[WEB4LIB] DNS Resolution of Log Files with Numeric IP Addresses

[Darryl Friesen]

> I'm looking for a program that will take a Web log with numeric IP
> addresses, do a DNS lookup on them, and write the resolved address
> back to the log file.  I am interested in doing this so that there
> is a permanent record of the resolved address in a log file that
> can be analyzed at any future date without having to deal with the
> problem that IP addresses constantly change.  (I know that Web
> servers can do DNS resolution as they write logs; that feature has
> been turned off for performance reasons).

Eric has already recommended a good DNS resolver, so I won't bother.  I will
say that, depending on your network, your resolved web server log may not be
accurate. If your institution uses dynamic assignement of IP addresses and
hostnames, it's possible that the hostname you get when you look up the IP
address may not be the same as when the actual request was made.  For
example, my desktop machine has a static hostname (gollum.usask.ca) but a
dynamic IP address.  If I were to lookup the IP address from our log file
for a request made a week ago, it's very likely that the IP address will not
resolve to gollum.usask.ca, but some other machine in my department.

We got around this by having our Apache server to the DNS lookups for us
again (we too had it turned off), and haven't noticed that much of an impact
on performance.  It's important for us to know, at the time of the request,
what the hostname of the computer is.

This may not be a factor for you, but I thought I'd point it out.


- Darryl

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  Darryl Friesen, B.Sc., Programmer/Analyst    Darryl.Friesen at usask.ca
  Education & Research Technology Services,     http://gollum.usask.ca/
  Information Technology Services Division,
  University of Saskatchewan
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  "Go not to the Elves for counsel, for they will say both no and yes"