Internet Engineering Task Force (IETF) D. Lopez

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
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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.

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

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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.

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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

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+-+-+ +-+-+
|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

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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

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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].

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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.

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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

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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.

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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.

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RFC 8253 PCEPS October 2017

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.

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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>.

Lopez, et al. Standards Track [Page 22]

RFC 8253 PCEPS October 2017

[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.

Lopez, et al. Standards Track [Page 23]

RFC 8253 PCEPS October 2017

[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>.

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RFC 8253 PCEPS October 2017

[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.

Lopez, et al. Standards Track [Page 25]

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Authors' Addresses

Diego R. Lopez
Telefonica I+D
Don Ramon de la Cruz, 82
Madrid 28006
Spain

Phone: +34 913 129 041
Email: [email protected]

Oscar Gonzalez de Dios
Telefonica I+D
Don Ramon de la Cruz, 82
Madrid 28006
Spain

Phone: +34 913 129 041
Email: [email protected]

Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China

Email: [email protected]

Dhruv Dhody
Huawei
Divyashree Techno Park, Whitefield
Bangalore, KA 560066
India

Email: [email protected]

Lopez, et al. Standards Track [Page 26]