wdiff rfc7965.alt-original rfc7965.txt

Network Working Group
Internet Engineering Task Force (IETF) M. Chen
Internet-Draft
Request for Comments: 7965 W. Cao
Intended status:
Category: Standards Track Huawei
Expires: January 22, 2017
ISSN: 2070-1721 A. Takacs
Ericsson
P. Pan
July 21,
August 2016

LDP Extensions for Pseudowire
Binding to LSP Label Switched Path (LSP) Tunnels
draft-ietf-pals-mpls-tp-pw-over-bidir-lsp-09.txt

Abstract

Many transport services require that user traffic, in the form of
Pseudowires (PW), (PWs), be delivered via either a single co-routed
bidirectional tunnel or two unidirectional tunnels that share the
same routes. This document defines an optional extension to the
Label Distribution Protocol (LDP) that enables the binding between
PWs and the underlying Traffic Engineering (TE) tunnels. The
extension applies to both single-segment and multi-segment PWs.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 5741.

Information about the current status of this document, any errata,
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material or to cite them other than as "work in progress."

This Internet-Draft will expire on January 22, 2017.
http://www.rfc-editor.org/info/rfc7965.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. LDP Extensions . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.
3.1. PSN Tunnel Binding Tunnel-Binding TLV . . . . . . . . . . . . . . . . . 5
2.1.1.
3.1.1. PSN Tunnel Sub-TLV . . . . . . . . . . . . . . . . . 6
3.
4. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 8
4.
5. PSN Binding Operation for SS-PW . . . . . . . . . . . . . . . 9
5.
6. PSN Binding Operation for MS-PW . . . . . . . . . . . . . . . 11
6.
7. PSN Tunnel Select Considerations . . . . . . . . . . . . . . 13
7.
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8.
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8.1.
9.1. LDP TLV Types . . . . . . . . . . . . . . . . . . . . . . 13
8.1.1.
9.1.1. PSN Tunnel Sub-TLVs . . . . . . . . . . . . . . . . . 13
8.2. 14
9.2. LDP Status Codes . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . 14
10.1. Normative References . . . . . . . . . . 15
Acknowledgements . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 15 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16

1. Introduction

Pseudo Wire Emulation Edge-to-Edge (PWE3) [RFC3985] is a mechanism to
emulate layer Layer 2 services, such as Ethernet Point-to-Point circuits.
Such services are emulated between two Attachment Circuits, and the
Pseudowire (PW)-encapsulated layer
Pseudowire-encapsulated Layer 2 service payload is transported via
Packet Switching Network (PSN) tunnels between Provider Edges (PEs).
PWE3 typically uses the Label Distribution Protocol (LDP) [RFC5036]
or Resource ReserVation Protocol-Traffic Reservation Protocol - Traffic Engineering (RSVP-
TE) (RSVP-TE)
[RFC3209] LSPs Label Switched Paths (LSPs) as PSN tunnels. The PEs select
and bind the Pseudowires to PSN tunnels independently. Today, there
is no standardized protocol-based provisioning mechanism to associate
PWs
to with PSN tunnels, tunnels; such associations must be managed via
provisioning or other private methods.

PW-to-PSN Tunnel binding Binding has become increasingly common and important
in many deployment scenarios, , as it allows service providers to
provide offer
service level agreements to their customers for such traffic
attributes as bandwidth, latency, and availability.

The requirements for explicit control of PW-to-LSP mapping has been are
described in Section 5.3.2 of [RFC6373]. Figure 1 illustrates how
PWs can be bound to particular LSPs.

