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RFC 8253

PCEPS: Usage of TLS to Provide a Secure Transport for the Path Computation Element Communication Protocol (PCEP)

Pages: 26
Proposed Standard
Errata
Updates:  5440

Top   ToC   RFC8253 - Page 1
Internet Engineering Task Force (IETF)                          D. Lopez
Request for Comments: 8253                           O. Gonzalez de Dios
Updates: 5440                                             Telefonica I+D
Category: Standards Track                                          Q. Wu
ISSN: 2070-1721                                                 D. Dhody
                                                                  Huawei
                                                            October 2017


       PCEPS: Usage of TLS to Provide a Secure Transport for the
         Path Computation Element Communication Protocol (PCEP)

Abstract

The Path Computation Element Communication Protocol (PCEP) defines the mechanisms for the communication between a Path Computation Client (PCC) and a Path Computation Element (PCE), or among PCEs. This document describes PCEPS -- the usage of Transport Layer Security (TLS) to provide a secure transport for PCEP. The additional security mechanisms are provided by the transport protocol supporting PCEP; therefore, they do not affect the flexibility and extensibility of PCEP. This document updates RFC 5440 in regards to the PCEP initialization phase procedures. 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 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8253.
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Copyright Notice

   Copyright (c) 2017 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
   (https://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
   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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5 3. Applying PCEPS . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Initiating TLS Procedures . . . . . . . . . . . . . . . . 5 3.3. The StartTLS Message . . . . . . . . . . . . . . . . . . 8 3.4. TLS Connection Establishment . . . . . . . . . . . . . . 13 3.5. Peer Identity . . . . . . . . . . . . . . . . . . . . . . 15 3.6. Connection Establishment Failure . . . . . . . . . . . . 16 4. Discovery Mechanisms . . . . . . . . . . . . . . . . . . . . 16 4.1. DANE Applicability . . . . . . . . . . . . . . . . . . . 17 5. Backward Compatibility . . . . . . . . . . . . . . . . . . . 17 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 6.1. New PCEP Message . . . . . . . . . . . . . . . . . . . . 18 6.2. New Error-Values . . . . . . . . . . . . . . . . . . . . 19 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 8. Manageability Considerations . . . . . . . . . . . . . . . . 20 8.1. Control of Function and Policy . . . . . . . . . . . . . 20 8.2. Information and Data Models . . . . . . . . . . . . . . . 21 8.3. Liveness Detection and Monitoring . . . . . . . . . . . . 21 8.4. Verifying Correct Operations . . . . . . . . . . . . . . 21 8.5. Requirements on Other Protocols . . . . . . . . . . . . . 22 8.6. Impact on Network Operation . . . . . . . . . . . . . . . 22 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 9.1. Normative References . . . . . . . . . . . . . . . . . . 22 9.2. Informative References . . . . . . . . . . . . . . . . . 23 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction

The Path Computation Element Communication Protocol (PCEP) [RFC5440] defines the mechanisms for the communication between a Path Computation Client (PCC) and a Path Computation Element (PCE), or between two PCEs. These interactions include requests and replies that can be critical for a sustainable network operation and adequate resource allocation; therefore, appropriate security becomes a key element in the PCE infrastructure. As the applications of the PCE framework evolve and more complex service patterns emerge, the definition of a secure mode of operation becomes more relevant. The Security Considerations section of [RFC5440] analyzes the potential threats to PCEP and their consequences; it also discusses several mechanisms for protecting PCEP against security attacks, without making a specific recommendation on a particular one or defining their application in depth. Moreover, [RFC6952] states the importance of ensuring PCEP communication confidentiality, especially when PCEP communication endpoints do not reside in the same Autonomous System (AS), as the interception of PCEP messages could leak sensitive information related to computed paths and resources. Transport Layer Security (TLS) [RFC5246] is one of the solutions that seems most adequate among those mentioned in these documents, as it provides support for peer authentication, message encryption, and integrity. TLS provides well-known mechanisms to support key configuration and exchange, as well as means to perform security checks on the results of PCE Discovery (PCED) procedures via the Interior Gateway Protocol (IGP) [RFC5088] [RFC5089]. This document describes a security container for the transport of PCEP messages; therefore, it does not affect the flexibility and extensibility of PCEP. This document describes how to apply TLS to secure interactions with PCE, including initiation of the TLS procedures, the TLS handshake mechanism, the TLS methods for peer authentication, the applicable TLS ciphersuites for data exchange, and the handling of errors in the security checks. In the rest of this document, we refer to this usage of TLS to provide a secure transport for PCEP as "PCEPS". Within this document, PCEP communications are described through a PCC-PCE relationship. The PCE architecture also supports PCE-PCE communication; this is achieved by requesting the PCE to fill the role of a PCC, as usual. Thus, in this document, the PCC refers to a PCC or a PCE initiating the PCEP session and acting as a client.
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2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Applying PCEPS

