Ethereal-users: Re: [Ethereal-users] Not seeing RTP or RTCP traffic on Win2K

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From: Guy Harris <guy@xxxxxxxxxx>
Date: Thu, 31 Jan 2002 18:29:10 -0800 (PST)
> For some reason I don't see any RTP and RTCP protocol traffic (even labeled
> as UDP). I set up an RTP session on a local machine (both ends on the same
> machine as ethereal) and I don't seem to capture the messages I'm looking
> for.

If the packets show up, but are just shown as UDP, then the response you
got was correct.

However, if "even labeled as UDP" means you're not seeing the packets at
all, then it probably means that you're not capturing on the loopback
device - if both ends are on the same machine, the packets will probably
go over an internal loopback interface rather than over an Ethernet or
other "real" interface.  (Yes, even if you're not using 127.0.0.1 as the
source or destination address.)

On some OSes, such as the BSDs, Linux, and Digital UNIX, you can capture
on the loopback interface, which would be named "lo" or "lo0" or
something such as that.

On other OSes, such as Solaris and Windows, you can't capture on the
loopback interface, so you won't be able to capture traffic between two
processes on the same machine; such is life.