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I have a DHCP server that serves leases to several houndred, maybe up to a thousand, different clients on an average day. The pool consists of 242 IPs, and due to the highly dynamic nature of the network, it's enough 99% of the time (most devices are gone from the network in a few minutes), despite having a lease time of 3600.

Now, imagine if more clients than that connect to the network during an hour. The sollution is obvious: Decrease lease time, or increase the DHCP pool, however, what i would like to know: What happens when dhcpd has exhausted the pool? Are new DHCP requests simply ignored?

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2 Answers 2

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Your system will simply stop assigning IP addresses once the leases have been exhausted. This will also be reflected in the DHCP server's /var/log/messages. E.g. "No free leases".

DHCPDISCOVER from 00:40:ee:40:38:f8 via eth0: network 10.1.1.0/24: no free leases

On the device side, they will either get 0.0.0.0 or self-assigned 169.x.x.x addresses...

Is expanding your subnet an option?

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  • plenty of options, that being one of them. It's not a realy problem, i would just prefer to know what the result would if no action was taken.
    – Jarmund
    Sep 11, 2012 at 20:32
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If your DHCP pool has been exhausted then your server will stop giving out addresses - it will not use up the oldest unused lease.

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    is this part of the standard behavior of DHCP? Is there any way to set DHCP to lease unused/freed leases?
    – ultrajohn
    Dec 9, 2019 at 4:16

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