Question: Since the internet connection in our house does break down from time to time I set up a little experiment:

For the last two month, one of my machines is pinging google.com on an half-hourly basis. One measurement consists of 50 pings.

I now calculated the mean percentage of packets lost for each hour of the day:
![percent of lost packets](https://i.stack.imgur.com/uzAMk.png)

My questions:

1. Could this peak in the evening be caused by choosing google.com as the ping destination?
2. Would you recommend using an other destination and which?
3. Does this indicate that something is wrong with my connection?
4. What would be a better strategy to measure where exactly the problem in our internet connection is? Our ISP tells us it is working fine so I try to aggregate some proof...

Regards!

Edit: I forgot to mention that the machine is directly connected to the router (no WiFi). And the router is pinged as well, with no packet loss at all.

Answer: 
This more than likely is a result of congestion somewhere along the line. It could be your router but more likely an upstream provider.

You don't state how you're doing the 50 pings e.g. what time interval, are you waiting for one to fail/succeed before the next or firing 50 off all at once (flood pinging).

Such a loss during periods of high congestion is not unusual in my experience. It can be down to lower prioritisation for ICMP traffic but more likely is happening for the same percentage of all connections - it's just TCP will gracefully resend and reorder packets so you are less likely to notice.

To gain a better picture of the situation I would suggest you implement the following:

1. Increase the interval between your pings
2. Ping an IP address for google not the domain - google.com will return a number of A records and it may be you're using different end IPs (and hence routing differently) without knowing it
3. Record the mean time to respond; see if this correlates with loss - if it does so you see higher ping roundtrip times and higher loss then it indicates congestion. You could then investigate by storing traceroute logs instead and see if there is a likely bottleneck somewhere where you're seeing suddenly increased times
4. Try pinging more than google. When I've benchmarked network performance in the past I've done it using 4 or 5 good end-points (again with the IP address not the hostname) so you can rule out congestion or a specific problem within just google's network causing you to question your entire connection
This is typical of most residential ISP accounts. You're seeing a peak due to network congestion as people get home after work, then go on-line for the whole evening. This sort of evening peak is especially pronounced in high-tech communities with lots of on-line gamers (like where I live, here in Redmond, home of Microsoft.)