Network Working Group Luca Martini (ED)
Internet Draft Eric C. Rosen
Expiration Date: December 2005 Cisco Systems, Inc.
Nasser El-Aawar Toby Smith
Level 3 Communications, LLC. Laurel Networks, Inc.
Giles Heron
Tellabs
June 2005
Pseudowire Setup and Maintenance using the Label Distribution Protocol
draft-ietf-pwe3-control-protocol-17.txt
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Abstract
Layer 2 services (such as Frame Relay, Asyncronus Transfer Mode,
Ethernet) can be "emulated" over an MPLS backbone by encapsulating
the layer 2 Packet Data Units (PDU) and then transmitting them over
"pseudowires". It is also possible to use pseudowires to provide
low-rate Time Dividion Multiplexed and a Synchronous Optical
NETworking circuit emulation over a MPLS enabled network. This
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document specifies a protocol for establishing and maintaining the
pseudowires, using extensions to Label Distribution Protocol (LDP).
Procedures for encapsulating layer 2 PDUs are specified in a set of
companion documents.
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Table of Contents
1 Specification of Requirements ........................ 4
2 Introduction ......................................... 4
3 The Pseudowire Label ................................. 6
4 Details Specific to Particular Emulated Services ..... 8
4.1 IP Layer2 Transport .................................. 8
5 LDP .................................................. 8
5.1 LDP Extensions ....................................... 9
5.2 The PWid FEC Element ................................. 9
5.3 The Generalized PWid FEC Element ..................... 11
5.3.1 Attachment Identifiers ............................... 12
5.3.2 Encoding the Generalized ID FEC Element .............. 13
5.3.2.1 Interface Parameters TLV ............................. 15
5.3.2.2 PW Grouping TLV ...................................... 15
5.3.3 Signaling Procedures ................................. 16
5.4 Signaling of Pseudo Wire Status ...................... 17
5.4.1 Use of Label Mappings Messages. ...................... 17
5.4.2 Signaling PW status. ................................. 18
5.4.3 Pseudowire Status Negotiation Procedures ............. 19
5.5 Interface Parameters sub-TLV ......................... 21
6 Control Word ......................................... 22
6.1 PW types for which the control word is REQUIRED ...... 22
6.2 PW types for which the control word is NOT mandatory . 22
6.3 LDP label Withdrawal procedures ...................... 23
6.4 Sequencing Considerations ............................ 24
6.4.1 Label Advertisements ................................. 24
6.4.2 Label Release ........................................ 25
7 IANA Considerations .................................. 25
7.1 LDP TLV TYPE ......................................... 25
7.2 LDP Status Codes ..................................... 25
7.3 FEC Type Name Space .................................. 26
8 Security Considerations .............................. 26
8.1 Data-plane Security .................................. 26
8.2 Control Protocol Security ............................ 27
9 Intellectual Property Statement ...................... 28
10 Full Copyright Statement ............................. 29
11 Acknowledgments ...................................... 29
12 Normative References ................................. 29
13 Informative References ............................... 29
14 Author Information ................................... 30
15 Additional Contributing Authors ...................... 31
Ap A C-bit Handling Procedures Diagram .................... 34
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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 RFC 2119.
2. Introduction
In [FRAME], [ATM], and [ETH] it is explained how to encapsulate a
layer 2 Protocol Data Unit (PDU) for transmission over an MPLS
enabled network. Those documents specify that a "pseudowire header",
consisting of a demultiplexor field, will be prepended to the
encapsulated PDU. The pseudowire demultiplexor field is put on before
transmitting a packet on a pseudowire. When the packet arrives at the
remote endpoint of the pseudowire, the demultiplexor is what enables
the receiver to identify the particular pseudowire on which the
packet has arrived. To actually transmit the packet from one
pseudowire endpoint to another, the packet may need to travel through
a "Public switched Network (PSN) tunnel"; this will require an
additional header to be prepended to the packet.
Accompanying documents [CEP, SAToP] specify methods for transporting
time division multiplexed (TDM) digital signals (TDM circuit
emulation) over a packet-oriented MPLS enabled network. The
transmission system for circuit-oriented TDM signals is the
Synchronous Optical Network (SONET)[SDH]/Synchronous Digital
Hierarchy (SDH) [ITUG]. To support TDM traffic, which includes voice,
data, and private leased line service, the pseudowires must emulate
the circuit characteristics of SONET/SDH payloads. The TDM signals
and payloads are encapsulated for transmission over pseudowires. To
this encapsulation is prepended a pseudowire demultiplexor and a PSN
tunnel header.
[SAToP] describe methods for transporting low-rate time division
multiplexed (TDM) digital signals (TDM circuit emulation) over PSNs,
while [CEP] similarly describes transport of high-rate TDM
(SONET/SDH). To support TDM traffic the pseudowires must emulate the
circuit characteristics of the original T1, E1, T3, E3, SONET or SDH
signals. [SAToP] does this by encapsulating an arbitrary but constant
amount of the TDM data in each packet, while the other methods
encapsulate TDM structures.
In this document, we specify the use of the MPLS Label Distribution
Protocol, LDP [RFC3036], as a protocol for setting up and maintaining
the pseudowires. In particular, we define new TLVs, FEC elements,
parameters and codes for LDP, which enable LDP to identify
pseudowires and to signal attributes of pseudowires. We specify how a
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pseudowire endpoint uses these TLVs in LDP to bind a demultiplexor
field value to a pseudowire, and how it informs the remote endpoint
of the binding. We also specify procedures for reporting pseudowire
status changes, passing additional information about the pseudowire
as needed, and for releasing the bindings.
In the protocol specified herein, the pseudowire demultiplexor field
is an MPLS label. Thus the packets which are transmitted from one end
of the pseudowire to the other are MPLS packets which must be
transmitted through a MPLS tunnel. However if the pseudowire
endpoints are immediately adjacent, and penultimate hop popping
behaviour is in use, the MPLS tunnel may not be necessary. Any sort
of PSN tunnel can be used, as long as it is possible to transmit MPLS
packets through it. The PSN tunnel can itself be an MPLS LSP, or any
other sort of tunnel which can carry MPLS packets. Procedures for
setting up and maintaining the MPLS tunnels are outside the scope of
this document.
