suggestion to improve dhcpd behavior regarding default setting of max-lease-time statement

[Fons de Jongh]

Dear DHCP Hackers,
 
My name is Fons de Jongh and I work at Novell as a technical support engineer. I understood from S Kalyanasundaram, who is a developer at Novell, that you can verify my suggestion for dhcpd, and may-be approve it in case it makes sense.
 
Okay, here I start...
 
I have installed dhcp-server-3.0.3-23.38 on SuSE Linux Enterprise Server 10.
 
One can configure a 'default-lease-time' and a 'max-lease-time' statement with the 'global parameters' of a DHCP server or with any declaration. As desired, dhcpd will use the configured statements of a declaration that is most specific to the IP address to be offered/allocated (yiaddr) for the setting of the IP Address Lease Time option (option 51) in DHCPOFFER and DHCPACK reply messages.
 
Apparently the default value of 'max-lease-time' is 86400 seconds (1 day). However, this is not mentioned with the description of the 'max-lease-time' statement in the manual page of dhcpd.conf. So dhcpd administrators cannot be aware of this hardcoded limit.
 
The consequential behavior of dhcpd is that if one does not configure a 'max-lease-time' statement, but only a 'default-lease-time' statement with a value greater than 86400 seconds, dhcpd will return an IP Address Lease Time of 86400 seconds with option 51 in DHCPOFFER and DHCPACK messages, regardless to the higher setting of the 'default-lease-time' statement.
 
Hence, if one configures a 'default-lease-time' statement with a value greater than 86400 seconds, one must also configure a 'max-lease-time' statement with the same value as 'default-lease-time' or higher, in order to make dhcpd return the desired configuration of 'default-lease-time' with option 51 in DHCPOFFER and DHCPACK messages. This condition is not described in the manual page of dhcpd.conf, so dhcpd administrators do not know they should set a 'max-lease-time' greater than or equal to the 'default-lease-time' if they configure a 'default-lease-time' greater than 86400 seconds.
 
My suggestion is to change the default setting of 'max-lease-time' to a variable value instead of the current hardcoded constant 86400. I suggest to make the default value of 'max-lease-time' equal to the value of 'default-lease-time', so that if one configures the 'default-lease-time' only, the 'max-lease-time' will never limit the 'default-lease-time'.
 
An alternate suggestion to handle the same configuration conflict is to make the default setting of 'max-lease-time' 0xFFFFFFFF (infinite), but that may result into undesired behavior when clients request for an infinite lease time per DHCP option 51 in a DHCPREQUEST message.
 
Please let me know if you agree with my suggestion to make the default value of 'max-lease-time' equal to the value of 'default-lease-time' or if you have comments or questions.
 
Thank you and kind regards,
 
Fons de Jongh
Novell Technical Services