requirements must consider the entire I2RS architecture and
   specify where security functions may be hosted and what criteria
   should be met in order to address any new attack vectors exposed by
   deploying this architecture.  Environment security for I2RS has to be
   considered for the complete I2RS architecture and not only on the
   protocol interface.

   This document is structured as follows:

   o  Section 2 describes the terminology used in this document,

   o  Section 3 describes how the I2RS plane can be securely isolated
      from the management plane, control plane, and forwarding plane.

   The subsequent sections of the document focus on the security within
   the I2RS plane.

   o  Section 4 analyses how the I2RS access control policies can be
      deployed throughout the I2RS plane in order to limit access to the
      routing system resources to authorized components with the
      authorized privileges.  This analysis examines how providing a
      robust communication system between the components aids the access
      control.

   o  Section 5 details how I2RS keeps applications isolated from
      another and without affecting the I2RS components.  Applications
      may be independent, with different scopes, owned by different
      tenants.  In addition, the applications may modify the routing
      system in an automatic way.

   Motivations are described before the requirements are given.



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   The reader is expected to be familiar with the I2RS problem statement
   [RFC7920], I2RS architecture, [RFC7921], traceability requirements
   [RFC7922], I2RS Pub/Sub requirements [RFC7923], I2RS ephemeral state
   requirements [I-D.ietf-i2rs-ephemeral-state], I2RS protocol security
   requirements [section 4.3)">I-D.ietf-i2rs-protocol-security-requirements].

2.  Terminology and Acronyms

   - Environment Security Requirements :   Security requirements
         specifying how the environment a protocol operates in needs to
         be secured.  These requirements do not specify the protocol
         security requirements.

   - I2RS plane:   The environment the I2RS process is running on.  It
         includes the applications, the I2RS client, and the I2RS agent.

   - I2RS user:   The user of the I2RS client software or system.

   - I2RS access control policies:   The policies controlling access of
         the routing resources by applications.  These policies are
         divided into policies applied by the I2RS client regarding
         applications and policies applied by the I2RS agent regarding
         I2RS clients.

   - I2RS client access control policies:   The access control policies
         processed by the I2RS client.

   - I2RS agent access control policies:   The access control policies
         processed by the I2RS agent.

2.1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  I2RS Plane Isolation

   Isolating the I2RS plane from other network planes (the management,
   forwarding, and control planes) is fundamental to the security of the
   I2RS environment.  Clearly differentiating the I2RS components from
   the rest of the network device does the following:

   1.  protects the I2RS components from vulnerabilities in other parts
       of the network,

   2.  protects other systems vital to the health of the network from
       vulnerabilities in the I2RS plane.



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   Separating the I2RS plane from other network control and forwarding
   planes is similar to the best common practice of placing software
   into software containers within modules with clear interfaces to
   exterior modules.  In a similar way, although the I2RS plane cannot
   be completely isolated from other planes, it can be carefully
   designed so the interactions between the I2RS plane and other planes
   can be identified and controlled.  The following is a brief
   description of how the I2RS plane positions itself in regard to the
   other planes.

3.1.  I2RS Plane and Management plane

   The purpose of the I2RS plane is to provide a standard programmatic
   interface to the routing system resources to network oriented
   applications.  Routing protocols often run in a control plane and
   provide entries for the forwarding plane as shown in figure 1.  The
   I2RS plane contains the I2RS applications, the I2RS client, the north
   bound interface between the I2RS client and I2RS applications, the
   I2RS protocol, the I2RS agent, and the south bound API (SB API) to
   the routing system.  The communication interfaces in the I2RS plane
   are shown on the the left hand side of figure 1.

   The management plane contains the mangement application, the
   management client, the north bound API between the management client
   and management application, the mangement server, the management
   protocol (E.g.  RESTCONF) between mangement client and management
   server, and the south bound API between the management server and the
   control plane.  The communication interfaces associated with the
   management plane are shown on the right hand side of figure 2.

   The I2RS plane and the management plane both interact with the
   control plane on which the routing systems operate.  [RFC7921]
   describes several of these interaction points such as the local
   configuration, the static system state, routing, and signaling.  A
   routing resource may be accessed by I2RS plane, the mangement plane,
   or routing protocol(s) which creates the potential for overlapping
   access.  The southbound APIs can limit the scope of the management
   plane's and the I2RS plane's interaction with the routing resources.

   Security focus:

   Data can be read by I2RS plane from configuration as copy of
   configuration data, or by management plane as copies of the I2RS
   plane.  The problem is when the I2RS plane installs the routing plane
   as its new configuration or the management plane installs the I2RS
   plane information as management plane configuration.  In this
   circumstance, we define "infecting" as interfering with and leading
   into a incoherent state.  Planned interactions such as interactions



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   denoted in in two cooperating Yang data modules is not an incoherent
   state.

   The primary protection in this space is going to need to be
   validation rules on:

   o  the data being sent/received by the I2RS agent (including
      notification of changes that the I2RS agent sends the I2RS
      client),

   o  any data transferred between management datastores (configuration
      or operational state) and I2RS ephemeral control plane data
      stores;

   o  data transferred between I2RS Agent and Routing system,

   o  data transferred between a management server and the I2RS routing
      system,

   o  data transferred between I2RS agent and system (e.g. interfaces
      ephemeral configuration),

   o  data transferred between management server and the system (e.g.
      interface configuration).



























