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Versions: (draft-beard-rpsec-routing-threats) 00 01 02 03 04 05 06 07 RFC 4593

Network Working Group                                          A. Barbir
Internet-Draft                                           Nortel Networks
Expires: October 12, 2004                                      S. Murphy
                                                            Sparta, Inc.
                                                                 Y. Yang
                                                           Cisco Systems
                                                          April 13, 2004


                  Generic Threats to Routing Protocols
                  draft-ietf-rpsec-routing-threats-06

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on October 12, 2004.

Copyright Notice

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

Abstract

   Routing protocols are subject to attacks that can harm individual
   users or network operations as a whole. This document provides a
   description and a summary of generic threats that affect routing
   protocols in general. This work describes threats, including threat
   sources and capabilities, threat actions, and threat consequences as
   well as a breakdown of routing functions that might be separately
   attacked.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Routing Functions Overview . . . . . . . . . . . . . . . . . .  4
   3.  Generic Routing Protocol Threat Model  . . . . . . . . . . . .  5
     3.1   Threat Definitions . . . . . . . . . . . . . . . . . . . .  5
       3.1.1   Threat Sources . . . . . . . . . . . . . . . . . . . .  6
       3.1.2   Threat Consequences  . . . . . . . . . . . . . . . . .  6
   4.  Generally Identifiable Routing Threats . . . . . . . . . . . . 11
     4.1   Deliberate Exposure  . . . . . . . . . . . . . . . . . . . 11
     4.2   Sniffing . . . . . . . . . . . . . . . . . . . . . . . . . 11
     4.3   Traffic Analysis . . . . . . . . . . . . . . . . . . . . . 12
     4.4   Spoofing . . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.5   Falsification  . . . . . . . . . . . . . . . . . . . . . . 13
       4.5.1   Falsifications by Originators  . . . . . . . . . . . . 13
       4.5.2   Falsifications by Forwarders . . . . . . . . . . . . . 16
     4.6   Interference . . . . . . . . . . . . . . . . . . . . . . . 17
     4.7   Overload . . . . . . . . . . . . . . . . . . . . . . . . . 17
     4.8   Byzantine Failures . . . . . . . . . . . . . . . . . . . . 17
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
   6.1   Normative References . . . . . . . . . . . . . . . . . . . . 20
   6.2   Informative References . . . . . . . . . . . . . . . . . . . 20
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 20
   A.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 22
   B.  Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
       Intellectual Property and Copyright Statements . . . . . . . . 24
























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1.  Introduction

   Routing protocols are subject to threats and attacks that can harm
   individual users or the network operations as a whole. The document
   provides a summary of generic threats that affect routing protocols.
   In particular, this work identifies generic threats to routing
   protocols that include threat sources, threat actions, and threat
   consequences. A breakdown of routing functions that might be
   separately attacked is provided.

   This work should be considered as a precursor to developing a common
   set of security requirements for routing protocols. While it is well
   known that bad, incomplete, or poor implementations of routing
   protocols may, in themselves, lead to routing problems or failures,
   or may increase the risk of a network being attacked successfully,
   these issues are not considered here. This document only considers
   attacks against robust, well considered implementations of routing
   protocols, as outlined in OSPF [5], IS-IS [6], RIP [7] and BGP [8].

   The document is organized as follows: Section 2 provides a review of
   routing functions. Section 3 defines threats. In section 4, a
   discussion on generally identifiable routing threat actions is
   provided. Section 5 addresses security considerations.




























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2.  Routing Functions Overview

   This section provides an overview of common functions that are shared
   among various routing protocols. In general, routing protocols share
   the following functions:
   o  Transport Subsystem: The routing protocol transmits messages to
      its neighbors using some underlying protocol. For example, OSPF
      uses IP, while other protocols may run over TCP.
   o  Neighbor State Maintenance: Neighboring relationship formation is
      the first step for topology determination. For this reason,
      routing protocols may need to maintain state information. Each
      routing protocol may use a different mechanism for determining its
      neighbors in the routing topology. Some protocols have distinct
      exchanges through which they establish neighboring relationships,
      e.g., Hello exchanges in OSPF.
   o  Database Maintenance: Routing protocols exchange network topology
      and reachability information. The routers collect this information
      in routing databases with varying detail. The maintenance of these
      databases is a significant portion of the function of a routing
      protocol.

