PCE Working Group H. Pouyllau Internet-Draft Alcatel-Lucent Intended status: Standards Track R. Theillaud Expires: September 1, 2018 Marben Products J. Meuric France Telecom Orange H. Zheng (Editor) X. Zhang Huawei Technologies February 28, 2018 Extensions to the Path Computation Element Communication Protocol for Enhanced Errors and Notifications draft-ietf-pce-enhanced-errors-03.txt Abstract This document defines new error and notification TLVs for the PCE Communication Protocol (PCEP) [RFC5440]. It identifies the possible PCEP behaviors in case of error or notification. Thus, this draft defines types of errors and notifications and how they are disclosed to other PCEs in order to support predefined PCEP behaviors. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 1, 2018. Copyright Notice Copyright (c) 2018 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 Pouyllau, et al. Expires September 1, 2018 [Page 1] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 (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. Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 3 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1.1. Error use-case . . . . . . . . . . . . . . . . . . . . . 4 3.1.2. Notification use-case . . . . . . . . . . . . . . . . . . 4 4. PCEP Behaviors . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. PCEP Behaviors in Case of Error . . . . . . . . . . . . . . 5 4.2. PCEP Behaviors in Case of Notification . . . . . . . . . . 6 4.3. PCE Peer Identification . . . . . . . . . . . . . . . . . . 6 5. PCEP Extensions for Error and Notification Handling . . . . . 6 5.1. Propagation TLV . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Error-criticality TLV . . . . . . . . . . . . . . . . . . . 7 5.3. Notification type TLV . . . . . . . . . . . . . . . . . . . 7 5.4. Behaviors and TLV combinations . . . . . . . . . . . . . . 8 5.5. Propagation Restrictions Objects . . . . . . . . . . . . . 9 5.5.1. Time-To-Live Object (TTL) . . . . . . . . . . . . . . . . 10 5.5.2. DIFFUSION-LIST Object (DLO) . . . . . . . . . . . . . . . 10 5.5.3. Rules Applied to Existing Errors and Notifications . . . 12 6. Error and Notification Scenarios . . . . . . . . . . . . . . 16 6.1. Error Behavior Type 1 . . . . . . . . . . . . . . . . . . . 16 6.2. Error Behavior Type 2 . . . . . . . . . . . . . . . . . . . 17 6.3. Error Behavior Type 4 . . . . . . . . . . . . . . . . . . . 17 6.4. Error Behavior Type 5 . . . . . . . . . . . . . . . . . . . 18 6.5. Notification Behavior Type 1 . . . . . . . . . . . . . . . 19 6.6. Notification Behavior Type 2 . . . . . . . . . . . . . . . 19 6.7. Notification Behavior Type 3 . . . . . . . . . . . . . . . 20 6.8. Notification Behavior Type 4 . . . . . . . . . . . . . . . 20 7. Security Considerations . . . . . . . . . . . . . . . . . . . 21 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 8.1. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . . 21 8.2. New DLO object . . . . . . . . . . . . . . . . . . . . . . 21 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 9.1. Normative References . . . . . . . . . . . . . . . . . . . 22 9.2. Informational References . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 Pouyllau, et al. Expires September 1, 2018 [Page 2] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 1. Terminology PCE terminology is defined in [RFC4655]. PCEP Peer: An element involved in a PCEP session (i.e. a PCC or a PCE). Source PCC: the PCC, for a given path computation query, initiating the first PCEP request, which may then trigger a chain of successive requests. Target PCE: the PCE that can compute a path to the destination without having to query any other PCE. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Introduction The PCE Communication Protocol [RFC5440] is designed to be flexible and extensible in order to allow future evolutions or specific constraint support such as proposed in [RFC7470]. Crossing different PCE implementations (e.g. from different providers or due to different releases), a PCEP request may encounter unknown errors or notification messages. In such a case, the PCEP RFC [RFC5440] specifies to send a specific error code to the PCEP peer. In the context of path computation crossing different routing domains or autonomous systems, the number of different PCE system specificities is potentially high, thus possibly leading to divergent and unstable situations. Such phenomenon can also occur in homogeneous cases since PCE systems have their own policies that can introduce differences in requests treatment even for requests having the same destination. In order to generalize PCEP behaviors in the case of heterogeneous PCE systems, new objects have to be defined. Dealing with heterogeneity is a major challenge considering PCE applicability, particularly in multi-layer and multi-domain contexts. Thus, extending such error codes and PCEP behaviors accordingly would improve interoperability among different PCEP implementations and would solve some of these issues. However, some of them would still remain (e.g. the divergences in request treatment introduced by different policies). The purpose of this draft is to identify and specify new optional TLVs and objects in order to generalize PCEP behaviors. Pouyllau, et al. Expires September 1, 2018 [Page 3] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 3.1. Examples The two following scenarios underline the need for a normalization of the PCEP behaviors according to existing error or notification types. 