The mechanism to be used for allocation of IP
address for this interface.
The value negotiation can be used only for PPP
and MLPPP interfaces which support obtaining of
IP addresses through negotiation.
The dynamic(3) option takes an IP
address dynamically from the available
server (dhcp/bootp/rarp) according to the
protocol specified in ifIpAddrAllocProtocol.
If the method specified is manual and the IP
address is not provided (then the interface
would be treated as a un-numbered interface.