Ethereal-users: Re: [Ethereal-users] help:reduce the performance of application using ethereal

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From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Sun, 9 Nov 2003 15:09:15 -0800
On Sun, Nov 09, 2003 at 10:55:56PM +0800, Ching Tung Lo wrote:
> I want to use ethereal to collect UDP packets to measure the
> performance of DNS server. 
> But It seemed to lower the performance of DNS server when I used the
> command of "tethereal -l -V port 53" to collect UDP packets. 
> Do you think it is a good method to measure the performance of DNS
> using ethereal?

If you're doing it by running Ethereal - or Tethereal or tcpdump - on a
machine other than the DNS server, capturing shouldn't affect the
server's performance; however, that might be difficult to do if you're
on a switched network.

If you run it on the DNS server, you might have better performance if
you do

	tethereal -w capture_file.pcap port 53

and then analyze by reading "capture_file.pcap" later - that way, it
just has to write packets to a file, it doesn't have to analyze the
packets while it's capturing.

If you only want traffic to or from the DNS server, specifying

	tethereal -p -w capture_file.pcap port 53

might help (although if you're on a switched network you probably won't
see other machines' traffic anyway).