3.1.1. Error use-case PCE(i-1) has sent a request to PCE(i) which has also sent a request to PCE(i+1). PCE(i-1) and PCE(i+1) have the same error semantic but not PCE(i). If PCE(i+1) throws an error type and value unknown by PCE(i). PCE(i) could then adopt any other behaviors and sends back to PCE(i-1) an error of type 2 (Capability not supported), 3 (Unknown Object) or 4 (Not supported Object) for instance. As a consequence, the path request would be cancelled but the error has no meaning for PCE(i-1) whereas if PCE(i) had simply forwarded the error sent by PCE(i+1), it would have been understood by PCE(i-1). 3.1.2. Notification use-case PCE(i-1) has sent a request to PCE(i) which has also sent a request to PCE(i+1) but PCE(i+1) is overloaded. Without extensions, PCE(i+1) should send a notification of type 2 and a value flag giving its estimated congestion duration. PCE(i) can choose to stop the path computation and send a NO_PATH reply to PCE(i-1). Hence, PCE(i-1) ignores the congestion duration on PCE(i+1) and could seek it for further requests. 4. PCEP Behaviors One of the purposes of the PCE architecture is to compute paths across networks, but an added value is to compute such paths in inter-area/layer/domain environments. The PCE Communication Protocol [RFC5440] is based on the Transport Communication Protocol (TCP). Thus, to compute a path within the PCE architecture, several TCP/PCEP sessions have to be set up, in a peer-to-peer manner, along a set of identified PCEs. When the PCEP session is up for two PCEP peers, the PCC of the first PCE System (the source PCC) sends a PCReq message. If the PCC does not receive any reply before the dead timer is out, then it goes back to the idle state. A PCC can expect two kinds of replies: a PCRep message containing one or more valid paths (EROs) or a negative PCRep message containing a NO-PATH object. Beside PCReq and PCRep messages, notification and error messages, named respectively PCNtf and PCErr, can be sent. There are two types of notification messages: type 1 is for cancelling pending requests and type 2 for signaling a congestion of the PCE. Several error Pouyllau, et al. Expires September 1, 2018 [Page 4] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 values are described in [RFC5440]. The error types concerning the session phase begin at 2, error type 1 values are dedicated to the initialization phase. As the PCE Communication Protocol is built to work in a peer-to-peer manner (i.e. supported by a TCP Connection), it supposes that the "deadtimer" of the source PCC is long enough to support the end-to- end distributed path computation process. The exchange of messages in the PCE Communication Protocol is described in details when PCEP is in states OpenWait and KeepWait in [RFC5440]. When the session is up, message exchange is defined in [RFC5440]. [RFC5441] describes the Backward Recursive Path Computation (BRPC) procedure, and, because it considers an inter- domain path computation, gives a bigger picture of the possible behaviors when the session is up. Detailed behavior is mostly let free to any specific implementation. The following sections identifies the PCEP behaviors in case of error or notification and also introduce the requirement of PCEP peer identification in both cases. 4.1. PCEP Behaviors in Case of Error [RFC5440] specifies that "a PCEP Error message is sent in several situations: when a protocol error condition is met or the request is not compliant with the PCEP specification". On this basis, and according to the other RFCs, the identified PCEP behaviors are the followings: o "Propagation": the received message requires to be propagated forwardly or backwardly (depending on which PCEP peer has sent the message) to a set of PCEP peers; o "Criticality level": in different RFCs, error-types affects the state of the PCEP request or session in different manners; hence, different level of criticality can be observed: o * Low-level of criticality: the received message does not affect the PCEP connection and further answer can still be expected; * Medium-level of criticality: the received message does not affect the PCEP connection but the request(s) is(are) cancelled; * High-level of criticality: the received message indicates that the PCEP peer will close the session with its peer (and so Pouyllau, et al. Expires September 1, 2018 [Page 5] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 pending requests associated by the error, if any, are cancelled.) The high-level of criticality has been extracted from [RFC5440] which associates such a behavior to error-type of 1 (errors raised during the PCEP session establishment). Hence, such errors are quite specific. For the sake of completeness, they have been included in this document. 4.2. PCEP Behaviors in Case of Notification Notification messages can be employed in two different manners: during the treatment of a PCEP request, or independently from it to advertise information (in [RFC5440], the request ID list within a PCNtf message is optional). Hence, three different types of behaviors can be identified: o "Local": the notification does not imply any forward or backward propagation of the message; o "Request-specific propagation": the received message requires to be propagated forwardly or backwardly (depending on which peer has sent the message) to the PCEP peers; o "Non request-specific propagation": the received message must be propagated to any known peers (e.g. if PCE discovery is activated) or to a list of identified peers. 4.3. PCE Peer Identification The propagation of errors and notifications affects the state of the PCEP peers along the chain. In some cases, for instance a notification that a PCE is overloaded, the identification of the PCEP peer - or that the sender PCE is not the direct neighbor - might be an important information for the PCEP peers receiving the message. 