PCE Working Group D. Dhody
Internet-Draft U. Palle
Intended status: Experimental Huawei Technologies India Pvt
Expires: February 18, 2013 Ltd
August 17, 2012
Supporting explicit-path per destination in Path Computation Element
Communication Protocol (PCEP) P2MP Path Request Message.
draft-dhody-pce-pcep-p2mp-per-destination-02
Abstract
The ability to determine paths of point-to-multipoint (P2MP)
Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
Traffic Engineering Label Switched Paths (TE LSPs) is one the key
requirements for Path Computation Element (PCE). [RFC6006] and
[PCE-P2MP-PROCEDURES] describes these mechanisms for intra and inter
domain environment.
Explicit Path in this document refers to the configured list of
network elements that MUST be traversed or MUST be excluded in the
final path computation. This should not be confused with the RSVP
terminology. Network elements can further be strict or loose hop.
This document describes extensions to the PCE communication Protocol
(PCEP) to define explicit-path per destination in P2MP context.
Status of This Memo
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This Internet-Draft will expire on February 18, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Need to Define Explicit Path Per Destination . . . . . . . . . 4
3.1. Inter Domain P2MP Path Computation . . . . . . . . . . . . 4
3.2. Intra Domain P2MP Path Computation . . . . . . . . . . . . 6
3.3. Backward Compatibility . . . . . . . . . . . . . . . . . . 8
4. Detailed Description . . . . . . . . . . . . . . . . . . . . . 8
4.1. Objective . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Request Message Format . . . . . . . . . . . . . . . . . . 8
4.3. Ordering Destinations in END-POINTS Objects . . . . . . . 9
4.3.1. Example . . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Manageability Considerations . . . . . . . . . . . . . . . . . 12
7.1. Control of Function and Policy . . . . . . . . . . . . . . 12
7.2. Information and Data Models . . . . . . . . . . . . . . . 13
7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 13
7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 13
7.5. Requirements On Other Protocols . . . . . . . . . . . . . 13
7.6. Impact On Network Operations . . . . . . . . . . . . . . . 13
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 13
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1. Introduction
The Path Computation Element (PCE) architecture is defined in
[RFC4655]. [RFC5862] mentions a P2MP PCE MUST be able to provide to
the path computation a limiting set of nodes that can be used as
branches for a P2MP path computation, or to provide a list of nodes
that must not be used as branch points. This document mention the
need to specify the branch points (or explict path) per destination.
[RFC6006] describe a PCE-based path computation procedure to compute
optimal constrained (G)MPLS P2MP TE LSPs. It also defines the format
of path request message used in P2MP, which limits explicit path in
form of IRO/XRO; to be applied to full P2MP tunnel and thus to only
the common path to all leaves.
This document describes the need for supporting explicit-path per
destination in intra and inter-domain P2MP scenario. It further
lists the path request format and mode of operations
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
The following terminology is used in this document.
Explicit-Path: Set of network elements configured by the
administrator that MUST be traversed or MUST be excluded.
IRO: Include Route Object.
PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph and applying computational
constraints.
P2MP: Point-to-Multipoint
P2P: Point-to-Point
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RRO: Record Route Object
RSVP: Resource Reservation Protocol
TE LSP: Traffic Engineering Label Switched Path.
XRO: Exclude Route Object.
3. Need to Define Explicit Path Per Destination
3.1. Inter Domain P2MP Path Computation
In the Figure 1 below, D1 is the root domain; D5 and D6 are the
destination domains.
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|
| +-------------+ +----------------+
| |D 3 | |D 6 |
| | +--+| | +--+ |
| | | || | | | |
| | +--+ +--+| | +--+ +--+ |
| | | | | | | | |
| | *--+ | | +--+ |
| | / +--+ | | +--+ |
| |/ | | | | | | |
| / +--+ | | +--+ +--+ |
| /| +--+ |+--------------+| | | |
|/ | | | ++-+ +-++ +--+ |
+-------------+/ | +--+ || | | || |
| /| | ++-+ +-++ |
| +--*|| +-------------+| |+----------------+
| | ||| | +--+ |
| +--+|| | | | |
| +--+ || | +--+ |
| | | || | |
| +--+ || | |
| || | +--+ |
|+--+ || | | | |
|| | || | +--+ |
|+--+ || | |
| || | +--+ |
| +--+ || +------------+ | | | |+----------------+
| | | || |D 2 +-++ +--+ +-++ D 5 |
| +--+ || | | || | || |
| || | +-++ +-++ |
| +--+|| | +--+ | | D 4 || +--+ |
| | ||| | | | | +--------------+| | | |
| +--*|| | +--+ | | +--+ |
| \| | | | +--+ |
|D 1 |\ | +--+ | | +--+ | | |
+-------------+|\ | | | | | | | +--+ |
| \| +--+ +--+ | +--+ |
| \ | | | |
| |\ +--+ | +--+ |
| | \ +--+ | | | | |
| | \| | | | +--+ |
| | *--+ | | |
| | | | |
| +------------+ +----------------+
|
|
As 100 | AS 200
|
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Figure 1: Domain Topology Example
[PCE-P2MP-PROCEDURES] defines inter-domain P2MP path computation
procedure and assumes that the sequence of domains for a path (the
path domain tree) will be known in advance due to deployment and
commercial limitations (e.g., inter-AS peering agreements). In the
Figure 2 below, the P2MP tree spans 5 domains. Destination in D6
would use the domain-sequence: D1-D3-D4-D6; and destination in D5
would use the domain-sequence: D1-D3-D4-D5.