   In a routing protocol there are message exchanges that are intended
   for the control of the state of the protocol. For example, neighbor
   maintenance messages carry such information. On the other hand, there
   are messages that are used to exchange information that is intended
   to be used in the forwarding function. These messages effects the
   data (information) part of the routing protocol. For example,
   messages that are used to maintain the database.























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3.  Generic Routing Protocol Threat Model

   The model developed in this section can be used to identify threats
   to any routing protocol. It examines attacks which can be launched
   against routing from subverted entities within the routing system and
   from entities outside the routing system. Both of these types of
   entities are called unauthorized entities.

   Routing protocols are subject to threats at various levels. For
   example,  an attacker may attack messages that carry control
   information in a routing protocol to break a neighboring (e.g.,
   peering, adjacency) relationship. This type of attack can impact the
   network routing behavior in the affected routers and likely the
   surrounding neighborhood. An attacker may attack messages that carry
   data information to break a database exchange between two routers. An
   attacker who is able to introduce bogus data can have a strong effect
   on the behavior of routing in the neighborhood.

   At the routing function level, threats can affect the transport
   subsystem, where the routing protocol can be subject to attacks on
   its underlying protocol. At the neighbor state maintenance level,
   there are threats that can lead to attacks that can disrupt the
   neighboring relationship with widespread consequences. For example,
   in BGP, if a router receives a CEASE message, it can lead to breaking
   its neighboring relationship to other routers.

   There are threats against the database maintenance functionality. For
   example, the information in the database must be authentic and
   authorized. Threats that jeopardize this information can affect the
   routing functionality in the overall network. For example, if an OSPF
   router sends LSAs with the wrong Advertising Router, the receivers
   will compute an SPF tree that is incorrect and might not forward the
   traffic. If a BGP router advertises a NLRI that it is not authorized
   to advertise, then receivers might forward that NLRI's traffic toward
   that router and the traffic would not be deliverable. A PIM router
   might transmit a JOIN message to receive multicast data it would
   otherwise not receive.

3.1  Threat Definitions

   In this work, a threat is defined as a motivated, capable adversary.
   This characterization of threats clearly distinguishes threats from
   attacks. By modeling the motivations (attack goals) and capabilities
   of the adversaries who are threats, one can better understand what
   classes of attacks these threats may mount and thus what types of
   countermeasures will be required to deal with these attacks. In [1],
   a threat is defined as a potential for violation of security, which
   exists when there is a circumstance, capability, action, or event



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   that could breach security and cause harm. Threats can be categorized
   based on various rules, such as threat sources, threat actions,
   threat consequences, threat consequence zones, and threat consequence
   periods.

3.1.1  Threat Sources

   There are many sources for threats that may affect routing protocols.
   In some cases, unauthorized entities such as attackers may illegally
   participate in the routing operations. In other circumstances, there
   are threats to routing protocols from entities that are running
   incorrect code, or using invalid configurations.

   Threats can originate from outsiders or insiders. An insider is an
   authorized participant in the routing protocol. An outsider is any
   other host or network. A particular router determines if a host is an
   outsider or an insider.

   In general, threats can be classified into the following categories
   based on their sources [2]:
   o  Threats that result from subverted links: A link becomes subverted
      when an attacker gains access to (or control) it through a
      physical medium. The attacker can then take control over the link.
      This threat can result from the lack (or the use of weak) access
      control mechanisms as applied to physical mediums or channels. The
      attacker may eavesdrop, replay, delay, or drop routing messages,
      or break routing sessions between authorized routers, without
      participating in the routing exchange.
   o  Threats that result from subverted devices (e.g. routers): A
      subverted device (router) is an authorized router that may have
      been broken into by an attacker. The attacker can use the
      subverted device to inappropriately claim authority for some
      network resources, or violate routing protocols, such as
      advertising invalid routing information.

3.1.2  Threat Consequences

   A threat consequence is a security violation that results from a
   threat action [1]. The compromise to the behavior of the routing
   system can damage a particular network or host or can damage the
   operation of the network as a whole.

