Ethereal-dev: Re: [ethereal-dev] Capturing on ppp0 when ppp0 is not yet up

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From: Guy Harris <guy@xxxxxxxxxx>
Date: Wed, 2 Feb 2000 15:27:02 -0800 (PST)
> It would be easier to capture on ppp0 if we could ask Ethereal to capture
> on ppp0 before ppp0 comes up.
> 
> Is this possible.

That's up to the operating system, not Ethereal.  Ethereal does report
only "up" interfaces in the combo box, but you're not restricted to
specifying interfaces that are in the combo box list.  The underlying OS
mechanism may not let you open those interfaces for capture, but there's
not much Ethereal can do about that.

> It would allow us to see the first few packets ...

...assuming the underlying OS sends them to the capture mechanism.  If
"the first few packets" are, say, LCP packets, you'd better be running
an OS that provides LCP packets to the packet-capture mechanism; note
that Linux and, I suspect, Windows 9x and Windows NT, are among the OSes
that do *NOT* do so.  FreeBSD appears to, from a quick look at its PPP
code, provide them to the packet-capture mechanism; others may do so as
well.