wdiff rfc7392.alt-original rfc7392.txt

Network Working Group
Internet Engineering Task Force (IETF) P. Dutta
Internet-Draft
Request for Comments: 7392 M. Bocci
Intended status:
Category: Standards Track Alcatel-Lucent
Expires: March 14, 2015
ISSN: 2070-1721 L. Martini
Cisco Systems
September 10,
November 2014

Explicit Path Routing for Dynamic Multi-Segment Pseudowires
draft-ietf-pwe3-mspw-er-06

Abstract

Dynamic Multi-Segment Pseudowire (MS-PW) setup

When set up through an explicit
path path, dynamic Multi-Segment
Pseudowires (MS-PWs) may be required to provide a simple solution for
1:1 protection with diverse primary and backup MS-PWs for a service,
or to enable controlled signaling (strict or loose) for special MS-PWs. MS-
PWs. This document specifies the extensions and procedures required
to enable dynamic MS-PWs to be established along explicit paths.

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].

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-
Drafts is at http://datatracker.ietf.org/drafts/current/.

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,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

This Internet-Draft will expire on March 14, 2015.
http://www.rfc-editor.org/info/rfc7392.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language and Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2
3. Explicit Path in MS-PW Signaling . . . . . . . . . . . . . . 3
3.1. S-PE Addressing . . . . . . . . . . . . . . . . . . . . . 3
3.2. Explicit Route TLV (ER-TLV) . . . . . . . . . . . . . . . 3
3.3. Explicit Route Hop TLV (ER-Hop TLV) . . . . . . . . . . . 4 3
3.4. ER-Hop Semantics . . . . . . . . . . . . . . . . . . . . 4
3.4.1. ER-Hop Type: IPv4 Prefix . . . . . . . . . . . . . . 4
3.4.2. ER-Hop Type: IPv6 Prefix . . . . . . . . . . . . . . 4
3.4.3. ER-Hop Type: L2 PW Address . . . . . . . . . . . . . 4
4. Explicit Route TLV Processing . . . . . . . . . . . . . . . . 6 5
4.1. Next-Hop Selection . . . . . . . . . . . . . . . . . . . 6
4.2. Adding ER Hops to the Explicit Route TLV . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . 8
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9 10

1. Introduction

Procedures for dynamically establishing multi-segment pseudowires Multi-Segment Pseudowires
(MS-PWs), where their paths are automatically determined using a
dynamic routing protocol, are defined in [RFC7267]. For 1:1
protection of MS-PWs with primary and backup paths, MS-PWs need to be
established through a diverse set of S-PEs (Switching Provider-Edges) Switching Provider Edges (S-PEs)
to avoid any single points of failure at the PW level. [RFC7267]
allows this through BGP-based mechanisms. This document defines an
additional mechanism that allows the ST-PE (Source Source Terminating PEs) Provider Edges
(ST-PEs) to explicitly choose the path that a PW would take through
the intervening S-PEs. Explicit path routing of dynamic MS-PWs may
also be required for controlled set-up setup of dynamic MS-PWs and network
resource management.

Note that in many deployments the ST-PE will not have a view of the
topology of S-PEs and so the explicit route will need to be supplied
from a management application. How that management application
determines the explicit route is outside the scope of this document.

2. Requirements Language and Terminology

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].

This document uses the terminology defined in [RFC7267], [RFC4447]and [RFC4447],
and [RFC5036].

The following additional terminology is used:

Abstract Node: A group of nodes (S-PEs) representing an explicit hop
along the path of an MS-PW. An abstract node is identified by an
IPv4, IPv6 IPv6, or S-PE address.

3. Explicit Path in MS-PW Signaling

This section describes the LDP (Label Label Distribution Protocol) Protocol (LDP)
extensions required for signaling explicit paths in dynamic MS-PW
set-up
setup messages. An explicitly routed MS-PW is set up using a Label
Mapping message that carries an ordered list of the S-PEs which that the
MS-PW is expected to traverse. The ordered list is encoded as a
series of Explicit Route (ER) Hop TLVs (ER-Hop TLVs) encoded in an ER-TLV
that is carried in a Label Mapping message.

