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Re: Capturing packets when no IP address is assigned to the capturing interface

Jason Mitchell <> writes:

> On 6/7/21 8:06 AM, Greg Troxel wrote:
>> As mlelstv@ said, it's almost certainly about UP, not address.
>> So, after booting.
>> ifconfig foo0 up
>> tcpdump  -i foo0
>> and see how that goes.
> You're both absolutely correct. Thanks! That also solves the bridging
> problem for me as well.

That's good -- and note that it is not a bug that an interface that is
not UP doesn't do anything.

> But Staffan had an IP address configured prior to trying to set up
> bridging with the tap interface, so that doesn't explain why that
> (bridging multiple physical interfaces and a tap interface with an IP
> address on the tap) didn't work for him.

It is very likely that there is a bug lurking in the parts of NetBSD
that Staffan is using.

> I read that some (most)
> wireless interfaces don't support bridging. I wonder if that's the
> problem in his case. Here are the two links about wireless not
> supporting bridging:

There is no fundamental reason why bridging should work or not work
depending on the link-layer technology of an Ethernet-like interface.
There is some complexity about 802.11 interfaces in other than BSS or
HOSTAP modes, probably.    But, Linux docs don't apply.

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