Automatic allocation

[dhcp at lermytte.be]

Hello,

RFC2131 talks about "automatic allocation" as a possible way to map clients to IP addresses. 
How can I do this with the ISC DHCP server? Or is it just a matter of setting a high 
(infinite?) lease time? I have seen implementations that negotiate a relatively low lease time 
with the client, while still having another parameter to specify the "permanence" of the 
mapping. Anything like this in ISC DHCP?

Regards,
Christophe L.