One document matched: draft-ietf-l3vpn-ppvpn-terminology-02.txt
Differences from draft-ietf-l3vpn-ppvpn-terminology-01.txt
Network Working Group Loa Andersson
Internet-Draft Tove Madsen
Expires: November 30, 2004 TLA-group
June 1, 2004
PPVPN terminology
draft-ietf-l3vpn-ppvpn-terminology-02.txt
Status of this Memo
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and any of which I become aware will be disclosed, in accordance with
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This Internet-Draft will expire on November 30, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. PPVPN Terminology . . . . . . . . . . . . . . . . . . . . . . 5
3. Provider Provisioned Virtual Private Network services . . . . 6
3.1 IP-only LAN-like Service (IPLS) . . . . . . . . . . . . . 6
3.2 Layer 2 VPN (L2VPN) . . . . . . . . . . . . . . . . . . . 6
3.3 Layer 3 VPN (L3VPN) . . . . . . . . . . . . . . . . . . . 6
3.4 Pseudo Wire (PW) . . . . . . . . . . . . . . . . . . . . . 6
3.5 Transparent LAN Service (TLS) . . . . . . . . . . . . . . 7
3.6 Virtual LAN (VLAN) . . . . . . . . . . . . . . . . . . . . 7
3.7 Virtual Leased Line Service (VLLS) . . . . . . . . . . . . 7
3.8 Virtual Private LAN Service (VPLS) . . . . . . . . . . . . 7
3.9 Virtual Private Network (VPN) . . . . . . . . . . . . . . 7
3.10 Virtual Private Switched Network (VPSN) . . . . . . . . . 8
3.11 Virtual Private Wire Service (VPWS) . . . . . . . . . . . 8
4. Classification of VPNs . . . . . . . . . . . . . . . . . . . . 9
5. Building blocks . . . . . . . . . . . . . . . . . . . . . . . 11
5.1 Customer Edge device (CE) . . . . . . . . . . . . . . . . 11
5.1.1 Device based CE naming . . . . . . . . . . . . . . . . 11
5.1.2 Service based CE naming . . . . . . . . . . . . . . . 12
5.2 Provider Edge (PE) . . . . . . . . . . . . . . . . . . . . 12
5.2.1 Device based PE naming . . . . . . . . . . . . . . . . 12
5.2.2 Service based PE naming . . . . . . . . . . . . . . . 13
5.2.3 Distribution based PE naming . . . . . . . . . . . . . 13
5.3 Core . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.3.1 Provider router (P) . . . . . . . . . . . . . . . . . 14
5.4 Naming in specific Internet drafts . . . . . . . . . . . . 14
5.4.1 Layer 2 PE (L2PE) . . . . . . . . . . . . . . . . . . 14
5.4.2 Logical PE (LPE) . . . . . . . . . . . . . . . . . . . 14
5.4.3 PE-CLE . . . . . . . . . . . . . . . . . . . . . . . . 14
5.4.4 PE-Core . . . . . . . . . . . . . . . . . . . . . . . 14
5.4.5 PE-Edge . . . . . . . . . . . . . . . . . . . . . . . 14
5.4.6 PE-POP . . . . . . . . . . . . . . . . . . . . . . . . 15
5.4.7 VPLS Edge (VE) . . . . . . . . . . . . . . . . . . . . 15
6. Functions . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1 Attachment Circuit (AC) . . . . . . . . . . . . . . . . . 16
6.2 Backdoor Links . . . . . . . . . . . . . . . . . . . . . . 16
6.3 Endpoint discovery . . . . . . . . . . . . . . . . . . . . 16
6.4 Flooding . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.5 MAC address learning . . . . . . . . . . . . . . . . . . . 16
6.5.1 Qualified learning . . . . . . . . . . . . . . . . . . 16
6.5.2 Unqualified learning . . . . . . . . . . . . . . . . . 17
6.6 Signalling . . . . . . . . . . . . . . . . . . . . . . . . 17
7. 'Boxes' . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1 Aggregation box . . . . . . . . . . . . . . . . . . . . . 18
7.2 Customer Premises Equipment (CPE) . . . . . . . . . . . . 18
7.3 Multi Tenant Unit (MTU) . . . . . . . . . . . . . . . . . 18
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8. Packet Switched Network (PSN) . . . . . . . . . . . . . . . . 19
8.1 Route Distinguisher (RD) . . . . . . . . . . . . . . . . . 19
8.2 Route Reflector . . . . . . . . . . . . . . . . . . . . . 19
8.3 Route Target (RT) . . . . . . . . . . . . . . . . . . . . 19
8.4 Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.5 Tunnel multiplexor . . . . . . . . . . . . . . . . . . . . 20
8.6 Virtual Channel (VC) . . . . . . . . . . . . . . . . . . . 20
8.7 VC label . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.8 Inner label . . . . . . . . . . . . . . . . . . . . . . . 20
8.9 VPN Routing and Forwarding (VRF) . . . . . . . . . . . . . 20
8.10 VPN Forwarding Instance (VFI) . . . . . . . . . . . . . . 20
8.11 Virtual Switch Instance (VSI) . . . . . . . . . . . . . . 20
8.12 Virtual Router (VR) . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.1 Normative References . . . . . . . . . . . . . . . . . . . . 24
11.2 Informative References . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 26
Intellectual Property and Copyright Statements . . . . . . . . 27
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1. Introduction
There are 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.
