PCE Working Group E. Crabbe
Internet-Draft Individual Contributor
Intended status: Standards Track I. Minei
Expires: September 5, 2017 Google, Inc.
S. Sivabalan
Cisco Systems, Inc.
R. Varga
Pantheon Technologies SRO
March 4, 2017
PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model
draft-ietf-pce-pce-initiated-lsp-08
Abstract
The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to Path Computation Clients (PCCs) requests.
The extensions for stateful PCE provide active control of
Multiprotocol Label Switching (MPLS) Traffic Engineering Label
Switched Paths (TE LSP) via PCEP, for a model where the PCC delegates
control over one or more locally configured LSPs to the PCE. This
document describes the creation and deletion of PCE-initiated LSPs
under the stateful PCE model.
Requirements Language
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].
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 http://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."
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This Internet-Draft will expire on September 5, 2017.
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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Architectural Overview . . . . . . . . . . . . . . . . . . . 4
3.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Operation Overview . . . . . . . . . . . . . . . . . . . 4
4. Support of PCE-initiated LSPs . . . . . . . . . . . . . . . . 6
4.1. Stateful PCE Capability TLV . . . . . . . . . . . . . . . 6
5. PCE-initiated LSP Instantiation and Deletion . . . . . . . . 7
5.1. The LSP Initiate Message . . . . . . . . . . . . . . . . 7
5.2. The R flag in the SRP Object . . . . . . . . . . . . . . 8
5.3. LSP Instantiation . . . . . . . . . . . . . . . . . . . . 9
5.3.1. The Create Flag . . . . . . . . . . . . . . . . . . . 11
5.3.2. The SPEAKER-IDENTITY-ID TLV . . . . . . . . . . . . . 11
5.4. LSP Deletion . . . . . . . . . . . . . . . . . . . . . . 12
6. LSP delegation and Cleanup . . . . . . . . . . . . . . . . . 12
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8.1. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . 14
8.2. LSP Object . . . . . . . . . . . . . . . . . . . . . . . 14
8.3. SRP object . . . . . . . . . . . . . . . . . . . . . . . 14
8.4. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 14
8.5. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9.1. Malicious PCE . . . . . . . . . . . . . . . . . . . . . . 15
9.2. Malicious PCC . . . . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . 17
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
[RFC5440] describes the Path Computation Element Communication
Protocol (PCEP). PCEP defines the communication between a Path
Computation Client (PCC) and a Path Control Element (PCE), or between
PCE and PCE, enabling computation of Multiprotocol Label Switching
(MPLS) for Traffic Engineering Label Switched Path (TE LSP)
characteristics.
Stateful pce [I-D.ietf-pce-stateful-pce] specifies a set of
extensions to PCEP to enable stateful control of TE LSPs between and
across PCEP sessions in compliance with [RFC4657]. It includes
mechanisms to effect LSP state synchronization between PCCs and PCEs,
delegation of control of LSPs to PCEs, and PCE control of timing and
sequence of path computations within and across PCEP sessions and
focuses on a model where LSPs are configured on the PCC and control
over them is delegated to the PCE.
This document describes the setup, maintenance and teardown of PCE-
initiated LSPs under the stateful PCE model, without the need for
local configuration on the PCC, thus allowing for a dynamic network
that is centrally controlled and deployed.
2. Terminology
This document uses the following terms defined in [RFC5440]: PCC,
PCE, PCEP Peer.
This document uses the following terms defined in [RFC8051]: Stateful
PCE, Delegation.
This document uses the following terms defined in
[I-D.ietf-pce-stateful-pce]: Redelegation Timeout Interval, State
Timeout Interval, LSP State Report, LSP Update Request.
The following terms are defined in this document:
PCE-initiated LSP: LSP that is instantiated as a result of a request
from the PCE.
The message formats in this document are specified using Routing
Backus-Naur Format (RBNF) encoding as specified in [RFC5511].
