Internet Engineering Task Force Q. Zhao, Ed.
Internet-Draft Huawei Technology
Intended Status: Standards Track Daniel King
Expires: January 12, 2009 Old Dog Consulting
July 12, 2009
Extensions to the Path Computation Element Communication Protocol
(PCEP) for Point-to-Multipoint Traffic Engineering Label Switched Paths
draft-ietf-pce-pcep-p2mp-extensions-03.txt
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Abstract
Point-to-point Multiprotocol Label Switching (MPLS) and Generalized
MPLS (GMPLS) Traffic Engineering Label Switched Paths (TE LSPs) may
be established using signaling techniques, but their paths may first
be determined. The Path Computation Element (PCE) has been
identified as an appropriate technology for the determination of the
paths of P2MP TE LSPs.
This document describes extensions to the PCE communication Protocol
(PCEP) to handle requests and responses for the computation of paths
for P2MP TE LSPs.
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 RFC 2119 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . .
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . .
3. Protocol Procedures and Extensions . . . . . . . . . . . . . .
3.1. P2MP Capability Advertisement . . . . . . . . . . . . . .
3.1.1. Extend the TLV in the Existing PCE Discovery
Protocol . . . . . . . . . . . . . . . . . . . . . . .
3.1.2. Open Message Extension . . . . . . . . . . . . . . . .
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3.2. P2MP LSPs Efficient Presentation . . . . . . . . . . . . .
3.3. Indication of P2MP Path Computation Request/Reply . . . .
3.3.1. The Extension of RP Object . . . . . . . . . . . . . .
3.3.2. The New P2MP END-POINTS Object . . . . . . . . . . . .
3.4. Request Message Formats . . . . . . . . . . . . . . . . .
3.5. Reply Message Formats . . . . . . . . . . . . . . . . . .
3.6. P2MP Objective Functions and Metric Types . . . . . . . .
3.6.1. New Object Functions . . . . . . . . . . . . . . . . .
3.6.2. New Metric Object Types . . . . . . . . . . . . . . .
3.7. Non-Support of P2MP Path Computation. . . . . . . . . . .
3.8. Non-Support by Back-Level PCE Implementations. . . . . . .
3.9. P2MP TE Path Re-optimization Request . . . . . . . . . . .
3.10. Adding/pruning Leaves . . . . . . . . . . . . . . . . . .
3.11. Branch Nodes . . . . . . . . . . . . . . . . . . . . . . .
3.12. Synchronization of P2MP TE Path Computation Requests . . .
3.13. Request and Response Fragmentation . . . . . . . . . . . .
3.13.1 Request Fragmentation Procedure . . . . . . . . . . . .
3.13.2 Response Fragmentation Procedure . . . . . . . . . . .
3.13.3 Fragmentation Examples . . . . . . . . . . . . . . . .
3.14. UNREACH_DESTINATION object . . . . . . . . . . . . . . . .
3.15. P2MP PCEP Error Object . . . . . . . . . . . . . . . . . .
3.16. PCEP NO-PATH Indicator . . . . . . . . . . . . . . . . . .
4. Manageability Considerations . . . . . . . . . . . . . . . . .
4.1. Control of Function and Policy . . . . . . . . . . . . . .
4.2. Information and Data Models . . . . . . . . . . . . . . .
4.3. Liveness Detection and Monitoring . . . . . . . . . . . .
4.4. Verifying Correct Operation . . . . . . . . . . . . . . .
4.5. Requirements on Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . . .
4.6. Impact on Network Operation . . . . . . . . . . . . . . .
5. Security Considerations . . . . . . . . . . . . . . . . . . .
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . .
6.1 New Object Functions . . . . . . . . . . . . . . . . . . .
6.2 New Metric Object Types . . . . . . . . . . . . . . . . .
5.3 UNREACH_DESTINATION objects . . . . . . . . . . . . . . .
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .
8. References . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1. Normative References . . . . . . . . . . . . . . . . . . .
8.2. Informative References . . . . . . . . . . . . . . . . . .
9. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .
