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Versions: 00 01 02 03 04 05 06 07 08 09 10                              
Routing Protocol Security                                   B. Christian
Requirements                                       KMC Telecom Solutions
Internet-Draft                                                  B. Akyol
Expires: June 13, 2005                                          R. White
                                                           Cisco Systems
                                                                 J. Haas
                                                   Next Hop Technologies
                                                               S. Murphy
                                             Trusted Information Systems
                                                       December 13, 2004


                       BGP Security Requirements
                     draft-ietf-rpsec-bgpsecrec-00

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   This Internet-Draft will expire on June 13, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   The security of BGP is critical to the proper operation of
   large-scale internetworks, both public and private.  While securing
   the information transmitted between two BGP speakers is a relatively



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   easy technical matter, securing BGP, as a routed system, is more
   complex.  This document describes a set of requirements for securing
   BGP, including securing peering relationships between BGP speakers,
   and authenticating the routing information carried within BGP.















































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1.  Introduction

   Threats to networking protocols generally fall under one of the three
   categories as defined in RFC 2196 [1]:
   o  Unauthorized access to resources and/or information
   o  Unintended and/or unauthorized disclosure of information
   o  Denial of service

   A number of attacks can be realized which, if exploited, can lead to
   one of the above mentioned threats.  These are typically classified
   as passive attacks and active attacks.  Passive attacks are ones
   where an attacker simply reads information off the network and
   obtains confidential and/or private information.  Active attacks are
   ones where the attacker writes data to the network and can include
   replay attacks, message insertion, message deletion, message
   modification and man-in-the-middle attacks.  These attacks are often
   combined.

   Attacks that do not involve direct manipulation of BGP, and the
   information contained within it, are outside the scope of this
   document.  When possible, the requirements will attempt to minimize
   the extent of the damage that occurs when end systems come under
   attack.

   The intent of this requirements document is to prevent attacks that
   originate false data or create invalid routing paths and therefore
   addresses issues relating to data integrity and peer entity
   authentication.  As described in RFC 3552 [2], data integrity
   protection ensures that data is not modified in transit and peer
   entity authentication ensures that there is a reasonable guarantee
   that the sender and recipient of the data are the intended parties.

   Guaranteed packet delivery is not part of the BGP protocol security
   model.  Just because a packet is addressed to a specific destination
   does not mean it will be received, even with a "secure" route.  For
   example: an attacker could have compromised an intermediate router
   and installed a static route for target address A.B.C.D pointing to
   an inappropriate direction or an attacker might splice into a circuit
   between two secure routers and install a device that diverts A.B.C.D
   traffic without requiring the compromise of control plane devices.











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2.  Deployment Requirements

   We have determined, through discussion with with several large
   internetwork operators and equipment vendors, that the following
   attributes are important to the ongoing performance of interdomain
   routing systems such as BGP:
   o  Convergence Speed: Convergence speed is a major concern to many
      operators of large scale internetworking systems.  Networks, and
      internetworks, are carrying ever increasing amounts of information
      that is time and delay sensitive; increasing convergence times can
      adversely affect the usability of the network, and the ability of
      an internetwork to grow.  BGP's convergence speed, with a security
      system in operation, SHOULD be equivalent to BGP running without
      the security system in operation.  This includes the preservation
      of optimizations currently used to produce acceptable convergence
      speeds on current hardware, including update packing, peer groups,
      and others.  Current timers, including hold timers, keepalive
      timers, and the peering process, SHOULD NOT be impacted by the
      security system.  Two types of verification MAY be offered for the
      NLRI and the AS_PATH in order to allow for a selection of
      optimizations:
      *  Contents of the UPDATE message SHOULD be authenticated in
         real-time as the UPDATE message is processed.
      *  The route information base MAY be authenticated periodically or
         in an event driven manner by scanning the data and verifying
         the originating AS and the verifiability of the AS-PATH list.
      All BGP implementations that implement security MUST utilize at
      least one of the above methods for validating routing information.
      Real time verification is preferred in order to prevent transitive
      failures based on periodic or event driven scan intervals.
   o  Incremental Deployment: We will not be able to deploy a newly
      secured BGP protocol instantaneously and will be unable to dictate
      a partitioning of large internetworks by the operators.  BGP MUST
      support both secured and unsecured routes with the security system
      in place.  The security system MUST allow the forming of peering
      relationships between secure and non-secure BGP speakers, and MUST
      be backward compatible in the message formatting, transmission,
      and processing of routing information carried through a mixed
      security environment.  Message formatting in a fully secured
      environment MAY be handled in a non-backward compatible fashion.
   o  Trust level Variability: Each secured environment may have
      different levels of requirements in terms of what is acceptable or
      unacceptable.  In environments that require strict security it may
      not be acceptable to temporarily route to a destination while
      waiting for security verification to be performed.  However, in
      many commercial environments the rapidity of route installation
      may be of paramount importance; in order to facilitate the more
      common occurence of route withdrawl due to network failure.  Based