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      APIs that interact with the
      I2RS Plane and Management Plane

     I2RS applications     Mangement applications
      || NB API                  NB API ||
      ||                                ||
      I2RS plane           management plane
      || control plane     configuration||
      || datastore            datastore ||
      ||                                ||
      ||SB API                   SB API ||
      ---------------------------------------
      | Routing System with protocols       |<protocols>
      | control plane                       |
      | (applied datastore)                 |
      +-------------------------------------+
      |  forwarding plane                   |
      +-------------------------------------+
      |   system                            |
      +-------------------------------------+

      Figure 1 - North Bound (NB) APIs and
                 South Bound (SB) APIs


3.2.  I2RS Plane and Forwarding Plane

   Applications hosted by the I2RS client belong to the I2RS plane.  It
   is difficult to constrain these applications to the I2RS plane, or
   even to limit their scope within the I2RS plane.  Applications using
   I2RS may also interact with components outside the I2RS plane.  For
   example an application may use a management client to configure the
   network and monitored events via an I2RS agent as figure 4 shows.

    +--------------------------------------+
    |       Application                    |
    +--------------------------------------+
      || NB API                 NB API ||
      || I2RS client        mgt client ||
      ||                               ||
       I2RS protocol        mgt protocol
                            (NETCONF/RESTCONF)

      figure 2

   Applications may also communicate with multiple I2RS clients in order
   to have a broader view of the current and potential states of the
   network and the I2RS plane itself.  These varied remote communication



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   relationships between applications using the I2RS protocol to change
   the forwarding plane make it possible for an individual application
   to be an effective attack vector against the operation of the
   network, a router's I2RS plane, the forwarding plane of the routing
   system, and other planes (management and control planes).

   Prevention measures:

   Systems should consider the following prevention errors:

   application validation -  There is little the I2RS plane can do to
      validate applications with which it interacts.  The I2RS client
      passes the I2RS agent an unique identifier for the application so
      that an application's actions can be traced back to the
      application.

   Validation against common misconfigurations or errors -  One way of
      securing the interfaces between application, the I2RS plane, and
      the forwarding plane is to limit the information accepted and to
      limit the rate information is accepted between these three
      software planes.  Another method is to perform rudimentary checks
      on the results of any updates to the forwarding plane.

3.3.  I2RS Plane and Control Plane

   The network control plane consists of the processes and protocols
   that discover topology, advertise reachability, and determine the
   shortest path between any location on the network and any
   destination.  I2RS client configures, monitors or receives events via
   the I2RS agent's interaction with the routing system including the
   process that handles the control plane signalling protocols (BGP,
   ISIS, OSPF, etc.), route information databases (RIBs), and interface
   databases.  In some situations, to manage an network outage or to
   control traffic, the I2RS protocol may modify information in the
   route database or the configuration of routing process.  While this
   is not a part of normal processing, such action allows the network
   operator to bypass temporary outages or DoS attacks.

   This capability to modify the routing process information carries
   with it the risk that the I2RS agent may alter the normal properties
   of the routing protocols which provide normal loop free routing in
   the control plane.  For example, information configured by the I2RS
   agent into routing process or RIBs could cause forwarding problems or
   routing loops.  As a second example, state which is inserted or
   deleted from routing processes (control traffic, counters, etc.)
   could cause the routing protocols to fail to converge or loop).

   Prevention measures:



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   The I2RS implementation can provide internal checks after a routing
   system protocol change that it is still operating correctly.  These
   checks would be specific to the routing protocol the I2RS Agent would
   change.  For example, if a BGP maximum prefix limit for a BGP peer is
   lowered then the BGP peer should not allow the number prefixes
   received from that peer to exceed this number.

3.4.  Requirements

   To isolate I2RS transactions from other planes, it is required that:

   SEC-ENV-REQ 1:  Application-to-routing system resources
                   communications should use an isolated communication
                   channel.  Various levels of isolation can be
                   considered.  The highest level of isolation may be
                   provided by using a physically isolated network.
                   Alternatives may also consider logical isolation
                   (e.g. using vLAN).  In a virtual environment that
                   shares a common infrastructure, encryption may also
                   be used as a way to enforce isolation.  Encryption
                   can be added by using a secure transport required by
                   the I2RS protocol security
                   [section 4.3)">I-D.ietf-i2rs-protocol-security-requirements], and
                   sending the non-confidential I2RS data (designed for
                   a non-secure transport) over a secure transport.

   SEC-ENV-REQ 2:  The interface used by the routing element to receive
                   I2RS transactions via the I2RS protocol (e.g. the IP
                   address) SHOULD be a dedicated physical or logical
                   interface.  As previously mentioned, a dedicated
                   physical interface may contribute to a higher
                   isolation.  Isolation may also be achieved by using a
                   dedicated IP address or a dedicated port.

   SEC-ENV-REQ 3:  An I2RS agent SHOULD have specific permissions for
                   interaction with each routing element and access to
                   the routing element should governed by policy
                   specific to the I2RS agent's interfaces (network,
                   routing system, system, or cross-datastore).

