PCE Working Group V. Kondreddy
Internet-Draft M. Negi
Intended status: Standards Track Huawei Technologies
Expires: April 11, 2016 October 9, 2015
Optimizations of PCEP Link-State(LS) Synchronization Procedures
draft-kondreddy-pce-pcep-ls-sync-optimizations-00
Abstract
For a Path Computation Element (PCE) to perform its computations, it
is important that Link-State (and TE) information be complete and
accurate each time. This requires a reliable Link-State
Synchronization mechanism between the PCE and path computation
clients (PCCs), and between cooperating PCEs. The basic mechanism
for Link-State Synchronization is part of the PCEP Link-State (and
TE) draft. This draft presents motivations for optimizations to the
base PCEP Link-State (and TE) procedure and specifies the required
Path Computation Element Communication Protocol (PCEP) extensions.
Status of This Memo
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This Internet-Draft will expire on April 11, 2016.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. LS Synchronization Avoidance . . . . . . . . . . . . . . . . 4
3.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. LS Synchronization Avoidance Procedure . . . . . . . . . 4
4. Incremental LS Synchronization . . . . . . . . . . . . . . . 8
4.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Incremental Synchronization Procedure . . . . . . . . . . 9
5. PCE-triggered Initial Synchronization . . . . . . . . . . . . 11
5.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 11
5.2. PCE-triggered Initial LS Synchronization Procedure . . . 11
6. PCE-triggered Re-synchronization . . . . . . . . . . . . . . 12
6.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 12
6.2. PCE-triggered LS Re-synchronization Procedure . . . . . . 12
7. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Link-State(LS) Report Message . . . . . . . . . . . . . . 13
7.2. Capability Advertisement . . . . . . . . . . . . . . . . 14
7.3. Advertising Support of Synchronization Optimizations . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8.1. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 15
8.2. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 16
8.3. LS-CAPABILITY Flags . . . . . . . . . . . . . . . . . . . 16
9. Manageability Considerations . . . . . . . . . . . . . . . . 17
9.1. Control of Function and Policy . . . . . . . . . . . . . 17
9.2. Information and Data Models . . . . . . . . . . . . . . . 17
9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 17
9.4. Verify Correct Operations . . . . . . . . . . . . . . . . 17
9.5. Requirements On Other Protocols . . . . . . . . . . . . . 17
9.6. Impact On Network Operations . . . . . . . . . . . . . . 18
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. Ackwonoledgement . . . . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
12.1. Normative References . . . . . . . . . . . . . . . . . . 18
12.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Contributor Addresses . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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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.dhodylee-pce-pcep-ls] describes a set of extensions to PCEP to
provide Link-State (and TE) distribution. This draft presents
motivations for optimizations to the base PCEP Link-State transport
procedure and specifies the required Path Computation Element
Communication Protocol (PCEP) extensions. This draft specifies
following optimizations for Link-State Synchronization and the
corresponding PCEP procedures and extensions:
o Link-State Synchronization Avoidance: To skip Link-State (and TE)
synchronization if the state has survived and not changed during
session restart.(See Section 3)
o Incremental Link-State Synchronization: To do incremental (delta)
Link-State (and TE) Synchronization when possible.(See Section 4)
o PCE-triggered Initial Synchronization: To let PCE control the
timing of the initial Link-State (and TE) Synchronization.(See
Section 5)
o PCE-triggered Re-synchronization: To let PCE re-synchronize the
Link-State (and TE) information for sanity check.(See Section 6)
1.1. 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].
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.dhodylee-pce-pcep-ls]: LSRpt, Link-State (and TE), LS
Link-State (and TE): "LS" is interchangably used for the keyword
"Link-State (and TE)".
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.
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The following terms are defined in this document:
LS-DB: Link-State (and TE) Database.
LS Sync: LS Synchronization, an operation to send LS information
synchronization request to PCC by LSRpt message with LS-ID 0.
LS-Info: One LS information (i.e. LS Node/Link/Prefix defined in I-
D.dhodylee-pce-pcep-ls).
3. LS Synchronization Avoidance
3.1. Motivation
The purpose of LS Synchronization is to provide a checkpoint-in-time
state replica of a PCC's Link-State (and TE) information in a PCE.
