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Date: Wed, 12 Jul 2023 17:24:14 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: "Zekri, Ishay" <Ishay.Zekri@dell.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>, "edumazet@google.com"
 <edumazet@google.com>, "Panina, Alexandra" <Alexandra.Panina@dell.com>,
 "Barcinski, Bartosz" <Bartosz.Barcinski@dell.com>
Subject: Re: MCVLAN device do not honor smaller mtu than physical device
Message-ID: <20230712172414.54ef3ca8@kernel.org>
In-Reply-To: <BN0PR19MB5310720D5344A0EBDFC66D9D9F36A@BN0PR19MB5310.namprd19.prod.outlook.com>
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On Wed, 12 Jul 2023 09:06:20 +0000 Zekri, Ishay wrote:
> Hi,
> 
> We experiencing an issue in which MACVLAN MTU does not limit the frame size,
> i.e. the limitation is coming from the physical device MTU.
> Kernel version: 5.3.18
> 
> As described in the case below:
> https://unix.stackexchange.com/questions/708638/macvlan-device-do-not-honor-smaller-mtu-than-physical-device 
> 
> it seems like this issue might have a fix.
> 
> If there was a known kernel issue that was fixed, I really apricate if you can provide to me the commit in which it was fixed.

In the post above you seem to be pinging the local IP address.

129: K9AT9i1G2x@eth6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether ba:c7:36:3f:9a:76 brd ff:ff:ff:ff:ff:ff
    inet 192.168.15.40/21 scope global K9AT9i1G2x
         ^^^^^^^^^^^^^
 # ping -c 3 -M do -s 8972 192.168.15.40
                           ^^^^^^^^^^^^^

Local traffic gets routed thru the loopback interface which has 
the default MTU of 64k. Did you try to ping something outside
of the host?