What is MPLS (Multiprotocol Label Switching)?

Introduction

Multiprotocol Label Switching is a technology that allows efficient data transmission across networks. Network operators and service providers widely employ it to ensure high quality as well as reliable services for their customers. By understanding the working principles of MPLS, one can proficiently design, configure, troubleshoot, and optimize these networks. In this blog post, we will focus on MPLS by explaining its fundamentals, how it operates, when it is utilized, and how it compares to technologies like SD-WAN.

Let’s first understand what it is without wasting any more time.

What is MPLS?

MPLS stands for Multiprotocol Label Switching—a routing technique that emerged in the 1990s. It makes use of labels to direct data packets from one network node to another. Unlike IP routing methods that rely on network addresses to determine destinations, it utilizes labels to identify pre-established paths between endpoints. This approach enables efficient and more secure data delivery compared to IP routing.

Let’s take an example to understand better.

Imagine you are driving on a highway with many exits, each leading to a different city. In traditional networking, each packet of data is like a car that needs to stop at each exit to ask for directions to reach its final destination. With MPLS, it’s like having a special GPS system that assigns a unique label to each car (packet) at the entrance of the highway. This label tells the “exit points” (routers) exactly where to send the car without needing to stop and ask for directions. This process makes data transmission faster and more efficient.

Now that we have a basic understanding of it, let’s discuss its history.

History of MPLS

The concept of MPLS was first originated in 1996 by a group of engineers from Cisco, IBM, and StrataCom in order to create a high-speed switching technology. After this, in the year 1997, the first MPLS draft was published by IETF. This draft outlines the basic architecture as well as functionality of MPLS.

In the next year, 1998, in order to develop and standardize MPLS, an MPLS working group was established by IETF.

The IETF then published RFC 3031 in 2001. This defines the MPLS architecture, and for the first time, the label distribution protocol concept was introduced.

In 2002, the IETF published RFC 3346, which defined MPLS-TE. This allows network operators to optimize network resource usage.

MPLS continues to evolve with time to support newer network technologies.

How Does MPLS (Multiprotocol Label Switching) Work?

To understand the functioning of MPLS, we must draw a comparison with the Internet routing process. When data is transmitted over the Internet, it is divided into units known as packets. Each packet carries a header that holds information regarding its origin and destination. Within this header lies the destination IP address, which serves as an address for the intended recipient device.

These packets traverse through a series of routers, acting as network intermediaries. Upon receiving a packet, each router looks at the packet’s header, consults its routing table, and determines where to forward it. The routing table contains information regarding pathways to various networks based on factors like distance, congestion, and costs. It’s worth noting that these routing tables can change, depending totally on the network conditions and traffic patterns.

Nonetheless, this traditional routing does have limitations. These are:

• It can consume an amount of time and resources as each router needs to process the packet header and consult its routing table.
• The unpredictability arises from the fact that packets can follow different paths to reach the same destination, depending on the state of the routing tables at each router.

MPLS addresses these challenges by taking a different approach to routing. It makes use of labels in order to identify paths. A label is a short identifier attached to each packet of the first router in an MPLS network (known as an ingress router). This label instructs routers in the network on how to forward the packet along a predefined path called a label-switched path (LSP). The last router in the network, called the egress router, removes the label and delivers the packet to its final destination.

The advantage of using labels is their simplicity and speed compared to IP addresses. Routers within an MPLS network don’t have to consult their routing tables for each packet; they need to swap the label with a new one corresponding to the next hop in the path. This reduces routing and minimizes latency. It also ensures that all packets follow the same route.

The assignment and distribution of labels occurs through a protocol called Label Distribution Protocol (LDP), which operates among routers within an MPLS network. LDP creates LSPs by utilizing data from the IP routing protocols, like OSPF or BGP. Additionally, LDP keeps track of the status of these LSPs. It further updates whenever there are alterations in the network topology or traffic requirements.

MPLS Header

The MPLS header, positioned between Layer 2 and Layer 3, consists of a 20-bit label, 3-bit experimental (Exp) or traffic class field for QoS, 1-bit Bottom of Stack (BoS) indicator, and 8-bit Time to Live (TTL) field allowing efficient and flexible packet forwarding. We have shown the format of the header with the help of an image.

Components of MPLS

The main components with which the functionality of the MPLS label can be enabled are:

Label/ Label Value

As we already know, in the case of MPLS, each packet is assigned a label. This label can further be used to forward packets between MPLS-enabled routers. The label value is a 20-bit number and is mainly used to forward packets along the LDP (Label Distribution Path).

Traffic Class Field (EXP)

It is a 3-bit field that is mainly used to indicate the packet’s priority. This field is mainly used to map the packet to a specific PHB (Per-Hop Behavior) at each LSR.  This will ensure that the packet receives the desired QoS treatment.

