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Versions: 00 draft-ietf-opsec-nmasc

OPSEC                                                          R. Bonica
Internet-Draft                                          Juniper Networks
Expires: April 16, 2006                                         S. Ahmed
                                                     Booz Allen Hamilton
                                                        October 13, 2005


            Network Management Access Security Capabilities
                      draft-bonica-opsec-nmasc-00

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   This Internet-Draft will expire on April 16, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document describes how network management stations can
   communicate with the devices that they manage using either the in-
   band network, an out-of-band network, or a virtual out-of-band
   network.  This document also evaluates each access method in terms of
   its security capabilities and lists the device capabilities needed to
   support each method.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions Used In This Document  . . . . . . . . . . . .  3
   2.  Network Management Access Methods  . . . . . . . . . . . . . .  3
   3.  In-band Access . . . . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  Vulnerabilities  . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Required Security Capabilities . . . . . . . . . . . . . .  4
     3.3.  Analysis . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Out-of-Band Access . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Vulnerabilities  . . . . . . . . . . . . . . . . . . . . .  6
     4.2.  Required Security Capabilities . . . . . . . . . . . . . .  6
     4.3.  Analysis . . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Virtual Out-of-band Access . . . . . . . . . . . . . . . . . .  7
     5.1.  Vulnerabilities  . . . . . . . . . . . . . . . . . . . . .  8
     5.2.  Required Security Capabilities . . . . . . . . . . . . . .  8
     5.3.  Analysis . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  Normative References . . . . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12





























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1.  Introduction

   The Framework for Operational Security Capabilities [1] outlines the
   proposed effort of the IETF OPSEC working group.  This includes
   producing a series of drafts to codify knowledge gained through
   operational experience about feature sets that are needed to securely
   deploy and operate managed network elements providing transit
   services at the data link and IP layers.  Current plans include
   separate capabilities documents for Packet Filtering; Event Logging;
   In-Band and Out-of-Band Management; Configuration and Management
   Interfaces; AAA; and Documentation and Assurance.  This document
   describes in-band management, out-of-band-management, and a hybrid
   approach, called virtual out-of-band management.

1.1.  Conventions Used In This Document

   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 [2].


2.  Network Management Access Methods

   Network management stations can communicate with the devices that
   they manage using either the in-band network, an out-of-band network,
   or a virtual out-of-band network.  The following sections describe
   each of the above mentioned network management access methods.


3.  In-band Access



          User1----- R1----User2
                    / \
                   /   \
                  /     \
                 /       \
                R2--------R3
               / \       / \
              /   \     /   \
             /     \   /     \
           NMS1 User3 User4  NMS2


   Figure 1: In-Band Access

   Figure 1 depicts two network management stations (NMS1 and NMS2)



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   managing three routers (R1-R3).  Network management stations use the
   in-band network to communicate with the routers that they manage.
   Therefore, network management traffic is intermixed with user traffic
   on in-band network interfaces.

3.1.  Vulnerabilities

   RFC 3871 [3] identifies the following security vulnerabilities
   associated with in-band management:

   1.  Saturation of customer lines or interfaces can make the device
       unmanageable unless out-of-band management resources have been
       reserved.

   2.  Since public interfaces/channels are used, it is possible for
       attackers to directly address and reach the device and to attempt
       management functions.

   3.  In-band management traffic on public interfaces may be
       intercepted, however this would typically require a significant
       compromise in the routing system.

   4.  Public interfaces used for in-band management may become
       unavailable due to bugs (e.g., buffer overflows being exploited)
       while out-of-band interfaces (such as a serial console device)
       remain available.

   Expanding upon the final point, listed above, the in-band network can
   be misconfigured, such that the managed device becomes isolated with
   regard to the network management stations.  When this happens,
   operators cannot access the router in order to remedy the
   configuration error.  They become reliant upon physical access to the
   managed device.

3.2.  Required Security Capabilities

   RFC 3871 requires the following security capabilities to mitigate the
   effects of the above mentioned vulnerabilities:

   1.  Increased priority for management traffic

   2.  Use of strong cryptography

   3.  Selection of cryptographic parameters

   4.  Use of cryptographic algorithms subject to open review





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   5.  Use of management protocols subject to open review

3.3.  Analysis

   The cryptographic methods mentioned in Section 3.2 prevent users from
   accessing management functions and eavesdropping on management
   traffic.  The strength of the cryptographic algorithms deployed
   should be a determined by cost and perceived threat.