5. PCEP Extensions for Error and Notification Handling This section describes extensions to support error and notification with respect to the PCEP behavior description defined in Section 4. This document does not intend to modify errors and notification types previously defined in existing documents (e.g. [RFC5440], [RFC5441], etc.). Pouyllau, et al. Expires September 1, 2018 [Page 6] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 5.1. Propagation TLV To support the propagation behavior mentioned in Section 4.1 and Section 4.2, a new optional TLV is defined, which can be carried in PCEP-ERROR and NOTIFICATION objects, to indicate whether a message has to be propagateed or not. The allocation from the "PCEP TLV Type Indicators" sub-registry will be assigned by IANA and the request is documented in Section 8. The description is "Propagation", the length value is 2 bytes and the value field is 1 byte. The value field is set to default value 0 meaning that the message MUST NOT be propagated. If the value field is set to 1, the message MUST be propagated. Section 5.5 specifies the destination and to limit the number of messages. 5.2. Error-criticality TLV To support the shutdown behavior mentioned in Section 4.1, we extend the PCEP-ERROR object by creating a new optional TLV to indicate whether an error is recoverable or not. The allocation from the "PCEP TLV Type Indicators" sub-registry will be assigned by IANA and the request is documented in Section 8. The description is "Error-criticality", the length value is 2 bytes and the value field is 1 byte. The value field is set to default value 0 meaning that the error has a low-level of criticality (so further messages can be expected for this request). If the value field is set to 1, the error has a medium-level of criticality and requests whose identifiers appear in the same message MUST be cancelled (so no further messages can be expected for these requests). If the value field is set to 2, the error has a high- level of criticality, the connection for this PCEP session is closed by the sender PCE peer. 5.3. Notification type TLV To support the request-specific behavior mentioned in Section 4.2, we extend the NOTIFICATION object by creating a new optional TLV to indicate whether the notification is request-specific or not. The allocation from the "PCEP TLV Type Indicators" sub-registry will be assigned by IANA and the request is documented in Section 8. The description is "Notification Type", the length value is 2 bytes and the value field is 1 byte. The value field is set to default value 0 meaning that the notification is not request-specific. If the value field is set to 1, the notification is request-specific. Pouyllau, et al. Expires September 1, 2018 [Page 7] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 If according to RFC5440 a notification contains a request-id, then the value field of the Notification type TLV MUST be set to 1. 5.4. Behaviors and TLV combinations The propagation behavior MAY be combined with all criticality levels, thus leading to 6 different behaviors. In the case of a criticality level of 2, the session is closed by the PCE peer which sends the message. Hence, the criticality level is purely informative for the PCE peer which receives the message. If it is combined with a propagation behavior, then the PCE propagating the message MUST indicate the same level of criticality if it closes the session. Otherwise, it MUST use a criticality level of 1 if it does not close the session. For a PCErr message, all the possible behaviors described in Section 4.1 can be covered with TLVs included in a PCEP-ERROR object. The following table captures all combinations of error behaviors: | Error \Propogation| 0 | 1 | | criticallity\ Value | ( No |(Propogation | | value \ | Propagation) | Required) | |------------------------------------------------------| | 0 (low) | Type 1 | Type 4 | | 1 (medium) | Type 2 | Type 5 | | 2 (high) | Type 3 | Type 6 | |------------------------------------------------------| o "Error Behavior Type 1" : Local Error with a low level of criticality; o "Error Behavior Type 2": Local Error with a medium level of criticality; o "Error Behavior Type 3": Local Error with a high level of criticality; o "Error Behavior Type 4": Propagated Error with a low level of criticality; o "Error Behavior Type 5": Propagated Error with a medium level of criticality; o "Error Behavior Type 6": Propagated Error with a high level of criticality; Pouyllau, et al. Expires September 1, 2018 [Page 8] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 For a notification message, the behaviors are covered as ensued, with TLVs included in a NOTIFICATION object: | \Propogation | 0 | 1 | | Notification\ Value | (No | (Propogation | | type value \ | Propagation) | Required) | |--------------------------------------------------------| | 0 (non request-specific)| Type 1 | Type 3 | | 1 (request-specific) | Type 2 | Type 4 | |--------------------------------------------------------| o "Notification Behavior Type 1": TLV "Propagation" with value 0 and TLV "Notification Type" with value 0; o "Notification Behavior Type 2": TLV "Propagation" with value 0 and TLV "Notification Type" with value 1; o "Notification Behavior Type 3": TLV "Propagation" with value 1 and TLV "Notification Type" with value 0; o "Notification Behavior Type 4": TLV "Propagation" with value 1 and TLV "Notification Type" with value 1; 5.5. Propagation Restrictions Objects In order to limit the propagation of errors and notifications, the following mechanisms SHOULD be used: