SD-WAN vs MPLS: Exploring Differences

Have you ever experienced the frustration of tracking a package from a distant retailer and observing its erratic stops across the country? The way Internet Protocol (IP) routing works is similar to this scenario. IP packets do not carry any information beyond the destination IP address.

Therefore, each router makes an independent forwarding decision for each packet based solely on the packet’s network-layer header. When a packet arrives at a router, the router must determine where to send it next by referring to complex routing tables. This process is repeated at each hop along the route until the packet finally reaches its destination. Routing decisions at each hop results in poor performance for delay sensitive traffic like video or voice.

Define MPLS
MPLS (Multi-Protocol Label Switching) is a well known networking technology that has already been widely used for many years now. Unlike other network protocols that rely on source and destination addresses to route traffic, MPLS routes traffic using predetermined labels. This makes it a popular choice for businesses looking to connect their remote branch offices with their data center or headquarters, providing them with reliable and secure access to data and applications.

How Does MPLS Work
MPLS assigns each packet a forwarding class of service (CoS) based on its label. These classes indicate the type of traffic being carried, such as voice or video.

MPLS separates traffic based on performance and reserves the fastest, low-latency path for real-time apps like voice and video to ensure high quality.

Labels attached to each packet provide routers with additional information beyond what they previously had to work with.

Which Layer of OSI MPLS Belongs
MPLS is a service that doesn't fit neatly into the OSI seven-layer hierarchy, and is sometimes classified as Layer 2.5 because it separates forwarding mechanisms from the underlying data-link service.

MPLS routers establish a label-switched path (LSP), a predetermined path to route traffic based on criteria in the FEC, which is used for forwarding tables for any underlying protocol.

When an end user sends traffic into the MPLS network, an MPLS label is added by an ingress MPLS router that sits on the network edge.

The MPLS Label consists of four sub-parts: the Label, Experimental bits, Bottom-of-Stack, and Time-To-Live.

These parts help MPLS routers to determine where the packet should be forwarded and set the priority that the labeled packet should have. The Bottom-of-Stack tells MPLS routers if they are the last leg of the journey, and the Time-To-Live identifies how many hops the packet can make before it is discarded.

Advantages and Disadvantages of MPLS
MPLS provides many benefits including
Scalability
Improved Performance
Better Bandwidth Utilization
Reduced Network Congestion
Better End-User Experience.
Although MPLS doesn't provide encryption, it is a virtual private network that is segregated from the public Internet, making it a secure transport mode. It is not prone to denial-of-service attacks which might affect networks.

On the downside, an MPLS connection is more expensive than a typical internet connection. Additionally, MPLS was designed for companies with several geographically dispersed remote branch offices that backhaul the majority of traffic to enterprise data centers. However, modern businesses are increasingly directing traffic to and from cloud providers, making MPLS less than optimal.

MPLS and Cloud Networks
As companies have shifted to the cloud, MPLS-based networks have become inefficient because they route traffic through central choke points. Instead, it is more effective to send traffic directly to the cloud. Moreover, the increased use of cloud services, video and mobile apps has led to higher bandwidth requirements, and MPLS services are challenging to scale on demand.

Although MPLS was a significant innovation, there are newer technologies that better meet the needs of today's network architectures. Software-defined WANs (SD-WAN) are designed with cloud connectivity in mind, which is why many businesses are replacing or supplementing their MPLS networks with SD-WAN.

Compare MPLS vs SD-WAN
To put it simply, MPLS and SD-WAN are both technologies used to connect remote locations together, but they work in different ways.

MPLS is a network protocol that provides guaranteed performance for real-time traffic, but it is expensive to deploy and inflexible to change.

SD-WAN is a newer technology that uses software-defined networking concepts to route traffic along the most efficient path, regardless of the underlying transport mechanism. Though it does not offer guaranteed performance as MPLS but its not flexible and cost effective.
While MPLS requires predetermined routes that are difficult to change, SD-WAN is transport-agnostic and allows for centralized policy application across all WAN devices. SD-WAN is also significantly less expensive to deploy and operate than MPLS.

Has Demand for MPLS reduced
Many network professionals are viewing MPLS and SD-WAN as two competing technologies. SD-WAN is gaining momentum, while MPLS usage decreased by 24% from 2019 to 2020. During the COVID-19 pandemic, the need to connect data centers to remote workers further increased the interest in SD-WAN, causing many to speculate whether SD-WAN will kill off MPLS entirely.

However, experts believe that MPLS and SD-WAN can coexist. Smaller companies that have moved to an all-cloud IT model can likely sunset MPLS and shift to an all-broadband WAN. Larger enterprises, which have already invested in MPLS networking, will likely take a hybrid approach, keeping MPLS for legacy on-net applications and using SD-WAN to offload Internet traffic such as cloud applications.

MPLS is still ideal for point-to-point connections and real-time applications like telepresence. SD-WAN can actually improve the performance of an MPLS connection by dynamically routing network traffic in the most efficient way possible. Ultimately, enterprise WAN architects need to weigh the reliable but costly performance of MPLS against the cheaper but less reliable performance of the Internet. While improvements in other networking technologies have made internet traffic more reliable, there will always be a need for the ultra-high reliability of MPLS for some applications.