3.1. Overview

The steps involved in establishing a PCEPS session are as follows: 1. Establishment of a TCP connection. 2. Initiation of the TLS procedures by the StartTLS message from PCE to PCC and from PCC to PCE. 3. Negotiation and establishment of a TLS connection. 4. Start exchange of PCEP messages as per [RFC5440]. This document uses the standard StartTLS procedure in PCEP instead of using a different port for the secured session. This is done to avoid requesting allocation of another port number for PCEPS. The StartTLS procedure makes more efficient use of scarce port numbers and allows simpler configuration of PCEP. Implementations SHOULD follow the best practices and recommendations for using TLS, as per [RFC7525]. It should be noted that this procedure updates what is defined in Sections 4.2.1 and 6.7 of [RFC5440] regarding the initialization phase and the processing of messages prior to the Open message. The details of processing, including backward compatibility, are discussed in the following sections.

3.2. Initiating TLS Procedures

Since PCEP can operate either with or without TLS, it is necessary for a PCEP speaker to indicate whether it wants to set up a TLS connection or not. For this purpose, this document specifies a new PCEP message called "StartTLS". Thus, the PCEP session is secured via TLS from the start, before the exchange of any other PCEP message (including the Open message). This document thus updates [RFC5440], which requires the Open message to be the first PCEP message that is exchanged. In the case of a PCEP session using TLS, the StartTLS
Top   ToC   RFC8253 - Page 6
   message will be sent first.  Also, a PCEP speaker that supports PCEPS
   MUST NOT start the OpenWait timer after the TCP establishment;
   instead, it starts a StartTLSWait timer as described in Section 3.3.

   The PCEP speaker MAY discover that the PCEP peer supports PCEPS or
   can be preconfigured to use PCEPS for a given peer (see Section 4 for
   more details).  An existing PCEP session cannot be secured via TLS;
   the session MUST be closed and re-established with TLS as per the
   procedure described in this document.

   The StartTLS message is a PCEP message sent by a PCC to a PCE and by
   a PCE to a PCC in order to initiate the TLS procedure for PCEP.  The
   PCC initiates the use of TLS by sending a StartTLS message.  The PCE
   agrees to the use of TLS by responding with its own StartTLS message.
   If the PCE is configured to only support TLS, it may send the
   StartTLS message immediately upon TCP connection establishment;
   otherwise, it MUST wait to see if the PCC's first message is an Open
   or a StartTLS message.  The TLS negotiation and establishment
   procedures are triggered once the PCEP speaker has sent and received
   the StartTLS message.  The Message-Type field of the PCEP common
   header for the StartTLS message is set to 13.

   Once the TCP connection has been successfully established, the first
   message sent by the PCC to the PCE and by the PCE to the PCC MUST be
   a StartTLS message for PCEPS.  Note that this is a significant change
   from [RFC5440], where the first PCEP message is the Open message.

   A PCEP speaker receiving a StartTLS message, after any other PCEP
   exchange has taken place (by receiving or sending any other messages
   from either side), MUST treat it as an unexpected message and reply
   with a PCEP Error (PCErr) message with Error-Type set to 25 (PCEP
   StartTLS failure) and Error-value set to 1 (Reception of StartTLS
   after any PCEP exchange), and it MUST close the TCP connection.

   Any message received prior to the StartTLS or Open message MUST
   trigger a protocol error condition causing a PCErr message to be sent
   with Error-Type set to 25 (PCEP StartTLS failure) and Error-value set
   to 2 (Reception of any other message apart from StartTLS, Open, or
   PCErr), and it MUST close the TCP connection.

   If the PCEP speaker that does not support PCEPS receives a StartTLS
   message, it will behave according to the existing error mechanism
   described in Section 6.2 of [RFC5440] (if the message is received
   prior to an Open message) or Section 6.9 of [RFC5440] (if an unknown
   message is received).  See Section 5 for more details.
Top   ToC   RFC8253 - Page 7
   If the PCEP speaker that only supports PCEPS connections (as a local
   policy) receives an Open message, it MUST treat it as an unexpected
   message and reply with a PCErr message with Error-Type set to 1 (PCEP
   session establishment failure) and Error-value set to 1 (reception of
   an invalid Open message or a non Open message), and it MUST close the
   TCP connection.

