I have a client that has Exchange on their server and a Cisco ASA 5505. I have noticed that they lose about 50% or so of their pings when pining the Internet. I have switched out firewalls and that made no difference. I have found that when the NAT statement is removed from the ASA for Exchange, then none of the pings are dropped when pinging the Internet. This same behavior occurs on both firewalls. When a PC with a static IP address from the ISP is hooked directly to the cable modem none of the pings are dropped. I have tried doing NAT 2 different ways, but get the same result. The ISP, Wow! (Used to be Knology), says that the modem needs to be replaced, It was replaced a few days ago.
I have seen where there have been issues with IP addresses from an ISP. Does anyone else know what could be causing the pings to drop when using NAT?