+------+ +------+
---AC1 ---|..............PWs...............|---AC1---
---...----| PE1 |=======LSPs=======| PE2 |---...---
---ACn ---| |-------Links------| |---ACn---
+------+ +------+

Figure 1: Explicit PW-to-LSP binding scenario Binding Scenario

There are two PEs (PE1 and PE2) connected through multiple parallel
links that may be on different physical fibers. Each link is managed
and controlled as a bi-directional bidirectional LSP. At each PE, there are a large
number of bi-directional bidirectional user flows from multiple Ethernet interfaces
(access circuits in the figure). Each user flow uses utilizes a pair of uni-directional
unidirectional PWs to carry bi-directional bidirectional traffic. The operators
need to make sure that the user flows (that is, the PW-
pairs) PW-pairs) are
carried on the same fiber or bidirectional LSP.

There are a number of reasons behind this requirement. First, due to
delay and latency constraints, traffic going over different fibers
may require a large amount of expensive buffer memory to compensate
for the differential delay at the headend head-end nodes. Further, the
operators may apply different protection mechanisms on different
parts of the network (e.g., to deloy deploy 1:1 protection in one part and
1+1 protection in other parts). As such, operators may prefer to
have a user's traffic traverse the same fiber. That implies that
both forwarding and reserve direction PWs that belong to the same
user flow need to be mapped to the same co-routed bi-directional bidirectional LSP
or two LSPs with the same route.

Figure 2 illustrates a scenario where PW-LSP binding is not applied.

+----+ +--+ LSP1 +--+ +----+
+-----+ | PE1|===|P1|======|P2|===| PE2| +-----+
| |----| | +--+ +--+ | |----| |
| CE1 | |............PW................| | CE2 |
| |----| | +--+ | |----| |
+-----+ | |======|P3|==========| | +-----+
+----+ +--+ LSP2 +----+

Figure 2: Inconsistent SS-PW to LSP binding scenario SS-PW-to-LSP Binding Scenario

LSP1 and LSP2 are two bidirectional connections on diverse paths.
The operator needs to deliver a bi-directional bidirectional flow between PE1 and
PE2. Using existing mechanisms, it's possible that PE1 may select
LSP1 (PE1-P1-P2-PE2) as the PSN tunnel for traffic from PE1 to PE2,
while selecting LSP2 (PE2-P3-PE1) as the PSN tunnel for traffic from
PE2 to PE1.

Consequently, the user traffic is delivered over two disjoint disjointed LSPs
that may have very different service attributes in terms of latency
and protection. This may not be acceptable as a reliable and
effective transport service to the customer.

A similar problem may also exist in multi-segment PWs (MS-PWs), where
user traffic on a particular PW may hop over different networks on in
forward and reverse directions.

One way to solve this problem is by introducing manual provisioning
at each PE to bind the PWs to the underlying PSN tunnels. However,
this is prone to configuration errors and does not scale.

This document introduces an automatic solution by extending
Forwarding Equivalence Class (FEC) 128/129 PW based on [RFC4447].

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. LDP Extensions

This document defines a new optional TLV, the PSN Tunnel Binding Tunnel-Binding TLV,
to communicate tunnel/LSPs tunnel/LSP selection and binding requests between PEs.
The TLV carries a PW's binding profile and provides explicit or
implicit information for the underlying PSN tunnel binding Tunnel-Binding operation.

The binding operation applies in both single-segment (SS) and multi-
segment (MS) scenarios.

The extension supports two types of binding requests:

1. Strict binding: the The requesting PE will choose and explicitly
indicate the LSP information in the requests; the receiving PE
MUST obey the requests, requests; otherwise, the PW will not be
established.

2. Co-routed binding: the The requesting PE will suggest an underlying
LSP to a remote PE. On receive, Upon receipt, the remote PE has the option
to use the suggested LSP, LSP or reply to the information for an
alternative.

In this document, the terminology of term "tunnel" is identical to the "TE Tunnel"
defined in Section 2.1 of [RFC3209], which is uniquely identified by
a SESSION object that includes the Tunnel end point endpoint address, the
Tunnel ID ID, and the Extended Tunnel ID. The terminology term "LSP" is identical
to the "LSP tunnel" defined in Section 2.1 of [RFC3209], which is
uniquely identified by the SESSION object together with the
SENDER_TEMPLATE (or FILTER_SPEC) object that consists of the LSP ID
and the Tunnel endpoint address.

