One document matched: draft-ietf-ppvpn-vpls-requirements-01.txt
Differences from draft-ietf-ppvpn-vpls-requirements-00.txt
PPVPN Working Group
Internet Draft
Document: draft-ietf-ppvpn-vpls-requirements-01.txt
Category: Informational
October 2002 Waldemar Augustyn
Expires: April 2003 (editor)
Giles Heron Pascal Menezes
PacketExchange Ltd Terabeam
Vach Kompella Hamid Ould-Brahim
TiMetra Networks Nortel Networks
Marc Lasserre Tissa Senevirathne
Riverstone Networks
Requirements for Virtual Private LAN Services (VPLS)
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
For potential updates to the above required-text see:
http://www.ietf.org/ietf/1id-guidelines.txt
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1 Abstract
This draft describes service requirements related to emulating a
virtual private LAN over an IP or MPLS network infrastructure. The
service is called VPLS. It is a class of Provider Provisioned
Virtual Private Network [2]. The general requirements can be found
in [3].
2 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 [4].
3 Definitions
3.1 VPLS
Virtual Private LAN Service, a case of L2VPN service distinguished
by the support of L2 broadcast. The term is also used, when clear
from the context, to refer to a particular instance of VPLS service.
A VPLS service allows the connection of multiple sites in a single
broadcast domain over a provider managed IP or MPLS network. All
customer sites in the VPLS appear to be on the same LAN regardless
of their location.
3.2 VPLS Domain
A Layer 2 VPN that is composed of a community of interest of L2 MAC
addresses and VLANs. Each VPLS Domain MAY have multiple VLANs in it.
3.3 VLAN
A customer VLAN identification using some scheme such as IEEE 802.1Q
tags, port configuration or any other means. A VPLS service can be
extended to recognize customer VLANs as specified in 6.1 .
3.4 VLAN Flooding Scope (VLAN Broadcast Domain)
The scope of flooding for a given VLAN. In a VPLS service, a VLAN
flooding scope is identical to the flooding scope of the VPLS it is
part of. If a VPLS service is extended to recognize customer VLANs,
the VLAN flooding scope is limited to the broadcast domain of each
recognized VLAN.
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3.5 VSI
Virtual Switching Instance. A virtual layer 2 forwarding entity that
is closed to a VPLS domain membership. VSI forwarding can be based
on MAC addresses, VLAN tags, policies, topologies, filters, QoS
parameters, and other relevant information on a per VPLS basis.
4 Introduction
Traditionally, the typical connectivity between a service provider
and a customer is a WAN link with some type of a point-to-point
protocol. This arrangement was borne out of the necessity to
traverse TDM circuits originally designed for voice traffic. The
introduction of WAN links to network architectures significantly
increased the complexity of network topologies and required highly
skilled personnel to manage and maintain the network.
One solution to the above has been for service providers to deploy
emulated LAN services known in this context as "Transparent LAN"
services. These have typically been offered using a mesh of ATM PVCs
between locations. While this technique reduced complexity for the
customer, it proved inadequate in the area of scaling and ease of
management on the provider side.
The aim of this effort is to develop a Virtual Private LAN Service,
VPLS, that scales well, is simple to manage, and is based on the
existing MPLS or IP backbone.
VPLS emulates a flat LAN with learning and switching capabilities.
In a given LAN, there is a reasonably small set of MAC devices with
a limited number of MAC addresses to learn and manage. There is no
need for additional routing protocol support between the CE and the
PE devices. In the VPLS model, the service is transparent to the
customer's choice of routing protocol. Moreover, VPLS services also
benefit from being transparent to higher layer protocols, so the
same technology can transport, for example, IPv4, IPv6, MPLS as well
as legacy protocols such as IPX and OSI.
The VPLS model, while offering significant benefits for both
customers and service providers, retains all the quintessential
characteristics of L2 networks including their well known
limitations e.g. the maximum practical number of hosts on a single
LAN, etc. A likely application of this model is to connect a few
sites with only a single customer router at each site, or a small
number of customer hosts, at each site, connected via the VPLS.
The scope of this document will be limited to supporting Ethernet as
the access framing technology for VPLS implementation.
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5 VPLS Reference Model
The following diagram shows a VPLS reference model where PE devices
that are VPLS-capable provide a logical interconnect such that CE
devices belonging to a specific VPLS appear to be connected by a
single logical Ethernet bridge. A VPLS can contain a single VLAN or
multiple, tagged VLANs.