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      on the two divergent requirements, the security system MUST
      support a range of possible outputs for local determination of the
      trust level for a specific route.  Any given route should be
      trustable to a locally configured degree, based on the
      completeness of security information for the update and other
      factors.  The security system SHOULD allow the operator to
      determine whether the speed of convergence is more important than
      security operations, or security operations are more important
      than the speed of convergence.  This facilitates the incremental
      deployment of security on systems not designed to support
      increased processing requirements imposed by the security system.








































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3.  The Trust Model

   In examining the various environments in which BGP is deployed, and
   through discussions with various operators working with the context
   of the public Internet, and other internetworks, it is apparent that
   trust models are largely environment specific.  For instance, in the
   public Internet, a distributed trust model, following the current
   transitive trust pattern of contractual and peering arrangements,
   would fit the the business models of the participants.  In other
   environments a hierarchical trust model would work better.  Thus, any
   trust system specified in a security mechanism designed for BGP must
   be flexible, and support both a true distributed trust model and a
   fully hierarchical trust model.

   Since hierarchical trust models are a subset (or a special case of) a
   distributed trust model, any security system designed for BGP MUST
   support a distributed trust model, and MUST also support a
   hierarchical trust model, if desired.

   If two internetworks using differing trust models are interconnected
   they MUST be able to interoperate using locally determined levels of
   trust to compensate for differences in their trust models.





























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4.  The AS-Path Attribute and NLRI Authentication

   BGP distributes routing information across the Internet (between BGP
   speakers) using BGP UPDATE messages.  The UPDATE message contains
   withdrawn routes, path attributes and one or more NLRIs (Network
   Layer Reachability Information is synonymous with advertised prefix).
   For the remainder of this section, we will focus on the AS-Path
   Attribute and the NLRI.  Attributes such as local pref are locally
   specific and, as such, are protected by BGP session security.

   The AS_PATH for specific prefixes must be protected in any proposed
   security system in three ways:
   o  Authorization of Originating AS: For all prefixes announced in
      BGP, the originating AS MUST be verifiable through the trust model
      as the authorized announcer of the prefix.  The verification
      mechanism must account for existing BGP mechanisms such as
      summarization.  For the purpose of this document the term
      verifiable is defined as the resultant of a secured routing
      systems as described in this document.  The term specifically
      indicates the ability to validate the originator of a specific
      prefix (or block of IP addresses) and the ability to validate the
      session through which the prefix was received
   o  The AS_PATH list MUST correspond to a verifiable list of
      autonomous systems based on the peering topology of the network.
   o  Announcing AS Check: For all BGP peers, a BGP Implementation MUST
      ensure that the first element of the AS_PATH list corresponds to
      the locally configured AS of that peer.

   There are many ways in which a differential between the speed of
   prefix/AS path attribute propagation and the information validating
   the the prefix/AS path attribute information can be exploited to
   attack the routing system on a temporary basis.  These types of
   attacks are dominantly exploitative of the moment in time it takes to
   follow the withdraw of a NLRI with an update.  As a result of this
   potential for temporary disruption, BGP security solutions MUST
   propagate security information at the same rate as the BGP updates
   and withdrawls.  The following items are required to propagate at the
   same rate:
   o  The distribution of key information used by individual actors
      within the system, including the keys used by individual
      autonomous systems to sign certificates and other objects
   o  The distribution of information about the AS authorized to
      advertise a given block of IP addresses (or an address space)
   o  The distribution of information about connectivity between
      autonomous systems and autonomous system polices, if such
      information is to be distributed within the security system.





