logging the lease time *sent* to clients in an "on commit" block

Glenn Satchell Glenn.Satchell at uniq.com.au
Mon May 21 13:24:46 UTC 2007

>Date: Mon, 21 May 2007 13:50:31 +0100
>From: Phil Mayers <p.mayers at imperial.ac.uk>
>To: dhcp-users at isc.org
>CC: "Niall O'Reilly" <Niall.oReilly at ucd.ie>
>Subject: Re: logging the lease time *sent* to clients in an "on commit" block
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>Niall O'Reilly wrote:
>> Hash: SHA1
>> On 18 May 2007, at 16:44, Phil Mayers wrote:
>>> What syntax can I use to get the ACTUAL IP address lease time (option
>>> 51) the server sends to the client? We have a need to do detailed
>>> logging of leases handed out including the lease time.
>> 	Why use an "on commit" action to duplicate what dhcpd is already
>> 	writing to the leases file?
>> 	Parsing the leases file "offline" at regular intervals can't be
>> 	much more difficult than doing the same with your logs, and avoids
>> 	extra processing during allocation or renewal of each lease.
>Well, thanks for the suggestion but that's not really what I'm looking 
>for, for two reasons:
>  1. the leases file doesn't list fixed addresses
>  2. I'm looking for <20 seconds turnaround time between the lease 
>granted and it making it into the logging system.
>There are loads of ways to work around this; since I'm generating the 
>DHCP configs and our config is simple enough that lease times are 
>dependent on IP address only, I could dump a mapping of IP -> leasetime 
>at config generation time; but it seems silly that the "on commit" has 
>access to all the info except that.
>Does anyone know if it's possible or not?

I haven't actually tested it, but option dhcp-lease-time looks like the
right thing. You may also need to check option dhcp-message-type to
make sure you are recording it for the right type of packet as this can
also be set on DHCPREQUEST. Details on possible values in dhcp-options
man page.


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