Network Working Group Luca Martini
Internet Draft Maciek Konstantynowicz
Expiration Date: December 2009 Sami Boutros
Intended status: Standards Track Siva Sivabalan
Cisco
Thomas D. Nadeau Gianni Del Vecchio
BT Swisscom
June 3, 2009
Signaling Root-Initiated Point-to-Multipoint Pseudowires using LDP
draft-martini-pwe3-p2mp-pw-00.txt
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Abstract
This document specifies a mechanism to signal Point-to-Multipoint
(P2MP) Pseudowires (PW) tree using LDP. Such a mechanism is suitable
for any Layer 2 VPN service requiring P2MP connectivity over an IP or
MPLS-enabled PSN. A P2MP PW established via the proposed mechanism is
root initiated.
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Table of Contents
1 Specification of Requirements ........................ 2
2 Introduction ......................................... 2
3 Terminology .......................................... 4
4 Signaling the P2MP PW ................................ 4
4.1 PW ingress to egress incompatibility issues .......... 5
4.2 P2MP PW FEC Element .................................. 6
4.3 Group ID usage ....................................... 8
4.4 Generic Label TLV .................................... 8
4.5 Transport LSP TLV .................................... 9
5 P2MP PW status ....................................... 10
6 Security Considerations .............................. 11
7 IANA Considerations .................................. 11
7.1 FEC Type Name Space .................................. 11
7.2 LDP TLV TYPE ......................................... 11
8 References ........................................... 11
8.1 Normative References ................................. 11
8.2 Informative References ............................... 12
9 Author's Addresses ................................... 12
1. Specification of Requirements
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. Introduction
A Point-to-Multipoint (P2MP) Pseudowire (PW) emulates the essential
attributes of a unidirectional P2MP Telecommunications service such
as P2MP ATM over PSN. A major difference between a Point-to-Point
(P2P) PW outlined in [RFC3985] and a P2MP PW is that the former is
intended for bidirectional service whereas the latter is intended for
both unidirectional, or bidirectional service. Requirements for P2MP
PW are described in [P2MP-PW-REQ].
P2MP PW can be constructed as either Single Segment (P2MP SS-PW) or
Multi Segment (P2MP MS-PW) Pseudowires as mentioned in [P2MP-PW-REQ].
P2MP MS-PW is outside the scope of this document. A reference model
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for P2MP PW is depicted in Figure 1 below. A transport LSP associated
with a P2MP SS-PW SHOULD be a P2MP MPLS LSP (i.e., P2MP TE tunnel
established via RSVP-TE [RFC4875] or P2MP LSP established via mLDP
[mLDP]) spanning from the ingress PE to the egress PE(s) of the P2MP
SS-PW tree. For example, in Figure 1, PW1 can be associated with a
P2MP TE tunnel or P2MP LSP setup using [mLDP] originating from PE1
and terminating at PE2 and PE3.
|<--------------P2MP PW---------------->|
Native | | Native
Service | |<--PSN1->| |<--PSN2->| | Service
(AC) V V V V V V (AC)
| +-----+ +------+ +------+ |
| | | | P1 |=========|T-PE2 |AC3 | +---+
| | | | .......PW1.........>|-------->|CE3|
| |T-PE1|=========| . |=========| | | +---+
| | .......PW1........ | +------+ |
| | . |=========| . | +------+ |
| | . | | . |=========|T-PE3 |AC4 | +---+
+---+ |AC1 | . | | .......PW1.........>|-------->|CE4|
|CE1|------->|... | | |=========| | | +---+
+---+ | | . | +------+ +------+ |
| | . | +------+ +------+ |
| | . |=========| P2 |=========|T-PE4 |AC5 | +---+
| | .......PW1..............PW1.........>|-------->|CE5|
| | |=========| |=========| | | +---+
| +-----+ +------+ +------+ |
Figure 1: P2MP PW
Mechanisms for establishing P2P SS-PW using LDP are described in
[RFC4447]. In this document, we specify a method to signal P2MP PW
using LDP. In particular, we define new TLVs, parameters, and status
codes to facilitate LDP to signal and maintain P2MP PWs.
Note that even though the traffic flow from an ingress PE to egress
PEs is P2MP in nature, it may be desirable for any egress PE to send
unidirectional P2P traffic destined only to the ingress PE. The
proposed mechanism takes such an option into consideration.
The P2MP PW requires an MPLS LSP to carry the PW traffic. the PW MPLS
packet will be encapsulated according to the methods described in
[RFC5332].
