draft-ietf-l2vpn-vpls-bgp-06.txt   draft-ietf-l2vpn-vpls-bgp-07.txt 
Network Working Group K. Kompella, Ed. Network Working Group K. Kompella, Ed.
Internet-Draft Y. Rekhter, Ed. Internet-Draft Y. Rekhter, Ed.
Expires: July 1, 2006 Juniper Networks Expires: December 19, 2006 Juniper Networks
December 28, 2005 June 17, 2006
Virtual Private LAN Service Virtual Private LAN Service (VPLS) Using BGP for Auto-discovery and
draft-ietf-l2vpn-vpls-bgp-06 Signaling
draft-ietf-l2vpn-vpls-bgp-07
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2006).
Abstract Abstract
Virtual Private LAN (Local Area Network) Service (VPLS), also known Virtual Private LAN Service (VPLS), also known as Transparent LAN
as Transparent LAN Service, and Virtual Private Switched Network Service, and Virtual Private Switched Network service, is a useful
service, is a useful Service Provider offering. The service offers a Service Provider offering. The service offers a Layer 2 Virtual
Layer 2 Virtual Private Network (VPN); however, in the case of VPLS, Private Network (VPN); however, in the case of VPLS, the customers in
the customers in the VPN are connected by a multipoint Ethernet LAN, the VPN are connected by a multipoint Ethernet Local Area Network
in contrast to the usual Layer 2 VPNs, which are point-to-point in (LAN), in contrast to the usual Layer 2 VPNs, which are point-to-
nature. point in nature.
This document describes the functions required to offer VPLS, a This document describes the functions required to offer VPLS, a
mechanism for signaling a VPLS, and rules for forwarding VPLS frames mechanism for signaling a VPLS, and rules for forwarding VPLS frames
across a packet switched network. across a packet switched network.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Scope of this Document . . . . . . . . . . . . . . . . . . 4 1.1. Scope of this Document . . . . . . . . . . . . . . . . . . 4
1.2. Conventions used in this document . . . . . . . . . . . . 5 1.2. Conventions used in this document . . . . . . . . . . . . 5
1.3. Changes from version 05 to 06 . . . . . . . . . . . . . . 5 1.3. Changes from version 06 to 07 . . . . . . . . . . . . . . 5
1.4. Changes from version 04 to 05 . . . . . . . . . . . . . . 5 1.4. Changes from version 04 to 05 . . . . . . . . . . . . . . 6
1.5. Changes from version 03 to 04 . . . . . . . . . . . . . . 6 1.5. Changes from version 03 to 04 . . . . . . . . . . . . . . 6
2. Functional Model . . . . . . . . . . . . . . . . . . . . . . . 7 2. Functional Model . . . . . . . . . . . . . . . . . . . . . . . 8
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 8
2.2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 8 2.2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 9
2.3. Interactions . . . . . . . . . . . . . . . . . . . . . . . 8 2.3. Interactions . . . . . . . . . . . . . . . . . . . . . . . 9
3. Control Plane . . . . . . . . . . . . . . . . . . . . . . . . 10 3. Control Plane . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Autodiscovery . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Autodiscovery . . . . . . . . . . . . . . . . . . . . . . 11
3.1.1. Functions . . . . . . . . . . . . . . . . . . . . . . 10 3.1.1. Functions . . . . . . . . . . . . . . . . . . . . . . 11
3.1.2. Protocol Specification . . . . . . . . . . . . . . . . 11 3.1.2. Protocol Specification . . . . . . . . . . . . . . . . 12
3.2. Signaling . . . . . . . . . . . . . . . . . . . . . . . . 11 3.2. Signaling . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.1. Label Blocks . . . . . . . . . . . . . . . . . . . . . 12 3.2.1. Concepts . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.2. VPLS BGP NLRI . . . . . . . . . . . . . . . . . . . . 12 3.2.2. PW Setup and Teardown . . . . . . . . . . . . . . . . 14
3.2.3. PW Setup and Teardown . . . . . . . . . . . . . . . . 13 3.2.3. Signaling PE Capabilities . . . . . . . . . . . . . . 15
3.2.4. Signaling PE Capabilities . . . . . . . . . . . . . . 14 3.3. BGP VPLS Operation . . . . . . . . . . . . . . . . . . . . 16
3.3. BGP VPLS Operation . . . . . . . . . . . . . . . . . . . . 15 3.4. Multi-AS VPLS . . . . . . . . . . . . . . . . . . . . . . 17
3.4. Multi-AS VPLS . . . . . . . . . . . . . . . . . . . . . . 16 3.4.1. a) VPLS-to-VPLS connections at the ASBRs. . . . . . . 18
3.4.1. a) VPLS-to-VPLS connections at the ASBRs. . . . . . . 17
3.4.2. b) EBGP redistribution of VPLS information between 3.4.2. b) EBGP redistribution of VPLS information between
ASBRs. . . . . . . . . . . . . . . . . . . . . . . . . 17 ASBRs. . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.3. c) Multi-hop EBGP redistribution of VPLS 3.4.3. c) Multi-hop EBGP redistribution of VPLS
information between ASes. . . . . . . . . . . . . . . 18 information between ASes. . . . . . . . . . . . . . . 20
3.4.4. Allocation of VE IDs Across Multiple ASes . . . . . . 19 3.4.4. Allocation of VE IDs Across Multiple ASes . . . . . . 20
3.5. Multi-homing and Path Selection . . . . . . . . . . . . . 19 3.5. Multi-homing and Path Selection . . . . . . . . . . . . . 21
3.6. Hierarchical BGP VPLS . . . . . . . . . . . . . . . . . . 20 3.6. Hierarchical BGP VPLS . . . . . . . . . . . . . . . . . . 21
4. Data Plane . . . . . . . . . . . . . . . . . . . . . . . . . . 22 4. Data Plane . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 22 4.1. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 23
4.2. Forwarding . . . . . . . . . . . . . . . . . . . . . . . . 22 4.2. Forwarding . . . . . . . . . . . . . . . . . . . . . . . . 23
4.2.1. MAC address learning . . . . . . . . . . . . . . . . . 22 4.2.1. MAC address learning . . . . . . . . . . . . . . . . . 23
4.2.2. Aging . . . . . . . . . . . . . . . . . . . . . . . . 23 4.2.2. Flooding . . . . . . . . . . . . . . . . . . . . . . . 23
4.2.3. Flooding . . . . . . . . . . . . . . . . . . . . . . . 23 4.2.3. "Split Horizon" Forwarding . . . . . . . . . . . . . . 24
4.2.4. Broadcast and Multicast . . . . . . . . . . . . . . . 23 5. Deployment Options . . . . . . . . . . . . . . . . . . . . . . 25
4.2.5. "Split Horizon" Forwarding . . . . . . . . . . . . . . 24 6. Security Considerations . . . . . . . . . . . . . . . . . . . 26
4.2.6. Qualified and Unqualified Learning . . . . . . . . . . 24
4.2.7. Class of Service . . . . . . . . . . . . . . . . . . . 25
5. Deployment Options . . . . . . . . . . . . . . . . . . . . . . 26
6. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8.1. Normative References . . . . . . . . . . . . . . . . . . . 29 8.1. Normative References . . . . . . . . . . . . . . . . . . . 29
8.2. Informative References . . . . . . . . . . . . . . . . . . 29 8.2. Informative References . . . . . . . . . . . . . . . . . . 29
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 31 Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 31
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 32 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33
Intellectual Property and Copyright Statements . . . . . . . . . . 34 Intellectual Property and Copyright Statements . . . . . . . . . . 34
1. Introduction 1. Introduction
Virtual Private LAN Service (VPLS), also known as Transparent LAN Virtual Private LAN (Local Area Network) Service (VPLS), also known
Service, and Virtual Private Switched Network service, is a useful as Transparent LAN Service, and Virtual Private Switched Network
service offering. A Virtual Private LAN appears in (almost) all service, is a useful service offering. A Virtual Private LAN appears
respects as an Ethernet LAN to customers of a Service Provider. in (almost) all respects as an Ethernet LAN to customers of a Service
However, in a VPLS, the customers are not all connected to a single Provider. However, in a VPLS, the customers are not all connected to
LAN; the customers may be spread across a metro or wide area. In a single LAN; the customers may be spread across a metro or wide
essence, a VPLS glues together several individual LANs across a area. In essence, a VPLS glues together several individual LANs
packet-switched network to appear and function as a single LAN ([7]). across a packet-switched network to appear and function as a single
This is accomplished by incorporating MAC address learning, flooding LAN ([9]).
and forwarding functions in the context of pseudowires that connect
these individual LANs across the packet-switched network.
This document details the functions needed to offer VPLS, and then This document describes the functions needed to offer VPLS, and goes
goes on to describe a mechanism for the autodiscovery of the on to describe a mechanism for signaling a VPLS, as well as a
endpoints of a VPLS as well as for signaling a VPLS. It also mechanism for transport of VPLS frames over tunnels across a packet
describes how VPLS frames are transported over tunnels across a switched network. The signaling mechanism uses BGP as the control
packet switched network. The autodiscovery and signaling mechanism plane protocol. This document also briefly discusses deployment
uses BGP as the control plane protocol. This document also briefly options, in particular, the notion of decoupling functions across
discusses deployment options, in particular, the notion of decoupling devices.
functions across devices.
Alternative approaches include: [13], which allows one to build a Alternative approaches include: [14], which allows one to build a
Layer 2 VPN with Ethernet as the interconnect; and [12]), which Layer 2 VPN with Ethernet as the interconnect; and [13]), which
allows one to set up an Ethernet connection across a packet-switched allows one to set up an Ethernet connection across a packet-switched
network. Both of these, however, offer point-to-point Ethernet network. Both of these, however, offer point-to-point Ethernet
services. What distinguishes VPLS from the above two is that a VPLS services. What distinguishes VPLS from the above two is that a VPLS
offers a multipoint service. A mechanism for setting up pseudowires offers a multipoint service. A mechanism for setting up pseudowires
for VPLS using the Label Distribution Protocol (LDP) is defined in for VPLS using the Label Distribution Protocol (LDP) is defined in
[8]. [10].