2.1.

3.1. PSN Tunnel Binding Tunnel-Binding TLV

The PSN Tunnel Binding Tunnel-Binding TLV is an optional TLV and MUST be carried in
the LDP Label Mapping message [RFC5036] if PW to LSP PW-to-LSP binding is
required. The format 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| PSN Tunnel Binding (TBD1) | Binding(0x0973)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|S|T| Unallocated flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ PSN Tunnel Sub-TLV ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: PSN Tunnel Binding Tunnel-Binding TLV

The U-bit and F-bit are defined in Section 3.3 [RFC5036]. Since the
PSN Tunnel Binding Tunnel-Binding TLV is an optional TLV, the U-bit MUST be set to 1
so that a receiver MUST silently ignore this TLV if unknown to it,
and continue processing the rest of the message.

A receiver of this TLV is not allowed to forward the TLV further when
it does not know the TLV. So, the F-bit MUST be set to 0.

The PSN Tunnel Binding Tunnel-Binding TLV type is TBD1. 0x0973.

The Length field is 2 octets in length. long. It defines the length in octets
of the value field (including Flags, Reserved, and sub-TLV fields).

The Flag field is 2 octets in length, length and three flags are defined in
this document. The rest of the unallocated flags MUST be set to zero
when
sending, sending and MUST be ignored when received.

C (Co-routed path) bit: This bit informs the remote T-PE/S-PEs T-PEs/S-PEs
about the properties of the underlying LSPs. When set, the remote
T-PE/S-PEs SHOULD select the co-routed LSP (as the forwarding
tunnel) as the reverse PSN tunnel. If there is no such tunnel
available, it may trigger the remote T-PE/S-PEs T-PEs/S-PEs to establish a
new LSP.

S (Strict) bit: This bit instructs the PEs with respect to the
handling of the underlying LSPs. When set, the remote PE MUST use
the tunnel/
LSP tunnel/LSP specified in the PSN Tunnel Sub-TLV as the PSN
tunnel on the reverse direction of the PW, or the PW will fail to
be established.

Either the C-bit or the S-bit MUST be set. The C-bit and S-bit
are mutually exclusive from each other, and they cannot be set
in the same message. If a status code set to "both C-bit and
S-bit are set" or "both C-bit and S-bit are clear" are is received,
a Label Release message with the status code set to "The C-bit
or S-bit unknown" (TBD5) (0x0000003C) MUST be replied, the reply, and the PW
will not be established.

T (Tunnel Representation) bit: This bit indicates the format of
the LSP tunnels. When the bit is set, the tunnel uses the tunnel
information to identify itself, and the LSP Number fields in the
PSN Tunnel sub-
TLV sub-TLV (Section 2.1.1) 3.1.1) MUST be set to zero.
Otherwise, both the tunnel and LSP information of the PSN tunnel
are required. The default is set. The motivation for the T-bit
is to support the MPLS protection operation where the LSP Number
fields may be ignored.

The Reserved field is 2 octets in length and is left for future use.

2.1.1.

3.1.1. PSN Tunnel Sub-TLV

PSN Tunnel Sub-TLVs are designed for inclusion in the PSN Tunnel Tunnel-
Binding TLV to specify the tunnel/LSPs to which a PW is required to
bind.

Two sub-TLVs are defined: the The IPv4 and IPv6 Tunnel sub-TLVs.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(TBD2) Type (1) | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Node ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Tunnel Number | Source LSP Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Node ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Tunnel Number | Destination LSP Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3

Figure 4: IPv4 PSN Tunnel sub-TLV format Sub-TLV 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type(TBD3) Type (2) | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Source Node ID ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Tunnel Number | Source LSP Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Destination Node ID ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Tunnel Number | Destination LSP Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5: IPv6 PSN Tunnel sub-TLV format Sub-TLV Format

The definition of the Source and Destination Global/Node IDs and Tunnel/
LSP
Tunnel/LSP Numbers are derived from [RFC6370]. This is to describe describes the
underlying LSPs. Note that the LSPs in this notation are globally
unique. The ITU-T style identifiers [RFC6923] are not used in this
document.