9.1. Contributors . . . . . . . . . . . . . . . . . . . . . .
10. Intellectual Property Consideration. . . . . . . . . . . . . .
11. Disclaimer of Validity . . . . . . . . . . . . . . . . . . . .
12. Full Copyright Statement . . . . . . . . . . . . . . . . . . .
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1. Introduction
The Path Computation Element (PCE) defined in [RFC4655] is an entity
that is capable of computing a network path or route based on a
network graph, and applying computational constraints. A Path
Computation Client (PCC) may make requests to a PCE for paths to be
computed.
[RFC4875] describes how to set up point-to-multipoint (P2MP) Traffic
Engineering Label Switched Paths (TE LSPs) for use in Multiprotocol
Label Switching (MPLS) and Generalized MPLS (GMPLS) networks.
The PCE is identified as a suitable application for the computation
of paths for P2MP TE LSPs [PCE-P2MP-APP].
The PCE communication protocol (PCEP) is designed as a communication
protocol between PCCs and PCEs for point-to-point (P2P) path
computations and is defined in [RFC5440]. However, that
specification does not provide a mechanism to request path
computation of P2MP TE LSPs.
This document presents extensions to PCEP to support P2MP path
computation satisfying the set of requirements described in [PCE-
P2MP-REQ].
This document relies on the semantics of PCEP for requesting path
computation for P2MP TE LSPs. A P2MP LSP is comprised of multiple
source-to-leaf (S2L) sub-LSPs. These S2L sub-LSPs are set up between
ingress and egress LSRs and are appropriately combined by the branch
LSRs using computation result from PCE to result in a P2MP TE LSP.
One request message from a PCC may signal one or more S2L sub-LSP
path computation requests to the PCE for a single P2MP LSP with
certain constraints. Hence the S2L sub-LSPs belonging to a P2MP LSP
can use one path computation request message or be split across
multiple path computation messages.
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1.1 Terminology
Terminology used in this document
TE LSP: Traffic Engineered Label Switched Path.
LSR: Label Switch Router.
OF: Objective Function: A set of one or more optimization criterion
(criteria) used for the computation of a single path (e.g. path cost
minimization), or the synchronized computation of a set of paths
(e.g. aggregate bandwidth consumption minimization, etc.).
P2MP: Point-to-Multipoint.
P2P: Point-to-Point.
This document also uses the terminology defined in [RFC4655],
[RFC4875], and [RFC5440].
2. Requirements
This section summarizes the PCEP requirements specific to Point to
Multipoint as described in [PCE-P2MP-REQ].
R1: Indication of P2MP Path Computation Request.
R2: Indication of P2MP Objective Functions.
R3: Non-Support of P2MP Path Computation.
R4: Non-Support by Back-Level PCE Implementations.
R5: Specification of Destinations.
R6: Indication of P2MP Paths.
R7: Multi-Message Requests and Responses.
R8: Non-Specification of Per-Destination Constraints and Parameters.
R9: Path Modification and Path Diversity.
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R10: Reoptimization of P2MP TE LSPs.
R11: Addition and Removal of Destinations from Existing Paths.
R12: Specification of Applicable Branch Nodes.
R13: Capabilities Exchange.
R14: The PCC should be able to request a PCE to compute secondary
P2MP path tree with partial path diversity for specific leaves or a
specific S2L sub-path.
R15: Sender of the request message can specify if the return result
from the PCE need to be represented in the compressed format or not.
3. Protocol Procedures and Extensions
The following sections describe the protocol extensions to satisfy
the requirements specified in the previous section.
3.1. P2MP Capability Advertisement
3.1.1. Extend the TLV in the Existing PCE Discovery Protocol
Since the [RFC5088] has specified that we can not add additional sub-
TLV to the PCED TLV, we will define new bits to go in the existing 32
bits PCE Caps Flags to indicate the capability of P2MP for the PCC
and PCE.
3.1.2. Open Message Extension
Based on the Capabilities Exchange requirement described in [PCE-
P2MP-REQ], if a PCE does not advertise its P2MP capability through
discovery and the capability is not configured to the PCC, we need to
use PCEP to allow a PCC to discover which PCEs with which it
communicates support P2MP path computation. To satisfy this
requirement, we extend the OPEN object format by including a new
defined TLV for the capability of P2MP in the optional field. The
new defined capability TLV allows the PCE to advertise its path
computation capabilities.
