Routing Working Group                                    M. Jethanandani
Internet-Draft                                                  K. Patel
Intended status: Informational                        Cisco Systems, Inc
Expires: December 29, 2011                                      L. Zheng
                                                           June 27, 2011

 Analysis of BGP, LDP, PCEP, and MSDP Security According to KARP Design


   This document analyzes BGP, LDP, PCEP and MSDP according to
   guidelines set forth in section 4.2 of

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119]..

Status of this Memo

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   This Internet-Draft will expire on December 29, 2011.

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Contributing Authors . . . . . . . . . . . . . . . . . . .  3
     1.2.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Current State of BGP, LDP, PCEP and MSDP . . . . . . . . . . .  5
     2.1.  Transport level  . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Keying mechanisms  . . . . . . . . . . . . . . . . . . . .  6
     2.3.  LDP  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
       2.3.1.  Spoofing attacks . . . . . . . . . . . . . . . . . . .  6
       2.3.2.  Privacy Issues . . . . . . . . . . . . . . . . . . . .  7
       2.3.3.  Denial of Service Attacks  . . . . . . . . . . . . . .  7
     2.4.  PCEP . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     2.5.  MSDP . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Optimal State for BGP, LDP, PCEP, and MSDP . . . . . . . . . .  9
     3.1.  LDP  . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Gap Analysis for BGP, LDP, PCEP and MSDP . . . . . . . . . . . 10
     4.1.  LDP  . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.2.  PCEP . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   5.  Security Requirements  . . . . . . . . . . . . . . . . . . . . 12
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16

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1.  Introduction

   In March 2006 the Internet Architecture Board (IAB) in its "Unwanted
   Internet Traffic" workshop described an attack on core routing
   infrastructure as an ideal attack with the most amount of damage.  It
   called for the tightening the security of the core routing

   This document performs the initial analysis of the current state of
   BGP, LDP, PCEP and MSDP according to the requirements of
   [draft-ietf-karp-design-guide].  This draft builds on several
   previous analysis efforts into routing security.  The OPSEC working
   group put together Issues with existing Cryptographic Protection
   Methods for Routing Protocols
   [draft-ietf-opsec-routing-protocols-crypto-issues] an analysis of
   cryptographic issues with routing protocols and
   draft-hartman-ospf-analysis-01 which has a analysis for OSPF.

   Section 2 looks at the current state of the four routing protocols.
   Section 3 goes into what the optimal state would be for the three
   routing protocols according to KARP Design Guidelines
   [draft-ietf-karp-design-guide] and Section 4 does a analysis of the
   gap between the existing state and the optimal state of the protocols
   and suggest some areas where we need to improve.

1.1.  Contributing Authors

   Anantha Ramaiah, Mach Chen

1.2.  Abbreviations

   BGP - Border Gateway Protocol

   DoS - Denial of Service

   KARP - Key and Authentication for Routing Protocols

   KDF - Key Derivation Function

   KEK - Key Encrypting Key

   KMP - Key Management Protocol

   LDP - Label Distribution Protocol

   LSR - Label Switch Routers

   MAC - Message Authentication Code

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   MKT - Master Key Tuple

   MSDP - Multicast Source Distribution Protocol

   MD5 - Message Digest algorithm 5

   OSPF - OPen Shortest Path First

   PCEP - Path Computation Element Protocol

   TCP - Transmission Control Protocol

   UDP - User Datagram Protocol

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2.  Current State of BGP, LDP, PCEP and MSDP

   This section looks at the underlying transport protocol and key
   mechanisms built for the protocol.  It describes the security
   mechanisms built into BGP, LDP, PCEP and MSDP.

2.1.  Transport level

   At a transport level, routing protocols are subject to a variety of
   DoS attacks.  Such attacks can cause the routing protocol to become
   congested with the result that routing updates are supplied too
   slowly to be useful or in extreme case prevent route convergence
   after a change.

   Routing protocols use several methods to protect themselves.  Those
   that run on TCP use access list to permit packets only from know
   sources.  These access lists also help edge routers from attacks
   originating from outside the protected cloud.  In addition for edge
   routers running eBGP, TCP LISTEN is run only on interfaces on which
   its peers have been discovered or that are configured to expect
   sessions on.

   GTSM [RFC5082] describes a generalized Time to Live (TTL) security
   mechanism to protect a protocol stack from CPU-utilization based
   attacks.TCP Robustness [RFC5961] recommends some TCP level
   mitigations against spoofing attacks targeted towards long lived
   routing protocol sessions.

