Re: Capturing external packets sent to loopback (FreeBSD) ?

[Guy Harris via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

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> From: Guy Harris <gharris () sonic net>
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> Date: Mon, 24 Feb 2020 09:54:31 -0800
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> On Feb 24, 2020, at 6:15 AM, Ray Bellis via tcpdump-workers <tcpdump-workers () lists tcpdump org> wrote:
>
> > I've got a daemon that listens on a virtual IP address, that is itself
> > attached to a cloned loopback interface on FreeBSD.
>
> What do you mean by "loopback" here?  The term "loopback interface" generally means "fake interface that sends packets 
> from the machine to itself" on UN*Xes, e.g. the lo0 interface on most UN*Xes or just lo on Linux.  Is that the type of 
> interface on which you're capturing?
>
> If so...
>
> > Packets for that daemon could be arriving from multiple physical
> > interfaces, and that's what's taxing me just now.
> >
> > I would -really- like to be able to process those packets without
> > needing a per-interface thread or process (or other code changes) but it
> > seems FreeBSD (and Linux FWIW) will only capture packets on that
> > loopback IP that also -originated- on the loopback.
>
> ...why would packets be delivered on the loopback interface if they arrived on a physical interface?
>
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