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My IIS 6.0 webserver is logging many thousands of entries that contain "UNKNOWN" in the the IP address field, that is the; Client IP Address (c-ip) option in IIS logging properties.

I would say that its only affecting 5% of the log, but I would like to find out how a request can end up with no IP address, or at least cause IIS to log the "unknown" value.

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Do you have a proxy/load-balancer in front of your server - or are you using FastCGI? –  pauska Nov 28 '11 at 10:49
    
the server did previously use a custom written Isapi filter used in conjunction with an implementation of Pound reverse proxy, but this is no longer activated, the traffic come straight from the firewall to the webserver and back out again. –  Mark Nov 28 '11 at 12:49
    
oh and no we are not using FastCGI, thanks. –  Mark Nov 28 '11 at 12:58

1 Answer 1

I strongly suspect IIS isn't logging the unknown value, but that a filter is.

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