Internet DRAFT - draft-ietf-pce-stateful-sync-optimizations
draft-ietf-pce-stateful-sync-optimizations
PCE Working Group E. Crabbe
Internet-Draft Oracle
Intended status: Standards Track I. Minei
Expires: September 28, 2017 Google, Inc.
J. Medved
Cisco Systems, Inc.
R. Varga
Pantheon Technologies SRO
X. Zhang
D. Dhody
Huawei Technologies
March 27, 2017
Optimizations of Label Switched Path State Synchronization Procedures
for a Stateful PCE
draft-ietf-pce-stateful-sync-optimizations-10
Abstract
A stateful Path Computation Element (PCE) has access to not only the
information disseminated by the network's Interior Gateway Protocol
(IGP), but also the set of active paths and their reserved resources
for its computation. The additional Label Switched Path (LSP) state
information allows the PCE to compute constrained paths while
considering individual LSPs and their interactions. This requires a
state synchronization mechanism between the PCE and the network, PCE
and path computation clients (PCCs), and between cooperating PCEs.
The basic mechanism for state synchronization is part of the stateful
PCE specification. This document presents motivations for
optimizations to the base state synchronization procedure and
specifies the required Path Computation Element Communication
Protocol (PCEP) extensions.
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
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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."
This Internet-Draft will expire on September 28, 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
(http://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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. State Synchronization Avoidance . . . . . . . . . . . . . . . 4
3.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. State Synchronization Avoidance Procedure . . . . . . . . 4
3.2.1. IP Address change during session re-establishment . . 9
3.3. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . 10
3.3.1. LSP State Database Version Number TLV . . . . . . . . 10
3.3.2. Speaker Entity Identifier TLV . . . . . . . . . . . . 11
4. Incremental State Synchronization . . . . . . . . . . . . . . 12
4.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Incremental Synchronization Procedure . . . . . . . . . . 13
5. PCE-triggered Initial Synchronization . . . . . . . . . . . . 16
5.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 16
5.2. PCE-triggered Initial State Synchronization Procedure . . 17
6. PCE-triggered Re-synchronization . . . . . . . . . . . . . . 18
6.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 18
6.2. PCE-triggered State Re-synchronization Procedure . . . . 18
7. Advertising Support of Synchronization Optimizations . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8.1. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 20
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8.2. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 21
8.3. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 21
9. Manageability Considerations . . . . . . . . . . . . . . . . 21
9.1. Control of Function and Policy . . . . . . . . . . . . . 21
9.2. Information and Data Models . . . . . . . . . . . . . . . 21
9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 22
9.4. Verify Correct Operations . . . . . . . . . . . . . . . . 22
9.5. Requirements On Other Protocols . . . . . . . . . . . . . 22
9.6. Impact On Network Operations . . . . . . . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 23
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
13.1. Normative References . . . . . . . . . . . . . . . . . . 23
13.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
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.
[I-D.ietf-pce-stateful-pce] describes a set of extensions to PCEP to
provide stateful control. A stateful PCE has access to not only the
information carried by the network's Interior Gateway Protocol (IGP),
but also the set of active paths and their reserved resources for its
computations. The additional state allows the PCE to compute
constrained paths while considering individual LSPs and their
interactions. This requires a state synchronization mechanism
between the PCE and the network, PCE and PCC, and between cooperating
PCEs. [I-D.ietf-pce-stateful-pce] describes the basic mechanism for
state synchronization. This document specifies following
optimizations for state synchronization and the corresponding PCEP
procedures and extensions:
o State Synchronization Avoidance: To skip state synchronization if
the state has survived and not changed during session restart.
(See Section 3.)
o Incremental State Synchronization: To do incremental (delta) state
synchronization when possible. (See Section 4.)
o PCE-triggered Initial Synchronization: To let PCE control the
timing of the initial state synchronization. (See Section 5.)
o PCE-triggered Re-synchronization: To let PCE re-synchronize the
state for sanity check. (See Section 6.)
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Support for each of the synchronization optimization capabilities is
advertised during the PCEP initialization phase. See Section 7 for
the new flags defined in this document. The handling of each flag is
described in the relevant section.
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, LSP State Database.
This document uses the following terms defined in
[I-D.ietf-pce-stateful-pce]: Redelegation Timeout Interval, LSP State
Report, LSP Update Request.
Within this document, when describing PCE-PCE communications, one of
the PCEs fills the role of a PCC. This provides a saving in
documentation without loss of function.
3. State Synchronization Avoidance
3.1. Motivation
The purpose of state synchronization is to provide a checkpoint-in-
time state replica of a PCC's LSP state in a stateful PCE. State
synchronization is performed immediately after the initialization
phase ([RFC5440]). [I-D.ietf-pce-stateful-pce] describes the basic
mechanism for state synchronization.
