It appears the internet speed test that xfinity provides on their web site produces a vastly higher download speed that 3rd party tests. Is this a well known isuse? Doing tests side by side on the same machine, I get close to 600Mbps on xfinity and about half that externally.
That's because their speed testing servers lie on *their* network's edge, therefore they are not subject to any third party's potential backbone / routing / distance related latency issues etc.
Thanks. Makes sense. Would you expect such a dramatic difference. B2B I ran the test from xfinity and it tells me 589Mbps and through the test by this site ( speedtest.net) I get 247Mbps. The upload is virtually the same at 17Mbps.