Tip: Disable Connectivity (PING/ICMP ECHO) Checks In Routers To Avoid Connection Loss After Recent Network Upgrades

Recently, Xfinity forced me replace a stable, working cable modem (Zoom 5341J) with a newer model (Motorola MB7420), which is a successor design and also an excellent DOCSIS 3.0 device.

For about three weeks after the modem replacement our residential connection was again solid, although the Motorola MB7420 may be more sensitive to RFI (Radio Frequency Interference) than its predecessor the Zoom 5341J was, as it seemed to accumulate corrected and uncorrected errors when placed near other network equipment, in the same location as the previous modem.

This may or may not have been coincidental, as the cable network downstream signal levels, S/N and upstream power levels were starting to degrade near the end of the three week period, the connection was becoming unstable, and I was preparing to report the issues to Xfinity for remediation.

Then, we received a notice from Xfinity that major upgrades were going to be performed in our area on Thursday, March 30, 2023, so decided to wait and see if our connection stability and signal levels would improve.

They did, and we are thankful for that. We now have "perfect" signal, S/N and power levels both down and upstream, and they are 100% stable.

What DID change, cause a big problem and require a lot of troubleshooting was the fact that after the upgrade Xfinity's gateway servers (which are specified by the DHCP configuration passed to your router) no longer respond to "ping" (ICMP ECHO) requests.

Before the upgrade, routers that rely on a "connectivity check" to determine whether or not to switch over to a secondary Internet connection using an automatic,  periodic ping request sent to Xfinity's gateway worked fine. They would receive a response to the ping, consider the router's WAN connection to the modem active, and forward connections to the Internet via that route.

After the upgrade, routers that rely on a "connectivity check" using ping will receive no response, and conclude that the connection to the modem or gateway is inactive. Unless the router is configured to use an alternate connection when the cable connection fails, the router will think there is no route to the Internet, and ping checks to web sites such as google.com will report "no route to host."

No devices connected to the router will be able to reach any Internet address, nor will the cable modem's diagnostic pages (if provided) be accessible, since the cable modem is also connected to the WAN port that the router uses to reach the Internet, and thinks is down.

So, if you can (1) connect to the net with a direct connection between a PC and your cable modem, (2) can't connect to the net when your router is connected to your cable modem, and (3) recently had a system upgrade performed in your area, disable all "connectivity checking" in your router that targets any gateway IP address specified by the DHCP information provided by Xfinity.

Once you do that, your router/gateway should work as it did before the upgrade, without any other configuration changes needed. :)