Wireguard's minimum MTU for IPv6-over-IPv4 tunnels
Recently while traveling, I went to activate my wireguard VPN connection, but it failed with the error RTNETLINK answers: No such device. That seemed a bit odd, since I could see that the wireguard device was indeed being created. After a bit of Google search, I came upon this blog post with a pointer to a mailing list discussion.
It turns out that IPv6 requires a minimum MTU of 1280, and when I checked the MTU of my wireguard link it was only 1200. Thankfully the host wifi network supported larger MTUs, and after a quick config edit I was back up and running once again.
I only ever use my IPv4 endpoints when traveling, since at home I run native IPv6 everywhere. However, this was the first time I’ve encountered an issue like this while using wireguard. Chalk it up to random things we learn throughout life.