WireGuard MTU/MSS Performance Question | pfSense Router

Without doing anything, my WireGuard performance on my pfSense router started to degrade significantly. Basically, my Internet was not working as my download speed was in the kbps range while my upload was perfectly fine at over 100Mbps.

After some troubleshooting, I found that setting my MSS lower than my previous settings brought me back to the old speeds. To learn from this unfortunate event, how and why did this happen?

My old MTU and MSS settings were 1420.
My new MTU and MSS settings are 1420 and 1280.

Are there better settings?

If you could clarify MTU and MSS in relation to WireGuard, that would also help me a lot too.

Help greatly appreciated!

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1420 is correct for Wireguard and what you should set the interface to. Christian McDonald covers that in this video at the 23:00 mark:

I know the video and Christian’s YouTube channel. Can you elaborate on the MSS please?

I don’t have a video on it, but Cloudflare has a nice write up in their learning center:

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