+-----+ +-----+
+ CE1 +--+ +---| CE2 |
+-----+ | ........................ | +-----+
VPLS A | +----+ +----+ | VPLS A
+--| PE |--- Service ---| PE |--+
+----+ Provider +----+
/ . Backbone . \ - /\-_
+-----+ / . | . \ / \ / \ +-----+
+ CE +--+ . | . +--\ Access \----| CE |
+-----+ . +----+ . | Network | +-----+
VPLS B .........| PE |......... \ / VPLS B
+----+ ^ -------
| |
| |
+-----+ |
| CE3 | +-- Logical bridge
+-----+
VPLS A
Separate L2 broadcast domains are maintained on a per VPLS basis by
PE devices. Such domains are then mapped onto tunnels in the service
provider network. These tunnels can either be specific to a VPLS
(e.g. as with IP) or shared among several VPLSs (e.g. as with MPLS
tunnel LSPs). In the above diagram, the top PE routers maintain
separate forwarding instances for VPLS A and VPLS B.
The CE-to-PE links can either be direct physical links, e.g.
100BaseTX, or logical links, e.g. ATM PVC, T1/E1 TDM, or RFC1490-
encapsulated links, over which bridged Ethernet traffic is carried.
The PE-to-PE links carry tunneled Ethernet frames using different
tunneling technologies (e.g., GRE, IPSec, MPLS, L2TP, etc.).
Each PE device learns remote MAC addresses, and is responsible for
proper forwarding of the customer traffic to the appropriate end
nodes. It is responsible for guaranteeing each VPLS topology is loop
free.
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6 VPLS General Requirements
6.1 Layer 2 Domain representation
A VPLS system MUST distinguish different customer domains. Each of
these customer domains MUST appear as a L2 broadcast domain network
behaving like a LAN (Local Area Network). These domains are referred
to as VPLS domains.
A VPLS MAY span multiple service providers. Each VPLS MUST carry a
unique identification within a VPLS system. It is RECOMMENDED that
VPLS identification be globally unique.
Each VPLS domain MUST be capable of learning and forwarding based on
MAC addresses thus emulating an Ethernet virtual switch to the
customer CE devices attached to PEs.
A VPLS system MAY recognize customer VLAN identification. In that
case, a VLAN MUST be recognized in the context of the VPLS it is
part of. If customer VLANs are recognized, separate VLAN broadcast
domains SHOULD be maintained.
A provider's implementation of a VPLS system SHOULD NOT constrain
the customer's ability to configure LAN topologies, tags, 802.1 p-
bits, or any other Layer 2 parameters.
6.2 VPLS Topology
The VPLS system MAY be realized using one or more network tunnel
topologies to interconnect PEs, ranging from simple point-to-point
to distributed hierarchical arrangements. The typical topologies
include:
o point-to-point
o point-to-multipoint, a.k.a. hub and spoke
o any-to-any, a.k.a. full mesh
o mixed, a.k.a. partial mesh
o hierarchical
Regardless of the topology employed, the service to the customers
MUST retain the typical LAN any-to-any connectivity. This
requirement does not imply that all traffic characteristics (such as
bandwidth, QoS, delay, etc.) be necessarily the same between any two
end points.
6.3 Redundancy and Failure Recovery
The VPLS infrastructure SHOULD provide redundant paths to assure
high availability. The reaction to failures SHOULD result in an
attempt to restore the service using alternative paths.
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The intention is to keep the restoration time small. It is
RECOMMENDED that the restoration time be less than the time it takes
the CE devices, or customer L2 control protocols, to detect a
failure in the VPLS.
In cases where the provider knows a priori about impending changes
in network topology, the network SHOULD have the capability to
reconfigure without a loss, duplication, or re-ordering of customer
packets. This situation typically arises with planned network
upgrades or scheduled maintenance activities.
6.4 Policy Constraints
A VPLS system MAY employ policy constraints governing various
interconnection attributes for VPLS domains. Typical attributes
include:
o Selection of available network infrastructure
o QoS services needed
o Protection services needed
o Availability of higher level service access points (see 9.7 )
Policy attributes SHOULD be advertised via the VPLS system's control
plane.
6.5 PE nodes
The PE nodes are the devices in the VPLS system that store
information related to customer VPLS domains and employ methods to
forward customer traffic based on that information. In this
document, the PE nodes are meant in logical sense. In the actual
implementations, the PE nodes may be comprised of several physical
devices. Conversely, a single physical device may contain more than
one PE node.