3.1. S-PE Addressing

An S-PE address is used to identify a given S-PE among the set of
S-PEs belonging to the PSNs Packet Switched Networks (PSNs) that may be
used by an MS-PW. Each S-PE MUST be assigned an address as specified
in [RFC7267] Section 3.2. 3.2 of [RFC7267]. An S-PE that is capable of dynamic MS-PW MS-
PW signaling, but has not been assigned an S-PE address, and that
receives a Label Mapping message for a dynamic MS-PW MUST follow the
procedures of [RFC7267] in Section 3.2. 3.2 of [RFC7267].

3.2. Explicit Route TLV (ER-TLV)

The ER-TLV specifies the path to be taken by the MS-PW being
established. Each hop along the path is represented by an abstract
node, which is a group of one or more S-PEs, identified by an IPv4,
an IPv6
IPv6, or an S-PE address. The ER-TLV format is as per Section 4.1 of
[RFC3212].

The ER-TLV contains one or more Explicit Route Hop ER-Hop TLVs (ER-Hop TLVs) as defined in
Section 3.3.

3.3. Explicit Route Hop TLV (ER-Hop TLV)

The contents of an ER-TLV are a series of variable length variable-length ER-Hop
TLVs. Each hop contains the identification of an "Abstract Node" "abstract node"
that represents the hop to be traversed. The ER-Hop TLV format is as
specified in Section 4.2 of [RFC3212].

[RFC3212] defines three four ER-Hop TLV Types: IPv4 Prefix, IPv6 Prefix,
and
Autonomous System. System Number, and LSP-ID. This document specifies the
following new ER-
Hop ER-Hop TLV Type:

Value Type
------ ------------------------ --------------------------------
0x0805 L2 PW address Address of PW Switching Point

ER-Hop TLV

Details of ER Hop the ER-Hop semantics are defined in Section 3.4.

3.4. ER-Hop Semantics

This section describes the various semantics associated with the
ER-Hop TLV.

3.4.1. ER-Hop Type: IPv4 Prefix

The semantics of the IPv4 ER-Hop TLV Type are specified in [RFC3212] [RFC3212],
Section 4.7.1.

3.4.2. ER-Hop Type: IPv6 Prefix

The semantics of the IPv6 ER-Hop TLV Type are specified in [RFC3212] [RFC3212],
Section 4.7.2.

3.4.3. ER-Hop Type: L2 PW Address

The semantics of the L2 PW Address ER-Hop TLV Type, which contains
the L2 PW Address derived from the Generalized PWid FEC Forwarding
Equivalence Class (FEC) AII type Type 2 structure as defined in [RFC5003],
are 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| ER Hop ER-Hop Type | Length = 18 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Reserved | PreLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AII Type=02 | Length | Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global ID (contd.) | Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix (contd.) | AC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

U/F
These bits MUST be set to zero and the procedures of
[RFC5036] followed when the TLV is not known to the
receiving node.

Type
A fourteen-bit field carrying the value of the ER-Hop 3,
L2 PW Address, Value = TBD 0x0805.

Length
Specifies the length of the value field in bytes = 18.

L Bit
Set to indicate Loose a loose hop.
Cleared to indicate a strict hop.

Reserved
Zero on transmission. Ignored on receipt.

PreLen
Prefix Length 1-96 (including the length of the Global ID,
Prefix
Prefix, and AC ID fields).

All other fields (AII Type, Length, Global ID, Prefix, and AC ID)
define the L2 PW Address and are to be set and interpreted as
defined in Section 3.2 of [RFC5003].

4. Explicit Route TLV Processing

4.1. Next-Hop Selection

A PW Label Mapping Message message containing an explicit route Explicit Route TLV specifies
the next hop for a given MS-PW path. Selection of this next hop by
the ST-PE or S-PE inserting the ER Hop ER-Hop TLV may involve a selection
from a set of possible alternatives. The mechanism for making a
selection from this set is implementation specific and is outside of the
scope of this document. The mechanism used to select a particular
path is also outside of the scope of this document, but each node MUST
determine a loop-free path if it is to signal the MS-
PW. [RFC6073] MS-PW. [RFC6073],
Section 7.6 provides a mechanism by which a node can check that the
path taken by an MS-PW does not include loops.

