L3VPN Working Group Loa Andersson
Internet-Draft Tove Madsen
TLA¡group
Expiration Date: September 2004
22 March 2004
PPVPN terminology
<draft-ietf-l3vpn-ppvpn-terminology-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [RFC2026].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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Internet-Drafts are draft documents valid for a maximum of six
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For potential updates to the above required-text see:
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Abstract
The provider provisioned VPN solutions have attracted a great deal
of interest. Memos proposing different and overlapping solutions
have been discussed on the PPVPN mailing list and in the Working
Group meetings. This has lead to the development of a partly new
set of concepts used to describe the set of VPN services. To a
certain extent there is more than one term covering the same
concept and sometimes the same term covers more than one concept.
The terminology needs to be made clearer and more intuitive. This
document seeks to fill at least part of that need.
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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
[RFC2119].
Table of contents
1. Introduction ..................................................... 3
2. PPVPN Terminology ................................................ 4
3. Provider Provisioned Virtual Private Network services ............. 5
3.1 IP-only LAN-like Service (IPLS)............................... 5
3.2 Layer 2 VPN (L2VPN) .......................................... 5
3.3 Layer 3 VPN (L3VPN) .......................................... 5
3.4 Pseudo Wire (PW) ............................................. 5
3.5 Transparent LAN Service (TLS)................................. 6
3.6 Virtual LAN (VLAN) ........................................... 6
3.7 Virtual Leased Line Service (VLLS)............................ 6
3.8 Virtual Private LAN Service (VPLS)............................ 6
3.9 Virtual Private Network (VPN)................................. 7
3.10 Virtual Private Switched Network (VPSN)...................... 7
3.11 Virtual Private Wire Service (VPWS).......................... 7
4. Classification of VPNs ........................................... 8
5. Building blocks .................................................. 9
5.1 Customer Edge device (CE) .................................... 9
5.1.1 Device based CE naming................................. 10
5.1.2 Service based CE naming................................ 10
5.2 Provider Edge (PE) .......................................... 11
5.2.1 Device based PE naming................................. 11
5.2.2 Service based PE naming................................ 11
5.2.3 Distribution based PE naming........................... 12
5.3 Core ........................................................ 13
5.3.1 Provider router (P) ................................... 13
5.4 Naming in specific Internet drafts........................... 13
5.4.1 Layer 2 PE (L2PE) ..................................... 13
5.4.2 Logical PE (LPE) ...................................... 13
5.4.3 PE-CLE ................................................ 13
5.4.4 PE-Core ............................................... 13
5.4.5 PE-Edge ............................................... 13
5.4.6 PE-POP ................................................ 13
5.4.7 VPLS Edge (VE) ........................................ 14
6. Functions ....................................................... 14
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6.1 Attachment Circuit (AC) ..................................... 14
6.2 Backdoor Links .............................................. 14
6.3 Endpoint discovery .......................................... 14
6.4 Flooding .................................................... 14
6.5 MAC address learning ........................................ 15
6.5.1 Qualified learning .................................... 15
6.5.2 Unqualified learning .................................. 15
6.6 Signalling .................................................. 15
7. 'Boxes' ......................................................... 15
7.1 Aggregation box ............................................. 15
7.2 Customer Premises Equipment (CPE)............................ 16
7.3 Multi Tenant Unit (MTU) ..................................... 16
8. Packet Switched Network (PSN) ................................... 16
8.1 Route Distinguisher (RD) .................................... 16
8.2 Route Reflector ............................................. 17
8.3 Route Target (RT) ........................................... 17
8.4 Tunnel ...................................................... 17
8.5 Tunnel multiplexor .......................................... 17
8.6 Virtual Channel (VC) ........................................ 17
8.7 VC label .................................................... 18
8.8 Inner label ................................................. 18
8.9 VPN Routing and Forwarding (VRF)............................. 18
8.10 VPN Forwarding Instance (VFI)............................... 18
8.11 Virtual Switch Instance (VSI)............................... 18
8.12 Virtual Router (VR) ........................................ 18
9. Acknowledgements ................................................ 19
10. Authors' Contact ............................................... 19
11. Normative References ........................................... 19
12. Non-Normative References ....... Fel! Bokmrket r inte definierat.
1. Introduction
There is a comparatively large number of memos being submitted to
the former PPVPN, and L2VPN, L3VPN and PWE3 working groups that
all address the same problem space, provider provisioned virtual
private networking for end customers. The memos address a wide
range of services, but there is also a great deal of commonality
among the proposed solutions.
