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Routing Protocol Security                              B. Christian, Ed.
Requirements                                                   Microsoft
Internet-Draft                                            T. Tauber, Ed.
Intended status: Informational                                   Comcast
Expires: May 7, 2009                                    November 3, 2008


                       BGP Security Requirements
                     draft-ietf-rpsec-bgpsecrec-10

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on May 7, 2009.

Abstract

   The security of BGP, the Border Gateway Protocol, 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 easy technical matter, securing BGP, as a
   routing system, is more complex.  This document describes a set of
   requirements for securing BGP and the routing information carried
   within BGP.







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Table of Contents

   1.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  System Description . . . . . . . . . . . . . . . . . . . .  3
     2.2.  Threats  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.3.  Areas to secure  . . . . . . . . . . . . . . . . . . . . .  4
   3.  Underlying Assumptions regarding BGP . . . . . . . . . . . . .  5
   4.  Operational Requirements . . . . . . . . . . . . . . . . . . .  8
     4.1.  Convergence speed  . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Incremental deployment . . . . . . . . . . . . . . . . . .  9
     4.3.  Conditions for initialization  . . . . . . . . . . . . . .  9
     4.4.  Local controls for secure UPDATE acceptance  . . . . . . . 10
     4.5.  Processing on Routers  . . . . . . . . . . . . . . . . . . 10
     4.6.  Configuration on Routers . . . . . . . . . . . . . . . . . 11
   5.  Infrastructure Requirements  . . . . . . . . . . . . . . . . . 11
   6.  The Trust Model  . . . . . . . . . . . . . . . . . . . . . . . 12
   7.  The AS_PATH Attribute and NLRI Authentication  . . . . . . . . 12
   8.  Address Allocation and Advertisement . . . . . . . . . . . . . 14
   9.  Logging  . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   10. NLRI and Path Attribute Tracking . . . . . . . . . . . . . . . 15
   11. Transport Layer Protection . . . . . . . . . . . . . . . . . . 15
   12. Key Management . . . . . . . . . . . . . . . . . . . . . . . . 16
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   14. Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     15.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix 1.  Acknowledgements  . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
   Intellectual Property and Copyright Statements . . . . . . . . . . 18




















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1.  Requirements Language

   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 RFC 2119 [RFC2119].


2.  Introduction

2.1.  System Description

   BGP is described in RFC4271 [RFC4271], as a path-vector routing
   protocol.  BGP speakers typically exchange information about
   reachable destinations (expressed as address prefixes) in an
   internetwork through pair-wise peering sessions.  Once this
   information has been exchanged, each BGP speaker locally determines a
   loop free path to each reachable destination, based on local policy
   or policy indicators such as community values and LOCAL_PREF which
   may be carried in the UPDATE, and the AS_PATH data carried in the BGP
   UPDATE messages.

   Each BGP speaker represents an Autonomous System (AS).  All of the
   BGP speakers within an AS operate under a common administrative
   policy.

2.2.  Threats

   Violations of security for network and information systems generally
   fall under one of the three categories as defined in RFC  2196
   [RFC2196]:

   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 security violations.  Attacks against
   communications are typically classified as passive or active
   wiretapping attacks.  Passive attacks are ones where an attacker
   simply observes information traversing the network, violating
   confidentiality or identifying a means of engaging in further
   attacks.  Active attacks are ones where the attacker modifies data in
   transit.  Such attacks include replay attacks, message insertion,
   message deletion, and message modification attacks.  Some attacks may
   be effected by sending data from any where in the Internet.  Other
   active attacks require a "man-in-the-middle" capability, i.e., the



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   attacker must be in a position where traffic passes through an
   attacker-controlled device.  Attacks against BGP may be used by an
   attacker to facilitate a wide variety of active or passive
   wiretapping attacks against subscriber traffic.

   Attacks that do not involve direct manipulation of BGP, and the
   information contained within BGP, are outside the scope of this
   document, except as relates to transport layer of the BGP session as
   discussed here and in related documents.

