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IETF RFC 5252
OSPF-Based Layer 1 VPN Auto-Discovery
Last modified on Monday, June 30th, 2008
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Network Working Group I. Bryskin
Request for Comments: 5252 ADVA Optical Networking
Category: Standards Track L. Berger
LabN Consulting, LLC
July 2008
OSPF-Based Layer 1 VPN Auto-Discovery
 Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document defines an Open Shortest Path First (OSPF) based Layer
1 Virtual Private Network (L1VPN) auto-discovery mechanism. This
mechanism enables provider edge (PE) devices using OSPF to
dynamically learn about the existence of each other, and attributes
of configured customer edge (CE) links and their associations with
L1VPNs. This document builds on the L1VPN framework and requirements
and provides a L1VPN basic mode auto-discovery mechanism.
Table of Contents
1. Introduction ....................................................2
1.1. Overview ...................................................2
1.2. Terminology ................................................3
1.3. Conventions Used in This Document ..........................4
2. L1VPN LSA and Its TLVs ..........................................4
2.1. L1VPN LSA ..................................................4
2.2. L1VPN INFO TLV .............................................6
3. L1VPN LSA Advertising and Processing ............................7
3.1. Discussion and Example .....................................7
4. Backward Compatibility ..........................................8
5. Security Considerations .........................................9
6. IANA Considerations .............................................9
7. Acknowledgments .................................................9
8. References ......................................................9
8.1. Normative References .......................................9
8.2. Informative References ....................................10
Bryskin & Berger Standards Track PAGE 1 
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
1. Introduction
1.1. Overview
The framework for Layer 1 VPNs is described in [RFC 4847]. Basic mode
operation is further defined in [RFC 5251]. The L1VPN Basic Mode
(L1VPN-BM) document [RFC 5251] identifies the information that is
necessary to map customer information (ports identifiers) to provider
information (identifiers). It also states that this mapping
information may be provided via provisioning or via an auto-discovery
mechanism. This document provides such an auto-discovery mechanism
using Open Shortest Path First (OSPF) version 2. Use of OSPF version
3 and support for IPv6 are out of scope of this document and will be
defined separately.
Figure 1 shows the L1VPN basic service being supported using OSPF-
based L1VPN auto-discovery. This figure shows two PE routers
interconnected over a GMPLS backbone. Each PE is attached to three
CE devices belonging to three different L1VPN connections. In this
network, OSPF is used to provide the VPN membership, port mapping,
and related information required to support basic mode operation.
PE PE
+---------+ +--------------+
+--------+ | +------+| | +----------+ | +--------+
| VPN-A | | |VPN-A || | | VPN-A | | | VPN-A |
| CE1 |--| |PIT || OSPF LSAs | | PIT | |-| CE2 |
+--------+ | | ||<----------->| | | | +--------+
| +------+| Distribution| +----------+ |
| | | |
+--------+ | +------+| | +----------+ | +--------+
| VPN-B | | |VPN-B || ------- | | VPN-B | | | VPN-B |
| CE1 |--| |PIT ||--( GMPLS )--| | PIT | |-| CE2 |
+--------+ | | || (Backbone) | | | | +--------+
| +------+| -------- | +----------+ |
| | | |
+--------+ | +-----+ | | +----------+ | +--------+
| VPN-C | | |VPN-C| | | | VPN-C | | | VPN-C |
| CE1 |--| |PIT | | | | PIT | |-| CE2 |
+--------+ | | | | | | | | +--------+
| +-----+ | | +----------+ |
+---------+ +--------------+
Figure 1: OSPF Auto-Discovery for L1VPNs
See [RFC 5195] for a parallel L1VPN auto-discovery that uses BGP. The
OSPF approach described in this document is particularly useful in
networks where BGP is not typically used.
Bryskin & Berger Standards Track PAGE 2
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
The approach used in this document to provide OSPF-based L1VPN auto-
discovery uses a new type of Opaque Link State Advertisement (LSA)
that is referred to as an L1VPN LSA. The L1VPN LSA carries
information in TLV (type, length, value) structures. An L1VPN-
specific TLV is defined below to propagate VPN membership and port
information. This TLV is referred to as the L1VPN Info TLV. The
L1VPN LSA may also carry Traffic Engineering (TE) TLVs; see [RFC 3630]
and [RFC 4203].
1.2. Terminology
The reader of this document should be familiar with the terms used in
[RFC 4847] and [RFC 5251]. The reader of this document should also be
familiar with [RFC 2328], [RFC 5250], and [RFC 3630]. In particular,
the following terms:
L1VPN - Layer 1 Virtual Private Network
CE - Customer (edge) network element directly connected to the
provider network (terminates one or more links to one or more
PEs); it is also connected to one or more Cs and/or other CEs
C - Customer network element that is not connected to the provider
network but is connected to one or more other Cs and/or CEs
PE - Provider (edge) network element directly connected to one or
more customer networks (terminates one or more links to one or
more CEs associated with the same or different L1VPNs); it is
also connected to one or more Ps and/or other PEs
P - Provider (core) network element that is not directly connected to
any customer networks; P is connected to one or more other Ps
and/or PEs
LSA - OSPF link State Advertisement
LSDB - Link State Database: a data structure supported by an IGP
speaker
PIT - Port Information Table
CPI - Customer Port Identifier
PPI - Provider Port Identifier
Bryskin & Berger Standards Track PAGE 3
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
1.3. Conventions Used in This Document
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. L1VPN LSA and Its TLVs
This section defines the L1VPN LSA and its TLVs.