D3 D6
/ \ /
D1 D4
\
D5
Figure 2: Domain Sequence Tree
Since different destinations will have different domain sequence
within the domain tree, it requires domain-sequence to be encoded in
form of IRO to be attached per destination. It cannot be encoded for
all destinations.
Thus domain-sequence encoded in form IRO (as per [DOMAIN-SEQ]) should
be attached to destinations and not attached to full P2MP tree.
3.2. Intra Domain P2MP Path Computation
Administrator at the source can exert stronger control by providing
explicit path (include, exclude, loose etc) per destination.
In Figure 3 shows the common path over which a common explicit path
in form of IRO and/or XRO can be set.
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+---+
| F |
/*---+
//
//
//
//
+---+ +---+ +---+ +---* +---+
| A +--+ B +--+ C +--+ D +---------+ E |
+---+ +---+ +---+ +---*\ +---+
| | \\
| | \\
| | \\
| | \\
|<-----common path------>| *---+
| | | G |
| | +---+
Explicit Path Here
Figure 3: Example
But as shown in Figure 4, once new destinations are added and branch
points are much nearer to ingress causing common path to reduce, the
administrator would not be able to apply the explicit path as before.
+---+ +---+
| H | | F |
*---+ /*---+
// //
// //
/ //
// //
+---+ +---* +---+ +---* +---+
| A +--+ B +--+ C +--+ D +---------+ E |
+---+ +---+ +---* +---*\ +---+
| | \\ \\
| | \\ \\
|<-------->| \\ \\
| Common | \\ \\
| path | *---+ *---+
| | | I | | G |
| | +---+ +---+
| |
| |
Figure 4: Example
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3.3. Backward Compatibility
Basic MPLS TE P2MP Tunnel configurations for various operators
support the configuration of explicit-path per destination. In some
operators where preconfigured path must be setup, during
configurations the path to each destination is configured as an
explicit path and attached to each destination.
It makes sense to apply explict path per destination instead of the
full P2MP tree.
4. Detailed Description
4.1. Objective
[RFC6006] defines Request Message Format and Objects, along with
<end-point-rro-pair-list>. This section introduce the concept of
<iro-list>, <xro-list> and <metric-list> which are added to the <end-
point-rro-pair-list> to support 'per destination'.
Use of <iro-list>, <xro-list> to carry explicit-path per destination
in intra-domain scenario.
Use of <iro-list> to carry domain-sequence per destination in inter-
domain scenario.
Use of <metric-list> to carry metric value of each calculated path
encoded in <rro-list>. In case of reoptimization of a P2MP tree,
each calculated S2L path MUST be accompanied by metric value.
4.2. Request Message Format
To carry explicit path for each destination, <END-POINTS> objects
need to be ordered and grouped in a way such that IRO object, XRO
object, RRO object and METRIC object can be associated with each
destination.
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The format of PCReq message is modified as follows:
<PCReq Message>::= <Common Header>
<request>
where:
<request>::= <RP>
<end-point-iro-xro-rro-metric-list>
[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
[<LOAD-BALANCING>]
where:
<end-point-iro-xro-rro-metric-list> ::=
<END-POINTS>
[<IRO-List>]
[<XRO-List>]
[<RRO-List>]
[<metric-list>]
[<end-point-iro-xro-rro-metric-list >]
<RRO-List>::=<RRO>[<BANDWIDTH>][<RRO-List>]
<metric-list>::=<METRIC>[<metric-list>]
<IRO-List>::=<IRO>[<IRO-List>]
<XRO-List>::=<XRO>[<XRO-List>]
From [RFC6006] usage of <end-point-rro-pair-list> is changed to <end-
point-iro-xro-rro-metric-list> in this document.
Note that the new format is backward compatible to [RFC6006] format.
4.3. Ordering Destinations in END-POINTS Objects
Multiple destinations are encoded into a single ENDPOINTS object,
Each Endpoint maybe followed by multiple lists of IROs, XROs, RROs or
METRICs. The first <IRO> object would belong to the first
destination, the second <IRO> object to the second destination and
hence forth. The first <XRO> object would belong to the first
destination, the second <XRO> object to the second destination and
hence forth...
Note that a destination (P2MP tree leaf) MAY have
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o both <IRO> and <XRO>
o <IRO> only
o <XRO> only
o No explicit path
To maintain the ordering between the destination and objects in the
list, there MAYBE a need to divide a set of destinations into
multiple ENDPOINTS, this explained in below example.
