SD WAN vs MPLS: SD WAN to replace MPLS! (and other myths)

Posted by SAS on Jan 2, 2018 03:19:00 PM

There are lots of opinions about SD WAN.  Many concern SD WAN vs MPLS, and some may be driven more by vested interest than good sense.  We've been surprised by some of the views, so we thought we should try to set the record straight.   Here are six commonly heard myths about SD WAN vs MPLS, along with our view of the real situation.


The main differences between SDWAN and MPLS?

SD WAN stands for Software-defined Wide Area Network and MPLS stands for Multiprotocol label switching.  There are a number of core differences between them, such as:

  1. SD WAN is an overlay technology.
  2. MPLS is one of several options for the underlay and (along with VPLS, the internet, and other networks) might provide connectivity for an SD WAN network.
  3. SD WAN involves software-defined operation with real-time changes as conditions change, whereas MPLS typically involves static hardware routers.
  4. MPLS predominantly connects sites to a private WAN infrastructure, whereas SD WAN usually involves multiple connection circuits at each site, and leverages internet alongside other technologies.
  5. In many geographies (although notably not in the UK), MPLS has a history of being more expensive than internet connectivity, meaning that businesses have often been able to save money on international connectivity when they use SD WAN, since it facilitates the blending of internet with private networks.

Since SD WAN and MPLS aren’t the same thing it’s slightly illogical to say that one will replace the other.  SD WAN solutions may be the future but they still need an underlay!

So, if it's not the replacement, will SD WAN lead to the demise of MPLS?   We expect it will cause a decline, but not the demise; at least, not for a considerable time.  Let's examine the drivers that might cause SD WAN to impact MPLS.   

Why do people choose SD WAN over a traditional MPLS?

An SD WAN network can be less expensive than an MPLS network, particularly for large international networks.  SD WAN can make for a more flexible network and can facilitate the changes required to support migrating to Cloud. 

WAN cost and performance

One way in which SD WAN will impact MPLS is that it makes it easier to use alternatives to MPLS for your networking underlay.  A good example would be the internet.

Will we start moving our networking traffic from MPLS to the internet?   

That depends.  If it were to make sense to do that, the internet would need to be a better or cheaper networking technology; perhaps just good enough and cheaper.

So, is an SD WAN solution with internet circuits better, cheaper or both?   

That depends on your situation.

If you're running everything from the cloud you might not care very much about having MPLS performance. However, if you're running a real-time or latency-sensitive application over highly-utilised circuits, you might be concerned about packet loss and latency. You might, therefore, be concerned that the internet is not good enough.

Similarly, if you're an international business with hundreds of branch offices outside the UK then you would certainly find opportunities to save money by moving traffic from MPLS to locally sourced internet.  However, if many of your sites are in the UK then that benefit breaks down. MPLS circuits are not far more expensive than the internet in the UK. In some cases, we've seen them to be cheaper! 

Download our free guide for SD WAN to help guide you through the myths and jargon you may come across along your journey to implementing your own solution.

So, is there another way to save money on an MPLS network?

Hybrid networking

Actually, there is another way to save money compared to MPLS, and that is to use a hybrid network. People frequently define a hybrid network as the connection of a site to both MPLS and the internet (to save money), enabled by SD WAN.  We don't think that definition is great, on two counts. 

First, it excludes the many benefits (to cost, installation speed and performance) of blending multiple technologies from multiple carriers. We see a hybrid network as the fusion of multiple technologies (MPLS, VPLS, Internet and the many access technologies they employ) from multiple carriers. 

Second, it implies SD WAN is a required driver for hybrid networking. Most of our customers have run a hybrid network without an SD WAN service for many years.

So, if anything it's Hybrid networking that might cause the decline of MPLS.

An aside on internet performance

Let's go back to the point about internet performance for a minute. You can get similar latency out of a Dedicated Internet Access (DIA) circuit than you can out of MPLS. One major UK carrier has a latency SLA that is better for their DIA service than it is for their MPLS service before Class of Service prioritisation is applied.

Really?  How is that achieved?