State synchronization is not always necessary following a PCEP
session restart. If the state of both PCEP peers did not change, the
synchronization phase may be skipped. This can result in significant
savings in both control-plane data exchanges and the time it takes
for the stateful PCE to become fully operational.
3.2. State Synchronization Avoidance Procedure
State synchronization MAY be skipped following a PCEP session restart
if the state of both PCEP peers did not change during the period
prior to session re-initialization. To be able to make this
determination, state must be exchanged and maintained by both PCE and
PCC during normal operation. This is accomplished by keeping track
of the changes to the LSP state database, using a version tracking
field called the LSP State Database Version Number.
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The INCLUDE-DB-VERSION (S) bit in the stateful PCE capability TLV
(Section 7) is advertised on a PCEP session during session startup to
indicate that the LSP State Database Version Number is to be included
when the LSPs are reported to the PCE. The LSP State Database
Version Number, carried in LSP-DB-VERSION TLV (see Section 3.3.1), is
owned by a PCC and it MUST be incremented by 1 for each successive
change in the PCC's LSP state database. The LSP State Database
Version Number MUST start at 1 and may wrap around. Values 0 and
0xFFFFFFFFFFFFFFFF are reserved. If either of the two values are
used during LSP state (re)-synchronization, the PCE speaker receiving
this value MUST send back a PCErr with Error-type 20 Error-value TBD6
(suggested value - 6) 'Received an invalid LSP DB Version Number',
and close the PCEP session. Operations that trigger a change to the
local LSP state database include a change in the LSP operational
state, delegation of an LSP, removal or setup of an LSP or change in
any of the LSP attributes that would trigger a report to the PCE.
If the include LSP DB version capability is enabled, a PCC MUST
increment its LSP State Database Version Number when the
'Redelegation Timeout Interval' timer expires (see
[I-D.ietf-pce-stateful-pce] for the use of the Redelegation Timeout
Interval).
If both PCEP speakers set the S flag in the OPEN object's STATEFUL-
PCE-CAPABILITY TLV to 1, the PCC MUST include the LSP-DB-VERSION TLV
in each LSP object of the PCRpt message. If the LSP-DB-VERSION TLV
is missing in a PCRpt message, the PCE will generate an error with
Error-Type 6 (mandatory object missing) and Error-Value TBD1
(suggested value - 12) 'LSP-DB-VERSION TLV missing' and close the
session. If the include LSP DB version capability has not been
enabled on a PCEP session, the PCC SHOULD NOT include the LSP-DB-
VERSION TLV in the LSP Object and the PCE MUST ignore it were it to
receive one.
If a PCE's LSP state database survived the restart of a PCEP session,
the PCE will include the LSP-DB-VERSION TLV in its OPEN object, and
the TLV will contain the last LSP State Database Version Number
received on an LSP State Report from the PCC in the previous PCEP
session. If a PCC's LSP State Database survived the restart of a
PCEP session, the PCC will include the LSP-DB-VERSION TLV in its OPEN
object and the TLV will contain the latest LSP State Database Version
Number. If a PCEP speaker's LSP state database did not survive the
restart of a PCEP session or at startup when the database is empty,
the PCEP speaker MUST NOT include the LSP-DB-VERSION TLV in the OPEN
object.
If both PCEP speakers include the LSP-DB-VERSION TLV in the OPEN
Object and the TLV values match, the PCC MAY skip state
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synchronization and the PCE does not wait for the end of
synchronization marker [I-D.ietf-pce-stateful-pce]. Otherwise, the
PCC MUST perform full state synchronization (see
[I-D.ietf-pce-stateful-pce]) or incremental state synchronization
(see Section 4 if this capability is advertised) to the stateful PCE.
In other words, if the incremental state synchronization capability
is not advertised by the peers, based on the LSP database version
number match either the state synchronization is skipped or a full
state synchronization is performed. If the PCC attempts to skip
state synchronization, by setting the SYNC Flag to 0 and PLSP-ID to a
non-zero value on the first LSP State Report from the PCC as per
[I-D.ietf-pce-stateful-pce], the PCE MUST send back a PCErr with
Error-Type 20 Error-Value TBD2 (suggested value - 2) 'LSP Database
version mismatch', and close the PCEP session.
If state synchronization is required, then prior to completing the
initialization phase, the PCE MUST mark any LSPs in the LSP database
that were previously reported by the PCC as stale. When the PCC
reports an LSP during state synchronization, if the LSP already
exists in the LSP database, the PCE MUST update the LSP database and
clear the stale marker from the LSP. When it has finished state
synchronization, the PCC MUST immediately send an end of
synchronization marker. The end of synchronization marker is a Path
Computation State Report (PCRpt) message with an LSP object
containing a PLSP-ID of 0 and with the SYNC flag set to 0
([I-D.ietf-pce-stateful-pce]). The LSP-DB-VERSION TLV MUST be
included in this PCRpt message. On receiving this state report, the
PCE MUST purge any LSPs from the LSP database that are still marked
as stale.
