Is it at least remotely possible that someone exerted an ARP Spoofing attack on your network? That would explain the behavior - poisoned ARP caches would cause your devices to incorrectly address outbound frames containing IP packets. This is of course hard to prove at this point.
Are you using any gateway redundancy protocol like HSRP, VRRP or GLBP? Also, were you perhaps able to specifically detect an anomaly in the ARP tables, like an obviously incorrect MAC address being mapped to an IP address? Where exactly were the ARP tables incorrect - on the distribution switch or on the servers (end hosts)?
thanks for the response. We are using HSRP on the VLAN1115 interface on the Dist Switch. and the Vlan160 interface on the dist switch. I don't think he specifically saw the anomaly, but his extended, non-timeout ping of the server ip address, combined with the incrementing of matches on the ACL, told him the server was getting the ping, but it became obvious that the server didn't not know the return trip.. (We kind of determined that before anyway). So, he figured since some these devices had no real configuration, that the problem was either a bug, or the server had the wrong Mac address of its DFGW. Hence, he cleared ARP Cache.. Still trying to make sense of it..
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