4.3.1. Example
Destination 1 has include IRO1 and exclude XRO1
Destination 2 has only include IRO2
Destination 3 has only exclude XRO3
Destination 4 has only exclude XRO4
Destination 5 has none
Here if we try to encode all destinations in one <ENDPOINT> and
objects in list, we will not map XRO3 to destination 3, the rule is
to map sequentially and thus XRO3 will belong to destination 2.
To avoid this we must break the set of destinations into two sets as
shown below
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+-----------------------------+
| Leaf Type |
+-----------------------------+
| Source IP |
+-----------------------------+
+------> | Destination 1 | <ENDPOINT>
| +-----------------------------+
| +-> | Destination 2 |
| * +-----------------------------+
| * | Destination 5 |
| * +-----------------------------+
| *
| * +-----------------------------+
+----*-> | IRO1 |
| * +-----------------------------+
| * | HOPI 1-1 |
| * +-----------------------------+
| * | .... | <IRO-List>
| * +-----------------------------+ with 2 IRO1, IRO2
| +-> | IRO2 |
| +-----------------------------+
| | HOPI 2-1 |
| +-----------------------------+
| | .... |
| +-----------------------------+
|
| +-----------------------------+
+-----> | XRO1 |
+-----------------------------+ <XRO-List>
| HOPX 1-1 | with 1 XRO1
+-----------------------------+
| .... |
+-----------------------------+
ENDPOINT1 carries destination 1, 2 and 5 and corresponding <iro-list>
and <xro-list>. Here Destination 1 has IRO1 and XRO1; Destination 2
has IRO2; and Destination 5 has none.
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+-----------------------------+
| Leaf Type |
+-----------------------------+
| Source IP |
+-----------------------------+
+------> | Destination 3 | <ENDPOINT>
| +-----------------------------+
| +-> | Destination 4 |
| * +-----------------------------+
| *
| * +-----------------------------+
+----*-> | XRO3 |
* +-----------------------------+
* | HOPX 3-1 |
* +-----------------------------+
* | .... | <XRO-List>
* +-----------------------------+ with 2 XRO3, XRO4
+-> | XRO4 |
+-----------------------------+
| HOPX 4-1 |
+-----------------------------+
| .... |
+-----------------------------+
ENDPOINT2 carries destination 3 and 4 and corresponding <xro-list>
only. Here destination 3 maps to XRO3 and Destination 4 to XRO4.
5. IANA Considerations
TBD
6. Security Considerations
PCEP security mechanisms as described in [RFC6006] and
[PCE-P2MP-PROCEDURES] are applicable for this document. This
document does not add any new security threat.
7. Manageability Considerations
7.1. Control of Function and Policy
Mechanisms defined in this document do not add any new control
function/policy requirements in addition to those already listed in
[RFC6006].
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7.2. Information and Data Models
Mechanisms defined in this document do not imply any new MIB
requirements in addition to those already listed in [PCE-P2MP-MIB].
7.3. 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 [RFC6006].
7.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC6006].
7.5. Requirements On Other Protocols
Mechanisms defined in this document do not imply any requirements on
other protocols in addition to those already listed in [RFC6006].
7.6. Impact On Network Operations
Mechanisms defined in this document do not have any impact on network
operations in addition to those already listed in [RFC6006].
8. Acknowledgments
We would like to thank Pradeep Shastry, Suresh babu, Quintin Zhao,
Daniel King and Chen Huaimo for their useful comments and
suggestions.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997.
9.2. Informative References
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture",
RFC 4655, August 2006.
[RFC5862] Yasukawa, S. and A. Farrel, "Path Computation
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Clients (PCC) - Path Computation Element (PCE)
Requirements for Point-to-Multipoint MPLS-TE",
RFC 5862, June 2010.
[RFC6006] Zhao, Q., King, D., Verhaeghe, F., Takeda, T.,
Ali, Z., and J. Meuric, "Extensions to the
Path Computation Element Communication
Protocol (PCEP) for Point-to-Multipoint
Traffic Engineering Label Switched Paths",
RFC 6006, September 2010.
[PCE-P2MP-PROCEDURES] Zhao, Q., Dhody, D., Ali, Z., Saad,, T.,
Sivabalan,, S., and R. Casellas, "PCE-based
Computation Procedure To Compute Shortest
Constrained P2MP Inter-domain Traffic
Engineering Label Switched Paths (draft-ietf-
pce-pcep-inter-domain-p2mp-procedures-02)",
May 2012.
[PCE-P2MP-MIB] Zhao, Q., Dhody, D., Palle, U., and D. King,
"Management Information Base for the PCE
Communications Protocol (PCEP) When Requesting
Point-to-Multipoint Services
(draft-zhao-pce-pcep-p2mp-mib-05)",
August 2012.
[DOMAIN-SEQ] Dhody, D., Palle, U., and R. Casellas,
"Standard Representation Of Domain Sequence
(draft-ietf-pce-pcep-domain-sequence-01)",
July 2012.
Authors' Addresses
Dhruv Dhody
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: dhruv.dhody@huawei.com
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Udayasree Palle
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: udayasree.palle@huawei.com
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