Note that a PCE/PCC MAY force state synchronization by not including
the LSP-DB-VERSION TLV in its OPEN object.
Since a PCE does not make changes to the LSP State Database Version
Number, a PCC should never encounter this TLV in a message from the
PCE (other than the OPEN message). A PCC SHOULD ignore the LSP-DB-
VERSION TLV, were it to receive one from a PCE.
Figure 1 shows an example sequence where the state synchronization is
skipped.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|--Open--, |
| DBv=42 \ ,---Open--|
| S=1 \ / DBv=42 |
| \/ S=1 |
| /\ |
| / `-------->| (OK to skip sync)
(Skip sync) |<--------` |
| . |
| . |
| . |
| |
|--PCRpt,DBv=43,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=44,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=45,SYNC=0-->|
| |
Figure 1: State Synchronization Skipped
Figure 2 shows an example sequence where the state synchronization is
performed due to LSP state database version mismatch during the PCEP
session setup. Note that the same state synchronization sequence
would happen if either the PCC or the PCE would not include the LSP-
DB-VERSION TLV in their respective Open messages.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|--Open--, |
| DBv=46 \ ,---Open--|
| S=1 \ / DBv=42 |
| \/ S=1 |
| /\ |
| / `-------->| (Expect sync)
(Do sync) |<--------` |
| |
|--PCRpt,DBv=46,SYNC=1-->| (Sync start)
| . |
| . |
| . |
|--PCRpt,DBv=46,SYNC=0-->| (Sync done)
| . |(Purge LSP State
| . | if applicable)
| . |
|--PCRpt,DBv=47,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=48,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=49,SYNC=0-->|
| |
Figure 2: State Synchronization Performed
Figure 3 shows an example sequence where the state synchronization is
skipped, but because one or both PCEP speakers set the S Flag to 0,
the PCC does not send LSP-DB-VERSION TLVs in subsequent PCRpt
messages to the PCE. If the current PCEP session restarts, the PCEP
speakers will have to perform state synchronization, since the PCE
does not know the PCC's latest LSP State Database Version Number
information.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|--Open--, |
| DBv=42 \ ,---Open--|
| S=0 \ / DBv=42 |
| \/ S=0 |
| /\ |
| / `-------->| (OK to skip sync)
(Skip sync) |<--------` |
| . |
| . |
| . |
|------PCRpt,SYNC=0----->| (Regular
| | LSP State Report)
|------PCRpt,SYNC=0----->| (Regular
| | LSP State Report)
|------PCRpt,SYNC=0----->|
| |
Figure 3: State Synchronization Skipped, no LSP-DB-VERSION TLVs sent
from PCC
3.2.1. IP Address change during session re-establishment
There could be a case during PCEP session re-establishment when the
PCC's or PCE's IP address can change. This includes, but is not
limited to, the following cases:
o A PCC could use a physical interface IP address to connect to the
PCE. In this case, if the line card that the PCC connects from
changes, then the PCEP session goes down and comes back up again,
with a different IP address associated with a new line card.
o The PCC or PCE may move in the network, either physically or
logically, which may cause its IP address to change. For example,
the PCE may be deployed as a virtual network function (VNF) and
another virtualized instance of the PCE may be populated with the
original PCE instance's state, but be given a different IP
address.
To ensure that a PCEP peer can recognize a previously connected peer,
each PCEP peer includes the SPEAKER-ENTITY-ID TLV described in
Section 3.3.2, in the OPEN message.
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This TLV is used during the state synchronization procedure to
identify the PCEP session as a re-establishment of a previous session
that went down. Then state synchronization optimizations such as
state sync avoidance can be applied to this session. Note that this
usage is only applicable within the State Timeout Interval
[I-D.ietf-pce-stateful-pce]. After the State Timeout Interval
expires, all state associated with the PCEP session is removed, which
includes the SPEAKER-ENTITY-ID received. Note that the PCEP session
initialization [RFC5440] procedure remains unchanged.
3.3. PCEP Extensions
A new INCLUDE-DB-VERSION (S) bit is added in the stateful
capabilities TLV (see Section 7 for details).
3.3.1. LSP State Database Version Number TLV
The LSP State Database Version Number (LSP-DB-VERSION) TLV is an
optional TLV that MAY be included in the OPEN object and the LSP
object.
This TLV is included in the LSP object in the PCRpt message to
indicate the LSP DB version at the PCC. This TLV SHOULD NOT be
included in other PCEP messages (PCUpd, PcReq, PCRep) and MUST be
ignored if received.
