Troubleshooting Slow Speed Tests with DPI-SSL on SonicWall NSA 4700

Experiencing drastically reduced speeds during speed tests when DPI-SSL is enabled on your SonicWall NSA 4700? You're not alone. Many users have reported similar issues, where download and upload speeds plummet significantly when DPI-SSL is active. This article explores potential causes and solutions based on community discussions and expert recommendations.

The Problem: DPI-SSL Impacting Speed Test Performance

Users of the SonicWall NSA 4700 firewall have reported a peculiar problem: While using a SonicWall firewall, with DPI-SSL enabled, their internet speed tests show a significant drop in performance. Initially, speeds may appear normal (e.g., 999 Mbps), but quickly degrade to much lower values (e.g., 80-90 Mbps). Disabling DPI-SSL resolves the speed issue, suggesting a direct correlation.

Understanding DPI-SSL and Its Potential Bottlenecks

DPI-SSL (Deep Packet Inspection over SSL) is a crucial security feature that decrypts and inspects SSL/TLS encrypted traffic for threats. While essential for security, this process is resource-intensive and can introduce performance bottlenecks if not properly configured.

Potential Causes and Solutions

Here's a breakdown of potential causes and troubleshooting steps, drawing from community experiences:

• TCP Stream Reassembly:
  • The Issue: Gateway AV with TCP Stream reassembly enabled can severely impact speed test results.
  • The Solution: Ensure that "TCP Stream" is disabled in your Gateway AV settings.
• Firmware Issues:
  • The Issue: Specific firmware versions can introduce DPI-SSL performance regressions. For example, version 7.1.2 appears to have caused problems for some users.
  • The Solution:
    • Downgrade Firmware: Downgrading to a previous, more stable firmware version may resolve the issue. One user reported success downgrading to SonicOS 7.1.2-7019-R3835-HF50694.
    • Hotfixes: Contact SonicWall support for potential hotfixes addressing DPI-SSL performance issues.
    • Monitor Firmware Updates: Stay informed about future firmware releases that address known DPI-SSL bugs.
    • Caution: Before downgrading, be aware that some users reported issues with adding URLs to URI lists, potentially causing a failover. Test changes in a maintenance window.
• Resource Constraints:
  • The Issue: The SonicWall NSA 4700 may be under-resourced to handle the load of DPI-SSL, especially with high traffic volumes.
  • The Solution:
    • Monitor CPU and Memory Usage: Check the firewall's CPU and memory usage when DPI-SSL is enabled. High utilization suggests resource constraints.
    • Optimize DPI-SSL Policies: Fine-tune DPI-SSL policies to exclude trusted traffic or less critical applications from inspection.
• SonicWall Support Ticket:
  • The Issue: If the above steps don't resolve the problem, it could be a more complex, device-specific issue.
  • The Solution: Open a support ticket with SonicWall. Provide detailed information about the issue, the steps you've taken, and your network configuration.

Community Experiences and Insights

The SonicWall community is an excellent resource for troubleshooting. Users frequently share their experiences and solutions to common problems. In this case, multiple users experienced the same speed degradation with DPI-SSL enabled after upgrading to version 7.1.2. This shared experience highlights the potential for firmware-related issues.

Key Takeaways

• DPI-SSL can significantly impact speed test performance on SonicWall NSA 4700 firewalls.
• Firmware version is a critical factor; downgrading or applying hotfixes may resolve the issue.
• Optimize DPI-SSL policies and ensure TCP Stream reassembly is disabled.
• Monitor firewall resource utilization.
• Don't hesitate to open a support ticket with SonicWall for further assistance.

By systematically troubleshooting these potential causes, you can effectively address slow speed test issues related to DPI-SSL on your SonicWall NSA 4700 and restore optimal network performance.