[strongSwan] Troubleshooting VPN performance

[Zach Cutlip]

Hello,

I'm using StrongSwan in a road warrior configuration that allows me to
VPN all my smartphone and laptop traffic through my home internet
connection. When I'm away from home, my devices automatically connect
from my MacBook and iPhone.

This works really well, with speeds generally approaching my home
internet service's upstream limit of 10Mbps, which is the bottleneck.

The only exception is when I'm on the commuter bus to and from work
using the bus's WiFi. The on-bus WiFi's speed without the VPN
connected is generally around 15-30 Mbps, as tested by fast.com (over
HTTPS, so caching shouldn't be an issue) as well as ssh/scp. However,
when I connect to the VPN while on the bus, the performance becomes
nearly unusable; less than 1Mbps, sometimes around a few hundred Kbps.

In case it matters, I'm guessing the bus uses some sort of cellular
backhaul. The public IP address block belongs to Clearwire, which I
think is owned by Sprint.

I'm not sure how I would begin troubleshooting this:
- Is there any particular way should I configure logging on either the
server or the client?
- Are there any particular things I should look for in the longs?
- Is there anything I should look for in packet captures either on the
client or the server?
- Any other things I should look for?

Thanks,
Zach