[Dnsmasq-discuss] dnsmasq caching lease file?

[richardvoigt at gmail.com]

>
> You're confusing configuration with DHCP leases. If you map an IP address
> to MAC address in the nova-br100.conf file, then the VM will take out a
> DHCP for a fixed time. Until that lease expires, the IP address will not be
> given to another VM, even if you change the nova-br100.conf file. Look at
> the logs: dnsmasq will log that it's not using the configured address,
> because it's in use elsewhere.


Might be worth mentioning the one feature that avoids this behavior -- if
both mac addresses are listed in a single dhcp-host directive, then dnsmasq
will transfer the IP address.  Originally designed for use with laptops
that move between wired and wireless interface on the same subnet, IIRC.

>From the man page:

"As a special case, in DHCPv4, it is possible to include more than one
hardware address. eg: *
--dhcp-host=11:22:33:44:55:66,12:34:56:78:90:12,192.168.0.2* This allows an
IP address to be associated with multiple hardware addresses, and gives
dnsmasq permission to abandon a DHCP lease to one of the hardware addresses
when another one asks for a lease. Beware that this is a dangerous thing to
do, it will only work reliably if only one of the hardware addresses is
active at any time and there is no way for dnsmasq to enforce this. It is,
for instance, useful to allocate a stable IP address to a laptop which has
both wired and wireless interfaces."
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