High packet loss rate (~20%)

Please start here if you wish;

https://forums.xfinity.com/conversations/your-home-network/connection-troubleshooting-tips/602da777c5375f08cdea3db9 

... Ping from my laptop to the very next hop of the wifi router (a comcast's gateway 24.xxx.xxx.xxx) => NG, 18~20% loss​​ ...

Are you connecting via Wifi or Ethernet? If Wifi, it's best to switch to an Ethernet cable connection if possible for testing.

Network connection problems like this are often due to poor coax connections or damaged coax cable, usually in or near your home. Running the cable through a surge protector, a defective splitter, or too many splitters can cause signal problems as well. If there is an amplifier in the line make sure it's getting power. 

If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips. If you still need help, please post your Internet plan speed and the following information from your modem:

• model number
• downstream: power levels, SNR (or MER), error counts, and uptime
  
• upstream: power levels
• event log, if available (Be sure to remove or blot out any MAC addresses. Forum security processing considers them "personal information" and may prevent the event log from posting if these are present.)

If you can't find the problem or you'd rather have Comcast take care of it and an employee does not respond to your message here, call them at the phone number on your bill or 1-800-Comcast, or use one of the options on https://www.xfinity.com/support/contact-us/. It's not likely they can fix the problem remotely. If not, insist they send a tech out to identify the cause and correct it.

If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit ($70-$100) unless you have their Service Protection Plan ( https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device or anything outside your home you shouldn't be charged.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

I'm not saying that you don't have an issue but measuring packet loss by pinging devices that are designed to pass traffic (routers or switches) is not a reliable troubleshooting technique. The primary role of these infrastructure devices is to forward the traffic that they receive rather than respond to a request to reply. You'd be better off choosing an actual host on the internet to test against. Something like 8.8.8.8 will give you more accurate results.

Thank you so much everyone, I don't know why well, but it seemed to be fixed after I "explicitly restarted" the modem.

I powered off/on the modem several times, but it didn't work. Instead, I logged-in the modem via 192.168.100.1 and pushed the restart button on the admin UI. After rebooting the packet loss has gone. I wonder, is there any difference between "power off/on" and "explicitly restart via UI" the modem?

> Something like 8.8.8.8 will give you more accurate results.

Yeah I was doing against 8.8.8.8 as well. The result was the same (20% loss.)