1.1. Scope of this Document 1.1. Scope of this Document
This document has four major parts: defining a VPLS functional model; This document has four major parts: defining a VPLS functional model;
defining a control plane for setting up VPLS; defining the data plane defining a control plane for setting up VPLS; defining the data plane
for VPLS (encapsulation and forwarding of data); and defining various for VPLS (encapsulation and forwarding of data); and defining various
deployment options. deployment options.
The functional model underlying VPLS is laid out in Section 2. This The functional model underlying VPLS is laid out in Section 2. This
describes the service being offered, the network components that describes the service being offered, the network components that
interact to provide the service, and at a high level their interact to provide the service, and at a high level their
interactions. interactions.
The control plane described in this document uses Multiprotocol BGP The control plane described in this document uses Multiprotocol BGP
[3] to establish VPLS service, i.e., for the autodiscovery of VPLS [4] to establish VPLS service, i.e., for the autodiscovery of VPLS
members and for the setup and teardown of the pseudowires that members and for the setup and teardown of the pseudowires that
constitute a given VPLS instance. Section 3 focuses on this, and constitute a given VPLS instance. Section 3 focuses on this, and
also describes how a VPLS that spans Autonomous System boundaries is also describes how a VPLS that spans Autonomous System boundaries is
set up, as well as how multi-homing is handled. Using BGP as the set up, as well as how multi-homing is handled. Using BGP as the
control plane for VPNs is not new (see [13], [10] and [9]): what is control plane for VPNs is not new (see [14], [6] and [11]): what is
described here is based on the mechanisms proposed in [10]. described here is based on the mechanisms proposed in [6].
The forwarding plane and the actions that a participating Provider The forwarding plane and the actions that a participating Provider
Edge (PE) router offering the VPLS service must take is described in Edge router offering the VPLS service must take is described in
Section 4. Section 4.
In Section 5, the notion of 'decoupled' operation is defined, and the In Section 5, the notion of 'decoupled' operation is defined, and the
interaction of decoupled and non-decoupled PEs is described. interaction of decoupled and non-decoupled Provider Edge routers is
Decoupling allows for more flexible deployment of VPLS. described. Decoupling allows for more flexible deployment of VPLS.
1.2. Conventions used in this document 1.2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 ([1]). document are to be interpreted as described in RFC 2119 ([1]).
1.3. Changes from version 05 to 06 1.3. Changes from version 06 to 07
[NOTE to RFC Editor: this section is to be removed before [NOTE to RFC Editor: this section is to be removed before
publication.] publication.]
Changes in response to GenART review. Note: the DISCUSSes below are referred to by id; they can be accessed
at https://datatracker.ietf.org/public/
pidtracker.cgi?command=view_comment&id=[ID]
Updated Abstract and Introduction to make it clear that VPLS is an Updated title of doc to reflect use of BGP. (Fenner's DISCUSS id
Ethernet-based service. 44901).
Added sections on Aging, Broadcast and Multicast, Qualified and Addressed Russ Housley's DISCUSSes on Figure 6 and Section 6 (ids
Unqualified learning and CoS. Also added a section on scaling the 44778 and 44779).
BGP control plane. These were requested for consistency between the
BGP and LDP VPLS documents.
Added a section clarifying the concepts of label blocks, why they are Addressed Sam Hartman's DISCUSS on the Security Considerations (id
necessary and how they are used. 48432).
For multi-AS operation, added a short introduction to the three Resolution of Kessens' DISCUSS (id 44870):
options, comparing their usage.
Lots of clean-up: consistent usage of terms, expansion of acronyms 1. Reference to RFC 4364 has been made normative. There is no
before use, references. normative text in ref draft-kompella-l2vpn-l2vpn -- any such text
has long since been incorporated directly into this document.
2. Description and IANA section updated.
3. Expanded section (b) of Section 3.4 to clarify the data plane
operation for option b.
4. Updated Section 3.5 to clarify that a VPLS customer can run STP
independent of whether the SP uses multi-homing or not.
5. P bit text deleted (left over from an earlier edit.)
6. Addressed (hopefully) by Sam's DISCUSS.
7. Updated Security Considerations to incorporate the techniques
described in RFC 4364 for inter-AS VPNs. Also, added a paragraph
stating that misconfiguration could cause inter-VPLS connections,
just as can happen with RFC 4364.
Updated references; added reference to RFC 4023.
1.4. Changes from version 04 to 05 1.4. Changes from version 04 to 05
[NOTE to RFC Editor: this section is to be removed before [NOTE to RFC Editor: this section is to be removed before
publication.] publication.]
Updated IANA section to reflect agreement with authors of [9] that
Updated IANA section to reflect agreement with authors of [11] that
the two docs should use the same AFI for L2VPN information. the two docs should use the same AFI for L2VPN information.
Addressed comments received from Alex Zinin. No technical changes, Addressed comments received from Alex Zinin. No technical changes,
but a more complete description to cover the issues that Alex raised: but a more complete description to cover the issues that Alex raised:
1. encoding of BGP NEXT_HOP for the new AFI/SAFI is not described 1. encoding of BGP NEXT_HOP for the new AFI/SAFI is not described
2. VE ID, Block offset, Block size, Label base are not described 2. VE ID, Block offset, Block size, Label base are not described
anywhere anywhere
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---- / | ---- ---- / | ----
/ \/ \ / \ CE = Customer Edge Device / \/ \ / \ CE = Customer Edge Device
| A3 CE3 --CE4 A4 | PE = Provider Edge Router | A3 CE3 --CE4 A4 | PE = Provider Edge Router
\ / \ / u-PE = Layer 2 Aggregation \ / \ / u-PE = Layer 2 Aggregation
---- ---- A<n> = Customer site n ---- ---- A<n> = Customer site n
Figure 1: Example of a VPLS Figure 1: Example of a VPLS
2.1. Terminology 2.1. Terminology
Terminology similar to that in [10] is used: a Service Provider (SP) Terminology similar to that in [6] is used: a Service Provider (SP)
network with P (Provider-only) and PE (Provider Edge) routers, and network with P (Provider-only) and PE (Provider Edge) routers, and
customers with CE (Customer Edge) devices. Here, however, there is customers with CE (Customer Edge) devices. Here, however, there is
an additional concept, that of a "u-PE", a Layer 2 PE device used for an additional concept, that of a "u-PE", a Layer 2 PE device used for
Layer 2 aggregation. The notion of u-PE is described further in Layer 2 aggregation. The notion of u-PE is described further in
Section 5. PE and u-PE devices are "VPLS-aware", which means that Section 5. PE and u-PE devices are "VPLS-aware", which means that
they know that a VPLS service is being offered. We will call these they know that a VPLS service is being offered. We will call these
VPLS edge devices, which could be either a PE or an u-PE, a VE. VPLS edge devices, which could be either a PE or an u-PE, a VE.
In contrast, the CE device (which may be owned and operated by either In contrast, the CE device (which may be owned and operated by either
the SP or the customer) is VPLS-unaware; as far as the CE is the SP or the customer) is VPLS-unaware; as far as the CE is
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tunnels, established by RSVP-TE or LDP. These tunnels are tunnels, established by RSVP-TE or LDP. These tunnels are
established independently of the services offered over them; the established independently of the services offered over them; the
signaling and establishment of these tunnels are not discussed in signaling and establishment of these tunnels are not discussed in
this document. this document.
"Flooding" and MAC address "learning" (see Section 4) are an integral "Flooding" and MAC address "learning" (see Section 4) are an integral
part of VPLS. However, these activities are private to an SP device, part of VPLS. However, these activities are private to an SP device,
i.e., in the VPLS described below, no SP device requests another SP i.e., in the VPLS described below, no SP device requests another SP
device to flood packets or learn MAC addresses on its behalf. device to flood packets or learn MAC addresses on its behalf.
All the PEs participating in a VPLS are assumed to be fully meshed in All the PEs participating in a VPLS are assumed to be fully meshed
the data plane, i.e., there is a bidirectional pseudowire between with pseudowires specific to that VPLS, i.e., every (ingress) PE can
every pair of PEs participating in that VPLS, and thus every send a VPLS packet to the egress PE(s) directly, without the need for
(ingress) PE can send a VPLS packet to the egress PE(s) directly, an intermediate PE (see Section 4.2.3.) This places a stringent
without the need for an intermediate PE (see Section 4.2.5.) This requirement on VPLS signaling (see Section 3.6.)
requires that VPLS PEs are logically fully meshed in the control
plane so that a PE can send a message to another PE to set up the
necessary pseudowires. See Section 3.6 for a discussion on
alternatives to achieve a logical full mesh in the control plane.
2.3. Interactions 2.3. Interactions
VPLS is a "LAN Service" in that CE devices that belong to VPLS V can VPLS is a "LAN Service" in that CE devices that belong to VPLS V can
interact through the SP network as if they were connected by a LAN. interact through the SP network as if they were connected by a LAN.
VPLS is "private" in that CE devices that belong to different VPLSs VPLS is "private" in that CE devices that belong to different VPLSs
cannot interact. VPLS is "virtual" in that multiple VPLSs can be cannot interact. VPLS is "virtual" in that multiple VPLSs can be
offered over a common packet switched network. offered over a common packet switched network.
PE devices interact to "discover" all the other PEs participating in PE devices interact to "discover" all the other PEs participating in
the same VPLS, and to exchange demultiplexors. These interactions the same VPLS, and to exchange demultiplexors. These interactions
are control-driven, not data-driven. are control-driven, not data-driven.
u-PEs interact with PEs to establish connections with remote PEs or u-PEs interact with PEs to establish connections with remote PEs or
u-PEs in the same VPLS. This interaction is control-driven. u-PEs in the same VPLS. This interaction is control-driven.
PE devices can participate simultaneously in both VPLS and IP VPNs PE devices can participate simultaneously in both VPLS and IP VPNs
([10]). These are independent services, and the information ([6]). These are independent services, and the information exchanged
exchanged for each type of service is kept separate as the Network for each type of service is kept separate as the Network Layer
Layer Reachability Information (NLRI) used for this exchange have Reachability Information (NLRI) used for this exchange have different
different Address Family Identifiers (AFI) and Subsequent Address Address Family Identifiers (AFI) and Subsequent Address Family
Family Identifiers (SAFI). Consequently, an implementation MUST Identifiers (SAFI). Consequently, an implementation MUST maintain a
maintain a separate routing storage for each service. However, separate routing storage for each service. However, multiple
multiple services can use the same underlying tunnels; the VPLS or services can use the same underlying tunnels; the VPLS or VPN label
VPN label is used to demultiplex the packets belonging to different is used to demultiplex the packets belonging to different services.
services.