A Time-To-Live(TTL) object: to limit the number of PCEP peers that will recursively receive the message; A DIFFUSION-LIST object (DLO): to specify the PCEP peer addresses or domains of PCEP peers the message must be propagate to; History mechanism: if a PCEP peer keeps track of the messages it has relayed, it could avoid propagating an error or notification it has already received. Such mechanisms SHOULD be used jointly or independently depending the error or notification behaviors they are associated to. Note that, a non request-specific propagated notification (i.e., "Notification Behavior Type 3") MUST include a DLO and SHOULD include a TTL. The conditions of use for the TTL and DIFFUSION-LIST object are described in sections below. Pouyllau, et al. Expires September 1, 2018 [Page 9] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 5.5.1. Time-To-Live Object (TTL) The TTL value is set to any integer value to indicate the number of PCEP peers that will recursively receive the message. The TLL object SHOULD be used with propagated errors or notifications ("Propagation" TLV with value 1 in PCEP-ERROR or NOTIFICATION objects). Each PCEP peer MUST decrement the TTL value before propagating the message. When the TTL value becomes 0, the message is no more propagated. If the message to be propagated is request-specific ("Propagation" TLV with value 1 in PCEP-ERROR or NOTIFICATION objects, and "Notification Type" TLV with value 1 in a NOTIFICATION object), and there is no TTL or DIFFUSION-LIST object included, the message MUST reach the source PCC (or alternatively the target PCE). 5.5.2. DIFFUSION-LIST Object (DLO) The DIFFUSION-LIST Object can be carried within a PCErr and a PCNtf message and can either be used in a message sent by a PCC to a PCE or vice versa. The DLO MAY be used with propagated errors (TLV "Propagation"at value 1 in PCEP-ERROR object) and request-specific propagated notifications (i.e., "Notification Behavior Type 4"). Furtheremore, it MUST be used with non request-specific propagated notifications (i.e., "Notification Behavior Type 3"). DIFFUSION-LIST Object-Class is TBD (Suggested 41). DIFFUSION-LIST Object-Type is 1. The format of the DIFFUSION-LIST object body is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Flags | Target-type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // (Sub-objects) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Reserved (8 bits): This field MUST be set to zero on transmission and MUST be ignored on receipt. Flags (16 bits): No flags are currently defined. Unassigned flags MUST be set to zero on transmission and MUST be ignored on receipt. Pouyllau, et al. Expires September 1, 2018 [Page 10] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 Target-type (8 bits): restricts the diffusion to certain peers. The following values are currently defined: 0: Any PCEP peer indicated in the list must be reached. 1: Only PCEs must be reached (and not PCC). 2: All PCEP peers with which a session is still opened must be reached. The DLO is made of sub-objects similar to the IRO defined in [RFC5440]. The following sub-object types are supported. Type Sub-object 1 IPv4 address 2 IPv6 address 4 Unnumbered Interface ID 5 OSPF area ID 32 Autonomous System number 33 Explicit eXclusion Route Sub-object (EXRS) If the error or notification codes target specific PCEP peers, a DIFFUSION-LIST object avoids partially flooding all PCEP peers. Any PCEP peer receiving a PCErr or PCNTf message containing a PCEP-ERROR or a NOTIFICATION object with a TLV "Propagation" at value 1 and where a DLO appears, MUST remove from the DLO the addresses of the PCEP peers to whom it will propagate the message, before sending them the message. This is performed by adding the PCEP peer addresses to the Explicit eXclusion Route Sub-object of the DLO. If a DIFFUSION- LIST object is empty, the PCEP peer MUST NOT propagate the message to any peer. Note that, a Diffusion List Object could contain strict or loose addresses to refer to a network domain (e.g. an Autonomous System number, an OSPF area, an IP address). Hence, the PCEP peers targeted by the message would be the PCEP peers covering the corresponding domain. If an address is loose, each time a PCEP peer forwards a message to another PCEP peer of this address, it MUST add it own address to the Explicit eXclusion Route Sub-object (EXRS) of the DLO for any forwarded messages. Hence, a PCE SHOULD avoid forwarding the same message repeated to the same set of peers. Finally, when an address is loose, the forwarding SHOULD be restrained indicating what type of PCEP peers are targeted (i.e. PCE and/or PCC). Hence, a Target-Type is specified. Pouyllau, et al. Expires September 1, 2018 [Page 11] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 5.5.3. Rules Applied to Existing Errors and Notifications Many existing normative references states on error definitions (see for instance [RFC5440], [RFC5441],[RFC5455], [RFC5521], [RFC5557], [RFC5886], [RFC6006], [RFC8231], [RFC8232],[RFC8253], [RFC8281], [RFC8306], [I-D.ietf-pce-lsp-setup-type], [I-D.ietf-pce-association-group]). According to the definitions provided in this document, the follwoing rules are applicable: Error-type 1, described in [RFC5440], relates to PCEP session establishement failures. All errors of this type are local (not to be propagated). Hence, if a "Propagation" TLV is added to the error message it MUST be set to value 0. Error-values 1,2,6,7 have a high level of criticality. Hence, if the "Error- criticality" TLV is included within a PCErr message of type 1 and value 1,2,6 or 7, it MUST have a value of 2. Error-type 2,3,4, "Capability not