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.
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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 the core
documents from the L2VPN and L3VPN working groups, i.e.
[I-D.ietf-l3vpn-requirements] , [I-D.ietf-l2vpn-requirements],
[I-D.ietf-l3vpn-framework], [I-D.ietf-l2vpn-l2-framework], and
[I-D.ietf-l3vpn-framework]. The intention is to create a
comprehensive and unified set of concepts for these documents, and by
extension for the entire PPVPN area. To do so it is also necessary
to give some of the development the concepts of the area have been
through.
The document is structured in four major sections. Section 4 lists
the different services that have 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 [I-D.ietf-l3vpn-requirements].
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:
o it is assumed that the CE devices (see 5.1) are hosts or routers,
not switches
o 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
[I-D.ietf-l2vpn-l2-framework].
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
[I-D.ietf-l3vpn-framework].
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 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
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[I-D.martini-l2circuit-trans-mpls]. Encapsulation formats readily
used in VPWS, VPLS and PWs are described in
[I-D.martini-l2circuit-encap-mpls]. Requirements for PWs are found
in [I-D.ietf-pwe3-requirements] and [I-D.ietf-pwe3-arch] 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. The term 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 term VLLS has been replaced by term VPWS. VLLS was used in now
dated document intended to create metrics by which it should have
been possible to compare different L2VPN solutions. 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
[I-D.ietf-l2vpn-requirements], [I-D.ietf-l2vpn-vpls-ldp], and
[I-D.ietf-l2vpn-vpls-bgp].
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.
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
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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 [I-D.ietf-l3vpn-framework] 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)
The term VPSN has been replaced by the term 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
[I-D.ietf-l3vpn-requirements] and L2VPN [I-D.ietf-l2vpn-requirements]
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
[I-D.kompella-ppvpn-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
[I-D.ietf-l2vpn-l2-framework].
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4. Classification of VPNs
The terminology used in [I-D.ietf-l3vpn-generic-reqts] 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:
Figure 1
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 [I-D.ietf-l3vpn-framework]).
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) [I-D.ietf-l3vpn-framework].
Virtual Router (VR) style: A PE-based VPN approach in which the PE
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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 [I-D.ietf-l3vpn-vpn-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 [I-D.ietf-l3vpn-rfc2547bis].
RFC 2547 Style: The term has been used by the L3VPN to describe the
extensions of the VPNs defined in the informational RFC2547. This
term has now been replaced by the term BGP/MPLS IP VPNs.
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5. Building blocks
Starting with specifications of L3VPNs, e.g. the 2547 specification
[RFC2547] and [I-D.ietf-l3vpn-rfc2547bis] and Virtual Routers
[I-D.ietf-l3vpn-vpn-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 in relation to the work done on L3VPNs
[I-D.ietf-l3vpn-framework]. The concept has been modified e.g. when
L2VPNs and CE-based VPNs were defined, this is addressed further in
the sub- sections of this section.
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).
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
learned in the provider network.
A CE-R could be used to access both L2 and L3 services.
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5.1.1.2 Customer Edge Switch (CE-bS)
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.
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.
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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)
A PE-S is a L2 device that participates in e.g. a switched 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.
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.
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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.
5.3 Core
5.3.1 Provider router (P)
The P is defined as a router in the core network that does not 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 the now expired
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.
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5.4.6 PE-POP
An alternative name for the U-PE suggested in now the expired
Internet Draft "VPLS architectures".
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 device used by a
provider network to hand off a VPLS to a customer. In this document
the VE is called a VPLS-PE. This name has dated.
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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 [I-D.ietf-l3vpn-framework].
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 [I-D.ietf-l3vpn-requirements]. 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.
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.
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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.
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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.
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-xxx] 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.
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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 [I-D.ietf-l3vpn-rfc2547bis] is an 8-byte value
that together with a 4 byte IPv4 address identifies a VPN-IPv4
address family. If two VPNs use the same IPv4 address prefix, the
PEs translate 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.
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 [I-D.ietf-l3vpn-framework].
8.3 Route Target (RT)
A Route Target attribute [I-D.ietf-l3vpn-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 [I-D.ietf-l3vpn-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.
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8.5 Tunnel multiplexor
A tunnel multiplexor is an entity that is sent with the packets
traversing the tunnel to make it possible to decide to which instance
of a service a packet belongs and from which sender it was received.
