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OpenVPN / ovpn-dco

OpenVPN Data Channel Offload in the linux kernel
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DCO and ipv6 #55

Closed atoy40 closed 9 months ago

atoy40 commented 9 months ago

Hello,

I tested to connect to my server through his ipv6 public address. The connexion has established without any issue, but the performance looks really bad ! It drop from 80mb/s to less than a mb/s in a simple speed test. Simple question, is DCO limited to the ipv4 socket ?

One more information, my server is configured with "proto udp6", has both an ipv4 and an ipv6 and is fast when i'm connecting to the v4 address, slow on the v6.

Thanks Anthony.

ordex commented 9 months ago

Hi @atoy40 and thanks for the report. There is no limitation on IPv6 therefore no drop is really expected. Have you checked whether you have some MTU issue which is causing packets to be dropped due to their size?

atoy40 commented 9 months ago

It seems than setting tun-mtu to 1420 on both side fix the problem, I can see max packet size of 1444 on the physical link of the server (probably ipv4 encapsulated packets). One more question, is fragment and mssfix options respected when DCO is in use ?

Anthony.

cron2 commented 9 months ago

DCO is incompatible with fragment - so when that option is used, OpenVPN disables use of DCO.

mssfix is communicated to kernel, but as far as I know, Linux kernel side is not handling it yet ("to be implemented later, there might be an existing function to do this, ..."). So with Linux DCO it's a no-op today.

ordex commented 9 months ago

closing this issue as no direct problem with IPv6 exists.