PCE Working Group E. Crabbe
Internet-Draft
Intended status: Standards Track I. Minei
Expires: July 16, 2015 Google, Inc.
J. Medved
Cisco Systems, Inc.
R. Varga
Pantheon Technologies SRO
X. Zhang
D. Dhody
Huawei Technologies
January 12, 2015
Optimizations of Label Switched Path State Synchronization Procedures
for a Stateful PCE
draft-ietf-pce-stateful-sync-optimizations-02
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
reliable 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 draft 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 July 16, 2015.
Copyright Notice
Copyright (c) 2015 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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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
3.3. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . 9
3.3.1. LSP State Database Version Number TLV . . . . . . . . 9
3.3.2. Speaker Entity Identifier TLV . . . . . . . . . . . . 10
4. Incremental State Synchronization . . . . . . . . . . . . . . 11
4.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Incremental Synchronization Procedure . . . . . . . . . . 12
5. PCE-triggered Initial Synchronization . . . . . . . . . . . . 15
5.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 15
5.2. PCE-triggered Initial State Synchronization Procedure . . 15
6. PCE-triggered Re-synchronization . . . . . . . . . . . . . . 16
6.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 16
6.2. PCE-triggered State Re-synchronization Procedure . . . . 16
7. Advertising Support of Synchronization Optimizations . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 18
8.2. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 19
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8.3. STATEFUL-PCE-CAPABILITY TLV . . . . . . . . . . . . . . . 19
9. Manageability Considerations . . . . . . . . . . . . . . . . 20
9.1. Control of Function and Policy . . . . . . . . . . . . . 20
9.2. Information and Data Models . . . . . . . . . . . . . . . 20
9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 20
9.4. Verify Correct Operations . . . . . . . . . . . . . . . . 20
9.5. Requirements On Other Protocols . . . . . . . . . . . . . 20
9.6. Impact On Network Operations . . . . . . . . . . . . . . 20
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 21
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
13.1. Normative References . . . . . . . . . . . . . . . . . . 21
13.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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 reliable 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 draft 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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2. Terminology
This document uses the following terms defined in [RFC5440]: PCC,
PCE, PCEP Peer.
This document uses the following terms defined in
[I-D.ietf-pce-stateful-pce] : Delegation, Redelegation Timeout
Interval, LSP State Report, LSP Update Request, LSP State Database.
Within this document, when describing PCE-PCE communications, the
requesting PCE 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.
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 node should send back a PCErr with Error-
type 20 Error-value TBD (suggested value - 6) 'Received an invalid
LSP DB Version Number', and close the PCEP session. Operations that
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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.
State synchronization avoidance is advertised on a PCEP session
during session startup using the INCLUDE-DB-VERSION (S) bit in the
capabilities TLV (see Section 7). The peer may move in the network,
either physically or logically, which may cause its connectivity
details and transport-level identity (such as IP address) to change.
To ensure that a PCEP peer can recognize a previously connected peer
even in face of such mobility, each PCEP peer includes the SPEAKER-
ENTITY-ID TLV described in Section 3.3.2 in the OPEN message.
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 TBD
(suggested value - 12) 'LSP-DB-VERSION TLV missing' and close the
session. If state synchronization avoidance 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 SHOULD ignore it were 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, 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
synchronization. Otherwise, the PCC MUST perform full state
synchronization (see [I-D.ietf-pce-stateful-pce]) or incremental
state synchronization (see Section 4) to the stateful PCE. If the
PCC attempts to skip state synchronization (i.e., the SYNC Flag = 0
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 TBD (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
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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.
If state synchronization avoidance 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).
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
3.3. 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.
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=[TBD] | Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP State DB Version Number |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: LSP-DB-VERSION TLV format
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The type of the TLV is [TBD] and it has a fixed length of 8 octets.
The value contains a 64-bit unsigned integer, representing the LSP
State DB Version Number.
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=[TBD] | Length (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Speaker Entity Identifier //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SPEAKER-ENTITY-ID TLV format
The type of the TLV is [TBD] 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.
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.
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 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.
PCEP extensions for stateful PCEs to perform LSP synchronization
SHOULD allow: incremental LSP state synchronization between session
restarts. Note this does not exclude the need for a stateful PCE to
request a full LSP DB synchronization.
4.2. Incremental Synchronization Procedure
[I-D.ietf-pce-stateful-pce] describes state synchronization and
Section 3 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]. If a PCC has to force full LSP DB
synchronization due to reasons including but not limited: (1) local
policy configured at the PCC; (2) no sufficient LSP state caches for
incremental update, the PCC can set the D flag to 0. Note a PCC may
have to bring down the current session and force a full LSP-DB
synchronization with D flag set to 0 in the subsequent open message.
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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.
It is not necessary for a PCC to store a complete history of LSP
Database change, but rather remember the LSP state changes (including
LSP modification, setup and deletion) that happened between the PCEP
session(s) restart in order to carry out incremental state
synchronization. After the synchronization procedure finishes, the
PCC can dump this history information. 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 only when
performing incremental LSP state update. So a PCC needs to remember
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the LSP state changes that happened when an existing PCEP session to
a stateful PCE goes down in the hope of doing incremental
synchronisation when the session is re-established.
If a PCC finds out it does not have sufficient information to
complete incremental synchronisation 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 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.
5.2. PCE-triggered Initial State Synchronization Procedure
Support of PCE-triggered state synchronization is advertised during
session startup using the TRIGGERED-INITIAL-SYNC (F) bit in the
STATEFUL-PCE-CAPABILITY TLV (see Section 7).