   Explanation:

   When the I2RS agent performs an action on a routing element, the
   action is performed in a process (or processes) associated with a
   routing process.  For example, in a typical UNIX system, the user is
   designated with a user id (uid) and belongs to groups designated by
   group ids (gid).  If such a user id (uid) and group id (gid) is the
   identifier for the routing processes peforming routing tasks in the



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   control plane, then the I2RS Agent process would communicate with
   these routing processes.  It is important that the I2RS agent has its
   own unique identifier and the routing processes have their own
   identifier so that access control can uniquely filter data between
   I2RS Agent and routing processes.

   The specific policy that the I2RS agent uses to filter data from the
   network or from different processes on a system (routing, system or
   cross-datastore) should be specific to the I2RS agent.  For example,
   the network access filter policy that the I2RS agent uses should be
   uniquely identifiable from the configuration datastore updated by a
   management protocol.

   SEC-ENV-REQ 4:  The I2RS plane should be informed when a routing
                   system resource is modified by a user outside the
                   I2RS plane access.  Notifications from the control
                   plane SHOULD not be allowed to flood the I2RS plane,
                   and rate limiting (or summarization) is expected to
                   be applied.  These routing system notifications MAY
                   translated to the appropriate I2RS agent
                   notifications, and passed to various I2RS clients via
                   notification relays.

   Explanation:

   This requirements is also described in section 7.6 of [RFC7921] for
   the I2RS client, and this section extends it to the entire I2RS plane
   (I2RS agent, client, and application).

   A routing system resource may be accessed by management plane or
   control plane protocols so a change to a routing system resource may
   remain unnoticed unless and until the routing system resource
   notifies the I2RS plane by notifying the I2RS agent.  Such
   notification is expected to trigger synchronization of the I2RS
   resource state between the I2RS agent and I2RS client - signalled by
   the I2RS agent sending a notification to an I2RS client.

   The updated resource should be available in the operational state if
   there is a yang module referencing that operational state, but this
   is not always the case.  In the cases where operational state is not
   updated, the I2RS SB (southbound) API should include the ability to
   send a notification.

   SEC-ENV-REQ 5:  I2RS plane should define an "I2RS plane overwrite
                   policy".  Such policy defines how an I2RS is able to
                   update and overwrite a resource set by a user outside
                   the I2RS plane.  Such hierarchy has been described in
                   section 6.3 and 7.8 of [RFC7921]



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   Explanation:

   A key part of the I2RS architecture is notification regarding routing
   system changes across the I2RS plane (I2RS client to/from I2RS
   agent).  The security environment requirements above (SEC-ENV-REQ-03
   to SEC-ENV-REQ-05) provide the assurance that the I2RS plane and the
   routing systems the I2RS plane attaches to remains untouched by the
   other planes or the I2RS plane is notificed of such changes.
   Section 6.3 of [RFC7921] describes how the I2RS agent within the I2RS
   plane interacts with forwarding plane's local configuration, and
   provides the example of an overwrite policy between the I2RS plane
   and local configuration (instantiated in 2 Policy Knobs) that
   operators may wish to set.  The prompt notification of any outside
   overwrite is key to the architecture and proper interworking of the
   I2RS Plane.

4.  I2RS Access Control for Routing System Resources

   This section provides recommendations on how the I2RS plane's access
   control should be designed to protect the routing system resources.
   These security policies for access control only apply within the I2RS
   plane.  More especially, the policies are associated to the
   applications, I2RS clients and I2RS agents, with their associated
   identity and roles.

   The I2RS deployment of I2RS applications, I2RS clients, and I2RS
   agents can be located locally in a closed environment or distributed
   over open networks.  The normal case for routing system management is
   over an open environment.  Even in a closed environment, access
   control policies should be carefully defined to be able to, in the
   future, carefully extend the I2RS plane to remote applications or
   remote I2RS clients.

   [I-D.ietf-i2rs-protocol-security-requirements] defines the security
   requirements of the I2RS protocol between the I2RS client and the
   I2RS agent over a secure transport.  This section focuses on I2RS
   access control architecture (section 4.1), access control policies of
   the I2RS agent (section 4.2), the I2RS client (section 4.3), and the
   application (section 4.4).

4.1.  I2RS Access Control Architecture

   Overview:

   Applications access the routing system resource via numerous
   intermediate nodes.  The application communicates with an I2RS
   client.  In some cases, the I2RS client is only associated with a
   single application attached to one or more agents (case a and case b



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   in figure 4 below).  In other cases, the I2RS client may be connected
   to two applications (case c in figure 4 below), or the I2RS may act
   as a broker (agent/client device shown in case d in figure 4 below).
   The I2RS client broker approach provides scalability to the I2RS
   architecture as it avoids each application being registered to the
   I2RS agent.  Similarly, the I2RS access control should be able to
   scale to numerous applications.

   The goal of the security environment requirements in this section are
   to control the interactions between the applications and the I2RS
   client, and the interactions between the I2RS client and the I2RS
   agent.  The key challenge is that the I2RS architecture puts the I2RS
   Client in control of the stream of communication (application to I2RS
   client and I2RS client to the I2RS agent).  The I2RS agent must trust
   the I2RS client's actions without having an ability to verify the
   I2RS client's actions.



