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This has lead to the development of a partly new set of concepts
used to describe this set of VPN services. To a certain extent
there is more than one term covering the same concept and
sometimes the same term covers more than one concept. The
terminology needs to be made clearer and more intuitive.
This document seeks to fill at least part of the need and proposes
a foundation for a unified terminology for the L2VPN, L3VPN
working groups; in some cases the parallel concepts within the
PWE3 working group are used as references.
2. PPVPN Terminology
The concepts and terms in this list are gathered from Internet
Drafts sent to the L2VPN and L3VPN mailing lists (earlier PPVPN
mailing list) and RFCs relevant to the L2VPN and L3VPN working
groups. The focus is on terminology and concepts that are specific
to the PPVPN area, but this is not strictly enforced, e.g. there
are concepts and terms within the PWE3 and (Generalized) MPLS
areas that are closely related. We've tried to find the earliest
use of terms and concepts.
This document intends to fully cover the concepts within five core
documents from the L2VPN and L3VPN working groups the "Generic
Requirements for Provider Provisioned VPN" [GENERIC], the "A
Framework for Layer 3 Provider Provisioned Virtual Private
Networks" [L3VPN-frmwrk], the "Service requirements for Layer 3
Provider Provisioned Virtual Private Networks" [PPVPN-req], the
"L2VPN Framework [L2VPN-frmwrk] and "Service Requirements for
Layer 2 Provider Provisioned Virtual Private Networks" [L2VPN-
req]. The intention is to create a comprehensive and unified set
of concepts for these documents, and by extension for the entire
PPVPNarea.Todosoitisalsonecessarytogivesomeofthe
development the concepts of the area have been through.
The document is structured in four major sections. Section 4 lists
the different services that has been/will be specified, Section 5
lists the building blocks that are used to specify those services,
section 6 lists the functions needed in those services and section
7 list some typical devices used in customer and provider
networks.
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3. Provider Provisioned Virtual Private Network services
In this section we define the terminology that relates the set of
services to solutions specified by the L2VPN and L3VPN working
groups. The concept "pseudo wire" that belongs to the PWE3 working
group is included for reference purposes. For requirements in
provider provisioned VPNs see [PPVPN-req].
In this section all abbreviations are listed in alphabetic order.
3.1 IP-only LAN-like Service (IPLS)
An IPLS is very like a VPLS (see 3.8), except that:
- it is assumed that the CE devices (see 5.1) are hosts or
routers, not switches
- it is assumed that the service will only need to carry IP
packets, and supporting packets such as ICMP and ARP;
otherwise layer 2 packets which do not contain IP are not
supported.
While this service is a functional subset of the VPLS service, it
is considered separately because it may be possible to provide it
using different mechanisms, which may allow it to run on certain
hardware platforms that cannot support the full VPLS functionality
[PPVPN-L2-frmwrk].
3.2 Layer 2 VPN (L2VPN)
Three types of L2VPNs are described in this document, Virtual
Private Wire Service (VPWS) (section 3.11), Virtual Private LAN
Service (VPLS)(section 3.8), and IP-only LAN-like Service
(IPLS)(section 3.1).
3.3 Layer 3 VPN (L3VPN)
An L3VPN is a solution that interconnects several sets of hosts
and routers and allows them to communicate based on L3 addresses,
see [L3VPN-frmwrk].
