Wake Up Your Redundant WAN Link

Many enterprises I speak with are looking to leverage low-cost, Internet lines for backup or even to offload traffic from more expensive MPLS connections. The Hybrid WAN, as this approach is called, is too complex to be built with conventional routing. Here are the three steps you can follow to build a Hybrid WAN in minutes with Silver Peak Dynamic Path Control.

Taking advantage of redundant WAN links has been a challenge with conventional routing. For those who have tried to do this in the past, you know the routing policies can be difficult to configure and manage. Routing doesn’t distinguish between traffic types so IT cannot match the application requirements to the line characteristics. Without a lot of manual intervention or advanced routing setup, a redundant WAN link just sits idle in many environments.

A key component of Software Defined Wide Area Networks (SD-WAN), such as Silver Peak Unity, addresses the Hybrid WAN problem. Path control, or in the case of Silver Peak Dynamic Path Control, intelligently routes traffic based on application requirements and path conditions. Silver Peak Dynamic Path Control, for example, makes packet-by-packet decisions based on the availability, latency, packet loss, and bandwidth of the path.

Identify Your Application Requirements

Having the ability to easily mix-and-match different types of infrastructure forces you to better understand application requirements. Every organization has its own application availability requirements depending on the relative criticality of the application to the business. Every application also has its own performance needs; some applications can tolerate higher amounts of loss while others need lower latency. You need to identify these availability requirements and performance characteristics, and then map those requirements onto the underlying WAN infrastructure at the location. (Gartner research director Andrew Lerner wrote an excellent report, “Bandwidth Doesn’t Matter; Availability Drives Enterprise Network Costs”, on this point detailing a methodology.)

For our purposes, we’ll assume a few simple rules:

1. Real-time traffic such as voice, video and VDI should always use the link with the least amount of packet loss to provide a higher quality experience to users.

2. Storage replication should use the link with the lowest amount of latency to ensure consistent replication performance.

3. Load balance all other WAN traffic across available links.

Our sample implementation is also straightforward, but the same principles apply regardless of the number of locations. We have a remote location connected to a data center via MPLS and the Internet. Each connection will have different characteristics, but in this case we focus on packet loss (see Figure 1).

Figure 1: Sample network configuration
Fig. 1: Sample network configuration (click to enlarge)

The Steps

Before we configure Dynamic Path Control on the Silver Peak, there are a couple of things we need to do.

1. Configure the Silver Peak tunnels. In this case there are two tunnels between the two sites: MPLS and Internet VPN.

2. Depending on how the Silver Peak is configured and connected into the environment each of the tunnels will need to be routed down the correct link, this is typically achieved through a static route on your core switch or router. We will not cover that in this article.

Step 1: Configure Interfaces & Tunnels

For a two WAN link scenario with an MPLS link and an Internet link we will first need to configure our tunnels on the Silver Peak appliances. Each of the tunnels will source from a unique IP address on the Silver Peak so that we can route them down the appropriate link.

Configuring tunnels
Fig. 2: Configuring tunnels (click to enlarge)

We also have enabled our Forward Error Correction (FEC) feature on both tunnels to correct for packet loss whenever packets are lost in transmit. You can think of FEC like RAID 5 for packets. If a packet is lost on transmission, Silver Peak will simply rebuild the lost packet from parity. FEC can provide a cleaner, lower packet loss path across any type of WAN link.

Enable Forward Error Correction
Fig. 3: Enable Forward Error Correction (click to enlarge)

Step 2: Configure Dynamic Path Control to Route the Packets

Now that we have two tunnels, one going across our MPLS link and the other going across our Internet link we need to configure Dynamic Path Control to direct the traffic down the appropriate links based on the metrics we mentioned above:

1. Send all real-time traffic down the link with the least amount of packet loss

For real-time traffic we will configure a policy and select the Real-Time classified applications groups under the Application section, for the path we select low-loss.

Configure real-time traffic
Fig. 4: Configure real-time traffic (click to enlarge)

2. Send all storage replication traffic down the link with the lowest latency

To configure storage replication to use the low latency link we simply select the Replication classified applications and set them to use the low latency link under path.

Configure storage replication traffic
Fig. 5: Configure storage replication traffic (click to enlarge)

3. Load balance all other WAN traffic across available links.

To load balance the rest of the traffic in the environment we can simply change the default application group which will cover everything not classified under the real-time and replication groups. For the default group we will simply tell it to load balance the traffic across both the Internet and MPLS WAN links.

Load balance all other WAN traffic
Fig. 7: Load balance all other WAN traffic (click to enlarge)

Step 3: Repeat at your remote site and you’re done!

The end result of these changes will allow your Real-Time Traffic to always use the link with the lowest loss, replication traffic to always use the link with the lowest latency and all other traffic to load balance across both connections. (Figure 8)

Figure 8: Sample network configuration enabling a Hybrid WAN Design
Figure 8: Sample network configuration enabling a Hybrid WAN Design (click to enlarge)

As you can see configuring the Silver Peak to perform advanced routing decisions across two or more WAN links for your traffic based off of quality metrics and the ability to load balance across multiple WAN link types is a simple, click through process. Dynamic Path Control provides the ability to bring your redundant lines to life, providing more bandwidth and better reliability for your critical applications.