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     a) I2RS application-client pair talking
        to one I2RS agent

     +-----------+     +---------+      +-------+
     |   I2RS    |=====| I2RS    |======| I2RS  |
     |application|     | client 1|      | agent |
     +-----------+     +---------+      +-------+

     b) I2RS application client pair talking to
        two i2RS agents
                                       +--------+
     +-------------+   +---------+     | I2RS   |
     |   I2RS      |===| I2RS    |=====| agent 1|
     |application 1|   | client 1|     +--------+
     |             |   |         |     +--------+
     |             |   |         |=====| I2RS   |
     +-------------+   +---------+     | agent 2|
                                       +--------+

     c) two applications talk to 1 client
                                      +--------+
     +-------------+   +--------+     | I2RS   |
     |   I2RS      |===|I2RS    |=====| agent 1|
     |application 1|   |client 1|     +--------+
     +-------------+   |        |     +--------+
     +-------------+   |        |=====| I2RS   |
     |  I2RS       |   |        |     | agent 2|
     |application 2|===|        |     +--------+
     +-------------+   +--------+

     d) I2RS Broker (agent/client
                                     +--------+
     +-------------+  +--------+     | I2RS   |
     |   I2RS      |==|I2RS    |=====|agent 3/|
     |application 1|  |client 1|   ==|client 3+----+
     +-------------+  +--------+   | +--+-----+    |
                                   |    |          |
     +-------------+  +--------+   |  +-------+ +--|----+
     |  I2RS       |  |I2RS    |===|  |I2RS   | |I2RS   |
     |application 2|==|client 2|      |agent 1| |agent 2|
     +-------------+  +--------+      +-------+ +-------+

     figure 3








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4.1.1.  Access control Enforcement Scope

   SEC-ENV-REQ 6:  I2RS access control should be performed through the
                   whole I2RS plane.  It should not be enforced by the
                   I2RS agent only within the routing element.  Instead,
                   the I2RS client should enforce the I2RS client access
                   control against applications and the I2RS agent
                   should enforce the I2RS agent access control against
                   the I2RS clients.  The mechanisms for the I2RS client
                   access control are not in scope of the I2RS
                   architecture [RFC7921], which exclusively focuses on
                   the I2RS agent access control provided by the I2RS
                   protocol.

   Explanation:

   This architecture results in a layered and hierarchical or multi-
   party I2RS access control.  An application will be able to access a
   routing system resource only if both the I2RS client is granted
   access by the I2RS agent and the application is granted access by the
   I2RS client.

4.1.2.  Notification Requirements

   SEC-ENV-REQ 7:  When an access request to a routing resource is
                   refused by one party (the I2RS client or the I2RS
                   agent), the requester (e.g the application) as well
                   as all intermediaries should indicate the reason the
                   access has not been granted, and which entity
                   rejected the request.

   Explanation:

   In case the I2RS client access control or the I2RS agent access
   control does not grant access to a routing system resource, the
   application should be able to determine whether its request has been
   rejected by the I2RS client or the I2RS agent as well as the reason
   that caused the reject.

   SEC-REQ-07 indicates the I2RS agent may reject the request because
   the I2RS client is not an authorized I2RS client or lacks the
   privileges to perform the requested transaction (read, write, start
   notifications or logging).  The I2RS client should be notified of the
   reason the I2RS agent rejected the transaction due to a lack of
   authorization or privileges, and the I2RS client should return a
   message to the application indicating the I2RS agent reject the
   transaction with an indication of this reason.  Similarly, if the
   I2RS client does not grant the access to the application, the I2RS



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   client should also inform the application.  An example of an error
   message could be, "Read failure: you do not have read permission",
   "Write failure: you do not have write permission", or "Write failure:
   resource accessed by someone else".

   This requirement has been written in a generic manner as it relates
   to the following interactions:

   o  interactions between the application and the I2RS client,

   o  interactions between the I2RS client and the I2RS agent at a
      content level (Protocol security requirements are described by
      [section 4.3)">I-D.ietf-i2rs-protocol-security-requirements]), and

   o  interactions between the I2RS agent and the I2RS routing system
      (forwarding plane, control plane, and routing plane).

4.1.3.  Trust

   SEC-ENV-REQ 8:  In order to provide coherent access control policies
                   enforced by multiple parties (e.g. the I2RS client or
                   the I2RS agent), theses parties should trust each
                   other, and communication between them should also be
                   trusted (e.g.  TLS) in order to reduce additional
                   vectors of attacks.

   SEC-ENV-REQ 9:  I2RS client or I2RS agent SHOULD also be able to
                   refuse a communication with an application or an I2RS
                   client when the communication channel does not
                   fulfill enough security requirements.

   Explanation:

   The participants in the I2RS Plane (I2RS client, I2RS agent, and I2RS
   application) exchange critical information, and to be effective the
   communication should be trusted and free from security attacks.

   The I2RS client or the I2RS agent should be able to reject messages
   over a communication channel that can be easily hijacked, like a
   clear text UDP channel.

