RFC3442 support case when client requests the Classless Static Routes option and also requests either or both of the Router option and the Static Routes option
As per RFC3442:
DHCP Server Administrator Responsibilities
Many clients may not implement the Classless Static Routes option.
DHCP server administrators should therefore configure their DHCP
servers to send both a Router option and a Classless Static Routes
option, and should specify the default router(s) both in the Router
option and in the Classless Static Routes option.
When a DHCP client requests the Classless Static Routes option and
also requests either or both of the Router option and the Static
Routes option, and the DHCP server is sending Classless Static Routes
options to that client, the server SHOULD NOT include the Router or
Static Routes options.
This should be discussed if Kea should follow this once support of Classless Static Routes is implemented.
Source: !2135 (comment 414489)