As noted in Section 1, in many deployments the ST-PE will not have a
view of the topology of S-PEs and so the path will need to be
supplied from a management application.

If a loop free loop-free path cannot be found by an ST-PE or S-PE, then a node
MUST NOT attempt to signal the MS-PW. For an S-PE, if it cannot
determine a loop free loop-free path, then the received Label Mapping message
MUST be released with a status code of "PW Loop Detected" as per
Section 4.2.3 of [RFC7267].

To determine the next hop for the MS-PW path, a node performs the
following steps. Note that these procedures assume that a valid S-PE
address has been assigned to the node, as per Section 3.1, above.

1. The node receiving the Label Mapping Message message that contains an ER-
TLV
ER-TLV MUST evaluate the first ER Hop. ER-Hop. If the L bit is not set
in the first ER Hop ER-Hop and if the node is not part of the abstract
node described by the first ER Hop (i.e ER-Hop (i.e., it does not lie within
the prefix as determined by the prefix length specified in the
ER-Hop TLV), it has received the message in error. Therefore,
the node MUST reply with a Label Release Message message with a "Bad
Initial ER
Hop ER-Hop Error" (0x04000004) status code. If the L bit is
set and the local node is not part of the abstract node described
by the first ER Hop, ER-Hop, the node selects a next hop that is along
the path to the abstract node described by the first ER Hop. ER-Hop. If
there is no ER-Hop TLV contained in the ER-TLV, the message is
also in
error error, and the node SHOULD return a "Bad Explicit Routing
TLV Error" (0x04000001) status code in a Label Release Message message
sent to the upstream node. Note that this statement does not
preclude a Label mapping Mapping message with no ER-TLV. If a Label
Mapping message with no ER-TLV is received, then it MUST be
processed as per [RFC7267].

2. If there are no further ER-Hop TLVs following the first ER-Hop
TLV, this indicates the end of the explicit route. The Explicit
Route TLV MUST be removed from the Label Mapping message. This
node may or may not be the end of the PW. Processing continues
as per Section 4.2, where a new explicit route Explicit Route TLV MAY be added
to the Label Mapping Message. message.

3. If a second ER Hop ER-Hop TLV does exist, and the node is also a part of
the abstract node described by the second ER-Hop, then the node
deletes the first ER-Hop and continues processing with step 2,
above. Note that this makes the second ER Hop ER-Hop into the first ER ER-
Hop for the iteration for the next PW segment.

4. The node determines if it is topologically adjacent to the
abstract node described by the second ER Hop. ER-Hop. That is, it is
directly connected to the next node by a PW control plane control-plane
adjacency. If so, the node selects a particular next hop which that is
a member of the abstract node. The node then deletes the first
ER-Hop and continues processing as per Section 4.2, below.

5. Next, the node selects a next hop within the abstract node of the
first ER Hop ER-Hop that is along the path to the abstract node of the
second ER Hop. ER-Hop. If no such path exists exists, then there are two cases:

A. If the second ER Hop ER-Hop is a strict ER Hop, then there is an
error
error, and the node MUST return a Label Release Message message to
the upstream node with a "Bad Strict Node Error" (0x04000002)
status code.

B. Otherwise, if the second ER Hop ER-Hop is a loose ER Hop, then the
node selects any next hop that is along the path to the next
abstract node. If no path exists within the MPLS domain,
then there is an error, and the node MUST return a Label
Release Message message to the upstream node with a "Bad Loose Node
Error" (0x04000003) status code.

6. Finally, the node replaces the first ER Hop ER-Hop with any ER Hop that
denotes an abstract node containing the next hop. This is
necessary so that when the explicit route is received by the next
hop, it will be accepted.

7. Progress the Label Mapping Message message to the next hop.

4.2. Adding ER Hops to the Explicit Route TLV

After selecting a next hop, the node MAY alter the explicit route in
the following ways.

