2-1 MPLS Explained

Key Concepts

• MPLS Overview
• Label Switching
• Label Distribution Protocol (LDP)
• MPLS Forwarding
• MPLS Applications

MPLS Overview

Multiprotocol Label Switching (MPLS) is a data-carrying technique that provides a way to move data quickly and efficiently across networks. MPLS operates at the layer 2.5 of the OSI model, sitting between the data link layer (layer 2) and the network layer (layer 3). It uses labels to forward packets, which allows for faster and more efficient routing compared to traditional IP routing.

Label Switching

Label switching is the core mechanism of MPLS. Instead of using the destination IP address to determine the next hop, MPLS uses a short, fixed-length value called a label. This label is attached to each packet and is used by routers to make forwarding decisions. This approach reduces the complexity of routing decisions and speeds up packet forwarding.

Example

Consider a packet traveling through an MPLS network. As the packet enters the network, it is assigned a label by the ingress router. Each subsequent router along the path uses this label to forward the packet, without needing to perform complex IP lookups. The egress router removes the label and forwards the packet based on its IP address.

Label Distribution Protocol (LDP)

LDP is the protocol used to distribute labels between MPLS-enabled routers. LDP allows routers to exchange label information and establish label-switched paths (LSPs). These LSPs are used to forward packets through the MPLS network. LDP ensures that each router has the necessary label information to forward packets efficiently.

Example

In an MPLS network, routers A and B need to establish an LSP. Router A sends an LDP message to Router B, proposing a label for a specific IP prefix. If Router B agrees, it sends an LDP message back to Router A, confirming the label. This exchange establishes the LSP, allowing packets to be forwarded using the agreed-upon label.

MPLS Forwarding

MPLS forwarding involves the use of a forwarding equivalence class (FEC) to group packets that should follow the same path through the network. Each FEC is associated with a specific label, and packets belonging to the same FEC are forwarded using the same LSP. This allows for efficient traffic engineering and load balancing within the MPLS network.

Example

Suppose a company has two branches connected via an MPLS network. Traffic from Branch A to Branch B is assigned to a specific FEC and label. All packets belonging to this FEC are forwarded along the same LSP, ensuring consistent and efficient delivery of traffic between the branches.

MPLS Applications

MPLS has several applications, including:

• VPNs: MPLS is widely used to create Virtual Private Networks (VPNs) that securely connect remote sites.
• Traffic Engineering: MPLS allows for the optimization of network resources by controlling the paths that different types of traffic take through the network.
• QoS: MPLS can be used to prioritize certain types of traffic, ensuring that critical applications receive the necessary bandwidth and performance.

Example

A service provider uses MPLS to create a VPN for a large enterprise. The enterprise's remote offices are connected via an MPLS network, ensuring secure and efficient communication. Additionally, the service provider uses MPLS traffic engineering to optimize the network for different types of traffic, such as voice, video, and data.

Conclusion

Understanding Multiprotocol Label Switching (MPLS) is essential for designing and managing efficient and scalable network infrastructures. By mastering the concepts of label switching, LDP, MPLS forwarding, and MPLS applications, network professionals can leverage MPLS to enhance network performance, security, and flexibility. This knowledge is crucial for anyone pursuing the CCNP Service Provider certification.