[Bug 292760] [bridge] MTU of bridge inteface limits MTU of bridge-based vlans in despite of vlanmtu flag

From: <bugzilla-noreply_at_freebsd.org>
Date: Tue, 27 Jan 2026 17:52:11 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=292760

Marek Zarychta <zarychtam@plan-b.pwste.edu.pl> changed:

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--- Comment #1 from Marek Zarychta <zarychtam@plan-b.pwste.edu.pl> ---
(In reply to vova from comment #0)   
That's not a bug but a feature. An 802.1Q frame is 4 bytes longer by design, so
please use MTU 1504 for your bridge and its members if MTU 1500 on the children
is required.

> while on normal interface, it works differently:
This part is done in hardware, and the device driver should take care of
keeping the MTUs between the parent and child interfaces consistent.
Unfortunately, it sometimes doesn't work either; please see bug 260260.

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