netdev - Re: [PATCH net-next 03/10] ovpn: set skb->ignore_df = 1 before sending IPv6 packets out

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Message-ID: <ab526609-ec26-4641-9245-7e806d68117e@openvpn.net>
Date: Tue, 13 May 2025 11:01:40 +0200
From: Antonio Quartulli <antonio@...nvpn.net>
To: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Sabrina Dubroca <sd@...asysnail.net>, Gert Doering <gert@...enie.muc.de>
Subject: Re: [PATCH net-next 03/10] ovpn: set skb->ignore_df = 1 before
 sending IPv6 packets out

On 13/05/2025 10:51, Paolo Abeni wrote:
> On 5/13/25 9:51 AM, Antonio Quartulli wrote:
>> On 13/05/2025 09:37, Paolo Abeni wrote:
>>> On 5/9/25 4:26 PM, Antonio Quartulli wrote:
>>>> IPv6 user packets (sent over the tunnel) may be larger than
>>>> the outgoing interface MTU after encapsulation.
>>>> When this happens ovpn should allow the kernel to fragment
>>>> them because they are "locally generated".
>>>>
>>>> To achieve the above, we must set skb->ignore_df = 1
>>>> so that ip6_fragment() can be made aware of this decision.
>>>
>>> Why the above applies only to IPv6? AFAICS the same could happen even
>>> for IPv4.
>>
>> For IPv4 we have the 'df=0' param that is passed to
>> udp_tunnel_xmit_skb(), which basically leads to the same result.
> 
> You need to include (an expanded/more describing version of) the above
> in the commit message.

Will do!
Thanks a lot.

Regards,

> 
> /P
> 

-- 
Antonio Quartulli
OpenVPN Inc.