Network Working Group Luca Martini
Internet Draft Chris Metz
Expiration Date: December 2009 Cisco Systems Inc.
Intended status: Standards Track
Thomas D. Nadeau
Matthew Bocci BT
Florin Balus
Mustapha Aissaoui Mike Duckett
Alcatel-Lucent Bellsouth
June 3, 2009
Segmented Pseudowire
draft-ietf-pwe3-segmented-pw-12.txt
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Abstract
This document describes how to connect pseudowires (PW) between two
distinct PW control planes or PSN domains. The PW control planes may
belong to independent autonomous systems, or the PSN technology is
heterogeneous, or a PW might need to be aggregated at a specific PSN
point. The PW packet data units are simply switched from one PW to
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another without changing the PW payload.
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Table of Contents
1 Specification of Requirements ........................ 4
2 Terminology .......................................... 5
3 Introduction ......................................... 5
4 General Description .................................. 7
5 PW Switching and Attachment Circuit Type ............. 10
6 Applicability ........................................ 10
7 MPLS-PW to MPLS-PW Switching ......................... 10
7.1 Static Control plane switching ....................... 11
7.2 Two LDP control planes using the same FEC type ....... 11
7.2.1 FEC 129 Active/Passive T-PE Election Procedure ....... 12
7.3 LDP FEC 128 to LDP using the generalized FEC 129 ..... 12
7.4 LDP Switching Point PE TLV ........................... 13
7.4.1 PW Switching Point Sub-TLVs .......................... 14
7.4.2 Adaptation of Interface Parameters ................... 15
7.5 Group ID ............................................. 16
7.6 PW Loop Detection .................................... 16
8 MPLS-PW to L2TPv3-PW Control Plane Switching ......... 16
8.1 Static MPLS and L2TPv3 PWs ........................... 17
8.2 Static MPLS PW and Dynamic L2TPv3 PW ................. 17
8.3 Static L2TPv3 PW and Dynamic LDP/MPLS PW ............. 17
8.4 Dynamic LDP/MPLS and L2TPv3 PWs ...................... 17
8.4.1 Session Establishment ................................ 18
8.4.2 Adaptation of PW Status message ...................... 18
8.4.3 Session Tear Down .................................... 19
8.5 Adaptation of L2TPv3 AVPs to Interface Parameters .... 19
8.6 Switching Point TLV in L2TPv3 ........................ 20
8.7 L2TPv3 and MPLS PW Data Plane ........................ 20
8.7.1 Mapping the MPLS Control Word to L2TP ................ 21
9 Operation And Management ............................. 22
9.1 Extensions to VCCV to Support MS-PWs ................. 22
9.2 MPLS-PW to MPLS-PW OAM Data Plane Indication ......... 22
9.3 Signaling OAM Capabilities for Switched Pseudowires .. 23
9.4 OAM Capability for MS-PWs Demultiplexed using MPLS ... 23
9.4.1 MS-PW and VCCV CC Type 1 ............................. 24
9.4.2 MS-PW and VCCV CC type 2 ............................. 24
9.4.3 MS-PW and VCCV CC type 3 ............................. 24
9.5 MS-PW VCCV Operations ................................ 24
9.5.1 VCCV Echo Message Processing ......................... 25
9.5.1.1 Sending a VCCV Echo Request .......................... 26
9.5.1.2 Receiving a VCCV Echo Request ........................ 26
9.5.1.3 Receiving a VCCV Echo Reply .......................... 27
9.5.2 Detailed VCCV procedures ............................. 27
9.5.2.1 End to End Connectivity Verification Between T-PEs ... 27
9.5.2.2 Partial Connectivity Verification from T-PE .......... 28
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9.5.2.3 Partial connectivity verification between S-PEs ...... 28
9.5.2.4 MS-PW Path Verification .............................. 29
9.5.2.5 MS-PW Path Trace ..................................... 30
10 Mapping Switched Pseudowire Status ................... 31
10.1 S-PE initiated PW status messages .................... 32
10.1.1 Local PW2 transmit direction fault ................... 33
10.1.2 Local PW1 transmit direction fault ................... 34
10.1.3 Local PW2 receive direction fault .................... 34
10.1.4 Local PW1 receive direction fault .................... 34
10.1.5 Clearing Faults ...................................... 34
10.2 PW status messages and S-PE TLV processing ........... 35
10.3 T-PE processing of PW status messages ................ 35
10.4 Pseudowire Status Negotiation Procedures ............. 35
10.5 Status Dampening ..................................... 35
11 Peering Between Autonomous Systems ................... 35
12 Security Considerations .............................. 36
12.1 Data Plane Security .................................. 36
12.1.1 VCCV Security considerations ......................... 36
12.2 Control Protocol Security ............................ 36
13 IANA Considerations .................................. 37
13.1 L2TPv3 AVP ........................................... 37
13.2 LDP TLV TYPE ......................................... 38
13.3 LDP Status Codes ..................................... 38
13.4 L2TPv3 Result Codes .................................. 38
13.5 New IANA Registries .................................. 38
14 Normative References ................................. 39
15 Informative References ............................... 40
16 Author's Addresses ................................... 41
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].
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2. Terminology
- PW Terminating Provider Edge (T-PE). A PE where the customer-
facing attachment circuits (ACs) are bound to a PW forwarder. A
Terminating PE is present in the first and last segments of a
MS-PW. This incorporates the functionality of a PE as defined in
[RFC3985].
- Single-Segment Pseudowire (SS-PW). A PW setup directly between
two T-PE devices. Each PW in one direction of a SS-PW traverses
one PSN tunnel that connects the two T-PEs.
- Multi-Segment Pseudowire (MS-PW). A static or dynamically
configured set of two or more contiguous PW segments that behave
and function as a single point-to-point PW. Each end of a MS-PW
by definition MUST terminate on a T-PE.
- PW Segment. A part of a single-segment or multi-segment PW, which
traverses one PSN tunnel in each direction between two PE
devices, T-PEs and/or S-PEs.
- PW Switching Provider Edge (S-PE). A PE capable of switching the
control and data planes of the preceding and succeeding PW
segments in a MS-PW. The S-PE terminates the PSN tunnels of the
preceding and succeeding segments of the MS-PW.
3. Introduction
The PWE3 Architecture [RFC3985], defines the signaling and
encapsulation techniques for establishing SS-PWs between a pair of
terminating PEs and in the vast majority of cases this will be
sufficient. MS-PWs are most useful in two general cases:
-i. When it is not possible, desirable or feasible to establish
a PW control channel between the terminating source and
destination PEs. At a minimum PW control channel
establishment requires knowledge of and reachability to the
remote (terminating) PE IP address. The local (terminating)
PE may not have access to this information related to
topology, operational or security constraints.
An example is the inter-AS L2VPN scenario where the
terminating PEs reside in different provider networks (ASes)
and it is the practice to cryptogtaphiclly sign all control
traffic exchanged between two networks. Technically a SS-PW
could be used but this would require tp cryptogtaphiclly
sign on ALL terminating source and destination PE nodes. An
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MS-PW allows the providers to confine MD5 key administration
to just the PW switching points connecting the two domains.
A second example might involve a single AS where the PW
setup path between the terminating PEs is computed by an
external entity (i.e. client-layer routing protocol). Assume
a full mesh of PWE3 control channels established between
PE-A, PE-B and PE-C. A client-layer L2 connection tunneled
through a PW is required between terminating PE-A and PE-C.
The external entity computes a PW setup path that passes
through PE-B. This results in two discrete PW segments being
built: one between PE-A and PE-B and one between PE-B and
PE-C. The successful client-layer L2 connection between
terminating PE-A and terminating PE-C requires that PE-B
performs the PWE3 switching process.
A third example involves the use of PWs in hierarchical
IP/MPLS networks. Access networks connected to a backbone
use PWs to transport customer payloads between customer
sites serviced by the same access network and up to the edge
of the backbone where they can be terminated or switched
onto a succeeding PW segment crossing the backbone. The use
of PWE3 switching between the access and backbone networks
can potentially reduce the PWE3 control channels and routing
information processed by the access network T-PEs.
It should be noted that PWE3 switching does not help in any
way to reduce the amount of PW state supported by each
access network T-PE.
-ii. PWE3 signaling and encapsulation protocols are different.
The terminating PEs are connected to networks employing
different PW signaling and encapsulation protocols. In this
case it is not possible to use a SS-PW. A MS-PW with the
appropriate interworking performed at the PW switching
points can enable PW connectivity between the terminating
PEs in this scenario.
A more detailed discussion of the requirements pertining to MS-PWs
can be found in [RFC5254].
There are four different signaling protocols that are defined to
signal PWs:
-i. Static configuration of the PW (MPLS or L2TPv3).