   If a PCC supports PCEPS connections and allows non-PCEPS connections
   (as a local policy), it MUST first try to establish PCEPS by sending
   a StartTLS message, and in case it receives a PCErr message from the
   PCE, it MAY retry to establish a connection without PCEPS by sending
   an Open message.  If a PCE supports PCEPS connections and allows
   non-PCEPS connections (as a local policy), it MUST wait to respond
   after TCP establishment, based on the message received from the PCC.
   In case of a StartTLS message, the PCE MUST respond by sending a
   StartTLS message and moving to TLS establishment procedures as
   described in this document.  In case of an Open message, the PCE MUST
   respond with an Open message and move to the PCEP session
   establishment procedure as per [RFC5440].  If a PCE supports PCEPS
   connections only (as a local policy), it MAY send a StartTLS message
   to the PCC without waiting to receive a StartTLS message from the
   PCC.

   If a PCEP speaker that is unwilling or unable to negotiate TLS
   receives a StartTLS message, it MUST return a PCErr message (in the
   clear) with Error-Type set to 25 (PCEP StartTLS failure) and Error-
   value set to:

   o  3 (Failure, connection without TLS is not possible) if it is not
      willing to exchange PCEP messages without the solicited TLS
      connection, and it MUST close the TCP session.

   o  4 (Failure, connection without TLS is possible) if it is willing
      to exchange PCEP messages without the solicited TLS connection,
      and it MUST close the TCP session.  The receiver MAY choose to
      attempt to re-establish the PCEP session without TLS next.
      Re-establishing the PCEP session without TLS SHOULD be limited to
      only one attempt.

   If the PCEP speaker supports PCEPS and can establish a TLS
   connection, it MUST start the TLS connection negotiation and
   establishment steps described in Section 3.4 before the PCEP
   initialization procedure (see Section 4.2.1 of [RFC5440]).

   After the exchange of StartTLS messages, if the TLS negotiation fails
   for some reason (e.g., the required mechanisms for certificate
   revocation checking are not available), both peers MUST immediately
   close the connection.
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   A PCEP speaker that does not support PCEPS sends the Open message
   directly, as per [RFC5440].  A PCEP speaker that supports PCEPS, but
   has learned in the last exchange the peer's willingness to
   re-establish the session without TLS, MAY send the Open message
   directly, as per [RFC5440].  Re-establishing the PCEP session without
   TLS SHOULD be limited to only one attempt.

   Given the asymmetric nature of TLS for connection establishment, it
   is relevant to identify the roles of each of the PCEP peers in it.
   The PCC SHALL act as the TLS client, and the PCE SHALL act as the TLS
   server as per [RFC5246].

   As per the recommendation from [RFC7525] to avoid downgrade attacks,
   PCEP peers that support PCEPS SHOULD default to strict TLS
   configuration, i.e., not allowing non-TLS PCEP sessions to be
   established.  PCEPS implementations MAY provide an option to allow
   the operator to manually override strict TLS configuration and allow
   unsecured connections.  Execution of this override SHOULD trigger a
   warning about the security implications of permitting unsecured
   connections.

3.3. The StartTLS Message

The StartTLS message is used to initiate the TLS procedure for a PCEPS session between the PCEP peers. A PCEP speaker sends the StartTLS message to request negotiation and establishment of a TLS connection for PCEP. On receiving a StartTLS message from the PCEP peer (i.e., when the PCEP speaker has sent and received the StartTLS message), it is ready to start the negotiation and establishment of TLS and move to the steps described in Section 3.4. The collision resolution procedures described in [RFC5440] for the exchange of Open messages MUST be applied by the PCEP peers during the exchange of StartTLS messages. The format of a StartTLS message is as follows: <StartTLS Message>::= <Common Header> The StartTLS message MUST contain only the PCEP common header with the Message-Type field set to 13. Once the TCP connection has been successfully established, the PCEP speaker MUST start a timer called the "StartTLSWait timer". After the expiration of this timer, if neither the StartTLS message nor a PCErr/Open message (in case of failure and PCEPS not being supported by the peer, respectively) has been received, the PCEP speaker MUST send a PCErr message with Error-Type set to 25 (PCEP StartTLS
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   failure) and Error-value set to 5 (No StartTLS message (nor PCErr/
   Open) before StartTLSWait timer expiry), and it MUST release the TCP
   connection.  A RECOMMENDED value for the StartTLSWait timer is 60
   seconds.  The value of the StartTLSWait timer MUST NOT be less than
   that of the OpenWait timer.

   The following figures illustrate the various interactions between a
   PCC and a PCE, based on the support for the PCEPS capability, during
   the PCEP session initialization.

