Implementation of ETHERNET/MPLS network aggregation for the provision of multiple services – MPLS and VPN

This article presents extracts of modules 4 and 5 of the course: “IMPLEMENTATION OF ETHERNET/MPLS NETWORK AGGREGATION FOR THE PROVISION OF MULTIPLE SERVICES”, which will be used for distance learning by the Inter-American Telecommunication Commission (CITEL) Regional Training Center, and the ITU Network of Excellence Node: Catholic University of Uruguay (UCU).

In this course, in the framework of the IP multiple service networks, fundamental aspects of technologies and concepts of access and Ethernet/MPLS aggregation, the VPLS and VPN will be analyzed. The modules included are:

1 – XDSL, Metro Ethernet, other technologies and services.

2 – Concepts of the DSL Forum, DSL and Ethernet Aggregation.

3 – Concepts of the IEEE, Ethernet Aggregation. Other technologies.

4 – Multiprotocol Label Switching – MPLS and IETF Concepts.

5 – MPLS network services.

Specifically, module 4 of the course introduces MPLS (Multiprotocol Label Switching) technology and its main applications, placing particular emphasis on the functionality of Traffic Engineering.  In addition, module 5 presents first a series of points to take into account when implementing a MPLS network with quality of service support. On the other hand, it covers different VPN services that these MPLS networks can provide.

We present here the following extract from module 4 in which some of the possible reasons driving the implementation of MPLS are given.

Reasons - Multiprotocol Label Switching - Motivation

The explosive growth of the Internet presents a serious challenge for the service providers and equipment manufacturers. These providers are facing challenges such as how to create differentiated services and optimize the use of the networks.  These providers nowadays resolve these problems in different ways:

• Increasing band width
• Increasing the number of large capacity routers within the network
• Optimizing the use of available band width

MPLS is able to combine the characteristic intelligence properties of routing with the speed typical of the concept of switching. It provides a significant benefit both for pure IP based networks and for those that use IP jointly with ATM.

MPLS technology is a key factor in the scalability of Virtual Private Networks (VPNs) permitting, among other things, the provision of  point-to-point Quality of Service (QoS) in a network.

Multprotocol Label Switching (MPLS) represents the latest evolution in routing/forwarding technologies. MPLS provides a solution that combines the control of IP routing with the simplicity of Layer 2 switching. MPLS provides a platform that supports the deployment of advanced services resolving a number of problems, in that it:

• Solves the problems of scalability associated with the current deployment of IP over ATM (model overlay)
• Significantly reduces the operational complexity of networks
• Facilitates the implementation of new routing capacities that extend the conventional IP routing techniques
• Offers a standard solution enabling interoperability between the equipment of different providers
• Facilitates the implementation of VPNs both at Layer 2 and Layer 3 level
• Enables Traffic Engineering

An extract from module 5 is given below, where some possible VPN types are introduced to be implemented in MPLS networks.

With the arrival of new technologies such as MPLS, new ways of building VPNs have become popular, including Layer 2 and Layer 3 VPNs based on provider edge (PE) equipment. Figure 3 shows a diagram with the possible classification of VPNs established by the IETF.

Figure 3: Terminology for Provider Provisioned VPN

The terminology used in the diagram is defined in RFC 4026 (Provider Provisioned VPN Terminology) given below:

• PPVPN: Provider Provisioned VPN is a VPN provisioned by the service provider.
• CE-based VPN: An implementation of VPNs where the service provider network has no knowledge of the VPN of the client. VPN information is limited to client equipment (CE). All the specific procedures of the VPN are made in the CE; the PEs have no knowledge that the traffic they are processing corresponds to a VPN.
• PE-based VPN: In this type of VPNs, the service provider network knows that the traffic belongs to a VPN. The PEs maintain the users’ VPNs guaranteeing the isolation of the VPN traffic of different clients. Since the PEs maintain the information corresponding to the VPNs, the CEAS can behave as if they were connected to a private network. In this way, the CEAS do not need any change or extra functionality to be connected to a VPN of this type.
• VPN LAYER 3: A layer 3 VPN interconnects an group of equipment based on their own IP addresses. There are two types of Layer 3 VPNs:
• VPN BGP/MPLS: is a VPN based on PEs where these PEs keep independent forwarding tables for each VPN.
• Virtual Router: is a VPN where the PEs keep a complete logical router for each supported VPN. Each virtual router keeps a unique forwarding table and a unique routing protocol.
• VPN LAYER 2: There are three types of Layer 2 VPNs:
• VPWS: Virtual Private Wire Service is a point-to-point circuit that connects two Customer Edge devices. A logical link is established over a network of packets. The CEs can be routers, switches or a host.
• VPLS: Virtual Private Lan Service is a service that emulates all the functionality of a traditional LAN. A VPLS makes it possible to interconnect several LAN segments over a packet of networks and to simulate that they are located in a single LAN segment.
• IPLS: IP Only Lan-Like Service is like a VPLS except it can be assumed:
  • that the CEs are hosts or routers (excepting switches)
  • that the service only transports IP packets (IPv4 – IPv6) and supports packets such as ICMP and ARP (other Layer 2 packets that do not contain IP are not supported)

While this service is functionally a sub-group of the VPLS service, it is considered as separate because it can be provisioned by using different mechanisms, which makes it possible for it to be implemented in platforms that do not support VPLSs.

Throughout this chapter, the implementation of three types of VPNs over the described MPLS networks will be covered in detail: VPWS, VPLS and VPN BGP/MPLS.

Gustavo Sandler y Javier Emicuri
Universidad Católica de Uruguay