3.4 Pseudo Wire (PW)
The PWE3 working group within the IETF specifies the pseudo wire
technology. A pseudo wire is an emulated point-to-point connection
over a packet switched network that gives the possibility to
interconnect two nodes with any L2 technology. The PW shares some
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of the building blocks and architecture constructs with the point
to multipoint solutions, e.g. PE (see 5.2) and CE (see 5.1). An
early solution for PWs is described in [martini-tran].
Encapsulation formats readily used in VPWS, VPLS and PWs are
described in [martini-encap]. Requirements for PWs are found in
[PWE3-req] and [PWE3-frmwrk] presents an architectural framework
for PWs.
3.5 Transparent LAN Service (TLS)
TLS was an early name used to describe the VPLS service, it was
used e.g. in the now dated draft-lasserre-tls-mpls-00.txt. This
draft has been merged into the working group VPLS solution using
LDP as a signalling protocol. TLS has been replaced by VPLS, which
is the current term.
3.6 Virtual LAN (VLAN)
A VLAN is a way of separating traffic on a LAN, e.g. between
different departments within a company. This acronym is not
defined by former PPVPN working group, but is defined by IEEE
802.1Q. The VLANID is used to mark an Ethernet frame with a tag to
create user groups on a LAN.
3.7 Virtual Leased Line Service (VLLS)
The VLLS has been replaced by VPWS. VPWS was used in now dated
document intended to create metrics by which it should have been
possible to compare different L2VPN solutions (draft-ppvpn-
metrics.00.txt). This document has now expired and the work
terminated.
3.8 Virtual Private LAN Service (VPLS)
A VPLS is a provider service that emulates the full functionality
of a traditional Local Area Network. A VPLS makes it possible to
interconnect several LAN segments over a packet switched network
(PSN) and makes the remote LAN segments behave as one single LAN.
For an early work on defining a solution and protocol for a VPLS
see [L2VPN-req], [Lasserre-vkompella], and [Kompella-VPLS].
In a VPLS the provider network emulates a learning bridge and
forwarding decisions are taken based on MAC addresses or MAC
addresses and VLAN tag.
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3.9 Virtual Private Network (VPN)
VPN is a generic term that covers the use of public or private
networks to create groups of users that are separated from other
network users and may communicate among them as if they were on a
private network. It is possible to enhance the level of separation
e.g. by end-to-end encryption, this is however outside the scope
of IETF VPN working group charters. This VPN definition is from
[RFC2764].
In the [L3VPN-frmwrk] the term VPN is used to refer to a specific
set of sites as either an intranet or an extranet that have been
configured to allow communication. Note that a site is a member of
at least one VPN, and may be a member of many VPNs.
In this document "VPN" is also used as a generic name for all
services listed in section 3.
3.10 Virtual Private Switched Network (VPSN)
A VPSN is replaced by VPLS. The VPSN abbreviation was used e.g. in
the now dated draft-vkompella-ppvpn-vpsn-reqmts-00.txt. The
requirements has been merged into the L3VPN [PPVPN-req] and L2VPN
[L2VPN-req] requirements.
3.11 Virtual Private Wire Service (VPWS)
A Virtual Private Wire Service (VPWS) is a point-to-point circuit
(link) connecting two Customer Edge devices. The CE in the
customer network is connected to a PE in the provider network via
an Attachment Circuit (see 6.1); the Attachment Circuit is either
a physical or a logical circuit.
The PE's in the core network are connected via a PW.
The CE devices can be routers, bridges, switches or hosts. In some
implementations a set of VPWSs is used to create a multi-site
L2VPN network. An example of a VPWS solution is described in
[L2VPN].
A VPWS differs from a VPLS (section 3.8) in that the VPLS is point
to multipoint, while the VPWS is point to point. See [L2VPN-
frmwrk].
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4. Classification of VPNs
The terminology used in [GENERIC] is defined based on the figure
below.
