How to create a backup pool?

Jukka Laaksola jukka.laaksola at
Wed Jul 19 12:33:07 UTC 2006

Simon Hobson wrote:
> Jukka Laaksola wrote:
>>So normally I would share public IPs from pool A to customers but if all
>>public IPs are in use then next customers will get private IPs
>>(10.10.10.x) from a backup pool. All of those private IPs are NATted to
>>one public IP.
>>The configuration should give first all public IPs and after that start
>>to give IPs from private IPs. Is this possible somehow?
> OK, two methods come to mind, neither are perfect but may just manage 
> 'enough' to get you by !
> 1) Run a monitor that enables a pool as required
> Well that's it really, write a script that periodically checks the 
> status of your leases and if it detects that there are no free 
> addresses in the main pool will re-configure the server to allow it 
> to use addresses from the backup pool. When it detects free addresses 
> then you reconfigure the server again - but be aware that this will 
> most likely cause a client in the backup pool to switch address (and 
> thus lose all existing connections) on lease renewal.

That's the way I was wondering to do it if there's no support for pool 
priority in dhcpd. Propably disabling backup pool should be manual 

> Much better of course to ensure that you have enough addresses for customers !

Of course, but this is just way ensure that all customers can always 
surf on the web. There will be alerts to admins when almost all IPs are 
in use.

Thanks for the fast answers!

Jukka Laaksola
Netland Oy

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