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IETF RFC 5251
Layer 1 VPN Basic Mode
Last modified on Monday, June 30th, 2008
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Network Working Group D. Fedyk, Ed.
Request for Comments: 5251 Nortel
Category: Standards Track Y. Rekhter, Ed.
Juniper Networks
D. Papadimitriou
Alcatel-Lucent
R. Rabbat
Google
L. Berger
LabN
July 2008
Layer 1 VPN Basic Mode
 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 describes the Basic Mode of Layer 1 VPNs (L1VPNs).
L1VPN Basic Mode (L1VPN BM) is a port-based VPN. In L1VPN Basic
Mode, the basic unit of service is a Label Switched Path (LSP)
between a pair of customer ports within a given VPN port topology.
This document defines the operational model using either provisioning
or a VPN auto-discovery mechanism, and the signaling extensions for
the L1VPN BM.
Fedyk, et al. Standards Track PAGE 1 
RFC 5251 L1VPN Basic Mode July 2008
Table of Contents
1. Introduction ....................................................3
1.1. Conventions Used in This Document ..........................4
2. Layer 1 VPN Service .............................................4
3. Addressing, Ports, Links, and Control Channels ..................7
3.1. Service Provider Realm .....................................7
3.2. Layer 1 Ports and Index ....................................7
3.3. Port and Index Mapping .....................................8
4. Port-Based L1VPN Basic Mode ....................................10
4.1. L1VPN Port Information Tables .............................11
4.1.1. Local Auto-Discovery Information ...................12
4.1.2. PE Remote Auto-Discovery Information ...............12
4.2. CE-to-CE LSP Establishment ................................14
4.3. Signaling .................................................15
4.3.1. Signaling Procedures ...............................15
4.3.1.1. Shuffling Sessions ........................16
4.3.1.2. Stitched or Nested Sessions ...............17
4.3.1.3. Other Signaling ...........................18
4.4. Recovery Procedures .......................................19
5. Security Considerations ........................................20
6. References .....................................................21
6.1. Normative References ......................................21
6.2. Informative References ....................................22
7. Acknowledgments ................................................23
Fedyk, et al. Standards Track PAGE 2
RFC 5251 L1VPN Basic Mode July 2008
1. Introduction
This document describes the Basic Mode of Layer 1 VPNs (L1VPN BM)
that is outlined in [RFC 4847]. The applicability of Layer 1 VPNS is
covered in [RFC 5253]. In this document, we consider a layer 1
service provider network that consists of devices that support GMPLS
(e.g., Lambda Switch Capable (LSC) devices, optical cross-connects,
Synchronous Optical Network / Synchronous Digital Hierarchy
(SONET/SDH) cross-connects, etc.). We partition these devices into P
(provider) and PE (provider edge) devices. In the context of this
document we will refer to the former devices as just "P", and to the
latter devices as just "PE". The Ps are connected only to the
devices within the provider's network. The PEs are connected to the
other devices within the network (either Ps or PEs), as well as to
the devices outside of the service provider network. We'll refer to
such other devices as Customer Edge (CE) devices. An example of a CE
would be a GMPLS-enabled device that is either a router, an SDH
cross-connect, or an Ethernet switch.
[RFC 4208] defines signaling from the CE to the PE. In [RFC 4208], the
term "Core Node (CN)" corresponds to P and PE nodes, and the term
"Edge Node (EN)" corresponds to CE nodes. We additionally define an
"edge Core Node" corresponding to a PE.
Figure 1 illustrates the components in an L1VPN network.
+---+ +---+
| P |....| P |
+---+ +---+
/ \
+-----+ +-----+ +--+
+--+ | PE | | |----| |
|CE|----| | | | |CE|
+--+\ +-----+ | |----| |
\ | | PE | +--+
\ +-----+ | |
\| PE | | | +--+
| | | |----|CE|
+-----+ +-----+ +--+
\ /
+---+ +---+
| P |....| P |
+---+ +---+
Figure 1: Generalized Layer 1 VPN Reference Model
Fedyk, et al. Standards Track PAGE 3
RFC 5251 L1VPN Basic Mode July 2008
This document specifies how the L1VPN Basic Mode service can be
realized using off-line provisioning or VPN auto-discovery,
Generalized Multi-Protocol Label Switching (GMPLS) Signaling
[RFC 3471], [RFC 3473], Routing [RFC 4202], and LMP [RFC 4204]
mechanisms.
L1VPN auto-discovery has similar requirements [RFC 4847] to L3VPN
auto-discovery. As with L3VPNs, there are protocol choices to be
made with auto-discovery. Section 4.1.1 deals with the information
that needs to be discovered.
GMPLS routing and signaling are used without extensions within the
service provider network to establish and maintain LSC or SONET/SDH
(Time Division Multiplexing (TDM)) connections between service
provider nodes. This follows the model in [RFC 4208].
In L1VPN Basic Mode, the use of LMP facilitates the population of the
Port Information Tables of the service provider. Indeed, LMP MAY be
used as an option to automate local CE-to-PE link discovery. LMP
also MAY augment routing (in enhanced mode) as well as failure
handling capabilities.
Consideration of inter-AS and inter-provider L1VPNs requires further
analysis beyond the scope of this document.
1.1. 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].
This document expects that the reader is familiar with the
terminology defined and used in [RFC 3945], [RFC 3471], [RFC 3473],
[RFC 3477], [RFC 4201], [RFC 4202], [RFC 4204], [RFC 4208], and the
documents referenced therein.
