How to avoid serving IPs at host section with fixed-address to other clients

Folke Ashberg fashberg at etkn.de
Thu Jul 31 17:48:17 UTC 2014


Hi there,

i would wonder if there is no one who can find a trick for me to solve 
this problem:

I have a /24 network serving from 1.1.1.4 to 1.1.1.254 (prefix changed 
for anonymity)

subnet 1.1.1.0 netmask 255.255.255.0 {
    pool {
        range 1.1.1.4   1.1.1.254;
        /* snipp */


After a user logs in at a WLAN captive portel  the radius-server starts 
my script which creates a fixed-address with OMAPI/omshell.

This is working very well and stable.

Such section gets added dynamically to the dhcpd.leases file:

host gm-123 {
   dynamic;
   hardware ethernet 20:16:d8:65:19:a5;
   fixed-address 1.1.1.198;
}


So my intension is to change the dynamically assigned addresses into a 
fixed ones.

But the big problem is that isc-dhcp still serves that fixed-addresses 
to other clients, because the address is still inside the range.

Is there any mechanism to tell ISC not to serve addresses seen in host { 
fixed-address } ?

The range cannot be touched with omapi, also a lease cannot be created 
or change to state=8 (reservation).

Splitting the network to fixed-entries and dynamically assigned ones is 
a bad idea: First of all the user would already have an IP from the 
dynamic range and the other no go is that with splitting i loose the 
flexibilty of assigning the rare adresses (there are about 200 clients).

Any way to achieve this without regeneration dhcpd.conf and reload 
(ugliest way in my eyes).


Thanks in advance for any hints

Folke



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