Re: vlan and bpf

[Greg Troxel <gdt%lexort.com@localhost>]

Robert Elz <kre%munnari.OZ.AU@localhost> writes:

>     Date:        Fri, 15 Dec 2023 12:11:17 -0500
>     From:        Greg Troxel <gdt%lexort.com@localhost>
>     Message-ID:  <rmiv88zmlvu.fsf%s1.lexort.com@localhost>
>
>   | This patch has not even been compiled, [...]

It compiled, the system runs, and dhcpd is no longer seeing requests
from the vlan as if they are on the parent.  tcpdump does not see the
vlan requests on the parent.  (It does see the replies, because I did't
adjust the output path.)

> Something like that ought to be optional (don't much care which way
> the default is set, nor whether some application ioctl, or a system
> sysctl, or both, gets to control it) but there are times when monitoring
> the parent interface and seeing all the vlan traffic on it is useful.

I agree in principle but I don't think the current behavior does what
you want.

How to you believe the vlan traffic should appear, in terms of bits in a
bpf frame?

Do you need to know, for each packet, if it was a non-vlan (untagged)
packet, vs a tagged packet?  If so, do you need to know what the tag
value was?