                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | StartTLS            |
                    | msg                 |
                    |-------              |
                    |       \   StartTLS  |
                    |        \  msg       |
                    |         \  ---------|
                    |          \/         |
                    |          /\         |
                    |         /  -------->|
                    |        /            |
                    |<------              |
                    |:::::::::TLS:::::::::|
                    |:::::Establishment:::|
                    |                     |
                    |                     |
                    |:::::::PCEP::::::::::|
                    |                     |

            Figure 1: Both PCEP speakers support PCEPS (strict)
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                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | StartTLS            |
                    | msg                 |
                    |-------              |
                    |       \   StartTLS  |
                    |        \  msg       |
                    |         \  ---------|
                    |          \/         |
                    |          /\         |
                    |         /  -------->|
                    |        /            |
                    |<------              |
                    |:::::::::TLS:::::::::| TLS Establishment
                    |:::::Establishment:::| Failure; both
                    |                     | peers close
                                            the session

      Figure 2: Both PCEP speakers support PCEPS (strict) but cannot
                               establish TLS
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                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |  Does not support
                    | StartTLS            |  PCEPS and thus
                    | msg                 |  sends Open
                    |-------              |
                    |       \   Open      |
                    |        \  msg       |
                    |         \  ---------|
                    |          \/         |
                    |          /\         |
                    |         /  -------->|
                    |        /            |
                    |<------              |
                    |                     |
                    |<--------------------| Send Error
                    |       PCErr         | Type=1,Value=1
                    |                     | (non-Open message
                    |<--------------------|  received)
                    |       Close         |
                    ///////// TCP /////////
                    //////re-establish/////
          Send Open | Open                |
          this time | msg                 |
                    |-------              |
                    |       \   Open      |
                    |        \  msg       |
                    |         \  ---------|
                    |          \/         |
                    |          /\         |
                    |         /  -------->|
                    |        /            |
                    |<------              |

     Figure 3: PCE does not support connection with PCEPS, whereas PCC
                 supports connection with or without PCEPS
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                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | StartTLS            |
                    | msg                 | PCE waits
                    |-------------------->| for PCC and
                    |            StartTLS | responds with
                    |<--------------------| Start TLS
                    |                     |
                    |:::::::::TLS:::::::::|
                    |:::::Establishment:::|
                    |                     |
                    |                     |
                    |:::::::PCEP::::::::::|
                    |                     |

   Figure 4: Both PCEP speakers support connection with or without PCEPS


                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | StartTLS            |
                    | msg                 | PCE waits
                    |-------------------->| for PCC
                    |               PCErr |
                    |<--------------------| Send Error
                    |                     | Type=25,Value=3
                    |                     | (Failure, connection
                    |<--------------------|  without TLS is not
                    |       Close         |  possible)

      Figure 5: Both PCEP speakers support connection with or without
                PCEPS, but PCE cannot start TLS negotiation
Top   ToC   RFC8253 - Page 13
                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | Open                |
                    | msg                 | PCE waits
                    |-------------------->| for PCC and
                    |                Open | responds with
                    |<--------------------| Open
                    |                     |
                    |:::::::PCEP::::::::::|
                    |                     |

   Figure 6: PCE supports connection with or without PCEPS, whereas PCC
                  does not support connection with PCEPS

3.4. TLS Connection Establishment

Once the establishment of TLS has been agreed upon by the PCEP peers, the connection establishment SHALL follow the following steps: 1. Immediately negotiate a TLS session according to [RFC5246]. The following restrictions apply: * Support for TLS v1.2 [RFC5246] or later is REQUIRED. * Support for certificate-based mutual authentication is REQUIRED. * Negotiation of a ciphersuite providing for integrity protection is REQUIRED. * Negotiation of a ciphersuite providing for confidentiality is RECOMMENDED. * Support for and negotiation of compression is OPTIONAL. * PCEPS implementations MUST, at a minimum, support negotiation of the TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 [RFC6460] and SHOULD support TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 as well. Implementations SHOULD support the NIST P-256 (secp256r1) curve [RFC4492]. In addition, PCEPS implementations MUST support negotiation of the mandatory-to-implement ciphersuites required by the versions of TLS that they support from TLS 1.3 onwards.
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   2.  Peer authentication can be performed in any of the following two
       REQUIRED operation models:

       *  TLS with X.509 certificates using Public-Key Infrastructure
          Exchange (PKIX) trust models:

          +  Implementations MUST allow the configuration of a list of
             trusted Certification Authorities (CAs) for incoming
             connections.

          +  Certificate validation MUST include the verification rules
             as per [RFC5280].

          +  PCEPS implementations SHOULD incorporate revocation methods
             (Certificate Revocation List (CRL) downloading, Online
             Certificate Status Protocol (OCSP), etc.) according to the
             trusted CA policies.

          +  Implementations SHOULD indicate their trusted CAs.  For TLS
             1.2, this is done using "certificate_authorities" on the
             server side (see Section 7.4.4 of [RFC5246]) and the
             "TrustedAuthorities" extension on the client side (see
             Section 6 of [RFC6066]).