The TLV type number will be assigned by IANA, the LENGTH value is 2
bytes. The value field is set to default value 0.
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Note that the capability TLV is meaningful only for a PCE so it will
typically appear only in one of the two Open messages during PCE
session establishment. However, in case of PCE cooperation (e.g.,
inter-domain), when a PCE behaving as a PCC initiates a PCE session
it SHOULD also indicate its Path Computation capability.
3.2. P2MP LSPs Efficient Presentation
In the request message of the adding of leaves, optimization of P2MP
TE LSPs as specified in [PCE-P2MP-REQ], and in the reply message, we
need to pass an existing P2MP LSP between the PCC and PCE. In these
cases, we need new path objects for efficiently passing the existing
P2MP LSP between PCE to PCC.
We suggest to using the ERO/SERO and RRO/SRRO to represent each
individual S2L sub-LSP. The contents of ERO/RRO are same as defined
in the [RFC5440] and the contents of SERO and SRRO are same as
defined in RFC4875 for the RSVP extension of P2MP except we need
assign the new class and type for all of them.
3.3. Indication of P2MP Path Computation Request/Reply
The existing P2P RP object is extended so that it can signal to the
receiver of the request or reply message that it is for P2P or P2MP
path computation. Also the END-POINT object is extended to improve
the efficiency of the message exchange between PCC and PCE in the
case of P2MP path computation.
3.3.1. The Extension of RP Object
The PCE path computation request/reply message adds an explicit
parameter to allow a receiving PCE to identify that the request/reply
is for a P2MP path and also to specify if the route is represented in
the compress format or not.
The F bit
The M bit is added in the flag bits field of the RP object to signal
the receiver of the message that the request/reply is for P2MP or
not.
The E bit is added in the flag bits field of the RP object to signal
the receiver of the message that the route is in the compress format
or not.
The extended format of the RP object body to include the F bit, M
bit and the E bit is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |F|E|M| |O|B|R| Pri |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request-ID-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: RP Object Body Format
The following flags are added in this draft:
o M ( P2MP bit - 1 bit):
0: This indicates that this is not PCReq/PCRrep for P2MP.
1: This indicates that this is PCReq or PCRep message for P2MP.
o E ( ERO-compression bit - 1 bit):
0: This indicates that the route is not in the compressed
format.
1: This indicates that the route is in the compressed format.
o F ( RP fragmentation bit - 1 bit):
0: This indicates that the RP is not fragmented or it is the
last piece of the fragmented RP.
1: This indicates that the RP is fragmented and this is not
the last piece of the fragmented RP and the receiver
need to wait until it receives an RP with the same RP-ID
and with the F bit is set to 0.
3.3.2. The New P2MP END-POINTS Object
To represent the end points for a P2MP path efficiently, we define a
new type of end-points object for P2MP path.
With this new END-POINTS object, the PCE path computation request
message is expanded in a way such that it allows a single request
message to list multiple destinations.
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There are 4 types of leaves in a P2MP request:
o New leaves to add;
o Old leaves to remove;
o Old leaves whose path can be modified/reoptimized;
o Old leaves whose path must be left unchanged.
A given END-POINTS object gathers the leaves of a given type. The
type of leaf in a given END-POINTS object is identified by the END-
POINTS object leaf type field.
So four values are possible for the leaf type field:
1. New leaves to add;
2. Old leaves to remove;
3. Old leaves whose path can be modified/reoptimized;
4. Old leaves whose path must be left unchanged.
With this new END-POINTS object, the END-POINTS portions of a request
message for the multiple destinations can be roughly reduced up to
50% for a P2MP path where a single source address has a very large
number of destinations.
Note that A P2MP path computation request can mix the different type
of leaves by including several END-POINTS object per RP object as
shown in PCReq BNF format in next section.
The format of the new END-POINTS object body for IPv4 (Object-Type 3)
is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Leaf type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The New P2MP END-POINTS Object Body Format for IPv4
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The format of the END-POINTS object body for IPv6 (Object-Type 4) is
as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Leaf type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Source IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination IPv6 address (16 bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The New P2MP END-POINTS Object Body Format for IPv6
The END-POINTS object body has a variable length of multiple of 4
bytes for IPv4 and multiple of 16 bytes for IPv6.
