ipv6 connexion fail - ipv4 OK

[Roman Mamedov]

On Thu, 26 Aug 2021 13:14:00 +0200
Daniel <tech at tootai.net> wrote:

> Correction
> 
> Le 25/08/2021 à 17:25, Daniel a écrit :
> > Hi list,
> > 
> > I setup wireguard on a server running Debian 11 and get it to work with 
> > 2 clients (Debian 11 and Ubuntu 20.04). Clients and server are on 
> > separate networks, one client behind a FW the other direct on Internet, 
> > no FW at all (VPS).
> > 
> > With this setup and ipv4 connection to the public IP of the server, 
> > everything is working as expected, ipv4 as well as ipv6 are passing 
> > smoothly.
> > 
> > Now I want to connect using the ipv6 address of the wg interface as both 
> > clients and server have ULA ipv6.
> 
> Here is GUA to read.
> 
> > This fail, wg show that connection is 
> > established but VPN is not usable. It's not a FW problem as I can ssh to 
> > the ipv6 address, as well as a netcat test from/to server IP -from each 
> > client- on an UDP port is working properly. Also, 
> > net.ipv6.conf.all.forwarding=1 is activated in sysctl.conf
> > 
> > All network stuff is done in /etc/network/interfaces which call the 
> > config file. The ipv6 address of the server is affected _to the 
> > wireguard interface_ (in ipv4 it's another interface who take care of 
> > the public address)
> > 
> > Server version is wireguard-tools v1.0.20210223.
> > 
> > If someone have any hint, thanks to share ;)
> 

IPv6 requires the in-WG MTU to be 20 bytes less than when running over IPv4.
Try reducing it accordingly.

-- 
With respect,
Roman