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5.  Address Allocation and advertisement

   As part of the regular operation of the Internet, addresses that are
   allocated to an organization may be, and are quite commonly,
   advertised by a different organizations.  Common reasons for this
   practice include multi-homing and route reduction for the purposes of
   resource conservation.  There are two modes of delegation:
   o  A BGP speaker and listener have chosen to restrict the amount of
      received prefixes for the listener.  The listener has chosen to
      honor route announcements sent in a summary fashion by the
      speaker.
   o  Address space that is being delegated is part of a larger
      allocation that is owned by an autonomous system.  The owner then
      delegates the smaller block to another AS for purposes of
      advertisement.  This mode is commonly observed in multi-homing.

   These two modes lead to a single common requirement: Any BGP Security
   solution MUST support delegation of an address block of any size
   regardless of its relationship to other address blocks to another
   entity via verifiable means.

   An associated delegation criteria is the requirement to allow for
   non-BGP IP end user implementations.  As a result, all secured BGP
   implementations MUST allow for the propagation of a prefix by more
   than one originator AS within normal network convergence times.


























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6.  NLRI and Path Attribute Tracking

   Non-repudiation of routing updates, the ability for a receiver to
   know exactly who originated and forwarded a routing update, is a
   desirable trait.  In order to rapidly identify agressors and parties
   at fault for route table disruption it is important to track and log
   prefix origination information along with associated security
   information.

   Any security system SHOULD provide a method to allow the receiver of
   an update to verify that the originator actually originated the
   update, and that the AS's listed in the AS_PATH actually forwarded
   the update.

   The data generated by logging may be very large depending on the
   number of peers, the number of prefixes received, the authentication
   model used, and routing policies.  As such, efficient data structures
   and storage mechanisms MUST be developed to allow for an effective
   means of reproducing incidents and outages

   Path and NLRI attributes MUST be logged using a standard format.  The
   format must be scalable with the amount of data logged and the
   frequency of log generation.  The frequency of log generation should
   be controllable by the operator.  The logging mechanisms for the
   tracked information MUST be standardized across all platforms.
   Logging ability both on and off line is considered highly desirable.

























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7.  Transport Protection

   Transport protection is an important aspect of BGP routing protocol
   security.  The potential to create a linked transport/NLRI/AS-PATH
   authentication mechanism should not be overlooked and may provide for
   the accelerated deployment of a BGP security system.  Current
   security mechanisms for BGP transport are inadequate and require
   significant operator interaction to maintain a respectable level of
   security.

   Any proposed security mechanism MUST include provisions for securing
   both internal BGP and external BGP peering sessions.  Key maintenance
   can be especially onerous to the operators.  The number of keys
   required and the maintenance of keys (update/withdraw/renew) may have
   an additive affect to a barrier to deployment.  A highly securable
   BGP routing system SHOULD require no more than three keys and each
   key should be updateable within similar timeframes as prefix
   propagation.  The preferred number of keys is ONE per AS.

   Transport protection systems SHOULD function as a component of the
   BGP routing protocol security mechanism.  This includes the use of
   the same key generation/management systems as the rest of the
   security system.

8  References

   [1]  Fraser, "RFC 2196 - Site Security Handbook", September 1997.

   [2]  Rescorla, Korver and Internet Architecture Board, "RFC 3552 -
        Guidelines for Writing RFC Text on Security Considerations",
        July 2003.


Authors' Addresses

   Blaine Christian
   KMC Telecom Solutions
   1545 U.S. Highway 206
   Bedminster, NJ  07921
   US


   Bora Akyol
   Cisco Systems
   170 Tasman Drive
   San Jose, CA  95134
   US




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   Russ White
   Cisco Systems
   7025 Kit Creek Road
   Research Triangle Park, NC  95134
   US


   Jeffrey Haas
   Next Hop Technologies
   825 Victors Way Suite 100
   Ann Arbor, MI  48108
   US


   Sandy Murphy
   Trusted Information Systems
   3060 Washington Road
   Glenwood, MD  21378
   US
































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Appendix A.  Acknowledgements

   The following individuals contributed to the development and review
   of this draft.  Steve Kent, Mike Tibodeau, Thomas Renzy, Kaarthik
   Sivakumar, Tao Wan, Radia Perlman, and Merike Kaeo.

   This draft was developed based on conversations with various network
   operators including Chris Morrow, Jared Mauch, Tim Battles, and Ryan
   McDowell.










































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