This document deals only with the setup and maintenance of point-to-
point pseudowires. Neither point to multipoint nor multipoint to
point pseudowires are discussed.
QoS related issues are not discussed in this document. The following
two figures describe the reference models which are derived from
[RFC3985] to support the PW emulated services.
|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudo Wire ------>| |
| | | |
|Attachment| |<-- PSN Tunnel -->| |Attachment|
| Circuit V V V V Circuit |
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
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+-----------------+ +-----------------+
|Emulated Service | |Emulated Service |
|(e.g., TDM, ATM) |<==== Emulated Service ===>|(e.g., TDM, ATM) |
+-----------------+ +-----------------+
| Payload | | Payload |
| Encapsulation |<====== Pseudo Wire ======>| Encapsulation |
+-----------------+ +-----------------+
|PW Demultiplexer | |PW Demultiplexer |
| PSN Tunnel, |<======= PSN Tunnel ======>| PSN Tunnel, |
| PSN & Physical | | PSN & Physical |
| Layers | | Layers |
+-------+---------+ ___________ +---------+-------+
| / |
+===============/ PSN ===============+
/
_____________/
Figure 2: PWE3 Protocol Stack Reference Model
For the purpose of this document, PE1 will be defined as the ingress
router, and PE2 as the egress router. A layer 2 PDU will be received
at PE1, encapsulated at PE1, transported, decapsulated at PE2, and
transmitted out of PE2.
3. The Pseudowire Label
Suppose it is desired to transport layer 2 PDUs from ingress LSR PE1
to egress LSR PE2, across an intervening MPLS enabled network. We
assume that there is a MPLS tunnel from PE1 to PE2. That is, we
assume that PE1 can cause a packet to be delivered to PE2 by
encapsulating the packet in a "MPLS tunnel header" and sending the
result to one of its adjacencies. The MPLS tunnel is an MPLS Label
Switched Path (LSP), hence putting on a MPLS tunnel encapsulation is
a matter of pushing on an MPLS label.
We presuppose that a large number of pseudowires can be carried
through a single MPLS tunnel. Thus it is never necessary to maintain
state in the network core for individual pseudowires. We do not
presuppose that the MPLS tunnels are point to point; although the
pseudowires are point to point, the MPLS tunnels may be multipoint to
point. We do not presuppose that PE2 will even be able to determine
the MPLS tunnel through which a received packet was transmitted.
(E.g., if the MPLS tunnel is an LSP, and penultimate hop popping is
used, when the packet arrives at PE2 it will contain no information
identifying the tunnel.)
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When PE2 receives a packet over a pseudowire, it must be able to
determine that the packet was in fact received over a pseudowire, and
it must be able to associate that packet with a particular
pseudowire. PE2 is able to do this by examining the MPLS label which
serves as the pseudowire demultiplexor field shown in Figure 2. Call
this label the "PW label".
When PE1 sends a layer 2 PDU to PE2, it creates a MPLS packet by
adding the PW label to the packet, thus creating the first entry of
the label stack. If the PSN tunnel is an MPLS LSP the PE1 pushes
another label (the tunnel label) on to the packet as the second entry
of the label stack. The PW label is not visible again until the MPLS
packet reaches PE2. PE2's disposition of the packet is based on the
PW label.
If the payload of the MPLS packet is, for example, an ATM AAL5 PDU,
the PW label will generally correspond to a particular ATM VC at PE2.
That is, PE2 needs to be able to infer from the PW label the outgoing
interface and the VPI/VCI value for the AAL5 PDU. If the payload is a
Frame Relay PDU, then PE2 needs to be able to infer from the PW label
the outgoing interface and the DLCI value. If the payload is an
Ethernet frame, then PE2 needs to be able to infer from the PW label
the outgoing interface, and perhaps the VLAN identifier. This process
is uni-directional, and will be repeated independently for bi-
directional operation. It is REQUIRED to assign the same PW ID, and
PW type for a given circuit in both directions. The group ID (see
below) MUST NOT be required to match in both directions. The
transported frame MAY be modified when it reaches the egress router.
If the header of the transported layer 2 frame is modified, this MUST
be done at the egress LSR only. Note that the PW label must always
be at the bottom of the packet's label stack and labels MUST be
allocated from the per-platform label space.
This document does not specify a method for distributing the MPLS
tunnel label or any other labels that may appear above the PW label
on the stack. Any acceptable method of MPLS label distribution will
do. This document specifies a protocol for assigning and distributing
the PW label. This protocol is LDP, extended as specified in the
remainder of this document. An LDP session must be set up between the
pseudowire endpoints. LDP MUST be used in its "downstream
unsolicited" mode. LDP's "liberal label retention" mode SHOULD be
used.
In addition to the protocol specified herein, static assignment of PW
labels may be used, and implementations of this protocol SHOULD
provide support for static assignment.
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This document specifies all the procedures necessary to set up and
maintain the pseudowires needed to support "unswitched" point to
point services, where each endpoint of the pseudowire is provisioned
with the identify of the other endpoint. There are also protocol
mechanisms specified herein which can be used to support switched
services, and which can be used to support other provisioning models.
However, the use of the protocol mechanisms to support those other
models and services is not described in this document.
4. Details Specific to Particular Emulated Services
4.1. IP Layer2 Transport
This mode carries IP packets over a Pseudo-Wire. The encapsulation
used is according to [RFC3032]. The PW control word MAY be inserted
between the MPLS label stack and the IP payload. The encapsulation of
the IP packets for forwarding on the attachment circuit is
implementation specific, part of the NSP function [RFC3985], and is
outside the scope of this document.
5. LDP
The PW label bindings are distributed using the LDP downstream
unsolicited mode described in [LDP]. The PEs will establish an LDP
session using the Extended Discovery mechanism described in [LDP,
section 2.4.2 and 2.5].
An LDP Label Mapping message contains a FEC TLV, a Label TLV, and
zero or more optional parameter TLVs.