All forwarding decisions related to customer VPLS traffic MUST be
made by PE nodes. This requirement prohibits any other network
components from altering decisions made by PE nodes.
6.6 PE-PE Interconnection and Tunneling
A VPLS system MUST provide for connectivity between each pair of PE
nodes. The connectivity is referred to as transport tunneling or
simply tunneling.
There are several choices for implementing transport tunnels. Some
popular choices include MPLS, IP in IP tunnels, variations of
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802.1Q, etc. Regardless of the choice, the existence of the tunnels
and their operations MUST be transparent to the customers.
6.7 PE-CE Interconnection and Profiles
A VPLS system MUST provide for connectivity between PE nodes and CE
nodes. That connectivity is referred to as an Attachment Circuit
(AC). Attachment Circuits MAY span networks of other providers or
public networks.
There are several choices for implementing ACs. Some popular choices
include Ethernet, ATM (DSL), Frame Relay, MPLS-based virtual
circuits etc. Regardless of the choice, the ACs MUST use Ethernet
frames as the Service Protocol Data Unit (SPDU).
A CE access connection over an AC MUST be bi-directional in nature.
PE devices MAY support multiple ACs on a single physical interface.
In such cases, PE devices MUST NOT rely on customer controlled
parameters for distinguishing between different access connections.
For example, if VLAN tags were used for that purpose, the provider
would be controlling the assignment of the tag values and would
strictly enforce compliance by the CEs.
An AC connection, whether direct or virtual, MUST maintain all
committed characteristics of the customer traffic, such as QoS,
priorities etc. The characteristics of an AC connection are only
applicable to that connection.
7 Control Plane Requirements
7.1 Provider Edge Signaling
The control protocols SHOULD provide methods for signaling between
PEs. The signaling SHOULD inform of membership, tunneling
information, and other relevant parameters.
The infrastructure MAY employ manual configuration methods to
provide this type of information.
The infrastructure SHOULD use policies to scope the membership and
reachability advertisements for a particular VPLS.
7.2 VPLS Membership Discovery
The control plane and/or the management plane SHOULD provide methods
to discover the PEs which connect CEs forming a VPLS.
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7.3 Support for Layer 2 control protocols
The VPLS system's control protocols SHOULD allow transparent
operation of Layer 2 control protocols employed by customers.
A VPLS system MUST ensure that loops be prevented. This can be
accomplished through a loop free topologies or appropriate
forwarding rules. Control protocols such as Spanning Tree (STP) or
similar could be employed. The system's control protocols MAY use
indications from customer control protocols, e.g. STP, to improve
the operation of a VPLS.
7.4 Scaling Requirements
In a VPLS system, the control plane traffic increases with the
growth of VPLS membership. Similarly, the control plane traffic
increases with the number of supported VPLS domains. The rate of
growth of the associated control plane traffic SHOULD be linear.
The use of control plane resources increases with the number of
hosts connected to a VPLS. The rate of growth of the demand for
control process resources SHOULD be linear. The control plane MAY
offer means for enforcing a limit on the number of customer hosts
attached to a VPLS.
8 Data Plane Requirements
8.1 Transparency
VPLS service is intended to be transparent to Layer 2 customer
networks. It SHOULD NOT require any special packet processing by
the end users before sending packets to the provider's network.
8.2 QoS and packet re-ordering
A VPLS system SHOULD have capabilities to enforce QoS parameters.
The queuing and forwarding policies SHOULD preserve packet order for
packets with the same QoS parameters.
The service SHOULD not duplicate packets.
8.3 Broadcast Domain
The Broadcast Domain is defined as the flooding scope of a Layer 2
network. A separate Broadcast Domain MUST be maintained for each
VPLS.
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In addition to VPLS Broadcast Domains, a VPLS system MAY recognize
customer VLAN Broadcast Domains. In that case, the system SHOULD
maintain a separate VLAN Broadcast Domain for each customer VLAN. A
VLAN Broadcast Domain MUST be a subset of the owning VPLS Broadcast
Domain.
8.4 MAC address learning
A VPLS service SHOULD derive all topology and forwarding information
from packets originating at customer sites. Typically, MAC
addresses learning mechanisms are used for this purpose.
In a VPLS system, MAC address learning MUST take place on a per
Virtual Switching Instance (VSI) basis, i.e. in the context of a
VPLS and, if supported, in the context of VLANs therein.
8.5 Unicast, Unknown Unicast, Multicast, and Broadcast forwarding
VPLS MUST be aware of the existence and the designated roles of
special MAC addresses such as Multicast and Broadcast addresses.