Bottom of the Stack (BoS)

It is a single bit that indicates whether a packet is at the bottom of the label stack. When a packet is received with the BoS bit set, the LSR knows that it has reached the end of the label stack and can begin processing the packet. If the BoS bit is not set, the LSR continues to process the label stack until it reaches the bottom.

Time to Live (TTL)

The TTL (Time to Live) field is mainly used to prevent packets from circulating indefinitely in the network. Each time a packet is forwarded, the TTL is decremented by 1. And if TTL reaches 0, the packet is discarded. With this, one can easily prevent packets from looping infinitely in the network.

When is MPLS used?

MPLS is used in various applications where high performance, reliability, and data security are crucial aspects of transmission requirements. Here are a few examples of the applications:

Voice over IP (VoIP): It guarantees the quality of service (QoS) for voice traffic, ensuring latency, jitter, and packet loss.

Private networks (VPNs): It enables the creation of secure and private connections between various locations through encryption and tunneling techniques.

Is MPLS Layer 2 or Layer 3?

Being a hybrid protocol that functions across these two levels, it is neither technically layer 2 nor layer 3 in the traditional sense. Layer 2 technologies like Ethernet, Frame Relay, and ATM may all have their packets encapsulated by MPLS, which then forwards them based on labels that don’t depend on layer 3 addresses like IP or IPv6. MPLS, however, also uses layer 3 protocols, such as IP or BGP, to create pathways and distribute labels across endpoints. As a result, it is a layer 2.5 that connects layers 2 and 3.

Future of MPLS

As networking advances, it is important to say that MPLS will adapt too in order to ensure seamless data transmission. Also, it lays the foundations for the future, where networks are faster, more secure, and more efficient. With the increasing demand for high-bandwidth, low-latency networks, MPLS will assist in accommodating emerging technologies like 5G, IoT, and Cloud computing.

It will also integrate with newer protocols in order to ensure seamless communication and efficient data transfer. Other than this, we expect to see increased adoption of autonomous networks which heavily rely on MPLS.  The reason behind this is that MPLS allows real-time decision-making and rapid response time.

The increase in edge computing will lead to greater reliance on MPLS. This will allow data processing as well as analysis at the edge of the network.

Most of the time, everyone gets confused with MPLs and SD-WAN. Below, we have explained the basic benefits each can provide for better outcomes.

MPLS vs SD-WAN

When we talk about MPLS, it’s a proven technology that offers various benefits such as high performance, reliability, and security for network traffic. Apart from that, it also has low latency and jitter that makes it a crucial choice for VoIP. Like every other technology, it also has some limitations, such as being quite expensive and complex to deploy as well as to manage.

On the other hand, SD-WAN is a newer technology as compared to it. It also has benefits such as offering flexibility, scalability, and cost-efficiency for network traffic. It can also be utilized to dynamically route traffic over multiple links from different sources.

In the end, the choice between it and SD-WAN totally depends on the needs as well as the preferences of each organization.

Benefits of MPLS in Networking

Some of the benefits of MPLS in networking are:

• Faster Network Convergence: It helps networks recover quickly from failures, reducing downtime and increasing productivity.
• Improved Quality of Service (QoS): It ensures high-quality handling of real-time applications like video and voice.
• Enhanced Security: It provides secure connectivity, protecting data from unauthorized access.
• Scalability and Flexibility: It supports large, complex networks and allows for easy addition of new sites and applications.
• Simplified Network Management: It streamlines network operation and maintenance, reducing administrative burdens.
• Cost-Effective: It reduces network infrastructure costs by minimizing the need for multiple protocols and networks.

Drawbacks of MPLS in Networking

Some of the drawbacks of using MPLS in networking are:

• Complexity: It is a complex technology that requires specialized skills and training to implement and manage.
• High Cost: It is a premium service that can be expensive, especially for small to medium-sized businesses.
• Vendor-specific: It providers often have proprietary networks, making it difficult to switch providers if needed.
• Limited Flexibility: It networks can be inflexible, making it challenging to make changes to the network.
• Security Concerns: It networks can be vulnerable to security threats if not properly secured.

Frequently Asked Questions

Q1. Is MPLS a LAN or a WAN?

MPLS is one the common methods to construct the connections between various LANs and that further makes WAN.

Q2. What are the three types of MPLS?

The three types of MPLS are: Layer 2 VPN, Layer 3 VPN, and Layer 2 Circuits.

Q3. What is an example of MPLS?

MPLS can be used for applications that require immediate data delivery for the purpose of voice or video calls.

Q4. Why is MPLS still used?

MPLS is still used because it offers fast and reliable data transmission, supports multiple protocols and services, and enables efficient network management and scalability.

Conclusion

MPLS is one of the powerful technologies that assist in the fast and efficient transmission of data over a network. In this blog, we have covered MPLS in detail, along with its use, how it works, and a detailed comparison between SD-WAN.