According to the user manual, under Security -> Advanced Security there is a checkbox for "ignore Ping Packet from WAN port to Router" and "Forbid Ping Packet From LAN Port"

I got the check marks to activate by by enabling the DOS protection button

In Security>Advanced

DOS protection though is not active according to what I read in C5 manual unless you have certain statistics configured(which I don't) which is good ...........won't slow down router.

Router now shows no response to Ping at Steve Gibsons site now

Thanks