The format of the LSP-DB-VERSION 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=TBD5 | Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP State DB Version Number |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: LSP-DB-VERSION TLV format
The type of the TLV is TBD5 and it has a fixed length of 8 octets.
The value contains a 64-bit unsigned integer, carried in network byte
order, representing the LSP State DB Version Number.
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3.3.2. Speaker Entity Identifier TLV
The Speaker Entity Identifier TLV (SPEAKER-ENTITY-ID) is an optional
TLV that MAY be included in the OPEN Object when a PCEP speaker
wishes to determine if state synchronization can be skipped when a
PCEP session is restarted. It contains a unique identifier for the
node that does not change during the lifetime of the PCEP speaker.
It identifies the PCEP speaker to its peers even if the speaker's IP
address is changed.
In case of a remote peer IP address change, a PCEP speaker would
learn the speaker entity identifier on receiving the open message but
it MAY have already sent its open message without realizing that it
is a known PCEP peer. In such a case, either a full synchronization
is done or PCEP session is terminated. This may be a local policy
decision. The new IP address is associated with the speaker entity
identifier for future either way. In the latter case when PCEP
session is re-established, it would be correctly associated with
speaker entity identifier and not be considered as an unknown peer.
The format of the SPEAKER-ENTITY-ID 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=TBD13 | Length (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Speaker Entity Identifier //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SPEAKER-ENTITY-ID TLV format
The type of the TLV is TBD13 and it has a variable length, which MUST
be greater than 0. The Value is padded to 4-octet alignment. The
padding is not included in the Length field. The value contains the
entity identifier of the speaker transmitting this TLV. This
identifier is required to be unique within its scope of visibility,
which is usually limited to a single domain. It MAY be configured by
the operator. Alternatively, it can be derived automatically from a
suitably-stable unique identifier, such as a MAC address, serial
number, Traffic Engineering Router ID, or similar. In the case of
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inter-domain connections, the speaker SHOULD prefix its usual
identifier with the domain identifier of its residence, such as
Autonomous System number, IGP area identifier, or similar to make
sure it remains unique.
The relationship between this identifier and entities in the Traffic
Engineering database is intentionally left undefined.
From a manageability point of view, a PCE or PCC implementation
SHOULD allow the operator to configure this Speaker Entity
Identifier.
If a PCEP speaker receives the SPEAKER-ENTITY-ID on a new PCEP
session, that matches with an existing alive PCEP session, the PCEP
speaker MUST send a PCErr with Error-type 20 Error-value TBD7
(suggested value - 7) 'Received an invalid Speaker Entity
Identifier', and close the PCEP session.
4. Incremental State Synchronization
[I-D.ietf-pce-stateful-pce] describes the LSP state synchronization
mechanism between PCCs and stateful PCEs. During the state
synchronization, a PCC sends the information of all its LSPs (i.e.,
the full LSP-DB) to the stateful PCE. In order to reduce the state
synchronization overhead when there is a small number of LSP state
change in the network between PCEP session restart, this section
defines a mechanism for incremental (Delta) LSP Database (LSP-DB)
synchronization.
4.1. Motivation
According to [I-D.ietf-pce-stateful-pce], if a PCE restarts and its
LSP-DB survived, PCCs with mismatched LSP State Database Version
Number will send all their LSPs information (full LSP-DB) to the
stateful PCE, even if only a small number of LSPs underwent state
change. It can take a long time and consume large communication
channel bandwidth.
Figure 6 shows an example of LSP state synchronization.
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+-----+
| PCE |
+-----+
/
/
/
/
+------+ +------+
| PCC1 |------------| PCC2 |
+------+ +------+
| |
| |
+------+ +------+
| PCC3 |------------| PCC4 |
+------+ +------+
Figure 6: Topology Example
Assuming there are 320 LSPs in the network, with each PCC having 80
LSPs. During the time when the PCEP session is down, 20 LSPs of each
PCC (i.e., 80 LSPs in total), are changed. Hence when PCEP session
restarts, the stateful PCE needs to synchronize 320 LSPs with all
PCCs. But actually, 240 LSPs stay the same. If performing full LSP
state synchronization, it can take a long time to carry out the
synchronization of all LSPs. It is especially true when only a low
bandwidth communication channel is available (e.g., in-band control
channel for optical transport networks) and there is a substantial
number of LSPs in the network. Another disadvantage of full LSP
synchronization is that it is a waste of communication bandwidth to
perform full LSP synchronization given the fact that the number of
LSP changes can be small during the time when PCEP session is down.
An incremental (Delta) LSP Database (LSP-DB) state synchronization is
described in this section, where only the LSPs underwent state change
are synchronized between the session restart. This may include
new/modified/deleted LSPs.