LS Synchronization is performed immediately after the initialization
phase ([RFC5440]). [I-D.dhodylee-pce-pcep-ls] describes the basic
mechanism for LS synchronization.
LS Synchronization is not always necessary following a PCEP session
restart. If the Link-State (and TE) information 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 PCE to become fully operational.
3.2. LS Synchronization Avoidance Procedure
LS Synchronization MAY be skipped following a PCEP session restart if
the Link-State (and TE) information of both PCEP peers did not change
during the period prior to session re-initialization. To be able to
make this determination, LS-DB must be exchanged and maintained by
both PCE and PCC during normal operation. This is accomplished by
keeping track of the changes to the Link-State (and TE) Database (LS-
DB), using a version tracking field called the LS-DB Version Number.
The LS-DB Version Number, carried in LS-DB-VERSION TLV (see
Section 7.2), is owned by a PCC and it MUST be incremented by 1 for
each successive change in the PCC's LS-DB. The LS-DB 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 LS re-
synchronization, the PCE speaker receiving this node should send back
a PCErr with Error-type TBD1 Error-value 1 'Received an invalid LS-DB
Version Number', and close the PCEP session. Operations that trigger
a change to the local LS-DB include but not limited to -
- a change in the link status or attributes(i.e. bandwidth, metric
etc), addition or deletion of link.
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- a change in the node attributes, addition or deletion of node.
- a change in the prefix attributes, addition or deletion of prefix.
LS Synchronization avoidance is advertised on a PCEP session during
session startup using the LS-INCLUDE-DB-VERSION (S) bit in the LS-
CAPABILITY TLV (see Section 7.3). 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 case of such mobility, each PCEP peer includes the SPEAKER-
ENTITY-ID TLV in the OPEN message. SPEAKER-ENTITY-ID TLV is
described in [I-D.ietf-pce-stateful-sync-optimizations]
If both PCEP speakers set the S flag in the OPEN object's LS-
CAPABILITY TLV to 1, the PCC MUST include the LS-DB-VERSION TLV in
each LS object of the LSRpt message. If the LS-DB-VERSION TLV is
missing in a LSRpt message, the PCE will generate an error with
Error-Type 6 (mandatory object missing) and Error-Value TBD2 'LS-DB-
VERSION TLV missing' and close the session. If LS Synchronization
avoidance has not been enabled on a PCEP session, the PCC SHOULD NOT
include the LS-DB-VERSION TLV in the LS object and the PCE SHOULD
ignore it, if it were to receive one.
If a PCE's LS-DB survived the restart of a PCEP session, the PCE will
include the LS-DB-VERSION TLV in its OPEN object, and the TLV will
contain the last LS-DB Version Number received on an LS Report from
the PCC in the previous PCEP session. If a PCC's LS-DB survived the
restart of a PCEP session, the PCC will include the LS-DB-VERSION TLV
in its OPEN object and the TLV will contain the latest LS-DB Version
Number. If a PCEP speaker's LS-DB did not survive the restart of a
PCEP session, the PCEP speaker MUST NOT include the LS-DB-VERSION TLV
in the OPEN object.
If both PCEP speakers include the LS-DB-VERSION TLV in the OPEN
Object and the TLV values match, the PCC MAY skip LS Synchronization.
Otherwise, the PCC MUST perform complete LS Synchronization. If the
PCC attempts to skip LS Synchronization (i.e., the SYNC Flag = 0 on
the first LS Report from the PCC, the PCE MUST send back a PCErr with
Error-Type TBD1 Error-Value 2 'LS-DB version mismatch', and close the
PCEP session.
If LS Synchronization is required, then prior to completing the
initialization phase, the PCE MUST mark any LS-Infos in the LS-DB
that were previously reported by the PCC as stale. When the PCC
reports a LS-Info during LS Synchronization, if the LS-Info already
exists in the LS-DB, the PCE MUST update the LS-DB and clear the
stale marker from the LS-Info. When it has finished LS
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Synchronization, the PCC MUST immediately send an end of LS
Synchronization marker. The end of synchronization marker is a LS
Report (LSRpt) message with an LS object containing a LS-ID of 0 and
with the SYNC flag set to 0. The LS-DB-VERSION TLV MUST be included
in this LSRpt message. On receiving this LS Report, the PCE MUST
purge any LS-Infos from the LS-DB that are still marked as stale. It
should be noted that PCE may receive the same Link-state and TE
information from multiple PCCs and the purging should take that into
account.