supported", "Unknown object" and "Not supported object" respectively, described in [RFC5440]: errors of this type MAY be propagated using the TLV "Propagation". Their level of criticality is defined as leading to cancel the path computation request (cf. [RFC5440]). Hence, if the "Error- criticality" TLV is included, it MUST have a value of 1. The error-value 4 of error-type 4 ("Unsupported parameter") associated to the BRPC procedure [RFC5441] SHOULD contain the "Propagation" TLV with a DIFFUSION-LIST object requesting a propagation to the PCC at the origin of the request. Error-type 5 refers to "Policy violation", error values for this type have been defined in [RFC5440], [RFC5541], [RFC5557], [RFC5886] and [RFC6006]. In [RFC5440], it is specified that the path computation request MUST be cancelled when an error of type 5 occurs. Hence, if the "Error-criticality" TLV is included, it MUST have a value of 1. As such errors might be conveyed to several PCEs, the "Propagation" TLV MAY be used. Error-type 6 described as "Mandatory object missing" in [RFC5440], leads to the cancellation of the path computation request. Hence, if the "Error-criticality" TLV is included, it MUST have a value of 1. The "Propagation" TLV MAY be used with such errors. The error-value of 4 for Monitoring object missing defined in [RFC5886] is no exception to the rule. Error-type 7 is described as "synchronized path computation request missing". In [RFC5440], it is specified that the reffered synchronized path computation request MUST be cancelled when an error of type 5 occurs. Hence, if the "Error-criticality" TLV is Pouyllau, et al. Expires September 1, 2018 [Page 12] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 included, it MUST have a value of 1. The "Propagation" TLV MAY be used with such errors. Error-type 8 is raised when a PCE receives a PCRep with an unknown request reference. If the "Propagation" TLV is used with error- type 8, it SHOULD be set at a value of 0. The "Error-criticality" TLV is not particularly relevant for error-type 8. Hence, if it used, it MUST have the value of 0. Error-type 9 is raised when a PCE attempts to establish a second PCEP session. The existing session must be preserved. Hence, if the "Error-criticality" TLV is included, it MUST have a value of 0. By definition, such an error message SHOULD NOT be propagated. Thus, if the "Propagation" TLV is used with error-type 9, it SHOULD be set at a value of 0. Error-type 10 which refers to the reception of an invalid object as described in [RFC5440] no indication is provided on the cancellation of the path computation request. Hence, if the "Error-criticality" TLV is included, it MUST have a value of 0. The "Propagation" TLV MAY be used with such errors with any value depending on the expected behavior. Error-type 11 relates to "Unrecognized EXRS subobject" and is described in [RFC5521]. No path computation request cancellation is required by [RFC5521]. Hence, if the "Error-criticality" TLV is included, it MUST have a value of 0. The "Propagation" TLV MAY be used with such errors with any value depending on the expected behavior. Error-type 12 refers to "Diffserv-aware TE error" and is described in [RFC5455]. Such errors are raised when the CLASSTYPE object of a PCReq is recognized but not supported by a PCE. [RFC5455] does not state about the path computation request when such errors are met. Hence, both "Propagation" and "Error-criticality" TLVs COULD be used within such error-types' messages and set to any specified values. Error-type 13 on "BRPC procedure completion failure" is described in [RFC5441]. [RFC5441] states that in such cases, the PCErr message MUST be relayed to the PCC. Hence, such messages SHOULD contain a "Propagation" TLV and a DIFFUSION-LIST object with a Target-Type of 0 and corresponding adresses or with a Target-Type of 2. It is not specified in [RFC5441] whether the path computation request should be canceled or not. If the procedure is not supported, it does not necessarily imply to cancel the path computation request if another procedure is able to read and write Pouyllau, et al. Expires September 1, 2018 [Page 13] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 VSPT objects. Thus, the "Error-criticality" TLV MAY be used with any value depending on the expected behavior. Error-type 15 refers to "Global Concurrent Optimization Error" defined in [RFC5557]. [RFC5557] states that the corresponding global concurrent path optimization MUST be cancelled at the PCC. Hence, if the "Error-criticality" TLV is included, it MUST have a value of 1. The "Propagation" TLV MAY be used with such errors. Error-type 16 relates to "P2MP Capability Error" defined in [RFC6006]. Such errors lead to the cancellation of the path computation request. Hence, if the "Error-criticality" TLV is included, it MUST have a value of 1. The "Propagation" TLV MAY be used with such errors. Error-type 17, titled "P2MP END-POINTS Error" is defined [RFC6006]. Such errors are thrown when a PCE tries to add or prune nodes to or from a P2MP Tree. [RFC6006] does not specify if such errors lead to cancel the path computation request. Hence, the "Error-criticality" and "Propagation" TLVs MAY be used with this type of error with any value depending on the expected behavior. Error-type 18 of "P2MP Fragmentation Error" is described [RFC6006] which does not specify whether the path computation request should be cancelled. But, as messages are fragmented, it is natural to think that the PCE should wait at least a bit for further messages. The "Error-criticality" TLV MAY be included in such error messages and is particularly adapted to differ the semantic of the