The build I'm using is Version 10.10 (August 2012).
We have many subnets in our topology and a few, among them, have devices which do not respond to ping for various reasons. While setting up the subnets, I audit them by performing a ping sweep and then from the CLI of the router/switch on which the L3 network terminates, I issue "show ip arp | inc Vlanx | exc INCOMPLETE" to find the devices which are active on a particular IP address but do not replying to ping. In cases where I'd see an entry in the ip ARP cache but where IPAM didn't not get a ping response, I'd mark the address as "reserved" in IPAM and add a comment to the entry as follows "Appears in ARP cache with MAC address xxxx.xxxx.xxxx". What I've noticed is that this information spontaneously disappears and reverts back to "Available". It doesn't happen to all of them. It seems random.
Is there another way I should be tracking IP addresses which cannot respond to ping? What is really going on in IPAM when an entry is marked as "Reserved"? Does the scan process skip over reserved entries? If it were up to me, I would still try to ping a "Reserved" entry (along with reverse DNS lookup and SNMP query) specifically to address cases where a host doesn't respond to ping due to policy. Either that or I'd add a fourth status option "Used - Unpingable" or something similar to denote entries which are not currently used but will be used at a later date vs. entries which are used but not reachable by ping.