   There are four types of threat consequences: disclosure, deception,
   disruption, and usurpation [1].
   o  Disclosure: Disclosure of routing information happens when a
      router successfully accesses the information without being
      authorized. Subverted links can cause disclosure, if routing
      exchanges lack confidentiality. Subverted devices (routers), can



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      cause disclosure, as long as they are successfully involved in the
      routing exchanges. Although inappropriate disclosure of routing
      information can pose a security threat or be part of a later,
      larger, or higher layer attack, confidentiality is not generally a
      design goal of routing protocols.
   o  Deception: This consequence happens when a legitimate router
      receives a forged routing message and believes it to be authentic.
      Subverted links and/or subverted devices (routers)can cause this
      consequence if the receiving router lacks the ability to check
      routing message integrity or origin authentication.
   o  Disruption: This consequence occurs when a legitimate router's
      operation is being interrupted or prevented. Subverted links can
      cause this by replaying, delaying, or dropping routing messages,
      or breaking routing sessions between legitimate routers. Subverted
      devices (routers) can cause this consequence by sending false
      routing messages, interfering with normal routing exchanges, or
      flooding unnecessary messages. (DoS is a common threat action
      causing disruption.)
   o  Usurpation: This consequence happens when an attacker gains
      control over a legitimate router's services/functions. Subverted
      links can cause this by delaying or dropping routing exchanges, or
      replaying out-dated routing information. Subverted routers can
      cause this consequence by sending false routing information or
      interfering routing exchanges.

   Note: an attacker does not have to directly control a router to
   control its services. For example, in Figure 1, Network 1 is
   dual-homed through Router A and Router B, and Router A is preferred.
   However, Router B is compromised and advertises a better metric.
   Consequently, devices on the Internet choose the path through Router
   B to reach Network 1. In this way, Router B steals the data traffic
   and Router A surrenders its control of the services to Router B. This
   depicted in Figure 1.


















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      +-------------+   +-------+
      |  Internet   |---| Rtr A |
      +------+------+   +---+---+
             |              |
             |              |
             |              |
             |            *-+-*
      +-------+           /     \
      | Rtr B |----------*  N 1  *
      +-------+           \     /
                           *---*



                      Figure 1: Dual-homed Network

   Several threat consequences might be caused by a single threat
   action. In Figure 1, there exist at least two consequences: routers
   using Router B to reach Network 1 are deceived, while Router A is
   usurped.

   Within the context of the threat consequences described above, damage
   that might result from attacks against the network as a whole may
   include:
   o  Network congestion: more data traffic is forwarded through some
      portion of the network than would otherwise need to carry the
      traffic,
   o  Blackhole: the consequence is that "packets go in, but go
      nowhere",
   o  Looping: data traffic is forwarded along a route that loops, so
      that the data is never delivered (resulting in network
      congestion),
   o  Partition: some portion of the network believes that it is
      partitioned from the rest of the network when it is not,
   o  Churn: the forwarding in the network changes (unnecessarily) at a
      rapid pace, resulting in large variations in the data delivery
      patterns (and adversely affecting congestion control techniques),
   o  Instability: the protocol becomes unstable so that convergence on
      a global forwarding state is not achieved, and
   o  Overload: the protocol messages themselves become a significant
      portion of the traffic the network carries.

   The damage that might result from attacks against a particular host
   or network address may include:
   o  Starvation: data traffic destined for the network or host is
      forwarded to a part of the network that cannot deliver it,
   o  Eavesdrop: data traffic is forwarded through some router or
      network that would otherwise not see the traffic, affording an



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      opportunity to see the data or at least the data delivery pattern,
   o  Cut: some portion of the network believes that it has no route to
      the host or network when it is in fact connected,
   o  Delay: data traffic destined for the network or host is forwarded
      along a route that is in some way inferior to the route it would
      otherwise take,
   o  Looping: data traffic for the network or host is forwarded along a
      route that loops, so that the data is never delivered

   It is important to consider all compromises, because some security
   solutions can protect against one attack but not against others.  It
   might be possible to design a security solution that protects against
   an attack that eavesdropped on one destination's traffic without
   protecting against an attack that overwhelmed a router. Similarly, it
   is possible to design a security solution that prevents a starvation
   attack against one host, but not against  a network wide resources.
   The security requirements must be clear as to  which compromises are
   being avoided and which compromises must be addressed by  other means
   (e.g., by administrative means outside the protocol).