PPVPN
________________|__________________
| |
Layer 2 Layer 3
______|_____ ______|______
| | | |
P2P P2M PE-based CE-based
(VPWS) _____|____ ______|____ |
| | | | |
VPLS IPLS BGP/MPLS Virtual IPsec
IP VPNs Router
The figure above presents a taxonomy of PPVPN technologies. Some
of the definitions are given below:
CE-based VPN: A VPN approach in which the shared service provider
network does not have any knowledge of the customer VPN. This
information is limited to CE equipment. All the VPN-specific
procedures are performed in the CE devices, and the PE devices are
not aware in any way that some of the traffic they are processing
is VPN traffic (see also [L3VPN-frmwrk]).
PE-Based VPNs: A Layer 3 VPN approach in which a service provider
network is used to interconnect customer sites using shared
resources. Specifically the PE device maintains VPN state,
isolating users of one VPN from users of another VPN. Because the
PE device maintains all required VPN state, the CE device may
behave as if it were connected to a private network. Specifically,
the CE in a PE-based VPN must not require any changes or
additional functionality to be connected to a PPVPN instead of a
private network.
The PE devices know that certain traffic is VPN traffic. They
forward the traffic (through tunnels) based on the destination IP
address of the packet, and optionally based on other information
in the IP header of the packet. The PE devices are themselves the
tunnel endpoints. The tunnels may make use of various
encapsulations to send traffic over the SP network (such as, but
not restricted to, GRE, IP-in-IP, IPsec, or MPLS tunnels) [L3VPN-
frmwrk].
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Virtual Router (VR) style: A PE-based VPN approach in which the PE
router maintains a complete logical router for each VPN that it
supports. Each logical router maintains a unique forwarding table
and executes a unique instance of the routing protocols. These
VPNs are described in [PPVPN-VR].
BGP/MPLS IP VPNs: A PE-based VPN approach in which the PE router
maintains separate forwarding environment for each VPN and a
separate forwarding table for each VPN. In order to maintain
multiple forwarding table instances while running only a single
BGP instance, BGP/MPLS IP VPNs mark route advertisements with
attributes that identify their VPN context. These VPNs are based
on the approach described in [RFC2547bis].
RFC 2547 Style: The term has been used by the L3VPN to describe
the extensions of the VPNs defined in the informational RFC2547.
ThistermhasnowbeenreplacedbyBGP/MPLSIPVPNs.
5. Building blocks
Starting with specifications of L3VPNs, e.g. the 2547
specification [RFC2547] and [RFC2547bis] and Virtual Routers
[PPVPN-VR], a way of describing the building blocks and allocation
of functions in VPN solutions was developed. The building blocks
are often used in day-to-day talk treated as if it were physical
boxes, common for all services.
However, for different reasons this is an over-simplification. Any
of the building blocks could be implemented across more than one
physical box. How common the use of such implementations will be
is beyond the scope of this document.
5.1 Customer Edge device (CE)
A CE is the name of the device with the functionality needed on
the customer premises to access the services specified by the
former PPVPN working group.
There are two different aspects that need to be considered in
naming CE devices. One could start with the type of device that is
used to implement the CE (see section 5.1.1). It is also possible
to use the service the CE provides and with the result it will be
a set of "prefixed CEs", (see section 5.1.2).
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It is common practice to use "CE" to indicate any of these boxes,
since it is very often unambiguous in the specific context.
5.1.1 Device based CE naming
5.1.1.1 Customer Edge Router (CE-R)
A CE-R is a router in the customer network interfacing the
provider network. There are many reasons to use a router in the
customer network, e.g. in an L3VPN using private IP addressing
this is the router that is able to do forwarding based on the
private addresses. Another reason to require the use of a CE-R on
the customer side is that one want to limit the number on MAC-
addresses that needs to be learnt in the provider network.
A CE-R could be used to access both L2 and L3 services.
5.1.1.2 Customer Edge Switch (CE-S)
A CE-S is a service aware L2 switch in the customer network
interfacing the provider network. In a VPWS or a VPLS it is not
strictly necessary to use a router in the customer network, a
layer 2 switch might very well do the job.
5.1.2 Service based CE naming
The list below is just examples and it will be extended as the
number of services increases.
5.1.2.1 L3VPN-CE
An L3VPN-CE is the device or set of devices on the customer
premises that attaches to a provider provisioned L3VPN, e.g. a
2547bis implementation.