To achieve this performance you need to stay on-net. If you use one carrier to connect several branch offices over the internet then the site to site traffic that stays on the carrier's network should enjoy sparkling performance. However, if you want to go outside of the carrier's DIA cloud then you'll lose that benefit: once on the open internet you're on a best-endeavours network that does not support end to end prioritisation. 

If the Internet is best-endeavours, why are people diverting traffic to it?

SaaS applications are encouraging a move to more internet-focussed networks

With cloud applications and platforms being accessed from the internet, companies are evaluating the best WAN architecture to reach these applications from remote sites. Traditionally, SaaS application traffic from branch office users has traversed the MPLS to the HQ and then broken out to the internet.  This adds another couple of legs of latency, which can limit performance and throughput,. Ultimately, it can limit cloud application performance.

SD WAN technology is application-aware. SD WAN devices are typically configured to recognise SaaS traffic and break out to the internet directly from the remote site. This trend acts to reduce traffic over the MPLS, hastening its decline.

The MPLS providers are fighting back by creating private connections with the associated Class of Service into the Cloud Provider’s networks, giving remote sites direct connectivity over the secure MPLS network. Private networks such as MPLS are always going to be slightly behind public networks such as Internet because it’s much easier for SaaS to be launched via the internet to all customers rather than to a subset with each carrier.

SD WAN will allow me to provision sites in an instant!

To consider this claim, we need to look at the connectivity. Once we see SD WAN as an overlay on top of underlying connectivity, it becomes clear that we cannot deploy an SD WAN site any faster than we can get connectivity to site.

How long for a new site?

For a brand new connection, Fibre Ethernet circuits take months to deliver, EFM circuits take several weeks and fixed broadband takes a couple of weeks. To get below that time you need to use 4G LTE circuits, which can have you connected within days if done well.  So, for a new site, it's clearly the provision of connectivity that defines the fastest you can connect. 

SD WAN can play a role in configuring the new site quickly onto the network, of course.  so it could help if you're in a terrible hurry and you opt for 4G rapid site deployment of a new site.   Incidentally, people new to 4G often don't appreciate how fast it can deliver and how many users it can support. We have had new sites connected within two days, and we've had it supporting up to 650 users.  

Like for like

Some SD WAN CPE providers claim that with SD WAN, their customer could provision a new site in minutes whereas with MPLS it would be months.  That's an unfair comparison because it compares an existing internet connection with a new MPLS connection!

In reality, if there was an existing internet connection then a simple IP Sec tunnel to a carrier’s secure VPN service would provide the solution as well: it doesn't need to be SD WAN.

However, this does highlight how SD WAN can bring great flexibility. If you have an existing internet circuit then you can connect it quickly with SD WAN, and you can adjust the balance of traffic quickly between MPLS and internet.  This can be particularly useful when moving apps to the cloud, which creates a shift in traffic.

SD WAN and Hybrid Networks are cheaper!

Sometimes! This is a common assertion whose accuracy depends upon what we're comparing. Traditionally, IP VPN was more expensive than Internet connections but nowadays we see carriers pricing them similarly in the UK. For example, in the UK a 50Mbps port on a 100Mbps Ethernet bearer can be the same whether it points to the internet or to the MPLS network.

There is still a difference internationally. International MPLS circuits can be a lot more expensive than a locally purchased internet circuit. However, MPLS brings the benefit of central procurement, billing and management.

Some people argue that (especially for Cloud applications), SD WAN could use multiple consumer-grade broadband circuits.  That may be cheaper than a traditional circuit, but you may also need a more expensive router to bond or load balance the multiple connections, which would reduce the cost-saving. 

It would also result in a consumer broadband service, which has lower availability and reliability and a longer time to fix.

Since the circuits are likely to share underlying infrastructure if one of them suffers a performance degradation then it's likely that they all will.

SD WAN will allow me to change my bandwidth and CoS settings in an instant!

Yes, possibly, but only if

  • This is a complete carrier SD WAN solution, rather than an CPE solution 
  • That particular provider has linked their front end quoting engine with their ordering process and their billing system.