3. Control Plane 3. Control Plane
There are two primary functions of the VPLS control plane: There are two primary functions of the VPLS control plane:
autodiscovery, and setup and teardown of the pseudowires that autodiscovery, and setup and teardown of the pseudowires that
constitute the VPLS, often called signaling. Section 3.1 and constitute the VPLS, often called signaling. Section 3.1 and
Section 3.2 describe these functions. Both of these functions are Section 3.2 describe these functions. Both of these functions are
accomplished with a single BGP Update advertisement; Section 3.3 accomplished with a single BGP Update advertisement; Section 3.3
describes how this is done by detailing BGP protocol operation for describes how this is done by detailing BGP protocol operation for
VPLS. Section 3.4 describes the setting up of pseudowires that span VPLS. Section 3.4 describes the setting up of pseudowires that span
Autonomous Systems. Section 3.5 describes how multi-homing is Autonomous Systems. Section 3.5 describes how multi-homing is
handled. handled.
3.1. Autodiscovery 3.1. Autodiscovery
Discovery refers to the process of finding all the PEs that Discovery refers to the process of finding all the PEs that
participate in a given VPLS instance. A PE can either be configured participate in a given VPLS. A PE can either be configured with the
with the identities of all the other PEs in a given VPLS, or the PE identities of all the other PEs in a given VPLS, or the PE can use
can use some protocol to discover the other PEs. The latter is some protocol to discover the other PEs. The latter is called
called autodiscovery. autodiscovery.
The former approach is fairly configuration-intensive, especially The former approach is fairly configuration-intensive, especially
since it is required that the PEs participating in a given VPLS are since it is required that the PEs participating in a given VPLS are
fully meshed (i.e., that every PE in a given VPLS establish fully meshed (i.e., that every PE in a given VPLS establish
pseudowires to every other PE in that VPLS). Furthermore, when the pseudowires to every other PE in that VPLS). Furthermore, when the
topology of a VPLS changes (i.e., a PE is added to, or removed from topology of a VPLS changes (i.e., a PE is added to, or removed from
the VPLS), the VPLS configuration on all PEs in that VPLS must be the VPLS), the VPLS configuration on all PEs in that VPLS must be
changed. changed.
In the autodiscovery approach, each PE "discovers" which other PEs In the autodiscovery approach, each PE "discovers" which other PEs
are part of a given VPLS by means of some protocol, in this case BGP. are part of a given VPLS by means of some protocol, in this case BGP.
This allows each PE's configuration to consist only of the identity This allows each PE's configuration to consist only of the identity
of the VPLS instance established on this PE, not the identity of of the VPLS instance established on this PE, not the identity of
every other PE in that VPLS instance -- that is auto-discovered. every other PE in that VPLS instance -- that is auto-discovered.
Moreover, when the topology of a VPLS changes, only the affected PE's Moreover, when the topology of a VPLS changes, only the affected PE's
configuration changes; other PEs automatically find out about the configuration changes; other PEs automatically find out about the
change and adapt. change and adapt.
3.1.1. Functions 3.1.1. Functions
A PE that participates in a given VPLS instance V must be able to A PE that participates in a given VPLS V must be able to tell all
tell all other PEs in VPLS V that it is also a member of V. A PE must other PEs in VPLS V that it is also a member of V. A PE must also
also have a means of declaring that it no longer participates in a have a means of declaring that it no longer participates in a VPLS.
VPLS. To do both of these, the PE must have a means of identifying a To do both of these, the PE must have a means of identifying a VPLS
VPLS and a means by which to communicate to all other PEs. and a means by which to communicate to all other PEs.
U-PE devices also need to know what constitutes a given VPLS; U-PE devices also need to know what constitutes a given VPLS;
however, they don't need the same level of detail. The PE (or PEs) however, they don't need the same level of detail. The PE (or PEs)
to which a u-PE is connected gives the u-PE an abstraction of the to which a u-PE is connected gives the u-PE an abstraction of the
VPLS; this is described in section 5. VPLS; this is described in section 5.
3.1.2. Protocol Specification 3.1.2. Protocol Specification
The specific mechanism for autodiscovery described here is based on The specific mechanism for autodiscovery described here is based on
[13] and [10]; it uses BGP extended communities [4] to identify [14] and [6]; it uses BGP extended communities [5] to identify
members of a VPLS, in particular, the Route Target community, whose members of a VPLS, in particular, the Route Target community, whose
format is described in [4]. The semantics of the use of Route format is described in [5]. The semantics of the use of Route
Targets is described in [10]; their use in VPLS is identical. Targets is described in [6]; their use in VPLS is identical.
As it has been assumed that VPLSs are fully meshed, a single Route As it has been assumed that VPLSs are fully meshed, a single Route
Target RT suffices for a given VPLS V, and in effect that RT is the Target RT suffices for a given VPLS V, and in effect that RT is the
identifier for VPLS V. identifier for VPLS V.
A PE announces (typically via I-BGP) that it belongs to VPLS V by A PE announces (typically via I-BGP) that it belongs to VPLS V by
annotating its NLRIs for V (see next subsection) with Route Target annotating its NLRIs for V (see next subsection) with Route Target
RT, and acts on this by accepting NLRIs from other PEs that have RT, and acts on this by accepting NLRIs from other PEs that have
Route Target RT. A PE announces that it no longer participates in V Route Target RT. A PE announces that it no longer participates in V
by withdrawing all NLRIs that it had advertised with Route Target RT. by withdrawing all NLRIs that it had advertised with Route Target RT.
skipping to change at page 12, line 5 skipping to change at page 12, line 51
Using a distinct BGP Update message to send a demultiplexor to each Using a distinct BGP Update message to send a demultiplexor to each
remote PE would require the originating PE to send N such messages remote PE would require the originating PE to send N such messages
for N remote PEs. The solution described in this document allows a for N remote PEs. The solution described in this document allows a
PE to send a single (common) Update message that contains PE to send a single (common) Update message that contains
demultiplexors for all the remote PEs, instead of N individual demultiplexors for all the remote PEs, instead of N individual
messages. Doing this reduces the control plane load both on the messages. Doing this reduces the control plane load both on the
originating PE as well as on the BGP Route Reflectors that may be originating PE as well as on the BGP Route Reflectors that may be
involved in distributing this Update to other PEs. involved in distributing this Update to other PEs.
3.2.1. Label Blocks
To accomplish this, we introduce the notion of "label blocks". A To accomplish this, we introduce the notion of "label blocks". A
label block, defined by a label base LB and a VE block size VBS, is a label block, defined by a label base LB and a block size VBS, is a
contiguous set of labels {LB, LB+1, ..., LB+VBS-1}. Here's how label contiguous set of labels {LB, LB+1, ..., LB+VBS-1}. Here's how label
blocks work. All PEs within a given VPLS are assigned unique VE IDs blocks work. All PEs within a given VPLS are assigned unique VE IDs
as part of their configuration. A PE X wishing to send a VPLS update as part of their configuration. A PE X wishing to send a VPLS update
sends the same label block information to all other PEs. Each sends the same label block information to all other PEs. Each
receiving PE infers the label intended for PE X by adding their receiving PE infers the label intended for PE X by adding their
(unique) VE ID to the label base. In this manner, each receiving PE (unique) VE ID to the label base. In this manner, each receiving PE
gets a unique demultiplexor for PE X for that VPLS. gets a unique demultiplexor for PE X for that VPLS.
This simple notion is enhanced with the concept of a VE block offset This simple notion is enhanced with the concept of a block offset
VBO. A label block defined by <LB, VBO, VBS> is the set {LB+VBO, LB+ VBO. A label block defined by <LB, VBO, VBS> is the set {LB+VBO, LB+
VBO+1, ..., LB+VBO+VBS-1}. Thus, instead of a single large label VBO+1, ..., LB+VBO+VBS-1}. Thus, instead of a single large label
block to cover all VE IDs in a VPLS, one can have several label block to cover all VE IDs in a VPLS, one can have several label
blocks, each with a different label base. This makes label block blocks, each with a different label base. This makes label block
management easier, and also allows PE X to cater gracefully to a PE management easier, and also allows PE X to cater gracefully to a PE
joining a VPLS with a VE ID that is not covered by the set of label joining a VPLS with a VE ID that is not covered by the set of label
blocks that that PE X has already advertised. blocks that that PE X has already advertised.
When a PE starts up, or is configured with a new VPLS instance, the When a PE starts up, or is configured with a new VPLS instance, the
BGP process may wish to wait to receive several advertisements for BGP process may wish to wait to receive several advertisements for
that VPLS instance from other PEs to improve the efficiency of label that VPLS instance from other PEs to improve the efficiency of label
block allocation. block allocation.
3.2.2. VPLS BGP NLRI 3.2.1. Concepts
The VPLS BGP NLRI described below, with a new AFI and SAFI (see [3]) The VPLS BGP NLRI described below, with a new AFI and SAFI (see [4])
is used to exchange VPLS membership and demultiplexors. is used to exchange VPLS membership and demultiplexors.
A VPLS BGP NLRI has the following information elements: a VE ID, a VE A VPLS BGP NLRI has the following information elements: a VE ID, a VE
Block Offset, a VE Block Size and a label base. The format of the Block Offset, a VE Block Size and a label base. The exact format is
VPLS NLRI is given below. The AFI is the L2VPN AFI (to be assigned given below.
by IANA), and the SAFI is the VPLS SAFI (65). The Length field is in
octets.