As defined in Section 4.6.1.2 Sections 4.6.1.1 and Section 4.6.2.2 4.6.1.2 of [RFC3209], the "Tunnel
endpoint address" is mapped to the Destination Node ID, and the
"Extended Tunnel ID" is mapped to the Source Node ID. Both IDs can
be either IPv4 or IPv6 addresses. The Node IDs are routable
addresses of the ingress LSR and egress LSR of the Tunnel/LSP.

A PSN Tunnel sub-TLV could be used to either identify either a tunnel or a
specific LSP. The T-bit in the Flag field defines the distinction as
such that, when the T-bit is set, the Source/Destination LSP Number
fields MUST be zero and ignored during processing. Otherwise, both
Source/Destination LSP Number fields MUST have the actual LSP IDs of
specific LSPs.

Each PSN Tunnel Binding Tunnel-Binding TLV MUST only have one such sub-TLV. When
sending, only one sub-TLV MUST be carried. When received, if there
are more than one sub-TLVs carried, only the first sub-TLV MUST be
used, the rest of the sub-TLVs MUST be ignored.

4. Theory of Operation

During PW setup, the PEs may choose to select the desired forwarding
tunnels/LSPs,
tunnels/LSPs and inform the remote T-PE/S-PEs T-PEs/S-PEs about the desired
reverse tunnels/LSPs.

Specifically, to set up a PW (or PW Segment), a PE may select a
candidate tunnel/LSP to act as the PSN tunnel. If none no candidate is
available or satisfies none satisfy the constraints, the PE will trigger and
establish a new tunnel/LSP. The selected tunnel/LSP information is
carried in the PSN Tunnel Binding Tunnel-Binding TLV and sent with the Label Mapping
message to the target PE.

Upon the reception of the Label Mapping message, the receiving PE
will process the PSN Tunnel Binding Tunnel-Binding TLV, determine whether it can
accept the suggested tunnel/LSP or to find the reverse tunnel/LSP
that meets the request, and respond with a Label Mapping message,
which contains the corresponding PSN Tunnel Binding Tunnel-Binding TLV.

It is possible that two PEs may request PSN binding Binding to the same PW or PW
segment over different tunnels/LSPs at the same time. There This may cause
collisions of tunnel/LSPs selection as both PEs assume the active
role.

As defined in (Section 7.2.1, [RFC6073]), each PE may be categorized
into active and passive roles:

1. Active PE: the The PE which that initiates the selection of the tunnel/
LSPs tunnel/LSPs
and informs the remote PE;
2. Passive PE: the The PE which that obeys the active PE's suggestion.

In the remaining rest of this document, we will elaborate upon the operation
for SS-PW and MS-PW:

1. SS-PW: In this scenario, both PEs for a particular PW may assume
the active roles.

2. MS-PW: One PE is active, while the other is passive. The PWs are
setup
set up using FEC 129.

5. PSN Binding Operation for SS-PW

As illustrated in Figure-5, Figure 6, both PEs (say, (e.g., PE1 and PE2) of a PW may
independently initiate the setup. To perform PSN binding, Binding, the Label
Mapping messages MUST carry a PSN Tunnel Binding Tunnel-Binding TLV, and the PSN
Tunnel sub-TLV MUST contains contain the desired tunnel/LSPs of the sender.

+----+ LSP1 +----+
+-----+ | PE1|====================| PE2| +-----+
| |----| | | |----| |
| CE1 | |............PW................| | CE2 |
| |----| | | |----| |
+-----+ | |====================| | +-----+
+----+ LSP2 +----+

Figure 6: PSN binding operation Binding Operation in SS-PW environment Environment

As outlined previously, there are two types of binding request: requests: co-
routed and strict.

