[EXTERNAL] extremely slow DHCPD startup time

[Shane Merritt]

I wanted to follow up to my own post in case someone else encounters this issue in the future. The problem I discovered was that DHCPD keeps a record of the last lease for a given client forever so that it can try to give the client that address again. We had over 300,000 leases in the leases file that were in a binding state other than active (e.g. expired, free). The majority of these were no doubt from client devices that will not ever show up on our network again. At the end of the semester, I stopped the primary and failover servers and ran a Perl script I wrote to go through and get rid of all these inactive leases.  The load times changed to seconds and we have suffered no ill effects in the nearly one month since I did this.

Shane Merritt
Office of Information Technology
The University of Alabama
smerritt at ua.edu


From: dhcp-users <dhcp-users-bounces at lists.isc.org> on behalf of Shane Merritt <smerritt at ua.edu>
Date: Thursday, August 4, 2022 at 2:01 PM
To: dhcp-users at lists.isc.org <dhcp-users at lists.isc.org>
Subject: [EXTERNAL] extremely slow DHCPD startup time
I have a failover pair of DHCP servers running 4.4.2-P1 that handle a DHCP for a very large wireless network (>75k devices active at any time). The leases file on these boxes is around 200 megabytes.  The problem I am having is when I need to make a change and restart, DHCPD takes over 25 minutes to start giving out addresses.  I assume this is due to the large lease file.  I see that there are tons of leases in the file that are “binding state free” that in some cases are months old.  Are there any suggestions to improve this situation?


Shane Merritt
Office of Information Technology
The University of Alabama
smerritt at ua.edu

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