2. Layer 1 VPN Service
Layer 1 VPN services on the interfaces of customer and service
provider ports MAY be any of the Layer 1 interfaces supported by
GMPLS. Since the mechanisms specified in this document use GMPLS as
the signaling mechanism, and since GMPLS applies to both SONET/SDH
(TDM) and LSC interfaces, it follows that L1VPN services include (but
are not restricted) to LSC- or TDM-based equipment. Note that this
document describes Basic Mode L1VPNs and as such requires that:
Fedyk, et al. Standards Track PAGE 4
RFC 5251 L1VPN Basic Mode July 2008
(1) GMPLS RSVP-TE is used for signaling both within the service
provider (between PEs), as well as between the customer and the
service provider (between CE and PE);
(2) GMPLS Routing on the CE-to-PE link is outside the scope of the
Basic Mode of operation of L1VPN; see [RFC 4847].
A CE is connected to a PE via one or more links. In the context of
this document, a link is a GMPLS Traffic Engineering (TE) link
construct, as defined in [RFC 4202]. In the context of this document,
a TE link is a logical construct that is a member of a VPN, hence
introducing the notion of membership to a set of CEs forming the VPN.
Interfaces at the end of each link are limited to either TDM or LSC
as supported by GMPLS. More specifically, a <CE, PE> link MUST be of
the type <X, LSC> or <Y, TDM> where X = PSC (Packet Switch Capable),
L2SC (Layer 2 Switch Capable), or TDM and Y = PSC or L2SC. In case
the LSP is not terminated by the CE, X MAY also = LSC and Y = TDM.
One of the applications of a L1VPN connection is to provide a
"virtual private lambda" or similar. In this case, the CE is truly
the endpoint in GMPLS terms, and its switching capability on the TE
link is not relevant (although its Generalized Protocol Identifier
(GPID) MUST be signaled and identical at both CEs, i.e., head-end and
tail-end CE).
Likewise, PEs could be any Layer 1 devices that are supported by
GMPLS (e.g., optical cross-connects, SDH cross-connects), while CEs
MAY be devices at layers 1, 2, and 3, such as an SDH cross-connect,
an Ethernet switch, and a router, respectively).
Each TE link MAY consist of one or more channels or sub-channels
(e.g., wavelength or wavelength and timeslot, respectively). For the
purpose of this discussion, all the channels within a given link MUST
have similar shared characteristics (e.g., switching capability,
encoding, type, etc.), and MAY be selected independently from the
CE's point of view. Channels on different links of a CE need not
have the same characteristics.
There MAY be more than one TE link between a given CE-PE pair. A CE
MAY be connected to more than one PE (with at least one port per PE).
And, conversely, a PE MAY have more than one CE from different VPNs
connected to it.
If a CE is connected to a PE via multiple TE links and all the links
belong to the same VPN, these links (referred to as component links)
MAY be treated as a single TE link using the link bundling constructs
[RFC 4201].
Fedyk, et al. Standards Track PAGE 5
RFC 5251 L1VPN Basic Mode July 2008
In order to satisfy the requirements of the L1VPN Basic Mode, it is
REQUIRED that for a given CE-PE pair at least one of the links
between them has at least one data bearing channel, and at least one
control bearing channel, or that there is IP reachability between the
CE and the PE that could be used to exchange control information.
A point-to-point link has two end-points: one on the CE and one on
the PE. This document refers to the former as "CE port", and to the
latter as "PE port". From the above, it follows that a CE is
connected to a PE via one or more ports, where each port MAY consist
of one or more channels or sub-channels (e.g., wavelength or
wavelength and timeslot, respectively), and all the channels within a
given port have shared similar characteristics and can be
interchanged from the CE's point of view. Similar to the definition
of a TE link, in the context of this document, ports are logical
constructs that are used to represent a grouping of physical
resources that are used to connect a CE to a PE on a per-L1VPN basis.
At any point in time, a given port on a PE is associated with at most
one L1VPN, or, to be more precise, with at most one Port Information
Table maintained by the PE (although different ports on a given PE
could be associated with different L1VPNs, or, to be more precise,
with different Port Information Tables). The association of a port
with a VPN MAY be defined by provisioning the relationship on the
service provider devices. In other words, the context of a VPN
membership in Basic Mode is enforced through service provider
control.
It is REQUIRED that the interface (that is between the CE and PE and
that is used for the purpose of signaling) be capable of
initiating/processing GMPLS protocol messages [RFC 3473] and of
following the procedures described in [RFC 4208].
An important goal of L1VPN service is the ability to support what is
known as "single-ended provisioning", where the addition of a new
port to a given L1VPN involves configuration changes only on the PE
that has this port. The extension of this model to the CE is outside
the scope of the L1VPN BM.
Another important goal in the L1VPN service is the ability to
establish/terminate an LSP between a pair of (existing) ports within
an L1VPN from the CE devices without involving configuration changes
in any of the service provider's devices. In other words, the VPN
topology is under the CE device control (assuming that the underlying
PE-to-PE connectivity is provided and allowed by the network).
Fedyk, et al. Standards Track PAGE 6
RFC 5251 L1VPN Basic Mode July 2008
The mechanisms outlined in this document aim to achieve the above
goals. Specifically, as part of the L1VPN service offering, these
mechanisms (1) enable the service provider to restrict the set of
ports to which a given port could be connected and (2) enable a CE to
establish the actual LSP to a subset of ports. Finally, the
mechanisms allow arbitrary L1VPN topologies to be supported;
including topologies ranging from hub-and-spoke to full mesh point-
to-point connections. Only point-to-point links are supported.