VPLS MUST forward these packets according to their intended
functional meaning and scope.
Broadcast packets MUST be flooded to all destinations.
Multicast packets MUST be flooded to all destinations. However, a
VPLS system MAY employ multicast snooping techniques, in which case
multicast packets SHOULD be forwarded only to their intended
destinations.
Unicast packets MUST be forwarded to their intended destinations.
Unknown Unicast packets MUST be flooded to all destinations in the
flooding scope of the VPLS (or VLAN). If the VPLS service relies on
MAC learning for its operations, it MUST assure proper forwarding of
packets with MAC addresses that have not been learned. Once
destination MAC addresses are learned, unicast packets SHOULD be
forwarded only to their intended destinations.
A provider MAY employ a method to limit the scope of flooding of
Unknown Unicast packets in cases where a customer desires to
conserve its bandwidth or wants to implement certain security
policies.
8.6 Virtual Switching Instance
VPLS Provider Edge devices MUST maintain a separate Virtual
Switching Instance (VSI) per each VPN. Each VSI MUST have
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capabilities to forward traffic based on customer's traffic
parameters such as MAC addresses, VLAN tags (if supported), etc. as
well as local policies.
VPLS Provider Edge devices MUST have capabilities to classify
incoming customer traffic into the appropriate VSI.
Each VSI MUST have flooding capabilities for its Broadcast Domain to
facilitate proper forwarding of Broadcast, Multicast and Unknown
Unicast customer traffic.
8.7 Minimum MTU
The VPLS service MUST support customer frames with payload 1500
bytes long. The service MAY offer support for longer frames.
The service MUST NOT fragment packets. Packets exceeding committed
MTU size MUST be discarded.
The committed minimum MTU size MUST be the same for a given instance
of VPLS. Different VPLS instances MAY have different committed MTU
sizes. If VLANs are supported, all VLANs within a given VPLS MUST
inherit the same MTU size.
8.8 Multilink Access
The VPLS service SHOULD support multilink access for CE devices.
The VPLS service MAY support multihome access for CE devices.
8.9 End-point VLAN tag translation
If VLANs are recognized, the VPLS system MAY support translation of
customers' VLAN tags. Such service simplifies connectivity of sites
that want to keep their tag assignments or sites that belong to
different administrative entities. In the latter case, the
connectivity is sometimes referred to as L2 extranet.
8.10 Support for MAC Services
VPLS are REQUIRED to provide MAC service compliant with IEEE 802.1D
specification [5] Section 6. Compliance with this section
facilitates proper operation of 802.1 LAN and seamless integration
of VPLS with bridged Local Area Networks. It is also useful to
compare [6], [7], and [8].
A MAC service in the context of VPLS is defined as the transfer of
user data between source and destination end stations via the
service access points using the information specified in the VSI.
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1. A PE device that provides VPLS MUST NOT be directly accessed by
end stations except for explicit management purposes.
2. All MAC addresses MUST be unique within a given broadcast domain.
3. The topology and configuration of the VPLS MUST NOT restrict the
MAC addresses of end stations
9 Management and Operations Requirements
9.1 VPLS configuration and monitoring
A VPLS system MUST have capabilities to configure, manage, and
monitor its different components.
It SHOULD be possible to create several disjoint instances of VPLS
systems within the same underlying network infrastructures.
The infrastructure SHOULD monitor all characteristics of the service
that are reflected in the customer SLA. This includes but is not
limited to bandwidth usage, packet counts, packet drops, service
outages, etc.
9.2 VPLS operations
The operations of a VPLS systems is controlled by an Administrative
Authority (Admin). The Admin is the originator of all operational
parameters of a VPLS system. Conversely, the admin is also the
ultimate destination for the status of the VPLS system and the
related statistical information. A typical VPLS system spans
several such Admins.
A VPLS system MUST support proper dissemination of operational
parameters to all elements of a VPLS system in the presence of
multiple Admins.
A VPLS system MUST employ mechanisms for sharing operational
parameters between different Admins. These mechanism MUST NOT
assume any particular structure of the different Admins. For
example the VPLS should not be relying on Admins forming a
hierarchy.
A VPLS system SHOULD support policies for proper selection of
operational parameters coming from different Admins. Similarly, a
VPLS system SHOULD support policies for selecting information to be
disseminated to different Admins.
A VPLS system SHOULD employ discovery mechanisms to minimize the
amount of operational information maintained by the Admins. For
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example, if an admin adds or removes a customer port on a given PE,
the remaining PEs should determine the necessary actions to take
without the Admins having to explicitly reconfigure those PEs.
