ITPRC NEWS - April, 2002 - http://www.itprc.com/
What is a "Layer 2 VPN?"
By Irwin Lazar
Day three of last week's MPLScon
conference in Virginia focused on the emerging use of MPLS to allow
carriers to offer network-based VPN services. Using MPLS a carrier
can create IP-layer (Layer 3) tunnels through their network, thus
providing isolation of customer traffic at a level equal to that of
other tunneling mechanisms such as ATM and Frame Relay.
However, most of the excitement and
interest at this conference was on yet another emerging use for MPLS
dubbed "Layer 2 VPNs." Layer 2 VPNs actually refer to
two different technologies that allow Layer 2 traffic (such as ATM,
Frame Relay, SONET/SDH or Ethernet) to be directly encapsulated within
MPLS label switch paths (e.g. circuits). At first this seems a bit
peculiar, after all, isn't IP carried by Layer 2 mechanisms?
Doesn't this approach violate the OSI model we all know and love so
From a service provider perspective
MPLS-based Layer 2 VPNs offer tremendous advantages. Providers can
use this technology to preserve existing services as they consolidate
multiple Layer 2 and Layer 3 networks to a single unified network
infrastructure. For example, a provider can simply continue to
offer Frame Relay or ATM services to their customers, even though the
traffic may never actually be carried by Frame or ATM switches.
Start-up carriers such as Masergy are
using Layer 2 emulation to provide Frame Relay and ATM services over
their IP network, thus making their services more competitive for
customers already familiar with existing Layer 2 services.
Two IETF working groups are currently
developing standards in this area. "Psuedowire Emulation
End-to-End (PWE3)" is developing standards for encapsulation of
Layer 2 frames and cells directly into MPLS. This working group is
the home of the "Martini Drafts" which are the most well known
standards proposals for accomplishing this task.
Meanwhile, The IETF's "Provider
Provisioned Virtual Private Networks (PPVPN)" working group is
defining methods for provisioning these new and emerging VPN services.
From this group you'll find the also famous "Kompella" drafts
which define methods for using BGP to provision Layer 2 VPNs.
From an enterprise perspective Layer 2
VPNs will most likely remain invisible. Providers will simply
continue to offer Layer 2 services as they always have. However,
the promise of a simplified network infrastructure may mean cost savings
for enterprises in the long run.
For additional reading:
PPVPN Working Group: http://www.ietf.org/html.charters/ppvpn-charter.html
PWE3 Working Group: http://www.ietf.org/html.charters/pwe3-charter.html
The MPLS Resource Center: http://www.mplsrc.com/
Irwin Lazar is a Senior Consultant for Burton
Group where he focuses on strategic planning and network
architecture for Fortune 500 enterprises as well as large service
providers. He is the conference director for
MPLScon and runs The MPLS Resource Center
Information Technology Professional's Resource Center.
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