In strict binding, a PE (e.g., PE1) will mandate that the other PE
(e.g., PE2) to use a specified tunnel/LSP (e.g. (e.g., LSP1) as the PSN tunnel
on the reverse direction. In the PSN Tunnel Binding Tunnel-Binding TLV, the S-bit
MUST be set, the C-bit MUST be cleared, and the Source and
Destination IDs/Numbers MUST be filled.

On receive,

Upon receipt, if the S-bit is set, as well as following the
processing procedure defined in Section 5.3.3 of [RFC4447], the
receiving PE
(i.e. (i.e., PE2) needs to determine whether to accept the
indicated tunnel/LSP in PSN Tunnel Sub-TLV.

If the receiving PE (PE2) is also an active PE, and may have
initiated the PSN binding Binding requests to the other PE (PE1), if the
received PSN tunnel/LSP is the same as it has been was sent in the Label Mapping
message by PE2, then the signaling has converged on a mutually agreed
upon Tunnel/LSP. The binding operation is completed.

Otherwise, the receiving PE (PE2) MUST compare its own Node ID
against the received Source Node ID as unsigned integers. If the
received Source Node ID is larger, the PE (PE2) will reply with a
Label Mapping message to complete the PW setup and confirm the
binding request. The PSN Tunnel Binding Tunnel-Binding TLV in the message MUST
contain the same Source and Destination IDs/Numbers as in the
received binding request, in the appropriate order (where the source
is PE2 and PE1 becomes the destination). On the other hand, if the
receiving PE (PE2) has a Node ID that is larger than the Source Node
ID carried in the PSN Tunnel Binding Tunnel-Binding TLV, it MUST reply with a Label
Release message with the status code set to "Reject - unable to use
the suggested tunnel/LSPs" tunnel/LSPs", and the received PSN Tunnel Binding Tunnel-Binding TLV,
and the PW will not be established.

To support co-routed binding, the receiving PE can select the
appropriated PSN tunnel/LSP for the reverse direction of the PW, so
long as the forwarding and reverse PSNs share the same route (links
and nodes).

Initially, a PE (PE1) sends a Label Mapping message to the remote PE
(PE2) with the PSN Tunnel Binding Tunnel-Binding TLV, with C-bit set, S-bit cleared,
and the appropriate Source and Destination IDs/Numbers. In case of
unidirectional LSPs, the PSN Tunnel Binding Tunnel-Binding TLV may only contain the
Source IDs/Numbers, IDs/Numbers; the Destination IDs/Numbers are set to zero and
left for PE2 to complete when responding to the Label Mapping
message.

On receive,

Upon receipt, since PE2 is also an active PE, and may have initiated
the PSN binding Binding requests to the other PE (PE1), if the received PSN
tunnel/LSP has the same route as the one that has been sent in the
Label Mapping message to PE1, then the signaling has converged. The
binding operation is completed.

Otherwise, PE2 needs to compare its own Node ID against the received
Source Node ID as unsigned integers. If the received Source Node ID
is larger, PE2 needs to find/establish a tunnel/LSP that meets the
co-routed constraint, and reply with a Label Mapping message with that has
a PSN Binding TLV that contains the Source and Destination IDs/Numbers IDs/
Numbers of the tunnel/LSP. On the other hand, if the receiving PE
(PE2) has a Node ID that is larger than the Source Node ID carried in
the PSN
Tunnel Binding Tunnel-Binding TLV, it MUST reply with a Label Release
message with that has a status code set to "Reject - unable to use the
suggested tunnel/LSPs"
(TBD4) (0x0000003B) and the received PSN Tunnel Tunnel-
Binding TLV.