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3. Terminology
FEC: Forwarding Equivance Class
LDP: Label Distribution Protocol
mLDP: Label Distribution Protocol for P2MP LSP
LSP: Label Switching Path
MS-PW: Multi-Segment Pseudowire
P2P: Point to Point
P2MP: Point to Multipoint
PE: Provider Edge
PW: Pseudowire
SS-PW: Single-Segment Pseudowire
S-PE: Switching Provider Edge Node of MS-PW
TE: Traffic Engineering
T-PE: Terminating Provider Edge Node of MS-PW
R-PE: Root-PE - PE initiating P2MP PW setup.
L-PE: Leaf-PE
4. Signaling the P2MP PW
In order to advertise labels as well as exchange PW related LDP
messages, PEs must establish LDP sessions among themselves using the
Extended Discovery Mechanisms. A PE discovers other PEs that are to
be connected via P2MP PWs either via manual configuration or
autodiscovery [BGP-AD].
P2MP PW requires that there is an active P2MP PSN LSP set up between
ingress and egress PEs. Note that the procedure to set up the P2MP
PSN LSP is different depending on the protocol used: RSVP-TE or mLDP.
In case of mLDP an egress PE can decide to join the P2MP LSP at any
time, while in case of RSVP-TE the P2MP LSP is set up by the ingress
PE, generally at the initial service provisioning time. It should be
noted that local policy can override any decision to join, add or
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prune existing or new PEs from the tree.
In any case the PW setup can ignore these differences, and simply
assume that the P2MP tunnel is available when needed.
The P2MP PW is initiated by the root (source) Provider Edge router
(R-PE), by simply sending an P2MP-PW LDP label mapping message to all
the Leaf Provider Edge routers L-PEs. This label mapping message will
contain the following:
-i. P2MP PW FEC element.
-ii. an Interface Parameters TLV, as described in [RFC4447] sec
5.3.2.1
-iii. a PW Grouping TLV, as described in [RFC4447] sec 5.3.2.2
-iv. a Transport LSP TLV.
-v. a label TLV for the upstream-assigned label R-PE to L-PE
direction.
-vi. MAY contain a downstream-assigned label for the L-PE to R-PE
direction.
The LDP liberal label retention mode is used, and per
[RFC5036] requirement the label request message MUST also be
supported.
The Upstream-assigned label is allocated according to the
rules in [RFC5331].
When an egress PE receives a PW Label Mapping Message, it
MUST verify the associated P2MP transport LSP is in place.
If the associated transport P2MP LSP is not in place, and
the transport LSP TLV type is LDP P2MP LSP, an egress PE
SHOULD attempt to join the P2MP transport associated with
the P2MP PW.
If the associated transport P2MP LSP is not in place, and
the transport LSP TLV type is RSVP-TE P2MP LSP, an egress PE
SHOULD await RSVP-TE P2MP LSP signaling from the ingress PE.
4.1. PW ingress to egress incompatibility issues
If an ingress R-PE signals a PW with a pw type, CW mode, or interface
parameters that a particular egress L-PE cannot accept, then the L-PE
must simply not enable the PW, and notify the user. In this case a PW
status message of 0x00000001 - Pseudowire Not Forwarding MUST also be
sent to the R-PE.
Note that this procedure does not apply if the L-PE had not been
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provisioned with this particular P2MP PW. In this case according to
the LDP liberal label retention rules, no action is taken.
4.2. P2MP PW FEC Element
[RFC4447] specifies two types of LDP FEC elements called "PWid FEC
Element" and "Generalized PWid FEC Element" used to signal P2P PWs.
We define a new type of FEC element called "P2MP PWid FEC Element"
whose type is 0x82 (Pending IANA Allocation) and is encoded 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|FEC Type = 0x82|C| PW Type | PW Info Length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | Length | AGI Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | SAII Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Transport LSP TLV (0x0971)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |PMSI Tunnel Typ| Transport LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Transport LSP ID (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional Parameters |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: P2MP PWid FEC Element
* PW Type:
15-bit representation of PW type, and the assigned values are
assigned by IANA.
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* C bit:
A value of 1 or 0 indicates whether control word is present or
absent for the P2MP PW.
* PW Info Length:
Sum of the lengths of AGI, SAII and Optional Parameters field in
octets. If this value is 0, then it references all PWs using the
specified grouping ID. In this case, there are no other FEC
element fields (AGI, SAII, etc.) present, nor any interface
parameters TLVs.
* AGI:
Attachment Group Identifier can be used to uniquely identify VPN
or VPLS instance associated with the P2MP PW. This has the same
format as that of the Generalized PWid FEC element [RFC4447].