The FEC TLV is used to indicate the meaning of the label. In the
current context, the FEC TLV would be used to identify the particular
pseudowire that a particular label is bound to. In this
specification, we define two new FEC TLVs to be used for identifying
pseudowires. When setting up a particular pseudowire, only one of
these FEC TLVs is used. The one to be used will depend on the
particular service being emulated and on the particular provisioning
model being supported.
LDP allows each FEC TLV to consist of a set of FEC elements. For
setting up and maintaining pseudowires, however, each FEC TLV MUST
contain exactly one FEC element.
The LDP base specification has several kinds of label TLVs, including
the Generic Label TLV as specified in [LDP] section 3.4.2.1. For
setting up and maintaining pseudowires, the Generic Label TLV MUST be
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used.
5.1. LDP Extensions
This draft specifies no new LDP messages.
This draft specifies the following new TLVs to be used with LDP:
TLV Specified in Section Defined for Message
PW Status TLV 5.4.2 Notification
PW Interface Parameters TLV 5.3.2.1 FEC
PW Grouping ID TLV 5.3.2.2 FEC
Additionally the following new FEC element type are defined:
FEC element Type Specified in Section Defined for Message
0x80 5.2 FEC
0x81 5.3 FEC
The following new LDP error codes are also defined:
Status Code Specified in Section
"Illegal C-Bit" 6.1
"Wrong C-Bit" 6.2
"Incompatible bit-rate" [CEP]
"CEP/TDM mis-configuration" [CEP]
"PW status" 5.4.2
"Unassigned/Unrecognized TAI" 5.3.3
"Generic Misconfiguration Error" [SaTOP]
"Label Withdraw PW Status Method Not Supported" 5.4.1
5.2. The PWid FEC Element
The PWid FEC element may be used whenever both pseudowire endpoints
have been provisioned with the same 32-bit identifier for the
pseudowire.
For this purpose a new type of FEC element is defined. The FEC
element type is 0x80 [note1], and is defined as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PWid (0x80) |C| PW type |PW info Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Parameter Sub-TLV |
| " |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- PW type
A 15 bit quantity containing a value which represents the type of
PW. Assigned Values are specified in "IANA Allocations for pseudo
Wire Edge to Edge Emulation (PWE3)" [IANA].
- Control word bit (C)
The bit (C) is used to flag the presence of a control word as
follows:
C = 1 control word present on this PW.
C = 0 no control word present on this PW.
Please see the section "C-Bit Handling Procedures" for further
explanation.
- PW information length
Length of the PW ID field and the interface parameters sub-TLV in
octets. If this value is 0, then it references all PWs using the
specified group ID and there is no PW ID present, nor any
interface parameter sub-TLVs.
- Group ID
An arbitrary 32 bit value which represents a group of PWs that is
used to create groups in the PW space. The group ID is intended
to be used as a port index, or a virtual tunnel index. To
simplify configuration a particular PW ID at ingress could be
part of the virtual tunnel for transport to the egress router.
The Group ID is very useful to send wild card label withdrawals,
or PW wild card status notification messages to remote PEs upon
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physical port failure.
- PW ID
A non-zero 32-bit connection ID that together with the PW type,
identifies a particular PW. Note that the PW ID and the PW type
MUST be the same at both endpoints.
- Interface Parameter Sub-TLV
This variable length TLV is used to provide interface specific
parameters, such as attachment circuit MTU.
Note that as the "interface parameter sub-TLV" are part of the
FEC, the rules of LDP make it impossible to change the interface
parameters once the pseudowire has been set up. Thus the
interface parameters field must not be used to pass information,
such as status information, which may change during the life of
the pseudowire. Optional parameter TLVs should be used for that
purpose.
Using the PWid FEC, each of the two pseudowire endpoints
independently initiates the set up of a unidirectional LSP. An
outgoing LSP and an incoming LSP are bound together into a single
pseudowire if they have the same PW ID and PW type.
5.3. The Generalized PWid FEC Element
The PWid FEC element can be used if a unique 32-bit value has been
assigned to the PW, and if each endpoint has been provisioned with
that value. The Generalized PWid FEC element requires that the PW
endpoints be uniquely identified; the PW itself is identified as a
pair of endpoints. In addition the endpoint identifiers are
structured to support applications where the identity of the remote
endpoints needs to be auto-discovered rather than statically
configured.
The "Generalized PWid FEC Element" is FEC type 0x81 (provisionally,
subject to assignment by IANA).
The Generalized PWid FEC Element does not contain anything
corresponding to the "Group ID" of the PWid FEC element. The
functionality of the "Group ID" is provided by a separate optional
LDP TLV, the "PW Grouping TLV", described below. The Interface
Parameters field of the PWid FEC element is also absent; its
functionality is replaced by the optional Interface Parameters TLV,
described below.
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5.3.1. Attachment Identifiers
As discussed in [RFC3985], a pseudowire can be thought of as
connecting two "forwarders". The protocol used to setup a pseudowire
must allow the forwarder at one end of a pseudowire to identify the
forwarder at the other end. We use the term "attachment identifier",
or "AI", to refer to the field which the protocol uses to identify
the forwarders. In the PWid FEC, the PWid field serves as the AI.
In this section we specify a more general form of AI which is
structured and of variable length.
Every Forwarder in a PE must be associated with an Attachment
Identifier (AI), either through configuration or through some
algorithm. The Attachment Identifier must be unique in the context of
the PE router in which the Forwarder resides. The combination <PE
router IP address, AI> must be globally unique.
It is frequently convenient to regard a set of Forwarders as being
members of a particular "group", where PWs may only be set up among
members of a group. In such cases, it is convenient to identify the
Forwarders relative to the group, so that an Attachment Identifier
would consist of an Attachment Group Identifier (AGI) plus an
Attachment Individual Identifier (AII).
An Attachment Group Identifier may be thought of as a VPN-id, or a
VLAN identifier, some attribute which is shared by all the Attachment
PWs (or pools thereof) which are allowed to be connected.