Note that a PCE/PCC MAY force LS Synchronization by not including the
LS-DB-VERSION TLV in its OPEN object.
Since a PCE does not make changes to the LS-DB 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 LS-DB-VERSION TLV, were
it to receive one from a PCE.
Figure 1 shows an example sequence where the LS synchronization is
skipped.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---Open--, |
|LS-DBv=82 \ ,---Open-----|
| S=1 \ /LS-DBv=82 |
| \/ S=1 |
| /\ |
| / `----------->| (OK to skip
(Skip |<---------` | LS sync)
LS sync)| . |
| . |
| . |
| |
|---LSRpt,LS-DBv=83,SYNC=0-->| (Regular
| | LS Report)
|---LSRpt,LS-DBv=84,SYNC=0-->| (Regular
| | LS Report)
|---LSRpt,LS-DBv=85,SYNC=0-->|
| |
Figure 1: LS Synchronization Skipped
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Figure 2 shows an example sequence where the LS Synchronization is
performed due to LS-DB Version mismatch during the PCEP session
setup. Note that the same LS Synchronization sequence would happen
if either the PCC or the PCE would not include the LS-DB-VERSION TLV
in their respective Open messages.
+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---Open--, |
|LS-DBv=86 \ ,---Open-----|
| S=1 \ /LS-DBv=82 |
| \/ S=1 |
| /\ |
| / `----------->| (Expect sync)
(Do |<---------` |
sync) | |
| |
|---LSRpt,LS-DBv=86,SYNC=1-->| (Sync start)
| . |
| . |
| . |
|---LSRpt,LS-DBv=86,SYNC=0-->| (Sync done)
| . |(Purge LS-Info
| . | if applicable)
| . |
|---LSRpt,LS-DBv=87,SYNC=0-->| (Regular
| | LS Report)
|---LSRpt,LS-DBv=88,SYNC=0-->| (Regular
| | LS Report)
|---LSRpt,LS-DBv=89,SYNC=0-->|
| |
Figure 2: LS Synchronization Performed
Figure 3 shows an example sequence where the LS Synchronization is
skipped, but because one or both PCEP speakers set the S Flag to 0,
the PCC does not send LS-DB-VERSION TLVs in subsequent LSRpt messages
to the PCE. If the current PCEP session restarts, the PCEP speakers
will have to perform LS Synchronization, since the PCE does not know
the PCC's latest LS-DB Version Number information.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---Open--, |
|LS-DBv=82 \ ,---Open-----|
| S=0 \ /LS-DBv=82 |
| \/ S=0 |
| /\ |
| / `----------->| (OK to skip
(Skip |<---------` | LS sync)
LS sync)| . |
| . |
| . |
| |
|--------LSRpt,SYNC=0------->| (Regular
| | LS Report)
|--------LSRpt,SYNC=0------->| (Regular
| | LS Report)
|--------LSRpt,SYNC=0------->|
| |
Figure 3: LS Synchronization Skipped, no LS-DB-VERSION TLVs sent from
PCC
4. Incremental LS Synchronization
[I-D.dhodylee-pce-pcep-ls] describes the LS synchronization mechanism
during session initialization between PCCs and PCEs. During the LS
synchronization, a PCC sends the information of its LS-DB to the PCE
based on the local policy. In order to reduce the LS Synchronization
overhead when there is a small number of LS-DB change in the network
between PCEP session restart, this section defines a mechanism for
incremental (Delta) LS synchronization.
4.1. Motivation
According to [I-D.dhodylee-pce-pcep-ls], if a PCEP session restarts,
PCCs send snapshot of LS-DB information to the PCE, though LS-DB did
not change. And as per Section 3 (LS Synchronization Avoidance
Procedure), if there is a change in a small number of LS-Infos. PCC
yet sends complete snapshot of LS-DB information to the PCE, which
takes a long time and consume large communication channel bandwidth.
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4.2. Incremental Synchronization Procedure
Section 3 describes LS Synchronization avoidance by using LS-DB-
VERSION TLV in its OPEN object. This section extends this idea to
only synchronize the delta (changes) in case of version mismatch.
