netdev - Re: [PATCH net] ip_tunnel: allow to inherit from VLAN encapsulated IP frames

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Date:   Sat, 9 Jul 2022 22:09:12 +0200
From:   Matthias May <matthias.may@...termo.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <yoshfuji@...ux-ipv6.org>, <dsahern@...nel.org>,
        <edumazet@...gle.com>, <pabeni@...hat.com>
Subject: Re: [PATCH net] ip_tunnel: allow to inherit from VLAN encapsulated IP
 frames


On 08/07/2022 02:01, Jakub Kicinski wrote:
> On Thu, 7 Jul 2022 15:59:10 +0200 Matthias May wrote:
>> Has setting the TOS for ip6gretap ever worked?
> 
> Not sure, looks like the code is there, but I haven't used it myself.
> I presume "0xa0" is not trying to set the ECN bits? I never remember
> which end has the ECN bits, those may well get nuked on the way.
> 
The ECN bits are the lowest 2 bits.
The DSCP value has to be a multiple of 4.

>> How should i go forward with this?
> 
> I think your example above shows that "tos 0xa0" does not work but the
> conversation was about inheritance, does "tos inherit" not work either?

Yes inherit does not work either. This is why i started setting it statically.
However I think I figured out what is going on.
Setting the TOS statically to 0xa0 does work... when the payload is IPv4 or IPv6,
which is also when inheriting works. For everything other type of payload, it is always 0x00.
This is different than with an IPv4 tunnel.
Should i consider this a bug that needs to be fixed, or is that the intended behaviour?

BR
Matthias

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