If, as part of executing the algorithm in Section 4.1, the explicit
route Explicit
Route TLV is removed, then the node MAY add a new explicit route Explicit Route TLV.

Otherwise, if the node is a member of the abstract node for the first
ER-Hop, then a series of ER Hops MAY be inserted before the First ER
Hop or the first ER Hop ER-Hop MAY be replaced. Each ER Hop in this series
MUST denote an abstract node that is a subset of the current abstract
node.

Alternately, if the first ER-Hop is a loose ER Hop, an arbitrary
series of ER Hops MAY be inserted prior to the first ER-Hop.

5. IANA Considerations

RFC5036

RFC 5036 [RFC5036] defines the LDP TLV name space space, which is
maintained by IANA as "LDP TLV Registry". IANA, in the LDP "TLV Type Name Space" registry. TLV
types for the Explicit Route TLV, the IPv4 Prefix ER-Hop TLV, and the
IPv6 Prefix ER-Hop TLV are already defined in the LDP TLV Registry. this registry.

IANA is requested to assign has assigned a further code point from the IETF consensus
portion of this registry as follows:

TLV Type Value Reference
------------------------------------ -------- --------- ------ -------------
L2 PW Address of Switching Point TBD 0x0805 This Document

A value of 0x0805 is requested.

6. Security Considerations

This document introduces no new security considerations over beyond those
discussed in [RFC5036], [RFC4447] [RFC4447], and [RFC7267]. The security
considerations detailed in those documents apply to the protocol
extensions described in this RFC.

As with [RFC7267], it should be noted that the path selection
mechanisms specified in this document enable the network to
automatically select the S-PEs that are used to forward packets on
the MS-PW. Appropriate tools, such as the Virtual Circuit
Connectivity Verification (VCCV) trace mechanisms specified in
[RFC6073], can be used by an operator of the network to verify the
path taken by the MS-PW and therefore be satisfied that the path does
not represent an additional security risk.

7. Acknowledgements

The authors gratefully acknowledge the contribution of the
RFC3212[RFC3212] authors through the specification of TLVs, which are
reused by this document. The authors also gratefully acknowledge the
input of Lizhong Jin.

8. Normative References

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

[RFC3212] Jamoussi, B., Andersson, L., Callon, R., Dantu, R., Wu,
L., Doolan, P., Worster, T., Feldman, N., Fredette, A.,
Girish, M., Gray, E., Heinanen, J., Kilty, T., and A.
Malis, "Constraint-Based LSP Setup using LDP", RFC 3212,
January 2002. 2002, <http://www.rfc-editor.org/info/rfc3212>.

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

[RFC5003] Metz, C., Martini, L., Balus, F., and J. Sugimoto,
"Attachment Individual Identifier (AII) Types for
Aggregation", RFC 5003, September 2007. 2007,
<http://www.rfc-editor.org/info/rfc5003>.

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

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

[RFC7267] Martini, L., Bocci, M., and F. Balus, "Dynamic Placement
of Multi-Segment Pseudowires", RFC 7267, June 2014.

7. 2014,
<http://www.rfc-editor.org/info/rfc7267>.

Appendix A. Acknowledgements

The authors gratefully acknowledge the contribution of the
RFC3212[RFC3212] RFC 3212
[RFC3212] authors through for the specification of TLVs, the ER TLV and the ER-Hop
TLV, which are reused by this document. The authors also gratefully
acknowledge the input of Lizhong Jin.

Authors' Addresses

Pranjal Kumar Dutta
Alcatel-Lucent
701 E E. Middlefield Road
Mountain View, California 94043
USA

Email:
United States

EMail: pranjal.dutta@alcatel-lucent.com

Matthew Bocci
Alcatel-Lucent
Voyager Place, Shoppenhangers Road
Maidenhead, Berks SL6 2PJ
UK

Email:
United Kingdom

EMail: matthew.bocci@alcatel-lucent.com

Luca Martini
Cisco Systems
9155 East Nichols Avenue, Suite 400
Englewood, Colorado 80112
USA

Email:
United States

EMail: lmartini@cisco.com