A customer of mine (I'm an IT-for-hire person) has Comcast business class cable internet service. A few weeks ago they started experiencing intermittent internet. They have a Comcast/Netgear combo device (router/modem/firewall) that we have configured for what they call "router mode," which I call "bridge mode." Either way, we have a static IP address that is passed through to our LAN, NAT and firewall in the device turned off. I have the IP address configured on one of the NICs in a Novell server. The second NIC in the server is for the LAN, with the server giving out DHCP. There have been no problems there. The Novell server also is our main app server and our email (Groupwise) server. When the internet is down, everything else works fine. And I changed out the WAN NIC twice. Point being there are no indications that the server is behaving in a way that would cause the internet problems.
Each morning when they show up for work the internet is down. They call me, and I start trying to ping both the IP of the Netgear (gateway address) and the server (static IP). Usually, I cannot get a response from either address. Occasionally I can get a response from the gateway, but not the server (and of course I can never get the server and not the gateway). This weekend I performed random ping tests to the gateway, and I caught it down at least 5 times.
Comcast has changed out the Netgear unit 2 times (meaning we've had 3 of the units). They monitored the device for several days and say it does not go "off-line." However, this morning they told me that, yet neither I nor the support rep could ping the gateway. She offered to "reset the modem" for me. As soon as she did, I could ping the gateway, the server, and the internet was up at the office.
Comcast's theory - after many, many support calls, as well as changing out the box twice - is that something on the client's network side is "locking up" their device (the Netgear).
Does that make any sense?