3.4. Request Message Formats
As per [RFC5511] the format of the PCReq message is as follows.
Please see Appendix A for a full set of RBNF fragments defined in
this document and the necessary code license.
Below is the message format for the request message:
<PCReq Message>::= <Common Header>
<request>
where:
<request>::= <RP>
<end-point-rro-pair-list>
[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
[<LOAD-BALANCING>]
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where:
<end-point-rro-pair-list>::=
<END-POINTS>[<RRO-List>][<BANDWIDTH>]
[<end-point-rro-pair-list>]
<RRO-List>::=<RRO>[<BANDWIDTH>][<RRO-List>]
<metric-list>::=<METRIC>[<metric-list>]
Figure 4: The Message Format for the Request Message
Note we preserve compatibility with the [RFC5440] definition of
<request>. At least one instance of <endpoints> must be present
in this definition.
3.5. Reply Message Formats
As per [RFC5511] the format of the PCRep message is as follows.
Please see Appendix A for a full set of RBNF fragments defined in
this document and the necessary code license.
Below is the message format for the reply message:
<PCRep Message>::= <Common Header>
<response>
<response>::=<RP>
[<end-point-path-pair-list>]
[<NO-PATH>]
[<attribute-list>]
where:
<end-point-path-pair-list>::=
[<END-POINTS>]<path>[<end-point-path-pair-list>]
<path> ::=(ERO)|(SERO)|<path>]
<attribute-list>::=[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
Figure 5: The Message Format for the Reply Message
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The optional END-POINTS in the reply message is used to specify which
paths are removed, changed, not changed, or added for the request.
The path is only needed for the end points which are added or
changed.
If the ERO-Compress bit was set to 1 in request then the path will be
formed by an ERO followed by a list of SERO. Otherwise it is a list
of ERO.
Note we preserve compatibility with the [RFC5440] definition of
<response> and the optional <end-point-pair-list> and <path>.
3.6. P2MP Objective Functions and Metric Types
3.6.1. New Object Functions
Six objective functions have been defined in [RFC5541] for P2P path
computation.
This document defines two additional objective functions, namely SPT
(Shortest Path Tree) and MCT (Minimum Cost Tree) that apply to P2MP
path computation. Hence two new objective function codes have to be
defined.
The description of the two new objective functions is as follows.
Objective Function Code: 7 (suggested value, to be assigned by IANA)
Name: Shortest Path Tree (SPT)
Description: Minimize the maximum source-to-leaf cost with respect to
a specific metric or to the TE metric used as the default metric when
the metric is not specified. (e.g. TE or IGP metric)
Objective Function Code: 8 (suggested value, to be assigned by IANA)
Name: Minimum Cost Tree (MCT)
Description: Minimize the total cost of the tree, that is the sum of
the costs of tree links, with respect to a specific metric or to the
TE metric used as the default metric when the metric is not
specified..
Processing these two new objective functions is subject to the rules
defined in [RFC5541].
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3.6.2. New Metric Object Types
There are three types defined for the <METRIC> object in [RFC5440],
namely, the IGP metric, the TE metric and the hop count metric. This
document defines three other types for the <METRIC> object: the P2MP
IGP metric, the P2MP TE metric, and the P2MP Hop Count metric. They
encode the sum of the metrics of all links of the tree. We propose
the following values for these new metric types (to be assigned by
IANA):
o P2MP IGP metric: T=4
o P2MP TE metric: T=5
o P2MP hop count metric: T=6
3.7. Non-Support of P2MP Path Computation.
o if a PCE receives a P2MP path request and it understands the P2MP
flag in RP object, but the PCE is not capable of P2MP computation,
the PCE MUST send a PCErr message with a PCEP-ERROR Object and an
Error-Value. The corresponding P2MP path computation request MUST
be cancelled. (Error-Type and Error-Value are defined in this
document).
o If the PCE does not understand the P2MP flag in the RP object,
then the PCE MUST send a PCErr message with a new error type
"Unknown RP flag".