-ii. LDP using FEC 128
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-iii. LDP using the generalized FEC 129
-iv. L2TPv3
4. General Description
A pseudowire (PW) is a mechanism that carries the essential elements
of an emulated service from one PE to one or more other PEs over a
PSN as described in Figure 1 and in [RFC3985]. Many providers have
deployed PWs as a means of migrating existing (or building new) L2VPN
services (e.g.. Frame Relay, ATM, or Ethernet) on to a PSN.
PWs may span multiple autonomous systems of the same or different
provider networks. In these scenarios PW control channels (i.e.
targeted LDP, L2TPv3) and PWs will cross AS boundaries.
Inter-AS L2VPN functionality is currently supported and several
techniques employing MPLS encapsulation and LDP signaling have been
documented [RFC4364]. It is also straightforward to support the same
inter-AS L2VPN functionality employing L2TPv3. In this document we
define methodology to switch a PW between two PW control planes.
|<-------------- Emulated Service ---------------->|
| |
| |<-------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnel -->| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | | PE1|==================| PE2| | +-----+
| |----------|............PW1.............|----------| |
| CE1 | | | | | | | | CE2 |
| |----------|............PW2.............|----------| |
+-----+ ^ | | |==================| | | ^ +-----+
^ | +----+ +----+ | | ^
| | Provider Edge 1 Provider Edge 2 | |
| | | |
Customer | | Customer
Edge 1 | | Edge 2
| |
native service native service
Figure 1: PWE3 Reference Model
There are two methods for switching a PW between two PW control
planes. In the first method (Figure 2), the two control planes
terminate on different PEs.
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|<-------Multi-Segment Pseudowire------->|
| PSN PSN |
AC | |<-1->| |<-2->| | AC
| V V V V V V |
| +----+ +-----+ +----+ +----+ |
+----+ | | |=====| | | |=====| | | +----+
| |-------|......PW1.......|--AC1--|......PW2......|-------| |
| CE1| | | | | | | | | | | |CE2 |
| |-------|......PW3.......|--AC2--|......PW4......|-------| |
+----+ | | |=====| | | |=====| | | +----+
^ +----+ +-----+ +----+ +----+ ^
| PE1 PE2 PE3 PE4 |
| ^ ^ |
| | | |
| PW stitching points |
| |
| |
|<-------------------- Emulated Service ---------------->|
Figure 2: PW Switching using ACs Reference Model
In Figure 2, pseudowires in two separate PSNs are stitched together
using native service attachment circuits. PE2 and PE3 only run the
control plane for the PSN to which they are directly attached. At PE2
and PE3, PW1 and PW2 are connected using attachment circuit AC1,
while PW3 and PW4 are connected using attachment circuit AC2.
Native |<------Multi-Segment Pseudowire------>| Native
Service | PSN PSN | Service
(AC) | |<-Tunnel->| |<-Tunnel->| | (AC)
| V V 1 V V 2 V V |
| +----+ +-----+ +----+ |
+----+ | |TPE1|===========|SPE1 |==========|TPE2| | +----+
| |------|..... PW.Seg't1.........PW.Seg't3.....|-------| |
| CE1| | | | | | | | | |CE2 |
| |------|..... PW.Seg't2.........PW.Seg't4.....|-------| |
+----+ | | |===========| |==========| | | +----+
^ +----+ +-----+ +----+ ^
| Provider Edge 1 ^ Provider Edge 2 |
| | |
| | |
| PW switching point |
| |
|<------------------ Emulated Service --------------->|
Figure 3: PW Control Plane Switching Reference Model
In Figure 3 SPE1 runs two separate control planes: one toward TPE1,
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and one Toward TPE2. The PW switching point (S-PE) is configured to
connect PW Segment 1 and PW Segement 3 together to complete the
multi-hop PW between TPE1 and TPE2. PW Segment 1 and PW Segment 3
MUST be of the same PW type, but PSN Tunnel 1 and PSN Tunnel 2 need
not be the same technology. In the latter case, if the PW is switched
to a different technology, the PEs must adapt the PDU encapsulation
between the different PSN technologies. In the case where PSN Tunnel
1 and PSN Tunnel 2 are the same technology the PW PDU does not need
to be modified, and PDUs are then switched between the pseudowires at
the PW label level.
It should be noted that it is possible to adapt one PSN technology to
a different one, for example MPLS over an IP or GRE [RFC4023]
encapsulation, but this is outside the scope of this document.
Further, one could perform an interworking function on the PWs
themselves at the S-PE, allowing conversion from one PW type to
another, but this is also outside the scope of this document.
This document describes procedures for building multi-segment
pseudowires using manual configuration of the switching point PE1.
Other documents may build on this base specification to automate the
configuration and selection of S-PE1. It should also be noted that a
PW can traverse multiple PW switching points along it's path, and the
edge PEs will not require any specific knowledge of how many S-PEs
the PW has traversed (though this may be reported for troubleshooting
purposes).
The general approach taken for MS-PWs is to connect the individual
control planes by passing along any signaling information immediately
upon reception. First the S-PE is configured to switch a PW segment
from a specific peer to another PW segment destined for a different
peer. No control messages are exchanged yet as the S-PE does not have
enough information to actually initiate the PW setup messages.
However, if a session does not already exist, a control protocol
(LDP/L2TP) session MAY be setup. In this model the MS-PW setup is
starting from the T-PE devices. Next once the T-PE is configured it
sends the PW control setup messages. These messages are received by
the S-PE, and immediately used to form the PW setup messages for the
next SS-PW of the MS-PW. If one of the S-PEs doesn't accept an LDP
Label Mapping message then a Label Release message may be sent back
to the originator T-PE depending on the cause of the error. LDP
liberal label retention mode still applies, hence if a PE is simply
not configured yet , the label mapping is stored for future use. A
MS-PW is declared UP only when all the constituent SS-PWs are UP.
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5. PW Switching and Attachment Circuit Type
The PWs in each PSN are established independently, with each PSN
being treated as a separate PW domain. For example, in Figure 2 for
the case of MPLS PSNs, PW1 is setup between PE1 and PE2 using the LDP
targeted session as described in [RFC4447], and at the same time a
separate pseudowire, PW2, is setup between PE3 and PE4. The ACs for
PW1 and PW2 at PE2 and PE3 MUST be configured such that they are the
same PW type e.g. ATM VCC, Ethernet VLAN, etc.
6. Applicability
The general applicability of MS-PWs and their relationship to L2VPNs
is described in [MS-PW-ARCH]. The applicability of a PW type, as
specified in the relevant RFC for that encapsulation (e.g. [RFC4717]
for ATM), applies to each segment. This section describes further
applicability considerations.
As with SS-PWs, the performance of any segment will be limited by the
performance of the underlying PSN. The performance may be further
degraded by the emulation process, and performance degradation may be
further degraded by traversing multiple PW segments. Furthermore, the
overall performance of an MS-PW is no better than the worst
performing segment of that MS-PW.
Since different PSN types may be able to achieve different maximum
performance objectives, it is necessary to carefully consider which
PSN types are used along the path of a MS-PW.
7. MPLS-PW to MPLS-PW Switching
Referencing Figure 3, T-PE1 set up PW segment 1 using the LDP
targeted session as described in [RFC4447], at the same time a
separate pseudowire PW segment 3 is setup to T-PE2. Each PW is
configured independently on the PEs, but on S-PE1 pseudowire PW
segment 1 is connected to pseudowire PW segment 3. PDUs are then
switched between the pseudowires at the PW label level. Hence the
data plane does not need any special knowledge of the specific
pseudowire type. A simple standard MPLS label swap operation is
sufficient to connect the two PWs, and in this case the PW adaptation
function cannot be used. However when pushing a new PSN label the TTL
SHOULD be set to 255, or some other locally configured fixed value.
This process can be repeated as many times as necessary, the only
limitation to the number of S-PEs traversed is imposed by the TTL
field of the PW MPLS Label. The setting of the TTL of the PW MPLS
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label is a matter of local policy on the originating PE, but SHOULD
be set to 255. However if the PW PDU contains an OAM packet then the
TTL can be set to the required value as explained later in this
document.
There are three MPLS to MPLS PW control planes:
-i. Static configuration of the PW.
-ii. LDP using FEC 128
-iii. LDP using the generalized FEC 129
This results in four distinct PW switching situations that are
significantly different, and must be considered in detail:
-i. PW Switching between two static control planes.
-ii. Static Control plane switching to LDP dynamic control plane.
