How to Monitor SD-WAN

How to Monitor SD-WAN

There are several factors that should be considered when implementing an SD-WAN solution. One of them is network monitoring. In this post, we review some SD-WAN challenges and how network monitoring can help overcome them.

Path Remediation and Failover

One of the benefits of SD-WAN is path remediation and automatic failover. This feature is available when a router has multiple connections, such as MPLS, broadband, and/or LTE. In this scenario, traffic can be routed through different lines, increasing reliability and quality. For example, if a link is experiencing high latency or packet loss, the router may send the traffic through a different link. Some SD-WAN solutions even duplicate packets across two links, increasing the chances that traffic will reach the other end.

These traffic changes may have an immediate positive impact but could negatively affect the end-to-end performance. For example, the router may route traffic across a link with lower speed, slowing down the connection. In the case of packet duplication, the overall bandwidth available to users is reduced. As a result, applications may perform slower than before the corrective action which causes users to complain. Troubleshooting these sorts of issues is very difficult without the right information.

End-to-End Network Tests

End-to-end network tests provide useful data to troubleshoot situations like the one illustrated earlier. For the most important services and applications used at the remote branch, a network monitoring tool should collect the following metrics:

  • Latency and packet loss to the remote application server (ICMP or TCP-based ping)
  • Jitter for voice and video communications (UDP iperf)
  • Number of network hops and path changes (traceroute/tracepath)
  • Throughput to other WAN sites and to the Internet (iperf, NDT and speedtest)

SD-WAN solutions may report some of these metrics, but they’re either passive or only take into consideration a limited portion of the network. This typically is the last mile where the SD-WAN appliances operate. 

A network monitoring tool for SD-WAN takes into account the whole end-to-end experience, from the user layer to the far end destination. Such a monitoring solution, relies on active network monitoring agents that are installed at the edge, either as a physical or a virtual appliance. The end-to-end network tests are run continuously, and results are retrieved in real-time and stored for historical review. 

End-User Experience Monitoring

Monitoring the end-user experience is another key element of an SD-WAN monitoring solution. There are many ways to capture the end-user experience, and a variety of tools in the market that aim to do so. Typically, end-user experience monitoring includes application-layer statistics and metrics such as:

  • DNS resolution time
  • HTTP loading time
  • Mean Opinion Score (MOS) for VoIP
  • WiFi performance metrics

When performance data generated by an active monitoring agent is paired to a passive data captured by an SD-WAN appliance, it results in a clear picture of network performance. The active data is useful to gather proactive alerts and troubleshoot in real-time performance issues. The passive data is used to give a clear understanding of how the bandwidth is consumed by users (“top talkers”) and applications (“top applications”) and update the network configuration if needed. The combination of the two technologies translates into reduced Time-To-Resolution of network and application issues, increased performance, and higher user satisfaction.