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3. Architectural Overview
3.1. Motivation
[I-D.ietf-pce-stateful-pce] provides active control over LSPs that
are locally configured on the PCC. This model relies on the Label
Edge Router (LER) taking an active role in delegating locally
configured LSPs to the PCE, and is well suited in environments where
the LSP placement is fairly static. However, in environments where
the LSP placement needs to change in response to application demands,
it is useful to support dynamic creation and tear down of LSPs. The
ability for a PCE to trigger the creation of LSPs on demand can make
possible agile software-driven network operation, and can be
seamlessly integrated into a controller-based network architecture,
where intelligence in the controller can determine when and where to
set up paths.
A possible use case is a software-driven network, where applications
request network resources and paths from the network infrastructure.
For example, an application can request a path with certain
constraints between two LSRs by contacting the PCE. The PCE can
compute a path satisfying the constraints, and instruct the head end
LSR to instantiate and signal it. When the path is no longer
required by the application, the PCE can request its teardown.
Another use case is dynamically adjusting aggregate bandwidth between
two points in the network using multiple LSPs. This functionality is
very similar to auto-bandwidth, but allows for providing the desired
capacity through multiple LSPs. This approach overcomes two of the
limitations auto-bandwidth can experience: 1) growing the capacity
between the endpoints beyond the capacity of individual links in the
path and 2) achieving good bin-packing through use of several small
LSPs instead of a single large one. The number of LSPs varies based
on the demand, and LSPs are created and deleted dynamically to
satisfy the bandwidth requirements.
Another use case is demand engineering, where a PCE with visibility
into both the network state and the demand matrix can anticipate and
optimize how traffic is distributed across the infrastructure. Such
optimizations may require creating new paths across the
infrastructure.
3.2. Operation Overview
A PCC or PCE indicates its ability to support PCE-provisioned dynamic
LSPs during the PCEP Initialization Phase via a new flag in the
STATEFUL-PCE-CAPABILITY TLV (see details in Section 4.1).
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The decision when to instantiate or delete a PCE-initiated LSP is out
of the scope of this document. To instantiate or delete an LSP, the
PCE sends a new message, the Path Computation LSP Initiate Request
(PCInitiate) message to the PCC. The LSP Initiate Request MUST
include the SRP and LSP objects ([I-D.ietf-pce-stateful-pce]), and
the LSP object MUST include the Symbolic Path Name TLV and MUST have
a PLSP-ID ([I-D.ietf-pce-stateful-pce]) of 0.
For an instantiation operation, the PCE MUST include the ERO and END-
POINTS object and may include various attributes as per [RFC5440].
The PCC creates the LSP using the attributes communicated by the PCE,
and local values for the unspecified parameters. It assigns a unique
PLSP-ID for the LSP and automatically delegates the LSP to the PCE.
It MUST also generate an LSP State Report (PCRpt) for the LSP,
carrying the newly assigned PLSP-ID and indicating the delegation via
the Delegate flag in the LSP object. In addition to the Delegate
flag, the PCC MUST also set the Create flag in the LSP object (see
Section 5.3.1), to indicate that the LSP was created as a result of a
PCInitiate message and SHOULD include the optional SPEAKER-IDENTITY-
ID TLV defined in [I-D.ietf-pce-stateful-sync-optimizations]
identifying the PCE that requested the LSP creation. This PCRpt
message MUST include the SRP object, with the SRP-id-number used in
the SRP object of the PCInitate message. The PCE MAY update the
attributes of the LSP via subsequent PCUpd messages. Subsequent LSP
State Report and LSP Update Request for the LSP will carry the PCC-
assigned PLSP-ID, which uniquely identifies the LSP. See details in
Section 5.3.
Once instantiated, the delegation procedures for PCE-initiated LSPs
are the same as for PCC-initiated LSPs as described in
[I-D.ietf-pce-stateful-pce], with the exception that the PCC cannot
revoke a delegation for a PCE-initiated LSP. This applies to the
case of a PCE failure as well. In order to allow for network cleanup
without manual intervention, the PCC SHOULD support removal of PCE-
initiated LSPs as one of the behaviors applied on expiration of the
State Timeout Interval [I-D.ietf-pce-stateful-pce]. The behavior
SHOULD be picked based on local policy, and can result either in LSP
removal, or into reverting to operator-defined default parameters.
See details in Section 6. A PCE MAY return a delegation to the PCC
in order to facilitate re-delegation of its LSPs to an alternate PCE.
To indicate a delete operation, the PCE MUST use the new R flag in
the SRP object in a PCInitiate message as described in Section 5.2.