In addition, if the received PSN tunnel/LSP end points endpoints do not match
the PW end points, endpoints, PE2 MUST reply with a Label Release message with
the status code set to "Reject - unable to use the suggested tunnel/LSPs"
(TBD4) tunnel/
LSPs" (0x0000003B) and the received PSN Tunnel Binding Tunnel-Binding TLV MUST also
be carried.

In both strict and co-routed bindings, if the T-bit is set, the LSP
Number field MUST be set to zero. Otherwise, the field MUST contain
the actual LSP number for the related PSN LSP.

After a PW is established, the operators may choose to move the PWs
from the current tunnel/LSPs to other tunnel/LSPs. Also Also, the
underlying PSN tunnel may break due to a network failure. When
either of these scenarios occur, a new Label Mapping message MUST be
sent to notify the remote PE of the changes. Note that when the
T-bit is set, the working LSP broken will not provide this update if
there are protection LSPs in place.

The message may carry a new PSN Tunnel Binding Tunnel-Binding TLV, which contains
the new Source and Destination Numbers/IDs. The handling of the new
message should be identical to what has been described in this
section.

However, if the new Label Mapping message does not contain the PSN
Tunnel Binding
Tunnel-Binding TLV, it declares the removal of any co-routed/strict
constraints. The current independent PW to PSN binding PW-to-PSN Binding will be used.

Further, as an implementation option, the PEs may choose not to
remove the traffic from an operational PW, PW until the completion of the
underlying PSN tunnel/LSP changes.

6. PSN Binding Operation for MS-PW

MS-PW uses FEC 129 for PW setup. We refer the operation to Figure-6. Figure 7 for this
operation.

+-----+ LSP1 +-----+ LSP2 +-----+ LSP3 +-----+
+---+ |T-PE1|======|S-PE1|======|S-PE2|======|T-PE2| +---+
| |---| | | | | | | |---| |
|CE1| |......................PW....................| |CE2|
| |---| | | | | | | |---| |
+---+ | |======| |======| |======| | +---+
+-----+ LSP4 +-----+ LSP5 +-----+ LSP6 +-----+

Figure 7: PSN binding operation Binding Operation in MS-PW environment Environment

When an active PE (that is, T-PE1) starts to signal a an MS-PW, a PSN
Tunnel Binding
Tunnel-Binding TLV MUST be carried in the Label Mapping message and
sent to the adjacent S-PE (that is, S-PE1). The PSN Tunnel Binding Tunnel-Binding
TLV includes the PSN Tunnel sub-TLV that carries the desired tunnel/
LSP of T-PE1's. T-PE1s.

For strict binding, the initiating PE MUST set the S-bit, clear the
C-bit
C-bit, and indicate the binding tunnel/LSP to the next-hop S-PE.

When S-PE1 receives the Label Mapping message, S-PE1 it needs to determine
if the signaling is for the forward or reverse direction, as defined
in Section 6.2.3 of [RFC7267].

If the Label Mapping message is for the forward direction, and S-PE1
accepts the requested tunnel/LSPs from T-PE1, S-PE1 MUST save the
tunnel/LSP information for reverse-direction processing later on. If
the PSN binding Binding request is not acceptable, S-PE1 MUST reply with a
Label Release Message to the upstream PE (T-PE1) with Status Code the status code
set to "Reject - unable to use the suggested tunnel/LSPs" (TBD4).
(0x0000003B).

Otherwise, S-PE1 relays the Label Mapping message to the next S-PE
(that is, S-PE2), with the PSN Tunnel sub-TLV carrying the
information of the new PSN tunnel/LSPs selected by S-PE1. S-PE2 and
subsequent S-PEs will repeat the same operation until the Label
Mapping message reaches to the remote T-PE (that is, T-PE2).

If T-PE2 agrees with the requested tunnel/LSPs, it will reply with a
Label Mapping message to initiate to the binding process on in the reverse
direction. The Label Mapping message contains the received PSN Tunnel Binding
Tunnel-Binding TLV for confirmation purposes.