          +  Implementations MUST follow the rules and guidelines for
             peer validation as defined in [RFC6125].  If an expected
             DNS name or IP address for the peer is configured, then the
             implementations MUST check them against the values in the
             presented certificate.  The DNS names and the IP addresses
             can be contained in the Common Name Identifier (CN-ID)
             [RFC6125] or the subjectAltName entries.  For verification,
             only one of these entries is considered.  The following
             precedence applies: for DNS name validation, DNS-ID
             [RFC6125] has precedence over CN-ID, and for IP address
             validation, subjectAltName:iPAddr has precedence over
             CN-ID.

          +  Implementations MAY allow the configuration of a set of
             additional properties of the certificate to check for a
             peer's authorization to communicate (e.g., a set of allowed
             values in URI-ID [RFC6125] or a set of allowed X.509 v3
             Certificate Policies).  The definitions of these properties
             are out of scope of this document.

       *  TLS with X.509 certificates using certificate fingerprints:
          Implementations MUST allow the configuration of a list of
          certificates that are trusted to identify peers, identified
          via the fingerprint of certificate octets encoded by the
Top   ToC   RFC8253 - Page 15
          Distinguished Encoding Rules (DER).  Implementations MUST
          support SHA-256 as defined by [SHS] as the hash algorithm for
          the fingerprint, but a later revision may demand support for a
          stronger hash function.

   3.  Start exchanging PCEP messages.

       *  Once the TLS connection has been successfully established, the
          PCEP speaker MUST start the OpenWait timer [RFC5440]; after
          the expiration of this timer, if no Open message has been
          received, the PCEP speaker sends a PCErr message and releases
          the TCP/TLS connection.

3.5. Peer Identity

Depending on the peer authentication method in use, PCEPS supports different operation modes to establish a peer's identity and whether it is entitled to perform requests or can be considered authoritative in its replies. PCEPS implementations SHOULD provide mechanisms for associating peer identities with different levels of access and/or authoritativeness, and they MUST provide a mechanism for establishing a default level for properly identified peers. Any connection established with a peer that cannot be properly identified SHALL be terminated before any PCEP exchange takes place. In TLS X.509 mode using fingerprints, a peer is uniquely identified by the fingerprint of the presented certificate. There are numerous trust models in PKIX environments, and it is beyond the scope of this document to define how a particular deployment determines whether a peer is trustworthy. Implementations that want to support a wide variety of trust models should expose as many details of the presented certificate to the administrator as possible so that the trust model can be implemented by the administrator. At least the following parameters of the X.509 certificate SHOULD be exposed: o Peer's IP Address o Peer's Fully Qualified Domain Name (FQDN) o Certificate Fingerprint o Issuer o Subject o All X.509 v3 Extended Key Usage
Top   ToC   RFC8253 - Page 16
   o  All X.509 v3 Subject Alternative Name

   o  All X.509 v3 Certificate Policies

   Note that the remote IP address used for the TCP session
   establishment is also exposed.

   [RFC8232] specifies a Speaker Entity Identifier TLV
   (SPEAKER-ENTITY-ID) as an optional TLV that is included in the OPEN
   object.  It contains a unique identifier for the node that does not
   change during the lifetime of the PCEP speaker.  An implementation
   would thus expose the speaker entity identifier as part of the X.509
   v3 certificate's subjectAltName:otherName, so that an implementation
   could use this identifier for the peer identification trust model.

   In addition, a PCC MAY apply the procedures described in "DNS-Based
   Authentication of Named Entities (DANE)" [RFC6698] to verify its peer
   identity when using DNS discovery.  See Section 4.1 for further
   details.

3.6. Connection Establishment Failure

In case the initial TLS negotiation or the peer identity check fails, according to the procedures listed in this document, both peers MUST immediately close the connection. The initiator SHOULD follow the procedure listed in [RFC5440] to retry session setup as per the exponential back-off session establishment retry procedure.

4. Discovery Mechanisms

This document does not specify any discovery mechanism for support of PCEPS. [PCE-DISCOVERY-PCEPS-SUPPORT] and [PCE-DISCOVERY-DNS] make the following proposals: o A PCE can advertise its capability to support PCEPS using the IGP's advertisement mechanism of the PCED information. The PCE-CAP-FLAGS sub-TLV is an optional sub-TLV used to advertise PCE capabilities. It is present within the PCED sub-TLV carried by OSPF or IS-IS. [RFC5088] and [RFC5089] provide the description and processing rules for this sub-TLV when carried within OSPF and IS-IS, respectively. PCE capability bits are defined in [RFC5088]. A new capability flag bit for the PCE-CAP-FLAGS sub-TLV that can be announced as an attribute to distribute PCEP security support information is proposed in [PCE-DISCOVERY-PCEPS-SUPPORT].
Top   ToC   RFC8253 - Page 17
   o  A PCE can advertise its capability to support PCEPS using DNS
      [PCE-DISCOVERY-DNS] by identifying the support of TLS.

