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Versions: 00 01 02 03 04 05 06 07 RFC 6952

Routing Working Group                                    M. Jethanandani
Internet-Draft                                         Ciena Corporation
Intended status: Informational                                  K. Patel
Expires: December 25, 2012                            Cisco Systems, Inc
                                                                L. Zheng
                                                           June 23, 2012

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


   This document analyzes BGP, LDP, PCEP and MSDP according to
   guidelines set forth in section 4.2 of Keying and Authentication for
   Routing Protocols Design Guidelines [RFC6518].

   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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 25, 2012.

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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
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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 . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     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  . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     4.2.  PCEP . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   5.  Transition and Deployment Considerations . . . . . . . . . . . 12
   6.  Security Requirements  . . . . . . . . . . . . . . . . . . . . 13
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17

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1.  Introduction

   In March 2006 the Internet Architecture Board (IAB) in its "Unwanted
   Internet Traffic" workshop documented in Report from the IAB workshop
   on Unwanted Traffic March 9-10, 2006 [RFC4948] described an attack on
   core routing infrastructure as an ideal attack with the most amount
   of damage.  Four main steps were identified for that tightening:

   1.  Create secure mechanisms and practices for operating routers.

   2.  Clean up the Internet Routing Registry [IRR] repository, and
       securing both the database and the access, so that it can be used
       for routing verifications.

   3.  Create specifications for cryptographic validation of routing
       message content.

   4.  Secure the routing protocols' packets on the wire.

   This document looking at the last bullet performs the initial
   analysis of the current state of BGP, LDP, PCEP and MSDP according to
   the requirements of KARP Design Guidelines [RFC6518].  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 [RFC6039] an
   analysis of cryptographic issues with routing protocols and Analysis
   of OSPF Security According to KARP Design Guide

   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 [RFC6518] 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

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   KDF - Key Derivation Function

   KEK - Key Encrypting Key

   KMP - Key Management Protocol

   LDP - Label Distribution Protocol

   LSR - Label Switch Routers

   MAC - Message Authentication Code

   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 use TCP as a transport protocol use access list to permit
   packets from know sources only.  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 routing 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.
   Sometimes routers can be subjected to a large number of
   authentication and integrity checks which can result in genuine
   requests failing.

   TCP MD5 [RFC2385] specifies 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.

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   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 document Crypto Algorithms for TCP-AO
   [RFC5926] describe steps 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.

   It should also be mentioned that those routers that have been
   configured with static keys have not seen the key changed.  The
   common reason given for not changing the key is the difficulty in
   coordinating the change, at least with TCP MD5.  It is well known
   that longer the same key is used, higher is the chance that it can be
   guessed, particularly if it is not a strong key.

   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.  These are 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

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   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
   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.

   Alternatively, one could move to using TCP-AO which provides for
   stronger MACs and protects against replays.

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.

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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.

   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 not considered strong enough for this

   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,
   including when an administrator with knowledge of the keys leaves the
   company, 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 [RFC6518].  As that document states, these
   routing protocols fall into the category of the one-to-one peering
   messages and will use peer keying protocol.  It covers issues that
   are common to the four protocols leaving protocol specific issues to

   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.  Defending TCP Against Spoofing
   Attacks [RFC4953] recommends ways to do just that.  In addition
   Improving TCP's Robustness to Blind In-Window Attacks.  [RFC5961]
   should also be followed and implemented.

   From a security perspective there is a lack of 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 when to start using the new keys or
   stop using old keys 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, as it
   applies to routers that do not store MKT across reboots.

   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.
   It is expected that authentication will cover the packet, i.e. the
   payload and the TCP header and will not cover the frame i.e. the link
   layer 2 header.

   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 nor should it result in a reset of the TCP connection in a
   way that the links/adjacencies are affected.  On the other hand,
   explicit key rollover requires a out of band key signaling mechanism.
   It can be triggered by either side and can be done anytime a security
   parameter changes e.g. an attack has happened, or a system
   administrator with access to the keys has left the company.  An
   example of this is IKE [RFC2409] but it could be any other new
   mechanisms also.

   As stated earlier TCP-AO [RFC5925] and its accompanying document

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   Crypto Algorithms for TCP-AO [RFC5926] suggest that two MAC
   algorithms that MUST be supported are HMAC-SHA-1-96 as specified in
   HMAC [RFC2104] and AES-128-CMAC-96 as specified in NIST-SP800-38B

   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
   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.  Transition and Deployment Considerations

   As stated in KARP Design Guidelines [RFC6518] it is imperative that
   the new authentication and security mechanisms defined support
   incremental deployment, as it is not feasible to deploy the new
   routing protocol authentication mechansim overnight.

   Typically authentication and security in a peer-to-peer protocol
   requires that both parties agree to the mechanisms that will be used.
   If an agreement is not reached the setup of the new mechanism will
   fail or will be deferred.  Upon failure, the routing protocols can
   fallback to the mechanisms that were already in place e.g. use static
   keys if that was the mechanism in place.  It is usually not possible
   for one end to use the new mechanism while the other end uses the
   old.  Policies can be put in place to retry upgrading after a said
   period of time, so a manual coordiantion is not required.

   If the automatic KMP requires use of public/private keys to exchange
   key material, the required CA root certificates may need to be
   installed to verify authenticity of requests initiated by a peer.
   Such a step does not require coordination with the peer except to
   decide what CA authority will be used.

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6.  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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7.  Acknowledgements

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

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8.  References

8.1.  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.

   [RFC6518]  Lebovitz, G. and M. Bhatia, "Keying and Authentication for
              Routing Protocols (KARP) Design Guidelines", RFC 6518,
              February 2012.

              Lebovitz, G. and M. Bhatia, "KARP Threats and
              Requirements", March 2012.

8.2.  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.

   [RFC4948]  Andersson, L., Davies, E., and L. Zhang, "Report from the
              IAB workshop on Unwanted Traffic March 9-10, 2006",
              RFC 4948, August 2007.

   [RFC4953]  Touch, J., "Defending TCP Against Spoofing Attacks",
              RFC 4953, July 2007.

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   [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
              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.

   [RFC6039]  Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues
              with Existing Cryptographic Protection Methods for Routing
              Protocols", RFC 6039, October 2010.

              Hartman, S., "Analysis of OSPF Security According to KARP
              Design Guide", March 2012.

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

Jethanandani, et al.    Expires December 25, 2012              [Page 16]

Internet-Draft      BGP, LDP, PCEP and MSDP Analysis           June 2012

Authors' Addresses

   Mahesh Jethanandani
   Ciena Corporation
   1741 Technology Drive
   San Jose, CA  95110

   Phone: + (408) 436-3313
   Email: mjethanandani@gmail.com

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

   Phone: +1 (408) 526-7183
   Email: keyupate@cisco.com

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

   Phone: +86 (10) 82882008
   Email: verozheng@huawei.com

Jethanandani, et al.    Expires December 25, 2012              [Page 17]

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