   Because ASes are autonomous in their operation, it is not possible to
   mandate secure operation by all ASes, nor would it be advisable to
   assume such operation.  Thus the primary goal of BGP security
   measures is to provide data to AS operators to enable BGP speakers to
   reject advertisements (UPDATE messages) that are not valid.  For
   example, UPDATE messages that represent erroneous binding of prefixes
   to an origin AS, or that advertise invalid paths (as defined later in
   this document) should be rejected.  Because BGP peering sessions take
   place in the context of TCP, the authentication and integrity
   guarantees usually associated with TCP need to be provided in the
   face of possible active wiretapping attacks.  Using the terminology
   established in RFC 3552 [RFC3552], these peering sessions should be
   afforded data origin and peer entity authentication and connection-
   oriented integrity.

   Security for subscriber traffic is outside the scope of this
   document, and of BGP security in general.  IETF standards for
   subscriber data security, e.g., IPsec, TLS, and S/MIME should be
   employed for such purposes.  While adoption of BGP security measures
   may preclude certain classes of attacks on subscriber traffic, these
   measures are not a substitute for use of subscriber-based security
   mechanisms of the sort noted above.

2.3.  Areas to secure

   There are two primary points where BGP may be secured; the data
   payload of the protocol and the data semantics of the protocol.

   The session between two BGP speakers can be secured such that the BGP
   data received by the BGP speakers can be cryptographically verified
   to have been transmitted by the peer BGP speaker and not a replay of
   previously transmitted legitimate data.  There are several existing
   IETF standards to choose from to ensure that this system functions
   with greater effectiveness than the current system.  An example might
   be IPsec.  Some in the Operator community have expressed concerns
   that requiring cryptographic validation could open another vector for
   a denial-of-service attack by flooding the processor with bogus
   packets which must be cryptographically invalidated before being



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   discarded.  Thus, any cryptographic mechanism used to secure BGP
   sessions MUST be evaluated with regard to this denial of service
   concern.

   There are also several questions we can ask about the information
   contained within a received UPDATE.

   o  Is the originating Autonomous System authorized to propagate the
      prefix we have received?

   o  Does the AS_PATH, received via an UPDATE, represent a valid path
      through the network?

   The determination of AS_PATH validity falls into two distinct
   categories.  These categories are ordered from least to most
   rigorous.

   o  Does the AS_PATH specified actually exist as a path in the network
      topology and, based on the AS_PATH, is it possible to traverse
      that path to reach a given prefix?  This AS_PATH Feasibility Check
      will be referred to later in this document.

   o  Has the UPDATE actually traveled via the path in the UPDATE?


3.  Underlying Assumptions regarding BGP

   In order to properly identify security requirements it is important
   to articulate the fundamental aspects of BGP as related to security
   requirements.  The following list presents the basic parameters and
   application concepts of BGP that are assumed by this document.

   o  Peer Communication: BGP traffic travels over TCP between peers, so
      BGP speakers assume the data delivery guarantees of TCP in a
      benign environment.  This includes ordered, error-free delivery of
      application traffic from a peer identified by an IP address, plus
      integrity of the control aspects of TCP.  From a security
      perspective, these guarantees need to be enforced in the context
      of possible active wiretapping.

   o  Routing and Reachability: BGP is a protocol used to convey routing
      and reachability information both internal and external to an
      Autonomous System.  Typically, interior BGP (iBGP) is used to
      distribute prefix reachability information in conjunction with an
      Interior Gateway Protocol (IGP) and is used by a distinct network
      administrative entity to convey internal routing policy regarding
      external and internal information.  Exterior BGP (eBGP) is
      typically used to distribute route/prefix reachability information



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      between two distinct routing entities and is used to signal eBGP
      preferences and policy decisions on an inter-AS basis.

