Can fixed addresses ever be taken by dynamic ranges

R Landster dchp_mailing at
Wed Jun 6 18:31:16 UTC 2007

Thanks for the information; it is good to know how things work.

On the other hand, I think there is merit to the system being able to 
avoid handing out IP addresses for those addresses assigned to 
fixed-address machines.

For example: you are in charge of a subnet and you would like all IP 
addresses that are not assigned to fixed-address IP addresses to be 
available to be handed out dynamically. If your fixed addresses are all 
in one continuous segment it is not hard to use pools or some such thing.

But what if your fixed addresses are scattered all over the place? It 
then becomes more of a chore to setup ranges or pools for dynamic 

It would be nice if the service had the option to reserve fixed-address 
addresses as really reserved.

So, the problem is pushed from the DHCP service to whatever application 
(or person) manages the IP addresses.

Thanks again

doug wrote:
> Everything in the range will be handed out, regardless of its use in 
> fixed statement. It is (wrongly) assumed admins are smart enough to not 
> double configure address. Scan the archives for details.
> Doug
> R Landster wrote:
>> I have a question concerning the algorithm used to choose the IP address 
>> upon a DHCP request.
>> Here is the complete dhcp configuration:
>> #### START OF dhcp.conf
>> authoritative ;
>> deny unknown-clients ;
>> subnet netmask {
>>    option routers ;
>>    range ;
>> }
>> {
>>    hardware ethernet 00:66:B7:86:FC:5F ;
>>    fixed-address ;
>> }
>> host MYLAPTOP
>> {
>>    hardware ethernet 00:B4:20:68:1E:77 ;
>> }
>> #### END OF dhcp.conf
>> Here is the question: Are there any circumstances under which the IP 
>> address '' would ever be leased out to MYLAPTOP?
>> For example, assume that MYLAPTOP has never been on the network. Is it 
>> possible that the DHCP service might give out Or is the 
>> DHCP service "smart" enough to realize that is meant for a 
>> specific machine, even if that machine is not (or never has been) on the 
>> network?
>> Thanks.

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