The details of how to construct the AGI and AII fields identifying
the pseudowire endpoints are outside the scope of this specification.
Different pseudowire application, and different provisioning models,
will require different sorts of AGI and AII fields. The
specification of each such application and/or model must include the
rules for constructing the AGI and AII fields.
As previously discussed, a (bidirectional) pseudowire consists of a
pair of unidirectional LSPs, one in each direction. If a particular
pseudowire connects PE1 with PE2, the PW direction from PE1 to PE2
can be identified as:
<PE1, <AGI, AII1>, PE2, <AGI, AII2>>,
and the PW direction from PE2 to PE1 can be identified by:
<PE2, <AGI, AII2>, PE1, <AGI, AII1>>.
Note that the AGI must be the same at both endpoints, but the AII
will in general be different at each endpoint. Thus from the
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perspective of a particular PE, each pseudowire has a local or
"Source AII", and a remote or "Target AII". The pseudowire setup
protocol can carry all three of these quantities:
- Attachment Group Identifier (AGI).
- Source Attachment Individual Identifier (SAII)
- Target Attachment Individual Identifier (TAII)
If the AGI is non-null, then the Source AI (SAI) consists of the AGI
together with the SAII, and the Target AI (TAI) consists of the TAII
together with the AGI. If the AGI is null, then the SAII and TAII
are the SAI and TAI respectively.
The interpretation of the SAI and TAI is a local matter at the
respective endpoint.
The association of two unidirectional LSPs into a single
bidirectional pseudowire depends on the SAI and the TAI. Each
application and/or provisioning model which uses the Generalized ID
FEC element must specify the rules for performing this association.
5.3.2. Encoding the Generalized ID FEC Element
FEC element type 0x81 [note1] is used. The FEC element is encoded
as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Gen PWid (0x81)|C| PW Type |PW info Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AGI Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ AGI Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type | Length | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAII Value (contd.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This document does not specify the AII, and AGI type field values;
specification of the type field values to use for a particular
application is part of the specification of that application. IANA
will assign these values using the method defined in the [IANA]
document.
The SAII, TAII, and AGI are simply carried as octet strings. The
length byte specifies the size of the Value field. The null string
can be sent by setting the length byte to 0. If a particular
application does not need all three of these sub-elements, it MUST
send all the sub-elements, but set the length to 0 for the unused
sub-elements.
The PW information length field, contains the length of the SAII,
TAII and, AGI combined 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.
Note that the interpretation of a particular field as AGI, SAII, or
TAII depends on the order of its occurrence. The type field
identifies the type of the AGI, SAII, or TAII. When comparing two
occurrences of an AGI (or SAII or TAII), the two occurrences are
considered to be identical if the type, length, and value fields of
one are identical, respectively, to those of the other.
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5.3.2.1. Interface Parameters TLV
This TLV MUST only be used when sending the Generalized PW FEC. It
specifies interface specific parameters. Specific parameters, when
applicable, MUST be used to validate that the PEs, and the ingress
and egress ports at the edges of the circuit, have the necessary
capabilities to interoperate with each other.
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| PW Intf P. TLV (0x096B) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLV Type | Length | Variable Length Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length Value |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[ note: TLV type 0x096B pending IANA allocation ]
A more detailed description of this field can be found in the section
"Interface Parameters Sub-TLV" below.
5.3.2.2. PW Grouping TLV
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|PW Grouping ID TLV (0x096C)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[ note: TLV type 0x096C pending IANA allocation ]
The PW Grouping ID is an arbitrary 32 bit value which represents an
arbitrary group of PWs. It is used create groups PWs; for example, a
PW Grouping ID can be used as a port index, and assigned to all PWs
that lead to that port. Use of the PW Grouping ID enables one to
send "wild card" label withdrawals, or "wild card" status
notification messages to remote PEs upon physical port failure.
Note Well: The PW Grouping ID is different than, and has no relation
to, the Attachment Group Identifier.
The PW Grouping ID TLV is not part of the FEC, and will not be
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advertised except in the PW FEC advertisement. The advertising PE MAY
use the wild card withdraw semantics, but the remote PEs MUST
implement support for wildcard messages. This TLV MUST only be used
when sending the Generalized PW ID FEC.
To issue a wildcard command (status or withdraw):
- Set the PW Info Length to 0 in the Generalized ID FEC Element.
- Send only the PW Grouping ID TLV with the FEC (No AGI/SAII/TAII
is sent).
5.3.3. Signaling Procedures
In order for PE1 to begin signaling PE2, PE1 must know the address of
the remote PE2, and a TAI. This information may have been configured
at PE1, or it may have been learned dynamically via some
autodiscovery procedure.
The egress PE (PE1), that has knowledge of the ingress PE, initiates
the setup by sending a Label Mapping Message to the ingress PE (PE2).
The Label Mapping message contains the FEC TLV, carrying the
Generalized PWid FEC Element (type 0x81). The Generalized PWid FEC
element contains the AGI, SAII and TAII information.
Next when PE2 receives such a Label Mapping message, PE2 interprets
the message as a request to set up a PW whose endpoint (at PE2) is
the Forwarder identified by the TAI. From the perspective of the
signaling protocol, exactly how PE2 maps AIs to Forwarders is a local
matter. In some Virtual Private Wire Services (VPWS) provisioning
models, the TAI might, e.g., be a string which identifies a
particular Attachment Circuit, such as "ATM3VPI4VCI5", or it might,
e.g., be a string such as "Fred" which is associated by configuration
with a particular Attachment Circuit. In VPLS, the AGI could be a
VPN-id, identifying a particular VPLS instance.
If PE2 cannot map the TAI to one of its Forwarders, then PE2 sends a
Label Release message to PE1, with a Status Code of
"Unassigned/Unrecognized TAI" , and the processing of the Label
Mapping message is complete.
[ note: Status Code 0x00000029 "Unassigned/Unrecognized TAI" as
defined in [IANA] pending IANA allocation ]
The FEC TLV sent in a Label Release message is the same as the FEC
TLV received in the Label Mapping being released (but without the
interface parameter TLV). More generally, the FEC TLV is the same in
all LDP messages relating to the same PW. In a Label Release this
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means that the SAII is the remote peer's AII and the TAII is the
sender's local AII.