4.1.4.  Sharing access control Information

   For the I2RS client:

   SEC-ENV-REQ 10: The I2RS client MAY request information on its I2RS
                   access control subset policies from the I2RS agent or
                   cache requests that have been rejected by the I2RS



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                   agent to limit forwarding unnecessary queries to the
                   I2RS agent.

   SEC-ENV-REQ 11: The I2RS client MAY support receiving notifications
                   when its I2RS access control subset policies have
                   been updated by the I2RS agent.

   Similarly, for the applications:

   SEC-ENV-REQ 12: The applications MAY request information on its I2RS
                   access control subset policies in order to limit
                   forwarding unnecessary queries to the I2RS client.

   SEC-ENV-REQ 13: The applications MAY subscribe to a service that
                   provides notification when its I2RS access control
                   subset policies have been updated.

   For both the application and the client:

   SEC-ENV-REQ 14: The I2RS access control should explicitly specify
                   accesses that are granted.  More specifically,
                   anything not explicitly granted should be denied
                   (default rule).

   Explanation:

   In order to limit the number of access requests that result in an
   error, each application or I2RS client can retrieve the I2RS access
   control policies that apply to it.  This subset of rules is
   designated as the "Individual I2RS access control policies".  As
   these policies are subject to changes, a dynamic synchronization
   mechanism should be provided.  However, such mechanisms may be
   implemented with different levels of completeness and dynamicity of
   the individual I2RS access control policies.  One example may be
   caching transaction requests that have been rejected.

   I2RS access control should be appropriately balanced between the I2RS
   client and the I2RS agent.  It remains relatively easy to avoid the
   complete disclosure of the access control policies of the I2RS agent.
   Relative disclosure of access control policies may allow leaking
   confidential information in case of misconfiguration.  It is
   important to balance the level of trust of the I2RS client and the
   necessity of distributing the enforcement of the access control
   policies.

   I2RS access control should not solely rely only on the I2RS client or
   the I2RS agent as illustrated below:




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   - 1) I2RS clients are dedicated to a single application:   In this
         case, it is likely that I2RS access control is enforced only by
         the I2RS agent, as the I2RS client is likely to accept all
         access requests of the application.  It is recommended that
         even in this case, I2RS client access control is not based on
         an "Allow anything from application" policy, but instead the
         I2RS client specifies accesses that are enabled.  In addition,
         the I2RS client may sync its associated I2RS access control
         policies with the I2RS agent to limit the number of refused
         access requests being sent to the I2RS agent.  The I2RS client
         is expected to balance benefits and problems with synchronizing
         its access control policies with the I2RS agent to proxy
         request validation versus simply passing the access request to
         the I2RS agent.

   - 2) A single I2RS client connects to multiple applications or
   acts as a broker for many applications:
            In this case the I2RS agent has a single I2RS client
            attached, so the I2RS client could be configured to enforce
            access control policies instead of the I2RS Agent.  In this
            circumstance, it is possible that the I2RS agent may grant
            an I2RS client high priviledges and blindly trust the I2RS
            client without enforcing access control policies on what the
            I2RS client can do.  Such a situation must be avoided as it
            could be used by malicious applications for a privilege
            escalation by compromising the I2RS client, causing the I2RS
            client to perform some action on behalf of the application
            that it normally does not have the privileges to perform.
            In order to mitigate such attacks, the I2RS client that
            connects to multiple applications or operates as a broker is
            expected to host application with an equivalent level of
            privileges.

4.1.5.  Sharing Access Control in Groups of I2RS Clients and Agents

   Overview:

   To distribute the I2RS access control policies between I2RS clients
   and I2RS agents, I2RS access control policies can also be distributed
   within a set of I2RS clients or a set of I2RS agents.

   Requirements:

   SEC-ENV-REQ 15: I2RS clients should be distributed and act as brokers
                   for applications that share roughly similar
                   permissions.





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   SEC-ENV-REQ 16: I2RS agents should avoid granting extra privileges to
                   their authorized I2RS client.  I2RS agents should be
                   shared by I2RS clients with roughly similar
                   permissions.  More explicitly, an I2RS agent shared
                   between I2RS clients that are only provided read
                   access to the routing system resources do not need to
                   perform any write access, so the I2RS client should
                   not be provided these accesses.

   SEC-ENV-REQ 17: I2RS clients and I2RS agents should be able to trace
                   [RFC7922] the various transactions they perform as
                   well as suspicious activities.  These logs should be
                   collected regularly and analysed by functions that
                   may be out of the I2RS plane.

   Explanation:

   This restriction for distributed I2RS clients to act as brokers only
   for applications with roughly the same privileges avoids the I2RS
   client having extra privileges compared to hosted applications, and
   discourages applications from performing privilege escalation within
   an I2RS client.  For example, suppose an I2RS client requires write
   access to the resources.  It is not recommended to grant the I2RS
   agent the write access in order to satisfy a unique I2RS client.
   Instead, the I2RS client that requires write access should be
   connected to an I2RS agent that is already shared by an I2RS client
   that requires write access.

   Access control policies enforcement should be monitored in order to
   detect violation of the policies or detect an attack.  Access control
   policies enforcement may not be performed by the I2RS client or the
   I2RS agent as violation may require a more global view of the I2RS
   access control policies.  As a result, consistency check and
   mitigation may instead be performed by the management plane.
   However, I2RS clients and I2RS agents play a central role.

