Technical Tip: How to test 10Gbps link speed performance on a FortiGate

[wcruvinel]

Description	This article offers insights into the complexities of testing 10G links and provides recommendations for accurate performance assessments. When testing the performance of a 10Gbps link, it is important to understand the complexity involved. It is recommended to read 'Technical Tip: Low Throughput Troubleshooting' first, as it is an essential first step for delving deeper into performance testing of links.
Scope	FortiGate.
Solution	When testing a 10Gbps link, keep the following in mind: Testing Tools vs. Everyday Use: Tools like iPerf can measure maximum link speed, but in everyday tasks such as file downloads and uploads, reaching the full 10Gbps speed is uncommon. To accurately assess maximum capacity, dedicated tools like iPerf should be used to generate the highest possible traffic and validate performance. The distance between source and destination: Latency (RTT) is the most important factor in estimating the maximum possible throughput of a TCP session and can also indicate the approximate geographical distance between two endpoints. In the real world, latency typically ranges from 7 to 10 ms per 1,000 km.; based on that, if a consistent latency of 100 ms is in place, it suggests a distance of approximately 10,000 km (or more) between endpoints. In such cases, the higher latency is a result of physical distance rather than a network issue. With latency (RTT) measured, the theoretical maximum speed can be determined using the following formula: Throughput = TCP Window Size/Latency. Check for Limitations: All components, including computers, cables, and network devices, must support 10G speeds. A single weak link can slow down the entire network. Understand Hardware Limits:  Even if equipment supports 10Gbps, it may struggle to maintain full speed under heavy loads when multiple protocols are running simultaneously in production, where is consuming significant system resources like CPU and memory. As a result, maintaining a constant 10Gbps speed may not always be possible, and it is recommended to keep monitoring resource availability before, during, and after speed tests to help ensure optimal performance. For a formal reference on this topic, consider reviewing RFC 793, which defines the Transmission Control Protocol (TCP). For a deeper dive into TCP performance and its relationship with window size and RTT, 'Computer Networks' by Andrew S. Tanenbaum is an excellent resource. Below are examples of how latency can interfere with the final capacity of a 10Gbps link. Example 1: Performance of a 10 Gbps Link with High Latency. Given: Link Capacity: 10 Gbps. TCP Window Size: Let's assume $65,535$ bytes (or 524,280 bits since there are 8 bits in a byte). Round Trip Time (Latency): 100 ms (or 0.1 seconds). Using the formula: Example 2: Performance of a 10 Gbps Link with Low Latency. Given: Link Capacity: 10 Gbps. TCP Window Size: Let's assume $65,535$ bytes (or 524,280 bits since there are 8 bits in a byte). Round Trip Time (Latency): 1 ms (or 0.001 seconds). Using the formula: Conclusion: Even with a 10Gbps connection, several factors can limit its full capacity, with latency being a key influence. Longer distances can significantly reduce speed, while shorter distances allow for performance closer to 10 Gbps. Since multiple factors impact internet speed, analyzing and testing these variables is essential for optimizing performance. Related articles: Technical Tip: Low throughput troubleshooting Troubleshooting Tip: Drops and slowness occurs when traffic sent from 10G to 1G link in np6 models w... Troubleshooting Tip: How to troubleshoot speed or bandwidth related issues over Site-to-Site IPsec t... Troubleshooting Tip: Error 'SSL-VPN slow file transfer issue' Technical Tip: Identifying a packet loss condition due to high CPU: NP7 versus NP6 Troubleshooting Tip: Cannot access network due to FortiGate traffic shaping anomaly Technical Tip: How to verify bandwidth passing through a FortiGate remotely Troubleshooting Tip: Known Issue – Decreased Throughput when traffic passes through the FortiGate-20... Technical Tip: TCP and ESP packets out of order Technical Tip: Understand the performance's differences on IPSec VPN and MPLS/P2P connection