9.3 CE Provisioning
The VPLS MUST require only minimal or no configuration on the CE
devices, depending on the CE device that connects into the
infrastructure.
9.4 Customer traffic policing
The VPLS service SHOULD provide the ability to police and/or shape
customer traffic entering and leaving the VPLS system.
9.5 Dynamic Service Signaling
A Provider MAY offer to customers an in-band method for selecting
services from the list specified in the SLA. A Provider MAY use the
same mechanism for reporting statistical data related to the
service.
9.6 Class of Service Model
The VPLS service MAY define a graded selection of classes of
traffic. These include, but are not limited to
o range of priorities
o best effort vs. guaranteed effort
o range of minimum delay characteristics
9.7 VPLS service access option.
The VPLS service SHOULD allow for a Provider based Service Access
for orderly injection of L3 or higher services to the customers'
VPLS networks.
In particular, the system SHOULD allow to build L3VPN services,
including L3 interworking schemes such as ARP mediation or similar.
As a value added service, a Provider MAY offer access to other
services such as, IP gateways, storage networks, content delivery
etc.
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9.8 Testing
The VPLS service SHOULD provide the ability to test and verify
operational and maintenance activities on a per VPLS basis and, if
supported, on a per VLAN basis.
9.9 Learning information from customer devices
The VPLS service SHOULD provide means for limiting the amount of
information learned from customer devices. For example, VPLS
implementations may limit the number of MAC addresses learned from
the customers' devices.
10 Security Requirements
10.1 Traffic separation
A VPLS system MUST provide traffic separation between different VPLS
domains. If VLANs are supported, the system MUST provide traffic
separation between customer VLANs within each VPLS domain.
10.2 Provider network protection.
A VPLS system MUST be immune to malformed or maliciously constructed
customer traffic. This includes but is not limited to duplicate or
invalid L2 addresses, customer side loops, short/long packets,
spoofed management packets, spoofed VLAN tags, etc.
The VPLS infrastructure devices MUST NOT be accessible from the
VPLS.
10.3 Value added security services
Value added security services such as encryption and/or
authentication of customer packets, certificate management, and
similar are OPTIONAL.
Security measures employed by the VPLS system SHOULD NOT restrict
implementation of customer based security add-ons.
11 References
1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
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2. Carugi, et al., "Service requirements for Provider Provisioned
Virtual Private Networks ", Work in progress, December 2001.
3. Nagarajan et al., " Generic Requirements for Provider Provisioned
VPN", Work in progress, September 2002.
4. Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
5. ANSI/IEEE Std 802.1D 1998 Edition, "Media Access Control (MAC)
Bridges", 1998.
6. IEEE Standard 802.1Q, "IEEE Standards for Local and Metropolitan
Area Networks: Virtual Bridged Local Area Networks", 1998.
7. IEEE Standard 802.1u-2001, "IEEE Standard for Local and
Metropolitan Area Networks: Virtual Bridged Local Area Networks -
Amendment 1: Technical and editorial corrections", 2001.
8. IEEE Standard 802.1v-2001, "IEEE Standard for Local and
Metropolitan Area Networks: Virtual Bridged Local Area Networks -
Amendment 2: VLAN Classification by Protocol and Port", 2001.
12 Acknowledgments
We would like to acknowledge extensive comments provided by Loa
Anderson, Joel Halpern, and Eric Rosen. The authors, also, wish to
extend appreciations to their respective employers and various other
people who volunteered to review this work and provided feedback.
13 Authors' Addresses
Waldemar Augustyn
Email: waldemar@nxp.com
Giles Heron
PacketExchange Ltd.
The Truman Brewery
91 Brick Lane
London E1 6QL
United Kingdom
Email: giles@packetexchange.net
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Vach Kompella
TiMetra Networks
274 Ferguson Dr.
Mountain View, CA 94043
Email: vkompella@timetra.com
Marc Lasserre
Riverstone Networks
5200 Great America Pkwy
Santa Clara, CA 95054
Phone: 408-878-6500
Email: marc@riverstonenet.com
Pascal Menezes
Terabeam
Phone: 206-686-2001
Email: pascal.menezes@terabeam.com
Hamid Ould-Brahim
Nortel Networks
P.O. Box 3511 Station C
Ottawa ON K1Y 4H7
Canada
Phone: 613-765-3418
Email: hbrahim@nortelnetworks.com
Tissa Senevirathne
Email: tsenevir@hotmail.com
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