-iii. Two LDP control planes using the same FEC type
-iv. LDP using FEC 128, to LDP using the generalized FEC 129
7.1. Static Control plane switching
In the case of two static control planes the S-PE MUST be configured
to direct the MPLS packets from one PW into the other. There is no
control protocol involved in this case. When one of the control
planes is a simple static PW configuration and the other control
plane is a dynamic LDP FEC 128 or generalized PW FEC, then the static
control plane should be considered identical to an attachment circuit
(AC) in the reference model of Figure 1. The switching point PE
SHOULD signal the appropriate PW status if it detects a failure in
sending or receiving packets over the static PW segment. Because the
PW is statically configured, the status communicated to the dynamic
LDP PW will be limited to local interface failures. In this case, the
S-PE PE behaves in a very similar manner to a T-PE, assuming an
active signaling role. This means that the S-PE will immediately send
the LDP Label Mapping message if the static PW is deemed to be UP.
7.2. Two LDP control planes using the same FEC type
The S-PE SHOULD assume an initial passive role. This means that when
independent PWs are configured on the switching point, the LSR does
not advertise the LDP PW FEC mapping until it has received at least
one of the two PW LDP FECs from a remote PE. This is necessary
because the switching point LSR does not know a priori what the
interface parameter field in the initial FEC advertisement will
contain.
The Pseudowire Identifier (PWID) , as defined in [RFC4447] is a
unique number between each pair of PEs. Hence Each SS-PW that forms
an MS-PW may have a different PWID. In the case of The Generalized PW
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FEC, the AGI/SAI/TAI may have to also be different for some, or
sometimes all, SS-PWs.
7.2.1. FEC 129 Active/Passive T-PE Election Procedure
When a MS-PW is signaled using FEC 129, each T-PE might independently
start signaling the MS-PW. If the MS-PW path is not statically
configured, in certain cases the signaling procedure could result in
an attempt to setup each direction of the MS-PW through different S-
PEs. To avoid this situation one of the T-PE MUST start the PW
signaling (active role), while the other waits to receive the LDP
label mapping before sending the respective PW LDP label mapping
message. (passive role). When the MS-PW path not statically
configured, the Active T-PE (the ST-PE) and the passive T-PE (the
TT-PE) MUST be identified before signaling is initiated for a given
MS-PW.
The determination of which T-PE assume the active role SHOULD be done
as follows:
The SAII and TAII are compared as unsigned integers, if the SAII is
larger, then the T-PE assumes the active role.
The selection process to determine which T-PE assumes the active role
MAY be superseded by manual provisioning. In this case one of the T-
PEs MUST be set to active role, and the other one MUST be set to
passive role.
7.3. LDP FEC 128 to LDP using the generalized FEC 129
When a PE is using the generalized FEC 129, there are two distinct
roles that a PE can assume: active and passive. A PE that assumes the
active role will send the LDP PW setup message, while a passive role
PE will simply reply to an incoming LDP PW setup message. The S-PE
PE, will always remain passive until a PWID FEC 128 LDP message is
received, which will cause the corresponding generalized PW FEC LDP
message to be formed and sent. If a generalized FEC PW LDP message is
received while the switching point PE is in a passive role, the
corresponding PW FEC 128 LDP message will be formed and sent.
PW IDs need to be mapped to the corresponding AGI/TAI/SAI and vice
versa. This can be accomplished by local S-PE configuration, or by
some other means, such as some form of auto discovery. Such other
means are outside the scope of this document.
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7.4. LDP Switching Point PE TLV
The edge to edge PW might traverse several switching points, in
separate administrative domains. For management and troubleshooting
reasons it is useful to record information about the switching points
that the PW traverses. This is accomplished by using a PW switching
Point TLV.
Sending the PW switching Point TLV (S-PE TLV) is OPTIONAL, however
the PE or S-PE MUST process the TLV upon reception. The "U" bit MUST
be set for backward compatibility with T-PEs that do not support the
MS-PW extensions described in the document. The S-PE TLV MAY appear
only once for each switching point traversed. The S-PE TLV is
appended to the PW FEC at each switching point, and the order of the
S-PE TLVs in the LDP message MUST be preserved. The S-PE TLV MUST be
sent if VCCV operation is required beyond the first MS-PW segment
from a T-PE.
The S-PE TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| PW sw TLV (0x096D) | PW sw TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Variable Length Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length Value |
| " " " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[note] LDP TLV type is pending IANA approval.
- PW sw TLV Length
Specifies the total length of all the following S-PE TLV fields
in octets
- Type
Encodes how the Value field is to be interpreted.
- Length
Specifies the length of the Value field in octets.
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- Value
Octet string of Length octets that encodes information to be
interpreted as specified by the Type field.
PW Switching point TLV Types are assigned by IANA according the the
process defined in the "IANA Allocations" section below.
For local policy reasons, a particular S-PE can filter out all S-PE
TLVs in a label mapping message that traverses it and not include
it's own S-PE TLV. In this case, from any upstream PE, it will
appear as if this particular S-PE is the T-PE. This might be
necessary , depending on local policy if the S-PE is at the service
provider administrative boundary. It should also be noted that
because there are no S-PE TLVs describing the path beyond the S-PE
that removed them, VCCV will only work as far as that S-PE .
7.4.1. PW Switching Point Sub-TLVs
The S-PE TLV contains sub-TLVs that describe various characteristics
of the S-PE traversed. Below are the definitions of PW Switching
Point Sub-TLVs defined in this document:
- PW ID of last PW segment traversed.
This is only applicable if the last PW segment traversed used LDP
FEC 128 to signal the PW. This sub-TLV type contains a PW ID in
the format of the PWID described in [RFC4447]. This is just a 32
bit unsigned integer number.
- PW Switching Point description string.
An optional description string of text up to 80 characters long.
- Local IP address of PW Switching Point.
The Local IP V4 or V6 address of the PW Switching Point. This is
an OPTIONAL Sub-TLV. In most cases this will be the local LDP
session IP address of the S-PE.
- Remote IP address of the last PW Switching Point traversed or of
the T-PE
The IP V4 or V6 address of the last PW Switching Point traversed
or of the T-PE. This is an OPTIONAL Sub-TLV. In most cases this
will be the remote IP address of the LDP session. This Sub-TLV
SHOULD only be included if there are no other S-PE TLV present
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from other S-PEs, or if the remote ip address of the LDP session
does not correspond to the "Local IP address of PW Switching
Point" TLV value contained in the last S-PE TLV.
- The FEC of last PW segment traversed.
This is only applicable if the last PW segment traversed used LDP
FEC 129 to signal the PW.
The Attachment Identifier of the last PW segment traversed. This
is encoded in 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- L2 PW address of PW Switching Point (recommended format).
This sub-TLV type contains a L2 PW address of PW Switching Point in
the format described in [RFC5003]. This includes the AII type field ,
and length, as well as the L2 PW address.
7.4.2. Adaptation of Interface Parameters
[RFC4447] defines several interface parameters, which are used by the
Network Service Processing (NSP) to adapt the PW to the Attachment
Circuit (AC). The interface parameters are only used at the end
points, and MUST be passed unchanged across the S-PE. However the
following interface parameters MAY be modified as follows:
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- 0x03 Optional Interface Description string This Interface
parameter MAY be modified, or altogether removed from the FEC
element depending on local configuration policies.
- 0x09 Fragmentation indicator This parameter MAY be inserted in
the FEC by the switching point if it is capable of re-assembly of
fragmented PW frames according to [RFC4623].
- 0x0C VCCV parameter This Parameter contains the CC type , and CV
type bit fields. The CV type bit field MUST be reset to reflect
the CV type supported by the S-PE. CC type bit field MUST have
bit 1 "Type 2: MPLS Router Alert Label " set to 0. The other bit
fields MUST be reset to reflect the CC type supported by the S-
PE.
7.5. Group ID
The Group ID (GR ID) is used to reduce the number of status messages
that need to be sent by the PE advertising the PW FEC. The GR ID has
local significance only, and therefore MUST be mapped to a unique GR
ID allocated by the S-PE PE.
7.6. PW Loop Detection
A switching point PE SHOULD inspect the PW switching Point TLV, to
verify that it's own IP address does not appears in it. If the PE's
IP address appears in a received PW switching Point TLV, the PE
SHOULD break the loop, and send a label release message with the
following error code:
Assignment E Description
0x0000003A 0 "PW Loop Detected"
[ note: error code pending IANA allocation ]
8. MPLS-PW to L2TPv3-PW Control Plane Switching
Both MPLS and L2TPv3 PWs may be static or dynamic. This results in
four possibilities when switching between L2TPv3 and MPLS.
-i. Switching between MPLS and L2TPv3 static control planes.
-ii. Switching between a static MPLS PW and a dynamic L2TPv3 PW.
-iii. Switching between a static L2TPv3 PW and a dynamic MPLS PW.