4.2. Incremental Synchronization Procedure
[I-D.ietf-pce-stateful-pce] describes state synchronization and
Section 3 of this document, describes state synchronization avoidance
by using LSP-DB-VERSION TLV in its OPEN object. This section extends
this idea to only synchronize the delta (changes) in case of version
mismatch.
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If both PCEP speakers include the LSP-DB-VERSION TLV in the OPEN
object and the LSP-DB-VERSION TLV values match, the PCC MAY skip
state synchronization. Otherwise, the PCC MUST perform state
synchronization. Incremental State synchronization capability is
advertised on a PCEP session during session startup using the DELTA-
LSP-SYNC-CAPABILITY (D) bit in the capabilities TLV (see Section 7).
Instead of dumping full LSP-DB to the stateful PCE again, the PCC
synchronizes the delta (changes) as described in Figure 7 when D flag
and S flag is set to 1 by both PCC and PCE. Other combinations of D
and S flags setting by PCC and PCE result in full LSP-DB
synchronization procedure as described in
[I-D.ietf-pce-stateful-pce]. By setting the D flag to zero in the
OPEN message, a PCEP speaker can skip the incremental synchronization
optimization, resulting in a full LSP DB synchronization.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|--Open--, |
| DBv=46 \ ,---Open--|
| S=1 \ / DBv=42 |
| D=1 \/ S=1 |
| /\ D=1 |
| / \ |
| / `-------->| (Expect Delta sync)
(Do sync)|<--------` | (DONOT Purge LSP
(Delta) | | State)
| |
(Delta Sync starts) |--PCRpt,DBv=46,SYNC=1-->|
| . |
| . |
| . |
| . |
|--PCRpt,DBv=46,SYNC=0-->| (Sync done,
| | PLSP-ID=0)
| |
|--PCRpt,DBv=47,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=48,SYNC=0-->| (Regular
| | LSP State Report)
|--PCRpt,DBv=49,SYNC=0-->|
| |
Figure 7: Incremental Synchronization Procedure
As per Section 3, the LSP State Database Version Number is
incremented each time a change is made to the PCC's local LSP State
Database. Each LSP is associated with the DB version at the time of
its state change. This is needed to determine which LSP and what
information needs to be synchronized in incremental state
synchronization. The incremental state sync is done from the last
LSP DB version received by the PCE to the latest DB version at the
PCC. Note that the LSP State Database Version Number can wrap
around, and in which case the incremental state sync would also wrap
till the latest DB version number at the PCC.
In order to carry out incremental state synchronization, it is not
necessary for a PCC to store a complete history of LSP Database
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change for all time, but remember the LSP state changes (including
LSP modification, setup and deletion), that the PCE did not get to
process during the session down. Note that, a PCC would be unaware
that a particular LSP report has been processed by the PCE before the
session to PCE went down. So a PCC implementation MAY choose to
store the LSP State Database Version Number with each LSP at the time
its status changed, so that when a session is re-established an
incremental synchronization can be attempted based on the PCE's last
LSP State Database Version Number. For an LSP that is deleted at the
PCC, the PCC implementation would need to remember the deleted LSP in
some way to make sure this could be reported as part of incremental
synchronization later. The PCC would discard this information based
on a local policy, or when it determines that this information is no
longer needed with sufficient confidence. In the example shown in
Figure 7, the PCC needs to store the LSP state changes that happened
between DB Version 43 to 46 and synchronizes these changes, when
performing incremental LSP state update.
If a PCC finds out it does not have sufficient information to
complete incremental synchronization after advertising incremental
LSP state synchronization capability, it MUST send a PCErr with
Error-Type 20 and Error-Value 5 'A PCC indicates to a PCE that it can
not complete the state synchronization' (defined in
[I-D.ietf-pce-stateful-pce]) and terminate the session. The PCC
SHOULD re-establish the session with the D bit set to 0 in the OPEN
message.
The other procedures and error checks remain unchanged from the full
state synchronization ([I-D.ietf-pce-stateful-pce]).
5. PCE-triggered Initial Synchronization
5.1. Motivation
In networks such as optical transport networks, the control channel
between network nodes can be realized through in-band overhead thus
has limited bandwidth. With a stateful PCE connected to the network
via one network node, it is desirable to control the timing of PCC
state synchronization so as not to overload the low communication
channel available in the network during the initial synchronization
(be it incremental or full) when the session restarts , when there is
comparatively large amount of control information needing to be
synchronized between the stateful PCE and the network. The method
proposed, i.e., allowing PCE to trigger the state synchronization, is
similar to the function proposed in Section 6 but is used in
different scenarios and for different purposes.