The exchange of CE routing or topology information to the service
provider is out of scope for L1VPN BM mode.
3. Addressing, Ports, Links, and Control Channels
GMPLS-established conventions for addressing and link numbering are
discussed in [RFC 3945]. This section builds on those definitions for
the L1VPN case where we now have customer and service provider
addresses in a Layer 1 context.
3.1. Service Provider Realm
It is REQUIRED that a service provider, or a group of service
providers that collectively offer L1VPN service, have a single
addressing realm that spans all PE devices involved in providing the
L1VPN service. This is necessary to enable GMPLS mechanisms for path
establishment and maintenance. We will refer to this realm as the
service provider addressing realm. It is further REQUIRED that each
L1VPN customer have its own addressing realm with complete freedom to
use private or public addresses. We will refer to such realms as the
customer addressing realms. Customer addressing realms MAY overlap
addresses (i.e., non-unique address) with each other, and MAY also
overlap addresses with the service provider realm.
3.2. Layer 1 Ports and Index
Within a given L1VPN, each port on a CE that connects the CE to a PE
has an identifier that is unique within that L1VPN (but need not be
unique across several L1VPNs). One way to construct such an
identifier is to assign each port an address that is unique within a
given L1VPN, and use this address as a port identifier. Another way
to construct such an identifier is to assign each port on a CE an
index that is unique within that CE, assign each CE an address that
is unique within a given L1VPN, and then use a tuple <port index, CE
address> as a port identifier. Note that both the port and the CE
address MAY be an address in several formats. This includes, but is
not limited to, IPv4 and IPv6. This identifier is part of the
Fedyk, et al. Standards Track PAGE 7
RFC 5251 L1VPN Basic Mode July 2008
Customer addressing Realm and is used by the CE device to identify
the CE port and the CE remote port for signaling. CEs do not know or
understand the service provider realm addresses.
Within a service provider network, each port on a PE that connects
that PE to a CE has an identifier that is unique within that network.
One way to construct such an identifier is to assign each port on a
PE an index that is unique within that PE, assign each PE an IP
address that is unique within the service provider addressing realm,
and then use a tuple <port index, PE IPv4 address> or <port index, PE
IPv6 address> as a port identifier within the service provider
network. Another way to construct such an identifier is to assign an
IPv4 or IPv6 address that is unique within the service provider
addressing realm to each such port. Either way, this IPv4 or IPv6
address is internal to the service provider network and is used for
GMPLS signaling within the service provider network.
As a result, each link connecting the CE to the PE is associated with
a CE port that has a unique identifier within a given L1VPN, and with
a PE port that has a unique identifier within the service provider
network. We'll refer to the former as the Customer Port Identifier
(CPI), and to the latter as the Provider Port Identifier (PPI).
3.3. Port and Index Mapping
This document requires that each PE port that has a PPI also has an
identifier that is unique within the L1VPN customer addressing realm
of the L1VPN associated with that port. One way to construct such an
identifier is to assign each port an address that is unique within a
given L1VPN customer addressing realm, and use this address as a port
identifier. Another way to construct such an identifier is to assign
each port an index that is unique within a given PE, assign each PE
an IP address that is unique within a given L1VPN customer addressing
realm (but need not be unique within the service provider network),
and then use a tuple <port index, PE IP address> that acts as a port
identifier. We'll refer to such port identifier as the VPN-PPI. See
Figure 2.
For L1VPNs, it is a requirement that service provider operations are
independent of the VPN customer's addressing realm and the service
provider addressing realm is hidden from the customer. To achieve
this, we define two identifiers at the PE, one customer facing and
the other service provider facing. The PE IP address used for the
VPN-PPI is independent of the PE IP address used for the PPI (as the
two are taken from different address realms, the former from the
customer's addressing realm and the latter from a VPN service
provider's addressing realm). If for a given port on a PE, the PPI
Fedyk, et al. Standards Track PAGE 8
RFC 5251 L1VPN Basic Mode July 2008
and the VPN-PPI port identifiers are unnumbered, then they both could
use exactly the same port index. This is a mere convenience since
the PPI and VPN_PPI can be in any combination of valid formats.
(Customer realm)
+----+ +----+
| |<Port Index> <Port Index> | |
| |CPI VPN-PPI | |
---| CE |-----------------------------| PE |---
| | <Port Index> | |
| | PPI | |
+----+ +----+
(Provider realm)
Figure 2: Customer/Provider Port/Index Mapping
Note, as stated earlier, that IP addresses used for the CPIs, PPIs,
and VPN-PPIs could be either IPv4 or IPv6 format addresses.
For a given link connecting a CE to a PE:
- If the CPI is an IPv4 address, then the VPN-PPI MUST be an IPv4
address as well since VPN-PPIs are created from the customer
address space. If the CPI is a <port index, CPI IPv4 address>
tuple, then the VPN-PPI MUST be a <port index, PE IPv4 address>
tuple for the same reason.
- If the CPI is an IPv6 address, then the VPN-PPI MUST be an IPv6
address as well since VPN-PPIs are created from the customer
address space. If the CPI is a <port index, CPI IPv6 address>
tuple, then the VPN-PPI MUST be a <port index, PE IPv6 address>
tuple for the same reason.
