netdev - Re: MCVLAN device do not honor smaller mtu than physical device

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20230712172414.54ef3ca8@kernel.org>
Date: Wed, 12 Jul 2023 17:24:14 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: "Zekri, Ishay" <Ishay.Zekri@...l.com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "edumazet@...gle.com"
 <edumazet@...gle.com>, "Panina, Alexandra" <Alexandra.Panina@...l.com>,
 "Barcinski, Bartosz" <Bartosz.Barcinski@...l.com>
Subject: Re: MCVLAN device do not honor smaller mtu than physical device

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@...6: <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?