   Increasing the priority of management traffic reduces, but does not
   eliminate, the risk associated with denial of service attacks against
   the router's management plane.  In order to completely eliminate this
   risk, a network would have to police high priority traffic at each
   ingress point as well as elevate the priority of management traffic.

   None of the capabilities mentioned in Section 3.2 address the final
   vulnerability mentioned in Section 3.1.  Failure of the in-band
   network will render the network unmanageable.  This is an inherent
   weakness of in-band management.


4.  Out-of-Band Access


                NMS1    NMS2
                  \      /
                 Management
                  Network
                    /|\
                   / | \
                  /  |  \
                 /  R1   \
                |  /   \  |
                | /User \ |
                |/Network\|
                R2--------R3
               / \       / \
              /   \     /   \
             /     \   /     \
           NMS1 User3 User4  NMS2


   Figure 2: Out-of-Band Access

   Figure 2 also depicts two network management stations managing three
   routers.  In this figure, the network management stations use a
   dedicated, out-of-band network to communicate with the routers that
   they manage.



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   Each router maintains a dedicated management interface.  The
   dedicated management interface is connected to the dedicated, out-of-
   band management network.  Management functions are accessible only
   through the dedicated management interface.  They are not accessible
   through any other interfaces.

   RFC 3871 assumes the following regarding out-of-band management:

      - The out-of-band management network is secure

      - There is no need for encryption of communication on out-of-band
      management interfaces

      - Security measures are in place to prevent unauthorized physical
      access

4.1.  Vulnerabilities

   Although RFC 3871 does not explicitly identify this as a
   vulnerability, if a router maintains only one dedicated management
   interface, that interface constitutes a single point of failure.  If
   the dedicated management interface fails, the router will become
   unmanageable (although it will continue to forward traffic).

   Therefore, a router should maintain at least two connections to the
   management network.  Many networks solve this problem by connecting
   both the dedicated management interface and a terminal server to the
   out-of-band management network.

4.2.  Required Security Capabilities

   RFC 3871 states that routers must not forward traffic between
   dedicated management interfaces and non-management interfaces.  The
   router must never forward a datagram received from a non-management
   interface through the dedicated management interface.  Likewise, the
   router must never forward a datagram received from the dedicated
   management interface through a non-management interface.

   Operators should refrain from activating dynamic routing protocols on
   the dedicated management interface.  Alternatively, they should rely
   upon direct or static routes.  If static routes are configured, they
   should be as specific as possible.

4.3.  Analysis

   Out-of-band management networks isolate network users from
   communication channels that are dedicated to network management.
   Therefore, network users cannot access management functions,



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   eavesdrop on management traffic or launch denial of service attacks
   against the network management plane.

   Although the dedicated management interface is somewhat susceptible
   to misconfiguration, it is less susceptible because its configuration
   is so simple (i.e., limited to interface definition and a few static
   routes).


5.  Virtual Out-of-band Access

                   -----

                  a\   /mgmt
                    \ /
         User1----  R1----User2
                   /  \
             |\a  /    \    a/|
             | \ /      \   / |
             --R2--------R3---
          mgmt / \       / \  mgmt
              /   \     /   \
             /     \   /     \
           NMS1 User3 User4  NMS2


   Figure 3: Virtual Out-of-Band Access

   Figure 3 is identical to Figure 1, except that three loop circuits
   have been added.  Each loop circuit connects an a-end interface to a
   dedicated management interface.  The function of these looping
   circuits is described below.

   In the figure, Routers R1-R3 provide a Layer 3 Virtual Private
   Network (VPN) [4] service.  Although the three routers can support a
   very large number of Virtual Routing and Forwarding (VRF) instances,
   for the purpose of example, we will say that they support only two.

   The first VRF supports access to the global Internet.  This VRF
   includes interfaces to User1, User2, User3 and User4.  It also
   contains several gateway interfaces to the global Internet (which are
   not included in the figure).

