Right, a DNS manager could do a redirect, but that would not be visible in the web server log.  It would only be visible in whatever is managing the DNS.

The request headers will also show if any and what cookies the user may have set.  Which it looks like is how your server determines if it should provide the client the desktop or mobile version.

How detailed are your log files?  Can you see the user-agent (browser name) Maybe you could ask your IT department to log request headers?  If that will make the log files too big, they can probably do it only for the 'problem' IPs, or only for cases that the webserver returns a 301.  I'll take a look if you like.  Email is in my profile.

Best,

-Eric

The problem can't be related to DNS.  If the problem was related to DNS, the request would never make it to your server, and you would never see anything related to the request in your log files.

Because you can see it in your log file, it is definitely happening on your own webserver (not some external problem).

The requesting IP is probobly not the problem, but it could be if your server automatically adds to a banned list any IP that requests > X pages in Y time - your server might think this is a DOS (denial of service) attack.... But if your server was set up to do this, your IT guys would probobly know about it.  This isn't something that is normally enabled 'out of the box' someone would need to intentionally activate a behavior like that.

More likely, is that there is another common denominator besides the requester IP...  I would guess that it's the user agent string (the browser or device the user is using).

Taking a quick look at what I think is your site, you have a mobile version available.  Google of course would be interested in what your site looks like to a mobile browser, and would send a 'fake' user agent string pretending to be so (a cell phone or a tablet etc...)  If your server sees this request, and tries to automatically redirect the browser to the mobile version of the site, then you would have your 301 code (which in this case is exactly what you intended, so your all set!)

There are probably a few other cases that could cause a 301 for just some IPs, but this is the only one that comes to mind at the moment.

Good Luck!

The problem can't be related to DNS.  If the problem was related to DNS, the request would never make it to your server, and you would never see anything related to the request in your log files.

Because you can see it in your log file, it is definitely happening on your own webserver (not some external problem).

The requesting IP is probobly not the problem, but it could be if your server automatically adds to a banned list any IP that requests > X pages in Y time - your server might think this is a DOS (denial of service) attack.... But if your server was set up to do this, your IT guys would probobly know about it.  This isn't something that is normally enabled 'out of the box' someone would need to intentionally activate a behavior like that.

More likely, is that there is another common denominator besides the requester IP...  I would guess that it's the user agent string (the browser or device the user is using).

Taking a quick look at what I think is your site, you have a mobile version available.  Google of course would be interested in what your site looks like to a mobile browser, and would send a 'fake' user agent string pretending to be so (a cell phone or a tablet etc...)  If your server sees this request, and tries to automatically redirect the browser to the mobile version of the site, then you would have your 301 code (which in this case is exactly what you intended, so your all set!)

There are probably a few other cases that could cause a 301 for just some IPs, but this is the only one that comes to mind at the moment.

Good Luck!

How detailed are your log files?  Can you see the user-agent (browser name) Maybe you could ask your IT department to log request headers?  If that will make the log files too big, they can probably do it only for the 'problem' IPs, or only for cases that the webserver returns a 301.  I'll take a look if you like.  Email is in my profile.

Best,

-Eric

The request headers will also show if any and what cookies the user may have set.  Which it looks like is how your server determines if it should provide the client the desktop or mobile version.