As a result of the deletion request, the PCC MUST remove all state
related to the LSP, and send a PCRpt with the R flag set in the LSP
object for the removed state. See details in Section 5.4.
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LSP State Synchronization procedures are described in section 5.4 of
[I-D.ietf-pce-stateful-pce]. During State Synchronization, a PCC
reports the state of its LSPs to the PCE using PCRpt messages and
setting the SYNC flag in the LSP Object. For PCE-initiated LSPs, the
PCC MUST also include the Create Flag in the LSP Object and SHOULD
include the SPEAKER-IDENTITY-ID TLV identifying the PCE that
requested the LSP creation. At the end of state synchronization, the
PCE SHOULD do a sanity check between the reported PCE-Initiated LSPs
and local configurations at PCE to initiate LSPs. For any mismatch,
the PCE SHOULD send a PCInitiate message to either initiate (again)
or remove the LSP.
4. Support of PCE-initiated LSPs
A PCEP speaker indicates its ability to support PCE-provisioned
dynamic LSPs during the PCEP Initialization phase. The Open Object
in the Open message contains the "Stateful PCE Capability" TLV,
defined in [I-D.ietf-pce-stateful-pce]. A new flag, the I (LSP-
INSTANTIATION-CAPABILITY) flag is introduced to indicate support for
instantiation of PCE-initiated LSPs. A PCE can initiate LSPs only
for PCCs that advertised this capability and a PCC will follow the
procedures described in this document only on sessions where the PCE
advertised the I flag.
4.1. Stateful PCE Capability TLV
The format of the STATEFUL-PCE-CAPABILITY TLV is shown in the
following figure:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |I|S|U|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+
Figure 1: STATEFUL-PCE-CAPABILITY TLV format
The type of the TLV is defined in [I-D.ietf-pce-stateful-pce] and it
has a fixed length of 4 octets.
The value comprises a single field - Flags (32 bits). The U and S
bits are defined in [I-D.ietf-pce-stateful-pce] and
[I-D.ietf-pce-stateful-sync-optimizations] respectively.
I (LSP-INSTANTIATION-CAPABILITY - 1 bit): If set to 1 by a PCC, the
I Flag indicates that the PCC allows instantiation of an LSP by a
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PCE. If set to 1 by a PCE, the I flag indicates that the PCE may
attempt to instantiate LSPs. The LSP-INSTANTIATION-CAPABILITY
flag must be set by both PCC and PCE in order to support PCE-
initiated LSP instantiation.
Unassigned bits are considered reserved. They MUST be set to 0 on
transmission and MUST be ignored on receipt.
5. PCE-initiated LSP Instantiation and Deletion
To initiate an LSP, a PCE sends a PCInitiate message to a PCC. The
message format, objects and TLVs are discussed separately below for
the creation and the deletion cases.
5.1. The LSP Initiate Message
A Path Computation LSP Initiate Message is referred to as PCInitiate
message. It is a PCEP message sent by a PCE to a PCC to trigger LSP
instantiation or deletion. The Message-Type field of the PCEP common
header for the PCInitiate message is set to 12 (suggested value, to
be assigned by IANA). The PCInitiate message MUST include the SRP
and the LSP objects, and MAY contain other objects, as discussed
later in this section. Missing SRP and LSP objects in the PCInitiate
message MUST trigger the same PCErr procedures as specified in
[I-D.ietf-pce-stateful-pce]). for PCUpd. LSP instantiation is done
by sending a PCInitiate message with an LSP object with the reserved
PLSP-ID 0. LSP deletion is done by sending a PCInitiate message with
an LSP object carrying the PLSP-ID of the LSP to be removed and an
SRP object with the R flag set (see Section 5.2).
The format of a PCInitiate message for LSP instantiation is as
follows:
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<PCInitiate Message> ::= <Common Header>
<PCE-initiated-lsp-list>
Where:
<PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
[<PCE-initiated-lsp-list>]
<PCE-initiated-lsp-request> ::= (<PCE-initiated-lsp-instantiation>|
<PCE-initiated-lsp-deletion>)
<PCE-initiated-lsp-instantiation> ::= <SRP>
<LSP>
<END-POINTS>
<ERO>
[<attribute-list>]
<PCE-initiated-lsp-deletion> ::= <SRP>
<LSP>
Where:
<attribute-list> is defined in [RFC5440] and extended by
PCEP extensions.