   The second VRF is dedicated to network management traffic.  This VRF
   includes the interfaces to NMS1 and NMS2, as well as the a-end of
   each looping interface.

   Each router maintains a dedicated management interface that functions



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   exactly as described in Section 4.  Management functions are
   accessible only through the dedicated management interface.  They are
   not accessible any other interfaces.

   The dedicated management interface is connected to the a-end of the
   looping circuit.  Therefore, it is accessible only through the
   management VRF.

   Note that the this section describes only one method of constructing
   a virtual out-of-band management network.  An operator could
   construct a virtual out-of-band management network from in-band
   pseudowires or an in-band Virtual Private LAN Service.  (Layer 3 VPN
   service is not required.)  Likewise, the looping interface need not
   consume two physical ports.  The same results can be achieved with a
   single, channelized interface or an internal interface.

5.1.  Vulnerabilities

   RFC 3871 is silent regarding virtual out-of-band network management.
   However, because virtual out-of-band management networks rely upon
   physically in-band channels, they are susceptible to the following
   vulnerabilities:

   1.  Saturation of an in-band trunk can make the device unmanageable.

   2.  Management traffic may be intercepted.  However this would
       typically require a significant compromise in the routing system.

   3.  Public interfaces used for management may become unavailable due
       to bugs (e.g., buffer overflows being exploited).

   Expanding upon the final point, listed above, the virtual out-of-band
   network can be misconfigured, such that the managed device becomes
   isolated with regard to the network management stations.  When this
   happens, operators cannot access the router in order to remedy the
   configuration error.  They become reliant upon physical access to the
   managed device.

5.2.  Required Security Capabilities

   In order to provide a secure management mechanism, the virtual out-
   of-band management network must effectively separate the management
   VPN from all user VPNs.  Traffic must never cross from the management
   VPN to a user VPN or vice versa.

   Routers must not forward traffic between dedicated management
   interfaces and non-management interfaces.  The router must never
   forward a datagram received from a non-management interface through



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   the dedicated management interface.  Likewise, the router must never
   forward a datagram received from the dedicated management interface
   through a non-management interface.

   Operators should refrain from activating dynamic routing protocols on
   the dedicated management interface.  Alternatively, they should rely
   upon direct or static routes.  If static routes are configured, they
   should be as specific as possible.

   Operators may also choose to elevate the priority of management
   traffic so that it will be preserved during periods of trunk
   congestion.

5.3.  Analysis

   None of the capabilities mentioned in Section 5.2 address the final
   vulnerability mentioned in Section 5.1.  Failure of the virtual out-
   of-band network will render the network unmanageable.  This is an
   inherent weakness of virtual management.


6.  Evaluation

   Based on the analysis above, we conclude that out-of-band management
   is both more secure and more reliable than either of the other
   options.  However, it is typically more expensive than either of the
   other options.

   When out-of-band management does not offer a feasible economic
   approach, operators must choose between in-band management with
   cryptographic protection or a virtual out-of-band management network.
   In either case, the operator must deal with some additional
   complexity.  So, operators should determine which class of threat
   (DoS, eavesdropping) poses the greatest risk to their network and
   choose a strategy accordingly.


7.  Security Considerations

   Security is the subject matter of this entire memo.

8.  Normative References

   [1]  Jones, G., "Framework for Operational Security Capabilities for
        IP Network  Infrastructure", draft-ietf-opsec-framework-00 (work
        in progress), June 2005.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement



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        Levels", BCP 14, RFC 2119, March 1997.

   [3]  Jones, G., "Operational Security Requirements for Large Internet
        Service Provider (ISP) IP Network Infrastructure", RFC 3871,
        September 2004.

   [4]  Rosen, E., "BGP/MPLS IP VPNs", draft-ietf-l3vpn-rfc2547bis-03
        (work in progress), October 2004.











































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Authors' Addresses

   Ronald P. Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, VA  20171
   US

   Email: rbonica@juniper.net


   Syed F. Ahmed
   Booz Allen Hamilton
   8283 Greensboro Drive
   McLean, VA  22102
   US

   Email: ahmed_syed@bah.com

































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   Internet Society.




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