Note: for a given port on the PE, whether the VPN-PPI of that port is
an IP address or a <port index, PE IP address> is independent of the
format of the PPI of that port.
This document assumes that assignment of the PPIs is controlled
solely by the service provider (without any coordination with the
L1VPN customers), while assignment of addresses used by the CPIs and
VPN-PPIs is controlled solely by the administrators of L1VPN. This
provides maximum flexibility. The L1VPN administrator is the entity
that controls the L1VPN service specifics for the L1VPN customers.
This function may be owned by the service provider but may also be
performed by a third party who has agreements with the service
provider. And, of course, each L1VPN customer could assign such
addresses on its own, without any coordination with other L1VPNs.
Fedyk, et al. Standards Track PAGE 9
RFC 5251 L1VPN Basic Mode July 2008
This document also requires IP connectivity between the CE and the PE
as specified earlier, which is used for the control channel between
CE and PE. This connectivity could be either a single IP hop, which
could be realized by either a dedicated link or by an L2 VPN, or an
IP private network, such as an L3VPN. The only requirement on this
connectivity is an unambiguous way to correlate a particular CE-to-PE
control channel with a particular L1VPN. When such a channel is
realized by a dedicated link, such a link should be associated with a
particular L1VPN. When such channel is realized by an L2VPN, a
distinct L2VPN should be associated with an L1VPN. When such channel
is realized by an L3VPN, a distinct L3VPN should be associated with
an L1VPN.
We'll refer to the CE's address of this channel as the CE Control
Channel Address (CE-CC-Addr), and to the PE's address of this channel
as the PE Control Channel Address (PE-CC-Addr). Both CE-CC-Addr and
PE-CC-Addr are REQUIRED to be unique within the L1VPN they belong to,
but are not REQUIRED to be unique across multiple L1VPNs. Control
channel addresses are not shared amongst multiple VPNs. Assignment
of CE-CC-Addr and PE-CC-Addr is controlled by the administrators of
the L1VPN.
Multiple ports on a CE could share the same control channel only as
long as all these ports belong to the same L1VPN. Likewise, multiple
ports on a PE could share the same control channel only as long as
all these ports belong to the same L1VPN.
4. Port-Based L1VPN Basic Mode
An L1VPN is a port-based VPN service where a pair of CEs could be
connected through the service provider network via a GMPLS-based LSP
within a given VPN port topology. It is precisely this LSP that
forms the basic unit of the L1VPN service that the service provider
network offers. If a port by which a CE is connected to a PE
consists of multiple channels (e.g., multiple wavelengths), the CE
could establish LSPs to multiple other CEs in the same VPN over this
single port.
In the L1VPN, the service provider does not initiate the creation of
an LSP between a pair of CE ports. The LSP establishment is
initiated by the CE. However, the SP, by using the
mechanisms/toolkit outlined in this document, restricts the set of
other CE ports, which may be the remote endpoints of LSPs that have
the given port as the local endpoint. Subject to these restrictions,
the CE-to-CE connectivity is under the control of the CEs themselves.
In other words, the SP allows a L1VPN to have a certain set of
Fedyk, et al. Standards Track PAGE 10
RFC 5251 L1VPN Basic Mode July 2008
topologies (expressed as a port-to-port connectivity matrix).
CE-initiated signaling is used to choose a particular topology from
that set.
For each L1VPN that has at least one port on a given PE, the PE
maintains a Port Information Table (PIT) associated with that L1VPN.
This table contains a list of <CPI, PPI> tuples for all the ports
within its L1VPN. In addition, for local PE ports of a given L1VPN,
the tuples also include the VPN-PPIs of these ports.
PE PE
+---------+ +--------------+
+--------+ | +------+| | +----------+ | +--------+
| VPN-A | | |VPN-A || | | VPN-A | | | VPN-A |
| CE1 |--| |PIT || Route | | PIT | |-| CE2 |
+--------+ | | ||<----------->| | | | +--------+
| +------+|Dissemination| +----------+ |
| | | |
+--------+ | +------+| | +----------+ | +--------+
| 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 3: Basic Mode L1VPN Service
4.1. L1VPN Port Information Tables
Figure 3 illustrates three VPNs, VPN-A, VPN-B, and VPN-C, with their
associated PITs. A PIT consists of local information as well as
remote information. It follows that a PIT on a given PE is populated
from two information sources:
1. The information related to the CEs' ports that are attached to
the ports local to that PE.
2. The information about the CEs connected to the remote PEs.
Fedyk, et al. Standards Track PAGE 11
RFC 5251 L1VPN Basic Mode July 2008
A PIT MAY be populated via provisioning or by auto-discovery
procedures. When provisioning is used, the entire table MAY be
populated by provisioning commands either at a console or by a
management system that may have some automation capability. As the
network grows, some form of automation is desirable.
For local information between a CE and a PE, a PE MAY leverage LMP to
populate the <CPI, VPN-PPI> link information. This local information
also needs to be propagated to other PEs that share the same VPN.
The mechanisms for this are out of scope for this document, but the
information needed to be exchanged is described in Section 4.1.1.
The PIT is by nature VPN-specific. A PE is REQUIRED to maintain a
PIT for each L1VPN for which it has member CEs locally attached. A
PE does not need to maintain PITs for other L1VPNs. However, the
full set of PITs with all L1VPN entries for multiple VPNs MAY also be
available to all PEs.