   o  Inter-AS UPDATE Message assumptions: When an AS distributes
      reachability information to a peer it is done with the intent of
      affecting routing decisions by the peer.  For example, with regard
      to a block of addresses represented by a prefix, AS-A may send
      peer AS-B an advertisement which is less specific (shorter in
      length of mask) and peer AS-C a more specific advertisement
      (longer mask).  This prefix distribution decision may have been
      made to provide a means for failure resolution between AS-A and
      AS-C, i.e., to provide a backup path for the addresses in
      question.  However, it should be noted that while AS-A tries to
      influence the routing decisions of AS-B and downstream ASes, AS-A
      is only providing inputs to a local decision by AS-B, a decision
      that is ultimately controlled by AS-B's local policy over which
      AS-A has no control.  UPDATE messages are sent between AS peers
      with the tacit authorization for those messages to be forwarded to
      others.  A notable exception to this assumption is the use of
      policy-based mechanisms between peers such as the NO-EXPORT
      community.  It is important to note that an UPDATE message itself
      generally is not re-transmitted.  Instead, an UPDATE message is
      regenerated continually as it passes from BGP speaker to BGP
      speaker.  Furthermore, UPDATE messages have no mechanism to
      indicate freshness (e.g., timestamps or sequence numbers).  This
      implies that messages may appear valid at any point in the life of
      a BGP peering session.  While the AS_PATH information is typically
      transitive it is, currently, not clearly mandated and many times
      is modified for various utilitarian reasons.

   o  It is important to note that while preferences regarding routing
      can be explicitly managed with direct peers it is markedly more
      difficult to influence routing decisions by ASes that are not
      directly adjacent.

   o  Inter-AS withdrawal message assumptions: The processing model of
      BGP RFC4271 [RFC4271] indicates that only the peer advertising
      NLRI information may withdraw it.  There are several instances
      where a withdrawal may occur.  Typical reasons for withdrawal
      include the determination of a better path, peer session failure,
      or local policy change.  There is no specified mechanism for
      indicating to a peer the reason for a route withdrawal.  Each
      withdrawal received via a valid peering session must be taken at
      face value.  There is no existing method to ensure that an AS will
      properly respond to a withdrawal message, e.g., withdraw the route
      and send such announcement to its neighbors.  Nor do mechanisms
      exist to ensure that old UPDATES are not re-propagated after a
      route was withdrawn and before it is legitimately re-advertised.



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   o  AS_PATH assumptions: Aside from the use of AS_SET, the AS_PATH is
      defined as an ordered list of the Autonomous Systems that an
      UPDATE has traversed.  The rightmost AS in the list is understood
      to be the originator of the BGP announcement.  Specifications
      state that the AS routing graph MUST be loop free.  This indicates
      that UPDATES received from an external peer which contain the
      local AS will be rejected.  Prepending one or more instances of an
      AS number on inbound advertisements (where the external peer's AS
      number is prepended) and outbound advertisements (where the local
      AS number is prepended) is a commonly used method to bias routing.
      Prepending a peer AS number on inbound UPDATEs is employed for
      biasing internal routing and forwarding management while
      prepending one's own AS number on outbound advertisement is
      typically used to bias forwarding and routing changes in external
      networks.  The latter practice is explicitly permitted by RFC4271
      [RFC4271], but the former is not.  Some operators, insert a remote
      AS number in an UPDATE, in order to cause the UPDATE to be dropped
      by that AS so that traffic will not traverse a given path.  Though
      this practice appears to run counter to the design of BGP,
      anecdotal evidence is that its use is not totally insignificant.
      While such a practice can be beneficial to legitimate operators,
      it presents a strong potential for misuse.  A proposed security
      system SHOULD address how to either address this concern or give
      specific information on this topic for consideration by the
      Operational community.

   o  Route Origination: BGP speakers may originate routes based on
      either configured internal data or on data received from peers via
      UPDATES.  An Autonomous System SHOULD only originate a prefix to
      its external peers if that prefix has been allocated to the
      administrators of that system, or if authorized by the prefix
      holder.