In [I-D.kompella-ppvpn-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
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 use
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 [I-D.ietf-l3vpn-framework].
8.11 Virtual Switch Instance (VSI)
In a layer 2 context a VSI is a virtual switching instance that
serves one single VPLS [I-D.ietf-l2vpn-l2-framework]. 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
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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
[I-D.ietf-l3vpn-vpn-vr].
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9. Security Considerations
This is a terminology document and as such don't have direct security
implications. Security considerations will be specific to the
solutions, framework and specification documents whose terminology is
collected and discussed in this document.
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10. 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.
Thomas Narten convered an almost final version of this document into
XML, after extracting an acceptable version out of Word became to
painful.
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11. References
11.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
11.2 Informative References
[I-D.ietf-l2vpn-l2-framework]
Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual
Private Networks (L2VPNs",
draft-ietf-l2vpn-l2-framework-04 (work in progress), March
2004.
[I-D.ietf-l2vpn-requirements]
Augustyn, W. and Y. Serbest, "Service Requirements for
Layer 2 Provider Provisioned Virtual Private Networks",
draft-ietf-l2vpn-requirements-01 (work in progress),
February 2004.
[I-D.ietf-l2vpn-vpls-bgp]
Kompella, K., "Virtual Private LAN Service",
draft-ietf-l2vpn-vpls-bgp-02 (work in progress), May 2004.
[I-D.ietf-l2vpn-vpls-ldp]
Lasserre, M. and V. Kompella, "Virtual Private LAN
Services over MPLS", draft-ietf-l2vpn-vpls-ldp-03 (work in
progress), April 2004.
[I-D.ietf-l3vpn-bgpvpn-auto]
Ould-Brahim, H., Rosen, E. and Y. Rekhter, "Using BGP as
an Auto-Discovery Mechanism for Layer-3 and Layer-2 VPNs",
draft-ietf-l3vpn-bgpvpn-auto-04 (work in progress), May
2004.
[I-D.ietf-l3vpn-framework]
Callon, R. and M. Suzuki, "A Framework for Layer 3
Provider Provisioned Virtual Private Networks",
draft-ietf-l3vpn-framework-00 (work in progress), July
2003.
[I-D.ietf-l3vpn-generic-reqts]
Nagarajan, A., "Generic Requirements for Provider
Provisioned Virtual Private Networks",
draft-ietf-l3vpn-generic-reqts-03 (work in progress),
February 2004.
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[I-D.ietf-l3vpn-requirements]
Carugi, M. and D. McDysan, "Service requirements for Layer
3 Provider Provisioned Virtual Private Networks:",
draft-ietf-l3vpn-requirements-00 (work in progress), July
2003.
[I-D.ietf-l3vpn-rfc2547bis]
Rosen, E., "BGP/MPLS IP VPNs",
draft-ietf-l3vpn-rfc2547bis-01 (work in progress),
September 2003.
[I-D.ietf-l3vpn-vpn-vr]
Knight, P., Ould-Brahim, H. and B. Gleeson, "Network based
IP VPN Architecture using Virtual Routers",
draft-ietf-l3vpn-vpn-vr-02 (work in progress), April 2004.
[I-D.ietf-pwe3-arch]
Bryant, S. and P. Pate, "PWE3 Architecture",
draft-ietf-pwe3-arch-07 (work in progress), March 2004.
[I-D.ietf-pwe3-requirements]
Xiao, X., "Requirements for Pseudo-Wire Emulation
Edge-to-Edge (PWE3)", draft-ietf-pwe3-requirements-08
(work in progress), January 2004.
[I-D.kompella-ppvpn-l2vpn]
Kompella, K., "Layer 2 VPNs Over Tunnels",
draft-kompella-ppvpn-l2vpn-02 (work in progress), June
2002.
[I-D.martini-l2circuit-encap-mpls]
Martini, L., "Encapsulation Methods for Transport of Layer
2 Frames Over IP and MPLS Networks",
draft-martini-l2circuit-encap-mpls-06 (work in progress),
November 2003.
[I-D.martini-l2circuit-trans-mpls]
Martini, L. and N. El-Aawar, "Transport of Layer 2 Frames
Over MPLS", draft-martini-l2circuit-trans-mpls-13 (work in
progress), December 2003.
[RFC2547] Rosen, E. and Y. Rekhter, "BGP/MPLS VPNs", RFC 2547, March
1999.
[RFC2764] Gleeson, B., Heinanen, J., Lin, A., Armitage, G. and A.
Malis, "A Framework for IP Based Virtual Private
Networks", RFC 2764, February 2000.
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Authors' Addresses
Loa Anderson
TLA-group
EMail: loa@pi.se
Tove Madsen
TLA-group
EMail: tove@niebelungen.net
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