2.1. L1VPN LSA
The format of a L1VPN LSA 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Type | Opaque ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L1VPN Info TLV |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Link TLV |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LS age
As defined in [RFC 2328].
Options
As defined in [RFC 2328].
LS Type
This field MUST be set to 11, i.e., an Autonomous System (AS)
scoped Opaque LSA [RFC 5250].
Opaque Type
The value of this field MUST be set to 5.
Bryskin & Berger Standards Track PAGE 4
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
Opaque ID
As defined in [RFC 5250].
Advertising Router
As defined in [RFC 2328].
LS Sequence Number
As defined in [RFC 2328].
LS checksum
As defined in [RFC 2328].
Length
As defined in [RFC 2328].
L1VPN Info TLV
A single TLV, as defined in Section 3.2, MUST be present. If more
than one L1VPN Info TLV is present, only the first TLV is
processed and the others MUST be ignored on receipt.
TE Link TLV
A single TE Link TLV (as defined in [RFC 3630] and [RFC 4203]) MAY
be included in a L1VPN LSA.
Bryskin & Berger Standards Track PAGE 5
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
2.2. L1VPN INFO TLV
The following TLV is introduced:
Name: L1VPN IPv4 Info
Type: 1
Length: Variable
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L1VPN TLV Type | L1VPN TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L1VPN Globally Unique Identifier |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PE TE Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Local Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
| L1VPN Auto-Discovery Information |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L1VPN TLV Type
The type of the TLV.
TLV Length
The length of the TLV in bytes, excluding the 4 bytes of the TLV
header and, if present, the length of the Padding field.
L1VPN Globally Unique Identifier
As defined in [RFC 5251].
PE TE Address
This field MUST carry an address that has been advertised by the
LSA originator per [RFC 3630] and is either the Router Address TLV
or Local interface IP address link sub-TLV. It will typically
carry the TE Router Address.
Link Local Identifier
This field is used to support unnumbered links. When an
unnumbered PE TE link is represented, this field MUST contain a
value advertised by the LSA originator per [RFC 4203] in a Link
Local/Remote Identifiers link sub-TLV. When a numbered link is
represented, this field MUST be set to 0.
Bryskin & Berger Standards Track PAGE 6
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
L1VPN Auto-discovery information
As defined in [RFC 5251].
Padding
A field of variable length and of sufficient size to ensure that
the TLV is aligned on a 4-byte boundary. This field is only
required when the L1VPN Auto-discovery information field is not
4-byte aligned. This field MUST be less than 4 bytes long, and
MUST NOT be present when the size of the L1VPN Auto-discovery
information field is 4-byte aligned.
3. L1VPN LSA Advertising and Processing
PEs advertise local <CPI, PPI> tuples in L1VPN LSAs containing L1VPN
Info TLVs. Each PE MUST originate a separate L1VPN LSA with AS
flooding scope for each local CE-to-PE link. The LSA MUST be
originated each time a PE restarts and every time there is a change
in the PIT entry associated with a local CE-to-PE link. The LSA MUST
include a single L1VPN Info TLV and MAY include a single TE Link TLV
as per [RFC 3630] and [RFC 4203]. The TE Link TLV carries TE
attributes of the associated CE-to-PE link. Note that because CEs
are outside of the provider TE domain, the attributes of CE-to-PE
links are not advertised via normal OSPF-TE procedures as described
in [RFC 3630] and [RFC 4203]. If more than one L1VPN Info TLVs and/or
TE Link TLVs are found in the LSA, the subsequent TLVs SHOULD be
ignored by the receiving PEs.
L1VPN LSAs are of AS-scope (LS type is set to 11) and therefore are
flooded to all PEs within the AS according to [RFC 5250]. Every time
a PE receives a new, removed, or modified L1VPN LSA, the PE MUST
check whether it maintains a PIT associated with the L1VPN specified
in the L1VPN globally unique identifier field. If this is the case
(the appropriate PIT will be found if one or more local CE-to-PE
links that belong to the L1VPN are configured), the PE SHOULD add,
remove, or modify the PIT entry associated with each of the
advertised CE-to-PE links accordingly. (An implementation MAY choose
to not remove or modify the PIT according to local policy or
management directives.) Thus, in the normal steady-state case, all
PEs associated with a particular L1VPN will have identical local PITs
for an L1VPN.
3.1. Discussion and Example
The L1VPN auto-discovery mechanism described in this document does
not prevent a PE from applying any local policy with respect to PIT
management. An example of such a local policy would be the ability
to configure permanent (static) PIT entries. Another example would
Bryskin & Berger Standards Track PAGE 7
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
be the ability to ignore information carried in L1VPN LSAs advertised
by a specific TE.