   Even when BGP, LDP, PCEP and MSDP sessions use access list they are
   subject to spoofing and man in the middle attacks.  Authentication
   and integrity checks allow the receiver of a routing protocol update
   to know that the message genuinely comes from the node that purports
   to have sent it and to know whether the message has been modified.

   TCP MD5 [RFC2385] specifies such a mechanism to protect BGP and other
   TCP based routing protocols via the TCP MD5 option.  TCP MD5 option
   provides a way for carrying an MD5 digest in a TCP segment.  This
   digest acts like a signature for that segment, incorporating
   information known only to the connection end points.  The MD5 key
   used to compute the digest is stored locally on the router.  This
   option is used by routing protocols to provide for session level
   protection against the introduction of spoofed TCP segments into any
   existing TCP streams, in particular TCP Reset segments.  TCP MD5 does
   not provide a generic mechanism to support key roll-over.

   However, the Message Authentication Codes (MACs) used by MD5 to
   compute the signature are considered to be too weak.  TCP-AO
   [RFC5925] and its companion documentCrypto Algorithms for TCP-AO

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   [RFC5926] is a step towards correcting both the MAC weakness and KMP.
   For MAC it specifies two MAC algorithms that MUST be supported.  They
   are HMAC-SHA-1-96 as specified in HMAC [RFC2104] and AES-128-CMAC-96
   as specified in NIST-SP800-38B [NIST-SP800-38B].  Cryptographic
   research suggests that both these MAC algorithms defined are fairly
   secure and are not known to be broken in any ways.  It also provides
   for additional MACs to be added in the future.

2.2.  Keying mechanisms

   For TCP-AO [RFC5925] there is no Key Management Protocol (KMP) used
   to manage the keys that are used for generating the Message
   Authentication Code (MAC).  It allows for a master key to be
   configured manually or for it to be managed from a out of band
   mechanism.  Most routers are configured with a static key that does
   not change over the life of the session.

   For point-to-point key management IKE [RFC2409] tries to solve the
   issue of key exchange under a SA.

2.3.  LDP

   Section 5 of LDP [RFC5036] states that LDP is subject to three
   different types of attacks.  It talks about spoofing, protection of
   privacy of label distribution and denial of service attacks.

2.3.1.  Spoofing attacks

   Spoofing attack for LDP occur both during the discovery phase and
   during the session communication phase.  Discovery exchanges using UDP

   Label Switching Routers (LSRs) indicate their willingness to
   establish and maintain LDP sessions by periodically sending Hello
   messages.  Receipt of a Hello message serves to create a new "Hello
   adjacency", if one does not already exist, or to refresh an existing

   Unlike all other LDP messages, the Hello messages are sent using UDP
   not TCP.  This means that they cannot benefit from the security
   mechanisms available with TCP.  LDP [RFC5036] does not provide any
   security mechanisms for use with Hello messages except to note that
   some configuration may help protect against bogus discovery events.

   Spoofing a Hello packet for an existing adjacency can cause the
   adjacency to time out and that can result in termination of the
   associated session.  This can occur when the spoofed Hello message

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   specifies a small Hold Time, causing the receiver to expect Hello
   messages within this interval, while the true neighbor continues
   sending Hello messages at the lower, previously agreed to, frequency.

   Spoofing a Hello packet can also cause the LDP session to be
   terminated directly.  This can occur when the spoofed Hello specifies
   a different Transport Address from the previously agreed one between
   neighbors.  Spoofed Hello messages are observed and reported as real
   problem in production networks.  Session communication using TCP

   LDP like other TCP based routing protocols specifies use of the TCP
   MD5 Signature Option to provide for the authenticity and integrity of
   session messages.  As stated above, some assert that MD5
   authentication is now considered by some to be too weak for this
   application.  A stronger hashing algorithm e.g SHA1, could be
   deployed to take care of the weakness.

2.3.2.  Privacy Issues

   LDP provides no mechanism for protecting the privacy of label
   distribution.  The security requirements of label distribution are
   similar to other routing protocols that need to distribute routing

2.3.3.  Denial of Service Attacks

   LDP is subject to Denial of Service (DoS) attacks both in its
   discovery mode as well as during the session mode.

   The discovery mode attack is similar to the spoofing attack except
   that when the spoofed Hello messages are sent with a high enough
   frequency can cause the adjacency to time out.

