DHCP 4.2.3-P2 is a production release of ISC DHCP. It contains fixes to correct the possible denial of service condition described in CVE-2011-4868.
DHCP 4.1-ESV-R4 is an Extended Support Version release of ISC DHCP. It fixes CVE-2011-4539 and replaces DHCP 4.1-ESV-R3.