When its upstream S-PE (S-PE2) receives the Label Mapping message,
the S-PE relays the Label Mapping message to its upstream adjacent
S-PE (S-PE1), with the previously saved PSN tunnel/LSP information in
the PSN Tunnel sub-TLV. The same procedure will be applied on
subsequent S-PEs, until the message reaches to T-PE1 to complete the PSN binding
Binding setup.

During the binding process, if any PE does not agree to the requested
tunnel/LSPs, it can send a Label Release Message to its upstream
adjacent PE with Status Code the status code set to "Reject - unable to use the
suggested tunnel/LSPs" (TBD4). (0x0000003B). In addition, if the received
PSN tunnel/LSP end points endpoints do not match the PW Segment end points, endpoints, the
receiving PE MUST reply with a Label Release message with the status
code set to "Reject - unable to use the suggested tunnel/LSPs" (TBD4)
(0x0000003B) and the received PSN Tunnel Binding Tunnel-Binding TLV MUST also be
carried.

For co-routed binding, the initiating PE (T-PE1) MUST set the C-bit,
reset the S-bit S-bit, and indicates indicate the suggested tunnel/LSP in the PSN
Tunnel sub-TLV to the next-hop S-PE (S-PE1).

During the MS-PW setup, the PEs have the option of ignoring the
suggested tunnel/LSP, and to select another tunnel/LSP for the
segment PW between itself and its upstream PE in reverse direction
only if the tunnel/LSP is co-routed with the forward one. Otherwise,
the procedure is the same as the strict binding.

The tunnel/LSPs may change after a MS-PW being has been established. When
a tunnel/LSP has changed, the PE that detects the change SHOULD
select an alternative tunnel/LSP for temporary use while negotiating
with other PEs following the procedure described in this section.

7. PSN Tunnel Select Considerations

As stated in Section 1 of this document, 1, the PSN tunnel that is used for binding can
be either a co-routed bi-directional bidirectional LSP or two LSPs with the same
route. The co-routed bi-directional bidirectional LSP has the characteristics that
both directions not only cross the same nodes and links links, but have the
same life span. But for the two LSPs case, even if they have the
same route at the beginning, it cannot be guaranteed that they will
always have the same route all the time. For example, when Fast
ReRoute (FRR) [RFC4090] is deployed for the LSPs, link or node
failure may make the two LSPs use different routes. So, if the
network supports co-routed bi-directional bidirectional LSPs, it is RECOMMENDED that
a co-routed bi-directional bidirectional LSP should be used; otherwise, two LSPs
with the same route may be used.

8. Security Considerations

The ability to control which LSP is used to carry traffic from a PW
can be a potential security risk both for denial of service and
traffic interception. It is RECOMMENDED that PEs do not accept the use
of LSPs identified in the PSN Tunnel Binding Tunnel-Binding TLV unless the LSP
end points
endpoints match the PW or PW segment end points. endpoints. Furthermore, it is
RECOMMENDED that PEs implement the LDP security mechanisms described
in [RFC5036] and [RFC5920].

9. IANA Considerations

8.1.

9.1. LDP TLV Types

This document defines a new TLV [Section 2.1 of this document] (Section 3.1) for inclusion in the
LDP Label Mapping message. IANA is requested to assign has assigned TLV type value (TBD1) to the new defined TLVs 0x0973
from LDP "TLV the "LDP TLV Type Name Space" registry.

8.1.1.

9.1.1. PSN Tunnel Sub-TLVs

This document defines two sub-TLVs [Section 2.1.1 of this document] (Section 3.1.1) for the PSN Tunnel Binding
Tunnel-Binding TLV. IANA is required to create has created a new PWE3
registry ("PSN subregistry titled
"PSN Tunnel Sub-TLV Name Space") Space" for PSN Tunnel sub-TLVs and to assign has
assigned Sub-TLV type values to the following sub-TLVs:

IPv4 PSN Tunnel sub-TLV - TBD2 1

IPv6 PSN Tunnel sub-TLV - TBD3 2

In addition, the values 0 and 255 in this new registry should be
reserved, and values 1-254 will be allocated by IETF Review.

