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Versions: 00 01 draft-ietf-mpls-ldp-gtsm

MPLS Working Group                                          C. Pignataro
Internet-Draft                                                  R. Asati
Intended status: Standards Track                           Cisco Systems
Expires: September 12, 2011                               March 11, 2011


  The Generalized TTL Security Mechanism (GTSM) for Label Distribution
                             Protocol (LDP)
                 draft-asati-pignataro-mpls-ldp-gtsm-01

Abstract

   The Generalized TTL Security Mechanism (GTSM) describes a generalized
   use of a packets Time to Live (TTL) (IPv4) or Hop Limit (IPv6) to
   verify that the packet was sourced by a node on a connected link,
   thereby protecting the router's IP control-plane from CPU utilization
   based attacks.  This technique improves security and is used by many
   protocols.  This document defines the GTSM use for Label Distribution
   Protocol (LDP).

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
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 12, 2011.

Copyright Notice

   Copyright (c) 2011 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Specification of Requirements . . . . . . . . . . . . . . . 3
     1.2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  GTSM Procedures for LDP . . . . . . . . . . . . . . . . . . . . 4
     2.1.  GTSM Flag in Common Hello Parameter TLV . . . . . . . . . . 4
     2.2.  GTSM Sending and Receiving Procedures for LDP Link
           Hello . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     2.3.  GTSM Sending and Receiving Procedures for LDP
           Initialization  . . . . . . . . . . . . . . . . . . . . . . 5
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6




























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1.  Introduction

   LDP [RFC5036] specifies two Discovery mechanisms, a Basic one and an
   Extended one, both using UDP transport.  The Basic Discovery
   mechanism is used to discover LSR neighbors that are directly
   connected at the link level, whereas the Extended Discovery mechanism
   is used to locate LSR neighbors that are not directly connected at
   the link level.  Once discovered (or located), the LSR neighbors can
   establish the LDP peering session, using the TCP transport
   connection.

   The Generalized TTL Security Mechanism (GTSM) [RFC5082] is a
   mechanism based on IPv4 Time To Live (TTL) or (IPv6) Hop Limit value
   verification so as to provide a simple and reasonably robust defense
   from infrastructure attacks using forged protocol packets from
   outside the network.  GTSM can be applied to any protocol peering
   session that is established between routers that are adjacent.
   Therefore, GTSM can fully benefit LDP protocol peering session
   established using Basic Discovery.

   This document specifies LDP enhancements to accommodate GTSM.  In
   particular, this document specifies the enhancements in the following
   areas:

   1.  Common Hello Parameter TLV of LDP Link Hello message

   2.  Sending and Receiving procedures for LDP Link Hello message

   3.  Sending and Receiving procedures for LDP Initilization message

   While GTSM specifies that it SHOULD NOT be enabled by default in
   order to remain backward-compatible with the unmodified protocol,
   this document specifies having GTSM for LDP be enabled by default but
   not be enforced unless both peers can detect each others' support for
   GTSM procedures as described in this document.

1.1.  Specification of Requirements

   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 [RFC2119].

1.2.  Scope

   This document defines procedures for LDP using IPv4 routing, but not
   for LDP using IPv6 routing, since the latter has GTSM built into the
   protocol definition [I-D.ietf-mpls-ldp-ipv6].




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   Additionally, this document applies to LDP peering sessions set up
   using Basic Discovery only.  LDP peering sessions set up using
   Extended Discovery are outside the scope of this document (see
   Section 5.5 of [RFC5082]).


2.  GTSM Procedures for LDP

2.1.  GTSM Flag in Common Hello Parameter TLV

   A new flag in Common Hello Parameter TLV, named G flag (for GTSM), is
   defined by this document.  An LSR indicates that it is capable of
   applying GTSM procedures, as defined in this document, to the
   subsequent LDP peering session, by setting the GTSM flag to 1.  The
   Common Hello Parameters TLV, defined in Section 3.5.2 of [RFC5036],
   is updated as shown in Figure 1.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0|0| Common Hello Parms(0x0400)|      Length                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Hold Time                |T|R|G|   Reserved              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     G, GTSM
        A value of 1 specifies that this LSR wishes to support GTSM
        procedures, where a value of 0 specifies that this LSR does not
        wish to support GTSM.

             Figure 1: GTSM Flag in Common Hello Parameter TLV

   The G flag is meaingful only if T and R flags are set to 0 (which
   must be the case for Basic Discovery), otherwise, the value of G flag
   should be ignored on receipt.