If the Label Mapping Message has a valid TAI, PE2 must decide whether
to accept it or not. The procedures for so deciding will depend on
the particular type of Forwarder identified by the TAI. Of course,
the Label Mapping message may be rejected due to standard LDP error
conditions as detailed in [LDP].
If PE2 decides to accept the Label Mapping message, then it has to
make sure that an PW LSP is set up in the opposite (PE1-->PE2)
direction. If it has already signaled for the corresponding PW LSP
in that direction, nothing more need be done. Otherwise, it must
initiate such signaling by sending a Label Mapping message to PE1.
This is very similar to the Label Mapping message PE2 received, but
with the SAI and TAI reversed.
Thus a bidirectional PW consists of two LSPs, where the FEC of one
has the SAII and TAII reversed wiht respect of the FEC of the other.
5.4. Signaling of Pseudo Wire Status
5.4.1. Use of Label Mappings Messages.
The PEs MUST send Label Mapping Messages to their peers as soon as
the PW is configured and administratively enabled, regardless of the
attachment circuit state. The PW label should not be withdrawn unless
the operator administratively configures the pseudo wire down (or the
PW configuration is deleted entirely). Using the procedures outlined
in this section a simple label withdraw method MAY also be supported
as a legacy means of signaling PW status and AC status. In any case
if the label-to-PW binding is not available the PW MUST be considered
in the down state.
Once, the PW status negotiation procedures are completed and if they
result in the use of the label withdraw method for PW status
communication, and this method is not supported by one of the PEs,
than that PE must send a Label Release Message to its peer with the
following error:
"Label Withdraw PW Status Method Not Supported"
If the label withdraw method for PW status communication is selected
for the PW, it will result in the Label Mapping Message being
advertised only if the attachment circuit is active. The PW status
signaling procedures described in this section MUST be fully
implemented.
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5.4.2. Signaling PW status.
The PE devices use an LDP TLV to indicate status to their remote
peers. This PW Status TLV contains more information than the
alternative simple Label Withdraw message.
The format of the PW Status TLV is:
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 Status (0x096A) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[ note: TLV type 0x096A pending IANA allocation ]
Where the status code is a 4 octet bit field is specified in the PW
IANA Allocations document [IANA]. The length specifies the length of
the Status Code field in octets (equal to 4).
Each bit in the status code field can be set individually to indicate
more then a single failure at once. Each fault can be cleared by
sending an appropriate Notification message with the respective bit
cleared. The presence of the lowest bit (PW Not Forwarding) acts only
as a generic failure indication when there is a link-down event for
which none of the other bits apply.
The Status TLV is transported to the remote PW peer via the LDP
Notification message. The general format of the Notification Message
is:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (TLV) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PW Status TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PWId FEC TLV or Generalized ID FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Status TLV status code is set to 0x00000028 "PW status", to
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indicate that PW status follows. Since this notification does not
refer to any particular message the Message Id, and Message Type
fields are set to 0. [ note: Status Code 0x00000028 as defined in
[IANA] pending IANA allocation ]
The PW FEC TLV SHOULD not include the interface parameter sub-TLVs as
they are ignored in the context of this message. When a PE's
attachment circuit encounters an error, use of the PW Notification
Message allows the PE to send a single "wild card" status message,
using a PW FEC TLV with only the group ID set, to denote this change
in status for all affected PW connections. This status message
contains either the PW FEC TLV with only the group ID set, or else it
contains the Generalized FEC TLV with only the PW Grouping ID TLV.
As mentioned above the Group ID field of the PWid FEC element, or the
PW Grouping ID TLV used with the Generalized ID FEC element, can be
used to send a status notification for all arbitrary sets of PWs.
This procedure is OPTIONAL, and if it is implemented the LDP
Notification message should be as follows: If the PWid FEC element is
used, the PW information length field is set to 0, the PW ID field is
not present, and the interface parameter sub-TLVs are not present. If
the Generalized FEC element is used, the AGI, SAII, and TAII are not
present,the PW information length field is set to 0, the PW Grouping
ID TLV is included, and the Interface Parameters TLV is omitted. For
the purpose of this document this is called the "wild card PW status
notification procedure", and all PEs implementing this design are
REQUIRED to accept such a notification message, but are not required
to send it.
5.4.3. Pseudowire Status Negotiation Procedures
When a PW is first set up the PEs MUST attempt to negotiate the usage
of the PW status TLV. This is accomplished as follows: A PE that
supports the PW Status TLV MUST include it the initial Label Mapping
message following the PW FEC, and the interface parameter sub-TLVs.
The PW Status TLV will then be used for the lifetime of the
Pseudowire. This is shown in the following diagram:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ PWId FEC or Generalized ID FEC +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Parameters |
| " |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Generic Label (0x0200) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| PW Status (0x0???) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If a PW Status TLV is included in the initial Label Mapping message
for a PW then if the Label Mapping message from the remote PE for
that PW does not include a PW status TLV or if the remote PE does not
support the PW Status TLV the PW will revert to the label withdraw
method of signaling PW status. Note that if the PW Status TLV is not
supported by the remote peer the peer will automatically ignore it
since the I(ignore) bit is set in the TLV. The PW Status TLV,
therefore, will not be present in the corresponding FEC advertisement
from the remote LDP peer resulting in exactly the above behavior.
If the PW Status TLV is not present following the FEC TLV in the
initial PW Label Mapping message received by a PE, then the PW Status
TLV will not be used and both PEs supporting the pseudowire will
revert to the label withdraw procedure for signaling status changes.
If the negotiation process results in the usage of the PW status TLV,
then the actual PW status is determined by the PW status TLV that was
sent within the initial PW Label Mapping message. Subsequent updates
of PW status are conveyed through the notification message
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5.5. Interface Parameters sub-TLV
This field specifies interface specific parameters. When applicable,
it MUST be used to validate that the PEs, and the ingress and egress
ports at the edges of the circuit, have the necessary capabilities to
interoperate with each other. The field structure is defined 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLV Type | Length | Variable Length Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Length Value |
| " |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The interface paramater sub-TLV type values are specified in "IANA
Allocations for pseudo Wire Edge to Edge Emulation (PWE3)" [IANA].