3.1.2.1  Threat Consequence Zone

   A threat consequence zone covers the area within which the network
   operations have been affected by threat actions. Possible threat
   consequence zones can be classified as: a single link or router,
   multiple routers (within a single routing domain), a single routing
   domain, multiple routing domains, or the global Internet. The threat
   consequence zone varies based on the threat action and origin.
   Similar threat actions that happened at different locations may cause
   totally different threat consequence. For example, when a compromised
   link breaks the routing session between a distribution router and a
   stub router, only reachability to and from the network devices
   attached to the stub router will be impaired. In other words, the
   threat consequence zone is a single router. In another case, if the
   compromised router is located between a customer edge router and its
   corresponding provider edge router, such an action might cause the
   whole customer site to lose its connection. In this case, the threat
   consequence zone might be a single routing domain.

3.1.2.2  Threat Consequence Periods

   Threat consequence period is defined as a portion of time during
   which the network operations are impacted by the threat consequences.
   The threat consequence period is influenced by, but not totally
   dependent on the duration of the threat action. In some cases, the
   network operations will get back to normal as soon as the threat
   action has been stopped. In other cases, however, threat consequences
   may persist longer than the threat action. For example, in the



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   original ARPANET link-state algorithm, some errors in a router
   introduced three instances of an LSA.  All of them flooded throughout
   the network continuously, until the entire network was power cycled
   [3].















































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4.  Generally Identifiable Routing Threats

   This section addresses generally identifiable and recognized threat
   actions against routing protocols. The threat actions are not
   necessarily specific to individual protocols but may be present in
   one or more of the common routing protocols in use today.

4.1  Deliberate Exposure

   Deliberate Exposure occurs when an attacker takes control of a router
   and intentionally releases routing information to other entities
   (e.g., the attacker, a web page, mail posting, other routers etc. )
   that, otherwise, should not receive the exposed information.

   The consequence of deliberate exposure is the disclosure of routing
   information.

   The threat consequence zone of deliberate exposure depends on the
   routing information that the attackers have exposed. The more
   knowledge they have exposed, the bigger the threat consequence zone.

   The threat consequence period of deliberate exposure might be longer
   than the duration of the action itself. The routing information
   exposed will not be out-dated until there is a topology change of the
   exposed network.

4.2  Sniffing

   Sniffing is an action whereby attackers monitor and/or record the
   routing exchanges between authorized routers. Attackers can use
   subverted links to sniff for routing information. Attackers can also
   sniff data plane information (however, this is out of scope of the
   current work).

   The consequence of sniffing is disclosure of routing information.

   The threat consequence zone of sniffing depends on the attacker's
   location, the routing protocol type, and the routing information that
   has been recorded. For example, if the subverted link is in an OSPF
   totally stubby area, the threat consequence zone should be limited to
   the whole area. An attacker that is sniffing a subverted link in an
   EBGP session can gain knowledge of multiple routing domains.

   The threat consequence period might be longer than the duration of
   the action. If an attacker stops sniffing a subverted link their
   acquired knowledge will not be out-dated until there is a topology
   change of the affected network.




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4.3  Traffic Analysis

   Traffic analysis is an action whereby attackers gain routing
   information by analyzing the characteristics of the data traffic on a
   subverted link. Traffic analysis threats can affect any data that is
   sent over a communication link. This threat is not peculiar to
   routing protocols and is included here for completeness.

   The consequence of data traffic analysis is the disclosure of routing
   information. For example, the source and destination IP addresses of
   the data traffic, and the type, magnitude, and volume of traffic can
   be disclosed.

   The threat consequence zone of the traffic analysis depends on the
   attacker's location and what data traffic has passed through. A
   subverted link at the network core should be able to disclose more
   information than its counterpart at the edge.

   The threat consequence period might be longer than the duration of
   the traffic analysis. After the attacker stops traffic analysis, its
   knowledge will not be out-dated until there is a topology change of
   the disclosed network.

4.4  Spoofing

   Spoofing occurs when an illegitimate device assumes the identity of a
   legitimate one. Spoofing in and of itself is often not the true
   attack. Spoofing is special in that it can be used to carry out other
   threat actions causing other threat consequences. An attacker can use
   spoofing as a means for launching other types of attacks. For
   example, if an attacker succeeds in spoofing the identity of a
   router, the attacker can act as a masquerading router. In other
   situations, the spoofing router can be used to send out unrealistic
   routing information that might cause the disruption of network
   services.