The remote information in the context of a VPN identifier (i.e., the
remote CEs of this VPN) MAY also be sent to the local CE belonging to
the same VPN. Exchange of this information is outside the scope of
this document.
4.1.1. Local Auto-Discovery Information
The information that needs to be discovered on a PE local port is the
local CPI and the VPN-PPI.
This information MAY be configured; or, if LMP is used between the CE
and PE, LMP MAY be used to exchange this information.
Once a CPI has been discovered, the corresponding VPN-PPI maps in a
local context to a VPN identifier and a corresponding PPI. One way
to enforce a provider-controlled VPN context is to pre-provision
VPN-PPIs with a VPN identifier. Other policy mechanisms to achieve
this are outside the scope of this document. In this manner, a
relationship of a CPI to a VPN and PPI port can be established when
the port is provisioned as belonging to the VPN.
4.1.2. PE Remote Auto-Discovery Information
This section provides the information that is carried by any auto-
discovery mechanism, and is used to dynamically populate a PIT. The
information provides a single <CPI, PPI> mapping. Each auto-
discovery mechanism will define the method(s) by which multiple <CPI,
PPI> mappings are communicated, as well as invalidated.
Fedyk, et al. Standards Track PAGE 12
RFC 5251 L1VPN Basic Mode July 2008
This information should be consistent regardless of the mechanism
used to distribute the information [RFC 5195], [RFC 5252].
The format of encoding a single <PPI, CPI> tuple is:
+---------------------------------------+
| PPI Length (1 octet) |
+---------------------------------------+
| PPI (variable) |
+---------------------------------------+
| CPI AFI (2 octets) |
+---------------------------------------+
| CPI (length) |
+---------------------------------------+
| CPI (variable) |
+---------------------------------------+
Figure 4: Auto-Discovery Information
The use and meaning of these fields are as follows:
PPI Length:
A one-octet field whose value indicates the length of the PPI
field.
PPI:
A variable-length field that contains the value of the PPI (either
an address or <port index, address> tuple). Note, PPI is always
encoded consistently within a provider domain so the format of the
PPI field is implicit within a given provider network.
CPI AFI:
A two-octet field whose value indicates the address family of the
CPI. This value is taken from [RFC 1700].
CPI Length:
A one-octet field whose value indicates the length of the CPI
field.
CPI:
A variable-length field that contains the CPI value (either an
address or <port index, address> tuple).
Fedyk, et al. Standards Track PAGE 13
RFC 5251 L1VPN Basic Mode July 2008
<PPI, CPI> tuples MUST also be associated with one or more globally
unique identifiers associated with a particular VPN. A globally
unique identifier can encode a VPN-ID, a route target, or any other
globally unique identifier. The globally unique identifiers are
under control of network providers. Uniqueness within a service
provider administrative domain is sufficient for Basic Mode
operation. In the case of multiple provider networks (which is
beyond the scope of this document), the globally unique identifier
need only be unique and consistent between the those providers. In
this document, we specify a generic encoding format for the globally
unique identifier common to all the auto-discovery mechanisms.
However, each auto-discovery mechanism will define the specific
method(s) by which the encoding is distributed and the association
with a <PPI, CPI> tuple is made. The encoding of the globally unique
identifier associated with the VPN is:
+------------------------------------------------+
| L1VPN globally unique identifier (8 octets) |
+------------------------------------------------+
Figure 5: Auto-Discovery Globally Unique Identifier Format
4.2. CE-to-CE LSP Establishment
In order to establish an LSP, a CE needs to identify all other CEs in
the CE's L1VPN that it wants to connect to. A CE may already have
obtained this information through provisioning or through some other
schemes (such schemes are outside the scope of this document).
Ports associated with a given CE-to-PE link MAY also have other
information, in addition to their CPI and PPI, associated with them
that describes characteristics and constraints of the channels within
these ports, such as encoding supported by the channels, bandwidth of
a channel, total unreserved bandwidth within the port, etc. This
information could be further augmented with the information about
certain capabilities of the service provider network (e.g., support
regeneration section overhead (RSOH), Data Communications Channel
(DCC) transparency, arbitrary concatenation, etc.). This information
is used to ensure that ports at each end of an LSP have compatible
characteristics, and that there are sufficient unallocated resources
to establish an LSP between these ports.
It may happen that for a given pair of ports within an L1VPN, each of
the CEs connected to these ports would concurrently try to establish
an LSP to the other CE. If having a pair of LSPs between a pair of
ports is viewed as undesirable, the way to resolve this is to require
Fedyk, et al. Standards Track PAGE 14
RFC 5251 L1VPN Basic Mode July 2008
the CE with the lower value of the CPI to terminate the LSP
originated by the CE. This option could be controlled by
configuration on the CE devices.
4.3. Signaling
In L1VPN BM, a CE needs to be configured with the CPIs of other
ports. Once a CE is configured with the CPIs of the other ports
within the same L1VPN, which we'll refer to as "target ports", the CE
uses a subset of GMPLS signaling to request the provider network to
establish an LSP to a target port.
For inter-CE connectivity, the CE originates a request that contains
the CPI of one of its ports that it wants to use for the LSP, and the
CPI of the target port. When the PE attached to the CE that
originated the request receives the request, the PE identifies the
appropriate PIT, and then uses the information in that PIT to find
out the PPI associated with the CPI of the target port carried in the
request. The PPI should be sufficient for the PE to establish an
LSP. Ultimately, the request reaches the CE associated with the
target CPI (note that the request still carries the CPI of the CE
that originated the request). If the CE associated with the target
CPI accepts the request, the LSP is established.