5.1.2.2 VPLS-CE
A VPLS-CE is the device or set of devices on the customer premises
that attaches to a provider provisioned VPLS.
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5.1.2.3 VPWS-CE
A VPWS-CE is the device or set of devices on the customer premises
that attaches to a provider provisioned VPWS.
5.2 Provider Edge (PE)
A PE is the name of the device or set of devices at the edge of
the provider network with the functionality that is needed to
interface the customer. PE, without further qualifications, is
very often used for naming the devices since it is made
unambiguous by the context.
In naming PEs there are three aspects that we need to consider,
the service they support, whether the functionality needed for
service is distributed across more than one device and the type of
device they are build on.
5.2.1 Device based PE naming
Both routers and switches may be used to implement PEs, however
the scaling properties will be radically different depending which
type of equipment is chosen.
5.2.1.1 Provider Edge Router (PE-R)
A PE-R is a L3 device that participates in the PSN (see section 8)
routing and forwards packets based on the routing information.
5.2.1.2 Provider Edge Switch (PE-S)
APE-SisaL2devicethatparticipatesine.g.aswitched
Ethernet taking forwarding decision packets based on L2 address
information.
5.2.2 Service based PE naming
5.2.2.1 L3VPN-PE
An L3VPN-PE is a device or set of devices at the edge of the
provider network interfacing the customer network, with the
functionality needed for an L3VPN.
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5.2.2.2 VPWS-PE
A VPWS-PE is a device or set of devices at the edge of the
provider network interfacing the customer network, with the
functionality needed for a VPWS.
5.2.2.3 VPLS-PE
A VPLS-PE is a device or set of devices at the edge of the
provider network interfacing the customer network, with the
functionality needed for a VPLS.
5.2.3 Distribution based PE naming
For scaling reasons it is in the VPLS/VPWS cases sometimes desired
to distribute the functions in the VPLS/VPWS-PE across more than
one device, e.g. is it feasible to allocate MAC address learning
on a comparatively small and in-expensive device close to the
customer site, while participation in the PSN signalling and set
up of PE to PE tunnels are done by routers closer to the network
core.
When distributing functionality across devices a protocol is
needed to exchange information between the Network facing PE (N-
PE) see section 5.2.3.1 and the User facing PE (U-PE) see section
5.2.3.2.
5.2.3.1 Network facing PE (N-PE)
The N-PE is the device to which the signalling and control
functions are allocated when a VPLS-PE is distributed across more
than one box.
5.2.3.2 User facing PE (U-PE)
The U-PE is the device to which the functions needed to take
forwarding or switching decision at the ingress of the provider
network.
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5.3 Core
5.3.1 Provider router (P)
ThePisdefinedasarouterinthecorenetworkthatdoesnot
have interfaces directly towards a customer. Hence a P router does
not need to keep VPN state and is VPN un-aware.
5.4 Naming in specific Internet drafts
5.4.1 Layer 2 PE (L2PE)
L2PE is the joint name of the devices in the provider network that
implement L2 functions needed for a VPLS or a VPWS.
5.4.2 Logical PE (LPE)
The term Logical PE (LPE) originates from a dated Internet Draft
"VPLS/LPE L2VPNs: Virtual Private LAN Services using Logical PE
Architecture" and was used to describe a set of devices used in a
provider network to implement a VPLS. In a LPE, VPLS functions are
distributed across small devices (PE-Edges/U-PE) and devices
attached to a network core (PE-Core/N-PE). In an LPE solution the
PE-edge and PE-Core can be interconnected by a switched Ethernet
transport network(s) or uplinks. The LPE will appear to the core
network as a single PE. In this document the devices that
constitutes the LPE is called N-PE and U-PE.
5.4.3 PE-CLE
An alternative name for the U-PE suggested in now dated Internet
Draft "VPLS architectures".
5.4.4 PE-Core
See the origins and use of this concept in section 5.4.2.
5.4.5 PE-Edge
See the origins and use of this concept in section 5.4.2.
