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Re: Broadcast traffic on vlans leaks into the parent interface on NetBSD-5.1

Brian Buhrow <> writes:

> [lots of details]

Everything you said sounds ok to me.

>       Fortunately, I believe there is an easy fix for this problem which
> preserves our ability to support the vlan extraction features of modern
> ethernet chips while preserving the historical behavior of the NetBSD
> stack.  If we move the code that sends the packet to the bpf engine to just
> above the code that implements the hardware decapsulation function in each
> driver, I believe historical functionality will be restored while enabling
> support for new capabilities in chips.

I don't follow this.  But if you have a patch, please post it.  What I
don't follow is that hardware vlan tagging support I think is about
returning the packet as it would appear on the vlan and having the vlan
tag in a control structure.  So a packet which has been handled that way
can't be sent to bpf_tap without reconstructing the on-the-wire

>       Greg, if youre stil reading, I believe you can test much of this
> theory by configuring a vlan on your vr(4) ethernet card, which doesn't
> have hardware vlan tag extraction, and you'll see tagged packets on the
> parent interface and untagged packets on the vlan interface when using bpf.

Yes, I did that.

> If you use bpf  on a vlan tag capable interface such as wm(4), you'll see
> untagged packets on both the parent and vlan interfaces associated with
> that card.

On netbsd-5/wm, I saw the packets on the parent, but not on the vlan.
So I think there is more to it.

>       If my tests prove this scenario is right and the change I propose
> fixes the behavior, is there any reason I shouldn't commit changes to
> implement it?

I think you should post it for review once you think it's ok.  This is
pretty tricky stuff and more eyes will perhaps avoid unintended

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