   The I2RS agent can trace transactions that an I2RS client requests it
   to perform, and to link this to the application via the secondary
   opaque identifier to the application.  This information is placed in
   a tracing log which is retrieved by management processes.  If a
   particular application is granted a level of privileges it should not
   have, then this tracing mechanism may detect this security intrusion
   after the intrusion has occurred.








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4.1.6.  Managing Access Control Policy

   Access control policies should be implemented so that the policies
   remain manageable in short and longer term deployments of the I2RS
   protocol and the I2RS plane.

   Requirements:

   SEC-ENV-REQ 18: access control should be managed in an automated way,
                   that is granting or revoking an application should
                   not involve manual configuration over the I2RS plane
                   (I2RS client, I2RS agent, and application).

   Explanation:

   Granting or configuring an application with new policy should not
   require manual configuration of I2RS clients, I2RS agents, or other
   applications.

   SEC-ENV-REQ 19: Access control should be scalable when the number of
                   application grows as well as when the number of I2RS
                   clients increases.

   Explanation:

   A typical implementation of a local I2RS client access control
   policies may result in creating manually a system user associated
   with each application.  Such an approach is not likely to scale when
   the number of applications increases into the hundreds.

   SEC-ENV-REQ 20: Access control should be dynamically managed and
                   easily updated.

   Explanation:

   Although the number of I2RS clients is expected to be lower than the
   number of applications, as I2RS agents provide access to the routing
   resource, it is of primary importance that an access can be granted
   or revoke in an efficient way.

   SEC-ENV-REQ 21: I2RS clients and I2RS agents should be uniquely
                   identified in the network to enable centralized
                   management of the I2RS access control policies.

   Explanation:






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   Centralized management of the access control policies of an I2RS
   plane with network that hosts several I2RS applications, clients and
   agents requires that each devices can be identified.

4.2.  I2RS Agent Access Control Policies

   Overview:

   The I2RS agent access control restricts routing system resource
   access to authorized identities - possible access policies may be
   none, read or write.  The initiator of an access request to a routing
   resource is always an application.  However, it remains challenging
   for the I2RS agent to establish its access control policies based on
   the application that initiates the request.

   First, when an I2RS client acts as a broker, the I2RS agent may not
   be able to authenticate the application.  In that sense, the I2RS
   agent relies on the capability of the I2RS client to authenticate the
   applications and apply the appropriated I2RS client access control.

   Second, an I2RS agent may not uniquely identify a piece of software
   implementing an I2RS client.  In fact, an I2RS client may be provided
   multiple identities which can be associated to different roles or
   privileges.  The I2RS client is left responsible for using them
   appropriately according to the application.

   Third, each I2RS client may contact various I2RS agent with different
   privileges and access control policies.

4.2.1.  I2RS Agent Access Control

   This section provides recommendations on the I2RS agent access
   control policies to keep I2RS access control coherent within the I2RS
   plane.

   Requirements:

   SEC-ENV-REQ 22: I2RS agent access control policies should be
                   primarily based on the I2RS clients as described in
                   [RFC7921].

   SEC-ENV-REQ 23: I2RS agent access control policies MAY be based on
                   the application if the application identity has been
                   authenticated by the I2RS client and passed via the
                   secondary identity to the I2RS agent.

   SEC-ENV-REQ 24: The I2RS agent should know which identity (E.g.
                   system user) performed the latest update of the



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                   routing resource.  This is true for an identity
                   inside and outside the I2RS plane, so the I2RS agent
                   can appropriately perform an update according to the
                   priorities associated to the requesting identity and
                   the identity that last updated the resource.

   SEC-ENV-REQ 25: the I2RS agent should have an "I2RS agent overwrite
                   Policy" that indicates how identities can be
                   prioritized.  This requirement is also described in
                   section 7.6 of [RFC7921].  Similar requirements exist
                   for components within the I2RS plane, but this is
                   within the scope of the I2RS protocol security
                   requirements
                   [section 4.3)">I-D.ietf-i2rs-protocol-security-requirements].

   Explanation:

   If the I2RS application is authenticated to the I2RS client, and the
   I2RS client is authenticated to the I2RS agent, and the I2RS client
   uses the opaque secondary identifier to pass an authenticated
   identifier to the I2RS agent, then this identifier may be used for
   access control.  However, caution should be taken when using this
   chain of authentication since the secondary identifier is intended in
   the I2RS protocol only to aid traceability.

   From the environment perspective the I2RS agent MUST be aware when
   the resource has been modified outside the I2RS plane by another
   plane (management, control, or forwarding).  The prioritization
   between the different planes should set a deterministic policy that
   allows the collision of two planes (I2RS plane and another plane) to
   be resolved via an overwrite policy in the I2RS agent.

   Similar requirements exist for knowledge about identities within the
   I2RS plane which modify things in the routing system, but this is
   within the scope of the I2RS protocol's requirements for ephemeral
   state [I-D.ietf-i2rs-ephemeral-state] and security requirements
   [section 4.3)">I-D.ietf-i2rs-protocol-security-requirements].