* SAII:
Source Attachment Individual Identifier is used to identify the
root of the P2MP PW. The root is represented using AII type 2
format specified in [RFC5003]. Note that the SAII can be omitted
by simply setting the length and type to zero.
* Transport LSP TLV:
A P2MP PW MUST be associated with a transport LSP. The Transport
LSP TLV contains the information required to identify the
transport LSP. Note that the Transport LSP TLV MUST immediately
follow the FEC , but is not part of the FEC, and SHOULD NOT be
used in other messages where the FEC is used.
* Optional Parameters:
The Optional Parameter field can contain some TLVs that are not
part of the FEC, but are necessary for the operation of the PW.
This document defines two such parameters: Interface Parameters
TLV, and Group ID TLV.
The Interface Parameters TLV and Group ID TLV specified in [RFC4447]
can also be used in conjunction with P2MP PW FEC. In this case, the
sender and receiver of these TLVs should follow the same rules and
procedures specified in [RFC4447]. Note that since the LDP label
mapping message is only sent by the R-PE to all the L-PEs it is not
possible to negotiate any interface parameters.
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4.3. Group ID usage
As Defined in [RFC4447] the Grouping TLV contains a group ID capable
of indicating an arbitrary group membership of a P2MP-PW. This groupd
ID can be used in LDP "wild card" status, and withdraw label
messages, as described in [RFC4447].
4.4. Generic Label TLV
For a given P2MP PW, a single upstream-assigned label is allocated by
ingress PE, and is advertised to all egress PEs using the Generig
Label TLV in the label mapping message containing the P2MP-PW FEC
element. The ingress PE imposes the upstream-assigned label on the
outbound packets sent over the P2MP-PW, and using this label, an
egress PE identifies the inbound packets arriving over the P2MP PW.
Even though the P2MP PW is unidirectional, it may be possible for an
ingress PE to receive traffic from any egress PE using a
unidirectional P2P PW in the reverse direction. For this purpose, the
ingress PE can also allocate a unique downstream-assigned label for
each egress PE from which it is intended to receive P2P traffic. In
other words, Label Mapping Message for a P2MP PW from an ingress PE
to an egress PE MUST carry a upstream-assigned label and MAY carry an
OPTIONAL downstream-assigned label.
As in the case of P2P PW signaling, P2MP PW labels are carried within
Generic Label TLV contained in LDP Label Mapping Message. A Generic
Label TLV is formatted and processed as per the rules and procedures
specified in [RFC4447]. But, as mentioned above, a Label Mapping
Message for a P2MP PW can have up to two Generic Label TLVs; one for
upstream-assigned label (always) and another for downstream-assigned
label (optional). In the case of two Generic Label TLVs, the first
TLV (from the beginning of the message) carries upstream-assigned
label and the next generic label TLV carries the downstream-assigned
label as shown below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Generic Label (0x0200) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Upstream-assigned P2MP Label (mandatory) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Generic Label (0x0200) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream-assigned P2P Label (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Generic Label TLVs in P2MP PW Label Mapping Message
Note that other type of TLVs may appear between the above generic
label TLVs, however any other generic label TLV MUST NOT appear
between the upstream-assigned P2MP Label TLV, and downstream-assigned
P2P Label TLV.
4.5. Transport LSP TLV
A P2MP PW MUST be associated with a transport LSP which can be
established using RSVP-TE or mLDP. Thus, a Label Mapping Message MUST
contain the identity of the transport LSP. For this purpose, this
specification introduces a new TLV called "Transport LSP TLV" which
has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Transport LSP TLV (0x0971)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |PMSI Tunnel Typ| Tunnel Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Tunnel Identifier (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Transport LSP TLV
Note: TLV number pending IANA allocation.
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* Reserved Flags:
Reserved bits Must be set to 0 when transmitting the message, and
ignored on receiving the message.
* PMSI Tunnel Type:
The Transport LSP Type identifies the type of technology used to
establish a transport LSP. The PMSI tunnel type is defined in
[L3VPN-MCAST].
* Tunnel Identifier:
The Tunnel containing the Transport LSP is identified by the
Tunnel Identifier which is defined in [L3VPN-MCAST].
Transport LSP TLV MUST be present only in the Label Mapping Message.
An ingress PE sends Label Mapping Message as soon as the transport
LSP ID associated with the P2MP PW is known (e.g., via configuration)
regardless of the operational state of the transport LSP. Similarly,
an ingress PE does not withdraw the labels when the corresponding
transport LSP goes down. Furthermore, an egress PE retains the P2MP
PW labels regardless of the operational status of the transport LSP.
Note that a given transport LSP can be associated with more than one
P2MP PW and all P2MP PWs will be sharing the same ingress PE and
egress PEs.