   o  Originating a route without the ability to forward the traffic
      associated with that route is, in most cases, in conflict with the
      intent of the BGP specification, notable exceptions include:

      *  Deployments that make use of route servers which are separate
         from forwarding devices

      *  Deployments that use the temporary propagation of prefixes in
         order to effectively block high bandwidth attacks (e.g., DDoS)
         against specific IP addresses (and the associated
         oversubscription of resources)

   o  Aggregation and de-aggregation: According to RFC4271 [RFC4271], if
      a BGP speaker chooses to aggregate a set of more specific prefixes
      into a less specific prefix then the ATOMIC_AGGREGATE attribute



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      SHOULD be set.  This creates a significant challenge for solutions
      to secure BGP because some origination information is removed
      (i.e. the more-specific information which triggered the generation
      of the aggregate).  Proposed solutions MUST indicate how
      aggregation will be accommodated.


4.  Operational Requirements

   We have determined, through discussion 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.

4.1.  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
   strive towards equivalence 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, etc.  Two types of
   verification MAY be offered for the NLRI and the AS_PATH in order to
   allow for a selection of optimizations:

   o  Contents of the UPDATE message SHOULD be authenticated in real-
      time as the UPDATE message is processed.

   o  The route information base MAY be authenticated periodically or in
      an event-driven manner by scanning the route-table data and
      verifying the originating AS and the validity 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 transient failures
   based on periodic or event-driven scan intervals.  See the section on
   "Local controls ..." below for more discussion.

   It is recognized that achieving all of these goals might prove very
   difficult or even impossible.







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4.2.  Incremental deployment

   It will not be feasible to deploy a newly secured BGP protocol
   throughout the public Internet instantaneously.  It also may not be
   possible to deploy such a protocol to all routers in a large AS at
   one time.  Any proposed solution MUST support an incremental
   deployment which will provide some benefit for those who participate.
   Because of this, there are several requirements that any proposed
   mechanism to secure BGP must consider.

   o  A BGP security mechanism MUST enable each BGP speaker to configure
      use of the security mechanism on a per-peer basis.

   o  A BGP security mechanism MUST provide backward compatibility 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 though care must be taken to ensure
      UPDATES can traverse intermediate routers which don't support the
      new format.

   o  In an environment where both secured and non-secured systems are
      interoperating a mechanism MUST exist for secured systems to
      identify whether an originator intended the information to be
      secured.

   o  Proposed solutions MUST provide comment and analysis of what
      security services the solution will provide in the case of
      incremental deployment scenarios (e.g, contiguous islands, non-
      contiguous islands, universal deployment).

   o  In an environment where secured service is in the process of being
      deployed a mechanism MUST exist to support a transition free of
      service interruption (caused by the deployment per se).

4.3.  Conditions for initialization

   A key factor in the robust nature of the existing internal and
   external relationships maintained in today's Internet is the ability
   to maintain and return to a significantly converged state without the
   need to rely on systems external to the routing system (the equipment
   that is performing the forwarding).  In order to ensure the rapid
   initialization and/or return to service of failed nodes it is
   important to reduce reliance on these external systems to the
   greatest extent possible.  Therefore, proposed systems SHOULD NOT
   require connections to external systems, beyond those directly
   involved in peering relationships, in order to return to full
   service.  Proposed systems MAY require post initialization



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   synchronization with external systems in order to synchronize
   security information.