3.8. Non-Support by Back-Level PCE Implementations.
If we accidentally send the P2MP request to a PCE which does not
support the PCEP P2MP extensions yet, then it will reject the request
because it cannot understand the new END-POINTS object.
3.9. P2MP TE Path Re-optimization Request
The re-optimization request for a P2MP TE path is specified by R bit
in the RP object similarly to the re-optimization request for a P2P
TE path. The only difference is that the user must insert the list
of RRO after each type of END-POINTS as described in the PCReq
message format section.
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So the PCReq message would look like this:
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 3
RRO list
OF (optional)
Figure 6: PCReq Message Example 1 for Optimization
In this example, we request re-optimization of path to all leaves
without adding or pruning leaves. That is only one END-POINT of type
3. The RRO list is representing the P2MP LSP before the optimization
and the modifiable path leaves are indicated in the END-POINTS
object.
Optionally it is possible to specify some leaves whose path cannot be
modified. The PCReq message would then look like this:
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 3
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 7: PCReq Message Example 2 for Optimization
3.10. Adding/pruning Leaves
When adding new leaves or removing old leaves to the existing P2MP
tree, by supplying a list of existing leaves, one may be able to
optimize the new P2MP tree. This section explains ways to add new
leaves or remove old leaves to the existing P2MP tree.
To add new leaves the user must build a P2MP request with an END-
POINTS with leaf type 1.
To Remove old leaves the user must build a P2MP request with an END-
POINTS with leaf type 2.
In any case it must also provides the list of old leaves and indicate
if they must be reoptimized or not by including END-POINTS with leaf
type 3 or 4 or both. In the future version, we may want to consider
to define error values when the condition is not satisfied (i.e.,
when there is no END-POINTS with leaf type 3 or 4, in the presence of
END-POINTS with leaf type 1 or 2).
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For old leaves the user must provide the old path as list of RROs
that immediately follows each END-POINTS object. In the future
version, we may want to consider to define error values when the
condition is not satisfied.
So eventually the following cases are possible when modifying an
existing P2MP LSP:
Case 1: Adding leaves with full reoptimization of existing paths
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 3
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 8: Adding Leaves with Full Reoptimization
Case 2: Adding leaves with partial reoptimization of existing paths
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 1
END-POINTS for leaf type 3
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 9: Adding Leaves with Partial Reoptimization
Case 3: Adding leaves without reoptimization of existing paths
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 3
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 10: Adding Leaves without Reoptimization
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Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 2
RRO list
END-POINTS for leaf type 3
RRO list
OF (optional)
Figure 11: Pruning Leaves with Full Reoptimization
Case 5: Pruning leaves with partial reoptimization of existing paths
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 2
RRO list
END-POINTS for leaf type 3
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 12: Pruning Leaves with Partial Reoptimization
Case 6: Pruning leaves without reoptimization of existing paths
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 2
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 13: Pruning Leaves without Reoptimization
Case 7: Adding and pruning leaves full reoptimization of existing
paths
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 1
END-POINTS for leaf type 2
RRO list
END-POINTS for leaf type 3
RRO list
OF (optional)
Figure 14: Adding and Pruning Leaves full Reoptimization
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Case 8: Adding and pruning leaves with partial reoptimization of
existing paths
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 1
END-POINTS for leaf type 2
RRO list
END-POINTS for leaf type 3
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 15: Adding and Pruning Leaves with Partial
Reoptimization
Case 9: Adding and pruning leaves without reoptimization of existing
paths
Common Header
RP with P2MP flag/R bits set
END-POINTS for leaf type 1
END-POINTS for leaf type 2
RRO list
END-POINTS for leaf type 4
RRO list
OF (optional)
Figure 16: Adding and Pruning Leaves without Reoptimization
3.11. Branch Nodes
Before computing the P2MP path, a PCE must be provided means to know
which nodes in the network are capable of acting as branch LSRs. A
PCE can discover such capability by using the mechanisms defined in
[PCE-P2MP-REQ].
3.12. Synchronization of P2MP TE Path Computation Requests
There are cases when multiple P2MP LSPs' computations need to be
synchronized. For example, one P2MP LSP is the backup of another
P2MP LSP. In this case, the path diversity for these two LSPs need
to be considered during the path computation.