5.4.6 PE-POP
An alternative name for the U-PE suggested in now dated Internet
Draft "VPLS architectures".
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5.4.7 VPLS Edge (VE)
The term VE originates from a dated Internet Draft on a
distributed transparent LAN service and was used to describe the
deviceusedbyaprovidernetworktohandoffaVPLStoa
customer. In this document the VE is called a VPLS-PE.
This name has dated.
6. Functions
In this section we have grouped a number of concepts and terms
that have to be performed to make the VPN services work.
6.1 Attachment Circuit (AC)
In a Layer 2 VPN the CE is attached to PE via an Attachment
Circuit (AC). The AC may be a physical or logical link.
6.2 Backdoor Links
Backdoor Links are links between CE devices that are provided by
the end customer rather than the SP; may be used to interconnect
CE devices in multiple-homing arrangements [L3VPN-frmwrk].
6.3 Endpoint discovery
Endpoint discovery is the process by which the devices that are
aware of a specific VPN service will find all customer facing
ports that belong to the same service.
The requirements on endpoint discovery and signalling are
discussed in [PPVPN-req]. It was also the topic in a now dated
Internet Draft reporting from a design team activity on VPN
discovery.
6.4 Flooding
Flooding is a function related to L2 and L3 services; when a PE
receives a frame with an unknown destination MAC-address, that
frame is send out over (flooded) every other interface.
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6.5 MAC address learning
MAC address learning is a function related to L2 services; when PE
receives a frame with an unknown source MAC-address the
relationship between that MAC-address and interface is learnt for
future forwarding purposes. In a layer 2 VPN solution from the
L2VPN WG, this function is allocated to the VPLS-PE.
6.5.1 Qualified learning
In qualified learning, the learning decisions at the U-PE are
based on the customer Ethernet frame's MAC address and VLAN tag,
if a VLAN tag exists. If no VLAN tag exists, the default VLAN is
assumed.
6.5.2 Unqualified learning
In unqualified learning, learning is based on a customer Ethernet
frame's MAC address only.
6.6 Signalling
Signalling is the process by which the PEs that have VPNs behind
them exchange information to set up PWs, PSN tunnels and tunnel
multiplexers. This process might be automated through a protocol
or done by manual configuration. Different protocols may be used
to establish the PSN tunnels and exchange the tunnel multiplexers.
7. 'Boxes'
We list a set of boxes that will typically be used in an
environment that supports different kinds of VPN services. We have
chosen to include some names of boxes that originate outside the
protocol specifying organisations.
7.1 Aggregation box
The aggregation box is typically an L2 switch that is service
unaware and is used only to aggregate traffic to more function
rich points in the network.
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7.2 Customer Premises Equipment (CPE)
The CPE equipment is the box that a provider places with the
customer. It serves two purposes, giving the customer ports to
plug in to and making it possible for a provider to monitor the
connectivity to the customer site. The CPE is typically a low cost
box with limited functionality and in most cases not aware of the
VPN services offered by the provider network.
The CPE equipment is not necessarily the equipment to which the CE
functions are allocated, but is part of the provider network and
used for monitoring purposes.
The CPE name is used primarily in network operation and deployment
contexts, and should not be used in protocol specifications.
7.3 Multi Tenant Unit (MTU)
An MTU [DTLS] is typically an L2 switch placed by a service
provider in a building where customers of that service provider
are located.
The MTU device name is used primarily in network operation and
deployment contexts, and should not be used in protocol
specifications, as it is also a used abbreviation for Maximum
Transmit Units.
8. Packet Switched Network (PSN)
A PSN is the network through which the tunnels supporting the VPN
services are set up.
8.1 Route Distinguisher (RD)
A Route Distinguisher [RFC2547bis] is an 8-byte value that
togetherwitha4byteIPv4addressidentifiesaVPN-IPv4address
family. If two VPNs use the same IPv4 address prefix, the PEs
translates these into unique VPN-IPv4 address prefixes. This
ensures that if the same address is used in two different VPNs, it
is possible to install two completely different routes to that
address, one for each VPN.