If the TRIGGERED-INITIAL-SYNC capability is not advertised 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 TBD (suggested value - 4) 'Attempt to trigger synchronization
when the TRIGGERED-SYNC capability has not been advertised' (see
Section 8.1).
A stateful PCE MAY choose to control the LSP-DB synchronization
process. To allow PCE to do so, PCEP speakers MUST set T bit to 1 to
indicate this (as described in Section 7). If the LSP-DB Version is
mis-matched, it can send a PCUpd message with PLSP-ID = 0 and SYNC =
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1 in order to trigger the LSP-DB synchronization process. 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. The PCC
SHOULD NOT send PCRpt messages to the stateful PCE before it triggers
the State Synchronization. This PCE-triggering capability can be
applied to both full and incremental state synchronization. If
applied to the later, 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 from the full state
synchronization ([I-D.ietf-pce-stateful-pce]).
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 synchronization is advertised 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 MUST first mark the
LSP as stale and then send a Path Computation State Update (PCUpd)
for it, 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
SHOULD ignore such updates if 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.
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
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with an LSP object containing a PLSP-ID of 0 and with the SYNC flag
set to 1. 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 TRIGGERED-RESYNC capability is not advertised 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
TBD (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.
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.
New flags are defined for the STATEFUL-PCE-CAPABILITY TLV defined in
[I-D.ietf-pce-stateful-pce]. Its format 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 |F|D|T|I|S|U|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: STATEFUL-PCE-CAPABILITY TLV Format
The value comprises a single field - Flags (32 bits):
U (LSP-UPDATE-CAPABILITY - 1 bit): defined in
[I-D.ietf-pce-stateful-pce].
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S (INCLUDE-DB-VERSION - 1 bit): if 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.
I (LSP-INSTANTIATION-CAPABILITY - 1 bit): defined in [I-D.ietf-pce-p
ce-initiated-lsp].
T (TRIGGERED-RESYNC - 1 bit): if 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.
D (DELTA-LSP-SYNC-CAPABILITY - 1 bit): if set to 1 by a PCEP
speaker, it indicates that the PCEP speaker allows incremental
(delta) state synchronization. See Section 4.2 for details.
F (TRIGGERED-INITIAL-SYNC - 1 bit): if set to 1 by both PCEP
Speakers, the PCE SHOULD trigger initial (first) state
synchronization. See Section 5.2 for details.
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.
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Error-Type Meaning Reference
6 Mandatory Object missing [RFC5440]
Error-Value= TBD(suggested This document
value 12): LSP-DB-VERSION TLV
missing
20 LSP State synchronization [I-D.ietf-pce-stateful-pce]
error
Error-Value= TBD(suggested This document
value 2): LSP Database version
mismatch.
Error-Value=TBD(suggested This document
value 3): The LSP-DB-VERSION
TLV Missing when state
synchronization avoidance is
enabled.
Error-Value=TBD(suggested This document
value 4): Attempt to trigger a
synchronization when the
PCE triggered synchronization
capability has not been
advertised.
Error-Value=TBD(suggested This document
value 6): No sufficient LSP
change information for
incremental LSP state
synchronization.
Error-Value=TBD(suggested This document
value 7): Received an invalid
LSP DB Version Number
8.2. PCEP TLV Type Indicators
This document defines the following new PCEP TLVs:
Value Meaning Reference
TBD(suggested value 23) LSP-DB-VERSION This document
TBD(suggested value 24) SPEAKER-ENTITY-ID This document
8.3. STATEFUL-PCE-CAPABILITY TLV
The following values are defined in this document for the Flags field
in the STATEFUL-PCE-CAPABILITY-TLV in the OPEN object:
Bit Description Reference
TBD(suggested value 26) TRIGGERED-INITIAL-SYNC This document
TBD(suggested value 27) DELTA-LSP-SYNC-CAPABILITY This document
TBD(suggested value 28) TRIGGERED-RESYNC This document
TBD(suggested value 30) INCLUDE-DB-VERSION This document
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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).
9.2. Information and Data Models
The PCEP MIB module SHOULD be extended to include advertised stateful
capabilities, and synchronization status.
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 this document do not have any impact on network
operations in addition to those already listed in [RFC5440] and
[I-D.ietf-pce-stateful-pce].
10. Security Considerations
The security considerations listed in [I-D.ietf-pce-stateful-pce]
apply to this document as well. However, because the protocol
modifications outlined in this document allow the PCE to control
state (re)-synchronization timing and sequence, it also introduces a
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new attack vector: 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 is free to drop any trigger re-synchronization
request without additional processing.
11. Acknowledgements
We would like to thank Young Lee, Jonathan Hardwick, Sergio Belotti
and Cyril Margaria for their comments and discussions.
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-10 (work in progress), October 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element
(PCE) Communication Protocol (PCEP)", RFC 5440, March
2009.
13.2. Informative References
[I-D.ietf-pce-pce-initiated-lsp]
Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
Extensions for PCE-initiated LSP Setup in a Stateful PCE
Model", draft-ietf-pce-pce-initiated-lsp-02 (work in
progress), October 2014.
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Authors' Addresses
Edward Crabbe
Email: edward.crabbe@gmail.com
Ina Minei
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: inaminei@google.com
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.sk
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
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Dhruv Dhody
Huawei Technologies
Leela Palace
Bangalore, Karnataka 560008
India
Email: dhruv.ietf@gmail.com
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