+------------------------------------+
| Length (2 octets) |
+------------------------------------+
| Route Distinguisher (8 octets) |
+------------------------------------+
| VE ID (2 octets) |
+------------------------------------+
| VE Block Offset (2 octets) |
+------------------------------------+
| VE Block Size (2 octets) |
+------------------------------------+
| Label Base (3 octets) |
+------------------------------------+
Figure 2: BGP NLRI for VPLS Information
A PE participating in a VPLS must have at least one VE ID. If the PE A PE participating in a VPLS must have at least one VE ID. If the PE
is the VE, it typically has one VE ID. If the PE is connected to is the VE, it typically has one VE ID. If the PE is connected to
several u-PEs, it has a distinct VE ID for each u-PE. It may several u-PEs, it has a distinct VE ID for each u-PE. It may
additionally have a VE ID for itself, if it itself acts as a VE for additionally have a VE ID for itself, if it itself acts as a VE for
that VPLS. In what follows, we will call the PE announcing the VPLS that VPLS. In what follows, we will call the PE announcing the VPLS
NLRI PE-a, and we will assume that PE-a owns VE ID V (either NLRI PE-a, and we will assume that PE-a owns VE ID V (either
belonging to PE-a itself, or to a u-PE connected to PE-a). belonging to PE-a itself, or to a u-PE connected to PE-a).
VE IDs are typically assigned by the network administrator. Their VE IDs are typically assigned by the network administrator. Their
scope is local to a VPLS. A given VE ID should belong to only one scope is local to a VPLS. A given VE ID should belong to only one
PE, unless a CE is multi-homed (see Section 3.5). PE, unless a CE is multi-homed (see Section 3.5).
A label block is a set of demultiplexor labels used to reach a given A label block is a set of demultiplexor labels used to reach a given
VE ID. A VPLS BGP NLRI with VE ID V, VE Block Offset VBO, VE Block VE ID. A VPLS BGP NLRI with VE ID V, VE Block Offset VBO, VE Block
Size VBS and label base LB communicates to its peers the following: Size VBS and label base LB implicitly announces
label block for V: labels from LB to (LB + VBS - 1), and label block for V: labels from LB to (LB + VBS - 1), and
remote VE set for V: from VBO to (VBO + VBS - 1). remote VE set for V: from VBO to (VBO + VBS - 1).
There is a one-to-one correspondence between the remote VE set and There is a one-to-one correspondance between the remote VE set and
the label block: VE ID (VBO + n) corresponds to label (LB + n). the label block: VE ID (VBO + n) corresponds to label (LB + n).
3.2.3. PW Setup and Teardown 3.2.2. PW Setup and Teardown
Suppose PE-a is part of VPLS foo, and makes an announcement with VE Suppose PE-a is part of VPLS foo, and makes an announcement with VE
ID V, VE Block Offset VBO, VE Block Size VBS and label base LB. If ID V, VE Block Offset VBO, VE Block Size VBS and label base LB. If
PE-b is also part of VPLS foo, and has VE ID W, PE-b does the PE-b is also part of VPLS foo, and has VE ID W, PE-b does the
following: following:
1. checks if W is part of PE-a's 'remote VE set': if VBO <= W < VBO 1. is W part of PE-a's 'remote VE set': if VBO <= W < VBO + VBS,
+ VBS, then W is part of PE-a's remote VE set. If not, PE-b then W is part of PE-a's remote VE set. If not, PE-b ignores
ignores this message, and skips the rest of this procedure. this message, and skips the rest of this procedure.
2. sets up a PW to PE-a: the demultiplexor label to send traffic 2. set up a PW to PE-a: the demultiplexor label to send traffic from
from PE-b to PE-a is computed as (LB + W - VBO). PE-b to PE-a is computed as (LB + W - VBO).
3. checks if V is part of any 'remote VE set' that PE-b announced, 3. is V part of any 'remote VE set' that PE-b announced: PE-b checks
i.e., PE-b checks if V belongs to some remote VE set that PE-b if V belongs to some remote VE set that PE-b announced, say with
announced, say with VE Block Offset VBO', VE Block Size VBS' and VE Block Offset VBO', VE Block Size VBS' and label base LB'. If
label base LB'. If not, PE-b MUST make a new announcement as not, PE-b MUST make a new announcement as described in
described in Section 3.3. Section 3.3.
4. sets up a PW from PE-a: the demultiplexor label over which PE-b 4. set up a PW from PE-a: the demultiplexor label over which PE-b
should expect traffic from PE-a is computed as: (LB' + V - VBO'). should expect traffic from PE-a is computed as: (LB' + V - VBO').
If Y withdraws an NLRI for V that X was using, then X MUST tear down If Y withdraws an NLRI for V that X was using, then X MUST tear down
its ends of the pseudowire between X and Y. its ends of the pseudowire between X and Y.
3.2.4. Signaling PE Capabilities The format of the VPLS NLRI is given below. The AFI is the L2VPN AFI
(to be assigned by IANA), and the SAFI is the VPLS SAFI (65). The
Length field is in octets.
+------------------------------------+
| Length (2 octets) |
+------------------------------------+
| Route Distinguisher (8 octets) |
+------------------------------------+
| VE ID (2 octets) |
+------------------------------------+
| VE Block Offset (2 octets) |
+------------------------------------+
| VE Block Size (2 octets) |
+------------------------------------+
| Label Base (3 octets) |
+------------------------------------+
Figure 2: BGP NLRI for VPLS Information
3.2.3. Signaling PE Capabilities
The following extended attribute, the "Layer2 Info Extended The following extended attribute, the "Layer2 Info Extended
Community", is used to signal control information about the Community", is used to signal control information about the
pseudowires to be setup for a given VPLS. This information includes pseudowires to be setup for a given VPLS. The extended community
the Encaps Type (type of encapsulation on the pseudowires), Control value is to be allocated by IANA (currently used value is 0x800A).
Flags (control information regarding the pseudowires) and the Maximum This information includes the Encaps Type (type of encapsulation on
Transmission Unit (MTU) to be used on the pseudowires. the pseudowires), Control Flags (control information regarding the
pseudowires) and the Maximum Transmission Unit (MTU) to be used on
the pseudowires.
The Encaps Type for VPLS is 19. The Encaps Type for VPLS is 19.
+------------------------------------+ +------------------------------------+
| Extended community type (2 octets) | | Extended community type (2 octets) |
+------------------------------------+ +------------------------------------+
| Encaps Type (1 octet) | | Encaps Type (1 octet) |
+------------------------------------+ +------------------------------------+
| Control Flags (1 octet) | | Control Flags (1 octet) |
+------------------------------------+ +------------------------------------+
skipping to change at page 14, line 45 skipping to change at page 16, line 4
| Encaps Type (1 octet) | | Encaps Type (1 octet) |
+------------------------------------+ +------------------------------------+
| Control Flags (1 octet) | | Control Flags (1 octet) |
+------------------------------------+ +------------------------------------+
| Layer-2 MTU (2 octet) | | Layer-2 MTU (2 octet) |
+------------------------------------+ +------------------------------------+
| Reserved (2 octets) | | Reserved (2 octets) |
+------------------------------------+ +------------------------------------+
Figure 3: Layer2 Info Extended Community Figure 3: Layer2 Info Extended Community
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| MBZ |C|S| (MBZ = MUST Be Zero) | MBZ |C|S| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 4: Control Flags Bit Vector Figure 4: Control Flags Bit Vector
With reference to Figure 4, the following bits in the Control Flags With reference to Figure 4, the following bits in the Control Flags
are defined; the remaining bits, designated MBZ, MUST be set to zero are defined; the remaining bits, designated MBZ, MUST be set to zero
when sending and MUST be ignored when receiving this community. when sending and MUST be ignored when receiving this community.
Name Meaning Name Meaning
C A Control word ([5]) MUST or MUST NOT be present when C If set to 1 (0), Control word MUST (NOT) be present when
sending VPLS packets to this PE, depending on whether C sending VPLS packets to this PE [10].
is 1 or 0, respectively S If set to 1 (0), Sequenced delivery of frames is (not)
S Sequenced delivery of frames MUST or MUST NOT be used required when sending VPLS packets to this PE.
when sending VPLS packets to this PE. depending on
whether S is 1 or 0, respectively
3.3. BGP VPLS Operation 3.3. BGP VPLS Operation
To create a new VPLS, say VPLS foo, a network administrator must pick To create a new VPLS, say VPLS foo, a network administrator must pick
a RT for VPLS foo, say RT-foo. This will be used by all PEs that a RT for VPLS foo, say RT-foo. This will be used by all PEs that
serve VPLS foo. To configure a given PE, say PE-a, to be part of serve VPLS foo. To configure a given PE, say PE-a, to be part of
VPLS foo, the network administrator only has to choose a VE ID V for VPLS foo, the network administrator only has to choose a VE ID V for
PE-a. (If PE-a is connected to u-PEs, PE-a may be configured with PE-a. (If PE-a is connected to u-PEs, PE-a may be configured with
more than one VE ID; in that case, the following is done for each VE more than one VE ID; in that case, the following is done for each VE
ID). The PE may also be configured with a Route Distinguisher (RD); ID). The PE may also be configured with a Route Distinguisher (RD);
skipping to change at page 15, line 38 skipping to change at page 16, line 41
RD-foo-a. PE-a then generates an initial label block and a remote VE RD-foo-a. PE-a then generates an initial label block and a remote VE
set for V, defined by VE Block Offset VBO, VE Block Size VBS and set for V, defined by VE Block Offset VBO, VE Block Size VBS and
label base LB. These may be empty. label base LB. These may be empty.
PE-a then creates a VPLS BGP NLRI with RD RD-foo-a, VE ID V, VE Block PE-a then creates a VPLS BGP NLRI with RD RD-foo-a, VE ID V, VE Block
Offset VBO, VE Block Size VBS and label base LB. To this, it Offset VBO, VE Block Size VBS and label base LB. To this, it
attaches a Layer2 Info Extended Community and a RT, RT-foo. It sets attaches a Layer2 Info Extended Community and a RT, RT-foo. It sets
the BGP Next Hop for this NLRI as itself, and announces this NLRI to the BGP Next Hop for this NLRI as itself, and announces this NLRI to
its peers. The Network Layer protocol associated with the Network its peers. The Network Layer protocol associated with the Network
Address of the Next Hop for the combination <AFI=L2VPN AFI, SAFI=VPLS Address of the Next Hop for the combination <AFI=L2VPN AFI, SAFI=VPLS
SAFI> is IP; this association is required by [3], Section 5. If the SAFI> is IP; this association is required by [4], Section 5. If the
value of the Length of the Next Hop field is 4, then the Next Hop value of the Length of the Next Hop field is 4, then the Next Hop
contains an IPv4 address. If this value is 16, then the Next Hop contains an IPv4 address. If this value is 16, then the Next Hop
contains an IPv6 address. contains an IPv6 address.
