dhcp fails with big dhcpd.leases

Simon Hobson dhcp1 at thehobsons.co.uk
Tue Aug 31 15:32:44 UTC 2010

dorian wrote:

>Aug 31 15:34:26 [dhcpd] DHCPDISCOVER from 00:23:6c:73:b3:29 (AMs-iPhone)
>via br0
>Aug 31 15:34:26 [dhcpd] DHCPOFFER on to 00:23:6c:73:b3:29
>(AMs-iPhone) via br0
>Aug 31 15:34:33 [dhcpd] DHCPDISCOVER from 00:19:d2:97:ca:81 (N0336) via br0
>Aug 31 15:34:33 [dhcpd] DHCPOFFER on to 00:19:d2:97:ca:81
>(N0336) via br0
>Aug 31 15:34:34 [dhcpd] DHCPREQUEST for from
>00:23:6c:2b:08:eb via br0: wrong network.
>Aug 31 15:34:34 [dhcpd] DHCPNAK on to 00:23:6c:2b:08:eb
>via br0
>Aug 31 15:34:34 [dhcpd] DHCPDISCOVER from 00:23:6c:73:b3:29 (AMs-iPhone)
>via br0
>Aug 31 15:34:34 [dhcpd] DHCPOFFER on to 00:23:6c:73:b3:29
>(AMs-iPhone) via br0
>so it is clearly visible that in case of the failure there is no
>DHCPACK  packets.

Actually, that log snippet shows no such thing. There is only ONE 
DHCP-Request, to which the server responds with a DHCP-Nack as the 
requested address is not valid. There are no more Requests from 
clients and hence there should be no more Acks to go with them.
What I do see are a number of DHCP-Offers which don't result in a 
DHCP-Request from clients. You need to be looking at why this is the 
case - are you sure there are no other (probably rogue) servers on 
the subnet ?

>2. the dhcpd.leases file size is the reason (or is it the only reason)?

No, it won't even be related to the problem - unless you are running 
out of disk space or have other storage problems.

The leases file is a log file - the server only ever appends to it, 
and during operations it never reads from it. It is only ever read 
during startup when it reads each lease in turn and populates it's 
internal tables. Even then, it does not (I assume) read the file into 
memory - it just has to parse each lease as it munches through the 

To avoid the file growing ever larger, the server will periodically 
clean up. It does this by writing out it's current in-memory tables 
to a new leases file, and swapping it into place by renaming the 
original file and then renaming the new file into place.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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