If both PCEP speakers include the LS-DB-VERSION TLV in the OPEN
object and the LS-DB-VERSION TLV values match, the PCC MAY skip LS
Synchronization. Otherwise, the PCC MUST perform LS Synchronization.
Incremental LS Synchronization capability is advertised on a PCEP
session during session startup using the LS-DELTA-SYNC-CAPABILITY (D)
bit in the capabilities TLV (see Section 7.3). Instead of dumping
full LS-DB to the PCE again, PCC synchronizes the delta (changes) as
described in Figure 4 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 complete LS Synchronization procedure as described in
[I-D.dhodylee-pce-pcep-ls]. If a PCC has to force complete LS
Synchronization due to reasons including but not limited: (1) local
policy configured at the PCC; (2) no sufficient LS-DB 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 complete LS
Synchronization with D flag set to 0 in the subsequent open message.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|---Open--, |
|LS-DBv=86 \ ,---Open-----|
| S=1 \ /LS-DBv=82 |
| D=1 \/ S=1 |
| /\ D=1 |
| / `----------->| (Expect Delta sync)
(Do |<---------` | (Donot purge
Delta | | LS-Infos)
sync) | |
|---LSRpt,LS-DBv=86,SYNC=1-->| (Delta Sync start)
| . |
| . |
| . |
|---LSRpt,LS-DBv=86,SYNC=0-->| (Sync done)
| | LS-ID=0)
| |
|---LSRpt,LS-DBv=87,SYNC=0-->| (Regular
| | LS Report)
|---LSRpt,LS-DBv=88,SYNC=0-->| (Regular
| | LS Report)
|---LSRpt,LS-DBv=89,SYNC=0-->|
| |
Figure 4: Incremental Synchronization Procedure
As per Section 3, the LS-DB Version Number is incremented each time a
change is made to the PCC's local LS-DB. Each LS-Info is associated
with the DB version at the time of change. This is needed to
determine which LS-Info needs to be synchronized in incremental LS
Synchronization.
PCC MAY store a then history of LS-DB change that happened between
the PCEP session(s) restart in order to carry out incremental LS
Synchronization. After the synchronization procedure finishes, the
PCC can dump this history information. In the example shown in
Figure 4, the PCC needs to store the LS-DB changes that happened
between DB Version 83 to 86 and synchronizes these changes only when
performing incremental LS-DB update. So a PCC needs to remember the
LS-DB changes that happened when an existing PCEP session to a PCE
goes down in the hope of doing incremental synchronization when the
session is re-established.
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If a PCC finds out it does not have sufficient information to
complete incremental synchronization after advertising incremental LS
Synchronization capability, it MUST send a PCErr with Error-Type TBD1
and Error-Value 3 'A PCC indicates to a PCE that it can not complete
the LS synchronization' and terminate the session.
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 PCE connected to the network via one
network node, it is desirable to control the timing of PCC LS
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 PCE and the network. The method proposed,
i.e., allowing PCE to trigger the LS 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 LS Synchronization Procedure
Support of PCE-triggered LS Synchronization is advertised during
session startup using the LS-TRIGGERED-INITIAL-SYNC (F) bit in the
LS-CAPABILITY TLV (see Section 7.3).
As per [I-D.dhodylee-pce-pcep-ls], LSRpt is sent from PCC to PCE,
this document extends the usage of LSRpt to trigger syncronization.
Where a PCC can send a LSRpt (for LS Sync) with an LS object
containing a LS-ID of 0 and with the SYNC flag set to 1. This LSRpt
message is the trigger for the PCC to enter the synchronization phase
and start sending LSRpt messages.
If the LS-TRIGGERED-INITIAL-SYNC capability is not advertised and the
PCC receives a LSRpt with the SYNC flag set to 1, it MUST send a
PCErr for LSRpt(LS Sync from PCE) with Error-Type TBD1 and Error-
Value 4 'Attempt to trigger synchronization when the PCE triggered
synchronization capability has not been advertised'.