2.4.  PCEP

   Attacks on PCEP [RFC5440] may result in damage to active networks.
   This may include computation responses, which if changed can cause
   protocols like LDP to setup sub-optimal or inappropriate LSPs.  In
   addition, PCE itself can be attacked by a variety of DoS attacks.
   Such attacks can cause path computations to be supplied too slowly to
   be of any value particularly as it relates to recovery or
   establishment of LSPs.

   As the RFC states, PCEP could be the target of the following attacks.

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   o  Spoofing (PCC or PCE implementation)

   o  Snooping (message interception)

   o  Falsification

   o  Denial of Service

   According to the RFC, inter-AS scenarios when PCE-to-PCE
   communication is required, attacks may be particularly significant
   with commercial as well as service-level implications.

   Additionally, snooping of PCEP requests and responses may give an
   attacker information about the operation of the network.  Simply by
   viewing the PCEP messages someone can determine the pattern of
   service establishment in the network and can know where traffic is
   being routed, thereby making the network susceptible to targeted
   attacks and the data within specific LSPs vulnerable.

   Ensuring PCEP communication privacy is of key importance, especially
   in an inter-AS context, where PCEP communication end-points do not
   reside in the same AS, as an attacker that intercepts a PCE message
   could obtain sensitive information related to computed paths and

2.5.  MSDP

   Similar to BGP and LDP, TCP MD5 [RFC2385] specifies a mechanism to
   protect TCP sessions via the TCP MD5 option.  But with a weak MD5
   authentication, TCP MD5 is considered too weak for this application.

   MSDP also advocates imposing a limit on number of source address and
   group addresses (S,G) that can be stored within the protocol and
   thereby mitigate state explosion due to any denial of service and
   other attacks.

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3.  Optimal State for BGP, LDP, PCEP, and MSDP

   The ideal state for BGP, LDP and MSDP protocols are when they can
   withstand any of the known types of attacks.

   Additionally, Key Management Protocol (KMP) for the routing sessions
   should help negotiate unique, pair wise random keys without
   administrator involvement.  It should also negotiate Security
   Association (SA) parameter required for the session connection,
   including key life times.  It should keep track of those lifetimes
   and negotiate new keys and parameters before they expire and do so
   without administrator involvement.  In the event of a breach, the
   keys should be changed immediately.

   The DoS attacks for BGP, LDP, PCEP and MSDP are attacks to the
   transport protocol, TCP in this case.  TCP should be able to
   withstand any of DoS scenarios by dropping packets that are attack
   packets in a way that does not impact legitimate packets.

   The routing protocols should provide a mechanism to determine
   authenticate and validate the routing information carried within the

3.1.  LDP

   For the spoofing kind of attacks that LDP is vulnerable to during the
   discovery phase, it should be able to determine the authenticity of
   the neighbors sending the Hello message.

   There is currently no requirement to protect the privacy of label
   distribution as labels are carried in the clear like other routing

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4.  Gap Analysis for BGP, LDP, PCEP and MSDP

   This section outlines the differences between the current state of
   the routing protocol and the desired state as outlined in section 4.2
   of KARP Design Guidelines [draft-ietf-karp-design-guide].  It covers
   issues that are common to the four protocols leaving protocol
   specific issues to sub-sections.

   At a transport level the routing protocols are subject to some of the
   same attacks that TCP applications are subject to.  These include but
   are not limited to DoS attacks.  Recommendations to make the
   transport protocol should be followed and implemented.  An example of
   such a draft is Improving TCP's Robustness to Blind In-Window
   Attacks. [RFC5961]

   From a security perspective we lack comprehensive KMP.  As an example
   TCP-AO [RFC5925] talks about coordinating keys derived from MKT
   between endpoints, but the MKT itself has to be configured manually
   or through a out of band mechanism.  Even when keys are configured
   manually, a method for their rollover has not been defined.  This
   leads to keys not being updated regularly which in itself increases
   the security risk.  Also TCP-AO does not address the issue of
   connectionless reset.

   Authentication, tamper protection, and encryption all require the use
   of keys by sender and receiver.  An automated KMP therefore has to
   include a way to distribute MKT between two end points with little or
   no administration overhead.  It has to cover automatic key rollover.

   There are two methods of automatic key rollover.  Implicit key
   rollover can be initiated after certain volume of data gets exchanged
   or when a certain time has elapsed.  This does not require explicit
   signaling.  On the other hand, explicit key rollover requires a out
   of band key signaling mechanism.  An example of this is IKE [RFC2409]
   but it could be any other new mechanisms also.