The SRP object is used to correlate between initiation requests sent
by the PCE and the error reports and state reports sent by the PCC.
Every request from the PCE receives a new SRP-ID-number. This number
is unique per PCEP session and is incremented each time an operation
(initiation, update, etc) is requested from the PCE. The value of
the SRP-ID-number MUST be echoed back by the PCC in PCErr and PCRpt
messages to allow for correlation between requests made by the PCE
and errors or state reports generated by the PCC. Details of the SRP
object and its use can be found in [I-D.ietf-pce-stateful-pce].
5.2. The R flag in the SRP Object
The format of the SRP object is shown Figure 2:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRP-ID-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The SRP Object format
The type object is defined in [I-D.ietf-pce-stateful-pce].
A new flag is defined to indicate a delete operation initiated by the
PCE:
R (LSP-REMOVE - 1 bit): If set to 1, it indicates a removal request
initiated by the PCE.
5.3. LSP Instantiation
LSP instantiation is done by sending an PCInitiate Message with an
LSP object with the reserved PLSP-ID 0. The LSP is set up using
RSVP-TE, extensions for other setup methods are outside the scope of
this draft.
Receipt of a PCInitiate Message with a non-zero PLSP-ID and the R
flag in the SRP object set to zero MUST result in a PCErr message of
type 19 (Invalid Operation) and value to be assigned by IANA,
suggested value 8 (Non-zero PLSP-ID in LSP initiation request).
For an instantiation request of an RSVP-signaled LSP, the destination
address may be needed. The PCC may determine it from a provided
object (e.g., ERO) or a local decision. Alternatively, the END-
POINTS object MAY be included to explicitly convey the destination
addresses to be used in the RSVP-TE signaling. The source address
may be either specified or left up to the PCC decision using the
0.0.0.0 value. For LSPs to be setup by other means (e.g., Segment
Routing), the END-POINTS object SHOULD be omitted.
The ERO Object is mandatory for an instantiation request. It
contains the ERO for the LSP. If the ERO Object is missing, the PCC
MUST send a PCErr message with Error-type=6 (Mandatory Object
missing) and Error-value=9 (ERO Object missing).
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The LSP Object MUST include the SYMBOLIC-PATH-NAME TLV, which will be
used to correlate between the PCC-assigned PLSP-ID and the LSP. If
the TLV is missing, the PCC MUST send a PCErr message with Error-
type=10 (Invalid object) and Error-value to be assigned by IANA,
suggested value 8, (SYMBOLIC-PATH-NAME TLV missing). The symbolic
name used for provisioning PCE-initiated LSPs must not have conflict
with the LSP name of any existing LSP in the PCC. (Existing LSPs may
be either statically configured, or initiated by another PCE). If
there is conflict with the LSP name, the PCC MUST send a PCErr
message with Error-type to be assigned by IANA, suggested value 23
(Bad Parameter value) and Error-value=1 (SYMBOLIC-PATH-NAME in use).
The only exception to this rule is for LSPs for which the State
timeout timer is running (see Section 6).
The PCE MAY include various attributes as per [RFC5440]. The PCC
MUST use these values in the LSP instantiation, and local values for
unspecified parameters. After the LSP setup, the PCC MUST send a
PCRpt to the PCE, reflecting these values. The SRP object in the
PCRpt message MUST echo the value of the PCInitiate message that
triggered the setup. LSPs that were instantiated as a result of a
PCInitiate message MUST have the Create flag (Section 5.3.1) set in
the LSP object.
If the PCC determines that the LSP parameters proposed in the
PCInitiate message are unacceptable, it MUST trigger a PCErr with
error-type to be assigned by IANA, suggested value 24 (PCE
instantiation error) and error-value=1 (Unacceptable instantiation
parameters). If the PCC encounters an internal error during the
processing of the PCInitiate message, it MUST trigger a PCErr with
error-type to be assigned by IANA, suggested vlaue 24 (PCE
instantiation error) and error-value=2 (Internal error).