4.4.  Local controls for secure UPDATE acceptance

   Each secured environment (e.g., public Internet vs. private
   internetwork) may have different metrics of what is acceptable or
   unacceptable with regard to routing security.  In environments that
   require strict security it may not be acceptable to temporarily route
   to a destination while waiting for path validation to be performed.
   However, in many environments the rapidity of route installation may
   be of paramount importance, e.g., in order to facilitate the common
   occurrence of route withdrawal due to network failure.  Based on the
   two divergent requirements, the following criteria apply:

   o  The security system MUST support a range of possible outputs for
      local determination of the trust level for a specific route so
      that routing preference and policy can be applied to its inclusion
      in the RIB.  Any given route should be trustable to a locally
      configured degree, based on the completeness of security
      information with a received UPDATE and other factors.  However,
      experience in the security community suggests that trying to
      assign trust ratings to inputs to a decision process usually adds
      considerable complexity to the management of the process.  This
      complexity, in turn, may undermine the security offered by the
      process.

   o  The security system SHOULD allow the operator to determine whether
      speed of convergence is more important than security, or whether
      security is 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.

4.5.  Processing on Routers

   The introduction of mechanisms to improve routing security will
   generally increase the processing performed by a router.  The
   increased processing typically will result from additional checks
   performed to determine the validity of UPDATEs, especially if these
   checks entail cryptographic operations.  Since currently deployed
   routers generally do not have hardware to accelerate cryptographic
   operations, these operations could impose a significant processing
   burden under some circumstances.  Thus proposed solutions should be
   evaluated carefully with regard to the processing burden they may
   impose, since deployment may be impeded if network operators perceive
   that a solution will impose a processing burden which either:




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   o  provokes substantial capital expense, or

   o  threatens to destabilize routers.

   Given the pervasive number of BGP-speaking routers in a typical ISP
   deployment, solutions can increase their appeal by minimizing the
   burden imposed on all BGP routers in favor of confining significant
   work loads to a relatively small number of devices.

   Optional features or increased assurance that provokes more pervasive
   processing load MAY be made available for deployments where the
   additional resources are economically justifiable.

   Some statement as to the expected performance measures and scaling as
   a function of prefixes, peers, NLRI, etc.  MUST be included with any
   proposed solution.

4.6.  Configuration on Routers

   It is undesirable to have long or very detailed configuration on
   routers, especially it needs to be synchronized on all of them.  Long
   configuration makes operating the device more difficult, and having
   to do very detailed configuration may hinder the adoption of the
   security solution; it should be possible to "just start using it" if
   possible.

   As above, a statement as to the expected configuration burden as a
   function of routers, peers, NLRI, ASNs, etc.  MUST be included with
   any proposed solution.  Additionally, some consideration SHOULD be
   given and statement made as to frequency of changes in the case of
   dynamic data.


5.  Infrastructure Requirements

   BGP security mechanisms MAY make use of a security infrastructure to
   distribute authenticated data that is an input to routing decisions.
   Such data may be needed to verify whether a given AS is authorized to
   originate an advertisement for a specified prefix, whether an given
   organization is the recognized holder of a block of address space or
   of an AS number, etc.  Any infrastructure used to distribute data in
   support of BGP security is subject to the following criteria:

   o  It MUST be resilient to attacks on the integrity of the data it
      contains.

   o  It MUST enable network operators to verify the entity which
      originated the data.



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   o  It MUST be sufficiently available so as to not degrade the
      existing pace of network operations.

   o  It SHOULD not introduce new organizational entities that have to
      be trusted in order to establish the authenticity of the data.


6.  The Trust Model

   In discussion with the operations community, concerns have emerged
   regarding the viability of a security system that requires agreement
   on a trust model dependent on a single root.  Current operational
   practice has many providers engaging in bilateral agreements and
   preserving the primacy of local policy choices.  The viability of a
   solution may well rest on the business imperatives of the provider
   community who may be unwilling to surrender their perceived autonomy
   or unable to come to communal agreement on this topic.

   In other environments, deployments may require an authority which has
   been selected by law or other institutional mandate.  Moreover, these
   two deployment types (single-rooted hierarchy or arbitrary
   association) may "touch" (i.e. be part of the same co-extensive BGP
   topology).

   Solutions MUST account for these differing types of deployments.