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-iv. Switching between a dynamic MPLS PW and a dynamic L2TPv3 PW.
8.1. Static MPLS and L2TPv3 PWs
In the case of two static control planes, the S-PE MUST be configured
to direct packets from one PW into the other. There is no control
protocol involved in this case. The configuration MUST include which
MPLS VC Label maps to which L2TPv3 Session ID (and associated Cookie,
if present) as well as which MPLS Tunnel Label maps to which PE
destination IP address.
8.2. Static MPLS PW and Dynamic L2TPv3 PW
When a statically configured MPLS PW is switched to a dynamic L2TPv3
PW, the static control plane should be considered identical to an
attachment circuit (AC) in the reference model of Figure 1. The
switching point PE SHOULD signal the appropriate PW status if it
detects a failure in sending or receiving packets over the static PW.
Because the PW is statically configured, the status communicated to
the dynamic L2TPv3 PW will be limited to local interface failures. In
this case, the S-PE PE behaves in a very similar manner to a T-PE,
assuming an active role.
8.3. Static L2TPv3 PW and Dynamic LDP/MPLS PW
When a statically configured L2TPv3 PW is switched to a dynamic
LDP/MPLS PW, then the static control plane should be considered
identical to an attachment circuit (AC) in the reference model of
Figure 1. The switching point PE SHOULD signal the appropriate PW
status (via an L2TPv3 SLI message) if it detects a failure in sending
or receiving packets over the static PW. Because the PW is
statically configured, the status communicated to the dynamic
LDP/MPLS PW will be limited to local interface failures. In this
case, the S-PE PE behaves in a very similar manner to a T-PE,
assuming an active role.
8.4. Dynamic LDP/MPLS and L2TPv3 PWs
When switching between dynamic PWs, the switching point always
assumes an initial passive role. Thus, it does not initiate an
LDP/MPLS or L2TPv3 PW until it has received a connection request
(Label Mapping or ICRQ) from one side of the node. Note that while
MPLS PWs are made up of two unidirectional LSPs bonded together by
FEC identifiers, L2TPv3 PWs are bidirectional in nature, setup via a
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3-message exchange (ICRQ, ICRP and ICCN). Details of Session
Establishment, Tear Down, and PW Status signaling are detailed below.
8.4.1. Session Establishment
When the S-PE receives an L2TPv3 ICRQ message, the identifying AVPs
included in the message are mapped to FEC identifiers and sent in an
LDP label mapping message. Conversely, if an LDP Label Mapping
message is received, it is either mapped to an ICRP message or causes
an L2TPv3 session to be initiated by sending an ICRQ.
Following are two example exchanges of messages between LDP and
L2TPv3. The first is a case where an L2TPv3 T-PE initiates an MS-PW,
the second is a case where an MPLS T-PE initiates an MS-PW.
PE 1 (L2TPv3) PW Switching Node PE3 (MPLS/LDP)
AC "Up"
L2TPv3 ICRQ --->
LDP Label Mapping --->
AC "UP"
<--- LDP Label Mapping
<--- L2TPv3 ICRP
L2TPv3 ICCN --->
<-------------------- MH PW Established ------------------>
PE 1 (MPLS/LDP) PW Switching Node PE3 (L2TPv3)
AC "Up"
LDP Label Mapping --->
L2TPv3 ICRQ --->
<--- L2TPv3 ICRP
<--- LDP Label Mapping
L2TPv3 ICCN --->
AC "Up"
<-------------------- MH PW Established ------------------>
8.4.2. Adaptation of PW Status message
L2TPv3 uses the SLI message to indicate a interface status change
(such as the interface transitioning from "Up" or "Down"). MPLS/LDP
PWs either signal this via an LDP Label Withdraw or the PW Status
Notification message defined in section 4.4 of [RFC4447].
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8.4.3. Session Tear Down
L2TPv3 uses a single message, CDN, to tear down a pseudowire. The CDN
message translates to a Label Withdraw message in LDP. Following are
two example exchanges of messages between LDP and L2TPv3. The first
is a case where an L2TPv3 T-PE initiates the termination of an MS-PW,
the second is a case where an MPLS T-PE initiates the termination of
an MS-PW.
PE 1 (L2TPv3) PW Switching Node PE3 (MPLS/LDP)
AC "Down"
L2TPv3 CDN --->
LDP Label Withdraw --->
AC "Down"
<-- LDP Label Release
<--------------- MH PW Data Path Down ------------------>
PE 1 (MPLS LDP) PW Switching Node PE3 (L2TPv3)
AC "Down"
LDP Label Withdraw --->
L2TPv3 CDN -->
<-- LDP Label Release
AC "Down"
<---------------- MH PW Data Path Down ------------------>
8.5. Adaptation of L2TPv3 AVPs to Interface Parameters
[RFC4447] defines several interface parameters which MUST be mapped
to the equivalent AVPs in L2TPv3 setup messages.
* Interface MTU
The Interface MTU parameter is mapped directly to the L2TP
Interface MTU AVP defined in [RFC4667]
* Max Number of Concatenated ATM cells
This interface parameter is mapped directly to the L2TP "ATM
Maximum Concatenated Cells AVP" described in section 6 of
[RFC4454].
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* Optional Interface Description String
This string may be carried as the "Call-Information AVP"
described in section 2.2 of [L2TP-INFOMSG]
* PW Type
The PW Type defined in [RFC4446] is mapped to the L2TPv3 "PW
Type" AVP defined in [L2TPv3].
* PW ID (FEC 128)
For FEC 128, the PW ID is mapped directly to the L2TPv3 "Remote
End ID" AVP defined in [L2TPv3].
* Generalized FEC 129 SAI/TAI
Section 4.3 of [RFC4667] defines how to encode the SAI and TAI
parameters. These can be mapped directly.
Other interface parameter mappings are unsupported when switching
between LDP/MPLS and L2TPv3 PWs.
8.6. Switching Point TLV in L2TPv3
When translating between LDP and L2TPv3 control messages, the PW
Switching Point TLV described earlier in this document is carried in
a single variable length L2TP AVP present in the ICRQ, ICRP messages,
and optionally in the ICCN message.
The L2TP "Switching Point AVP" is Attribute Type TBA-L2TP-AVP-1. The
AVP MAY be hidden (the L2TP AVP H-bit may be 0 or 1), the length of
the AVP is 6 plus the length of the series of Switching Point sub-
TLVs included in the AVP, and the AVP MUST NOT be marked Mandatory
(the L2TP AVP M-bit MUST be 0).
8.7. L2TPv3 and MPLS PW Data Plane
When switching between an MPLS and L2TP PW, packets are sent in their
entirety from one PW to the other, replacing the MPLS label stack
with the L2TPv3 and IP header or vice versa. There are some
situations where an additional amount of interworking must be
provided between the two data planes at the S-PE, however this is
outside the scope of this document.
Section 5.4 of [RFC3985] discusses the purpose of the various shim
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headers necessary for enabling a pseudowire over an IP or MPLS PSN.
For L2TPv3, the Payload Convergence and Sequencing function is
carried out via the Default L2-Specific Sublayer defined in [L2TPv3].
For MPLS, these two functions (together with PSN Convergence) are
carried out via the MPLS Control Word. Since these functions are
different between MPLS and L2TPv3, interworking between the two may
be necessary.
The L2TP L2-Specific Sublayer and MPLS Control Word are shim headers
which in some cases are not necessary to be present at all. For
example, an Ethernet PW with sequencing disabled will generally not
require an MPLS Control Word or L2TP Default L2-Specific Sublayer to
be present at all. In this case, Ethernet frames are simply sent from
one PW to the other without any modification beyond the MPLS and
L2TP/IP encapsulation and decapsulation.
The following section offers guidelines for how to interwork between
L2TP and MPLS for those cases where the Payload Convergence,
Sequencing, or PSN Convergence functions are necessary on one or both
sides of the switching node.
8.7.1. Mapping the MPLS Control Word to L2TP
The MPLS Control Word consists of (from left to right):
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 0 0| Reserved | Length | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-i. These bits are always zero in MPLS are not necessary to be
mapped to L2TP.
-ii. These six bits may be used for Payload Convergence depending
on the PW type. For ATM, the first four of these bits are
defined in [RFC4717]. These map directly to the bits defined
in [RFC4454]. For Frame Relay, these bits indicate how to
set the bits in the Frame Relay header which must be
regenerated for L2TP as it carries the Frame Relay header
intact.
-iii. L2TP determines its payload length from IP. Thus, this
Length field need not be carried directly to L2TP. This
Length field will have to be calculated and inserted for
MPLS when necessary.