If PE-a hears from another PE, say PE-b, a VPLS BGP announcement with If PE-a hears from another PE, say PE-b, a VPLS BGP announcement with
RT-foo and VE ID W, then PE-a knows that PE-b is a member of the same RT-foo and VE ID W, then PE-a knows that PE-b is a member of the same
VPLS (autodiscovery). PE-a then has to set up its part of a VPLS VPLS (auto-discovery). PE-a then has to set up its part of a VPLS
pseudowire between PE-a and PE-b, using the mechanisms in pseudowire between PE-a and PE-b, using the mechanisms in
Section 3.2. Similarly, PE-b will have discovered that PE-a is in Section 3.2. Similarly, PE-b will have discovered that PE-a is in
the same VPLS, and PE-b must set up its part of the VPLS pseudowire. the same VPLS, and PE-b must set up its part of the VPLS pseudowire.
Thus, signaling and pseudowire setup is also achieved with the same Thus, signaling and pseudowire setup is also achieved with the same
Update message. Update message.
If W is not in any remote VE set that PE-a announced for VE ID V in If W is not in any remote VE set that PE-a announced for VE ID V in
VPLS foo, PE-b will not be able to set up its part of the pseudowire VPLS foo, PE-b will not be able to set up its part of the pseudowire
to PE-a. To address this, PE-a can choose to withdraw the old to PE-a. To address this, PE-a can choose to withdraw the old
announcement(s) it made for VPLS foo, and announce a new Update with announcement(s) it made for VPLS foo, and announce a new Update with
a larger remote VE set and corresponding label block that covers all a larger remote VE set and corresponding label block that covers all
VE IDs that are in VPLS foo. This however, may cause some service VE IDs that are in VPLS foo. This however, may cause some service
disruption. An alternative for PE-a is to create a new remote VE set disruption. An alternative for PE-a is to create a new remote VE set
skipping to change at page 16, line 24 skipping to change at page 17, line 27
If PE-a's configuration is changed to remove VE ID V from VPLS foo, If PE-a's configuration is changed to remove VE ID V from VPLS foo,
then PE-a MUST withdraw all its announcements for VPLS foo that then PE-a MUST withdraw all its announcements for VPLS foo that
contain VE ID V. If all of PE-a's links to its CEs in VPLS foo go contain VE ID V. If all of PE-a's links to its CEs in VPLS foo go
down, then PE-a SHOULD either withdraw all its NLRIs for VPLS foo, or down, then PE-a SHOULD either withdraw all its NLRIs for VPLS foo, or
let other PEs in the VPLS foo know in some way that PE-a is no longer let other PEs in the VPLS foo know in some way that PE-a is no longer
connected to its CEs. connected to its CEs.
3.4. Multi-AS VPLS 3.4. Multi-AS VPLS
As in [13] and [10], the above autodiscovery and signaling functions As in [14] and [6], the above autodiscovery and signaling functions
are typically announced via I-BGP. This assumes that all the sites are typically announced via I-BGP. This assumes that all the sites
in a VPLS are connected to PEs in a single Autonomous System (AS). in a VPLS are connected to PEs in a single Autonomous System (AS).
However, sites in a VPLS may connect to PEs in different ASes. This However, sites in a VPLS may connect to PEs in different ASes. This
leads to two issues: 1) there would not be an I-BGP connection leads to two issues: 1) there would not be an I-BGP connection
between those PEs, so some means of signaling across ASes is needed; between those PEs, so some means of signaling across ASes may be
and 2) there may not be PE-to-PE tunnels between the ASes. needed; and 2) there may not be PE-to-PE tunnels between the ASes.
A similar problem is solved in [10], Section 10. Three methods are A similar problem is solved in [6], Section 10. Three methods are
suggested to address issue (1); all these methods have analogs in suggested to address issue (1); all these methods have analogs in
multi-AS VPLS. multi-AS VPLS.
Here is a diagram for reference: Here is a diagram for reference:
__________ ____________ ____________ __________ __________ ____________ ____________ __________
/ \ / \ / \ / \ / \ / \ / \ / \
\___/ AS 1 \ / AS 2 \___/ \___/ AS 1 \ / AS 2 \___/
\ / \ /
+-----+ +-------+ | +-------+ +-----+ +-----+ +-------+ | +-------+ +-----+
skipping to change at page 17, line 4 skipping to change at page 18, line 19
\___/ AS 1 \ / AS 2 \___/ \___/ AS 1 \ / AS 2 \___/
\ / \ /
+-----+ +-------+ | +-------+ +-----+ +-----+ +-------+ | +-------+ +-----+
| PE1 | ---...--- | ASBR1 | ======= | ASBR2 | ---...--- | PE2 | | PE1 | ---...--- | ASBR1 | ======= | ASBR2 | ---...--- | PE2 |
+-----+ +-------+ | +-------+ +-----+ +-----+ +-------+ | +-------+ +-----+
___ / \ ___ ___ / \ ___
/ \ / \ / \ / \ / \ / \
\__________/ \____________/ \____________/ \__________/ \__________/ \____________/ \____________/ \__________/
Figure 6: Inter-AS VPLS Figure 6: Inter-AS VPLS
As in the above reference, three methods for signaling inter-provider As in the above reference, three methods for signaling inter-provider
VPLS are given; these are presented in order of increasing VPLS are given; these are presented in order of increasing
scalability. Method (a) is the easiest to understand conceptually, scalability. Method (a) is the easiest to understand conceptually,
and the easiest to deploy; however, it requires an Ethernet and the easiest to deploy; however, it requires an Ethernet
interconnect between the ASes, and both VPLS control and data plane interconnect between the ASes, and both VPLS control and data plane
state on the AS border routers (ASBRs). Method (b) requires VPLS state on the AS border routers (ASBRs). Method (b) requires VPLS
control plane state on the ASBRs and MPLS on the AS-AS interconnect control plane state on the ASBRs and MPLS on the AS-AS interconnect.
(which need not be Ethernet). Method (c) requires MPLS on the AS-AS Method (c) requires MPLS on the AS-AS interconnect, but no VPLS state
interconnect, but no VPLS state of any kind on the ASBRs. of any kind on the ASBRs.
3.4.1. a) VPLS-to-VPLS connections at the ASBRs. 3.4.1. a) VPLS-to-VPLS connections at the ASBRs.
In this method, an AS Border Router (ASBR1) acts as a PE for all In this method, an AS Border Router (ASBR1) acts as a PE for all
VPLSs that span AS1 and an AS to which ASBR1 is connected, such as VPLSs that span AS1 and an AS to which ASBR1 is connected, such as
AS2 here. The ASBR on the neighboring AS (ASBR2) is viewed by ASBR1 AS2 here. The ASBR on the neighboring AS (ASBR2) is viewed by ASBR1
as a CE for the VPLSs that span AS1 and AS2; similarly, ASBR2 acts as as a CE for the VPLSs that span AS1 and AS2; similarly, ASBR2 acts as
a PE for this VPLS from AS2's point of view, and views ASBR1 as a CE. a PE for this VPLS from AS2's point of view, and views ASBR1 as a CE.
This method does not require MPLS on the ASBR1-ASBR2 link, but does This method does not require MPLS on the ASBR1-ASBR2 link, but does
require that this link carry Ethernet traffic, and that there be a require that this link carry Ethernet traffic, and that there be a
separate VLAN sub-interface for each VPLS traversing this link. It separate VLAN sub-interface for each VPLS traversing this link. It
further requires that ASBR1 does the PE operations (discovery, further requires that ASBR1 does the PE operations (discovery,
signaling, MAC address learning, flooding, encapsulation, etc.) for signaling, MAC address learning, flooding, encapsulation, etc.) for
all VPLSs that traverse ASBR1. This imposes a significant burden on all VPLSs that traverse ASBR1. This imposes a significant burden on
ASBR1, both on the control plane and the data plane, which limits the ASBR1, both on the control plane and the data plane, which limits the
number of multi-AS VPLSs. number of multi-AS VPLSs.
Note that in general, there will be multiple connections between a Note that in general, there will be multiple connections between a
pair of ASes, for redundancy. In this case, the Spanning Tree pair of ASes, for redundancy. In this case, the Spanning Tree
Protocol (STP) ([14]), or some other means of loop detection and Protocol (STP) ([15]), or some other means of loop detection and
prevention, must be run on each VPLS that spans these ASes, so that a prevention, must be run on each VPLS that spans these ASes, so that a
loop-free topology can be constructed in each VPLS. This imposes a loop-free topology can be constructed in each VPLS. This imposes a
further burden on the ASBRs and PEs participating in those VPLSs, as further burden on the ASBRs and PEs participating in those VPLSs, as
these devices would need to run a loop detection algorithm for each these devices would need to run a loop detection algorithm for each
such VPLS. How this may be achieved is outside the scope of this such VPLS. How this may be achieved is outside the scope of this
document. document.
3.4.2. b) EBGP redistribution of VPLS information between ASBRs. 3.4.2. b) EBGP redistribution of VPLS information between ASBRs.
This method requires I-BGP peerings between the PEs in AS1 and ASBR1 This method requires I-BGP peerings between the PEs in AS1 and ASBR1
in AS1 (perhaps via route reflectors), an E-BGP peering between ASBR1 in AS1 (perhaps via route reflectors), an E-BGP peering between ASBR1
and ASBR2 in AS2, and I-BGP peerings between ASBR2 and the PEs in and ASBR2 in AS2, and I-BGP peerings between ASBR2 and the PEs in
AS2. In the above example, PE1 sends a VPLS NLRI to ASBR1 with a AS2. In the above example, PE1 sends a VPLS NLRI to ASBR1 with a
label block and itself as the BGP nexthop; ASBR1 sends the NLRI to label block and itself as the BGP nexthop; ASBR1 sends the NLRI to
ASBR2 with new labels and itself as the BGP nexthop; and ASBR2 sends ASBR2 with new labels and itself as the BGP nexthop; and ASBR2 sends
the NLRI to PE2 with new labels and itself as the nexthop. the NLRI to PE2 with new labels and itself as the nexthop.
