SD-WAN vs MPLS: Making the Right Choice for Your Network

People often compare these as if they were competing circuits. They are not quite the same kind of thing, and the difference explains most of the trade-offs.

What MPLS is

MPLS, or Multiprotocol Label Switching, is a technique carriers use to forward traffic across their own network using labels instead of looking up an address at every hop. Carriers use it to build private virtual networks for each customer, with traffic separated from the public internet and from other customers. Because the carrier controls the path from end to end, it can offer classes of service with commitments on latency, jitter and packet loss. The service is a circuit and a managed network, sold together.

What SD-WAN is

SD-WAN, or software-defined wide area networking, is an overlay. Devices or software at each site build encrypted tunnels across the underlying transport, and a central controller sets the policy. The system continuously measures the quality of each path and steers each application onto the best one. It does not provide transport itself. It uses what you buy, which can be dedicated internet access, broadband, cellular, MPLS or a mix. The SD-WAN overview covers the architecture in more detail.

MPLS performance is predictable because the carrier controls the whole path and commits to targets for each class of service. A voice call that rides the real-time class on a properly configured MPLS circuit receives treatment that the public internet does not offer.

The internet is best-effort. No one guarantees a path across several networks. SD-WAN works around this by measuring each path continuously, moving traffic away from a degrading path within moments, and for sensitive traffic by duplicating packets across two paths or applying error correction. These techniques can make a pair of ordinary circuits perform very well for most applications. They cannot create capacity or remove a fault that affects both paths. If a service must hold a specified level no matter what, the answer is a circuit with a contractual commitment, whether that is MPLS or dedicated internet access with strong service levels. The SLA guide explains what those commitments do and do not cover.

Traditional MPLS networks were designed when applications lived in a central data centre. Traffic from branches went to the centre, and from there to the internet. As applications moved to the cloud, that design added delay and loaded central links with traffic that never needed to go there. SD-WAN allows each site to send cloud and internet traffic out directly, while keeping data centre traffic on private paths. This is the strongest single argument for SD-WAN in cloud-heavy organizations.

MPLS keeps traffic on a private carrier network, which many organizations value, but it does not encrypt the traffic by default and does not replace firewalls. SD-WAN tunnels over the internet are typically encrypted, which protects the traffic in transit. Moving to local breakout means branches reach the internet directly, so the security design must protect them with branch firewalling or a cloud-delivered security service. Treat the security design as part of the choice, not an add-on.

Avoid comparing price per megabit alone. The total cost of each option includes several items.

Check the contract end dates on existing circuits. Early termination charges can change the economics and the timing of a move.

Hybrid is often the most practical answer. Keep MPLS where it is needed, such as links to a data centre or a handful of critical sites, and run SD-WAN over MPLS plus internet circuits. Cloud and general traffic uses local internet breakout, while sensitive traffic stays on the private network. Over time, as contracts end and confidence grows, you can reduce the MPLS portion. The SD-WAN implementation guide sets out how to phase the move.

• Treating SD-WAN as a drop-in replacement for guaranteed circuits.
• Comparing price per megabit without comparing service commitments.
• Choosing cheap broadband for every site, including the ones that must not fail.
• Choosing two internet circuits that share a physical route.
• Ignoring the branch security design when moving to local breakout.
• Cancelling MPLS before the new network has proven itself.
• Overlooking early termination charges on existing contracts.

• What performance commitments apply to each circuit, and how are they measured and reported?
• Can the SD-WAN run over our existing MPLS, so we can phase the change?
• How do you prove that two circuits at a site do not share a failure point?
• What happens to voice quality when one path degrades?
• Who handles security at the branch when traffic goes directly to the internet?
• What are the exit terms, and who owns the equipment and configuration?

Does SD-WAN replace MPLS?

It can, but it does not have to. SD-WAN is an overlay that can run over MPLS, internet circuits or both. Many organizations reduce MPLS gradually and keep it where private transport or strict commitments are needed.

Is SD-WAN more secure than MPLS?

Not automatically. SD-WAN typically encrypts its tunnels, and MPLS separates traffic on a private network without encrypting it. Local breakout adds exposure unless branch security is built in. Both need firewalls and sound policy.

Can SD-WAN guarantee voice quality over broadband?

No one can guarantee quality over a best-effort path. SD-WAN improves the odds by steering traffic and protecting packets, but a fault affecting every path will still hurt. Use a circuit with service commitments for the sites where voice is critical.

Is SD-WAN cheaper?

It often lowers circuit cost, since internet access is generally less expensive than private circuits. Add hardware, licences, security and migration costs before you decide, and compare options at the same service quality.