The Length field is defined as the length of the interface parameter
including the parameter id and length field itself. Processing of the
interface parameters should continue when encountering unknown
interface parameters and they MUST be silently ignored.
- Interface MTU sub-TLV type
A 2 octet value indicating the MTU in octets. This is the Maximum
Transmission Unit, excluding encapsulation overhead, of the
egress packet interface that will be transmitting the
decapsulated PDU that is received from the MPLS enabled network.
This parameter is applicable only to PWs transporting packets and
is REQUIRED for these PW types. If this parameter does not match
in both directions of a specific PW, that PW MUST NOT be enabled.
- Optional Interface Description string sub-TLV type
This arbitrary, OPTIONAL, interface description string is used to
send a human-readable administrative string describing the
interface to the remote. This parameter is OPTIONAL, and is
applicable to all PW types. The interface description parameter
string length is variable, and can be from 0 to 80 octets.
Human-readable text MUST be provided in the UTF-8 charset using
the Default Language [RFC2277].
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6. Control Word
6.1. PW types for which the control word is REQUIRED
The Label Mapping messages which are sent in order to set up these
PWs MUST have c=1. When a Label Mapping message for a PW of one of
these types is received, and c=0, a Label Release message MUST be
sent, with an "Illegal C-bit" status code. In this case, the PW will
not be enabled.
6.2. PW types for which the control word is NOT mandatory
If a system is capable of sending and receiving the control word on
PW types for which the control word is not mandatory, then each such
PW endpoint MUST be configurable with a parameter that specifies
whether the use of the control word is PREFERRED or NOT PREFERRED.
For each PW, there MUST be a default value of this parameter. This
specification does NOT state what the default value should be.
If a system is NOT capable of sending and receiving the control word
on PW types for which the control word is not mandatory, then it
behaves exactly as if it were configured for the use of the control
word to be NOT PREFERRED.
If a Label Mapping message for the PW has already been received, but
no Label Mapping message for the PW has yet been sent, then the
procedure is the following:
-i. If the received Label Mapping message has c=0, send a Label
Mapping message with c=0, and the control word is not used.
-ii. If the received Label Mapping message has c=1, and the PW is
locally configured such that the use of the control word is
preferred, then send a Label Mapping message with c=1, and
the control word is used.
-iii. If the received Label Mapping message has c=1, and the PW is
locally configured such that the use of the control word is
not preferred or the control word is not supported, then act
as if no Label Mapping message for the PW had been received
(i.e., proceed to the next paragraph).
If a Label Mapping message for the PW has not already been received
(or if the received Label Mapping message had c=1 and either local
configuration says that the use of the control word is not preferred
or the control word is not supported), then send a Label Mapping
message in which the c bit is set to correspond to the locally
configured preference for use of the control word. (I.e., set c=1 if
locally configured to prefer the control word, set c=0 if locally
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configured to prefer not to use the control word or if the control
word is not supported).
The next action depends on what control message is next received for
that PW. The possibilities are:
-i. A Label Mapping message with the same c bit value as
specified in the Label Mapping message that was sent. PW
setup is now complete, and the control word is used if c=1
but not used if c=0.
-ii. A Label Mapping message with c=1, but the Label Mapping
message that was sent has c=0. In this case, ignore the
received Label Mapping message, and continue to wait for the
next control message for the PW.
-iii. A Label Mapping message with c=0, but the Label Mapping
message that was sent has c=1. In this case, send a Label
Withdraw message with a "Wrong C-bit" status code, followed
by a Label Mapping message that has c=0. PW setup is now
complete, and the control word is not used.
-iv. A Label Withdraw message with the "Wrong c-bit" status code.
Treat as a normal Label Withdraw, but do not respond.
Continue to wait for the next control message for the PW.
If at any time after a Label Mapping message has been received, a
corresponding Label Withdraw or Release is received, the action taken
is the same as for any Label Withdraw or Release that might be
received at any time.
If both endpoints prefer the use of the control word, this procedure
will cause it to be used. If either endpoint prefers not to use the
control word, or does not support the control word, this procedure
will cause it not to be used. If one endpoint prefers to use the
control word but the other does not, the one that prefers not to use
it is has no extra protocol to execute, it just waits for a Label
Mapping message that has c=0.
The diagram in Appendix A illustrates the above procedure.
6.3. LDP label Withdrawal procedures
As mentioned above, the Group ID field of the PWid FEC element, or
the PW Grouping ID TLV used with the Generalized ID FEC element, can
be used to withdraw all PW labels associated with a particular PW
group. This procedure is OPTIONAL, and if it is implemented the LDP
Label Withdraw message should be as follows: If the PWid FEC element
is used, the PW information length field is set to 0, the PW ID field
is not present, and the interface parameter sub-TLVs are not present.
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If the Generalized FEC element is used, the AGI, SAII, and TAII are
not present,the PW information length field is set to 0, the PW
Grouping ID TLV is included, and the Interface Parameters TLV is
omitted. For the purpose of this document this is called the "wild
card withdraw procedure", and all PEs implementing this design are
REQUIRED to accept such withdrawn message, but are not required to
send it. Note that the PW Grouping ID TLV only applies to PW using
the Generalized ID FEC element, while the Group ID only applies to
PWid FEC element.
The interface parameter sub-TLVs, or TLV, MUST NOT be present in any
LDP PW Label Withdraw or Label Release message. A wildcard Label
Release message MUST include only the group ID, or Grouping ID TLV. A
Label Release message initiated a PE router must always include the
PW ID.
6.4. Sequencing Considerations
In the case where the router considers the sequence number field in
the control word, it is important to note the following when
advertising labels
6.4.1. Label Advertisements
After a label has been withdrawn by the output router and/or released
by the input router, care must be taken to not advertise (re-use) the
same released label until the output router can be reasonably certain
that old packets containing the released label no longer persist in
the MPLS enabled network.
