10-06-2013, 12:45 PM
Summer Training Programme MPLS VPN
Summer Training.doc (Size: 324.5 KB / Downloads: 20)
MPLS Overview
Introduction
The exponential growth of the Internet over the past several years has placed a tremendous strain on the service provider networks. Not only has there been an increase in the number of users but there has been a multifold increase in connection speeds, backbone traffic and newer applications. Initially ordinary data applications required only store and forward capability in a best effort manner. The newer applications like voice, multimedia traffic and real-time e-commerce applications are pushing towards higher bandwidth and better guarantees, irrespective of the dynamic changes or interruptions in the network.
To honour the service level guarantees, the service providers not only have to provide large data pipes (which are also costlier), but also look for architectures which can provide & guarantee QoS guarantees and optimal performance with minimal increase in the cost of network resources.
MPLS technology enables Service Providers to offer additional services for their customers, scale their current offerings, and exercise more control over their growing networks by using its traffic engineering capabilities.
IP routing and MPLS
In conventional IP forwarding, a particular router will typically consider two packets to be in the same FEC( Forwarding Equivalence Class) if there is some address prefix X in that router's routing tables such that X is the "longest match" for each packet's destination address. As the packet traverses the network, each hop in turn reexamines the packet and assigns it to a FEC.
On the other hand, in MPLS, the assignment of a particular packet to a particular FEC is done just once, as the packet enters the network. The FEC to which the packet is assigned is encoded as a label. When a packet is forwarded to its next hop, the label is sent along with it. At subsequent hops, there is no further analysis of the packet's network layer header. Rather, the label is used as an index into a table which specifies the next hop, and a new label. The old label is replaced with the new label, and the packet is forwarded to its next hop.
MPLS terminology
IP-based networks typically lack the quality-of-service features available in circuit-based networks, such as Frame Relay and ATM. MPLS brings the sophistication of a connection-oriented protocol to the connectionless IP world. Based on simple improvements in basic IP routing, MPLS brings performance enhancements and service creation capabilities to the network.
MPLS stands for Multiprotocol Label Switching; multiprotocol because its techniques are applicable to ANY network layer protocol, of which IP is the most popular.
MPLS Network Structure
As shown in Fig, the basic composing unit of MPLS network is LSR, and the network consisting of LSRs is called MPLS domain. The LSR that is located at the edge of the domain and connected with other customer network is called Label Edge Router (LER). The LSR located inside the domain is called core LSR. The labeled packets are transmitted along the LSP composed of a series of LSRs. Among them, the import LSR is called Ingress, and the export LSR is called Egress.
MPLS Applications
MPLS-Based VPN
For traditional VPN, the transmission of the data flow between private networks on the public packet switched network is usually realized via such tunneling protocols as GRE, L2TP and PPTP, and LSP itself is the tunnel on the public network. The realization of VPN using MPLS is of natural advantages. The MPLS-based VPN connects the geographically different branches of the private network by using LSP, forming a united network.
MPLS-Based Traffic Engineering
Network congestion is the main problem affecting the backbone network performance. Usually the network is congested due to insufficient network resources or unbalanced network resources, which causes partial congestion. Traffic engineering is used to solve the congestion due to unbalanced load. Through monitoring network traffic and load on network element dynamically, then adjusting traffic management parameters and routing parameters as well as resource constraining parameters in real time, traffic engineering optimizes the network resources and prevents the network congestion accordingly.
The existing IGPs are all driven by the topology, and only the static connection of the network is taken into account. However, such dynamic status as bandwidth and traffic characteristics cannot be reflected. This is just the main reason resulting in unbalanced network load. MPLS, which is different from those of IGP, just satisfies the requirement of traffic engineering. MPLS supports the explicit LSP routing that is different from routing protocol path. Compared with traditional single IP packet forwarding, LSP is more convenient for management and maintenance.
MPLS QoS
QoS represents the set of techniques necessary to manage network bandwidth, delay, jitter, and packet loss. From a business perspective, it is essential to assure that the critical applications are guaranteed the network resources they need, despite varying network traffic load.
Service providers offering MPLS VPN and traffic engineering (TE) services can now differentiate themselves by providing varying levels of QoS for different types of network traffic. For example, voice-over-IP (VoIP) traffic receives service with assured minimums of delay and bandwidth, while e-commerce traffic might receive a minimum bandwidth guarantee (but not a delay guarantee). DiffServ is one of the QoS architectures for IP networks defined by the IETF. Cisco IOS MPLS supports the IETF DiffServ architecture by making the rich set of Cisco QoS functions MPLS aware, and by enabling the features to act on the MPLS packets.