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-iv. The Default L2-Specific Sublayer has a sequence number with
different semantics than that of the MPLS Control Word. This
difference eliminates the possibility of supporting
sequencing across the MS-PW by simply carrying the sequence
number through the switching point transparently. As such,
sequence numbers MAY be supported by checking the sequence
numbers of packets arriving at the switching point and
regenerating a new sequence number in the appropriate format
for the PW on egress. If this type of sequence interworking
at the switching node is not supported, and a T-PE requests
sequencing of all packets via the L2TP control channel
during session setup, the switching node SHOULD NOT allow
the session to be established by sending a CDN message with
Result Code set to 17 "sequencing not supported" (subject to
IANA Assignment).
9. Operation And Management
9.1. Extensions to VCCV to Support MS-PWs
Single-hop pseudowires are signaled using the Virtual Circuit
Connectivity Verification (VCCV) parameter included in the interface
parameter field of the PW ID FEC TLV or the sub-TLV interface
parameter of the Generalized PW ID FEC TLV as described in [RFC5085].
When a switching point exist between PE nodes, it is required to be
able to continue operating VCCV end-to-end across a switching point
and to provide the ability to trace the path of the MS-PW over any
number of segments.
This document provides a method for achieving these two objectives.
This method is based on re-using the existing VCCV CW and
decrementing the TTL of the PW label at each hop in the path of the
MS-PW.
9.2. MPLS-PW to MPLS-PW OAM Data Plane Indication
As stated above the S-PE MUST perform a standard MPLS label swap
operation on the MPLS PW label. By the rules defined in [RFC3032] the
PW label TTL MUST be decreased at every S-PE. Once the PW label TTL
reaches the value of 0, the packet is sent to the control plane to be
processed. Hence, by controlling the PW TTL value of the PW label it
is possible to select exactly which hop will respond to the VCCV
packet.
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9.3. Signaling OAM Capabilities for Switched Pseudowires
Similarly to SS-PW, MS-PW VCCV capabilities are signaled using the
VCCV parameter included in the interface parameter field of the PW ID
FEC TLV or the sub-TLV interface parameter of the Generalized PW ID
FEC TLV as described in [RFC5085].
In Figure 3 T-PE1 uses the VCCV parameter included in the interface
parameter field of the PW ID FEC TLV or the sub-TLV interface
parameter of the Generalized PW ID FEC TLV to indicate to the far end
T-PE2 what VCCV capabilities T-PE1 supports. This is the same VCCV
parameter as would be used if T-PE1 and T-PE2 were connected
directly. S-PE2, which is a PW switching point, as part of the
adaptation function for interface parameters, processes locally the
VCCV parameter then passes it to T-PE2. If there were multiple S-PEs
on the path between T-PE1 and T-PE2, each would carry out the same
processing, passing along the VCCV parameter. The local processing of
the VCCV parameter removes CC Types specified by the originating T-PE
that are not supported on the S-PE. For example, if T-PE1 indicates
supports CC Types 1,2,3 and the Then the S-PE removes the Router
Alert CC Type=2, leaving the rest of the TLV unchanged, and passes
the modified VCCV parameter to the next S-PE along the path.
The far end T-PE (T-PE2) receives the VCCV parameter indicating only
the CC types that are supported by the initial T-PE (T-PE1) and all
S-PEs along the PW path.
9.4. OAM Capability for MS-PWs Demultiplexed using MPLS
The VCCV parameter ID is defined as follows in [RFC4446]:
Parameter ID Length Description
0x0c 4 VCCV
The format of the VCCV parameter field 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 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0c | 0x04 | CC Types | CV Types |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0x01 Type 1: PWE3 control word with 0001b as first nibble
as defined in [RFC4385].
0x02 Type 2: MPLS Router Alert Label.
0x04 Type 3: MPLS PW De-multiplexor Label TTL = 1 (Type 3).
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9.4.1. MS-PW and VCCV CC Type 1
VCCV CC type 1 can be used for MS-PWs. However, if the CW is enabled
on user packets, VCCV CC type 1 MUST be used according to the rules
in [RFC5085]. When using CC type 1 for MS-PWs the PE transmitting
the VCCV packet MUST set the TTL to the appropriate value to reach
the destination S-PE. However if the packet is destined for the T-PE,
the TTL can be set to any value that is sufficient for the packet to
reach the T-PE.
9.4.2. MS-PW and VCCV CC type 2
VCCV CC type 2 is not supported for MS-PWs and MUST be removed form a
VCCV parameter field by the S-PE.
9.4.3. MS-PW and VCCV CC type 3
VCCV CC type 3 can be used for MS-PWs, however if the CW is enabled
VCCV type 1 is preferred according to the rules in [RFC5085]. Note
that for using the VCCV type 3, TTL method, the PE will set the PW
label TTL to the appropriate value necessary to reach the target PE,
otherwise the VCCV packet might be forwarded over the AC to the CPE.
9.5. MS-PW VCCV Operations
This document specifies four VCCV operations:
-i. End-to-end MS-PW connectivity verification. This operation
enables the connectivity of the MS-PW to be tested from
source T-PE to destination T-PE. In order to do this, the
sending T-PE must include the FEC used in the last segment
of the MS-PW to the destination T-PE in the VCCV-Ping echo
request. This information is either configured at the
sending T-PE or is obtained by processing the corresponding
sub-TLVs of the optional S-PE TLV, as described below.
-ii. Partial MS-PW connectivity verification. This operation
enables the connectivity of any contiguous subset of the
segments of a MS-PW to be tested from the source T-PE or a
source S-PE to a destination S-PE or T-PE. Again, the FEC
used on the last segment to be tested must be included in
the VCCV-Ping echo request message. This information is
determined by the sending T-PE or S-PE as in (i) above.
-iii. MS-PW path verification. This operation verifies the path of
the MS-PW, as returned by the S-PE TLV, against the actual
data path of the MS-PW. The sending T-PE or S-PE iteratively
sends a VCCV echo request to each S-PE along the MS-PW path,
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using the FEC for the corresponding MS-PW segment in the
switching point TLV. If the S-PE TLV information is correct,
then a VCCV echo reply showing that this is a valid router
for the FEC will be received. However, if the switching
point TLV information is incorrect, then this operation
enables the first incorrect switching point to be
determined, but not the actual path of the MS-PW beyond
that. This operation cannot be used when the MS-PW is
statically configured or when the S-PE TLV is not suported.
The processing of the PW switching TLV used for this
operation is described below. This operation is OPTIONAL.
-iv. MS-PW path trace. This operation traces the data path of the
MS-PW using FECs included in the Target FEC stack TLV
[RFC4379] returned by S-PEs or T-PEs in an echo reply
message. The sending T-PE or S-PE uses this information to
recursively test each S-PE along the path of the MS-PW in a
single operation in a similar manner to LSP trace. This
operation is able to determine the actual data path of the
MS-PW, and can be used for both statically configured and
signaled MS-PWs. Support for this operation is OPTIONAL.
Note that the above operations rely on intermediate S-PEs and/or the
destination T-PE to include the switching point TLV as a part of the
MS-PW setup process, or to include the Target FEC stack TLV in the
VCCV echo reply message. For various reasons, e.g. privacy or
security of the S-PE/T-PE, this information may not be available to
the source T-PE. In these cases, manual configuration of the FEC MAY
still be used.
9.5.1. VCCV Echo Message Processing
The challenge for the control plane is to be able to build the VCCV
echo request packet with the necessary information to reach the
desired S-PE or T-PE, for example the target FEC 128 PW sub-TLV of
the downstream PW segment that the packet is destined for. This could
be even more difficult in situations in which the MS-PW spans
different providers and Autonomous Systems.
For example, in Figure 3, T-PE1 has the FEC128 of the segment, PW
segment 1, but it does not readily have the information required to
compose the FEC128 of the following segment, PW segment 3, if a VCCV
echo request to be sent to T-PE2. This can be achieved by the methods
described in the following subsections.
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9.5.1.1. Sending a VCCV Echo Request
When performing a partial or end-to-end connectivity or path
verification, the sender of the echo request message requires the FEC
of the last segment to the target S-PE/T-PE node. This information
can either be configured manually or be obtained by inspecting the
corresponding sub-TLV's of the PW switching point TLV.
The necessary S-PE sub-TLVs are :
Type Description
0x01 PW ID of last PW segment traversed
0x03 Local IP address of PW Switching Point
0x04 Remote IP address of last PW Switching Point traversed or
of the T-PE
When performing an OPTIONAL MS-PW path trace operation, the T-PE will
automatically learn the target FEC by probing, one by one, the hops
of the MS-PW path, using the FEC returned in the Target FEC stack of
the previous VCCV echo reply.