Correspondingly, there are three tunnels: T1 from PE1 to ASBR1, T2
from ASBR1 to ASBR2, and T3 from ASBR2 to PE2. Within each tunnel,
the VPLS label to be used is determined by the receiving device;
e.g., the VPLS label within T1 is a label from the label block that
ASBR1 sent to PE1. The ASBRs are responsible for receiving VPLS
packets encapsulated in a tunnel, and performing the appropriate
label swap operations described next so that the next receiving
device can correctly identify and forward the packet.
The VPLS NLRI that ASBR1 sends to ASBR2 (and the NLRI that ASBR2 The VPLS NLRI that ASBR1 sends to ASBR2 (and the NLRI that ASBR2
sends to PE2) is identical to the VPLS NLRI that PE1 sends to ASBR1, sends to PE2) is identical to the VPLS NLRI that PE1 sends to ASBR1,
except for the label block. To be precise, the Length, the Route except for the label block. To be precise, the Length, the Route
Distinguisher, the VE ID, the VE Block Offset, and the VE Block Size Distinguisher, the VE ID, the VE Block Offset, and the VE Block Size
MUST be the same; the Label Base may be different. Furthermore, MUST be the same; the Label Base may be different. Furthermore,
ASBR1 must also update its forwarding path as follows: if the Label ASBR1 must also update its forwarding path as follows: if the Label
Base sent by PE1 is L1, the Label-block Size is N, the Label Base Base sent by PE1 is L1, the Label-block Size is N, the Label Base
sent by ASBR1 is L2, and the tunnel label from ASBR1 to PE1 is T, sent by ASBR1 is L2, and the tunnel label from ASBR1 to PE1 is T,
then ASBR1 must install the following in the forwarding path: then ASBR1 must install the following in the forwarding path:
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method is considerably more scalable than method (a). method is considerably more scalable than method (a).
3.4.3. c) Multi-hop EBGP redistribution of VPLS information between 3.4.3. c) Multi-hop EBGP redistribution of VPLS information between
ASes. ASes.
In this method, there is a multi-hop E-BGP peering between the PEs In this method, there is a multi-hop E-BGP peering between the PEs
(or preferably, a Route Reflector) in AS1 and the PEs (or Route (or preferably, a Route Reflector) in AS1 and the PEs (or Route
Reflector) in AS2. PE1 sends a VPLS NLRI with labels and nexthop Reflector) in AS2. PE1 sends a VPLS NLRI with labels and nexthop
self to PE2; if this is via route reflectors, the BGP nexthop is not self to PE2; if this is via route reflectors, the BGP nexthop is not
changed. This requires that there be a tunnel LSP from PE1 to PE2. changed. This requires that there be a tunnel LSP from PE1 to PE2.
This tunnel LSP can be created exactly as in [10], section 10 (c), This tunnel LSP can be created exactly as in [6], section 10 (c), for
for example using E-BGP to exchange labeled IPv4 routes for the PE example using E-BGP to exchange labeled IPv4 routes for the PE
loopbacks. loopbacks.
When PE1 wants to send a VPLS packet to PE2, it pushes the VPLS label When PE1 wants to send a VPLS packet to PE2, it pushes the VPLS label
corresponding to its own VE ID onto the packet. It then pushes the corresponding to its own VE ID onto the packet. It then pushes the
tunnel label(s) to reach PE2. tunnel label(s) to reach PE2.
This method requires no VPLS information (in either the control or This method requires no VPLS information (in either the control or
the data plane) on the ASBRs. The ASBRs only need to set up PE-to-PE the data plane) on the ASBRs. The ASBRs only need to set up PE-to-PE
tunnel LSPs in the control plane, and do label operations in the data tunnel LSPs in the control plane, and do label operations in the data
plane. Again, as in the case of method (b), the construction of plane. Again, as in the case of method (b), the construction of
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3.5. Multi-homing and Path Selection 3.5. Multi-homing and Path Selection
It is often desired to multi-home a VPLS site, i.e., to connect it to It is often desired to multi-home a VPLS site, i.e., to connect it to
multiple PEs, perhaps even in different ASes. In such a case, the multiple PEs, perhaps even in different ASes. In such a case, the
PEs connected to the same site can either be configured with the same PEs connected to the same site can either be configured with the same
VE ID or with different VE IDs. In the latter case, it is mandatory VE ID or with different VE IDs. In the latter case, it is mandatory
to run STP on the CE device, and possibly on the PEs, to construct a to run STP on the CE device, and possibly on the PEs, to construct a
loop-free VPLS topology. How this can be accomplished is outside the loop-free VPLS topology. How this can be accomplished is outside the
scope of this document; however, the rest of this section will scope of this document; however, the rest of this section will
describe in some detail the former case. describe in some detail the former case. Note that multi-homing by
the SP and STP on the CEs can co-exist; thus it is recommended that
the VPLS customer run STP if the CEs are able to.
In the case where the PEs connected to the same site are assigned the In the case where the PEs connected to the same site are assigned the
same VE ID, a loop-free topology is constructed by routing same VE ID, a loop-free topology is constructed by routing
mechanisms, in particular, by BGP path selection. When a BGP speaker mechanisms, in particular, by BGP path selection. When a BGP speaker
receives two equivalent NLRIs (see below for the definition), it receives two equivalent NLRIs (see below for the definition), it
applies standard path selection criteria such as Local Preference and applies standard path selection criteria such as Local Preference and
AS Path Length to determine which NLRI to choose; it MUST pick only AS Path Length to determine which NLRI to choose; it MUST pick only
one. If the chosen NLRI is subsequently withdrawn, the BGP speaker one. If the chosen NLRI is subsequently withdrawn, the BGP speaker
applies path selection to the remaining equivalent VPLS NLRIs to pick applies path selection to the remaining equivalent VPLS NLRIs to pick
another; if none remain, the forwarding information associated with another; if none remain, the forwarding information associated with
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speakers; speakers;
2. limiting BGP VPLS message passing to just the interested speakers 2. limiting BGP VPLS message passing to just the interested speakers
rather than all BGP speakers; and rather than all BGP speakers; and
3. simplifying the addition and deletion of BGP speakers, whether 3. simplifying the addition and deletion of BGP speakers, whether
for VPLS or other applications. for VPLS or other applications.
Fortunately, the use of BGP for Internet routing as well as for IP Fortunately, the use of BGP for Internet routing as well as for IP
VPNs has yielded several good solutions for all these problems. The VPNs has yielded several good solutions for all these problems. The
basic technique is hierarchy, using BGP Route Reflectors (RRs) ([6]). basic technique is hierarchy, using BGP Route Reflectors (RRs) ([8]).
The idea is to designate a small set of Route Reflectors which are The idea is to designate a small set of Route Reflectors which are
themselves fully meshed, and then establish a BGP session between themselves fully meshed, and then establish a BGP session between
each BGP speaker and one or more RRs. In this way, there is no need each BGP speaker and one or more RRs. In this way, there is no need
of direct full mesh connectivity among all the BGP speakers. If the of direct full-mesh connectivity among all the BGP speakers. If the
particular scaling needs of a provider requires a large number of particular scaling needs of a provider requires a large number of
RRs, then this technique can be applied recursively: the full mesh RRs, then this technique can be applied recursively: the full mesh
connectivity among the RRs can be brokered by yet another level of connectivity among the RRs can be brokered by yet another level of
RRs. The use of RRs solves problems 1 and 3 above. RRs. The use of RRs solves problems 1 and 3 above.
It is important to note that RRs, as used for VPLS and VPNs, are It is important to note that RRs, as used for VPLS and VPNs, are
purely a control plane technique. The use of RRs introduces no data purely a control plane technique. The use of RRs introduces no data
plane state and no data plane forwarding requirements on the RRs, and plane state and no data plane forwarding requirements on the RRs, and
does not in any way change the forwarding path of VPLS traffic. This does not in any way change the forwarding path of VPLS traffic. This
is in contrast to the technique of Hierarchical VPLS defined in [8]. is in contrast to the technique of Hierarchical VPLS defined in [10].
Another consequence of this approach is that it is not required that The problem of limiting BGP VPLS message passing to just the
one set of RRs handles all BGP messages, or that a particular RR interested BGP speakers is addressed by the use of Route Target
handle all messages from a given PE. One can define several sets of Filtering, described in [12]. This technique is orthogonal to the
RRs, for example a set to handle VPLS, another to handle IP VPNs and use of RRs, but works well in conjunction with RRs.
another for Internet routing. Another partitioning could be to have
some subset of VPLSs and IP VPNs handled by one set of RRs, and
another subset of VPLSs and IP VPNs handled by another set of RRs;
the use of Route Target Filtering (RTF), described in [11] can make
this simpler and more effective.
Finally, problem 2 (that of limiting BGP VPLS message passing to just It is not required that a given set of RRs handle all BGP messages.
the interested BGP speakers) is addressed by the use of RTF. This One can define several sets of RRs, for example a set to handle VPLS,
technique is orthogonal to the use of RRs, but works well in another to handle IP VPNs and another for Internet routing. Another
conjunction with RRs. RTF is also very effective in inter-AS VPLS; partitioning could be to have one subset of VPLSs and IP VPNs handled
more details on how RTF works and its benefits are provided in [11]. by one set of RRs, and another subset of VPLSs and IP VPNs handled by
another set of RRs; this can be accomplished by the use of Route
Target Filtering.
It is worth mentioning an aspect of the control plane that is often a It is worth mentioning an aspect of the control plane that is often a
source of confusion. No MAC addresses are exchanged via BGP. All source of confusion. No MAC addresses are exchanged via BGP. All
MAC address learning and aging is done in the data plane individually MAC address learning and aging is done in the data plane individually
by each PE. The only task of BGP VPLS message exchange is by each PE. The only task of BGP VPLS message exchange is auto-
autodiscovery and label exchange. discovery and label exchange. This means that once a PE joins a VPLS
and sends an update indicating this (and the labels to use), that PE
Thus, BGP processing for VPLS occurs when sends no more BGP updates for that VPLS until either the PE leaves
that VPLS, or a fairly serious event (such as a PE-CE link going
1. a PE joins or leaves a VPLS; or down) occurs.
2. a failure occurs in the network, bringing down a PE-PE tunnel or
a PE-CE link.
These events are relatively rare, and typically, each such event
causes one BGP update to be generated. Coupled with BGP's messaging
efficiency when used for signaling VPLS, these observations lead to
the conclusion that BGP as a control plane for VPLS will scale quite
well both in terms of processing and memory requirements.
