What to do if the NAT/ VPN Performance is lower than expected?

If the router's NAT speed test result is not as good as expected, we may take the following steps to troubleshoot.

1. Make sure the other device can get the expected speed through the same line.

If Vigor Router doesn't get the expected performance, please use a computer or another router to test the speed with the same line first.

2. Make sure the Physical Link Speed is correct

If the ISP provides a 300Mbps line but Vigor Router's WAN Port only links at 100Mbps physically, Vigor Router cannot get the 300Mbps throughput. We may try the "port ?" or "port wanfc ?" CLI command to adjust the physical link settings or add another switch between Vigor Router's WAN and the ISP modem and see if Vigor router can get the expected performance after that.

For DSL WAN, we can know its physical Link Speed in the Online Status page or by the CLI command "vdsl status". If Vigor links at the lower speed than other router does, we may try other DSL modem codes or adjust the SNR margin and see if the sync speed could be increased. Click here for more details.

3. Disable QoS and Bandwidth Limit functions

QoS and Bandwidth Limit functions will restrict Vigor Router's performance. Please disable the settings before running a speed test.

4. Use iPerf3 to test the speed

We verify Vigor Router's NAT/ VPN performance before releasing each firmware version and iPerf3 is the tool we used for measuring the router's performance here. While meeting a performance slow problem with other applications, e.g. FTP, SMB, www.speedtest.net, please use iPerf3 to test the performance for comparison. The performance may be different while testing with a single session or with multiple sessions. The suggested session number is 5, and the command is iperf3 -c <server ip> -P 5.

5. Enable Hardware Acceleration for getting the maximum speed.

Enabling Hardware Acceleration will increase the performance also. However, when Hardware Acceleration is enabled, the accelerated traffic will by-pass some functions, such as Traffic Graph and WAN Budget.

6. Reduce the MTU when the performance problem occurs on a specific site.

When the performance problem occurs on a specific site, we may reduce the MTU value on the router or the PC for a try. The WAN MTU setting can be changed in WAN >>Internet Access >>Details page.

VPN has additional TCP/UDP headers so the MTU for VPN is smaller. Use the command "vpn mss ?" to view and modify the settings when necessary.