4.1. DANE Applicability

DANE [RFC6698] defines a secure method to associate the certificate that is obtained from a TLS server with a domain name using DNS, i.e., using the TLSA DNS resource record (RR) to associate a TLS server certificate or public key with the domain name where the record is found, thus forming a "TLSA certificate association". The DNS information needs to be protected by DNS Security (DNSSEC). A PCC willing to apply DANE to verify server identity MUST conform to the rules defined in Section 4 of [RFC6698]. The implementation MUST support service certificate constraint (TLSA certificate usages type 1) with Matching type 1 (SHA2-256) as described in [RFC6698] and [RFC7671]. The server's domain name must be authorized separately, as TLSA does not provide any useful authorization guarantees.

5. Backward Compatibility

The procedures described in this document define a security container for the transport of PCEP requests and replies carried by a TLS connection initiated by means of a specific extended message (StartTLS) that does not interfere with PCEP speaker implementations not supporting it. A PCC that does not support PCEPS will send an Open message as the first message on TCP establishment. A PCE that only supports PCEPS will send a StartTLS message on TCP establishment. The PCC would consider the received StartTLS message as an error and behave according to the existing error mechanism of [RFC5440], i.e., it would send a PCErr message with Error-Type 1 (PCEP session establishment failure) and Error-value 1 (reception of an invalid Open message or a non Open message) and close the session. A PCC that support PCEPS will send a StartTLS message as the first message on TCP establishment. A PCE that does not support PCEPS would consider receiving a StartTLS message as an error, respond with a PCErr message with Error-Type 1 (PCEP session establishment failure) and Error-value 1 (reception of an invalid Open message or a non Open message), and close the session. If a StartTLS message is received at any other time by a PCEP speaker that does not implement PCEPS, it would consider it as an unknown message and would behave according to the existing error mechanism of [RFC5440], i.e., it would send a PCErr message with Error-Type 2 (Capability not supported) and close the session.
Top   ToC   RFC8253 - Page 18
   An existing PCEP session cannot be upgraded to PCEPS; the session
   needs to be terminated and re-established as per the procedure
   described in this document.  During the incremental upgrade, the PCEP
   speaker SHOULD allow session establishment with and without TLS.
   Once both PCEP speakers are upgraded to support PCEPS, the PCEP
   session is re-established with TLS; otherwise, a PCEP session without
   TLS is set up.  A redundant PCE MAY also be used during the
   incremental deployment to take over the PCE undergoing upgrade.  Once
   the upgrade is completed, support for the unsecured version SHOULD be
   removed.

   A PCE that accepts connections with or without PCEPS would respond
   based on the message received from the PCC.  A PCC that supports
   connection with or without PCEPS would first attempt to connect with
   PCEPS, and in case of error, it MAY retry to establish connection
   without PCEPS.  For successful TLS operations with PCEP, both PCEP
   peers in the network would need to be upgraded to support this
   document.

   Note that a PCEP implementation that supports PCEPS would respond
   with a PCErr message with Error-Type set to 25 (PCEP StartTLS
   failure) and Error-value set to 2 (Reception of any other message
   apart from StartTLS, Open, or PCErr) if any other message is sent
   before a StartTLS or Open message.  If the sender of the invalid
   message is a PCEP implementation that does not support PCEPS, it will
   not be able to understand this error.  A PCEPS implementation could
   also send the PCErr message as per [RFC5440] with Error-Type 1 (PCEP
   session establishment failure) and Error-value 1 (reception of an
   invalid Open message or a non Open message) before closing the
   session.

6. IANA Considerations

6.1. New PCEP Message

The following new message type has been allocated within the "PCEP Messages" sub-registry of the "Path Computation Element Protocol (PCEP) Numbers" registry: Value Description Reference ------------------------------------------------------- 13 StartTLS This document
Top   ToC   RFC8253 - Page 19

6.2. New Error-Values

The following new error types and error values have been allocated within the "PCEP-ERROR Object Error Types and Values" sub-registry of the "Path Computation Element Protocol (PCEP) Numbers" registry: Error-Type Meaning Error-value Reference --------------------------------------------------------------------- 25 PCEP StartTLS 0: Unassigned This document failure 1: Reception of This document StartTLS after any PCEP exchange 2: Reception of This document any other message apart from StartTLS, Open, or PCErr 3: Failure, connection This document without TLS is not possible 4: Failure, connection This document without TLS is possible 5: No StartTLS message This document (nor PCErr/Open) before StartTLSWait timer expiry