With the move towards Cloud, agility has been one of the big pushes of SD WAN.  But in what circumstances would you want to do this and how much are you willing to pay for the premium? We have seen customers ask for this and then baulk at the price which some complete SD WAN providers are charging. We have also seen customers ask for this who rarely make changes on their network. We have seen some suppliers offer this but only where they are on-net. And this doesn’t apply to ADSL and SuperFast services where by default you already get the maximum speed that the circuit can deliver.

In the UK, Ethernet PoPs are ubiquitous and access circuits are either full 100Mbps or 1Gbps. However,  internationally, where the carriers have fewer PoPs, the access circuits tend to be long-line with bandwidth throttled to save costs.

Look very carefully at the quotes you receive from your MPLS provider for international networking connections - they will often show the access circuit from the 3rd party as a 20/100Mbps with a 20Mbps MPLS port.

To have the ability to flex this circuit up to a bandwidth of 50Mbps, the MPLS provider would need their 3rd party to provide a 50/100Mbps access circuit from day 1, so the customer will pay for the privilege to invoke the SD-WAN capabilities.

Another theme of SD WAN is that the customer can provide their own local internet service to reduce cost but that raises the question of how the central management platform will be able to effect a change to a third-party circuit? So here, DIY Hybrid Networks and the complete SD WAN solution are at odds.

What we have seen is that customers aren’t happy with waiting 4 weeks to get a change of CoS or a bandwidth increase but what would be an acceptable amount of time? 2-5 days from quote to change?

It may be some time before there is a choice of carriers that will offer an integrated solution but in the meantime, there are providers that can do the individual steps, although manually, much more quickly than some traditional carriers.

If complete agility in this area is what you desire then your choice of carrier may be limited and costs maybe be higher but if you’re looking for more agility, there are many more options in the market.

SD WANs are easier to manage!

True, but the extent depends on whether you bought a managed network or taken a DIY approach in the past.

If you want to go down the DIY networking route, then an SD WAN overlay and functionality will be of great benefit, although the cost savings will more likely be realised if you have international sites. But with DIY, the internal IT team bears a much higher level of management overhead. When you buy a Managed WAN you are given access to consultants, profession installation services, a 24/7 global support service and a single bill. If there is a problem with one of the sites, your Managed Service Provider (MSP) will see it first and already be calling the site contact to resolve the issue. See this post for more information about finding a suitable managed network provider, and this one for guidance on choosing by between DIY and Managed SD WAN.

When you deploy a new site, Zero Touch deployments and central management will be beneficial to the Service Provider rather than the customer.  The customer should receive a better service at a slightly reduced cost, of course.

Carriers have tended to want to supply everything within a managed service and in particular the connectivity. Managed Service Providers may offer flexible management allowing customers to deploy their own connectivity and therefore be their own resolver groups whilst the MSP still maintains the overall ownership of the fault tickets.

Some MSP’s, such as SAS, have been providing application visibility way beyond that which is included in an SD WAN CPE solution for many years so the argument that SD WAN will be easier to manage really depends on what version of a WAN you currently have. If you have a pure international MPLS network where you manage the edge routers yourself then an SD WAN CPE solution, coupled with hybrid networking will certainly bring a great deal of benefits; operationally, technically and commercially.

SD WAN and Hybrid Networking allows my users to get to Cloud Apps (such as Microsoft 365) more quickly and therefore have a better experience!

True, maybe! The rise in applications being located in the public cloud rather than in a data centre has shifted the emphasis on how best to connect to the applications. Ideally, you would take the shortest path to each Cloud application.  Traditional WAN architectures tended to have public internet breakout at the head office. However, for cloud applications, local internet breakout would seem an obvious choice (therefore Hybrid Networking) with SD WAN CPE providing the security, visibility and management.

However, many carriers are now linking their MPLS networks to the major IaaS/PaaS/SaaS providers to provide the Quality of Service and security that customers require for Cloud. We have also seen some SD WAN providers developing Optimised IP networks over the internet to these applications and platforms so there is a variety of choices to suit all businesses.