A PCC MUST relay to the PCE errors it encounters in the setup of PCE-
initiated LSP by sending a PCErr with error-type to be assigned by
IANA, suggeseted value 24 (PCE instantiation error) and error-value=3
(Signaling error). The PCErr MUST echo the SRP-ID-number of the
PCInitiate message. The PCEP-ERROR object SHOULD include the RSVP
Error Spec TLV (if an ERROR SPEC was returned to the PCC by a
downstream node). After the LSP is set up, errors in RSVP signaling
are reported in PCRpt messages, as described in
[I-D.ietf-pce-stateful-pce].
A PCC SHOULD be able to place a limit on either the number of LSPs or
the percentage of resources that are allocated to honor PCE-initiated
LSP requests. As soon as that limit is reached, the PCC MUST send a
PCErr message of type 19 (Invalid Operation) and value to be assigned
by IANA (PCE-initiated limit reached) and is free to drop any
incoming PCInitiate messages without additional processing.
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Similarly, the PCE SHOULD be able to place a limit on either the
number of LSP initiation requests pending for a particular PCC, or on
the time it waits for a response (positive or negative) to a
PCInitiate request from a PCC and MAY take further action (such as
closing the session or removing all its LSPs) if this limit is
reached.
On successful completion of the LSP instantiation, the PCC assigns a
PLSP-ID, and immediately delegates the LSP to the PCE by sending a
PCRpt with the Delegate flag set.
5.3.1. The Create Flag
The LSP object is defined in [I-D.ietf-pce-stateful-pce] and included
here for easy reference.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PLSP-ID |Flags |C| O |A|R|S|D|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// TLVs //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The LSP Object format
A new flag, the Create (C) flag is introduced. On a PCRpt message,
the C Flag set to 1 indicates that this LSP was created via a
PCInitiate message. The C Flag MUST be set to 1 on each PCRpt
message for the duration of existence of the LSP. The Create flag
allows PCEs to be aware of which LSPs were PCE-initiated (a state
that would otherwise only be known by the PCC and the PCE that
initiated them).
5.3.2. The SPEAKER-IDENTITY-ID TLV
The optional SPEAKER-IDENTITY-ID TLV defined in
[I-D.ietf-pce-stateful-sync-optimizations] MAY be included in the LSP
object in a PCRpt message, as an optional TLV for LSPs for which the
C flag is 1. The SPEAKER-IDENTITY-ID TLV identifies the PCE which
initiated the creation of the LSP on all PCEP sessions, a state that
would otherwise only be known by the PCC and the PCE that initiated
the LSP. If the TLV appears in a PCRpt for an LSP for which the C
flag is 0, the TLV MUST be ignored the and the PCE MUST send a PCErr
message with Error-type 23 ("Bad parameter value") and error value 2
("Speaker identity included for an LSP that is not PCE-initiated").
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5.4. LSP Deletion
PCE-initiated removal of a PCE-initiated LSP is done by setting the R
(remove) flag in the SRP Object in the PCInitiate message from the
PCE. The LSP is identified by the PLSP-ID in the LSP object. If the
PLSP-ID is unknown, the PCC MUST generate a PCErr with error type 19,
error value 3, "Unknown PLSP-ID" ([I-D.ietf-pce-stateful-pce]). A
PLSP-ID of zero removes all LSPs that were initiated by the PCE. If
the PLSP-ID specified in the PCInitiate message is not delegated to
the PCE, the PCC MUST send a PCErr message indicating "LSP is not
delegated" (Error code 19, error value 1 as per
[I-D.ietf-pce-stateful-pce]. If the PLSP-ID specified in the
PCInitiate message was not created by a PCE, the PCC MUST send a
PCErr message indicating that the LSP is not PCE-initiated, Error
code 19, error value to be assigned by IANA, suggested value 9 (LSP
is not PCE-initiated). Following the removal of the LSP, the PCC
MUST send a PCRpt as described in [I-D.ietf-pce-stateful-pce]. The
SRP object in the PCRpt MUST include the SRP-ID-number from the
PCInitiate message that triggered the removal. The R flag in the SRP
object MUST be set.