7. Security Considerations

While the application of TLS satisfies the requirement on confidentiality as well as fine-grained, policy-based peer authentication, there are security threats that it cannot address. It may be advisable to apply additional protection measures, in particular in what relates to attacks specifically addressed to forging the TCP connection underpinning TLS, especially in the case of long-lived connections. One of these measures is the application of the TCP Authentication Option (TCP-AO) [RFC5925], which is fully compatible with and deemed as complementary to TLS. The mechanisms to configure the requirements to use TCP-AO and other lower-layer protection measures with a particular peer are outside the scope of this document.
Top   ToC   RFC8253 - Page 20
   Since computational resources required by the TLS handshake and
   ciphersuite are higher than unencrypted TCP, clients connecting to a
   PCEPS server can more easily create high-load conditions, and a
   malicious client might create a denial-of-service attack more easily.

   Some TLS ciphersuites only provide integrity validation of their
   payload and provide no encryption; such ciphersuites SHOULD NOT be
   used by default.  Administrators MAY allow the usage of these
   ciphersuites after careful weighting of the risk of relevant internal
   data leakage that can occur in such a case, as explicitly stated by
   [RFC6952].

   When using certificate fingerprints to identify PCEPS peers, any two
   certificates that produce the same hash value will be considered the
   same peer.  Therefore, it is important to make sure that the hash
   function used is cryptographically uncompromised, so that attackers
   are very unlikely to be able to produce a hash collision with a
   certificate of their choice.  This document mandates support for
   SHA-256 as defined by [SHS], but a later revision may demand support
   for stronger functions if suitable attacks on it are known.

   PCEPS implementations that continue to accept connections without TLS
   are susceptible to downgrade attacks as described in [RFC7457].  An
   attacker could attempt to remove the use of StartTLS messages that
   request the use of TLS as it pass on the wire in clear and could also
   attempt to inject a PCErr message that suggests attempting PCEP
   connection without TLS.

   The guidance given in [RFC7525] SHOULD be followed to avoid attacks
   on TLS.

8. Manageability Considerations

All manageability requirements and considerations listed in [RFC5440] apply to PCEP protocol extensions defined in this document. In addition, requirements and considerations listed in this section apply.

8.1. Control of Function and Policy

A PCE or PCC implementation SHOULD allow configuring the PCEP security via TLS capabilities as described in this document. A PCE or PCC implementation supporting PCEP security via TLS MUST support general TLS configuration as per [RFC5246]. At least the configuration of one of the trust models and its corresponding parameters, as described in Sections 3.4 and 3.5, MUST be supported by the implementation.
Top   ToC   RFC8253 - Page 21
   A PCEPS implementation SHOULD allow configuring the StartTLSWait
   timer value.

   PCEPS implementations MAY provide an option to allow the operator to
   manually override strict TLS configuration and allow unsecure
   connections.  Execution of this override SHOULD trigger a warning
   about the security implications of permitting unsecure connections.

   Further, the operator needs to develop suitable security policies
   around PCEP within his network.  The PCEP peers SHOULD provide ways
   for the operator to complete the following tasks in regards to a PCEP
   session:

   o  Determine if a session is protected via PCEPS.

   o  Determine the version of TLS, the mechanism used for
      authentication, and the ciphersuite in use.

   o  Determine if the certificate could not be verified and the reason
      for this circumstance.

   o  Inspect the certificate offered by the PCEP peer.

   o  Be warned if the StartTLS procedure fails for the PCEP peers that
      are known to support PCEPS via configurations or capability
      advertisements.

8.2. Information and Data Models

The PCEP MIB module is defined in [RFC7420]. The MIB module could be extended to include the ability to view the PCEPS capability, TLS-related information, and the TLS status for each PCEP peer. Further, to allow the operator to configure the PCEPS capability and various TLS-related parameters as well as to view the current TLS status for a PCEP session, the PCEP YANG module [PCEP-YANG] is extended to include TLS-related information.

8.3. Liveness Detection and Monitoring

Mechanisms defined in this document do not imply any new liveness detection and monitoring requirements in addition to those already listed in [RFC5440] and [RFC5246].

8.4. Verifying Correct Operations

A PCEPS implementation SHOULD log error events and provide PCEPS failure statistics with reasons.
Top   ToC   RFC8253 - Page 22

8.5. Requirements on Other Protocols

Mechanisms defined in this document do not imply any new requirements on other protocols. Note that Section 4 lists possible discovery mechanisms for support of PCEPS.

8.6. Impact on Network Operation

Mechanisms defined in this document do not have any significant impact on network operations in addition to those already listed in [RFC5440] and on the policy and management implications discussed above.