4. Data Plane 4. Data Plane
This section discusses two aspects of the data plane for PEs and This section discusses two aspects of the data plane for PEs and
u-PEs implementing VPLS: encapsulation and forwarding. u-PEs implementing VPLS: encapsulation and forwarding.
4.1. Encapsulation 4.1. Encapsulation
Ethernet frames received from CE devices are encapsulated for Ethernet frames received from CE devices are encapsulated for
transmission over the packet switched network connecting the PEs. transmission over the packet switched network connecting the PEs.
The encapsulation is as in [5], with one change: a PE that sets the P The encapsulation is as in [7].
bit in the Control Flags strips the outermost VLAN from an Ethernet
frame received from a CE before encapsulating it, and pushes a VLAN
onto a decapsulated frame before sending it to a CE.
4.2. Forwarding 4.2. Forwarding
VPLS packets are classified as belonging to a given service instance VPLS packets are classified as belonging to a given service instance
and associated forwarding table based on the interface over which the and associated forwarding table based on the interface over which the
packet is received. Packets are forwarded in the context of the packet is received. Packets are forwarded in the context of the
service instance based on the destination MAC address. The former service instance based on the destination MAC address. The former
mapping is determined by configuration. The latter is the focus of mapping is determined by configuration. The latter is the focus of
this section. this section.
4.2.1. MAC address learning 4.2.1. MAC address learning
As was mentioned earlier, the key distinguishing feature of VPLS is As was mentioned earlier, the key distinguishing feature of VPLS is
that it is a multipoint service. This means that the entire Service that it is a multipoint service. This means that the entire Service
Provider network should appear as a single logical learning bridge Provider network should appear as a single logical learning bridge
for each VPLS that the SP network supports. The logical ports for for each VPLS that the SP network supports. The logical ports for
the SP "bridge" are the customer ports as well as the pseudowires on the SP "bridge" are the customer ports on all of the VE on a given
a VE. Just as a learning bridge learns MAC addresses on its ports, service. Just as a learning bridge learns MAC addresses on its
the SP bridge must learn MAC addresses at its VEs. ports, the SP bridge must learn MAC addresses at its VEs.
Learning consists of associating source MAC addresses of packets with Learning consists of associating source MAC addresses of packets with
the (logical) ports on which they arrive; this association is the the (logical) ports on which they arrive; this association is the
Forwarding Information Base (FIB). The FIB is used for forwarding Forwarding Information Base (FIB). The FIB is used for forwarding
packets. For example, suppose the bridge receives a packet with packets. For example, suppose the bridge receives a packet with
source MAC address S on (logical) port P. If subsequently, the bridge source MAC address S on (logical) port P. If subsequently, the bridge
receives a packet with destination MAC address S, it knows that it receives a packet with destination MAC address S, it knows that it
should send the packet out on port P. should send the packet out on port P.
If a VE learns a source MAC address S on logical port P, then later 4.2.2. Flooding
sees S on a different port P', then the VE MUST update its FIB to
reflect the new port P'. A VE MAY implement a mechanism to damp
flapping of source ports for a given MAC address.
4.2.2. Aging
VPLS PEs SHOULD have an aging mechanism to remove a MAC address
associated with a logical port, much the same as learning bridges do.
This is required so that a MAC address can be relearned if it "moves"
from a logical port to another logical port, either because the
station to which that MAC address belongs really has moved, or
because of a topology change in the LAN that causes this MAC address
to arrive on a new port. In addition, aging reduces the size of a
VPLS MAC table to just the active MAC addresses, rather than all MAC
addresses in that VPLS.
The "age" of a source MAC address S on a logical port P is the time
since it was last seen as a source MAC on port P. If the age exceeds
the aging time T, S MUST be flushed from the FIB. This of course
means that every time S is seen as a source MAC address on port P,
S's age is reset.
An implementation SHOULD provide a configurable knob to set the aging
time T on a per-VPLS basis. In addition, an implementation MAY
accelerate aging of all MAC addresses in a VPLS if it detects certain
situations, such as a Spanning Tree topology change in that VPLS.
4.2.3. Flooding
When a bridge receives a packet to a destination that is not in its When a bridge receives a packet to a destination that is not in its
FIB, it floods the packet on all the other ports. Similarly, a VE FIB, it floods the packet on all the other ports. Similarly, a VE
will flood packets to an unknown destination to all other VEs in the will flood packets to an unknown destination to all other VEs in the
VPLS. VPLS.
In Figure 1 above, if CE2 sent an Ethernet frame to PE2, and the In Figure 1 above, if CE2 sent an Ethernet frame to PE2, and the
destination MAC address on the frame was not in PE2's FIB (for that destination MAC address on the frame was not in PE2's FIB (for that
VPLS), then PE2 would be responsible for flooding that frame to every VPLS), then PE2 would be responsible for flooding that frame to every
other PE in the same VPLS. On receiving that frame, PE1 would be other PE in the same VPLS. On receiving that frame, PE1 would be
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knew which CE "owned" that MAC address). knew which CE "owned" that MAC address).
On the other hand, if PE3 received the frame, it could delegate On the other hand, if PE3 received the frame, it could delegate
further flooding of the frame to its u-PE. If PE3 was connected to 2 further flooding of the frame to its u-PE. If PE3 was connected to 2
u-PEs, it would announce that it has two u-PEs. PE3 could either u-PEs, it would announce that it has two u-PEs. PE3 could either
announce that it is incapable of flooding, in which case it would announce that it is incapable of flooding, in which case it would
receive two frames, one for each u-PE, or it could announce that it receive two frames, one for each u-PE, or it could announce that it
is capable of flooding, in which case it would receive one copy of is capable of flooding, in which case it would receive one copy of
the frame, which it would then send to both u-PEs. the frame, which it would then send to both u-PEs.
4.2.4. Broadcast and Multicast 4.2.3. "Split Horizon" Forwarding
There is a well-known broadcast MAC address. An Ethernet frame whose
destination MAC address is the broadcast MAC address must be sent to
all stations in that VPLS. This can be accomplished by the same
means that is used for flooding.
There is also an easily recognized set of "multicast" MAC addresses.
Ethernet frames with a destination multicast MAC address MAY be
broadcast to all stations; a VE MAY also use certain techniques to
restrict transmission of multicast frames to a smaller set of
receivers, those that have indicated interest in the corresponding
multicast group. Discussion of this is outside the scope of this
document.
4.2.5. "Split Horizon" Forwarding
When a PE capable of flooding (say PEx) receives a broadcast Ethernet
frame, or one with an unknown destination MAC address, it must flood
the frame. If the frame arrived from an attached CE, PEx must send a
copy of the frame to every other attached CE, as well as to all other
PEs participating in the VPLS. If, on the other hand, the frame
arrived from another PE (say PEy), PEx must send a copy of the packet
only to attached CEs. PEx MUST NOT send the frame to other PEs,
since PEy would have already done so. This notion has been termed
"split horizon" forwarding, and is a consequence of the PEs being
logically fully meshed for VPLS.
Split horizon forwarding rules apply to broadcast and multicast
packets, as well as packets to an unknown MAC address.
4.2.6. Qualified and Unqualified Learning
The key for normal Ethernet MAC learning is usually just the
(6-octet) MAC address. This is called "unqualified learning".
However, it is also possible that the key for learning includes the
VLAN tag when present; this is called "qualified learning".
In the case of VPLS, learning is done in the context of a VPLS
instance, which typically corresponds to a customer. If the customer
uses VLAN tags, one can make the same distinctions of qualified and
unqualified learning. If the key for learning within a VPLS is just
the MAC address, then this VPLS is operating under unqualified
learning. If the key for learning is (customer VLAN tag + MAC
address), then this VPLS is operating under qualified learning.
Choosing between qualified and unqualified learning involves several
factors, the most important of which is whether one wants a single
global broadcast domain (unqualified), or a broadcast domain per VLAN
(qualified). The latter makes flooding and broadcasting more
efficient, but requires larger MAC tables. These considerations
apply equally to normal Ethernet forwarding and to VPLS.
4.2.7. Class of Service
In order to offer different Classes of Service within a VPLS, an When a PE capable of flooding receives a broadcast Ethernet frame, or
implementation MAY choose to map 802.1p bits in a customer Ethernet one with an unknown destination MAC address, it must flood the frame.
frame with a VLAN tag to an appropriate setting of EXP bits in the If the frame arrived from an attached CE, the PE must send a copy of
pseudowire and/or tunnel label, allowing for differential treatment the frame to every other attached CE, as well as to all PEs
of VPLS frames in the packet-switched network. participating in the VPLS. If the frame arrived from another PE,
however, the PE must only send a copy of the packet to attached CEs.
The PE MUST NOT send the frame to other PEs. This notion has been
termed "split horizon" forwarding, and is a consequence of the PEs
being logically fully meshed -- if a broadcast frame is received from
PEx, then PEx would have sent a copy to all other PEs.
To be useful, an implementation SHOULD allow this mapping function to Split horizon forwarding rules also apply to multicast frames (i.e.,
be different for each VPLS, as each VPLS customer may have their own those with a multicast destination MAC address). In this case, when
view of the required behavior for a given setting of 802.1p bits. a PE receives a multicast frame from another PE, the frame is
replicated and sent to the relevant subset of attached CEs; however,
it MUST NOT be sent to other PEs.
5. Deployment Options 5. Deployment Options
In deploying a network that supports VPLS, the SP must decide what In deploying a network that supports VPLS, the SP must decide what
functions the VPLS-aware device closest to the customer (the VE) functions the VPLS-aware device closest to the customer (the VE)
supports. The default case described in this document is that the VE supports. The default case described in this document is that the VE
is a PE. However, there are a number of reasons that the VE might be is a PE. However, there are a number of reasons that the VE might be
a device that does all the Layer 2 functions (such as MAC address a device that does all the Layer 2 functions (such as MAC address
learning and flooding), and a limited set of Layer 3 functions (such learning and flooding), and a limited set of Layer 3 functions (such
as communicating to its PE), but, for example, doesn't do full- as communicating to its PE), but, for example, doesn't do full-
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How they do learning and forwarding depends on whether or not there How they do learning and forwarding depends on whether or not there
is a u-PE; however, this is a local matter, and is not signaled. is a u-PE; however, this is a local matter, and is not signaled.
