Getting HTTP response with date before request date. Is that right?

Question

Say I sent a HTTP request at Thu, 22 Jun 2017 10:30:30 GMT.

Is it right if I got Thu, 22 Jun 2017 10:30:25 GMT in response Date header?

Which could be the cause?

Answer 1

Many servers and clients do not use NTP to synchronize their time to standard time. The response header should contain a timestamp from the server.

Time differences of seconds are common, and it is not unusual to have larger time differences. There are sites like time.is that will tell you how far the time on your computer is from standard time.

If you have access to the server, the command ntpq -nc peers will show how far the server is from standard time. This only works it the server is running an ntp server. Windows servers have slightly different commands.

If the response was served by a cache server, the date header could be from the original response. However, for such a small differences I would expect the above explanation to apply.