   There are a few cases where spoofing can be an attack in and of
   itself. For example, messages from an attacker which spoof the
   identity of a legitimate router may cause a neighbor relationship to
   form and deny the formation of the relationship with the legitimate
   router.

   The consequences of spoofing are:
   o  The disclosure of routing information: The spoofing router will be
      able to gain access to the routing information.
   o  The deception of peer relationship: The authorized routers, which
      exchange routing messages with the spoofing router, do not realize
      they are neighboring with a router that is faking another router's



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      identity.

   The threat consequence zone covers:
   o  The consequence zone of the fake peer relationship will be limited
      to those routers trusting the attacker's claimed identity.
   o  The consequence zone of the disclosed routing information depends
      on the attacker's location, the routing protocol type, and the
      routing information that has been exchanged between the attacker
      and its deceived neighbors.

   Note: This section focuses on addressing spoofing as a threat on its
   own. However, spoofing creates conditions for other threats. Other
   consequences are considered falsifications and are treated in the
   next section.

4.5  Falsification

   Falsification is an intentional action whereby false routing
   information is sent by a subverted router. To falsify the routing
   information, an attacker has to be either the originator or a
   forwarder of the routing information. It cannot be a receiver-only.
   False routing information describes the network in an unrealistic
   fashion, whether or not intended by the authoritative network
   administrator.

4.5.1  Falsifications by Originators

   An originator of routing information can launch the falsifications
   that are described in the next sections.

4.5.1.1  Overclaiming

   Overclaiming occurs when a subverted router advertises its control of
   some network resources, while in reality it does not, or the
   advertisement is not authorized. This is given in Figure 2 and Figure
   3.















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              +-------------+   +-------+   +-------+
              | Internet    |---| Rtr B |---| Rtr A |
              +------+------+   +-------+   +---+---+
                     |                          .
                     |                          |
                     |                          .
                     |                        *-+-*
                 +-------+                   /     \
                 | Rtr C |------------------*  N 1  *
                 +-------+                   \     /
                                              *---*


                        Figure 2: Overclaiming-1



        +-------------+   +-------+   +-------+
        |  Internet   |---| Rtr B |---| Rtr A |
        +------+------+   +-------+   +-------+
               |
               |
               |
               |                        *---*
           +-------+                   /     \
           | Rtr C |------------------*  N 1  *
           +-------+                   \     /
                                        *---*


                        Figure 3: Overclaiming-2

   The above figures provide examples of overclaiming. Router A, the
   attacker, is connected to the Internet through Router B. Router C is
   authorized to advertise its link to Network 1. In Figure 2, Router A
   controls a link to Network 1, but is not authorized to advertise it.
   In Figure 3, Router A does not control such a link. But in either
   case, Router A advertises the link to the Internet, through Router B.

   Compromised routers, unauthorized routers, and masquerading routers
   can overclaim network resources. The consequence of overclaiming
   includes:
   o  Usurpation of the overclaimed network resources. In Figure 2 and
      Figure 3, usurpation of Network 1 can occur when Router B (or
      other routers on the Internet, (not shown in the figures))
      believes that Router A provides the best path to reach the Network
      1. As a result, routers forward data traffic, destined to Network
      1 to Router A. The best result is that the data traffic uses an



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      unauthorized path, as in Figure 2. The worst case is that the data
      never reaches the destination Network 1, as in Figure 3. The
      ultimate consequence is Router A gaining control over Network 1's
      services, by controlling the data traffic.
   o  Usurpation of the legitimate advertising routers. In Figure 2 and
      Figure 3 Router C is the legitimate advertiser of Network 1. By
      overclaiming, Router A also controls (partially or totally) the
      services/functions provided by the Router C.  (This is NOT a
      disruption, because Router C is operating in a way intended by the
      authoritative network administrator.)
   o  Deception of other routers. In Figure 2 and Figure 3, Router B, or
      other routers on the Internet, might be deceived to believe the
      path through Router A is the best.
   o  Disruption of data planes on some routers. This might happen to
      routers that are on the path that is used by other routers to each
      the overclaimed network resources through the attacker. In Figure
      2 and Figure 3, when other routers on the Internet are deceived,
      they will forward the data traffic to Router B, which might be
      overloaded.