   There is a need to protect authenticity and validity of the routing/
   label information that is carried in the payload of the sessions.
   However, we believe that is outside the scope of this document at
   this time and is being addressed by SIDR WG.  Similar mechanisms
   could be used for intra-domain protocols.

4.1.  LDP

   As described in LDP [RFC5036], the threat of spoofed Basic Hellos can
   be reduced by accepting Basic Hellos on interfaces that LSRs trust,
   employing GTSM [RFC5082] and ignoring Basic Hellos not addressed to
   the "all routers on this subnet" multicast group.  Spoofing attacks

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   via Extended Hellos are potentially a more serious threat.  An LSR
   can reduce the threat of spoofed Extended Hellos by filtering them
   and accepting Hellos from sources permitted by an access list.
   However, performing the filtering using access lists requires LSR
   resource, and the LSR is still vulnerable to the IP source address
   spoofing.  Spoofing attacks can be solved by being able to
   authenticate the Hello messages, and an LSR can be configured to only
   accept Hello messages from specific peers when authentication is in

   LDP Hello Cryptographic Authentication
   [draft-zheng-mpls-ldp-hello-crypto-auth-01] suggest a new
   Cryptographic Authentication TLV that can be used as an
   authentication mechanism to secure Hello messages.

4.2.  PCEP

   PCE discovery according to its RFC is a significant feature for the
   successful deployment of PCEP in large networks.  This mechanism
   allows a PCC to discover the existence of suitable PCEs within the
   network without the necessity of configuration.  It should be obvious
   that, where PCEs are discovered and not configured, the PCC cannot
   know the correct key to use.  There are different approaches to
   retain some aspect of security, but all of them require use of a keys
   and a keying mechanism, the need for which has been discussed above.

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5.  Security Requirements

   This section describes requirements for BGP, LDP, PCEP and MSDP
   security that should be met within the routing protocol.

   As with all routing protocols, they need protection from both on-path
   and off-path blind attacks.  A better way to protect them would be
   with per-packet protection using a cryptographic MAC.  In order to
   provide for the MAC, keys are needed.

   Once keys are used, mechanisms are required to support key rollover.
   This should cover both manual and automatic key rollover.  Multiple
   approaches could be used.  However since the existing mechanisms
   provide a protocol field to identify the key as well as management
   mechanisms to introduce and retire new keys, focusing on the existing
   mechanism as a starting point is prudent.

   Finally, replay protection is required.  The replay mechanism needs
   to be sufficient to prevent an attacker from creating a denial of
   service or disrupting the integrity of the routing protocol by
   replaying packets.  It is important that an attacker not be able to
   disrupt service by capturing packets and waiting for replay state to
   be lost.

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6.  Acknowledgements

   We would like to thank Brian Weis for encouraging us to write this
   draft and providing comments on it.

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7.  References

7.1.  Normative References

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

   [RFC5926]  Lebovitz, G. and E. Rescorla, "Cryptographic Algorithms
              for the TCP Authentication Option (TCP-AO)", RFC 5926,
              June 2010.

              Lebovitz, G., "KARP Design Guidelines", September 2010.

7.2.  Informative References

              Dworking, "Recommendation for Block Cipher Modes of
              Operation: The CMAC Mode for Authentication", May 2005.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, November 1998.

   [RFC3547]  Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The
              Group Domain of Interpretation", RFC 3547, July 2003.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007.

   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
              Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, October 2007.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP

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              Authentication Option", RFC 5925, June 2010.

   [RFC5961]  Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
              Robustness to Blind In-Window Attacks", RFC 5961,
              August 2010.

              Manral, "Issues with existing Cryptographic Protection
              Methods for Routing Protocols", September 2010.

              Zheng, "LDP Hello Cryptographic Authentication",
              March 2011.

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Authors' Addresses

   Mahesh Jethanandani
   Cisco Systems, Inc
   170 Tasman Drive
   San Jose, CA  95134

   Phone: +1 (408) 527-8230

   Keyur Patel
   Cisco Systems, Inc
   170 Tasman Drive
   San Jose, CA  95134

   Phone: +1 (408) 526-7183

   Lianshu Zheng
   No. 3 Xinxi Road, Hai-Dian District
   Beijing,   100085

   Phone: +86 (10) 82882008

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