9.5.1.2. Receiving a VCCV Echo Request
Upon receiving a VCCV echo request the control plane on S-PEs (or the
target node of each segment of the MS-PW) validates the request and
responds to the request with an echo reply consisting of a return
code of 8 (label switched at stack-depth) indicating that it is an
S-PE and not the egress router for the MS-PW.
S-PEs that wish to reveal their downstream next-hop in a trace
operation should include the FEC of the downstream PW segment in the
Target FEC stack (as per Sections 3.2 and 4.5 of [RFC4379]) of the
echo reply message. FEC128 PWs MUST use the format shown in Section
3.2.09 of [RFC4379] for the sub-TLV in the Target FEC stack, while
FEC129 PWs MUST use the format shown in Section 3.2.10 of [RFC4379]
for the sub-TLV in the Target FEC stack. Note that an S-PE MUST NOT
include this FEC information in the reply if it has been configured
not to do so for administrative reasons, or for reasons explained
previously.
If the node is the T-PE or the egress node of the MS-PW, it responds
to the echo request with an echo reply with a return code of 3
(egress router).
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9.5.1.3. Receiving a VCCV Echo Reply
The operation to be taken by the node receiving the echo reply in
response to an echo request depends on the VCCV mode of operation
described above. See Section 9.5.2 for detailed procedures.
9.5.2. Detailed VCCV procedures
9.5.2.1. End to End Connectivity Verification Between T-PEs
In Figure 3, if T-PE1, S-PE and T-PE2 support Control Word , the PW
control plane will automatically negotiate the use of the CW. VCCV CC
type 3 will function correctly whether the CW is enable or not on the
PW. However VCCV type 1 for (which can be use for end to end
verification only), is only supported if the CW is enabled.
At the S-PE the data path operations include an outer label pop,
inner label swap and new outer label push. Note that there is no
requirement for the S-PE to inspect the CW. Thus, the end-to-end
connectivity of the multi-segment pseudowire can be verified by
performing all of the following steps:
-i. T-PE forms a VCCV-ping echo request message with the FEC
matching that of the last segment PW to the destination T-
PE.
-ii. T-PE sets the inner PW label TTL to the exact value to allow
the packet to reach the far end T-PE. ( the value is
determined by counting the number of S-PEs from the control
plane information ) Alternatively, if CC type 1 is supported
the packet can be encapsulated according to CC type 1 in
[RFC5085]
-iii. T-PE sends a VCCV packet that will follow the exact same
data path at each S-PE as that taken by data packets.
-iv. S-PE may performs an outer label pop, if PHP is disabled,
and will perform an inner label swap with TTL decrement, and
new outer label push.
-v. There is no requirement for the S-PE to inspect the CW.
-vi. The VCCV packet is diverted to VCCV control processing at
the destination T-PE.
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-vii. Destination T-PE replies using the specified reply mode,
i.e., reverse PW path or IP path.
9.5.2.2. Partial Connectivity Verification from T-PE
In order to trace part of the multi-segment pseudowire, the TTL of
the PW label may be used to force the VCCV message to 'pop out' at an
intermediate node. When the TTL expires, the S-PE can determine that
the packet is a VCCV packet by either checking the control word (CW)
, or if the CW is not in use by checking for a valid IP header with
UDP destination port 3503. The packet should then be diverted to
VCCV processing.
In Figure 3, if T-PE1 sends a VCCV message with the TTL of the PW
label equal to 1, the TTL will expire at the S-PE. T-PE1 can thus
verify the first segment of the pseudowire.
The VCCV packet is built according to [RFC4379] section 3.2.9 for FEC
128, or 3.2.10 for a FEC 129 PW. All the information necessary to
build the VCCV LSP ping packet is collected by inspecting the S-PE
TLVs.
Note that this use of the TTL is subject to the caution expressed in
[RFC5085]. If a penultimate LSR between S-PEs or between an S-PE and
a T-PE manipulates the PW label TTL, the VCCV message may not emerge
from the MS-PW at the correct S-PE.
9.5.2.3. Partial connectivity verification between S-PEs
Assuming that all nodes along an MS-PW support the Control Word CC
Type 3, VCCV between S-PEs may be accomplished using the PW label TTL
as described above. In Figure 3, the S-PE may verify the path between
it and T-PE2 by sending a VCCV message with the PW label TTL set to
1. Given a more complex network with multiple S-PEs, an S-PE may
verify the connectivity between it and an S-PE two segments away by
sending a VCCV message with the PW label TTL set to 2. Thus, an S-PE
can diagnose connectivity problems by successively increasing the
TTL. All the information needed to build the proper VCCV echo
request packet as described in [RFC4379] section 3.2.9 or 3.2.10 is
obtained automatically from the LDP label mapping that contains S-PE
TLVs.
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9.5.2.4. MS-PW Path Verification
As an example, in Figure 3, VCCV trace can be performed on the MS-PW
originating from T-PE1 by a single operational command. The following
process ensues:
-i. T-PE1 sends a VCCV echo request with TTL set to 1 and a FEC
containing the pseudowire information of the first segment
(PW1 between T-PE1 and S-PE) to S-PE for validation. If FEC
Stack Validation is enabled, the request may also include
additional sub-TLV such as LDP Prefix and/or RSVP LSP
dependent on the type of transport tunnel the segmented PW
is riding on.
-ii. S-PE validates the echo request with the FEC. Since it is a
switching point between the first and second segment it
builds an echo reply with a return code of 8 and sends the
echo reply back to T-PE1.
-iii. T-PE1 builds a second VCCV echo request based on the
infomation obtained from the control plane (S-PE TLV). It
then increments the TTL and sends it out to T-PE2. Note that
the VCCV echo request packet is switched at the S-PE
datapath and forwarded to the next downstream segment
without any involvement from the control plane.
-iv. T-PE2 receives and validates the echo request with the FEC.
Since T-PE2 is the destination node or the egress node of
the MS-PW it replies to T-PE1 with an echo reply with a
return code of 3 (Egress Router).
-v. T-PE1 receives the echo reply from T-PE2. T-PE1 is made
aware that T-PE2 is the destination of the MS-PW because the
echo reply has a return code of is 3. The trace process is
completed.
If no echo reply is received, or an error code is received from a
particular PE, the trace process MUST stop immediately, and no
packets MUST be sent further along the MS-PW.
For more detail on the format of the VCCV echo packet, refer to
[RFC5085] and [RFC4379]. The TTL here refers to that of the inner
(PW) label TTL.
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9.5.2.5. MS-PW Path Trace
As an example, in Figure 3, VCCV trace can be performed on the MS-PW
originating from T-PE1 by a single operational command. The following
OPTIONAL process ensues:
-i. T-PE1 sends a VCCV echo request with TTL set to 1 and a FEC
containing the pseudowire information of the first segment
(PW1 between T-PE1 and S-PE) to S-PE for validation. If FEC
Stack Validation is enabled, the request may also include
additional sub-TLV such as LDP Prefix and/or RSVP LSP
dependent on the type of transport tunnel the segmented PW
is riding on.
-ii. The S-PE validates the echo request with the FEC.
-iii. The S-PE builds an echo reply with a return code of 8 and
sends the echo reply back to T-PE1, appending the FEC128
information for the next segment along the MS-PW to the VCCV
echo reply packet using the Target FEC stack TLV (as per
Sections 3.2 and 4.5 of [RFC4379]).
-iv. T-PE1 builds a second VCCV echo request based on the
infomation obtained from the FEC stack TLV received in the
previous VCCV echo reply. It then increments the TTL and
sends it out to T-PE2. Note that the VCCV echo request
packet is switched at the S-PE datapath and forwarded to the
next downstream segment without any involvement from the
control plane.
-v. T-PE2 receives and validates the echo request with the FEC.
Since T-PE2 is the destination node or the egress node of
the MS-PW it replies to T-PE1 with an echo reply with a
return code of 3 (Egress Router).
-vi. T-PE1 receives the echo reply from T-PE2. T-PE1 is made
aware that T-PE2 is the destination of the MS-PW because the
echo reply has a return code of is 3. The trace process is
completed.
If no echo reply is received, or an error code is received from a
particular PE, the trace process MUST stop immediately, and no
packets MUST be sent further along the MS-PW.
For more detail on the format of the VCCV echo packet, refer to
[RFC5085] and [RFC4379]. The TTL here refers to that of the inner
(PW) label TTL.
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10. Mapping Switched Pseudowire Status
In the PW switching with attachment circuits case (Figure 2), PW
status messages indicating PW or attachment circuit faults MUST be
mapped to fault indications or OAM messages on the connecting AC as
defined in [PW-MSG-MAP].
In the PW control plane switching case (Figure 3), there is no
attachment circuit at the S-PE, but the two PWs are connected
together. Similarly, the status of the PWs are forwarded unchanged
from one PW to the other by the control plane switching function.
