dhcpd.leases Contains Lots of Very Old Leases

Simon Hobson dhcp1 at thehobsons.co.uk
Fri Feb 6 13:51:09 UTC 2009

Eric Kenny wrote:

>It seems that they are just the old and expired ones, which appears to be
>normal behavior after further reading.  However, I'm wondering if having
>to parse all of these entries is what's causing DHCP timeouts on the
>client end.
>We have about 100 /21 networks served with open ranges.

The leases file is only ever read at startup - at all other times it 
is write-only and the server uses it's internal structures.

You have about 200,000 available addresses. The server keeps 
structures in memory for all of those whether leased or not, so if 
you don't need all those addresses you will gain performance by 
reducing the size of pools. The reason expired leases are stored is 
to comply with the RFC that specifically requires the server to 
retail information to allow a client to be given the same address in 
future (subject to it not having been reused in the meantime).

I recall there being some discussion in the past about some tweaks 
(changing constants before compilation ?) to improve performance on 
large networks, but I can't recall any detail.

Simon Hobson

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