Clarification on fixed-address statement

Jack Kielsmeier jackkiel at
Fri Apr 29 20:06:21 UTC 2011


We are running ISC DHCP 3.1.0 in a failover configuration. I do know
that 3.1.0 is a somewhat old version, but it has worked well for us.

I am wondering if this is the expected behavior of fixed-address

Upon initial inspection, it seems that if you declare a fixed-address
for a MAC address, that IP address is reserved and can only be used by
the declared MAC address.

In reality, we are seeing the DHCP server hand out fixed-addresses to
any MAC. When the MAC address that is assigned the fixed-address asks for
an IP, DHCP will attempt to give it the fixed-address if it is free, but
will hand out another IP if it's unavailable.

Is this how fixed-address statements are supposed to work? If so, is
there a way to make sure only a specific MAC address can use a specific
IP address?

For reference, this is how we are declaring fixed-addresses:

host HOSTX { hardware ethernet xx:xx:xx:xx:xx:xx;fixed-address
###.###.###.###; }

I have stripped the MAC and IP address out.

Thank You,

Jack Kielsmeier <jackkiel at>
netINS Systems Administrator

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