However, it may sometimes be necessary to communicate fault status of
one of the locally attached PW segments at a S-PE. For LDP this can
be accomplished by sending an LDP notification message containing the
PW status TLV, as well as an OPTIONAL PW switching point TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1| Status (0x0300) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1| Status Code=0x00000028 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type=0 | PW Status TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Status TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Status TLV | PWId FEC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| PWId FEC or Generalized ID FEC |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| PW sw TLV (0x096D) | PW sw TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Variable Length Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Only one S-PE TLV can be present in this message. This message is
then relayed by each S-PE unchanged. The T-PE decodes the status
message and the included S-PE TLV to detect exactly where the fault
occurred. At the T-PE if there is no S-PE TLV included in the LDP
status notification then the status message can be assumed to have
originated at the remote T-PE.
The merging of the received LDP status and the local status for the
PW segments at an S-PE can be summarized as follows:
-i. When the local status for both PW segments is UP, the S-PE
passes any received AC or PW status bits unchanged, i.e.,
the status notification TLV is unchanged but the PWid in the
case of a FEC 128 TLV is set to the value of the PW segment
of the next hop.
-ii. When the local status for any of the PW segments is at
fault, the S-PE always sends the local status bits
regardless if the received status bits from the remote node
indicated that an upstream fault has cleared. AC status bit
are passed along unchanged.
10.1. S-PE initiated PW status messages
The PW fault directions are defined as follows:
+-------+
---PW1 receive---->| |-----PW2 Transmit---->
S-PE1 | S-PE2 | S-PE3
<--PW1 Transmit----| |<----PW2 Receive------
+-------+
Figure 4. S-PE and PW tx/rx directions.
When a local fault is detected by the S-PE, a PW status message is
sent in both directions along the PW. Since there are no attachment
circuits on an S-PE, only the following status messages are relevant:
0x00000008 - Local PSN-facing PW (ingress) Receive Fault
0x00000010 - Local PSN-facing PW (egress) Transmit Fault
Each S-PE needs to store only two 32-bit PW status words for each PW
segment: One for local failures , and one for remote failures
(normally received from another PE). The first failure will set the
appropriate bit in the 32-bit status word, and each subsequent
failure will be ORed to the appropriate PW status word. In the case
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of the PW status word storing remote failures, this rule has the
effect of a logical OR operation with the first failure received on
the particular PW segment.
It should be noted that remote failures received on an S-PE are just
passed along the MS-PW unchanged while local failures detected an an
S-PE are signalled on both PW segments.
A T-PE can receive multiple failures from S-PEs along the MH-PW,
however only the failure from the remote closest S-PE will be stored
(last pw status message received). The PW status word received are
just ORed to any existing remote PW status already stored on the T-
PE.
Given that there are two PW segments at a particular S-PE for a
particular MS-PW, referring to figure 4, there are four possible
failure cases as follows:
-i. PW2 Transmit direction fault
-ii. PW1 Transmit direction fault
-iii. PW2 Receive direction fault
-iv. PW1 Receive direction fault
Once a PW status notification message is initiated at a S-PE for a
particular PW status bit any further status message, for the same
status bit, received from an upstream neighbor is processed locally
and not forwarded until the S-PE original status error state is
cleared.
Each S-PE along the MS-PW MUST store any PW status messages
transiting it. If more then one status message with the same PW
status bit set is received by a T-PE, or S-PE only the last PW
status message is stored.
10.1.1. Local PW2 transmit direction fault
When this failure occurs the S-PE will take the following actions:
* Send a PW status message to S-PE3 containing "0x00000010 - Local
PSN-facing PW (egress) Transmit Fault"
* Send a PW status message to S-PE1 containing "0x00000008 - Local
PSN-facing PW (ingress) Receive Fault"
* Store 0x00000010 in the local PW status word for the PW segment
toward S-PE3.
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10.1.2. Local PW1 transmit direction fault
When this failure occurs the S-PE will take the following actions:
* Send a PW status message to S-PE1 containing "0x00000010 - Local
PSN-facing PW (egress) Transmit Fault"
* Send a PW status message to S-PE3 containing "0x00000008 - Local
PSN-facing PW (ingress) Receive Fault"
* Store 0x00000010 in the local PW status word for the PW segment
toward S-PE1.
10.1.3. Local PW2 receive direction fault
When this failure occurs the S-PE will take the following actions:
* Send a PW status message to S-PE3 containing "0x00000008 - Local
PSN-facing PW (ingress) Receive Fault"
* Send a PW status message to S-PE1 containing "0x00000010 - Local
PSN-facing PW (egress) Transmit Fault"
* Store 0x00000008 in the local PW status word for the PW segment
toward S-PE3.
10.1.4. Local PW1 receive direction fault
When this failure occurs the S-PE will take the following actions:
* Send a PW status message to S-PE1 containing "0x00000008 - Local
PSN-facing PW (ingress) Receive Fault"
* Send a PW status message to S-PE3 containing "0x00000010 - Local
PSN-facing PW (egress) Transmit Fault"
* Store 0x00000008 in the local PW status word for the PW segment
toward S-PE1.
10.1.5. Clearing Faults
Remote PW status fault clearing messages received by an S-PE will
only be forwarded if there are no corresponding local faults on the
S-PE. (local faults always supersede remote faults)
Once the local fault has cleared, and there is no corresponding (same
PW status bit set) remote fault, a PW status messages is sent out to
the adjacent PEs clearing the fault.
When a PW status fault clearing message is forwarded, the S-PE will
always send the S-PE TLV associated with the PE which cleared the
fault.
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10.2. PW status messages and S-PE TLV processing
When a PW status message is received that includes a S-PE TLV, the
S-PE TLV information MAY be stored, along with the contents of the PW
status Word according to the procedures described above. The S-PE TLV
stored is always the S-PE TLV that is associated with the PE that set
that particular last fault. If subsequent PW status message for the
same PW status bit are received the S-PE TLV will overwrite the
previously stored S-PE TLV.
10.3. T-PE processing of PW status messages
The PW switching architecture is based on the concept that the T-PE
should process the PW LDP messages in the same manner as if it was
participating in the setup of a PW segment. However T-PE
participating a MS-PW, SHOULD be able to process the S-PE TLV.
Otherwise the processing of PW status messages , and other PW setup
messages is exactly as described in [RFC4447].
10.4. Pseudowire Status Negotiation Procedures
Pseudowire Status signaling methodology, defined in [RFC4447], SHOULD
be transparent to the switching point.
10.5. Status Dampening
When the PW control plane switching methodology is used to cross an
administrative boundary it might be necessary to prevent excessive
status signaling changes from being propagated across the
administrative boundary. This can be achieved by using a similar
method as commonly employed for the BGP protocol route advertisement
dampening. The details of this OPTIONAL algorithm are a matter of
implementation, and are outside the scope of this document.
11. Peering Between Autonomous Systems
The procedures outlined in this document can be employed to provision
and manage MS-PWs crossing AS boundaries. The use of more advanced
mechanisms involving auto-discovery and ordered PWE3 MS-PW signaling
will be covered in a separate document.
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12. Security Considerations
This document specifies the LDP, L2TPv3, and VCCV extensions that are
needed for setting up and maintaining pseudowires. The purpose of
setting up pseudowires is to enable layer 2 frames to be encapsulated
and transmitted from one end of a pseudowire to the other. Therefore
we discuss the security considerations for both the data plane and
the control plane in the following sections.
12.1. Data Plane Security
Data plane security consideration as discussed in [RFC4447],
[L2TPv3], and [RFC3985] apply to this extension without any changes.
12.1.1. VCCV Security considerations
The VCCV technology for MS-PW offers a method for the service
provider to verify the data path of a specific PW. This involves
sending a packet to a specific PE and receiving an answer which
either confirms , or indicates that the information contained in the
packet is incorrect. This is a very similar process to the commonly
used IP ICMP ping , and TTL expired methods for IP networks. It
should be noted that when using VCCV Type 3 for PW when the CW is not
enabled, if a packet is crafted with a TTL greater then the number of
hops along the MS-PW path, or an S-PE along the path mis-processes
the TTL, the packet could mistakenly be forwarded out the attachment
circuit as a native PW packet. This packet would most likely be
treated as an error packet by the CE. However if this possibility is
not acceptable, the CW should be enabled to guarantee that a VCCV
packet will never be mistakenly forwarded to the AC.
12.2. Control Protocol Security
General security considerations with regard to the use of LDP are
specified in section 5 of RFC 3036. Security considerations with
regard to the L2TPv3 control plane are specified in [L2TPv3]. These
considerations apply as well to the case where LDP or L2TPv3 is used
to set up PWs.