   The threat consequence zone varies based on the consequence:
   o  Where usurpation is concerned, the consequence zone covers the
      network resources that are overclaimed by the attacker (Network 1
      in Figure 2 and 3), and the routers that are authorized to
      advertise the network resources but lose the competition against
      the attacker(Router C in Figure 2 and Figure 3).
   o  Where deception is concerned, the consequence zone covers the
      routers that do believe the attacker's advertisement and use the
      attacker to reach the claimed networks (Router B and other
      deceived  routers on the Internet in Figure 2 and Figure 3).
   o  Where disruption is concerned, the consequence zone includes the
      routers that are on the path of misdirected data traffic (Router B
      in Figure 2 and Figure 3).

   The threat consequence will cease when the attacker stops
   overclaiming, and will totally disappear when the routing tables are
   converged.  As a result the consequence period is longer than the
   duration of the overclaiming.

4.5.1.2  Misclaiming

   A misclaiming threat is defined as an action where an attacker is
   advertising its authorized control of some network resources in a way
   that is not intended by the authoritative network administrator. An
   attacker can eulogize or disparage when advertising these network
   resources. Subverted routers, unauthorized routers, and masquerading
   routers can misclaim network resources.




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   The threat consequences of misclaiming are similar to the
   consequences of overclaiming.

   The consequence zone and period are also similar to those of
   overclaiming.

4.5.2  Falsifications by Forwarders

   When a legitimate router forwards routing information, it must or
   must not modify the routing information, depending on the routing
   information and the routing protocol type. For example, in RIP, the
   forwarder must modify the routing information by increasing the hop
   count by 1. On the other hand, the forwarder must not modify the type
   1 LSA in OSPF. In general, forwarders in distance vector routing
   protocols are authorized to and must modify the routing information,
   while most forwarders in link state routing protocols are not
   authorized to and must not modify most routing information.

   As a forwarder authorized to modify routing message, an attacker
   might not forward necessary routing information to other authorized
   routers.


4.5.2.1  Misstatement

   This is defined as an action whereby the attacker describes route
   attributes in an incorrect manner. For example, in RIP, the attacker
   might increase the path cost by two hops instead of one. In BGP, the
   attacker might delete some AS numbers from the AS PATH.

   Where forwarding routing information should not be modified, an
   attacker can launch the following falsifications:
   o  Deletion: Attacker deletes valid data in the routing message.
   o  Insertion: Attacker inserts false data in the routing message.
   o  Substitution: Attacker replaces valid data in the routing message
      with false data.
   o  Replaying: Attacker replays out-dated data in the routing message.

   All types of attackers (compromised links, compromised routers,
   unauthorized routers, and masquerading routers) can falsify the
   routing information when they forward the routing messages.

   The threat consequences of these falsifications by forwarders are
   similar to those caused by originators: usurpation of some network
   resources and related routers; deception of routers using false
   paths; and disruption of data planes of routers on the false paths.
   The threat consequence zone and period are also similar.




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4.6  Interference

   Interference is a threat action where an attacker uses a subverted
   link or router to inhibit the exchanges by legitimate routers. The
   attacker can do this by adding noise, or by not forwarding packets,
   or by replaying out-dated packets, or by delaying responses, or by
   denial of receipts, or by breaking synchronization.

   Subverted, unauthorized and masquerading routers can slow down their
   routing exchanges or induce flapping in the routing sessions of
   legitimate neighboring routers.

   The consequence of interference is the disruption of routing
   operations.

   The consequence zone of interference varies based on the source of
   the threats:
   o  When a subverted link is used to launch the action, the threat
      consequence zone covers routers that are using the link to
      exchange the routing information. An attack on a link can cause
      consequences at the neighbor maintenance level that may lead to
      changes in the database. In this case, the consequences can be
      felt network-wide.
   o  When subverted routers, unauthorized routers, or masquerading
      routers are the attackers, the threat consequence zone covers
      routers with which the attackers are exchanging routing
      information.

   The threat consequences might disappear as soon as the interference
   is stopped, or might not totally disappear until the networks have
   converged. Therefore, the consequence period is equal or longer than
   the duration of the interference.


4.7  Overload

   Overload is defined as a threat action whereby attackers place excess
   burden on legitimate routers. For example, it is possible for an
   attacker to trigger a router to create an excessive amount of state
   that other routers within the network are not able to handle. In a
   similar fashion, it is possible for an attacker to overload database
   routing exchanges and thus influence the routing operations.

