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3 Common Problems Affecting SD-WAN Networks

 3 Common Problems Affecting SD-WAN Networks

Businesses often use SD-WAN to improve Internet, cloud, and UC performance. However, just like any other network, SD-WAN may encounter issues that impact user experience. So It’s important to be aware of these potential issues.

In general, most issues with SD-WAN stem from network bandwidth congestion or excessive usage of network device resources, often seen on the Local Loop or the customer Edge Router.

Furthermore, many of the issues in an ISP's backbone that can lead to SD-WAN problems originate from congestion on its peering and transit connections with other networks or service providers. Although ISP backbones are typically more dependable and sturdy than other network structures, problems may still occur.

Where SD-WAN Problems Come From

Historically, the most vulnerable point in a network has always been the last mile. This is the final segment of the network, which typically has the lowest speeds, limited route diversity, and numerous single points of failure.

This is why most SD-WAN issues occur on the last mile of the network. To counteract this, most SD-WAN networks utilize multiple links to function.

The idea is that, if a problem arises, it should not affect all links simultaneously, and the SD-WAN Edge Router should be able to balance network sessions across the best available link. However, relying solely on link diversity is not sufficient to eliminate all potential issues in SD-WAN networks.

The diagram below shows an SD-WAN network site communicating with a Data Center, Head Office or IaaS.

Fig 1.1- SDWAN Design

In an SD-WAN networks, problems can come from:

A. The Underlay
B. The Overlay
C. The LAN

Detecting Problems Related to SD-WAN

Before discussing the three most prevalent SD-WAN issues, it's essential to understand that there are various network problems that can affect your SD-WAN network. These can include:

  • Faulty cables or connectors
  • Network bandwidth congestion
  • Incorrect device configurations
  • Device software problems
  • High device resource usage
  • Physical/hardware issues
  • Human errors
  • DNS problems

To effectively identify and resolve SD-WAN issues, you need an SD-WAN Monitoring Tool to give you comprehensive visibility of your network.

SD-WAN Monitoring is a feature of a Network Performance Monitoring tool. This tool continually monitors end-to-end SD-WAN network performance from all your network locations to identify and troubleshoot problems.

Now we’re going to present 3 common SD-WAN problems using screenshots and examples from an SD-WAN Monitoring Tool.

1. High CPU Usage

The first SD-WAN problem is high resource usage on SD-WAN devices, which impacts all network sessions. This often happens when a network device lacks sufficient resources to handle the traffic volume. Here’s what that can look like:

  • The first graph shows the Internet SD-WAN user experience
  • The 2 bottom graphs show the experience of the Internet connections (ISP1 & ISP 2)

Fig 1.2- High CPU 

In the Dashboard we can see that:

  • High packet loss is causing poor performance for all the traffic passing through the SD-WAN network.
  • ISP #1 and ISP #2 are both being affected.

For both ISP #1 and #2 to be affected, the network issue must be occurring on a segment shared by both ISPs.

When ISPs #1 and #2 are experiencing performance issues, the CPU usage is at 100%.

This is not an issue with the local loop and there is no need to contact the ISP. This is a local problem where an excessive amount of traffic is being sent to that port, potentially from a different source.

The problem could be within the LAN or on the SD-WAN Edge Router itself. Edge Routers are a common source of issues as they are often security devices with many features and software, which can be resource-intensive and impact CPU usage.

Some possible solutions can include:

  • Looking at the firewall logs to understand if your traffic is legitimate or not.
  • Managing priorities in your Firewall to prioritize certain traffic.
  • Upgrading to a bigger network device or updating the firmware.

2. High Bandwidth Usage

The second SD-WAN issue is on the the underlay of ISP #2 caused by high bandwidth usage.

Here’s what that can look like:

  • The first graph displays Internet SD-WAN user experience
  • The 2 bottom graphs display experience of the Internet connections (ISP1 & ISP2)

Fig 1.2- High Bandwidth

In the Dashboard we can see that:

  • ISP #1 is not experiencing any performance issues, and has minimal jitter. The latency is consistent and the packet loss is always below 2%.
  • On the other hand, ISP #2 is experiencing a clear performance problem due to high packet loss.

When ISP #2 is experiencing high packet loss, we can observe that the bandwidth utilization surpasses the available 500mb service. From here, we can deduce that the excessive bandwidth usage is causing the packet loss.

This is not a problem with the local loop, and it is not necessary to contact the ISP. This is a local issue where a significant amount of traffic is being directed to that port, possibly from a different source.

Some possible solutions can include:

  • Managing priorities in your Firewall to prioritize some traffic.
  • Changing the backup schedule.
  • Rate limiting the flow of traffic.
  • Upgrading your Internet connection bandwidth.

3. Local Loop Issue

The 3rd most common SD-WAN problem is ISP Local Loop issue located on the underlay.

Here’s what that can look like:

  • The first graph displays the Internet SD-WAN user experience
  • The 2 bottom graphs display the experience of the Internet connections (ISP1 & ISP 2)

Fig 1.3- Local Loop

In the Dashboard we can see that:

  • ISP #1 is not experiencing any performance issues. There is minimal jitter and no packet loss.
  • On the other hand, ISP #2 is showing a clear performance problem.

In this scenario, the SD-WAN problem is present on the Local Loop, between the ISP Edge and the SD-WAN Edge Equipment. In this case, the issue is linked to the ISP, and they are accountable for resolving the problem.

Some possible solutions can include:

  • Using Visual traceroute to gather information about the problem.
  • Opening a support ticket with your ISP using the screenshots of Dashboards and Traceroutes.

Solving SD-WAN Problems

Your SD-WAN network is bound to experience problems, just like any other network. You just need to be ready for when it does.

Whether the problem is related to high bandwidth usage or high CPU usage with your network equipment, or problems on the local loop, an SD-WAN Monitoring Tool will help you immediately detect the problems, and begin the SD-WAN troubleshooting process.