This precaution is required to prevent the imposition router from
restarting packet forwarding with sequence number of 1 when it
receives a Label Mapping message that binds the same FEC to the same
label if there are still older packets persisting in the network with
sequence number between 1 and 32768. For example, if there is a
packet with sequence number=n where n is in the interval[1,32768]
traveling through the network, it would be possible for the
disposition router to receive that packet after it re-advertises the
label. Since the label has been released by the imposition router,
the disposition router SHOULD be expecting the next packet to arrive
with sequence number to be 1. Receipt of a packet with sequence
number equal to n will result in n packets potentially being rejected
by the disposition router until the imposition router imposes a
sequence number of n+1 into a packet. Possible methods to avoid this
is for the disposition router to always advertise a different PW
label, or for the disposition router to wait for a sufficient time
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before attempting to re-advertised a recently released label. This is
only an issue when sequence number processing at the disposition
router is enabled.
6.4.2. Label Release
In situations where the imposition router wants to restart forwarding
of packets with sequence number 1, the router shall 1) Send to
disposition router a Label Release Message, and 2) Send to
disposition router a Label Request message. When sequencing is
supported, advertisement of a PW label in response to a Label Request
message MUST also consider the issues discussed in the section on
Label Advertisements.
7. IANA Considerations
7.1. LDP TLV TYPE
This document uses several new LDP TLV types, IANA already maintains
a registry of name "TLV TYPE NAME SPACE" defined by RFC3036. The
following values are suggested for assignment:
TLV type Description
0x096A PW Status TLV
0x096B PW Interface Parameters TLV
0x096C Group ID TLV
7.2. LDP Status Codes
This document uses several new LDP status codes, IANA already
maintains a registry of name "STATUS CODE NAME SPACE" defined by
RFC3036. The following values are suggested for assignment:
0x00000024 "Illegal C-Bit"
0x00000025 "Wrong C-Bit"
0x00000026 "Incompatible bit-rate"
0x00000027 "CEP/TDM mis-configuration"
0x00000028 "PW status"
0x00000029 "Unassigned/Unrecognized TAI"
0x0000002A "Generic Misconfiguration Error"
0x0000002B "Label Withdraw PW Status Method Not Supported"
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7.3. FEC Type Name Space
This document uses two new FEC element types, 0x80 and 0x81 from the
registry "FEC Type Name Space" for the Label Distribution Protocol
(LDP RFC3036).
8. Security Considerations
This document specifies the LDP 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 in MPLS
and transmitted from one end of a Pseudowire to the other. Therefore
we treat the security considerations for both the data plane and the
control plane.
8.1. Data-plane Security
With regard to the security of the data plane, the following areas
must be considered:
- MPLS PDU inspection.
- MPLS PDU spoofing.
- MPLS PDU alteration.
- MPLS PSN protocol security.
- Access Circuit security.
- Denial of service prevention on the PE routers.
When a MPLS PSN is used to provide pseudowire service, there is a
perception that security MUST be at least equal to the currently
deployed layer2 native protocol networks that the MPLS/PW network
combination is emulating. This means that the MPLS enabled network
SHOULD be isolated from outside packet insertion in such a way that
it SHOULD not be possible to directly insert an MPLS packet into the
network. To prevent unwanted packet insertion, it is also important
to prevent unauthorized physical access to the PSN as well as
unauthorized administrative access to individual network elements.
As mentioned above, as MPLS enabled network, should not accept MPLS
packets from its external interfaces (i.e. interfaces to CE devices
or to other providers' networks) unless the top label of the packet
was legitimately distributed to the system from which the packet is
being received. If the packet's incoming interface leads to a
different SP (rather than to a customer), an appropriate trust
relationship must also be present, including the trust that the other
SP also provides appropriate security measures.
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The three main security problems faced when using an MPLS enabled
network to transport PWs are spoofing, alteration, and inspection.
First there is a possibility that the PE receiving PW PDUs will get a
PDU which appears to be from the PE transmitting the PW into the PSN,
but which was not actually transmitted by the PE originating the PW.
(I.e., the specified encapsulations do not by themselves enable the
decapsulator to authenticate the encapsulator.) A second problem is
the possibility that the PW PDU will be altered between the time it
enters PSN and the time it leaves the PSN. (I.e., the specified
encapsulations do not by themselves assure the decapsulator of the
packet's integrity.) A third problem is the possibility that the
PDU's contents will be seen while the PDU is in transit through the
PSN. (I.e., the specification encapsulations do not ensure privacy.)
How significant these issues are in practice depends on the security
requirements of the applications whose traffic is being sent through
the tunnel, and how secure is the PSN itself.
8.2. Control Protocol Security
General security considerations with regard to the use of LDP are
specified in section 5 of RFC 3036. Those considerations apply as
well to the case where LDP is used to set up Pseudowires.
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 LDP
session request MUST NOT be accepted unless its IP source address is
known to be the source of an "eligible" LDP peer. The set of
eligible peers could 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. (Obviously if the auto-discovery protocol were not trusted,
the set of "eligible peers" it produces could not be trusted.)
Even if an LDP 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.
The LDP MD5 authentication key option, as described in section 2.9 of
RFC 3036, MUST be implemented, and for a greater degree of security
it must be used. This provides integrity and authentication for the
LDP messages, and eliminates the possibility of source address
spoofing. Use of the MD5 option does not provide privacy, but privacy
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of the LDP control messages is not usually considered to be
important. As the MD5 option relies on the configuration of pre-
shared keys, it does not provide much protection against replay
attacks. In addition, its reliance on pre-shared keys may make it
very 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 LDP peer may be one of the eligible LDP 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.
9. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
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10. Full Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
11. Acknowledgments
The authors wish to acknowledge the contributions of Vach Kompella,
Vanson Lim, Wei Luo, Himanshu Shah, and Nick Weeds.
12. Normative References
[LDP] "LDP Specification." L. Andersson, P. Doolan, N. Feldman, A.