same error-type message: if it is included with a value of 0 then the PCE will still wait for further fragmented messages, when this waiting time ends, the TLV can be included with a value of 1 in order to finally cancel the request. The "Propagation" TLV MAY also be used with such errors. Error-type 19 of "Invalid Operation" is described in [RFC8231] and [RFC8281], which implies a wrong capability description for PCEP session. In this case, the PCErr message MUST be returned to PCC, and this message should contain a "Propagation" TLV and a DIFFUSION-LIST object with a Target-Type of 0 or 2. The "Error- criticality" TLV should be set to 2 in order to guanrantee the termination of PCEP session. Error-type 20 of "LSP State Synchronization Error" is described in [RFC8231] and [RFC8232], which cannot successfully sync up the LSP states. In this case, the "Error-criticality" TLV should be set to 2 in order to guanrantee the termination of PCEP session. The "Propagation" TLV MAY also be used with such errors. Pouyllau, et al. Expires September 1, 2018 [Page 14] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 Error-type 21 of "Invalid traffic engineering path setup type" is described in [I-D.ietf-pce-lsp-setup-type] . Such errors failed to find a matched path setup type and the PCEP sessions MUST be closed. In this case, the "Error-criticality" TLV should be set to 2 in order to guanrantee the termination of PCEP session. The "Propagation" TLV MAY also be used with such errors. Error-type 23 of "Bad parameter value" is described in [RFC8281] . Such errors occur when there is a conflict in path name of C flag not set for PCE initiation. In this case, the "Error-criticality" TLV may be set to either 0 or 1 to indicate whether the request is still valid, with the PCEP session open. The "Propagation" TLV MAY also be used with such errors. Error-type 24 of "LSP instantiation error" is described in [RFC8281] . Such errors occur when PCC detects problems when establishing the path, the message MUST relay to the PCE, therefore the "Propogation" TLV must be contained. The "Error- criticality" TLV may be set to either 0 or 1 to indicate whether the request is still valid, with the PCEP session open. Error-type 25 of "PCEP StartTLS failure" is described in [RFC8253]. Such errors indicate the security issue in transport layer. In this case, the "Error-criticality" TLV should be set to 2 in order to close the PCEP session. The "Propagation" TLV MAY also be used with such errors, depending on the detailed security conditions. Error-type 26 of "Association Error " is described in [I-D.ietf-pce-association-group] . Such errors occur when there is problem for LSP association. In this case, the "Error- criticality" TLV should be set to either 0 or 1 to indicate whether the request is still valid, with the PCEP session open. The "Propagation" TLV MAY also be used with such errors. Among the existing normative references, only the [RFC5440] defines some notification-types and values. The recommendations with respect to the TLVs definitions provided in this document are the followings: Notitification-type=1, Notification-value=1 or 2: a PCC, respectively a PCE, cancels a set of pending requests, such a notification SHOULD be propagated to the list of PCEP peers which were implied in the path computation requests. Hence, the NOTIFICATION object SHOULD contains the "Propagation" TLV with value 1 and the "Notification Type" TLV with value 1, together with a DIFFUSION-LIST object containing the list of PCEP peers. Pouyllau, et al. Expires September 1, 2018 [Page 15] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 Notitification-type=2, Notification-value=1 or 2: indicates to the PCC that the PCE is, respectively is no longer, in an overloaded state. Such a notification can be propagated or stay local. It is therefore RECOMMENDED to specify this behavior using the "Propagation" TLV and associated restriction mechanims. 6. Error and Notification Scenarios This section provides some examples depicting how the error and notification types described above can be used in a PCEP session. The origin of the errors or notifications is only illustrative and has no normative purpose. Sometimes the PCE features behind may be implementation-specific (e.g. detection of flooding). This section does not provide scenarios for errors with a high-level of critcity (i.e., Error behaviors 3 and 6) since such errors are very specific and until now have been normalized only during the session establishment (error-type of 1). 6.1. Error Behavior Type 1 In this example, a PCC attempts to establish a second PCEP session with the same PCE for another request. Consequently the PCE sends back an error message with error-type 9. This error stays local and does not affect the former session. The second session is ignored. If the "Propagation" TLV and "Error-criticality" TLV are used, they should be both set to value 0. +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ 1) Path computation | | event | | 2) PCE selection |----- Open Message--->| |<--- Open message ----| 3) Path computation |---- PCReq message--->| request X sent to | |4) Path computation the selected PCE | | request queued | | 5) Path computation | | event | | 6) PCE selection | | |----- Open Message--->|8) Session already | |opened |<--- PCErr message----| Error-type=9 | | Pouyllau, et al. Expires September 1, 2018 [Page 16] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 6.2. Error Behavior Type 2 In this example, the PCC sends a DiffServ-aware path computation request. If the PCE receiving the request does not support the indicated class-type, it thus sends back