However, the details of the operation of a u-PE and its interactions However, the details of the operation of a u-PE and its interactions
with PEs and other u-PEs is beyond the scope of this document. with PEs and other u-PEs is beyond the scope of this document.
6. Security Considerations 6. Security Considerations
The focus in Virtual Private LAN Service is the privacy of data, The focus in Virtual Private LAN Service is the privacy of data,
i.e., that data in a VPLS is only distributed to other nodes in that i.e., that data in a VPLS is only distributed to other nodes in that
VPLS and not to any external agent or other VPLS. Note that VPLS VPLS and not to any external agent or other VPLS. Note that VPLS
does not offer security or authentication: VPLS packets are sent in does not offer confidentiality, integrity, or authentication: VPLS
the clear in the packet-switched network, and a man-in-the-middle can packets are sent in the clear in the packet-switched network, and a
eavesdrop, and may be able to inject packets into the data stream. man-in-the-middle can eavesdrop, and may be able to inject packets
If security is desired, the PE-to-PE tunnels can be IPsec tunnels. into the data stream. If security is desired, the PE-to-PE tunnels
For more security, the end systems in the VPLS sites can use can be IPsec tunnels. For more security, the end systems in the VPLS
appropriate means of encryption to secure their data even before it sites can use appropriate means of encryption to secure their data
enters the Service Provider network. even before it enters the Service Provider network.
There are two aspects to achieving data privacy in a VPLS: securing There are two aspects to achieving data privacy in a VPLS: securing
the control plane, and protecting the forwarding path. Compromise of the control plane, and protecting the forwarding path. Compromise of
the control plane could result in a PE sending data belonging to some the control plane could result in a PE sending data belonging to some
VPLS to another VPLS, or blackholing VPLS data, or even sending it to VPLS to another VPLS, or blackholing VPLS data, or even sending it to
an eavesdropper, none of which are acceptable from a data privacy an eavesdropper, none of which are acceptable from a data privacy
point of view. Since all control plane exchanges are via BGP, point of view. Since all control plane exchanges are via BGP,
techniques such as in [2] help authenticate BGP messages, making it techniques such as in [2] help authenticate BGP messages, making it
harder to spoof updates (which can be used to divert VPLS traffic to harder to spoof updates (which can be used to divert VPLS traffic to
the wrong VPLS), or withdraws (denial of service attacks). In the the wrong VPLS), or withdraws (denial of service attacks). In the
multi-AS options (b) and (c), this also means protecting the inter-AS multi-AS options (b) and (c), this also means protecting the inter-AS
BGP sessions, between the ASBRs, the PEs or the Route Reflectors. BGP sessions, between the ASBRs, the PEs or the Route Reflectors.
Note that [2] will not help in keeping VPLS labels private -- knowing One can also use the techniques described in section 10 (b) and (c)
the labels, one can eavesdrop on VPLS traffic. However, this of [6], both for the control plane and the data plane. Note that [2]
requires access to the data path within a Service Provider network. will not help in keeping VPLS labels private -- knowing the labels,
one can eavesdrop on VPLS traffic. However, this requires access to
the data path within a Service Provider network.
There can also be misconfiguration leading to unintentional
connection of CEs in different VPLSs. This can be caused, for
example, by associating the wrong Route Target with a VPLS instance.
This problem, shared by [6], is for further study.
Protecting the data plane requires ensuring that PE-to-PE tunnels are Protecting the data plane requires ensuring that PE-to-PE tunnels are
well-behaved (this is outside the scope of this document), and that well-behaved (this is outside the scope of this document), and that
VPLS labels are accepted only from valid interfaces. For a PE, valid VPLS labels are accepted only from valid interfaces. For a PE, valid
interfaces comprise links from P routers. For an ASBR, a valid interfaces comprise links from P routers. For an ASBR, a valid
interface is a link from an ASBR in an AS that is part of a given interface is a link from an ASBR in an AS that is part of a given
VPLS. It is especially important in the case of multi-AS VPLSs that VPLS. It is especially important in the case of multi-AS VPLSs that
one accept VPLS packets only from valid interfaces. one accept VPLS packets only from valid interfaces.
MPLS-in-IP and MPLS-in-GRE tunneling are specified in [3]. If it is
desired to use such tunnels to carry VPLS packets, then the security
considerations described in Section 8 of that document must be fully
understood. Any implementation of VPLS that allows VPLS packets to
be tunneled as described in that document MUST contain an
implementation of IPsec that can be used as therein described. If
the tunnel is not secured by IPsec, then the technique of IP address
filtering at the border routers, described in Section 8.2 of that
document, is the only means of ensuring that a packet that exits the
tunnel at a particular egress PE was actually placed in the tunnel by
the proper tunnel head node (i.e., that the packet does not have a
spoofed source address). Since border routers frequently filter only
source addresses, packet filtering may not be effective unless the
egress PE can check the IP source address of any tunneled packet it
receives, and compare it to a list of IP addresses that are valid
tunnel head addresses. Any implementation that allows MPLS-in-IP
and/or MPLS-in-GRE tunneling to be used without IPsec MUST allow the
egress PE to validate in this manner the IP source address of any
tunneled packet that it receives.
7. IANA Considerations 7. IANA Considerations
IANA is asked to allocate an AFI for L2VPN information (suggested IANA is asked to allocate an AFI for L2VPN information (suggested
value: 25). [NOTE to IANA: This should be the same as the AFI value: 25). This should be the same as the AFI requested by [11].
requested by [9].]
IANA is asked to allocate an extended community value for the Layer2
Info Extended Community (suggested value: 0x800a).
8. References 8. References
8.1. Normative References 8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 [2] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC 2385, August 1998. Signature Option", RFC 2385, August 1998.
[3] Bates, T., "Multiprotocol Extensions for BGP-4", [3] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating MPLS in
draft-ietf-idr-rfc2858bis-07 (work in progress), August 2005. IP or Generic Routing Encapsulation (GRE)", RFC 4023,
March 2005.
[4] Rekhter, Y., "BGP Extended Communities Attribute", [4] Bates, T., "Multiprotocol Extensions for BGP-4",
draft-ietf-idr-bgp-ext-communities-09 (work in progress), draft-ietf-idr-rfc2858bis-10 (work in progress), March 2006.
July 2005.
[5] Martini, L., "Encapsulation Methods for Transport of Ethernet [5] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Over MPLS Networks", draft-ietf-pwe3-ethernet-encap-11 (work in Communities Attribute", RFC 4360, February 2006.
progress), December 2005.
[6] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks
(VPNs)", RFC 4364, February 2006.
[7] Martini, L., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, April 2006.
8.2. Informative References 8.2. Informative References
[6] Bates, T., Chandra, R., and E. Chen, "BGP Route Reflection - An [8] Bates, T., Chandra, R., and E. Chen, "BGP Route Reflection - An
Alternative to Full Mesh IBGP", RFC 2796, April 2000. Alternative to Full Mesh IBGP", RFC 2796, April 2000.
[7] Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual [9] Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual
Private Networks (L2VPNs)", draft-ietf-l2vpn-l2-framework-05 Private Networks (L2VPNs)", draft-ietf-l2vpn-l2-framework-05
(work in progress), June 2004. (work in progress), June 2004.
[8] Lasserre, M. and V. Kompella, "Virtual Private LAN Services [10] Lasserre, M. and V. Kompella, "Virtual Private LAN Services
over MPLS", draft-ietf-l2vpn-vpls-ldp-08 (work in progress), Using LDP", draft-ietf-l2vpn-vpls-ldp-09 (work in progress),
November 2005. June 2006.
[9] Ould-Brahim, H., "Using BGP as an Auto-Discovery Mechanism for
Layer-3 and Layer-2 VPNs", draft-ietf-l3vpn-bgpvpn-auto-06
(work in progress), June 2005.
[10] Rosen, E., "BGP/MPLS IP VPNs", draft-ietf-l3vpn-rfc2547bis-03 [11] Ould-Brahim, H., "Using BGP as an Auto-Discovery Mechanism for
(work in progress), October 2004. VR-based Layer-3 VPNs", draft-ietf-l3vpn-bgpvpn-auto-07 (work
in progress), April 2006.
[11] Marques, P., "Constrained VPN Route Distribution", [12] Marques, P., "Constrained VPN Route Distribution",
draft-ietf-l3vpn-rt-constrain-02 (work in progress), June 2005. draft-ietf-l3vpn-rt-constrain-02 (work in progress), June 2005.
[12] Martini, L., "Pseudowire Setup and Maintenance using the Label [13] Martini, L., "Pseudowire Setup and Maintenance using the Label
Distribution Protocol", draft-ietf-pwe3-control-protocol-17 Distribution Protocol", draft-ietf-pwe3-control-protocol-17
(work in progress), June 2005. (work in progress), June 2005.
[13] Kompella, K., "Layer 2 VPNs Over Tunnels", [14] Kompella, K., "Layer 2 VPNs Over Tunnels",
draft-kompella-l2vpn-l2vpn-00 (work in progress), January 2004. draft-kompella-l2vpn-l2vpn-01 (work in progress), January 2006.
[14] Institute of Electrical and Electronics Engineers, "Information [15] Institute of Electrical and Electronics Engineers, "Information
technology - Telecommunications and information exchange technology - Telecommunications and information exchange
between systems - Local and metropolitan area networks - Common between systems - Local and metropolitan area networks - Common
specifications - Part 3: Media Access Control (MAC) Bridges: specifications - Part 3: Media Access Control (MAC) Bridges:
Revision. This is a revision of ISO/IEC 10038: 1993, 802.1j- Revision. This is a revision of ISO/IEC 10038: 1993, 802.1j-
1992 and 802.6k-1992. It incorporates P802.11c, P802.1p and 1992 and 802.6k-1992. It incorporates P802.11c, P802.1p and
P802.12e. ISO/IEC 15802-3: 1998.", IEEE Standard 802.1D, P802.12e. ISO/IEC 15802-3: 1998.", IEEE Standard 802.1D,
July 1998. July 1998.
Appendix A. Contributors Appendix A. Contributors
skipping to change at page 34, line 41 skipping to change at page 34, line 41
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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