Hi there, since OpenVPN 2.4 clients are trying to connect via IPv6 if AAAA record and IPv6 connectivity is available. With NetworkManager (networkmanager-openvpn 1.2.6-1) there's no fallback to IPv4. Therefore udp6 was enabled server-side.
OpenVPN Clients with native IPv4+IPv6 over PPPoE (German Telekom DSL) are
only functional via IPv4. MTU issues occur when connecting via IPv6. Large
packets don't arrive at the client. Clients without PPPoE and a MTU of 1500
are working fine when connecting via IPv4 or IPv6.
OpenVPN 2.3.4-5+deb8u1 is used server-side w/o special mtu settings.
mode server
tls-server
proto udp6
multihome
float
comp-lzo
My guess:
mssfix has a default value of 1450, which is to small nowadays:
1450 + 8 UDP header + 40 IPv6 header + 8 PPPoE header = 1506
What would be the best way to solve that issue?
- set mssfix to 1444 at client and server
- work with link-mtu/tun-mtu/tun-mtu-extra/fragment
Thanks for any hints!
Andreas
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