9. References

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, <https://www.rfc-editor.org/info/rfc5246>. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, <https://www.rfc-editor.org/info/rfc5280>. [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, <https://www.rfc-editor.org/info/rfc5440>. [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066, January 2011, <https://www.rfc-editor.org/info/rfc6066>.
Top   ToC   RFC8253 - Page 23
   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <https://www.rfc-editor.org/info/rfc6698>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC7671]  Dukhovni, V. and W. Hardaker, "The DNS-Based
              Authentication of Named Entities (DANE) Protocol: Updates
              and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
              October 2015, <https://www.rfc-editor.org/info/rfc7671>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [SHS]      National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-4,
              DOI 10.6028/NIST.FIPS.180-4, August 2015,
              <http://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.180-4.pdf>.

9.2. Informative References

[PCE-DISCOVERY-DNS] Wu, Q., Dhody, D., King, D., Lopez, D., and J. Tantsura, "Path Computation Element (PCE) Discovery using Domain Name System(DNS)", Work in Progress, draft-wu-pce-dns-pce- discovery-10, March 2017. [PCE-DISCOVERY-PCEPS-SUPPORT] Lopez, D., Wu, Q., Dhody, D., Wang, Z., and D. King, "IGP extension for PCEP security capability support in the PCE discovery", Work in Progress, draft-wu-pce-discovery- pceps-support-07, March 2017.
Top   ToC   RFC8253 - Page 24
   [PCEP-YANG]
              Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
              YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              draft-ietf-pce-pcep-yang-05, July 2017.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492,
              DOI 10.17487/RFC4492, May 2006,
              <https://www.rfc-editor.org/info/rfc4492>.

   [RFC4513]  Harrison, R., Ed., "Lightweight Directory Access Protocol
              (LDAP): Authentication Methods and Security Mechanisms",
              RFC 4513, DOI 10.17487/RFC4513, June 2006,
              <https://www.rfc-editor.org/info/rfc4513>.

   [RFC5088]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
              January 2008, <https://www.rfc-editor.org/info/rfc5088>.

   [RFC5089]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "IS-IS Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
              January 2008, <https://www.rfc-editor.org/info/rfc5089>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC6460]  Salter, M. and R. Housley, "Suite B Profile for Transport
              Layer Security (TLS)", RFC 6460, DOI 10.17487/RFC6460,
              January 2012, <https://www.rfc-editor.org/info/rfc6460>.

   [RFC6614]  Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, DOI 10.17487/RFC6614, May 2012,
              <https://www.rfc-editor.org/info/rfc6614>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.
Top   ToC   RFC8253 - Page 25
   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <https://www.rfc-editor.org/info/rfc7420>.

   [RFC7457]  Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
              Known Attacks on Transport Layer Security (TLS) and
              Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
              February 2015, <https://www.rfc-editor.org/info/rfc7457>.

   [RFC8232]  Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
              and D. Dhody, "Optimizations of Label Switched Path State
              Synchronization Procedures for a Stateful PCE", RFC 8232,
              DOI 10.17487/RFC8232, September 2017,
              <https://www.rfc-editor.org/info/rfc8232>.

Acknowledgements

This specification relies on the analysis and profiling of TLS included in [RFC6614] and the procedures described for the StartTLS command in [RFC4513]. We would like to thank Joe Touch for his suggestions and support regarding the StartTLS mechanisms. Thanks to Daniel King for reminding the authors about manageability considerations. Thanks to Cyril Margaria for shepherding this document. Thanks to David Mandelberg for early SECDIR review comments as well as further review during IETF last call. Thanks to Dan Frost for the RTGDIR review and comments. Thanks to Dale Worley for the Gen-ART review and comments. Thanks to Tianran Zhou for the OPSDIR review. Thanks to Deborah Brungard for being the responsible AD and guiding the authors as needed. Also, thanks to Mirja Kuhlewind, Eric Rescorla, Warren Kumari, Kathleen Moriarty, Suresh Krishnan, Ben Campbell, and Alexey Melnikov for the IESG review and comments.
Top   ToC   RFC8253 - Page 26

Authors' Addresses

Diego R. Lopez Telefonica I+D Don Ramon de la Cruz, 82 Madrid 28006 Spain Phone: +34 913 129 041 Email: diego.r.lopez@telefonica.com Oscar Gonzalez de Dios Telefonica I+D Don Ramon de la Cruz, 82 Madrid 28006 Spain Phone: +34 913 129 041 Email: oscar.gonzalezdedios@telefonica.com Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China Email: sunseawq@huawei.com Dhruv Dhody Huawei Divyashree Techno Park, Whitefield Bangalore, KA 560066 India Email: dhruv.ietf@gmail.com