netmask and broadcast address

[christf]

In a l2 mesh we can globally set the netmask and broadcast addresses. ddhcp currently allows that relying on the appropriate dhcp options as specified by -o.

In l3 networks the netmask and broadcast address should be different for every node in the net.
To make matters worse, these values change when new blocks are reserved by ddhcpd for this given node.

Without subnet mask, dhclient (default on many linux distributions) will not accept default gateway and ipv4 will be broken.

I am not sure how best deal with that. I see two options:

• enhance hook events to allow calling hooks when blocks are reserved and released. Then this hook could use the socket to re-configure the dhcp options of ddhcpd in-flight.
• auto-adjust the netmask/broadcast address when not hard-coded via CLI. Since those dhcp-options are standard for every installation, they should always be delivered. If not specified, use a sane default.