   If two internetworks using differing trust models are interconnected
   they MUST be able to interoperate using locally determined levels of
   assurance to compensate for differences in these trust models.  Some
   acknowledgement is made that this requirement might render it
   difficult to discern an attack from a difference in trust model or
   implementation.  Any proposed solution MUST mitigate this risk.


7.  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 NLRI (Network Layer
   Reachability Information, synonymous with advertised prefix(es)).
   For the remainder of this section, we will focus on the AS_PATH
   Attribute and the NLRI.  Attributes such as MED are not transitive
   and, as such, are protected by BGP session security.

   The AS_PATH for specific prefixes may be protected in any proposed
   security system in four ways, outlined below.





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   o  Authorization of Originating AS: For the purposes of authorization
      of the originating AS, authorization means that it MUST be
      possible to verify that the origin AS has been authorized to
      originate the route by the prefix holder(s).

   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 the peer from which the UPDATE was
      received.

   o  AS_PATH Feasibility Check: The AS_PATH list may correspond to a
      valid list of autonomous systems according to the first
      verification category listed in the "Areas to Secure" Section
      above.  Further study will determine the extent to which this is a
      security requirement.

   o  Update Transit Check: Routing information carried through BGP may
      include information that can be used to verify the re-
      advertisement or modification by each autonomous system through
      which the UPDATE has passed.  This check is more rigorous than the
      "valid list of autonomous systems" above.  Further study will
      determine the extent to which this is a security requirement.

   The results of all of these checks should be made available to
   network operators.  Each network operator will decide, on a local
   basis, which of these checks to enable.

   There are many ways in which any difference between the speed of
   prefix/AS path attribute propagation and the availability of the
   information needed to validate the prefix/AS_PATH attribute
   information can be exploited to attack the routing system on a
   transient basis.  These types of attacks primarily exploit the time
   it takes to follow the withdrawal of a route via an UPDATE.  As a
   result of this potential for temporary disruption, BGP security
   solutions MUST be capable of distributing security information at the
   same rate as the BGP announcements and withdrawals propagate.

   All data needed by BGP routers to evaluate the validity of an
   advertisement MUST be made available to the routers in a timeframe
   consistent with the rate at which advertisement characteristics
   change.  Two examples are:

   o  the distribution of information about the AS(es) authorized to
      advertise a given block of IP addresses,

   o  the distribution of information about connectivity between
      autonomous systems and about autonomous system policies




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   Note that in today's operational Internet, the first two pieces of
   information, or their analogues, are not a part of the BGP routing
   system per se (e.g., information in Routing or Address registries.)
   They are consulted by most operators on an irregular basis and are
   not consulted in real time by the routing system.  Policy information
   that is explicitly carried in the routing system is inconsistently
   expressed and consulted in Routing registries by operators.  For
   instance, most providers are reticent to define their interconnection
   arrangements as transit or non-transit in Routing registries; some
   may do so, most do not.  However, the ability to change inter-AS
   traffic flows in real time is an important feature of the current
   Internet.


8.  Address Allocation and Advertisement

   As part of the regular operation of the Internet, addresses allocated
   to one organization may be, and are quite commonly, advertised by
   ASes belonging to other organizations.  Common reasons for this
   practice include multi-homing and route reduction for the purposes of
   resource conservation (e.g., aggregation).  There are two modes of
   delegation:

   o  A BGP speaker and listener have chosen to restrict the number 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 held by an autonomous system.  The holder 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 the ability of an address block holder to
   declare (in a secure fashion) the AS(es) that the holder authorizes
   to originate routes to its address block(s) or any portion thereof
   regardless of the relationship of the entities.

   An associated delegation criteria is the requirement to allow for
   non-BGP stub networks.  As a result, all secured BGP implementations
   MUST allow for the contemporaneous origination of a route for a
   prefix by more than one AS.