8.2. Review
[RFC5226].

9.2. LDP Status Codes

This document defines two new LDP status codes, IANA is requested to has assigned
status codes to these new defined codes from the LDP "STATUS
CODE NAME SPACE" "LDP Status Code
Name Space" registry.

"Reject - unable to use the suggested tunnel/LSPs" - TBD4 0x0000003B

"The C-bit or S-bit unknown" -TBD5 - 0x0000003C

The E bit is set to one 1 for both new codes.

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
G. Heron, "Pseudowire Setup and Maintenance Using the
Label Distribution Protocol (LDP)", RFC 4447,
DOI 10.17487/RFC4447, April 2006,
<http://www.rfc-editor.org/info/rfc4447>.

[RFC6370] Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
Profile (MPLS-TP) Identifiers", RFC 6370,
DOI 10.17487/RFC6370, September 2011,
<http://www.rfc-editor.org/info/rfc6370>.

10.2. Informative References

[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<http://www.rfc-editor.org/info/rfc3209>.

[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<http://www.rfc-editor.org/info/rfc3985>.

[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
DOI 10.17487/RFC4090, May 2005,
<http://www.rfc-editor.org/info/rfc4090>.

[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
October 2007, <http://www.rfc-editor.org/info/rfc5036>.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.

[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
<http://www.rfc-editor.org/info/rfc5920>.

[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui, "Segmented Pseudowire", RFC 6073,
DOI 10.17487/RFC6073, January 2011,
<http://www.rfc-editor.org/info/rfc6073>.

[RFC6373] Andersson, L., Ed., Berger, L., Ed., Fang, L., Ed., Bitar,
N., Ed., and E. Gray, Ed., "MPLS Transport Profile (MPLS-
TP) Control Plane Framework", RFC 6373,
DOI 10.17487/RFC6373, September 2011,
<http://www.rfc-editor.org/info/rfc6373>.

[RFC6923] Winter, R., Gray, E., van Helvoort, H., and M. Betts,
"MPLS Transport Profile (MPLS-TP) Identifiers Following
ITU-T Conventions", RFC 6923, DOI 10.17487/RFC6923, May
2013, <http://www.rfc-editor.org/info/rfc6923>.

[RFC7267] Martini, L., Ed., Bocci, M., Ed., and F. Balus, Ed.,
"Dynamic Placement of Multi-Segment Pseudowires",
RFC 7267, DOI 10.17487/RFC7267, June 2014,
<http://www.rfc-editor.org/info/rfc7267>.

Acknowledgements

The authors would like to thank Adrian Farrel, Kamran Raza, Xinchun
Guo, Mingming Zhu Zhu, and Li Xue for their comments and help in
preparing this document. Also this draft document benefits from the
discussions with Nabil Bitar, Paul Doolan, Frederic Journay, Andy
Malis, Curtis Villamizar, Luca Martini, Alexander Vainshtein, Huub
van Helvoort, Daniele Ceccarelli Ceccarelli, and Stewart Byant. Bryant.

We would especially like to acknowledge Ping Pan, a co-author coauthor on the
early draft versions of this document. It was a privilege to have
known him.

The coauthors of this document, the working group chairs, the
responsible AD, and the PALS Working Group working group wish to dedicate this RFC
to the memory of our friend and colleague Ping Pan, in recognition
for his devotion and hard work at the IETF.

Authors' Addresses

Mach(Guoyi) Chen
Huawei

Email: mach.chen@huawei.com

Wei Cao
Huawei

Email: wayne.caowei@huawei.com

Attila Takacs
Ericsson
Laborc u. 1.
Budapest 1037
Hungary

Email: attila.takacs@ericsson.com

Ping Pan