Note that a CE needs not establish an LSP to every target port that
the CE knows about, i.e., it is a local CE policy matter to select a
subset of target ports to which that CE will try to establish LSPs.
The procedures for establishing an individual connection between two
corresponding CEs is the same as the procedure specified for GMPLS
overlay [RFC 4208].
4.3.1. Signaling Procedures
When an ingress CE sends an RSVP Path message to an ingress PE, the
source IP address in the IP packet that carries the message is set to
the appropriate CE-CC-Addr, and the destination IP address in the
packet is set to the appropriate PE-CC-Addr. When the ingress PE
sends back to the ingress CE the corresponding Resv message, the
source IP address in the IP packet that carries the message is set to
the PE-CC-Addr, and the destination IP address is set to the CE-CC-
Addr.
Likewise, when an egress PE sends an RSVP Path message to an egress
CE, the source IP address in the IP packet that carries the message
is set to the appropriate PE-CC-Addr, and the destination IP address
in the packet is set to the appropriate CE-CC-Addr. When the egress
CE sends back to the egress PE the corresponding Resv message, the
Fedyk, et al. Standards Track PAGE 15
RFC 5251 L1VPN Basic Mode July 2008
source IP address in the IP packet that carries the message is set to
the CE-CC-Addr, and the destination IP address is set to the PE-CC-
Addr.
In addition to being used for IP addresses in the IP packet that
carries RSVP messages between CE and PE, CE-CC-Addr and PE-CC-Addr
are also used in the Next/Previous Hop Address field of the IF_ID
RSVP_Hop Object that is carried between CEs and PEs.
In the case where a link between CE and PE is a numbered non-bundled
link, the CPI and VPN-PPI of that link are used for the Type 1 or 2
TLVs of the IF_ID RSVP_Hop Object that is carried between the CE and
PE. In the case where a link between CE and PE is an unnumbered non-
bundled link, the CPI and VPN-PPI of that link are used for the IP
Address field of the Type 3 TLV. In the case where a link between CE
and PE is a bundled link, the CPI and VPN-PPI of that link are used
for the IP Address field of the Type 3 TLVs.
Additional processing related to unnumbered links is described in
Sections 3 ("Processing the IF_ID RSVP_HOP object") and 4.1
("Unnumbered Forwarding Adjacencies") of RFC 3477 [RFC 3477].
When an ingress CE originates a Path message to establish an LSP from
a particular port on that CE to a particular target port, the CE uses
the CPI of its port in the Sender Template object. If the CPI of the
target port is an IP address, then the CE uses it in the Session
object. And if the CPI of the target port is a <port index, IP
address> tuple, then the CE uses the IP address part of the tuple in
the Session object, and the whole tuple as the Unnumbered Interface
ID subobject in the Explicit Route Object (ERO).
There are two options for RSVP-TE sessions. One option is to have a
single RSVP-TE session end to end where the addresses of the customer
and the provider are swapped at the PE; this is termed shuffling.
The other option is when stitching or hierarchy is used to create two
LSP sessions, one between the provider PE(s) and another end-to-end
session between the CEs.
4.3.1.1. Shuffling Sessions
Shuffling sessions are used when the desire is to have a single LSP
originating at the CE and terminating at the far end CE. The
customer addresses are shuffled to provider addresses at the ingress
PE, and back to customer addresses at the egress PE by using the
mapping provided by the PIT.
Fedyk, et al. Standards Track PAGE 16
RFC 5251 L1VPN Basic Mode July 2008
When the Path message arrives at the ingress PE, the PE selects the
PIT associated with the L1VPN, and then uses this PIT to map CPIs
carried in the Session and the Sender Template objects to the
appropriate PPIs. Once the mapping is done, the ingress PE replaces
CPIs with these PPIs. As a result, the Session and the Sender
Template objects that are carried in the GMPLS signaling within the
service provider network carry PPIs, and not CPIs.
At the egress PE, the reverse mapping operation is performed. The PE
extracts the ingress/egress PPI values carried in the Sender Template
and Session objects (respectively). The egress PE identifies the
appropriate PIT to find the appropriate CPI associated with the PPI
of the egress CE. Once the mapping is retrieved, the egress PE
replaces the ingress/egress PPI values with the corresponding CPI
values. As a result, the Session and the Sender Template objects
(included in the GMPLS RSVP-TE Path message sent from the egress PE
to the egress CE) carry CPIs, and not PPIs.
Here also, for the GMPLS RSVP-TE Path messages sent from the egress
PE to CE, the source IP address (of the IP packet carrying this
message) is set to the appropriate PE-CC-Addr, and the destination IP
address (of the IP packet carrying this message) is set to the
appropriate CE-CC-Addr.
At this point, the CE's view is a single LSP that is point-to-point
between the two CEs with a virtual link between the PE nodes:
CE-PE(-)PE-CE. The L1VPN PE nodes have a view of the PE-to-PE LSP
segment in all its detail. The PEs MAY filter the RSVP-TE signaling,
i.e., remove information about the provider topology and replace it
with a view of a virtual link.
This translation of addresses and session IDs is termed shuffling and
is driven by the L1VPN Port Information Tables (see Section 4). This
MUST be performed for all RSVP-TE messages at the PE edges. In this
case, there is one CE-to-CE session.