4.2.2.  I2RS Client Access Control Policies

   Overview:

   The I2RS client access control policies are responsible for
   authenticating the application managing the privileges for the
   applications, and enforcing access control to resources by the
   applications.

   Requirements:



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   REQ 26: I2RS client should authenticate its applications.  If the
           I2RS client acts as a broker and supports multiple
           applications, it should authenticate each application.

   REQ 27: I2RS client should define access control policies associated
           to each applications.  An access to a routing resource by an
           application should not be forwarded immediately and
           transparently by the I2RS client based on the I2RS agent
           access control policies.  The I2RS client should first check
           whether the application has sufficient privileges, and if so
           send an access request to the I2RS agent.

   Explanation:

   If no authentication mechanisms have being provided between the I2RS
   client and the application, then the I2RS client must be dedicated to
   a single application.  By doing so, application authentication relies
   on the I2RS authentication mechanisms between the I2RS client and the
   I2RS agent.

   If an I2RS client has multiple identities that are associated with
   different privileges for accessing an I2RS agent(s), the I2RS client
   access control policies should specify the I2RS client identity with
   the access control policy.

4.2.3.  Application and Access Control Policies

   Overview

   Applications do not enforce access control policies.  Instead these
   are enforced by the I2RS clients and the I2RS agents.  This section
   provides recommendations for applications in order to ease I2RS
   access control by the I2RS client and the I2RS agent.

   Requirements:

   SEC-ENV-REQ 28: Applications SHOULD be uniquely identified by their
                   associated I2RS clients

   Explanation:

   Different application may use different methods (or multiple methods)
   to communicate with its associated I2RS client, and each application
   may not use the same form of an application identifier.  However, the
   I2RS client must obtain an identifier for each application.  One
   method for this identification can be a system user id.





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   SEC-ENV-REQ 29: Each application SHOULD be associated to a restricted
                   number of I2RS clients.

   Explanation:

   The I2RS client provides access to resource on its behalf and this
   access should only be granted for trusted applications, or
   applications with an similar level of trust.  This does not prevent
   an I2RS client to host a large number of applications with the same
   levels of trust.

   SEC-ENV-REQ 30: An application SHOULD be provided means and methods
                   to contact their associated I2RS client.

   Explanation:

   It is obvious when an I2RS client belongs to the application as part
   of a module or a library that the application can communicate with a
   I2RS client.  Similarly, if the application runs into a dedicated
   system with a I2RS client, it is obvious which I2RS client the
   application should contact.  If the application connects to the I2RS
   client remotely, the application needs some means to retrieve the
   necessary information to contact its associated I2RS client (e.g. an
   IP address or a FQDN).

5.  I2RS Application Isolation

   A key aspect of the I2RS architecture is the network oriented
   application that uses the I2RS high bandwidth programmatic interface
   to monitor or change one or more routing systems.  I2RS applications
   could be control by a single entity or serve various tenants of the
   network.  If multiple entities use an I2RS application to monitor or
   change the network, security policies must preserve the isolation of
   each entity's control and not let malicious entities controlling one
   I2RS application interfere with other I2RS applications.

   This section discusses both security aspects related to
   programmability as well as application isolation in the I2RS
   architecture.

5.1.  Robustness Toward Programmability

   Overview

   I2RS provides a programmatic interface in and out of the Internet
   routing system which provides the following advantages for security:

   o  the use of automation reduces configuration errors;



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   o  the programmatic interface enables fast network reconfiguration
      and agility in adapting to network attacks; and

   o  monitoring facilities to detect a network attack, and
      configuration changes which can help mitigate the network attack.

   Programmability allows applications to flexible control which may
   cause problems due to:

   o  applications which belong to different tenants with different
      objectives,

   o  applications which lack coordination resulting in unstable routing
      configurations such as oscillations between network
      configurations, and creation of loops.  For example, one
      application may monitor a state and change to positive, and a
      second application performs the reverse operation (turns it
      negative).  This fluctuation can cause a routing system to become
      unstable.

   The I2RS plane requires data and application isolation to prevent
   such situations from happening.  However, to guarantee the network
   stability constant monitoring and error detection are recommended.

   Requirement:

   SEC-ENV-REQ 31: The I2RS agents should monitor constantly parts of
                   the system for which I2RS clients or applications
                   have provided requests.  It should also be able to
                   detect any I2RS clients or applications causing
                   problems that may leave the routing system in an
                   unstable state.

   Explanation:

   In the least, monitoring consists of logging events and receiving
   streams of data.  I2RS Plane implementations should monitor the I2RS
   applications and I2RS clients for potential problems.  The cause for
   the I2RS clients or applications providing problematic requests can
   be failures in the implementation code or malicious intent. ]

5.2.  Application Isolation

5.2.1.  DoS

   Overview:





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   Requirements for robustness to DoS attacks have been addressed in the
   communication channel section [RFC7921].  This section focuses on
   requirements for application isolation that help prevent DoS.

   Requirements:

   SEC-ENV-REQ 32: In order to prevent DoS, it is recommended the I2RS
                   agent control the resources allocated to each I2RS
                   client.  I2RS clients that act as broker may not be
                   protected efficiently against these attacks unless
                   the broker performs resource controls for the hosted
                   applications.