a PCErr message with error- type=12 and error-value=1. If the "Propagation" TLV and "Error- criticality" TLV are present, they should carry value 0 and value 1 respectively. Consequently, the request is cancelled. +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ 1) Path computation | | event | | 2) PCE selection | | 3) Path computation |---- PCReq message--->| request X sent to | |4) Path computation the selected PCE | | request queued | | | |5) DiffServ class-type | | not supported | |6) Path computation | | request X | | cancelled |<--- PCErr message----| Error-type=12 | | 6.3. Error Behavior Type 4 In this example, a PCC sends a path computation requests with no P flag set (e.g. END-POINT object with P-flag cleared). This is detected by another PCE in the sequence. The path computation request can thus be treated but the P-Flag will be ignored. Hence, this error is not critical but the source PCC should be informed of this fact. So, a PCErr message with error-type 10 ("Reception of an invalid object"). The PCEP-ERROR object of the message contains a "Propagation" TLV at value 1 and a "Error-criticality" TLV at value 0. It is hence propagated backwardly to the source PCC. Pouyllau, et al. Expires September 1, 2018 [Page 17] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 +-+-+ +-+-+-+-+ +-+-+ |PCC| |PCE|PCC| |PCE| +-+-+ +-+-+-+-+ +-+-+ |---- PCReq message-->| | | | | | |---- PCReq message--->| | | | | | |1) Parameter is | | | not supported | | | | |<--- PCErr message----| Error-type=10 |<--- PCErr message---| | | | | 6.4. Error Behavior Type 5 In this example, PCEs are using the BRPC procedure to treat a path computation request [RFC5441]. However, one of the PCEs does not support a parameter of the request. Hence, a PCErr message with error-type 4 and error-value 4 is sent by this PCE and has to be forwarded to the source PCC. The PCEP-ERROR object includes a "Propagation" TLV at value 1 and "Error-criticality" TLV at value 1 and the message is propagated backwardly to the source PCC. Consequently, the request is cancelled. +-+-+ +-+-+-+-+ +-+-+ |PCC| |PCE|PCC| |PCE| +-+-+ +-+-+-+-+ +-+-+ |---- PCReq message-->| | | | | | |---- PCReq message--->| | | | | | |1) Unsupported | | | Parameter BRPC | | |2) Path | | | computation | | | request X | | | cancelled | |<--- PCErr message----| Error-type=4 |<--- PCErr message---| | | | | Pouyllau, et al. Expires September 1, 2018 [Page 18] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 6.5. Notification Behavior Type 1 In this example, a PCE sends a non request-specific notification indicating that, due to multiple sendings (or for other reasons), further requests from this PCC will be ignored. Hence, a PCNtf message is sent to the PCC with a NOTIFICATION object including the "Propagation" TLV at value 0 and a "Notification Type" TLV at value 0. +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ | | | |1) Further requests | | will be ignored | | |<--- PCNtf message----| | | 6.6. Notification Behavior Type 2 In this example, a PCE sends a request-specific notification indicating that, a set of pending requests are cancelled (e.g. notification-type=1, notification-value=1 as described in [RFC5440]). Hence, a PCNtf message is sent to the PCC with a NOTIFICATION object including a "Propagation" TLV at value 0 and a "Notification Type" TLV at value 1. +-+-+ +-+-+ |PCC| |PCE| +-+-+ +-+-+ 1) Path computation | | event | | 2) PCE selection | | 3) Path computation |---- PCReq message--->| request X sent to | |4) Path the selected PCE | | computation | | request queued | | | |5) Pending requests | | cancelled | | |<--- PCNtf message----|Notification-Type=1 | | Pouyllau, et al. Expires September 1, 2018 [Page 19] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 6.7. Notification Behavior Type 3 In this example, a PCE is temporarily congested. A PCNtf message with a NOTIFICATION object containing a "Propagation" TLV at value 1 and a "Notification Type" TLV at value 0 is send to a PCEP peer. This notification messge is propagated to a sequence of PCEs if necessary. Here, PCEk is congested and send a PCNtf message to PCEi with the approapriate TLVs, an OVERLOAD object as described in [RFC5886], and a DIFFUSION-LIST object indicating PCEj as a target of the notification. +-+--+ +-+--+ +-+--+ |PCEj| |PCEi| |PCEk| +-+--+ +-+--+ +-+--+ | | | | | |1)PCE is busy | | | for M minutes | | | (time-out update) | |<--- PCNtf message----| Notification-type=2 |<--- PCNtf message---| | 6.8. Notification Behavior Type 4 In this example, a PCE receives a request but it is temporarily congested. However, it can treat the request after few minutes which might cause some time-out in the predecessor PCE(s). Hence, a PCNtf message with a NOTIFICATION object containing a "Propagation" TLV at value 1 and a "Notification Type" TLV at value 1 is sent to the PCC and propagated backwardly in the sequence. Such a notification could include an OVERLOAD object as described in [RFC5886]. +-+-+ +-+-+-+-+ +-+-+ |PCC| |PCE|PCC| |PCE| +-+-+ +-+-+-+-+ +-+-+ |---- PCReq message-->| | | | | | |---- PCReq message--->| | | | | | |1)PCE is busy but | | | will answer to X | | | in M minutes | | | (time-out update) | |<--- PCNtf message----| Notification-type=2 |<--- PCNtf message---| | Pouyllau, et al. Expires September 1, 2018 [Page 20] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 7. Security Considerations Within the introduced set of TLVs, the "Propagation" TLV affects PCEP security considerations since it forces propagation behaviors. Thus, a PCEP implementation SHOULD activate stateful mechanism when receiving PCEP-ERROR or NOTIFICATION object including this TLV in order to avoid DoS attacks. 