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8.2 Route Reflector
A route reflector is a network element owned by a Service Provider
(SP) that is used to distribute BGP routes to the SP's BGP-enabled
routers [L3VPN-frmwrk].
8.3 Route Target (RT)
A Route Target attribute [RFC2547bis] can be thought of as
identifying a set of sites, or more precisely a set of VRFs (see
section 8.8).
Associating a particular Route Target with a route, allows that
route to be placed in all VRFs that are used for routing traffic
received from the corresponding sites.
A Route Target attribute is also a BGP extended community used in
[RFC2547], and [BGPVPN-auto]. A Route Target community is used to
constrain VPN information distribution to the set of VRFs. A route
target can be perceived as identifying a set of sites, or more
precisely a set of VRFs.
8.4 Tunnel
A tunnel is connectivity through a PSN that is used to send
traffic across the network from one PE to another. The tunnel
provides a mechanism to transport packets from one PE to another,
separation of one customer's traffic from another customer's
traffic is done based on tunnel multiplexers (see section 8.4).
How the tunnel is established depends on the tunnelling mechanisms
provided by the PSN, i.e. the tunnel could be based on e.g. the
IP-header, an MPLS label, the L2TP Session ID, or on the GRE Key
field.
8.5 Tunnel multiplexor
A tunnel multiplexor is an entity that is sent with the packets
traversing the tunnel to make possible to decide to which instance
of a service a packet belongs and from which sender it was
received. In [L2VPN] the tunnel multiplexor is formatted as an
MPLS label.
8.6 Virtual Channel (VC)
A VC is transported within a tunnel and identified by its tunnel
multiplexer. A virtual channel is identified by a VCI (Virtual
Channel Identifier). In the PPVPN context a VCI is a VC label or
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tunnel multiplexer and in the Martini case it is equal to the
VCID.
8.7 VC label
In an MPLS enabled IP network a VC label is an MPLS label, used to
identify traffic within a tunnel that belongs to a particular VPN,
i.e. the VC label is the tunnel multiplexer in networks that uses
MPLS labels.
8.8 Inner label
"Inner label" is another name for VC label (see section 8.6).
8.9 VPN Routing and Forwarding (VRF)
In networks running 2547 VPN's [RFC2547], PE routers maintain
VRF's. A VRF is a per-site forwarding table. Every site to which
the PE router is attached is associated with one of these tables.
A particular packet's IP destination address is looked up in a
particular VRF only if that packet has arrived directly from a
site, which is associated with that table.
8.10 VPN Forwarding Instance (VFI)
VPN Forwarding Instance (VFI) is a logical entity that resides in
a PE that includes the router information base and forwarding
information base for a VPN instance [L3VPN-frmwrk].
8.11 Virtual Switch Instance (VSI)
In a layer 2 context a VSI is a virtual switching instance that
serves one single VPLS [L2VPN-frmwrk]. A VSI performs standard LAN
(i.e., Ethernet) bridging functions. Forwarding done by a VSI is
based on MAC addresses and VLAN tags, and possibly other relevant
information on a per VPLS basis. The VSI is allocated to VPLS-PE
or in the distributed case to the U-PE.
8.12 Virtual Router (VR)
A Virtual Router (VR) is software and hardware based emulation of
a physical router. Virtual routers have independent IP routing and
forwarding tables and they are isolated from each other, see
[PPVPN-VR].
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9. Acknowledgements
Much of the content in this document is based on discussion in the
PPVPN design teams for "auto discovery" and "l2vpn".
Dave McDysan and Adrian Farrel have carefully reviewed the
document and given many useful suggestions.
10. Authors' Contact
Loa Andersson
TLA-group
loa@pi.se
Tove Madsen
TLA-group
tove@niebelungen.net
11. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described
in this document or the extent to which any license under such
rights might or might not be available; neither does it represent
that it has made any effort to identify any such rights.