The reason why it is required that the value specified in the PE TE
Address field of the L1VPN Info TLV matches a valid PE TE Router ID
or numbered TE Link ID is to ensure that CEs attached to this PE can
be resolved to the PE as it is known to the Traffic Engineering
Database (TED) and hence TE paths toward the CEs across the provider
domain can be computed.
Let us consider the example presented in Figure 2.
CE11 CE13
| |
CE22---PE1--------P------PE2
| |
CE15 PE3
|
CE24
Figure 2: Single Area Configuration
Let us assume that PE1 is connected to CE11 and CE15 in L1VPN1 and to
CE22 in L1VPN2; PE2 is connected to CE13 in L1VPN1; PE3 is connected
to CE24 in L1VPN2. In this configuration PE1 manages two PITs: PIT1
for L1VPN1 and PIT2 for L1VPN2; PE2 manages only PIT1; and PE3
manages only PIT2. PE1 originates three L1VPN LSAs, each containing
a L1VPN Info TLV advertising links PE1-CE11, PE1-CE22, and PE1-CE15,
respectively. PE2 originates a single L1VPN LSA for link PE2-CE13,
and PE3 originates a single L1VPN LSA for link PE3-CE24. In steady
state, the PIT1 on PE1 and PE3 will contain information on links
PE1-CE11, PE1-CE15, and PE2-CE13; PIT2 on PE1 and PE2 will contain
entries for links PE1-CE22 and PE3-CE24. Thus, all PEs will learn
about all remote PE-to-CE links for all L1VPNs supported by PEs.
Note that P in this configuration does not have links connecting it
to any L1VPNs. It neither originates L1VPN LSAs nor maintains any
PITs. However, it does participate in the flooding of all of the
L1VPN LSAs and hence maintains the LSAs in its LSDB. This is a cause
for scalability concerns and could prove to be problematic in large
networks.
4. Backward Compatibility
Neither the TLV nor the LSA introduced in this document present any
interoperability issues. Per [RFC 5250], OSPF speakers that do not
support the L1VPN auto-discovery application (Ps for example) just
Bryskin & Berger Standards Track PAGE 8
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
participate in the L1VPN LSAs flooding process but should ignore the
LSAs contents.
5. Security Considerations
The approach presented in this document describes how PEs dynamically
learn L1VPN-specific information. Mechanisms to deliver the VPN
membership information to CEs are explicitly out of scope of this
document. Therefore, the security issues raised in this document are
limited to within the OSPF domain.
This defined approach reuses mechanisms defined in [RFC 2328] and
[RFC 5250]. Therefore, the same security approaches and
considerations apply to this approach. OSPF provides several
security mechanisms that can be applied. Specifically, OSPF supports
multiple types of authentication, limits the frequency of LSA
origination and acceptance, and provides techniques to avoid and
limit impact database overflow. In cases where end-to-end
authentication is desired, OSPF's neighbor-to-neighbor authentication
approach can be augmented with an experimental extension to OSPF; see
[RFC 2154], which supports the signing and authentication of LSAs.
6. IANA Considerations
This document requests the assignment of an OSPF Opaque LSA type.
IANA has made the assignment in the form:
Value Opaque Type Reference
------- ----------- ---------
5 L1VPN LSA [RFC 5252]
7. Acknowledgments
We would like to thank Adrian Farrel and Anton Smirnov for their
useful comments.
8. References
8.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC 3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
Bryskin & Berger Standards Track PAGE 9
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
[RFC 4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC 5250] Berger, L., Bryskin, I., and A. Zinin, "The OSPF Opaque
LSA Option", RFC 5250, July 2008.
[RFC 5251] Fedyk, D., Ed., Rekhter, Y., Ed., Papadimitriou, D.,
Rabbat, R., and L. Berger, "Layer 1 VPN Basic Mode", RFC
5251, July 2008.
8.2. Informative References
[RFC 2154] Murphy, S., Badger, M., and B. Wellington, "OSPF with
Digital Signatures", RFC 2154, June 1997.
[RFC 4847] Takeda, T., Ed., "Framework and Requirements for Layer 1
Virtual Private Networks", RFC 4847, April 2007.
[RFC 5195] Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP-Based
Auto-Discovery for Layer-1 VPNs", RFC 5195, June 2008.
Authors' Addresses
Igor Bryskin
ADVA Optical Networking Inc
7926 Jones Branch Drive
Suite 615
McLean, VA 22102
EMail: ibryskin@advaoptical.com
Lou Berger
LabN Consulting, LLC
EMail: lberger@labn.net
Bryskin & Berger Standards Track PAGE 10
RFC 5252 OSPF-Based L1VPN Auto-Discovery July 2008
Full Copyright Statement
Copyright © The IETF Trust (2008).
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
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OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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Bryskin & Berger Standards Track PAGE 11
OSPF-Based Layer 1 VPN Auto-Discovery
RFC TOTAL SIZE: 23232 bytes
PUBLICATION DATE: Monday, June 30th, 2008
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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