   Any LSR not supporting GTSM for LDP, as defined in this document,
   would continue to ignore the G flag, independent of T and R flags'
   value, as per Section 3.5.2 of [RFC5036].

2.2.  GTSM Sending and Receiving Procedures for LDP Link Hello

   Firstly, LSRs using LDP Basic Discovery [RFC5036] send LDP Hello
   messages to link-level multicast address (224.0.0.2 or "all
   routers").  Such messages are never forwarded beyond one hop and
   assumed to have their IP TTL or Hop Count = 1.

   An LSR may indicate that it is capable of applying GTSM procedures to



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   the subsequent TCP/LDP peering session by setting the G flag (for
   GTSM) to 1 in Common Hello Parameter TLV in the LDP Link Hello
   message [RFC5036].

   An LSR, upon receiving an LDP Link Hello message, would recognize the
   presence of G flag (in Common Hello Parameter TLV) only if it
   supports GTSM for LDP, as specified in this document.  If an LSR
   recognizes the presence of G flag with the value =1 in the received
   LDP Link Hello message, then it must enforce GTSM for LDP in the
   subsequent TCP/LDP peering session with the neighbor that sent the
   Hello message, as specified in Section 2.3 of this document.

   If an LSR does not recognize the presence of G flag (in Common Hello
   Parameter TLV of Link Hello message), or recognizes the presence of G
   flag with the value = 0, then the LSR must not enforce GTSM for LDP
   in the subsequent TCP/LDP peering session with the neighbor that sent
   the Hello message.  This ensures backward compatibility as well as
   automatic GTSM de-activation.

   If an LSR that has sent the LDP Link Hello with G flag = 1, then the
   LSR must set IP TTL or Hop Count = 255 in the forthcoming Transport
   Connection(s) with that neighbor (LSR2, say).  Please see Section 2.3
   for more details about the TCP transport connection specifics.

2.3.  GTSM Sending and Receiving Procedures for LDP Initialization

   If an LSR that has sent and received LDP Link Hello with G flag = 1
   from the directly-connected neighbor (LSR2, say), then the LSR must
   enforce GTSM procedures, as defined in Section 3 of [RFC5082], in the
   forthcoming Transport Connection with that neighbor (LSR2, say).
   This means that the LSR must check for the incoming unicast packets'
   TTL or Hop Count to be 255 for the particular LDP/TCP peering session
   and decide the further processing as per the [RFC5082].

   If an LSR that has sent LDP Link Hello with G flag = 1, but received
   LDP Link Hello with G flag = 0 from the directly-connected neighbor
   (LSR3, say), then the LSR must not enforce GTSM procedures, as
   defined in Section 3 of [RFC5082], in the forthcoming Transport
   Connection with that neighbor (LSR2, say).


3.  IANA Considerations

   IANA is requested to assign the G, GTSM bit in the Common Hello
   Parameters TLV (see Figure 1 in Section 2.1), as per allocation
   policy defined at [I-D.asati-pignataro-mpls-ldp-iana].





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4.  Security Considerations

   This document increases the security for LDP, making it more
   resilient to off-link attacks.


5.  Acknowledgments

   The authors of this document do not make any claims on the
   originality of the ideas described.  The concept of GTSM for LDP has
   been proposed a number of times, and is documented in both the
   Experimental and Standards Track specifications of GTSM.  Among other
   people, we would like to acknowledge Enke Chen and Albert Tian for
   their document "TTL-Based Security Option for the LDP Hello Message".


6.  References

6.1.  Normative References

   [I-D.asati-pignataro-mpls-ldp-iana]
              Pignataro, C. and R. Asati, "Label Distribution Protocol
              (LDP) Internet Assigned Numbers Authority (IANA)
              Considerations Update",
              draft-asati-pignataro-mpls-ldp-iana-01 (work in progress),
              March 2011.

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

   [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.

6.2.  Informative References

   [I-D.ietf-mpls-ldp-ipv6]
              Manral, V., Papneja, R., and R. Asati, "Updates to LDP for
              IPv6", draft-ietf-mpls-ldp-ipv6-00 (work in progress),
              November 2010.








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Authors' Addresses

   Carlos Pignataro
   Cisco Systems
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: cpignata@cisco.com


   Rajiv Asati
   Cisco Systems
   7025-6 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: rajiva@cisco.com

































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