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Message-ID: <41113316.1010203@f5.com>
From: j.hall at f5.com (John Hall)
Subject: FW: Question for DNS pros
Mark wrote:
> ...
> Yup, the TCP SYN packets I see do the same with the IPID.
> (Embarrassed I missed that the first time I looked at them.) ;)
> ...
> I disagree, if it is a DNS *server* I would think it wouldn't respond
> with a RST. It would respond with a SERV FAIL because it's not
> authoritative for that domain.
Just about any response is useful for RTT/reachability measurement as long
as we can associate it back to the correct probe.
> Agreed Frank, why would they bother asking in the first place? How do
> you even know you are asking a DNS server? It could just be a
> mis-configured client. It would seem to me that would only provide
> you with the quickest way to query what may or may not be a DNS server
> that may or may not be authoritative for a domain.
Generally, 3-DNS queries only come from caching/forwarding DNS servers at
the client's site, so assuming we're talking to a DNS server there is
often a correct assumption. There are several probes that only require
a TCP/IP compliant box to respond.
> Although I think we may have resolved the issue of what is causing
> those strange packets... I would like to see a whitepaper or
> something describing how this technique improves the performance of,
> well; anything.
While there's a lot of complexity to global load balancing and each probe
method may be rendered useless in some circumstances, we've spent a lot
of time analyzing the metrics collected and load balancing decisions made
by 3-DNS groups at many of our customers sites; and we've found that the
3-DNS has improved the reliability and responsiveness of every site for
the great majority of it's customers. I'm not a marketeer, but you can
probably tell that I'm proud of our products. ;)
> The above paragraph is off topic. E-Mail me off list if you want to
> discuss that topic further.
>
> Regards,
> Mark
--
John Hall Test Manager - Switch Team F5 Networks, Inc.
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