   SEC-ENV-REQ 33: I2RS agent SHOULD not make a response redirection
                   unless the redirection is previously validated and
                   agreed by the destination.

   SEC-ENV-REQ 34: I2RS Applications should avoid the use of underlying
                   protocols that are not robust enough to protect
                   against reflection attacks.

   Explanation:

   The I2RS interface is used by applications to interact with the
   routing states.  If the I2RS client is shared between multiple
   applications, one application can use the I2RS client to perform DoS
   or DDoS attacks on the I2RS agent(s) and through the I2RS agents
   attack the network.  DoS attack targeting the I2RS agent would
   consist in providing requests that keep the I2RS agent busy for a
   long time.  These attacks on the I2RS agent may involve an
   application (requesting through an I2RS Client) heavy computation by
   the I2RS agent in order to block operations like disk access.

   Some DoS attacks may attack the I2RS Client's reception of
   notification and monitoring data streams over the network.  Other DoS
   attacks may focus on the application directly by performing
   reflection attacks to reflect traffic.  Such an attack could be
   performed by first detecting an application is related to monitoring
   the RIB or changing the RIB.  Reflection-based DoS may also attack at
   various levels in the stack utilizing UDP at the service to redirect
   data to a specific repository

   I2RS implementation should consider how to protect I2RS against such
   attacks.







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5.2.2.  Application Logic Control

   Overview

   This section examines how application logic must be designed to
   ensure application isolation.

   Requirements:

   SEC-ENV-REQ 35: Application logic should remain opaque to external
                   listeners.  Application logic may be partly hidden by
                   encrypting the communication between the I2RS client
                   and the I2RS agent.  Additional ways to obfuscate the
                   communications may involve sending random messages of
                   various sizes.  Such strategies have to be balanced
                   with network load.  Note that I2RS client broker are
                   more likely to hide the application logic compared to
                   I2RS client associated to a single application.

   Explanation:

   Applications use the I2RS interface in order to update the routing
   system.  These updates may be driven by behaviour on the forwarding
   plane or any external behaviours.  In this case, correlating
   observation with the I2RS traffic may enable the derivation the
   application logic.  Once the application logic has been derived, a
   malicious application may generate traffic or any event in the
   network in order to activate the alternate application.

6.  Security Considerations

   This whole document is about security requirements for the I2RS
   environment.  To protect personal privacy, any identifier (I2RS
   application identifier, I2RS client identifier, or I2RS agent
   identifier) should not contain personal identifiable information.

7.  IANA Considerations

   No IANA considerations for this requirements.

8.  Acknowledgments

   A number of people provided a significant amount of helpful comments
   and reviews.  Among them the authors would like to thank Russ White,
   Russ Housley, Thomas Nadeau, Juergen Schoenwaelder, Jeffrey Haas,
   Alia Atlas, and Linda Dunbar.





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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC7920]  Atlas, A., Ed., Nadeau, T., Ed., and D. Ward, "Problem
              Statement for the Interface to the Routing System",
              RFC 7920, DOI 10.17487/RFC7920, June 2016,
              <http://www.rfc-editor.org/info/rfc7920>.

   [RFC7921]  Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
              Nadeau, "An Architecture for the Interface to the Routing
              System", RFC 7921, DOI 10.17487/RFC7921, June 2016,
              <http://www.rfc-editor.org/info/rfc7921>.

   [RFC7922]  Clarke, J., Salgueiro, G., and C. Pignataro, "Interface to
              the Routing System (I2RS) Traceability: Framework and
              Information Model", RFC 7922, DOI 10.17487/RFC7922, June
              2016, <http://www.rfc-editor.org/info/rfc7922>.

   [RFC7923]  Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
              for Subscription to YANG Datastores", RFC 7923,
              DOI 10.17487/RFC7923, June 2016,
              <http://www.rfc-editor.org/info/rfc7923>.

   [I-D.ietf-i2rs-protocol-security-requirements]
              Hares, S., Migault, D., and J. Halpern, "I2RS Security
              Related Requirements", draft-ietf-i2rs-protocol-security-
              requirements-17 (work in progress), September 2016.

9.2.  Informative References

   [I-D.ietf-i2rs-ephemeral-state]
              Haas, J. and S. Hares, "I2RS Ephemeral State
              Requirements", draft-ietf-i2rs-ephemeral-state-23 (work in
              progress), November 2016.

   [I-D.ietf-netconf-rfc6536bis]
              Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", draft-ietf-
              netconf-rfc6536bis-01 (work in progress), March 2017.






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   [I-D.ietf-netmod-revised-datastores]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore
              Architecture", draft-ietf-netmod-revised-datastores-01
              (work in progress), March 2017.

Authors' Addresses

   Daniel Migault
   Ericsson
   8400 boulevard Decarie
   Montreal, QC   H4P 2N2
   Canada

   Phone: +1 514-452-2160
   Email: daniel.migault@ericsson.com


   Joel Halpern
   Ericsson

   Email: Joel.Halpern@ericsson.com


   Susan Hares
   Huawei
   7453 Hickory Hill
   Saline, MI  48176
   USA

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