4.3.1.2. Stitched or Nested Sessions
Stitching or Nesting options are dependent on the LSP switching
types. If the CE-to-CE and PE-to-PE LSPs are identical in switching
type and capacity, the LSP MAY be stitched together and the
procedures in [RFC 5150] apply. If the CE-to-CE LSPs and the PE-to-PE
LSPs are of not the same switching type, or are of different but
compatible capacity, the LSPs MAY be Nested and the procedures for
[RFC 4206] apply. As both Stitched and Nested LSP signaling
procedures involve a PE-to-PE session establishment compatible with
CE session parameters, they are described together.
Fedyk, et al. Standards Track PAGE 17
RFC 5251 L1VPN Basic Mode July 2008
When the Path Message arrives at the ingress PE, the PE selects the
PIT associated with the L1VPN, and then uses this PIT to map CPIs
carried in the Session and the Sender Template objects to the
appropriate PPIs. Once the mapping is done, a new PE-to-PE session
is established with the parameters compatible with the CE session.
Upon successful establishment of the PE-to-PE session, the CE
signaling request is sent to the egress PE.
At the ingress PE, when stitching and nesting are used, a PE-to-PE
session is established. This could be achieved by several means:
- Associating an already established PE-to-PE LSP or Forwarding
Adjacency LSP (FA-LSP) to the destination that meets the
requested parameters.
- Establishing a compliant PE-to-PE LSP segment.
At this point, the CE's view is a single LSP that is point-to-point
between the two CEs with a virtual node between the PE nodes:
CE-PE(-)PE-CE. The L1VPN PE nodes have a view of the PE-to-PE LSP
segment in all its detail. The PEs do not have to filter the RSVP-TE
signaling by removing information about the provider topology because
the PE-to-PE signaling is not visible to the CE nodes.
4.3.1.3 Other Signaling
An ingress PE may receive and potentially reject a Path message that
contains an Explicit Route Object and so cause the switched
connection setup to fail. However, the ingress PE may accept EROs,
which include a sequence of {<ingress PE (strict), egress CE CPI
(loose)>}.
- Path message without ERO: when an ingress PE receives a Path
message from an ingress CE that contains no ERO, it MUST calculate
a route to the destination for the PE-to-PE LSP and include that
route in an ERO, before forwarding the Path message. One exception
would be if the egress core node were also adjacent to this core
node.
- Path message with ERO: when an ingress PE receives a Path message
from an ingress CE that contains an ERO (of the form detailed
above), the former computes a path to reach the egress PE. It then
inserts this path as part of the ERO before forwarding the Path
message.
In the case of shuffling, the overlay rules for notification and RRO
processing are identical to the User-Network Intercase (UNI) or
Overlay Model [RFC 4208], which state that Edge PE MAY remove/edit
Fedyk, et al. Standards Track PAGE 18
RFC 5251 L1VPN Basic Mode July 2008
Provider Notification and RRO objects when passing the messages to
the CEs.
4.4. Recovery Procedures
Signaling:
A CE requests a network-protected LSP (i.e., an LSP that is protected
from PE-to-PE) by using the technique described in [RFC 4873].
Dynamic identification of merge nodes is supported via the LSP
Segment Recovery Flags carried in the Protection object (see Section
6.2 of [RFC 4873]).
Notification:
A Notify Request object MAY be inserted in Path or Resv messages to
indicate the address of a CE that should be notified of an LSP
failure. Notifications MAY be requested in both the upstream and
downstream directions:
- Upstream notification is indicated via the inclusion of a Notify
Request object in the corresponding Path message.
- Downstream notification is indicated via the inclusion of a
Notify Request object in the corresponding Resv message.
A PE receiving a message containing a Notify Request object SHOULD
store the Notify Node Address in the corresponding RSVP state block.
The PE SHOULD also include a Notify Request object in the outgoing
Path or Resv message. The outgoing Notify Node Address MAY be
updated based on local policy. This means that a PE, upon receipt of
this object from the CE, MAY update the value of the Notify Node
Address.
If the ingress CE includes a Notify Request object into the Path
message, the ingress PE MAY replace the received 'Notify Node
Address' by its own selected 'Notify Node Address', and in particular
the local TE Router_ID. The Notify Request object MAY be carried in
Path or Resv messages (Section 7 of [RFC 3473]). The format of the
Notify Request object is defined in [RFC 3473]. Per Section 4.2.1 of
[RFC 3473], Notify Node Addresses SHALL be set to either IPv4 or IPv6.
Inclusion of a Notify Request object is used to request the
generation of notifications upon failure occurrence but does not
guarantee that a Notify message will be generated.
Fedyk, et al. Standards Track PAGE 19
RFC 5251 L1VPN Basic Mode July 2008
5. Security Considerations
Security for L1VPNs is covered in [RFC 4847] and [RFC 5253]. In this
document, we discuss the security aspects with respect to the control
plane.
The association of a particular port with a particular L1VPN (or to
be more precise, with a particular PIT) is a configuration operation,
generally done manually by the service provider as part of the
service provisioning process. Thus, it cannot be altered via
signaling between CE and PE. This means that the signaling cannot be
used to deliver L1VPN traffic to the wrong customer. The operator
should apply appropriate security mechanisms to the management and
configuration process, and should consider data plane verification
techniques to protect against accidental misconfiguration. The
customer may also apply end-to-end (i.e., CE-to-CE) data plane
connectivity tests over the L1VPN connection to detect misconnection.