Fredette, B. Thomas. January 2001. RFC3036
[RFC3032] "MPLS Label Stack Encoding", E. Rosen, Y. Rekhter,
D. Tappan, G. Fedorkow, D. Farinacci, T. Li, A. Conta. RFC3032
[IANA] "IANA Allocations for pseudo Wire Edge to Edge Emulation
(PWE3)" Martini,Townsley, draft-ietf-pwe3-iana-allocation-08.txt
(work in progress), April 2004
13. Informative References
[CEP] "SONET/SDH Circuit Emulation Service Over Packet (CEP)",
draft-ietf-pwe3-sonet-11.txt (work in progress)
[SAToP] "Structure-Agnostic TDM over Packet (SAToP)",
draft-ietf-pwe3-satop-01.txt (work in progress)
[FRAME] "Frame Relay over Pseudo-Wires",
draft-ietf-pwe3-frame-relay-02.txt (work in progress )
[ATM] "Encapsulation Methods for Transport of ATM Cells/Frame Over IP
and MPLS Networks", draft-ietf-pwe3-atm-encap-05.txt (work in
progress)
Martini, et al. [Page 29]
Internet Draft draft-ietf-pwe3-control-protocol-17.txt June 2005
[PPPHDLC] "Encapsulation Methods for Transport of PPP/HDLC Frames
Over IP and MPLS Networks",
draft-ietf-pwe3-hdlc-ppp-encap-05.txt (work in progress)
[ETH] "Encapsulation Methods for Transport of Ethernet Frames Over
IP/MPLS Networks", draft-ietf-pwe3-ethernet-encap-06.txt.
(work in progress)
[802.3] "IEEE 802.3ac-1998" IEEE standard specification.
[SDH] American National Standards Institute, "Synchronous Optical
Network Formats," ANSI T1.105-1995.
[ITUG] ITU Recommendation G.707, "Network Node Interface For The
Synchronous Digital Hierarchy", 1996.
[RFC3985] "PWE3 Architecture" Bryant, et al., RFC3985.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations section in RFCs", BCP 26, RFC 2434, October
1998.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[note1] FEC element type 0x80,0x81 is pending IANA approval.
14. Author Information
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
e-mail: lmartini@cisco.com
Nasser El-Aawar
Level 3 Communications, LLC.
1025 Eldorado Blvd.
Broomfield, CO, 80021
e-mail: nna@level3.net
Martini, et al. [Page 30]
Internet Draft draft-ietf-pwe3-control-protocol-17.txt June 2005
Giles Heron
Tellabs
Abbey Place
24-28 Easton Street
High Wycombe
Bucks
HP11 1NT
UK
e-mail: giles.heron@tellabs.com
Eric C. Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
e-mail: erosen@cisco.com
Dan Tappan
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
e-mail: tappan@cisco.com
Toby Smith
Omega Corporate Center
1300 Omega Drive
Pittsburgh, PA 15205
Laurel Networks, Inc.
e-mail: tob@laurelnetworks.com
15. Additional Contributing Authors
Dimitri Stratton Vlachos
Mazu Networks, Inc.
125 Cambridgepark Drive
Cambridge, MA 02140
e-mail: d@mazunetworks.com
Martini, et al. [Page 31]
Internet Draft draft-ietf-pwe3-control-protocol-17.txt June 2005
Jayakumar Jayakumar,
Cisco Systems Inc.
225, E.Tasman, MS-SJ3/3,
San Jose, CA, 95134
e-mail: jjayakum@cisco.com
Alex Hamilton,
Cisco Systems Inc.
285 W. Tasman, MS-SJCI/3/4,
San Jose, CA, 95134
e-mail: tahamilt@cisco.com
Steve Vogelsang
Laurel Networks, Inc.
Omega Corporate Center
1300 Omega Drive
Pittsburgh, PA 15205
e-mail: sjv@laurelnetworks.com
John Shirron
Omega Corporate Center
1300 Omega Drive
Pittsburgh, PA 15205
Laurel Networks, Inc.
e-mail: jshirron@laurelnetworks.com
Andrew G. Malis
Tellabs
90 Rio Robles Dr.
San Jose, CA 95134
e-mail: Andy.Malis@tellabs.com
Vinai Sirkay
Reliance Infocomm
Dhirubai Ambani Knowledge City
Navi Mumbai 400 709
e-mail: vinai@sirkay.com
Martini, et al. [Page 32]
Internet Draft draft-ietf-pwe3-control-protocol-17.txt June 2005
Vasile Radoaca
Nortel Networks
600 Technology Park
Billerica MA 01821
e-mail: vasile@nortelnetworks.com
Chris Liljenstolpe
Cable & Wireless
11700 Plaza America Drive
Reston, VA 20190
e-mail: chris@cw.net
Dave Cooper
Global Crossing
960 Hamlin Court
Sunnyvale, CA 94089
e-mail: dcooper@gblx.net
Kireeti Kompella
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
e-mail: kireeti@juniper.net
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Internet Draft draft-ietf-pwe3-control-protocol-17.txt June 2005
Ap A C-bit Handling Procedures Diagram
------------------
Y | Received Label | N
-------| Mapping Msg? |--------------
| ------------------ |
-------------- |
| | |
------- ------- |
| C=0 | | C=1 | |
------- ------- |
| | |
| ---------------- |
| | Control Word | N |
| | Capable? |----------- |
| ---------------- | |
| Y | | |
| | | |
| ---------------- | |
| | Control Word | N | |
| | Preferred? |---- | |
| ---------------- | | |
| Y | | | |
| | | | ----------------
| | | | | Control Word |
| | | | | Preferred? |
| | | | ----------------
| | | | N | Y |
| | | | | |
Send Send Send Send Send Send
C=0 C=1 C=0 C=0 C=0 C=1
| | | |
----------------------------------
| If receive the same as sent, |
| PW setup is complete. If not: |
----------------------------------
| | | |
------------------- -----------
| Receive | | Receive |
| C=1 | | C=0 |
------------------- -----------
| |
Wait for the Send
next message Wrong C-Bit
|
Send Label
Mapping Message
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Martini, et al. [Page 35]
