Internet DRAFT - draft-ietf-pwe3-mspw-er
draft-ietf-pwe3-mspw-er
Network Working Group P. Dutta
Internet-Draft M. Bocci
Intended status: Standards Track Alcatel-Lucent
Expires: March 14, 2015 L. Martini
Cisco Systems
September 10, 2014
Explicit Path Routing for Dynamic Multi-Segment Pseudowires
draft-ietf-pwe3-mspw-er-06
Abstract
Dynamic Multi-Segment Pseudowire (MS-PW) setup through an explicit
path 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. 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 of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents 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.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
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
3.4. 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
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 . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Procedures for dynamically establishing 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)
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 Terminating 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 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
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from a management application. How that management application
determines the explicit route is outside the scope of this document.
2. Terminology
This document uses the terminology defined in [RFC7267], [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 or S-PE address.
3. Explicit Path in MS-PW Signaling
This section describes the LDP (Label Distribution Protocol)
extensions required for signaling explicit paths in dynamic MS-PW
set-up messages. An explicitly routed MS-PW is set up using a Label
Mapping message that carries an ordered list of the S-PEs which the
MS-PW is expected to traverse. The ordered list is encoded as a
series of Explicit Route (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 that may be used by an MS-PW. Each S-PE
MUST be assigned an address as specified in [RFC7267] Section 3.2.
An S-PE that is capable of dynamic 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]
Section 3.2.
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 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 TLVs (ER-Hop TLVs)
defined in Section 3.3.
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3.3. Explicit Route Hop TLV (ER-Hop TLV)
The contents of an ER-TLV are a series of variable length ER-Hop
TLVs. Each hop contains the identification of an "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 ER-Hop TLV Types: IPv4 Prefix, IPv6 Prefix,
and Autonomous System. This document specifies the following new ER-
Hop TLV Type:
Value Type
------ ------------------------
0x0805 L2 PW address of PW Switching Point
ER-Hop TLV
Details of ER Hop semantics are defined in Section 3.4.
3.4. ER-Hop Semantics
This section describes the various semantics associated with ER-Hop
TLV.
3.4.1. ER-Hop Type: IPv4 Prefix
The semantics of the IPv4 ER-Hop TLV Type are specified in [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]
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 AII type 2
defined in [RFC5003], are 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| 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
Length
Specifies the length of the value field in bytes = 18.
L Bit
Set to indicate 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 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].
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4. Explicit Route TLV Processing
4.1. Next-Hop Selection
A PW Label Mapping Message containing an 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 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] 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 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 path, then the received Label Mapping 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 that contains an ER-
TLV MUST evaluate the first ER Hop. If the L bit is not set in
the first ER Hop and if the node is not part of the abstract node
described by the first 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 with a "Bad Initial 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, the node selects a next hop that is along the path
to the abstract node described by the first ER Hop. If there is
no ER-Hop TLV contained in the ER-TLV, the message is also in
error and the node SHOULD return a "Bad Explicit Routing TLV
Error" (0x04000001) status code in a Label Release Message sent
to upstream node. Note that this statement does not preclude a
Label 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].
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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 TLV MAY be added
to the Label Mapping Message.
3. If a second 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 into the first 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. That is, it is
directly connected to the next node by a PW control plane
adjacency. If so, the node selects a particular next hop which
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 that is along the path to the abstract node of the
second ER Hop. If no such path exists then there are two cases:
A. If the second ER Hop is a strict ER Hop, then there is an
error and the node MUST return a Label Release Message to
upstream node with "Bad Strict Node Error" (0x04000002)
status code.
B. Otherwise, if the second 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 to upstream node with "Bad Loose Node Error"
(0x04000003) status code.
6. Finally, the node replaces the first 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 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.
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If, as part of executing the algorithm in Section 4.1, the explicit
route TLV is removed, the node MAY add a new 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 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 [RFC5036] defines the LDP TLV name space which is maintained
by IANA as "LDP TLV Registry". TLV types for the Explicit Route TLV,
IPv4 Prefix ER-Hop TLV, and the IPv6 Prefix ER-Hop TLV are already
defined in the LDP TLV Registry.
IANA is requested to assign 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 This Document
A value of 0x0805 is requested.
6. Security Considerations
This document introduces no new security considerations over
[RFC5036], [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.
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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.
[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.
[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.
[RFC5003] Metz, C., Martini, L., Balus, F., and J. Sugimoto,
"Attachment Individual Identifier (AII) Types for
Aggregation", RFC 5003, September 2007.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011.
[RFC7267] Martini, L., Bocci, M., and F. Balus, "Dynamic Placement
of Multi-Segment Pseudowires", RFC 7267, June 2014.
Authors' Addresses
Pranjal Kumar Dutta
Alcatel-Lucent
701 E Middlefield Road
Mountain View, California 94043
USA
Email: pranjal.dutta@alcatel-lucent.com
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Matthew Bocci
Alcatel-Lucent
Voyager Place, Shoppenhangers Road
Maidenhead, Berks SL6 2PJ
UK
Email: matthew.bocci@alcatel-lucent.com
Luca Martini
Cisco Systems
9155 East Nichols Avenue, Suite 400
Englewood, Colorado 80112
USA
Email: lmartini@cisco.com
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