Internet Does Not Work When Router Is Directly Connected To Modem, But Does If Connection Is Shared From PC

That is an interesting issue...

Based on what Windows is saying, it may be an issue with communication between your modem and the ISP's end, but to rule out some LAN based issues, you can do the following.

I would suggest placing your network in the non-working configuration (Internet->Modem->Router->Other devices), so we can determine where the point of failure is.

Once you're in this configuration, you'll need to do some tests using command prompt.

First, run the command "ipconfig", and confirm your PC is getting an IP address from the router, as well as the address the router is using (Default Gateway in Windows).

If there are no problems here, next we'll need to test connectivity at each hop on the way out of the network.

I would then try to ping the Default Gateway, which would be your router, to confirm your computer is able to communicate properly across the LAN. If this test is successful (all pings received responses), next attempt to ping your Internet gateway (the modem). You should be able to get this IP address from the router's web GUI, as the Gateway for the internet connection, or when the PC is directly connected, you should get the IP of the modem then, either way.

If pings to the gateway are successful, I would then ping out to an internet based address, something dependable like a DNS server (8.8.8.8 is my usual choice). If pings work here, then you're hitting the internet, and the problem is something deeper than I'm expecting. Otherwise, if pings fail here, I would expect it's an issue between your modem and the ISP. At this step, I would suggest running a continuous ping "ping -t x.x.x.x", and letting it run for a while (preferably long enough to go through the cases of the internet being up and down), to see if you have packet loss/bouncing over time.

Depending on where you find the point of failure is will change what the root cause will be, so if you aren't able to get this figured out, please provide some details on your results.

Hope this helps

Hm, it's definitely worth noting that a second device connecting to the network seems to cause the problem. I would definitely recommend testing this theory by having only one device attached to the network for long enough to confirm if it resolves the issue or not. If this IS a cause of the issue, to me it could point to a DHCP or NATing problem. All of your devices share the same internet facing IP address, so if they aren't being NATed properly, they may be losing connectivity to devices behind your router.

When the internet goes down, does it go down for all devices at the same time, and for the same length of time?

Also, your ping results are interesting - you're having trouble hitting your modem. If this was a problem with your circuit (the connection from your home to the outside world) you shouldn't see any connectivity problems until you start talking to internet based addresses (such as 8.8.8.8). This would lead me to believe the issue is within your LAN, most likely between the router and modem. Have you tried swapping cabling?

I would set up a continuous ping to the modem IP and see how often packets are successful. Are pings to that IP successful at the same time that your internet is working?

The request timed out messages are most likely because the device just isn't replying to pings, this may be by design by the ISP.

Since we can't ping that device, try running a continuous ping to an internet based address (I would ping an IP rather than a hostname such as google, since DNS won't work when the internet is down). When you run this ping, do you get random bits of success and failure, like a random back and forth, or consistent failure, and then consistent success (no matter how short lived) in any kind of pattern?

I know you said originally that the internet will sometimes work in the faulty configuration but will eventually go down, what is it that tends to resolve the issue? Do you have to reboot a specific piece of equipment? Or does the internet come back without any intervention from yourself?

That also leaves us with the multiple host issue - have you had a chance to test/confirm that the internet goes out when a second device is introduced to the network?

At this point, it still sounds like a LAN issue to me, but it's definitely an odd one (or it's obvious and we're both missing it).

You should be able to release/renew the IP address on your router, between the router and the modem. This should be through the web GUI for your router.

When the internet goes down, attempt to release/renew the IP address, to see if it is working. If you are unable to renew your IP when the internet is down, it sounds like an issue with the modem, since it can't give out DHCP while you are experiencing other issues.

If you are able to release and renew, and this resolves the issue, then I would think it is more likely a problem with the router, or at least communication between the router and modem.

If you are able to release and renew, but this does not resolve anything, I would say it points more towards the modem being the issue.

If you can afford to, you could try replacing the modem with one you bought yourself, a model with good reviews, Google and all that good stuff can guide you there. Otherwise, it may be time to go back after Charter. It's by no means uncommon to have the carrier come out and completely miss the issue while on site. They tend to look at it more closely if you refuse to let the tech leave your house until they fix it. (A not so uncommon thing customers like to do lol.) As long as you can reproduce the issue while a tech is at your house, they should be willing to help.

That is another interest piece of info - the issue may be related specifically to wifi vs wired connections. When everything drops, I assume you still have LAN connectivity as you've stated before, so this makes it seem unlikely that the router is choking itself resource-wise.

Honestly, it sounds almost like DHCP could be setup to allow the router's own LAN address to be assigned out, causing layer 3 communication out to the internet to die. LAN connectivity would be fine since you're communicating at layer 2 there. Though I find that unlikely, since it would be an insanely poor design on the router's part, and to be on 2 different routers is even more unlikely.

You could try turning off DHCP, as well as any unnecessary services, such as SIP ALG, and seeing if that may improve stability.

The last time I experienced this, I had an extreme amount of noise on the line coming into my house from the road, and this was only discovered after 3 other techs were sent out. Not that this is necessarily your situation, but wanting another tech to come out is by no means going to be a surprise to them, it's pretty common for long standing issues.

In regards to calling them...

The fact that rebooting the modem fixes the issue is probably the strongest point you can make. If your router is the problem, why is their device failing? Especially since you have stated your LAN connectivity remains intact, the router that you own does not appear to be operating improperly.

Second, most ISPs offer modem/router combos, or wifi routers to rent - I would ask a tech to come install one of their own devices. Since you have already purchased a new router, it's very unlikely to be your router. Especially if this is a brand new in box router, not refurbished or anything. Even if you don't intend to keep the router, ask them to do it to at least prove the issue out so you can troubleshoot further on your end (though I wouldn't bother telling them this is your plan, unless you're worried they'd charge you in some way for this, who knows with ISPs).

Since this issue has been ongoing since day 1, you've never had a steady state after all this troubleshooting. While the person you talk to might not give a damn, it could give a nudge in the right direction - generally new business/new deployments that have had issues from day 1 will get a little more attention.

Finally, just remember the squeaky wheel gets the oil. When you open a ticket with Charter (or pretty much any service provider), that ticket is going to be assigned to an individual or group, who at some level is held accountable. If a ticket keeps being escalated by a customer, it's eventually going to get attention, if only because the right person finally had it come across their desk. (We generally call once per our to ask for updates, and ask for an escalation to be placed on the ticket if there are no updates, until some kind of traction is made. Though this is on business accounts.)

Hope that helps

Yes, my apologies, this would require you to statically configure all of your devices on your network. But, you could just set up your computer and phone for the purposes of testing, and undo it once you have confirmed if that resolves anything.