What is MPLS?

MPLS, or Multiprotocol Label Switching, is a data forwarding technique that functions by routing traffic using pre-defined paths. It emerged in the 1990s as a better alternative to network routing. In traditional IP protocol, routers perform IP lookup at every node, leading to delays and time lags. In contrast, MPLS does label switching where the packet’s route is decided in advance.

In the MPLS network, only the first router performs a lookup, but after that, the routers just read the headers without having to crawl through the data packet’s information to check its IP address. This saves time and enables faster and more efficient packet transfers. 

An MPLS network is a hybrid service that operates between Layer 2 and 3 of the OSI hierarchy. In the OSI model, Layer 2 (Data Link) transfers data between nodes in a WAN or a LAN. Layer 3 (Network) routes data packets using IP protocols. While MPLS routes packets with the speed of Level 2, it preserves the scalability of level 3. 

Also see: What is Software-Defined Networking 

How Does Network Routing Work?

When information is sent over the internet, it is broken up into smaller chunks of data called packets. Each packet is assigned a port number and an attached header that contains information about the source and the destination IP address. For a packet to reach its final destination, it must be forwarded through several routers until it finally reaches the destination IP address. 

In traditional IP routing, data packets do not carry information other than the destination address. Since these packets don’t have any information on the route they’re supposed to take, they depend on the routers for further action.

Thus, to determine the packet’s next destination, routers must make independent decisions regarding the next stop by consulting a routing table. But each router’s individual routing decisions can cause a lag, making them unsuitable for latency-sensitive communications technology applications.

If you are looking for a method that can help data travel faster than standard IPs, then an MPLS is a good option.

Also see: Steps to Building a Zero Trust Network

How does Routing Work in MPLS?

To understand routing in MPLS, we must first understand what MPLS labels and routers are.    

MPLS Labels

In MPLS, data packets are affixed with one or more labels. These labels contain information about where the packet should go inside the MPLS network.

A label stack is composed of four parts:

  • Label: The label holds information about where the packet should go next.
  • Experimental (Exp): The 3 bits are used to specify QoS (Quality of Service).
  • Bottom of stack (BoS) flag: A network packet can have several labels stacked over each other. The BoS flag, when set to 1, shows the label that is at the bottom of the stack. Otherwise, its value is set to 0.
  • Time-to-live (TTL) field: The label’s TTL field represents the lifespan of the data or the maximum number of hops it can make before it’s dropped.  At each hop, its value is decremented by one till its value reaches zero.

Also see: Top Managed Service Providers

MPLS Routers

  • Label Edge Router: A Label Edge Router (LER) is situated at an MPLS network’s entry and exit point. The entry LER is known as Ingress LSR, while the last router is known as Egress LSR. Ingress LER assigns data labels on incoming unlabelled packets before sending them forward. When the packet reaches the exit point of the network, the Egress LER removes the label and replaces it with a standard IP address.
  • Label Switching Router: Label Switching Routers (LSRs) are located in the middle of the MPLS network and are responsible for forwarding packets within the MPLS domain. Once an LSR receives a packet, it adds/swaps a label and forwards it to the next hop.
  • Label Switching Path: Label Switching Paths (LSPs) are predetermined paths that packets take in the MPLS network.

With the help of LSPs, we can predetermine the path that packets will take, unlike IP forwarding, where a packet can follow any number of paths.  

MPLS Routing

Now that we have a fair idea of the architecture of an MPLS network, let us see how it works:

  • When the MPLS network receives a data packet, the first router, called the LER/Ingress router, assesses the destination and assigns a label to the data packet. This label decides the path the packet will follow.
  • Each packet can have more than one label, with the labels stacked in a last in/first out order.
  • Once the packet has been labeled, it moves through the LSRs or “transit nodes.” LSRs do not perform any IP lookup but simply scan the labels based on the topmost label and forward them to the right LSP.
  • A lookup involves determining what operation to perform on the label – ‘push,’ ‘swap,’ or ‘pop’ and selecting the next hop to which the packet needs to be sent.
  • Every consecutive router simply verifies the label and forwards the packet to the next router in the node.
  • At the “egress node,” where the packet leaves the MPLS network, the label is removed from the data packet and delivered via regular IP routing.

Also see: Best Network Virtualization Software & Products 

Here is a tabular form that shows the differences between IP and MPLS:

Properties MPLS IP
Connectivity Provided by a single carrier Multiple carriers
Layer of functioning Functions at level 2.5 Functions at level 3
Price Expensive Cheap
Traffic engineering Possible Not available
Scalability Scalable but less than IP Highly scalable
Type Hardware based Hardware independent 

Benefits of MPLS

MPLS provides numerous advantages to businesses. These are:

Protocol Agnostic

MPLS is protocol agnostic as it can work with various network protocols like Frame Relay, Serial, Metro, Ethernet, ATM, etc. Furthermore, since MPLS routers only read the labels attached to the packets, they don’t perform multiple router lookups. As a result, it lessens network congestion and leads to improved performance.

Supports Traffic Engineering

MPLS supports traffic engineering (TE) that reroutes traffic and avoids network congestion. Congestion occurs when there are inadequate resources to manage network traffic. If there is a congested path, TE will route the traffic through a less crowded path, ensuring minimal hold up. This is vital for high-priority or mission-critical apps that must reach the end destination without delay.

Decreases Downtime

The experimental bits in the MPLS label specify Quality of Service or QoS. QoS is a feature that prioritizes traffic flow. Thus, an MPLS network can prioritize traffic and ensure that more critical traffic passes first. This is necessary for video/voice communications where latency should be nil.  

Flexibility

In MPLS, the path is already predetermined. Thus, there is no heavy lifting involved.  Yet again, there is a great deal of flexibility in MPLS networks. With the help of traffic engineering, network traffic can be routed through less congested paths, improving throughput and customer satisfaction in the process. So, basically, with MPLS networks, you get the best of both worlds.

Also see: Containing Cyberattacks in IoT

What are the Disadvantages of MPLS?

Security

MPLS offers fewer security features when compared to traditional network providers. Most importantly, it is not encrypted, thus making it more vulnerable to cyberattacks. However, users can work with their service providers to set up encryption and safeguard their network from cybercriminals.  

Deployment

Setting up dedicated paths in MPLS takes a long time; sometimes, it can also continue for a few months, making it difficult for enterprises to scale up quickly. Additionally, MPLS networks are more suited for point-to-point connectivity and thus are not ideal for the cloud.

High Bandwidth Costs

A drawback of MPLS is that bandwidth costs are expensive. With consumers turning more to bandwidth-intensive content like videos, the high per-megabit price can be a disadvantage. 

Also see: Steps to Building a Zero Trust Network

The Future of MPLS

While the various benefits of MPLS make it a dependable solution for enterprises, the move to the cloud makes it an unviable option. SD-WAN is one of the many alternatives to MPLS that offers agility and cost-effective connections to organizations. Nevertheless, this does not mean that MPLS is dead — a more likely scenario is enterprises using a mix of both to meet their digital transformation needs. 

Susnigdha Tripathy
Susnigdha Tripathy
Susnigdha Tripathy is a full-time writer and editor who presently lives in Singapore. She has over ten years of experience writing, editing, and delivering exceptional content for her clients. She currently writes for Virtasant, a cloud technology company, and Krista Software, a provider of intelligent automation solutions. Her work also gets published on several high-ranking tech websites.

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