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5.2. PCE-triggered Initial State Synchronization Procedure
Support of PCE-triggered initial state synchronization is advertised
during session startup using the TRIGGERED-INITIAL-SYNC (F) bit in
the STATEFUL-PCE-CAPABILITY TLV (see Section 7).
In order to allow a stateful PCE to control the LSP-DB
synchronization after establishing a PCEP session, both PCEP speakers
MUST set F bit to 1 in the OPEN message. If the LSP-DB-VERSION TLV
is included by both PCEP speakers and the TLV value matches, the
state synchronization can be skipped as described in Section 3.2. If
the TLV is not included or the LSP-DB Version is mis-matched, the PCE
can trigger the state synchronization process by sending a PCUpd
message with PLSP-ID = 0 and SYNC = 1. The PCUpd message SHOULD
include an empty ERO (with no ERO sub-object and object length of 4)
as its intended path and SHOULD NOT include the optional objects for
its attributes for any parameter update. The PCC MUST ignore such an
update when the SYNC flag is set. If the TRIGGERED-INITIAL-SYNC
capability is not advertised by a PCE and the PCC receives a PCUpd
with the SYNC flag set to 1, the PCC MUST send a PCErr with the SRP-
ID-number of the PCUpd, Error-Type 20 and Error-Value TBD4 (suggested
value - 4) 'Attempt to trigger synchronization when the TRIGGERED-
SYNC capability has not been advertised' (see Section 8.1). If the
TRIGGERED-INITIAL-SYNC capability is advertised by a PCE and the PCC,
the PCC MUST NOT trigger state synchronization on its own. If the
PCE receives a PCRpt message before the PCE has triggered the state
synchronization, the PCE MUST send a PCErr with Error-Type 20 and
Error-Value TBD3 (suggested value - 3) 'Attempt to trigger
synchronization before PCE trigger' (see Section 8.1).
In this way, the PCE can control the sequence of LSP synchronization
among all the PCCs that are re-establishing PCEP sessions with it.
When the capability of PCE control is enabled, only after a PCC
receives this message, it will start sending information to the PCE.
This PCE-triggering capability can be applied to both full and
incremental state synchronization. If applied to the latter, the
PCCs only send information that PCE does not possess, which is
inferred from the LSP-DB version information exchanged in the OPEN
message (see Section 4.2 for detailed procedure).
Once the initial state synchronization is triggered by the PCE, the
procedures and error checks remain unchanged
([I-D.ietf-pce-stateful-pce]).
If a PCC implementation that does not implement this extension should
not receive a PCUpd message to trigger state synchronization as per
the capability advertisement, but if it were to receive it, it will
behave as per [I-D.ietf-pce-stateful-pce].
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6. PCE-triggered Re-synchronization
6.1. Motivation
The accuracy of the computations performed by the PCE is tied to the
accuracy of the view the PCE has on the state of the LSPs.
Therefore, it can be beneficial to be able to re-synchronize this
state even after the session has been established. The PCE may use
this approach to continuously sanity check its state against the
network, or to recover from error conditions without having to tear
down sessions.
6.2. PCE-triggered State Re-synchronization Procedure
Support of PCE-triggered state re-synchronization is advertised by
both PCEP speakers during session startup using the TRIGGERED-RESYNC
(T) bit in the STATEFUL-PCE-CAPABILITY TLV (see Section 7). The PCE
can choose to re-synchronize its entire LSP database or a single LSP.
To trigger re-synchronization for an LSP, the PCE sends a Path
Computation State Update (PCUpd) for the LSP, with the SYNC flag in
the LSP object set to 1. The PCE SHOULD NOT include any parameter
updates for the LSP, and the PCC MUST ignore such an update when the
SYNC flag is set. The PCC MUST respond with a PCRpt message with the
LSP state, SYNC Flag set to 0 and MUST include the SRP-ID-number of
the PCUpd message that triggered the resynchronization. If the PCC
cannot find the LSP in its database, PCC MUST also set the R (remove)
flag [I-D.ietf-pce-stateful-pce] in the LSP object in the PCRpt
message.
The PCE can also trigger re-synchronization of the entire LSP
database. The PCE MUST first mark all LSPs in the LSP database that
were previously reported by the PCC as stale and then send a PCUpd
with an LSP object containing a PLSP-ID of 0 and with the SYNC flag
set to 1. The PCUpd message MUST include an empty ERO (with no ERO
sub-object and object length of 4) as its intended path and SHOULD
NOT include the optional objects for its attributes for any parameter
update. The PCC MUST ignore such update if the SYNC flag is set.