In the case of LDP P2MP LSP, when an egress PE receives the Label
Mapping Message, it can initiate the process of joining the P2MP LSP
tree associated with the P2MP PW.
In the case of RSVP-TE P2MP LSP, only the ingress PE initiates the
signaling of P2MP LSP.
5. P2MP PW status
In order to support the proposed mechanism, a node MUST be capable of
handling PW status. As such, PW status negotiation procedure
described in [RFC4447] is not applicable to P2MP PW.
Once an egress PE successfully process a Label Mapping Message for a
P2MP PW, it MUST send appropriate PW status according to the
procedure specified [RFC4447] to notify the PW status. If there is no
PW status notification required, then no PW status notification is
sent. (for example if the P2MP PW is established and operational with
a status 0f 0x00000000 no pw status message is necessary).
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PW status message sent from any egress PE to ingress PE contains P2MP
PW FEC to identify the PW. Finally, an ingress PE also sends PW
status to egress PEs to reflect its view of a P2MP PW state.
6. Security Considerations
The security measures described in [RFC4447] is adequate for the
proposed mechanism.
7. IANA Considerations
7.1. FEC Type Name Space
This document uses a new FEC element types, number 0x82 will be
requested as an allocation from the registry "FEC Type Name Space"
for the Label Distribution Protocol (LDP RFC5036).
7.2. LDP TLV TYPE
This document uses a new LDP TLV types, IANA already maintains a
registry of name "TLV TYPE NAME SPACE" defined by RFC5036. The
following value is suggested for assignment:
TLV type Description
0x0971 Transport LSP TLV
8. References
8.1. Normative References
[RFC2119] Bradner. S, "Key words for use in RFCs to
Indicate Requirement Levels", RFC 2119, March, 1997.
[RFC4447] "Transport of Layer 2 Frames Over MPLS", Martini, L.,
et al., rfc4447 April 2006.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC5003] C. Metz, L. Martini, F. Balus, J. Sugimoto, "Attachment
Individual Identifier (AII) Types for Aggregation", RFC5003,
September 2007.
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[RFC5331] R. Aggarwal, Y. Rekhter, E. Rosen, "MPLS Upstream Label
Assignment and Context-Specific Label Space", rfc5331,
August 2008.
[RFC5332] T. Eckert, E. Rosen, Ed.,R. Aggarwal, Y. Rekhter,
"MPLS Multicast Encapsulations", rfc5332, August 2008.
[mLDP] I. Minei, K. Kompella, I. Wijnands, B. Thomas, "Label
Distribution Protocol Extensions for Point-to-Multipoint and
Multipoint-to-Multipoint Label Switched Paths",
draft-ietf-mpls-ldp-p2mp-06, Work In Progress, April 2009.
[RFC4875]
R. Aggarwal, Ed., D. Papadimitriou, Ed., S. Yasukawa, Ed.,
"Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs).", rfc4875, May 2007.
[L3VPN-MCAST] R. Aggarwal, E. Rosen, T. Morin, Y. Rekhter,
"BGP Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", Work in Progress, April 2009.
8.2. Informative References
[RFC3985] Stewart Bryant, et al., "PWE3 Architecture",
RFC3985
[BGP-AD] E. Rosen,W. Luo,B. Davie,V. Radoaca "Provisioning,
Autodiscovery, and Signaling in L2VPNs",
draft-ietf-l2vpn-signaling-08.txt May 2006.
[P2MP-PW-REQ] F. Jounay, et. al, "Requirements for Point
to Multipoint Pseudowire",
draft-ietf-pwe3-p2mp-pw-requirements-00.txt, Work in Progress,
September 2008.
9. Author's Addresses
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
e-mail: lmartini@cisco.com
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Sami Boutros
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
e-mail: sboutros@cisco.com
Siva Sivabalan
2000 Innovation Drive
Kanata, ONTARIO K2K 3E8
CANADA
e-mail: msiva@cisco.com
Maciek Konstantynowicz
10 New Square Park
Bedfont Lakes
Feltham, England TW14 8HA
UNITED KINGDOM
e-mail: mkonstan@cisco.com
Gianni Del Vecchio
Swisscom (Schweiz) AG
Zentweg 9
CH-3006 Bern
Switzerland
e-mail: Gianni.DelVecchio@swisscom.com
Thomas D. Nadeau
BT
BT Centre
81 Newgate Street
London EC1A 7AJ
United Kingdom
e-mail: tom.nadeau@bt.com
Full Copyright Statement
Copyright (c) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Acknowledgments
The authors wish to acknowledge the contributions of Ali Sajassi.
Expiration Date: December 2009
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