A PCE MAY choose to control the LS Synchronization process. To allow
PCE to do so, PCEP speakers MUST set T bit to 1 to indicate this (as
described in Section 7.3). If the LS-DB version is mis-matched, it
can send a LSRpt message with LS-ID = 0 and SYNC = 1 in order to
trigger the LS Synchronization process. In this way, the PCE can
control the sequence of LS Synchronization among all the PCCs that
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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
LSRpt messages to the PCE before it triggers the LS Synchronization.
This PCE-triggering capability can be applied to both full and
incremental LS Synchronization. If applied to the later, the PCCs
only send information that PCE does not possess, which is inferred
from the LS-DB version information exchanged in the OPEN message (see
Section 3.2) for detailed procedure).
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 LS-DB. Therefore, it can be
beneficial to be able to re-synchronize LS-DB even after the session
has been established. The PCE may use this approach to continuously
sanity check its LS-DB against the network, or to recover from error
conditions without having to tear down sessions.
6.2. PCE-triggered LS Re-synchronization Procedure
Support of PCE-triggered LS Synchronization is advertised during
session startup using the LS-TRIGGERED-RESYNC (T) bit in the LS-
CAPABILITY TLV (see Section 7.3).
The PCE triggers re-synchronization of the entire LS-DB. The PCE
MUST first mark all LS-Infos in the LS-DB that were previously
reported by the PCC as stale and then send a LSRpt (for LS Sync) with
an LS object containing a LS-ID of 0 and with the SYNC flag set to 1.
This LSRpt message is the trigger for the PCC to enter the
synchronization phase and start sending LSRpt messages. After the
receipt of the end-of-synchronization marker, the PCE will purge LS-
Infos which were not refreshed.
If the LS-TRIGGERED-RESYNC capability is not advertised and the PCC
receives a LSRpt with the SYNC flag set to 1, it MUST send a PCErr
with Error-Type TBD1 and Error-Value 4 'Attempt to trigger
synchronization when the TRIGGERED-SYNC capability has not been
advertised'.
Once the state re-synchronization is triggered by the PCE, the
procedures and error checks remain unchanged from the full state
synchronization ([I-D.dhodylee-pce-pcep-ls]). This would also
include PCE triggering multiple state re-synchronization requests
while synchronization is in progress.
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+-+-+ +-+-+
|PCC| |PCE|
+-+-+ +-+-+
| |
|<----LSRpt, SYNC=1 -----| Trigger
| (LSID=0) | re-sync
| |
|-----LSRpt, SYNC=1----->| (Sync start)
| . |
| . |
| . |
|-----LSRpt, SYNC=1----->|
| . |
| . |
| . |
| |
|-----LSRpt, SYNC=0----->| (End of sync marker
| | LS Report
| | for LS-ID=0)
| | (LS Sync done)
Figure 5: PCE Triggered Complete LS re-synchronization
7. PCEP Extensions
7.1. Link-State(LS) Report Message
A PCEP LS Report message (also referred to as LSRpt message) is a
PCEP message sent by a PCC to a PCE to report the LS information.
The definition of the LSRpt message from [I-D.dhodylee-pce-pcep-ls]
is extended to use LSRpt message with LS-ID = 0 to request LS
Synchronization from PCE to PCC.
If a PCC that does not support extention defined in this document
receives a LSRpt message, it will act according to existing behavior
of receiving invalid message. If a PCC supports the extention, but
did not set the flag T or F, and receives the LSRpt message, it sends
PCErr message as described earlier in section [x] and [y]. If a PCC
supports the extention and set the flag T or F, and receives the
LSRpt message without LS-ID as 0 and SYNC flag set, PCC will send an
error message with Error-Type TBD1 Error-Value 6 'Invalid LSRpt
message'.
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7.2. Capability Advertisement
The LS-DB Version Number is an carried in optional LS-DB-VERSION TLV
that MAY be included in the OPEN object and the LS object. This TLV
MUST NOT be included if LS-INCLUDE-DB-VERSION bit in LS-CAPABILITY
TLV is not set.
The format of the LS-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS-DB Version Number |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: LS-DB-VERSION TLV format
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 LS-DB
Version Number.
7.3. Advertising Support of Synchronization Optimizations
Support for each of the optimizations described in this document
requires advertising the corresponding capabilities during session
establishment.
New flags are defined for the LS-CAPABILITY TLV defined in
[I-D.dhodylee-pce-pcep-ls].