4.8  Byzantine Failures

   As described in [4], "A node with a Byzantine failure may corrupt
   messages, forge messages, delay messages, or send conflicting
   messages to different nodes". These faults may arise from routers



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   which have been subverted by an attacker or which have faulty
   hardware or software. In any case, they represent a threat to correct
   operation of routing and routing protocols.

   The ability of the network to function in the face of such defects is
   described as Byzantine robustness and would fall into the scope of a
   requirements document for routing protocol security which may build
   from the base established in this document.











































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5.  Security Considerations

   This entire document is security related. Specifically the document
   addresses security of routing protocols as associated with threats to
   those protocols. In a larger context, this work builds upon the
   recognition of the IETF community that signaling and control/
   management planes of networked devices need strengthening. Routing
   protocols can be considered part of that signaling and control plane.
   However, to date, routing protocols have largely remained unprotected
   and open to malicious attacks. This document discusses inter- and
   intra-domain routing protocol threats that are currently known and
   lays the foundation for other documents that will discuss security
   requirements for routing protocols. This document is protocol
   independent.





































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6.  References

6.1  Normative References

   [1]  Shirey, R, "Internet Security Glossary", RFC 2828 , May 2000.

   [2]  Smith, B et al., "Securing Distance-Vector Routing Protocols",
        Symposium on Network and  Distributed System Security , February
        1997.

   [3]  Rosen, E., "Vulnerabilities of Network Control Protocols: An
        Example, Computer Communication Review",  , July 1981.

   [4]  Perlman, R, "Network Layer Protocols with Byzantine Robustness",
        , August 1988 .

   [5]  Moy, J, "OSPF Version 2", RFC  2328, April   1998.

   [6]  Shen, N.  et. al., "Dynamic Hostname Exchange Mechanism for
        IS-IS", RFC 2763 , February  2000.

   [7]  Malkin, G., "RIP Version 2 Protocol Analysis", RFC 1721 ,
        November  1994.

6.2  Informative References

   [8]  Kent, S. et al., "Secure Border Gateway Protocol
        (Secure-BGP)", IEEE Journal on Selected Areas in Communications
        , April 2000.


Authors' Addresses

   Abbie Barbir
   Nortel Networks
   3500 Carling Avenue
   Nepean, Ontario  K2H 8E9
   Canada

   Phone:
   EMail: abbieb@nortelnetworks.com










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   Sandy Murphy
   Sparta, Inc.
   7075 Samuel Morse Drive
   Columbia, MD
   USA

   Phone: 410-872-1515 x206
   EMail: sandy@tislabs.com


   Yi Yang
   Cisco Systems
   7025 Kit Creek Road
   RTP, NC  27709
   USA

   Phone:
   EMail: yiya@cisco.com

































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Appendix A.  Acknowledgments

   This draft would not have been possible save for the excellent
   efforts and team work characteristics of those listed here.
   o  Dennis Beard- Nortel Networks
   o  Ayman Musharbash - Nortel Networks
   o  Jean-Jacques Puig, int-evry, France
   o  Paul Knight - Nortel Networks
   o  Elwyn Davies - Nortel Networks
   o  Ameya Dilip Pandit - Graduate student - University of Missouri
   o  Senthilkumar Ayyasamy - Graduate student - University of Missouri
   o  Stephen Kent- BBN
   o  Tim Gage - CISCO
   o  James Ng - CISCO
   o  Alvaro Retana - CISCO




































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Appendix B.  Acronyms

   AS - Autonomous system. Set of routers under a single technical
   administration. Each AS normally uses a single interior gateway
   protocol (IGP) and metrics to propagate routing information within
   the set of routers. Also called routing domain.

   AS-Path - In BGP, the route to a destination. The path consists of
   the AS numbers of all routers a packet must go through to reach a
   destination.

   BGP - Border Gateway Protocol. Exterior gateway protocol used to
   exchange routing information among routers in different autonomous
   systems.

   LSA - Link-State Announcement

   NLRI - Network layer reachability information. Information that is
   carried in BGP packets and is used by MBGP.

   OSPF - Open Shortest Path First. A link-state IGP that makes routing
   decisions based on the shortest-path-first (SPF) algorithm (also
   referred to as the Dijkstra algorithm).




























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