The Generalized TTL Security Mechanism (GTSM) for the Label Distribution Protocol (LDP)
RFC 6720

Internet Engineering Task Force (IETF)                      C. Pignataro
Request for Comments: 6720                                      R. Asati
Updates: 5036                                              Cisco Systems
Category: Standards Track                                    August 2012
ISSN: 2070-1721

           The Generalized TTL Security Mechanism (GTSM) for
                 the Label Distribution Protocol (LDP)

Abstract

   The Generalized TTL Security Mechanism (GTSM) describes a generalized
   use of a packet's 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 the
   Label Distribution Protocol (LDP).

   This specification uses a bit reserved in RFC 5036 and therefore
   updates RFC 5036.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6720.

Pignataro & Asati            Standards Track                    [Page 1]
RFC 6720                      GTSM for LDP                   August 2012

Copyright Notice

   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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
      1.1. Specification of Requirements ..............................3
      1.2. Scope ......................................................3
   2. GTSM Procedures for LDP .........................................4
      2.1. GTSM Flag in the Common Hello Parameter TLV ................4
      2.2. GTSM Sending and Receiving Procedures for LDP Link Hello ...5
      2.3. GTSM Sending and Receiving Procedures for LDP
           Initialization .............................................5
   3. LDP Peering Scenarios and GTSM Considerations ...................5
   4. Security Considerations .........................................6
   5. Acknowledgments .................................................7
   6. References ......................................................7
      6.1. Normative References .......................................7
      6.2. Informative References .....................................8

1.  Introduction

   LDP [RFC5036] specifies two peer discovery mechanisms, a Basic one
   and an Extended one, both using UDP transport.  The Basic Discovery
   mechanism is used to discover LDP peers that are directly connected
   at the link level, whereas the Extended Discovery mechanism is used
   to locate Label Switching Router (LSR) neighbors that are not
   directly connected at the link level.  Once discovered, 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

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RFC 6720                      GTSM for LDP                   August 2012

   session that is established between routers that are adjacent.
   Therefore, GTSM can protect an 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