[vbox-dev] DHCP Leases

Malcolm Clarke Malcolm.Clarke at brunel.ac.uk
Thu Feb 2 14:30:10 GMT 2017

Dear Developers

Our students have met a feature of the DHCP server that can cause some confusion.

If a NAT network is configured and a VM attached to that NAT network, then the MAC address and allocated IP address are recorded in the lease file of that NAT network (in order that the same IP address is reallocated). So far so good.

However, if the subnet address of the NAT network is later changed, the lease file is not cleared, and a machine continues to receive the original (on the old subnet) IP address. As this no longer matches the subnet address of the NAT router, the VM is effectively isolated and cannot function on the network.

As a workaround I have suggested to the students that they should edit the respective lease file. However, it would seem that the correct behaviour would be for the lease file to be cleared (or alternatively the subnet address in the lease file is changed to match the new subnet).

The problem for the students is that there is no outward indication of the leases that exist and how to manage them (e.g. delete). I understand that there should not be comprehensive DHCP management, however the behaviour should be made consistent.



Malcolm Clarke BSc (Hons), PhD
Reader in Telemedicine and Data Communication Systems
T +44 (0) 1895 265053

Brunel University London
College of Engineering, Design and Physical Sciences
Department of Computer Science

HNZW010, Heinz Wolff Building, Kingston Lane, Uxbridge, Middlesex, UB8 3PH


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