What does MPLS stands for?

MPLS stands for Multi-protocol label switching 

What is a Layer 2 MPLS VPN?

• Uses an MPLS network in the provider core to deliver Layer 2 services to the customers. 
• Uses EoSDH, IPRAN and IPCORE Backhaul for the connectivity.  
• Has Ethernet Interface (FE or GE) as connectivity to customer router.

Is MPLS an alternative to IP?

• \         No.
•          There are many, many things that MPLS can't do. It's a supplement to IP to provide additional connection oriented capabilities to the network.
•         MPLS is Layer 2.5 technology while IP is layer 3. 

What are the goals of a Layer 2 MPLS VPN?

•        A Layer 2 MPLS VPN is exactly the same as a Layer 2 VPN.
•          A Layer 2 MPLS VPN allows the use of a single network technology (namely, MPLS) to offer many services, including IP, Layer 2 VPNs, Layer 3 VPNs, MPLS traffic engineering, and Differentiated Services (DiffServ).
•          A single network architecture that offers multiple services is often referred to as a converged network.
•          A single access line to provide multiple services is also beneficial to a service provider.

What are alternate Layer 2 MPLS VPN proposals?

More than one Layer 2 MPLS VPN architecture has been under consideration by the Provider-provisioned Virtual Private Network Working Group (PPVPN WG) of the IETF. The primary proposals were known as draft-Kompella and draft-Martini, and these were the file names of the versions of those drafts as of November 2001:

■Draft-martini-l2circuit-trans-mpls-07.txt

■Draft-martini-l2circuit-encap-mpls-03.txt

■Draft-kompella-ppvpn-l2vpn-00.txt

Note:

Be sure to check the Internet Drafts http://www.ietf.org/ID.html section of the IETF Web site for updates, because the drafts change often. The answer to question number 12 explains the status of those drafts in November 2001.

When should a service provider deploy a Layer 2 MPLS VPN rather than another VPN technology?

The simplest case is when the service provider’s customer is already using a Layer 2 VPN. Migration is fairly straightforward in this case. Other situations where a Layer 2 MPLS VPN is preferable are when a service provider is using non-IP protocols or has a large number of routes in its network. An important factor to note in contrasting Layer

2 and Layer 3 MPLS VPNs is that Layer 2 MPLS VPNs usually require the provider’s customer to have more routing expertise.

How is a Layer 2 MPLS VPN different from a Layer 3 MPLS VPN?

The main difference, from the service provider’s point-of-view, is that there is no Layer 3 routing information exchange between the customer and the service provider. The other difference is that the service provider does not need to care nor to know what network-layer protocol the customer uses. On the flip side, Layer 2 MPLS VPNs currently require that all sites in the service provider’s customer network connect to the service provider with the same Layer 2 technology (for example, that all use Frame Relay). This Layer 2 dependence gives the customer Layer 3 independence, because the customer can run any Layer 3 protocol. There is also an intermediate solution, called Layer 2 interworking, whereby each

customer site can connect with a different Layer 2 technology, but the Layer 3 protocol is limited to IP. In a Layer 3 MPLS VPN, however, the various sites can connect with any technology.

How is it different from Circuit Cross-connect?

There are two major advantages of Layer 2 MPLS VPNs over Circuit Cross-connect: First, with Circuit Cross-connect, you must configure point-to-point circuits. Building a VPN in this manner is tedious, because adding or removing a site requires a fair amount of work, as well as touching lots of routers. With Layer 2 MPLS VPNs, you can configure a VPN specifically, so the configuration is much more straightforward. Adding or removing a site is also much simpler, and in many cases it involves touching only the one router attached to the site. Second, each Circuit Cross-connect requires a dedicated provider edge-to-provider edge label-switched path (PE-to-PE LSP), and this LSP must be signalled by using

RSVP. (Using Label Distribution Protocol [LDP] makes no sense in a Circuit Cross-connect, point-to-point scenario, because it employs a reverse-path tree approach.) Layer 2 MPLS VPNs use label stacking, so a single PE-to-PE LSP can be used for multiple VPNs and, in fact, for multiple services. This makes it an extremely scalable technology. Furthermore, this LSP can be set up through any means, including RSVP and LDP. Label-stacking techniques also support greater infrastructure scalability.

What are the benefits of a Layer 2 MPLS VPN to a service provider and to an enterprise customer?

To a service provider, this is a significant migration step toward a single IP- and MPLS-based infrastructure for all services. Existing tail-circuit technology (Frame Relay or ATM) can be re-used. This not only makes the transition familiar to operators and maximizes the service provider’s investment, but also retains the operational simplicity of those existing technologies (thus no responsibility for customer routing). Auto provisioning makes deployment easier at scale. By using label-stacking techniques, Layer 2 MPLS VPNs are specifically designed for scalability and for deployment in carrier-of-carriers environments. For enterprise customers, the scalability of this technology is well-suited to large corporations. 

MPLS can provide multiprotocol connectivity (IPX and SNA, for instance), and it also easily supports IP multicasting. Customers that are accustomed to managing their own routing domains can continue to do so. They can also deploy extra security, such as IPSec encryption.

Will MPLS replace Frame Relay or ATM as the VPN technology of choice?

·         Layer 2 or Layer 3 MPLS VPN can run on frame relay, ATM infrastructure. A common choice of technology for the service provider’s core network is SONET/SDH.
·         Layer 2 MPLS VPNs allow service providers full freedom to choose internal network technologies independent of the Layer 2 VPN service offerings.
·         Currently most VPN networks are based on MPLS technology. Customer prefer MPLS VPN because of its flexibility, scalability and multilevel protection offered by IP network.

Could IPSec be transported over Kompella and Martini Internet Draft-based VPN networks?

Certainly. If the customer wants more security than is provided by simple isolation, Encryption, or authentication, using IPSec or other means would complement Layer 2 MPLS VPNs well. In fact, this is highly recommended.