9.  Logging

   In order to facilitate auditing and troubleshooting, a logging



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   capability MUST be implemented that will indicate both negative and
   positive event behaviors.  This data SHALL be for consumption of the
   AS operating the device that is producing the logs.  Further, the
   information MAY be combined with data from other is ASes or devices
   with different implementations within the same AS for purposes of
   event correlation and tracking.  Here follow some considerations in
   this regard:

   o  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

   o  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.


10.  NLRI and Path Attribute Tracking

   The ability for a receiver to know the identity of each AS that
   originates and/or forwards a routing UPDATE is a desirable trait.  In
   order to rapidly identify attack points and parties at fault for
   route table disruption, it is important to be able to track and log
   prefix origination information along with associated security
   information.

   This capability can be afforded by implementation of the
   aforementioned directive that any security system SHOULD provide a
   method to allow the receiver of an UPDATE to verify that the
   originator is actually authorized to originate the update, and that
   the AS's listed in the AS_PATH actually forwarded the update.


11.  Transport Layer 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.  A detailed
   treatment of this topic is being developed in BGP Session Security
   Requirements [BGP Session Security Requirements].



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   Any proposed security mechanism MUST include provisions for securing
   both internal BGP and external BGP peering sessions.


12.  Key Management

   Current implementations and deployments of TCP-MD5 [RFC2385] exhibit
   serious shortcomings with regard of key management as described in
   RFC 3562 [RFC3562].

   Key management can be especially onerous for operators.  The number
   of keys required and the maintenance of keys (issue/revoke/renew) has
   had an additive effect as a barrier to deployment.  Thus automated
   means of managing keys, to reduce operational burdens, MUST be
   available in proposed BGP security systems.  These security systems
   MUST be resistant to compromise of session-level or device-level
   keys, i.e., the security implications of such compromises MUST be
   limited.


13.  IANA Considerations

   This document asks nothing of IANA.


14.  Security Considerations

   This document describes requirements for securing BGP as envisioned
   by the community.  Its completeness is likely not exhaustive but
   represents the broadest consensus.  As the understanding of the
   issues and possible residual vulnerabilities are refined, so these
   requirements may be revised in successor documents.


15.  References

15.1.  Normative References

   [RFC2119]  Bradner, "RFC 2119 - Key words for use in RFCs to Indcate
              Requirements Levels", March 1997.

   [RFC4271]  Rekhter, Li, and Hares, "RFC 4271 - A Border Gateway
              Protocol 4 (BGP-4)", October 2005.

15.2.  Informative References

   [RFC2196]  Fraser, "RFC 2196 - Site Security Handbook",
              September 1997.



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   [RFC3552]  Rescorla, Korver, and Internet Architecture Board, "RFC
              3552 - Guidelines for Writing RFC Text on Security
              Considerations", July 2003.

   [RFC2385]  Heffernan, "RFC 2385 - Protection of BGP Sessions via the
              TCP MD5 Signature Option", August 1998.

   [RFC3562]  Leech, "RFC 3562 - Key Management Considerations for the
              TCP MD5 Signature Option", July 2003.

   [BGP Session Security Requirements]
              Behringer, "BGP Session Security Requirements
              (draft-ietf-rpsec-bgp-session-sec-req-01.txt)",
              August 2007.


1.  Acknowledgements

   The following individuals contributed to the development and review
   of this draft.  Steve Kent, Russ White, Sandy Murphy, Jeff Haas, Bora
   Akyol, Susan Hares, Mike Tibodeau, Thomas Renzy, Kaarthik Sivakumar,
   Tao Wan, Radia Perlman, Pekka Savola, Iljitsch van Beijnum, Curtis
   Villamizar, Joe Touch, Geoff Huston, and Merike Kaeo.

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


Authors' Addresses

   Blaine Christian (editor)
   Microsoft


   Tony Tauber (editor)
   Comcast
   27 Industrial Avenue
   Chelmsford, MA  01824
   US

   Email: ttauber@1-4-5.net









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Full Copyright Statement

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