This PCUpd message is the trigger for the PCC to enter the
synchronization phase as described in [I-D.ietf-pce-stateful-pce] and
start sending PCRpt messages. After the receipt of the end-of-
synchronization marker, the PCE will purge LSPs which were not
refreshed. The SRP-ID-number of the PCUpd that triggered the re-
synchronization SHOULD be included in each of the PCRpt messages. If
the PCC cannot re-synchronize the entire LSP database, the PCC MUST
respond with PCErr message with Error-type 20 Error-value 5 'cannot
complete the state synchronization' [I-D.ietf-pce-stateful-pce], and
MAY terminate the session. The PCE MUST remove the stale mark for
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the LSP that were previously reported by the PCC. Based on the local
policy, the PCE MAY reattempt synchronization at a later time.
If the TRIGGERED-RESYNC capability is not advertised by a PCE and the
PCC receives a PCUpd with the SYNC flag set to 1, it MUST send a
PCErr with the SRP-ID-number of the PCUpd, Error-Type 20 and Error-
Value TBD4 (suggested value - 4) 'Attempt to trigger synchronization
when the TRIGGERED-SYNC capability has not been advertised' (see
Section 8.1).
Once the state re-synchronization is triggered by the PCE, the
procedures and error checks remain unchanged from the full state
synchronization ([I-D.ietf-pce-stateful-pce]). This would also
include PCE triggering multiple state re-synchronization requests
while synchronization is in progress.
If a PCC implementation that does not implement this extension should
not receive a PCUpd message to trigger re-synchronization as per the
capability advertisement, but if it were to receive it, it will
behave as per [I-D.ietf-pce-stateful-pce].
7. Advertising Support of Synchronization Optimizations
Support for each of the optimizations described in this document
requires advertising the corresponding capabilities during session
establishment time.
The STATEFUL-PCE-CAPABILITY TLV is defined in
[I-D.ietf-pce-stateful-pce]. This document defines following new
flags in the STATEFUL-PCE-CAPABILITY TLV:
Bit Description
TBD9 (suggested value 30) S bit (INCLUDE-DB-VERSION)
TBD10 (suggested value 27) D bit (DELTA-LSP-SYNC-CAPABILITY)
TBD11 (suggested value 26) F bit (TRIGGERED-INITIAL-SYNC)
TBD12 (suggested value 28) T bit (TRIGGERED-RESYNC)
If the S (INCLUDE-DB-VERSION) bit is set to 1 by both PCEP Speakers,
the PCC will include the LSP-DB-VERSION TLV in each LSP Object. See
Section 3.2 for details.
If the D (DELTA-LSP-SYNC-CAPABILITY) bit is set to 1 by a PCEP
speaker, it indicates that the PCEP speaker allows incremental
(delta) state synchronization. See Section 4.2 for details.
If the F (TRIGGERED-INITIAL-SYNC) bit is set to 1 by both PCEP
Speakers, the PCE SHOULD trigger initial (first) state
synchronization. See Section 5.2 for details.
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If the T (TRIGGERED-RESYNC) bit is set to 1 by both PCEP Speakers,
the PCE can trigger re-synchronization of LSPs at any point in the
life of the session. See Section 6.2 for details.
See Section 8.3 for IANA allocations.
8. IANA Considerations
This document requests IANA actions to allocate code points for the
protocol elements defined in this document.
8.1. PCEP-Error Object
IANA is requested to make the following allocation in the "PCEP-ERROR
Object Error Types and Values" registry.
Error-Type Meaning Reference
6 Mandatory Object missing [RFC5440]
Error-Value= TBD1(suggested This document
value 12): LSP-DB-VERSION TLV
missing
20 LSP State synchronization [I-D.ietf-pce-stateful-pce]
error
Error-Value= TBD2(suggested This document
value 2): LSP Database version
mismatch.
Error-Value=TBD3(suggested This document
value 3): Attempt to trigger
synchronization before PCE
trigger.
Error-Value=TBD4(suggested This document
value 4): Attempt to trigger a
synchronization when the
PCE triggered synchronization
capability has not been
advertised.
Error-Value=TBD6(suggested This document
value 6): Received an invalid
LSP DB Version Number.
Error-Value=TBD7(suggested This document
value 7): Received an invalid
Speaker Entity Identifier.
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8.2. PCEP TLV Type Indicators
IANA is requested to make the following allocation in the "PCEP TLV
Type Indicators" registry.
Value Meaning Reference
TBD5(suggested value 23) LSP-DB-VERSION This document
TBD13(suggested value 24) SPEAKER-ENTITY-ID This document
8.3. STATEFUL-PCE-CAPABILITY TLV
The STATEFUL-PCE-CAPABILITY TLV is defined in
[I-D.ietf-pce-stateful-pce] and a registry is requested to be
created to manage the flags in the TLV. IANA is requested to make
the following allocation in the aforementioned registry.
