First, I apologize if this question seems to be "all over the place". I've tried to sum it up as clearly as I could, but there are a lot of moving parts, so I've tried to be detailed with my explanation.
I handle a small network for the property management company I rent from, and over the past 5 weeks, we've had intermittent connection to the internet.
Specifically, we have a Comcast Business Class connection coming through a Cisco DPC3939B DOCSIS3 router that is supplied by Comcast. I have access to the customer admin panel, and everything I can see there, but nothing more.
On the LAN side, three of the four ethernet ports are connected to a Monoprice 10927 consumer-grade gigabit switch, and each switch runs Cat6 to one of four wall jacks on each floor (each floor is a 3 bedroom unit, plus a living room jack).
The fourth port is used as a direct connection, to eliminate a 'hop' and directly access the router's control panel.
I've changed this configuration up quite a bit, replacing those switches with Rosewill gigabit switches, attempted a few other consumer-grade routers using dd-wrt and OpenWRT, and directly connecting to the router with no other devices.
The internet connection issues are consistent regardless of the configuration, and speed tests indicate that none of these devices introduce a bottleneck to the WAN.
All of this leads me to believe the issue is between the Cisco device and "the internet."
Originally, this device was reporting frequent "T3 - Ranging Response Timeout" errors, but a level 2 technician corrected an issue on-site, and those errors have not appeared for the past 10 days or so.
Thinking it might be a DNS resolution issue, I've overridden the Comcast DNS servers with Dyn, OpenDNS, and Google's public servers, and none offer a resolution to the issue.
Further, running ping and traceroute tests from the Cisco device to public servers never indicate any amount of packet loss. Running the same tests from devices on the LAN also indicate no packet loss, suggesting to me that it's not a mere connectivity loss, but a specific type of transmission failure.
Still, we're getting intermittent connections and disconnects, and I'm stumped as to why this is happening.
The firewall settings on the Cisco device for both IPv4 and IPv6 are set to "disable firewall completely" and yet the following is appearing in the firewall log.
FW.LAN2WAN ACCEPT , 2510821 Attemps, 2015/4/21 Firewall Blocked
This may just be very poor description, but it reads to me as if 2.5 million outgoing requests have been blocked by the supposedly disabled firewall, and the device offers me no other information about them.
Am I misunderstanding the output of the very limited logs I have, or are the logs unclear? Is my logic sound in the changes I've made, or am I missing something glaring?