The synchronization can be done by just using the existing SVEC
functionality.
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Example of synchronizing two P2MP LSPs, each has two leaves for Path
Computation Request Messages is illustrated as below:
Common Header
SVEC for sync of LSP1 and LSP2
OF (optional)
END-POINTS1 for P2MP
RRO1 list
END-POINTS2 for P2MP
RRO2 list
Figure 17: PCReq Message Example for Synchronization
We propose that two new flags are also added to the SVEC object for
path dependent computation requests. The first new flag is to allow
the PCC to request that the PCE should compute a secondary P2MP path
tree with partial path diversity for specific leaves or a specific
S2L sub- path to the primary P2MP path tree. The second flag, would
allow the PCC to request that partial paths should be link
direction diverse.
3.13. Request and Response Fragmentation
In certain scenarios the request may not fit into a single request or
response message. For example, if a tree has many hundreds or
thousands of leaves. Then the request or response may need to
be fragmented into multiple messages.
The F bit has been outlined in section 3.3.1. The Extension of RP
Object, of this document. The F bit is used in the RP object header
to signal that the an intial request or response was too large to fit
into a single message and should therfore be fragmented into
multiple requests. In order to indentify the single request or
response, each message will use the same request ID.
3.13.1 Request Fragmentation Procedure
If the intial request is too large to fit into a single request
message the PCC will split the requst over multiple messages. Each
message sent to the PCE will have the F bit set in the RP object
to signify that the request has been fragmented into multiple
messages. In order to indentify that a series of request messages
represents a single request, each message will use the same
request ID.
The assumption is that request messages are reliably delivered
and in sequence since PCEP relies on TCP.
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3.13.2 Response Fragmentation Procedure
Once the PCE computes a path based on the intial request a
response is sent back to the PCC. If the response is too large to fit
into a single response message the PCE will split the requst over
multiple messages. Each message sent to the PCE with the F bit set
in the RP object to signify that the response has been fragmented
into multiple messages. In order to indentify that a series of
response messages represents a single request, each message will
use the same request ID.
The assumption is that response messages are reliably delivered
and in sequence since PCEP relies on TCP.
3.13.3 Fragmentation Examples
The following example illustrates the request message with Req-ID1,
which adds one leaf to a 1200 leaves existing tree, is sent to the
PCE. The assumption is that the one request message can hold up to
800 leaves. In these conditions, the original one message needs to be
sent over by two small messages, which have the Req-ID1 specified in
the RP object and F bit set for the first message.
Common Header
RP1 with Req-ID1 and P2MP flag and F bit set
OF (optional)
END-POINTS1 for P2MP
RRO1 list
Common Header
RP2 with Req-ID1 and P2MP flag and F bit cleared
OF (optional)
END-POINTS1 for P2MP
RRO1 list
To handle the case that the last fragmented message piece is lost, the
receiver side of the fragmented message may start a timer once it
receives the first piece of the fragmented message. When timer expires
and it still doesn't receive the last piece of the fragmented message,
it should send an error message to the receiver to signal that it
have recieved an incomplete message.
3.14. UNREACH_DESTINATION object
The PCE path computation request may fail because all or a subset of
the destinations are unreachable.
In such a case, the UNREACH-DESTINATION object allows the PCE to
optionally specify the list of unreachable destinations.
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This object can be present in PCRep messages. There can be up to one
such object per RP.
UNREACH_DESTINATION Object-Class is to be assigned by IANA.
UNREACH_DESTINATION Object-Type for IPv4 is to be assigned by IANA
UNREACH_DESTINATION Object-Type for IPv6 is to be assigned by IANA.