6. LSP delegation and Cleanup
PCE-initiated LSPs are automatically delegated by the PCC to the PCE
upon instantiation. The PCC MUST set the delegation bit to 1 in the
PCRpt that includes the assigned PLSP-ID. All subsequent messages
from the PCC to the PCE that initiated the LSP MUST have the
delegation bit set to 1. The PCC cannot revoke the delegation for
PCE-initiated LSPs for an active PCEP session. Sending a PCRpt
message with the delegation bit set to 0 to the PCE that initiated
the LSP results in a PCErr message of type 19 (Invalid Operation) and
error-value value to be assigned by IANA, suggested value 7,
(Delegation for PCE-initiated LSP cannot be revoked). The PCE MAY
further react by closing the session.
A PCE MAY return a delegation to the PCC, to allow for LSP transfer
between PCEs. Doing so MUST trigger the State Timeout Interval timer
([I-D.ietf-pce-stateful-pce]) for that particular LSP.
In case of PCEP session failure, control over PCE-initiated LSPs
reverts to the PCC at the expiration of the redelegation timeout. At
this point, the LSP is an "orphan" until the expiration of the State
Timeout timer. To obtain control of a PCE-initiated LSP, a PCE
(either the original or one of its backups) sends a PCInitiate
message, including just the SRP and LSP objects, and carrying the
PLSP-ID of the LSP it wants to take control of. On receipt of a
PCInitiate message with a PLSP-ID pointing to an orphan LSP, the PCC
MUST redelegate that LSP to the PCE. Any other non-zero PLSP-ID MUST
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result in the generation of a PCErr. The State Timeout timer for the
LSP is stopped upon the redelegation. After obtaining control of the
LSP, the PCE may remove it using the procedures described in this
document.
The State Timeout timer ensures that a PCE crash does not result in
automatic and immediate disruption for the services using PCE-
initiated LSPs. PCE-initiated LSPs are not be removed immediately
upon PCE failure. Instead, they are cleaned up on the expiration of
this timer. This allows for network cleanup without manual
intervention. The PCC SHOULD support removal of PCE-initiated LSPs
as one of the behaviors applied on expiration of the State Timeout
Interval [I-D.ietf-pce-stateful-pce]. The behavior SHOULD be picked
based on local policy, and can result either in LSP removal, or into
reverting to operator-defined default parameters.
7. Implementation Status
This section to be removed by the RFC editor.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC6982].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to RFC 6982, "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
Two vendors are implementing the extensions described in this draft
and have included the functionality in releases that will be shipping
in the near future. An additional entity is working on implementing
these extensions in the scope of research projects.
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8. IANA Considerations
8.1. PCEP Messages
IANA is requested to allocate a new message type within the "PCEP
Messages" sub-registry of the PCEP Numbers registry, as follows:
Value Meaning Reference
12 Initiate This document
8.2. LSP Object
[I-D.ietf-pce-stateful-pce] defines the LSP Object and requests that
IANA creates a registry to manage the value of the LSP Object's Flag
field. IANA is requested to allocate a new bit in the LSP Object
Flag Field registry, as follows:
Bit Description Reference
4 Create This document
8.3. SRP object
This document requests that a new sub-registry, named "SRP Object
Flag Field", is created within the "Path Computation Element Protocol
(PCEP) Numbers" registry to manage the Flag field of the SRP object.
New values are to be assigned by Standards Action [RFC5226]. Each
bit should be tracked with the following qualities: bit number
(counting from bit 0 as the most significant bit), description and
defining RFC.
