I am using my ASA 5510 as a DHCP server for a classroom environment. When the 25 computers are powered on, about 5 of them fail to obtain IP addresses, and when you manually renew the IP you get dhcp server not responding. If I Log into the ASA Firewall and make a change to the DHCP Scope (expand or contract the scope range) then all the computers will get IP addresses. Lease expiration is set to 3600 sec. and I see the DHCP leases listed in the ASA. Any ideas? All client computers are Vista SP2.