The format of the UNREACH_DESTINATION object body for IPv4 (Object-
Type=1) is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: UNREACH_DESTINATION Object Body for IPv4
The format of the UNREACH_DESTINATION object body for IPv6 (Object-
Type=2) is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination IPv6 address (16 bytes) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination IPv6 address (16 bytes) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: UNREACH_DESTINATION Object Body for IPv6
3.15. P2MP PCEP Error Object
To indicate errors associated with the P2MP path request, a new
Error-Type (16) and subsequent error-values are defined as follows
for inclusion in the PCEP-ERROR object:
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A new Error-Type (16) and subsequent error-values are defined as
follows:
Error-Type=16 and Error-Value=1: if a PCE receives a P2MP path
request and the PCE is not capable to satisfy the request due to
insufficient memory, the PCE MUST send a PCErr message with a PCEP
ERROR object (Error-Type=16) and an Error-Value(Error-Value=1). The
corresponding P2MP path computation request MUST be cancelled.
Error-Type=16; Error-Value=2: if a PCE receives a P2MP path request
and the PCE is not capable of P2MP computation, the PCE MUST send a
PCErr message with a PCEP-ERROR Object (Error-Type=16) and an Error-
Value (Error-Value=2). The corresponding P2MP path computation
request MUST be cancelled.
To indicate an error associated with policy violation, a new error
value "P2MP Path computation not allowed" should be added to an
existing error code for policy violation (Error-Type=5) as defined in
[RFC5440].
Error-Type=5; Error-Value=4: if a PCE receives a P2MP path
computation request which is not compliant with administrative
privileges (i.e., the PCE policy does not support P2MP path
computation), the PCE sends a PCErr message with a PCEP-ERROR Object
(Error-Type=5) and an Error-Value (Error-Value=4). The corresponding
P2MP path computation request MUST be cancelled.
3.16. PCEP NO-PATH Indicator
To communicate the reason(s) for not being able to find P2MP path
computation, the NO-PATH object can be used in the PCRep message.
The format of the NO-PATH object body is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV(s) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: The Format of the NO-PATH Object Body
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One new bit flags is defined in the NO-PATH-VECTOR TLV carried in
the NO-PATH Object:
0x20: when set, the PCE indicates that there is a reachability
problem with all or a subset of the P2MP destinations. Optionally
the PCE can specify the list of destination(s) that are not reachable
using the new UNREACH_DESTINATION object defined in section 3.6.
4. Manageability Considerations
[PCE-P2MP-REQ] describes various manageability requirements in
support of P2MP path computation when applying PCEP. This section
describes how manageability requirements mentioned in [PCE-P2MP-REQ]
are supported in the context of PCEP extensions specified in this
document.
Note that [RFC5440] describes various manageability considerations in
PCEP, and most of manageability requirements mentioned in [PCE-P2MP
P2MP] are already covered there.
4.1. Control of Function and Policy
In addition to configuration parameters listed in [RFC5440], the
following parameters MAY be required.
o P2MP path computations enabled or disabled.
o Advertisement of P2MP path computation capability enabled or
disabled (discovery protocol, capability exchange).
4.2. Information and Data Models
As described in [PCE-P2MP-REQ], MIB objects MUST be supported for
PCEP extensions specified in this document.
4.3. Liveness Detection and Monitoring
There are no additional considerations beyond those expressed in
[RFC5440], since [PCE-P2MP-REQ] does not address any additional
requirements.
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4.4. Verifying Correct Operation
There are no additional considerations beyond those expressed in
[RFC5440], since [PCE-P2MP-REQ] does not address any additional
requirements.
4.5. Requirements on Other Protocols and Functional Components
As described in [PCE-P2MP-REQ], the PCE MUST obtain information
about the P2MP signaling and branching capabilities of each LSR in
the network.
Protocol extensions specified in this document does not provide such
capability. Other mechanisms MUST be present.
4.6. Impact on Network Operation
It is expected that use of PCEP extensions specified in this document
does not have significant impact on network operations.
5. Security Considerations
As described in [PCE-P2MP-REQ], P2MP path computation requests are
more CPU-intensive and also use more link bandwidth. Therefore, it
may be more vulnerable to denial of service attacks. Therefore it is
more important that implementations conform to security requirements
of [RFC5440], and the implementor utilize those security features
6. IANA Considerations
A number of IANA considerations have been highlighted in previous
sections of this document. In summary, IANA is requested to make
allocations for the following PCEP parameters.
