Layer 2 Virtual Private Networks
Layer 2 Virtual Private Networks WG
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The L2VPN working group is responsible for defining and specifying a
limited number of solutions for supporting provider-provisioned Layer-2
Virtual Private Networks (L2VPNs). It will also address requirements
driven by cloud computing services and data centers as they apply to
Layer-2 VPN services.
Layer-2 VPNs defined by L2VPN operate over pseudowires (PWs) as
defined by the PWE3 WG or over IP or MPLS PSN tunnels. A L2VPN
emulates a "native" service over a PSN that is adequately faithful
to, but may not be entirely indistinguishable from the native
service itself. Further, following in the "edge-to-edge" nature
of the service, the L2VPN WG will not define any mechanisms
which exert control over the underlying PSN. When necessary it
may, however, recommend or require the use of existing PSN QoS
and path control mechanisms between the PEs which provide the
Layer-2 VPNs comprise the following:
1. Virtual Private LAN Service (VPLS) -- A Layer-2 service
that emulates a switched Ethernet (V)LAN across a PSN.
2. Virtual Private Wire Service (VPWS) -- A Layer-2 service that
provides point-to-point connectivity for a variety of link layers,
including Frame Relay, ATM, Ethernet, PPP, etc., across a PSN.
3. Virtual Private Multicast Service (VPMS) -- A Layer-2 service that
provides point-to-multipoint connectivity for a variety of link
layers across a PSN.
4. IP-only L2VPN, an IP-only service over a PSN. The WG will address
two specific types of IP-only L2VPN:
a) Point-to-point Layer-2 VPN. This service is similar to VPWS, but
also supports heterogenous Attachment Circuits at either end
of a single point-to-point service.
b) Multipoint-to-multipoint Layer-2 VPN. This service is similar
to VPLS, but learns IP and MAC address bindings from ARPs and
broadcast/multicast IP packets.
5. Ethernet VPN (E-VPN) - An enhanced Layer-2 service that
emulates an Ethernet (V)LAN across a PSN. E-VPN supports
load-sharing across multiple connections from a Layer-2 site
to an L2VPN service. E-VPN is primarily targeted to support
large-scale L2VPNs with resiliency requirements not satisfied
by other L2VPN solutions.
6. E-Tree, a Layer-2 service defined by the MEF, which provides
connectivity between one or more root nodes and one or more leaf
nodes, with the restriction that leaf nodes may only communicate
with root node(s) (and not with each other).
L2VPNs will make use of existing IETF specified mechanisms
unless there are technical reasons why the existing mechanisms
are insufficient or unnecessary.
The L2VPN WG is responsible for specification of the
discovery and membership of PEs participating in a Layer-2
VPN as well as the membership of CE devices for a specific
instance of an L2VPN.
The L2VPN WG will provide extensions of existing protocols
that will be discussed in protocol-specific WGs. In
particular, the L2VPN WG may define extensions to pseudowire
management mechanisms for VPLS. Those extensions will
be reviewed by the PWE3 WG to ensure they are aligned
with the overall design/architecture of PWE3.
The L2VPN WG will not define new encapsulations, control,
or resiliency mechanisms specifically related to pseudowires.
Furthermore, when the L2VPN solution is based on PWs, the
L2VPN WG will not define protocol inter-working between
an L2VPN and native service Layer-2 OAM or resiliency
mechanisms. The L2VPN WG may define how to operate native
service-layer control, OAM or resiliency mechanisms on
top of an L2VPN. In addition, it may define native data
plane and/or control plane interworking between an
L2VPN and an associated native Layer-2 service.
The L2VPN WG scope includes the following:
1. Discovery of PEs participating in a Layer-2 VPN and the
associated topology required for connectivity of the VPLS,
VPWS, VPMS or E-VPN service.
2. Signaling of information related to the discovery and
membership of PEs within a L2VPN. These procedures must
use PWE3 control and management procedures, or define
requirements for extensions of PWE3 protocols to suit
the needs of an L2VPN, when the L2VPN operates over PWs.
Once those requirements have been reviewed by the L2VPN WG,
they should be provided to the PWE3 WG to derive solutions.
3. MIBs for Layer-2 VPN solutions.
4. Specification of requirements, framework and solutions
that facilitate Operations Administration and Management
(OAM) of any type of L2VPN within the scope of the L2VPN
5. Mechanisms to permit optimization of multicast data
traffic within an L2VPN.
6. If transport does not involve PWs, mechanisms that
support load-balancing/multi-pathing between PEs
interconnecting a Layer-2 service using an L2VPN across
7. requirements for the multi-homing of CEs to several
VPLS or E-VPN PEs, inclusive of active/backup and active/
active (load-sharing) configurations. Based on these
requirements define VPLS or E-VPN control plane
solutions for achieving fast convergence after failure
of an active path in the PSN or on the AC side.
8. Enhancements to increase the scalability of the Control
Plane and Data Plane of L2VPN PE nodes, and of core nodes
that provide transport services for L2VPN.
9. Requirements and solutions for Auto-Discovery and
Signaling of Inter-AS L2VPNs, in addition to Inter-AS
solutions for multicast-optimized L2VPNs.
10. Requirements and solutions for supporting "E-Tree"
services using VPLS.