8. IANA Considerations IANA maintains a registry of PCEP parameters. This includes a sub- registry for PCEP Objects. IANA is requested to make an allocation from the sub-registry as follows. The values here are suggested for use by IANA. 8.1. PCEP TLV Type Indicators As described in Section 5.5 the newly defined TLVs allows a PCE to enforce specific error and notification behaviors within PCEP-ERROR and NOTIFICATION objects. IANA is requested to make the following allocations from the "PCEP TLV Type Indicators" sub-registry. Value Description Reference TBD(suggest 33) Propagation this document TBD(suggest 34) Error-criticality this document TBD(suggest 35) Notification type this document 8.2. New DLO object Pouyllau, et al. Expires September 1, 2018 [Page 21] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 Object-class Value Object-Type and Name Reference TBD(suggest 41) 1: Diffusion list object this document Target-Type Value Meaning Reference 0 Any PCEP peers this document 1 PCEs but excludes PCC-only peers this document 2 PCEs and PCCs this document with which a session is still opened Subobjects Reference 1: IPv4 prefix this document 2: IPv6 prefix this document 4: Unnumbered Interface ID this document 5: OSPF Area ID this document 32: Autonomous system number this document 33: Explicit Exclusion Route subobject (EXRS) this document 9. References 9.1. Normative References [I-D.ietf-pce-association-group] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H., Dhody, D., and Y. Tanaka, "PCEP Extensions for Establishing Relationships Between Sets of LSPs", draft- ietf-pce-association-group-04 (work in progress), August 2017. [I-D.ietf-pce-lsp-setup-type] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J. Hardwick, "Conveying path setup type in PCEP messages", draft-ietf-pce-lsp-setup-type-08 (work in progress), January 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Pouyllau, et al. Expires September 1, 2018 [Page 22] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, . [RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux, "A Backward-Recursive PCE-Based Computation (BRPC) Procedure to Compute Shortest Constrained Inter-Domain Traffic Engineering Label Switched Paths", RFC 5441, DOI 10.17487/RFC5441, April 2009, . [RFC5455] Sivabalan, S., Ed., Parker, J., Boutros, S., and K. Kumaki, "Diffserv-Aware Class-Type Object for the Path Computation Element Communication Protocol", RFC 5455, DOI 10.17487/RFC5455, March 2009, . [RFC5521] Oki, E., Takeda, T., and A. Farrel, "Extensions to the Path Computation Element Communication Protocol (PCEP) for Route Exclusions", RFC 5521, DOI 10.17487/RFC5521, April 2009, . [RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of Objective Functions in the Path Computation Element Communication Protocol (PCEP)", RFC 5541, DOI 10.17487/RFC5541, June 2009, . [RFC5557] Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path Computation Element Communication Protocol (PCEP) Requirements and Protocol Extensions in Support of Global Concurrent Optimization", RFC 5557, DOI 10.17487/RFC5557, July 2009, . [RFC5886] Vasseur, JP., Ed., Le Roux, JL., and Y. Ikejiri, "A Set of Monitoring Tools for Path Computation Element (PCE)-Based Architecture", RFC 5886, DOI 10.17487/RFC5886, June 2010, . [RFC6006] Zhao, Q., Ed., King, D., Ed., Verhaeghe, F., Takeda, T., Ali, Z., and J. Meuric, "Extensions to the Path Computation Element Communication Protocol (PCEP) for Point-to-Multipoint Traffic Engineering Label Switched Paths", RFC 6006, DOI 10.17487/RFC6006, September 2010, . Pouyllau, et al. Expires September 1, 2018 [Page 23] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 [RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE", RFC 8231, DOI 10.17487/RFC8231, September 2017, . [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, . [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, "PCEPS: Usage of TLS to Provide a Secure Transport for the Path Computation Element Communication Protocol (PCEP)", RFC 8253, DOI 10.17487/RFC8253, October 2017, . [RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for PCE-Initiated LSP Setup in a Stateful PCE Model", RFC 8281, DOI 10.17487/RFC8281, December 2017, . [RFC8306] Zhao, Q., Dhody, D., Ed., Palleti, R., and D. King, "Extensions to the Path Computation Element Communication Protocol (PCEP) for Point-to-Multipoint Traffic Engineering Label Switched Paths", RFC 8306, DOI 10.17487/RFC8306, November 2017, . 9.2. Informational References [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006, . [RFC7470] Zhang, F. and A. Farrel, "Conveying Vendor-Specific Constraints in the Path Computation Element Communication Protocol", RFC 7470, DOI 10.17487/RFC7470, March 2015, . Authors' Addresses Pouyllau, et al. Expires September 1, 2018 [Page 24] Internet-Draft Extensions to PCEP for Enhanced errors February 2018 Helia Pouyllau Alcatel-Lucent Route de Villejust NOZAY 91620 FRANCE Phone: + 33 (0)1 30 77 63 11 Email: helia.pouyllau@alcatel-lucent.com Remi Theillaud Marben Products 176 rue Jean Jaures Puteaux 92800 FRANCE Phone: + 33 (0)1 79 62 10 22 Email: remi.theillaud@marben-products.com Julien Meuric France Telecom Orange 2, avenue Pierre Marzin Lannion 22307 FRANCE Email: julien.meuric@orange-ftgroup.com Haomian Zheng (Editor) Huawei Technologies F3-1B, Huawei Industrial Base, Bantian, Longgang District Shenzhen, Guangdong 518129 P.R.China Email: zhenghaomian@huawei.com Xian Zhang Huawei Technologies G1-2, Huawei Industrial Base, Bantian, Longgang District Shenzhen, Guangdong 518129 P.R.China Email: zhang.xian@huawei.com Pouyllau, et al. Expires September 1, 2018 [Page 25]