Large networks and memory allocation in ISC DHCP

Runtime memory allocation in ISC DHCP differs between the IPv4 and IPv6 servers.

The DHCPv4 server will allocate memory structures at startup for each address in a network defined in dhcpd.conf. In most configurations this is not a problem but it can result in unexpected memory usage when defining a network containing millions of addresses (for example a /8.)

Because very large, sparse subnets are much more common in IPv6, the DHCPv6 server does not pre-allocate memory for every address in a subnet, only those that are used.