Is ISC DHCP server will take dynamically changing value??

Simon Hobson dhcp1 at
Tue Apr 24 09:01:43 UTC 2012

ameen.shajahan at wrote:
>My expectation is I have to change the subnet , lease range and lease time .
>So that the client will get the changed subnet , lease range and its 
>corresponding lease time.
>In simple words, whenever the changes happened in conf file client 
>can able to get the changes without restarting the server.

Firstly, you really need to understand the difference between 
"restart servICE" (ie restart the DHCP service) and "restart servER" 
(ie reboot the host). For typical size configurations, restarting the 
servICE with the ISC DHCP server takes a matter of seconds vs 
potentially minutes for the servER (ie host OS) to restart.
There really, really, REALLY is no problem restarting the DHCP 
servICE to reconfigure it - except in some very large and complicated 
setups which I very much doubt you are going to be using.

As Gerald says, just changing the configuration on the server will 
**NOT** reconfigure the clients - it just does not work like that. 
Once the server has issued a lease, teh client is free to use that 
address (and other information) for the lifetime of that lease (which 
may be anything from a few minutes to a few years depending on how 
the administrator has configured the server.

Changing the subnet on a network is not something you do lightly. 
I've done it a couple of times at work and it's a pian to do - it 
really is not something you should be doing very often (if at all). 
It takes time, and a lot of work - it's not just a matter of changing 
your DHCP ... You need to reconfigure your router(s), including 
keeping both subnets active with routing between them. Change all 
your DNS. Reconfigure all your statically configured devices. 
Reconfigured everything that refers to the address of a statically 
configured device (eg changing the address of the printer(s) on every 
client - been there, got the tee shirt !). And then spend the next 
few weeks on the tail end of support calls for things you've missed.

So, a few seconds to restart the DHCP service is neither here nor there.

I would suggest that instead of trying to figure out how to 
reconfigure a network quickly, you would be better off learning how 
to plan a network properly so you don't have to.

Simon Hobson

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author Gladys Hobson. Novels - poetry - short stories - ideal as
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