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|S|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: LS-CAPABILITY TLV Format
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The value comprises a single field - Flags (32 bits):
R (LS-REMOTE-BIT - 1 bit): Defined in [I-D.dhodylee-pce-pcep-ls]
S (LS-INCLUDE-DB-VERSION - 1 bit): If set to 1 by both PCEP speakers,
the PCC will include the LS-DB-VERSION TLV in each LS object. See
Section 3 for details.
T (LS-TRIGGERED-RESYNC - 1 bit): If set to 1 by both PCEP speakers,
the PCE can trigger re-synchronization of LS-Infos at any point in
the life of the session. See Section 6 for details.
D (LS-DELTA-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 for details.
F (LS-TRIGGERED-INITIAL-SYNC - 1 bit): If set to 1 by both PCEP
speakers, the PCE SHOULD trigger initial (first) LS synchronization.
See Section 5 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= TBD2 This document
LS-DB-VERSION TLV missing
TBD1 LS synchronization This document
error
Error-Value= TBD(suggested This document
value 1):Received an invalid
LSDB Version Number
Error-Value= TBD(suggested This document
value 2): LS-DB
version mismatch.
Error-Value=TBD(suggested This document
value 3): PCC indicates to a
PCE that it cannot complete
the LS Synchronization
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 5): LS-DB-VERSION
TLV Missing when LS
synchronization avoidance is
enabled.
Error-Value=TBD(suggested This document
value 6): Invalid LSRpt
message.
8.2. PCEP TLV Type Indicators
This document defines the following new PCEP TLVs:
Value Meaning Reference
TBD LS-DB-VERSION This document
8.3. LS-CAPABILITY Flags
The following values are defined in this document for the Flags field
in the LS-CAPABILITY TLV in the OPEN object:
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Bit Description Reference
TBD
(Suggested value 30) LS-INCLUDE-DB-VERSION This document
(Suggested value 29) LS-TRIGGERED-RESYNC This document
(Suggested value 28) LS-DELTA-SYNC-CAPABILITY This document
(Suggested value 27) LS-TRIGGERED-INITIAL-SYNC This document
9. Manageability Considerations
All manageability requirements and considerations listed in [RFC5440]
and [I-D.dhodylee-pce-pcep-ls] 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.
9.2. Information and Data Models
PCEP session configuration and information in the PCEP MIB module
SHOULD be extended to include advertised LS Capabilities, LS-DB
Version Number and LS synchronization status, Message statistics.
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 section 8.4 of [RFC5440] also apply to PCEP
protocol extensions defined in this document. In addition to
monitoring parameters defined in [RFC5440], a PCEP implementation
with LS-DB SHOULD provide the following parameters:
o Total number of LSRpt(Synchronization request) requests
o LS-DB Version Number and synchronization status
9.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any new requirements
on other protocols.
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9.6. Impact On Network Operations
Mechanisms defined in section 8.6 of [RFC5440] also apply to PCEP
protocol extensions defined in this document.
Additionally, a PCEP implementation SHOULD allow a limit to be placed
on the amount and rate of LSRpt messages sent by a PCEP speaker and
processed by the peer. It SHOULD also allow sending a notification
when a rate threshold is reached.
10. Security Considerations
The security considerations listed in [I-D.dhodylee-pce-pcep-ls]
apply to this document as well. However, because the protocol
modifications outlined in this document allow the PCE to control LS
Re-synchronization timing and sequence, it also introduces a 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. Ackwonoledgement
The document borrows some of the text and structure from
[I-D.ietf-pce-stateful-sync-optimizations].
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<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>.
[I-D.dhodylee-pce-pcep-ls]
Dhody, D., Lee, Y., and D. Ceccarelli, "PCEP Extension for
Distribution of Link-State and TE Information.", draft-
dhodylee-pce-pcep-ls-00 (work in progress), September
2015.
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12.2. 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-03 (work in
progress), October 2015.
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Appendix A. Contributor Addresses
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560037
India
EMail: dhruv.ietf@gmail.com
Authors' Addresses
Venugopal Reddy Kondreddy
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560037
India
EMail: venugopalreddyk@huawei.com
Mahendra Singh Negi
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560037
India
EMail: mahendrasingh@huawei.com
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