A Pseudowire connects two attachment circuits. It is important to
make sure that LDP connections are not arbitrarily accepted from
anywhere, or else a local attachment circuit might get connected to
an arbitrary remote attachment circuit. Therefore an incoming session
request MUST NOT be accepted unless its IP source address is known to
be the source of an "eligible" peer. The set of eligible peers could
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be pre-configured (either as a list of IP addresses, or as a list of
address/mask combinations), or it could be discovered dynamically via
an auto-discovery protocol which is itself trusted. (Note that if the
auto-discovery protocol were not trusted, the set of "eligible peers"
it produces could not be trusted.)
Even if a connection request appears to come from an eligible peer,
its source address may have been spoofed. So some means of
preventing source address spoofing must be in place. For example, if
all the eligible peers are in the same network, source address
filtering at the border routers of that network could eliminate the
possibility of source address spoofing.
For a greater degree of security, the LDP authentication option, as
described in section 2.9 of [RFC5036], or the Control Message
Authentication option of [L2TPv3] MAY be used. This provides
integrity and authentication for the control messages, and eliminates
the possibility of source address spoofing. Use of the message
authentication option does not provide privacy, but privacy of
control messages are not usually considered to be highly important.
Both the LDP and L2TPv3 message authentication options rely on the
configuration of pre-shared keys, making it difficult to deploy when
the set of eligible neighbors is determined by an auto-configuration
protocol.
When the Generalized ID FEC Element is used, it is possible that a
particular peer may be one of the eligible peers, but may not be the
right one to connect to the particular attachment circuit identified
by the particular instance of the Generalized ID FEC element.
However, given that the peer is known to be one of the eligible peers
(as discussed above), this would be the result of a configuration
error, rather than a security problem. Nevertheless, it may be
advisable for a PE to associate each of its local attachment circuits
with a set of eligible peers, rather than having just a single set of
eligible peers associated with the PE as a whole.
13. IANA Considerations
13.1. L2TPv3 AVP
This document uses a ne L2TP parameter, IANA already maintains a
registry of name "Control Message Attribute Value Pair" defined by
[RFC3438]. The following new value is required:
TBA-L2TP-AVP-1 - PW Switching Point AVP
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13.2. LDP TLV TYPE
This document 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
0x096D Pseudowire Switching TLV
13.3. LDP Status Codes
This document uses a new LDP status codes, IANA already maintains a
registry of name "STATUS CODE NAME SPACE" defined by RFC3036. The
following value is suggested for assignment:
Assignment E Description
0x0000003A 0 "PW Loop Detected"
13.4. L2TPv3 Result Codes
This document uses a new L2TPv3 status codes, IANA already maintains
a registry of name "L2TPv3 Result Codes". The following value is
suggested for assignment:
Assignment Description
TBD "sequencing not supported"
13.5. New IANA Registries
IANA needs to set up a registry of "PW Switching Point TLV Type".
These are 8-bit values. Types value 1 through 6 are defined in this
document. Type values 7 through 64 are to be assigned by IANA using
the "Expert Review" policy defined in RFC5226. Type values 65 through
127, 0 and 255 are to be allocated using the IETF consensus policy
defined in [RFC5226]. Types values 128 through 254 are reserved for
vendor proprietary extensions and are to be assigned by IANA, using
the "First Come First Served" policy defined in RFC5226.
The Type Values are assigned as follows:
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Type Length Description
0x01 4 PW ID of last PW segment traversed
0x02 variable PW Switching Point description string
0x03 4/16 Local IP address of PW Switching Point
0x04 4/16 Remote IP address of last PW Switching Point traversed
or of the T-PE
0x05 variable AI of last PW segment traversed
0x06 10 L2 PW address of PW Switching Point
14. Normative References
[RFC4385] " Pseudowire Emulation Edge-to-Edge (PWE3)
Control Word for Use over an MPLS PSN", S. Bryant, et al.,
RFC4385, February 2006.
[RFC4446] "IANA Allocations for Pseudowire Edge to Edge
mulation (PWE3)", L. Martini, RFC4446, April 2006.
[RFC4447] "Transport of Layer 2 Frames Over MPLS", Martini, L.,
et al., rfc4447 April 2006.
[RFC4364] "BGP/MPLS IP Virtual Private Networks (VPNs)", Rosen, E,
Rekhter, Y., RFC4364, February 2006
October 2004.
[L2TPv3] "Layer Two Tunneling Protocol (Version 3)", J. Lau,
M. Townsley, I. Goyret, RFC3931
[RFC5085] Nadeau, T., et al. "Pseudo Wire Virtual Circuit Connection
Verification (VCCV), A Control Channel for Pseudowires",
RFC5085 December 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations section in RFCs", BCP 26, RFC 5226, May 2008
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5003] C. Metz, L. Martini, F. Balus, J. Sugimoto, "Attachment
Individual Identifier (AII) Types for Aggregation", RFC5003,
September 2007.
[RFC4379] K. Kompella, G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC4379,
September 2007
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[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
15. Informative References
[RFC3985] Stewart Bryant, et al., PWE3 Architecture,
RFC3985
[RFC4023] "Encapsulating MPLS in IP or Generic
Routing Encapsulation (GRE)", Rosen, E, Rekhter, Y.
RFC4023, March 2005.
[RFC3985] "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture"
Bryant, et al., RFC 3985, March 2005.
[RFC4623] "Pseudowire Emulation Edge-to-Edge (PWE3) Fragmentation
and Reassembly", A. Malis, W. M. Townsley, RFC 4623, August 2006
[RFC4667] "Layer 2 Virtual Private Network (L2VPN)
Extensions for Layer 2 Tunneling Protocol (L2TP)", Luo, Wei,
RFC4667, W. Luo, September 2006
[L2TP-INFOMSG] "L2TP Call Information Messages", Mistretta,
Goyret, McGill, Townsley, draft-mistretta-l2tp-infomsg-01.txt,
( work in progress ), July 2004
[RFC4454] "Asynchronous Transfer Mode (ATM) over Layer 2
Tunneling Protocol Version 3 (L2TPv3)", Singh, Townsley,
Pignataro, RFC4454, May 2006
( work in progress ), March 2004.
[RFC4717] "Encapsulation Methods for Transport of (ATM)
MPLS Networks", Martini et al., RFC4717, December 2006
[RFC3438] W. M. Townsley, "Layer Two Tunneling Protocol
(L2TP) Internet"
[PW-MSG-MAP] "Pseudo Wire (PW) OAM Message Mapping", Nadeau et al,
draft-ietf-pwe3-oam-msg-map-10.txt, ( work in progress ),
April 2009
[RFC4379] "Detecting Multi-Protocol Label Switched (MPLS) Data
Plane Failures", RFC4379, February 2006.
[RFC3032] "MPLS Label Stack Encoding", RFC3032, January 2001
Martini, et al. [Page 40]
Internet Draft draft-ietf-pwe3-segmented-pw-12.txt June 3, 2009
[MS-PW-ARCH] "An Architecture for Multi-Segment Pseudo Wire Emulation
Edge-to-Edge", Bocci et al, draft-ietf-pwe3-ms-pw-arch-06.txt
February 2009
[RFC5254] "Requirements for Multi-Segment Pseudowire Emulation
Edge-to-Edge (PWE3)", N. Bitar, M. Bocci, L. Martini, RFC5254,
October 2008
16. Author's Addresses
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
e-mail: lmartini@cisco.com
Thomas D. Nadeau
BT
BT Centre
81 Newgate Street
London, EC1A 7AJ
United Kingdom
e-mail: tom.nadeau@bt.com
Chris Metz
Cisco Systems, Inc.
e-mail: chmetz@cisco.com
Mike Duckett
Bellsouth
Lindbergh Center
D481
575 Morosgo Dr
Atlanta, GA 30324
e-mail: mduckett@bellsouth.net
Matthew Bocci
Alcatel-Lucent
Grove House, Waltham Road Rd
White Waltham, Berks, UK. SL6 3TN
e-mail: matthew.bocci@alcatel-lucent.co.uk
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Florin Balus
Alcatel-Lucent
701 East Middlefield Rd.
Mountain View, CA 94043
e-mail: florin.balus@alcatel-lucent.com
Mustapha Aissaoui
Alcatel-Lucent
600, March Road,
Kanata, ON, Canada
e-mail: mustapha.aissaoui@alcatel-lucent.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
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Acknowledgments
The authors wish to acknowledge the contributions of Satoru
Matsushima, Wei Luo, Neil Mcgill, Skip Booth, Neil Hart, Michael Hua,
and Tiberiu Grigoriu.
Expiration Date: December 2009
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Martini, et al. [Page 43]