Information on the IETF's procedures with respect to rights in
standards-track and standards-related documentation can be found
in BCP-11. Copies of claims of rights made available for
publication and any assurances of licenses to be made available,
or the result of an attempt made to obtain a general license or
permission for the use of such proprietary rights by implementors
or users of this specification can be obtained from the IETF
Secretariat.
The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights which may cover technology that may be required
to practice this standard. Please address the information to the
IETF Executive Director.
12. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2026] S. Bradner "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996'
13. Informative References
[GENERIC] Nagarajan, A (ed), "Generic Requirements for Provider
Provisioned VPN", draft-ietf-l3vpn-generic-reqts-01.txt, Work in
Progress, Internet Draft, Aug 2003
[L2VPN-frmwrk] Andersson, L. and Rosen, E., "L2VPN Framework", draft-
ietf-l2vpn-l2-framework-01.txt, Work in Progress, Internet Draft,
Sept 2003
[L3VPN-frmwrk] Callon, R. and Suzuki, M.," A Framework for Layer 3
Provider Provisioned Virtual Private Networks", draft-ietf-l3vpn-
framework-00.txt, Work in Progress, Internet Draft, March 2003
[PPVPN-req] Carugi, M. and McDysan, D., "Service requirements for
Layer 3 Provider Provisioned Virtual Private Networks", draft-ietf-
l3vpn-requirements-00.txt, Work in Progress, Internet Draft, Oct 2003
[L2VPN-req] Augustyn, W., and Serbest, Y., "Service Requirements for
Layer 2 Provider Provisioned Virtual Private Networks", draft-ietf-
l2vpn-requirements-00.txt, Work in Progress, Internet Draft, May 2003
[BGPVPN-auto] Ould-Brahim, H., Rosen, E. and Rekhter, Y. "Using BGP
as an auto-discovery mechanism for network-based VPNs", draft-ietf-
l3vpn-bgpvpn-auto-00.txt, Work in progress, Internet Draft, July 2003
[kompella-VPLS] Kompella, K. "Virtual Private LAN Service", draft-
ietf-l2vpn-vpls-bgp-00.txt, Work in Progress, Internet Draft, May
2003
[L2VPN] Kompella, K., et.al. "Layer 2 VPNs Over Tunnels", draft-
kompella-ppvpn-l2vpn-03.txt, Work in Progress, June 2002
[lasserre-vkompella] Kompella, V. and Lasserre, M., "Virtual Private
LAN Services over MPLS" draft-ietf-l2vpn-vpls-ldp-00.txt, Work in
progress, Mar 2002
[martini-encap] Martini, L., et.al. "Encapsulation Methods for
Transport of Layer 2 Frames Over IP and MPLSNetworks", draft-martini-
l2circuit-encap-mpls-05.txt, Work in Progress, Internet Draft, April
2003
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[martini-tran] Martini, L., et.al. "Transport of Layer 2 Frames Over
MPLS", draft-martini-l2circuit-trans-mpls-11.txt, Work in progress,
Internet Draft, April 2003
[PPVPN-VR] Ould-Brahim, H., et.al. "Network-based IP VPN using
Virtual Routers", draft-ietf-l3vpn-vpn-vr-00.txt, Work in Progress,
Internet Draft, July 2002
[PWE3-arch] Prayson, P. and Bryant, S., "PWE3 Architecture", draft-
ietf-pwe3-arch-05.txt, Work in Progress, Internet Draft, August 2003
[PWE3-req] Xiao, X., "Requirements for Pseudo-Wire Emulation Edge-to-
Edge (PWE3)", draft-ietf-pwe3-requirements-06.txt, Work in progress,
Internet Draft, July 2003
[RFC2547] Rosen, E., et.al. "BGP/MPLS VPNs", rfc2547, March 1999
[RFC2547bis] Rosen, E., "BGP/MPLS IP VPNs", draft-ietf-l3vpn-
rfc2547bis-01.txt, Work in Progress, Internet Draft, September 2003
[RFC2764] Gleeson, B., et.al. "A Framework for IP Based Virtual
Private Networks", rfc2764, February 2000
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