BIND 10 #3242: Kea4: check if only remote traffic can be supported

[BIND 10 Development]

#3242: Kea4: check if only remote traffic can be supported
-------------------------------------+-------------------------------------
            Reporter:  tomek         |                        Owner:
                Type:  task          |  marcin
            Priority:  high          |                       Status:
           Component:  dhcp4         |  assigned
            Keywords:                |                    Milestone:  DHCP-
           Sensitive:  0             |  Kea0.9-alpha
         Sub-Project:  DHCP          |                   Resolution:
Estimated Difficulty:  24            |                 CVSS Scoring:
         Total Hours:  2             |              Defect Severity:  N/A
                                     |  Feature Depending on Ticket:
                                     |          Add Hours to Ticket:  2
                                     |                    Internal?:  0
-------------------------------------+-------------------------------------
Changes (by marcin):

 * hours:  0 => 2
 * estimatedhours:  0 => 24
 * totalhours:  0 => 2


Comment:

 I verified that this is broken in the current code. In my test the server
 was listening on the interface with a statically assigned IP address:
 172.15.0.1. The server had one subnet 172.16.0.0/24 configured. Client was
 attached directly to the server's interface and broadcasted Discover. The
 client's message was received via interface with the 172.15.0.1 address,
 address from the subnet 172.16.0.0/24 was assigned to this client and the
 Offer was sent via interface having 172.15.0.1 address.

 The proposed fix for it is that:
 - configuration mechanism checks for each activated interface whether its
 IP address belongs to one of the configured subnets. If it doesn't the
 info message is issued.
 - each packet received via such an interface should be instantly dropped
 and an appropriate info message should be issued in the log.

-- 
Ticket URL: <https://bind10.isc.org/ticket/3242#comment:4>
BIND 10 Development <http://bind10.isc.org>
BIND 10 Development