Bit Description Reference
TBD11 (suggested value 26) TRIGGERED-INITIAL-SYNC This document
TBD10 (suggested value 27) DELTA-LSP-SYNC-CAPABILITY This document
TBD12 (suggested value 28) TRIGGERED-RESYNC This document
TBD9 (suggested value 30) INCLUDE-DB-VERSION This document
9. Manageability Considerations
All manageability requirements and considerations listed in [RFC5440]
and [I-D.ietf-pce-stateful-pce] apply to PCEP protocol extensions
defined in this document. In addition, requirements and
considerations listed in this section apply.
9.1. Control of Function and Policy
A PCE or PCC implementation MUST allow configuring the state
synchronization optimization capabilities as described in this
document. The implementation SHOULD also allow the operator to
configure the Speaker Entity Identifier ( Section 3.3.2). Further,
the operator SHOULD be to be allowed to trigger the re-
synchronization procedures as per Section 6.2.
9.2. Information and Data Models
An implementation SHOULD allow the operator to view the stateful
capabilities advertised by each peer, and the current synchronization
status with each peer. To serve this purpose, the PCEP YANG module
[I-D.ietf-pce-pcep-yang] can be extended to include advertised
stateful capabilities, and synchronization status.
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9.3. 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].
9.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440] and [I-D.ietf-pce-stateful-pce].
9.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any new requirements
on other protocols.
9.6. Impact On Network Operations
Mechanisms defined in [RFC5440] and [I-D.ietf-pce-stateful-pce] also
apply to PCEP extensions defined in this document.
The state synchronization optimizations described in this document
can result in a reduction of the amount of data exchanged and the
time taken for a stateful PCE to be fully operational when a PCEP
session is re-established. The ability to trigger re-synchronization
by the PCE can be utilized by the operator to sanity check its state
and recover from any mismatch in state without tearing down the
session.
10. Security Considerations
The security considerations listed in [I-D.ietf-pce-stateful-pce]
apply to this document as well. However, this document also
introduces some new attack vectors. An attacker could spoof the
SPEAKER-ENTITY-ID and pretend to be another PCEP speaker. An
attacker may flood the PCC with triggered re-synchronization request
at a rate which exceeds the PCC's ability to process them, either by
spoofing messages or by compromising the PCE itself. The PCC can
respond with PCErr message as described in Section 6.2 and terminate
the session. Thus securing the PCEP session using Transport Layer
Security (TLS) [I-D.ietf-pce-pceps], as per the recommendations and
best current practices in [RFC7525], is RECOMMENDED. An
administrator could also expose the speaker entity id as part of the
certificate, for the peer identity verification.
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11. Acknowledgments
We would like to thank Young Lee, Sergio Belotti and Cyril Margaria
for their comments and discussions.
Thanks to Jonathan Hardwick for being the document shepherd and
provide comments and guidance.
Thanks to Tomonori Takeda for Routing Area Directorate review.
Thanks to Adrian Farrel for TSVART review and providing detailed
comments and suggestions.
Thanks to Daniel Franke for SECDIR review.
Thanks to Alvaro Retana, Kathleen Moriarty, and Stephen Farrell for
comments during the IESG evaluation.
Thanks to Deborah Brungard for being the responsible AD and guiding
the authors as needed.
12. Contributors
Gang Xie
Huawei Technologies
F3-5-B R&D Center, Huawei Industrial Base, Bantian, Longgang District
Shenzhen, Guangdong, 518129
P.R. China
Email: xiegang09@huawei.com
13. References
13.1. Normative References
[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>.
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13.2. Informative References
[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, <http://www.rfc-editor.org/info/rfc7525>.
[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>.
[I-D.ietf-pce-pcep-yang]
Dhody, D., Hardwick, J., Beeram, V., and j.
jefftant@gmail.com, "A YANG Data Model for Path
Computation Element Communications Protocol (PCEP)",
draft-ietf-pce-pcep-yang-02 (work in progress), March
2017.
[I-D.ietf-pce-pceps]
Lopez, D., Dios, O., Wu, W., and D. Dhody, "Secure
Transport for PCEP", draft-ietf-pce-pceps-11 (work in
progress), January 2017.
Authors' Addresses
Edward Crabbe
Oracle
EMail: edward.crabbe@gmail.com
Ina Minei
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
EMail: inaminei@google.com
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Jan Medved
Cisco Systems, Inc.
170 West Tasman Dr.
San Jose, CA 95134
US
EMail: jmedved@cisco.com
Robert Varga
Pantheon Technologies SRO
Mlynske Nivy 56
Bratislava 821 05
Slovakia
EMail: robert.varga@pantheon.tech
Xian Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Industrial Base, Bantian, Longgang District
Shenzhen, Guangdong 518129
P.R.China
EMail: zhang.xian@huawei.com
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: dhruv.ietf@gmail.com
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