6.1 New Object Functions
Objective Function Code: 7 (suggested value)
Name: Shortest Path Tree (SPT)
Objective Function Code: 8 (suggested value)
Name: Minimum Cost Tree (MCT)
6.2 New Metric Object Types
P2MP IGP metric: T=4 (suggested value)
P2MP TE metric: T=5 (suggested value)
P2MP hop count metric: T=6 (suggested value)
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6.3 UNREACH_DESTINATION objects
UNREACH_DESTINATION Object-Class
UNREACH_DESTINATION Object-Type for IPv4
UNREACH_DESTINATION Object-Type for IPv6
7. Acknowledgements
The authors would like to thank Adrian Farrel, Young Lee, Dan
Tappan, Autumn Liu and Huaimo Chen, and Eiji Oki for their valuable
comments on this draft.
8. References
8.1. Normative References
[RFC5440] Ayyangar, A., Farrel, A., Oki, E., Atlas, A., Dolganow,
A., Ikejiri, Y., Kumaki, K., Vasseur, J., and J. Roux,
"Path Computation Element (PCE) Communication Protocol
(PCEP)", RFC 5440, March 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
"Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"OSPF Protocol Extensions for Path Computation Element
(PCE) Discovery", RFC 5088, January 2008.
[RFC5511] Farrel, F., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, April 2009.
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[RFC5541]
Roux, J., Vasseur, J., and Y. Lee, "Encoding of Objective
Functions in the Path Computation Element Communication
Protocol (PCEP)", RFC5541, December 2008.
8.2. Informative References
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[PCE-P2MP-APP]
Yasukawa, S. and A. Farrel,
"draft-ietf-pce-p2mp-app-01.txt",
draft-ietf-pce-p2mp-app-01 (work in progress),
February 2009.
[PCE-P2MP-REQ]
Yasukawa, S. and A. Farrel, "PCC-PCE Communication
Requirements for Point to Multipoint Multiprotocol Label
Switching Traffic Engineering (MPLS-TE)",
draft-ietf-pce-p2mp-req-01 (work in progress),
February 2008.
9. Authors' Addresses
Quintin Zhao (editor)
Huawei Technology
125 Nagog Technology Park
Acton, MA 01719
US
Email: qzhao@huawei.com
Daniel King
Old Dog Consulting
UK
Email: daniel@olddog.co.uk
Fabien Verhaeghe
France
Email: fabien.verhaeghe@gmail.com
Tomonori Takeda
NTT Corporation
3-9-11, Midori-Cho
Musashino-Shi, Tokyo 180-8585
Japan
Email: takeda.tomonori@lab.ntt.co.jp
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Zafar Ali
Cisco systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: zali@cisco.com
Julien Meuric
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex,
julien.meuric@orange-ftgroup.com
9.1 Contributors
Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex,
France
Email: jeanlouis.leroux@orange-ftgroup.com
Mohamad Chaitou
France
Email: mohamad.chaitou@gmail.com
Appendix A. RBNF Code Fragments
This appendix contains the full set of code fragments defined in this
document.
Copyright (c) 2009 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
o Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
o Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the
distribution.
o Neither the name of Internet Society, IETF or IETF Trust, nor the
names of specific contributors, may be used to endorse or promote
products derived from this software without specific prior written
permission.
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Below is the message format for the request message:
<PCReq Message>::= <Common Header>
<request>
where:
<request>::= <RP>
<end-point-rro-pair-list>
[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
[<LOAD-BALANCING>]
where:
<end-point-rro-pair-list>::=
<END-POINTS>[<RRO-List>][<BANDWIDTH>]
[<end-point-rro-pair-list>]
<RRO-List>::=<RRO>[<BANDWIDTH>][<RRO-List>]
<metric-list>::=<METRIC>[<metric-list>]
Below is the bessage format for the reply message:
Below is the message format for the reply message:
<PCRep Message>::= <Common Header>
<response>
<response>::=<RP>
[<end-point-path-pair-list>]
[<NO-PATH>]
[<attribute-list>]
where:
<end-point-path-pair-list>::=
[<END-POINTS>]<path>[<end-point-path-pair-list>]
<path> ::=(ERO)|(SERO)|<path>]
<attribute-list>::=[<OF>]
[<LSPA>]
[<BANDWIDTH>]
[<metric-list>]
[<IRO>]
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