The following values are defined in this document:
Bit Description Reference
31 LSP-Remove This document
8.4. STATEFUL-PCE-CAPABILITY TLV
[I-D.ietf-pce-stateful-pce] defines the STATEFUL-PCE-CAPABILITY TLV
and requests that IANA creates a registry to manage the value of the
STATEFUL-PCE-CAPABILITY TLV's Flag field. IANA is requested to
allocate a new bit in the STATEFUL-PCE-CAPABILITY TLV Flag Field
registry, as follows:
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Bit Description Reference
29 I (LSP-INSTANTIATION- This document
CAPABILITY)
8.5. PCEP-Error Object
IANA is requested to allocate new error types and error values within
the "PCEP-ERROR Object Error Types and Values" sub-registry of the
PCEP Numbers registry, as follows:
Error-Type Meaning
10 Invalid Object
Error-value=8: SYMBOLIC-PATH-NAME TLV missing
19 Invalid operation
Error-value=6: PCE-initiated LSP limit reached
Error-value=7: Delegation for PCE-initiated LSP cannot
be revoked
Error-value=8: Non-zero PLSP-ID in LSP initiation
request
Error-value=9: LSP is not PCE-initiated
Error-value=10: PCE-initiated operation-frequency limit
reached
23 Bad parameter value
Error-value=1: SYMBOLIC-PATH-NAME in use
Error-value=2: Speaker identity included for an LSP
that is not PCE-initiated
24 LSP instantiation error
Error-value=1: Unacceptable instantiation parameters
Error-value=2: Internal error
Error-value=3: Signaling error
9. Security Considerations
The security considerations described in [I-D.ietf-pce-stateful-pce]
apply to the extensions described in this document. Additional
considerations related to a malicious PCE are introduced.
9.1. Malicious PCE
The LSP instantiation mechanism described in this document allows a
PCE to generate state on the PCC and throughout the network. As a
result, it introduces a new attack vector: an attacker may flood the
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PCC with LSP instantiation requests and consume network and LSR
resources, either by spoofing messages or by compromising the PCE
itself.
A PCC can protect itself from such an attack by imposing a limit on
either the number of LSPs or the percentage of resources that are
allocated to honor PCE-initiated LSP requests. As soon as that limit
is reached, the PCC MUST send a PCErr message of type 19 (Invalid
Operation) and value to be assigned by IANA, suggested value 6 (PCE-
initiated LSP limit reached) and is free to drop any incoming
PCInitiate messages for LSP instantiation without additional
processing.
Rapid flaps triggered by the PCE can also be an attack vector. A PCC
can protect itself from such an attack by imposing a limit on the
number of flaps per unit of time that it allows a PCE to generate.
As soon as that limit is reached, a PCC MUST send a PCErr message of
type 19 (Invalid Operation) and value to be assigned by IANA,
suggested value 10 (PCE-initiated operation frequency reached) and is
free to treat the session as having reached the limit in terms of
resources allocated to honor PCE-initiated LSP requests, either
permanently or for a locally-defined cool-off period.
9.2. Malicious PCC
The LSP instantiation mechanism described in this document requires
the PCE to keep state for LSPs that it instantiates and relies on the
PCC responding (with either a state report or an error message) to
requests for LSP instantiation. A malicious PCC or one that reached
the limit of the number of PCE-initiated LSPs, can ignore PCE
requests and consume PCE resources. A PCE can protect itself by
imposing a limit on the number of requests pending, or by setting a
timeout and it MAY take further action such as closing the session or
removing all the LSPs it initiated.
10. Acknowledgements
We would like to thank Jan Medved, Ambrose Kwong, Ramon Casellas,
Cyril Margaria, Dhruv Dhody, and Raveendra Trovi for their
contributions to this document.
11. References
11.1. Normative References
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[I-D.ietf-pce-stateful-pce]
Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
Extensions for Stateful PCE", draft-ietf-pce-stateful-
pce-18 (work in progress), December 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<http://www.rfc-editor.org/info/rfc5440>.
[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, DOI 10.17487/RFC5511, April
2009, <http://www.rfc-editor.org/info/rfc5511>.
[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<http://www.rfc-editor.org/info/rfc8051>.
11.2. Informative References
[I-D.ietf-pce-stateful-sync-optimizations]
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", draft-
ietf-pce-stateful-sync-optimizations-09 (work in
progress), February 2017.
[RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC4657, September
2006, <http://www.rfc-editor.org/info/rfc4657>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982,
DOI 10.17487/RFC6982, July 2013,
<http://www.rfc-editor.org/info/rfc6982>.
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Authors' Addresses
Edward Crabbe
Individual Contributor
Email: edward.crabbe@gmail.com
Ina Minei
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: inaminei@google.com
Siva Sivabalan
Cisco Systems, Inc.
170 West Tasman Dr.
San Jose, CA 95134
US
Email: msiva@cisco.com
Robert Varga
Pantheon Technologies SRO
Mlynske Nivy 56
Bratislava 821 05
Slovakia
Email: robert.varga@pantheon.tech
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