General • OVPN bottleneck issue

I'm trying to figure out why L2TP or OVPN connections are slow for TCP when device CPU is not overloaded. I setup a test using UDP OVPN between two routers. The routers are directly connected via 1Gb ethernet port. I setup the OVPN client to use null auth and null cipher.

Client Router - CCR2004 (ROS 7.16.2)
Server Router - CCR2116 (ROS 7.16.1)

When I run a bandwidth test between them (both directions) from Client router, I get:
TX/RX Total Average: 396.5 Mbps/62.8 Mbps


Client router CPU during test:
# CPU LOAD IRQ DISK
0 cpu0 31% 11% 0%
1 cpu1 47% 19% 0%
2 cpu2 45% 30% 0%
3 cpu3 44% 13% 0%


Server router CPU during test:
# CPU LOAD IRQ DISK
0 cpu0 3% 0% 0%
1 cpu1 1% 0% 0%
2 cpu2 3% 0% 0%
3 cpu3 6% 0% 0%
4 cpu4 0% 0% 0%
5 cpu5 8% 0% 0%
6 cpu6 33% 21% 0%
7 cpu7 7% 0% 0%
8 cpu8 5% 0% 0%
9 cpu9 2% 0% 0%
10 cpu10 6% 0% 0%
11 cpu11 1% 0% 0%
12 cpu12 3% 0% 0%
13 cpu13 4% 0% 0%
14 cpu14 56% 31% 0%
15 cpu15 0% 0% 0%

What is the bottleneck causing these devices with ~50% free CPU to not handle more traffic? I have tried:
- Added a change MSS rule applied to the TCP traffic to set MSS at 1400 or 1360.
- Tried connection count of 20, 40 and 80. No significant difference between these

Statistics: Posted by pkelly1603 — Tue Jan 07, 2025 10:50 pm

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