Data plane connectivity testing can be performed using the Link
Management Protocol (LMP) [RFC 4204].
Note that it is also possible to populate the local part of a PIT
using auto-discovery through LMP. LMP may be secured as described in
[RFC 4204]. Signaling between CE and PE is assumed to be over a
private link (for example, in-band or in-fiber) or a private network.
Use of a private link makes the CE-to-PE connection secure at the
same level as the data link described in the previous paragraphs.
The use of a private network assumes that entities outside the
network cannot spoof or modify control plane communications between
CE and PE. Furthermore, all entities in the private network are
assumed to be trusted. Thus, no security mechanisms are required by
the protocol exchanges described in this document.
However, an operator that is concerned about the security of their
private control plane network may use the authentication and
integrity functions available in RSVP-TE [RFC 3473] or utilize IPsec
([RFC 4301], [RFC 4302], [RFC 4835], [RFC 4306], and [RFC 2411]) for the
point-to-point signaling between PE and CE. See [MPLS-SEC] for a
full discussion of the security options available for the GMPLS
control plane.
Note further that a private network (e.g., Layer 2 VPN or Layer 3
VPN) might be used to provide control plane connectivity between a PE
and more than one CE. In this scenario, it is RECOMMENDED that each
L1 VPN customer have its own such private network. Then, the
security mechanisms provided by the private network SHOULD be used to
ensure security of the control plane communication between a customer
and a service provider.
Fedyk, et al. Standards Track PAGE 20
RFC 5251 L1VPN Basic Mode July 2008
6. References
6.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC 3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003.
[RFC 3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering
(RSVP-TE)", RFC 3477, January 2003.
[RFC 4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
Extensions in Support of Generalized Multi-Protocol Label
Switching (GMPLS)", RFC 4202, October 2005.
[RFC 4204] Lang, J., Ed., "Link Management Protocol (LMP)", RFC 4204,
October 2005.
[RFC 4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC 4208] Swallow, G., Drake, J., Ishimatsu, H., and Y. Rekhter,
"Generalized Multiprotocol Label Switching (GMPLS) User-
Network Interface (UNI): Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Support for the Overlay
Model", RFC 4208, October 2005.
[RFC 4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
"GMPLS Segment Recovery", RFC 4873, May 2007.
[RFC 5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008.
Fedyk, et al. Standards Track PAGE 21
RFC 5251 L1VPN Basic Mode July 2008
6.2. Informative References
[RFC 1700] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
October 1994.
[RFC 3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC 4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
in MPLS Traffic Engineering (TE)", RFC 4201, October 2005.
[RFC 4847] Takeda, T., Ed., "Framework and Requirements for Layer 1
Virtual Private Networks", RFC 4847, April 2007.
[RFC 2411] Thayer, R., Doraswamy, N., and R. Glenn, "IP Security
Document Roadmap", RFC 2411, November 1998.
[RFC 4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC 4302] Kent, S., "IP Authentication Header", RFC 4302, December
2005.
[RFC 4306] Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
Protocol", RFC 4306, December 2005.
[RFC 4835] Manral, V., "Cryptographic Algorithm Implementation
Requirements for Encapsulating Security Payload (ESP) and
Authentication Header (AH)", RFC 4835, April 2007.
[RFC 5195] Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP-Based
Auto-Discovery for Layer-1 VPNs", RFC 5195, June 2008.
[RFC 5252] Bryskin, I. and L. Berger, "OSPF-Based Layer 1 VPN Auto-
Discovery", RFC 5252, July 2008.
[RFC 5253] Takeda, T., Ed., "Applicability Statement for Layer 1
Virtual Private Network (L1VPN) Basic Mode", RFC 5253,
July 2008.
[MPLS-SEC] Fang, L., Ed., " Security Framework for MPLS and GMPLS
Networks", Work in Progress, February 2008.
Fedyk, et al. Standards Track PAGE 22
RFC 5251 L1VPN Basic Mode July 2008
7. Acknowledgments
The authors would like to thank Adrian Farrel, Hamid Ould-Brahim, and
Tomonori Takeda for their valuable comments.
Sandy Murphy, Charlie Kaufman, Pasi Eronen, Russ Housley, Tim Polk,
and Ron Bonica provided input during the IESG review process.
Authors' Addresses
Don Fedyk
Nortel Networks
600 Technology Park
Billerica, MA 01821
Phone: +1 (978) 288 3041
EMail: dwfedyk@nortel.com
Yakov Rekhter
Juniper Networks
1194 N. Mathilda Avenue
Sunnyvale, CA 94089
EMail: yakov@juniper.net
Dimitri Papadimitriou
Alcatel-Lucent
Fr. Wellesplein 1,
B-2018 Antwerpen, Belgium
Phone: +32 3 240-8491
EMail: Dimitri.Papadimitriou@alcatel-lucent.be
Richard Rabbat
Google Inc.
1600 Amphitheatre Pky
Mountain View, CA 95054
EMail: rabbat@alum.mit.edu
Lou Berger
LabN Consulting, LLC
Phone: +1 301-468-9228
EMail: lberger@labn.net
Fedyk, et al. Standards Track PAGE 23
RFC 5251 L1VPN Basic Mode July 2008
Full Copyright Statement
Copyright © The IETF Trust (2008).
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contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
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Fedyk, et al. Standards Track PAGE 24
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RFC TOTAL SIZE: 57599 bytes
PUBLICATION DATE: Monday, June 30th, 2008
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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